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  • 1.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University, USA.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University, USA.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Petrakov, Dmitry A.
    Ivanov, Mikhail N.
    Alexander, Orkhonselenge
    Rudoy, Alexei N.
    Walther, Michael
    Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia2016In: Journal of Maps, ISSN 1744-5647, E-ISSN 1744-5647, Vol. 12, no 1, 123-136 p.Article in journal (Refereed)
    Abstract [en]

    In this article, we present a map of the glacial geomorphology of the Altai andWestern Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 mresolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.

  • 2.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jon M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Lifton, N. A.
    Heyman, J.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Petrakov, D. A.
    Caffee, M. W.
    Ivanov, M. N.
    Hättestrand, Clas
    Stockholm Univ, Dept Phys Geog, Geomorphol & Glaciol, Stockholm, Sweden.
    Rogozhina, I.
    Usubaliev, R.
    Evaluating the timing of former glacier expansions in the Tian Shan: A key step towards robust spatial correlations2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 153, 78-96 p.Article in journal (Refereed)
    Abstract [en]

    The timing of past glaciation across the Tian Shan provides a proxy for past climate change in this critical area. Correlating glacial stages across the region is difficult but cosmogenic exposure ages have considerable potential. A drawback is the large observed scatter in Be-10 surface exposure data. To quantify the robustness of the dating, we compile, recalculate, and perform statistical analyses on sets of 10Be surface exposure ages from 25 moraines, consisting of 114 new and previously published ages. We assess boulder age scatter by dividing boulder groups into quality classes and rejecting boulder groups of poor quality. This allows us to distinguish and correlate robustly dated glacier limits, resulting in a more conservative chronology than advanced in previous publications. Our analysis shows that only one regional glacial stage can be reliably correlated across the Tian Shan, with glacier expansions occurring between 15 and 281 a during marine oxygen isotope stage (MIS) 2. However, there are examples of older more extensive indicators of glacial stages between MIS 3 and MIS 6. Paleoglacier extent during MIS 2 was mainly restricted to valley glaciation. Local deviations occur: in the central Kyrgyz Tian Shan paleoglaciers were more extensive and we propose that the topographic context explains this pattern. Correlation between glacial stages prior to late MIS 2 is less reliable, because of the low number of samples and/or the poor resolution of the dating. With the current resolution and spatial coverage of robustly-dated glacier limits we advise that paleoclimatic implications for the Tian Shan glacial chronology beyond MIS 2 are speculative and that continued work toward robust glacial chronologies is needed to resolve questions regarding drivers of past glaciation in the Tian Shan and Central Asia.

  • 3.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Caffee, Marc W.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Rogozhina, Irina
    Ivanov, Mikhail N.
    Petrakov, Dmitry A.
    Walther, Michael
    Rudoy, Alexei N.
    Zhang, Wei
    Orkhonselenge, Alexander
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lifton, Nathaniel A.
    Jansson, Krister N.
    Paleoglaciation on opposite flanks of the Ikh-Turgen Mountains, Central Asia: Importance of style of moraine deposition for 10-Be surface exposure datingManuscript (preprint) (Other academic)
    Abstract [en]

    The ages of marginal moraines that record extensive glacier expansions across the Altai Mountains of Central Asia are poorly documented. We present 18 10Be exposure ages from moraines in valleys on opposite flanks of the Ikh-Turgen Mountains. On the eastern side, exposure ages from a latero-frontal moraine indicate deglaciation during MIS 3 (45.3±2.7 ka) and MIS 2 (22.8±3.5 ka). Corresponding exposure ages, from the western side, indicate a more complex story with large scatter (~14-53 ka). Owing to their close proximity, the paleoglaciers should have responded similarly to climate forcing, yet they exhibited a distinctly different behavior. We propose that differences in glacier dynamics caused differences in ice-marginal depositional environments, explaining the scatter in exposure ages on the western side. This study shows the importance of style of deposition in chronological studies of glacial landforms and demonstrates that certain moraine types can be difficult to use as paleoclimate proxies.

  • 4.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Topographic and climatic controls on paleoglaciation patterns across the Tian Shan and Altai Mountains, Central AsiaManuscript (preprint) (Other academic)
    Abstract [en]

    Reconstructing spatial patterns of the extents and dynamics of paleoglaciers across Central Asia is key in understanding the mechanisms of global environmental change. The Tian Shan and Altai Mountains are located in the continental interior of Eurasia, at the confluence of several major climate systems. In order to test hypothesized patterns in paleoglacier extent, and to test the role of paleoclimate and mountain topography in modulating the evolution of these glacial systems, we perform a domain-wide terrain analysis. We first divide the Tian Shan and the Altai Mountains into six physiographic regions delineated by major drainage divides and outlining generalised climate zones. Thereafter we mine published datasets on the distribution of glaciers and glacial landforms, calculate their area-elevation distributions (hypsometry), and extract present-day regional equilibrium line altitudes (ELAs) and long-term average ELAs (paleo-ELAs). We show that the use of glacial landform hypsometry is an effective tool to quantify broad-scale paleoglaciation patterns and find that there is a regional variability in glacier extents across the Tian Shan and Altai Mountains. Reconstructed ELAs show pronounced spatial gradients; increasing ELAs from northern to southern Tian Shan, and increasing ELAs from the northern to both the southeastern and southwestern Altai Mountains. In contrast, maximum paleoglaciation patterns and paleo-ELAs were more uniform across the two mountain systems, with inter-regional topographic variability influencing moraine distributions and thus complicating regional paleo-ELA determinations. Because estimated paleo-ELAs were relatively uniform across the Tian Shan and Altai Mountains, the paleo-ELA lowering were most pronounced in the more continental southern and eastern regions. Our current data is insufficient to explain whether this observation is the result of a different regional paleoclimatic regime than today, or if paleoglaciers responded dynamically different to a paleoclimate forcing of the same magnitude. Our ELA reconstructions also lack temporal constraints, so we furthermore propose that future studies systematically compare hypsometry-derived ELA reconstructions with those stemming from surface energy mass balance models, other proxy records (i.e. lake- and ice core records), and from chronologically constrained ice-marginal moraines.  

  • 5.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lifton, Nathaniel A.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Petrakov, Dmitry A.
    Caffee, Marc W.
    Ivanov, Mikhail N.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Rogozhina, Irina
    Usubaliev, Ryskul
    Evaluating the timing of former glacier expansions in the Tian Shan: a key step towards robust spatial correlationsIn: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArticle in journal (Refereed)
    Abstract [en]

    The timing of past glaciation across the Tian Shan provides a proxy for past climate change in this critical area. Correlating glacial stages across the region is difficult but cosmogenic exposure ages have considerable potential. A drawback is the large observed scatter in 10Be surface exposure data. To quantify the robustness of the dating, we compile, recalculate, and perform statistical analyses on sets of 10Be surface exposure ages from 25 moraines, consisting of 114 new and previously published ages. We assess boulder age scatter by dividing boulder groups into quality classes and rejecting boulder groups of poor quality. This allows us to distinguish and correlate robustly dated glacier limits, resulting in a more conservative chronology than advanced in previous publications. Our analysis shows that only one regional glacial stage can be reliably correlated across the Tian Shan, with glacier expansions occurring between 15 and 28 ka during marine oxygen isotope stage (MIS) 2. However, there are examples of older more extensive indicators of glacial stages between MIS 3 and MIS 6. Paleoglacier extent during MIS 2 was mainly restricted to valley glaciation. Local deviations occur: in the central Kyrgyz Tian Shan paleoglaciers were more extensive and we propose that the topographic context explains this pattern. Correlation between glacial stages prior to late MIS 2 is less reliable, because of the low number of samples and/or the poor resolution of the dating. With the current resolution and spatial coverage of robustly-dated glacier limits we advise that paleoclimatic implications for the Tian Shan glacial chronology beyond MIS 2 are speculative and that continued work toward robust glacial chronologies is needed to resolve questions regarding drivers of past glaciation in the Tian Shan and Central Asia. 

  • 6. Fabel, D.
    et al.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Evaluating a cosmogenic nuclide calibration site at Mt Billingen, Sweden2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    During retreat of the Fennoscandian ice sheet, a large ice-dammed lake formed along its south-eastern margin. The ice damming this Baltic Ice Lake (BIL) was breached at the northern tip of Mt Billingen, resulting in a catastrophic drainage of _9400 km3 of meltwater and an associated lowering of the BIL by _25 m. This event occurred at _11500 calibrated 14C yr, determined using bio-, litho, and chrono-stratigraphic data from numerous lake and bog cores in the immediate vicinity of Mt Billingen (e.g. Björck, 1995) and the varve chronology from the Baltic Sea tied to the GRIP _18O record (Andrén et al., 2002). The dramatic fall in the level of the BIL is recorded by raised shorelines, isolation of lake basins, and changes in the characteristics of marine sediments (Bodén et al., 1997; Lambeck, 1999). We collected material for a pilot study from (1) scoured bedrock directly in the path of the meltwater outflow, (2) large (> 2m x 2m x 2m) sandstone boulders derived from the northern tip of Mt Billingen and transported by the flood, (3) bedrock from a meltwater-scoured area further down-current (called Klyftamon), and (4) cobbles from the surface of thick floodwater deposits downstream of the scoured Klyftamon bedrock surface. The results of 10Be analysis of these samples are internally consistent between the sampling locations, and we compare these to the available 14C data in order to assess the validity of the site as a potential calibration site for cosmogenic nuclide methods.

    Andrén, T., Lindeberg, G. and Andrén, E., 2002. Evidence of the final drainage of the Baltic Ice Lake and the brackish phase of the Yoldia Sea in glacial varves from the Baltic Sea. Boreas, 31: 226-238.

    Björck, S., 1995. A review of the history of the Baltic Sea, 13.0-8.0 ka BP. Quaternary International, 27: 19-40.

    Bodén, P., Fairbanks, R.G., Wright, J.D. and Burckle, L.H., 1997. High-resolution isotope records from southwest Sweden: The drainage of the Baltic Ice Lake and Younger Dryas ice margin oscillations. Paleoceanography, 12(1): 39-49.

    Lambeck, K., 1999. Shoreline displacements in southern-central Sweden and the evolution of the Baltic Sea since the last maximum glaciation. Journal of the Geological Society, London, 156: 465-486.

  • 7. Fabel, D.
    et al.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Björck, S.
    Caffee, M.
    Cosmogenic nuclide calibration: The Baltic Ice Lake drainage2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    During retreat of the Fennoscandian ice sheet, a large ice-dammed lake formed along its south-eastern margin. The ice damming this Baltic Ice Lake (BIL) was breached at the northern tip of Mt Billingen, resulting in a catastrophic drainage of ~8000 km3 of meltwater and an associated lowering of the BIL by ~25 m. This event occurred at ~11,500 calibrated 14C yr, determined using bio-, litho, and chrono-stratigraphic data from numerous lake and bog cores in the immediate vicinity of Mt Billingen and the varve chronology from the Baltic Sea tied to the GRIP 18O record.

    The dramatic fall in the level of the BIL is recorded by raised shorelines, isolation of lake basins, and changes in the characteristics of marine sediments. We collected material for a pilot study from (1) scoured bedrock directly in the path of the meltwater outflow, (2) large (> 2m x 2m x 2m) sandstone boulders derived from the northern tip of Mt Billingen and transported by the flood, (3) bedrock from a meltwater-scoured area further down-current (called Klyftamon), and (4) cobbles from the surface of thick floodwater deposits downstream of the scoured Klyftamon bedrock surface. The results of 10Be analysis of these samples

    are internally consistent between the sampling locations, and we compare these to the available 14C data in order to assess the validity of the site as a potential calibration site for cosmogenic nuclide methods

  • 8. Fabel, D.
    et al.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, J.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dahlgren, K.I.T.
    Retreat rate of the northern Fennoscandian Ice Sheet margin2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    The deglaciation chronologies of the northern and north-eastern margins of the Fennoscandian Ice Sheet are relatively poorly constrained. This is because the principal methodological tool to trace and date the deglaciation pattern, the occurrence of deglaciation varves, does not apply in the northernmost regions of Fennoscandia. Moreover, a paucity of radiocarbon dates allows for only a most generalised pattern for the post-Younger Dryas shrinkage of the ice sheet to its final deglaciation configuration in the northern Swedish mountains. We are tracing the deglaciation of the Fennoscandian Ice Sheet from its Younger Dryas terminal moraines in northern Norway and eastern Finland towards the northern Swedish mountains, using cosmogenic nuclide apparent exposure ages of depositional and erosional features related to the former ice sheet margin. Because the ice sheet had initially warm-based conditions close to its margin, the dominant morphology is one of eskers and aligned lineation systems such as crag-and-tails. Abundant meltwater has locally eroded bedrock to considerable depth and deposited fans or deltas perched above current local base levels. Subglacial conditions during final deglaciation close to the mountain range were cold-based, thus inhibiting the formation of eskers and lineation systems. However, there is a ubiquity of meltwater erosional imprints and occasional plucking scars where, locally, pressure-melting conditions were reached. Surface exposure ages from these different geomorphological settings should yield true deglaciation ages provided the following conditions are met, (i) erosion on crags of crag-and-tails, across transverse erosional scarps, and in meltwater channels has exposed bedrock surfaces without a prior exposure history, and (ii) depositional features contain exposed boulders without a prior exposure history. Results show that transverse erosional scarps and erratics yield reliable deglaciation ages, but that bedrock samples from meltwater channels and crag-and-tails and sediment samples from eskers occasionally yield unreliable deglaciation ages due to cosmogenic nuclide inheritance and potential shielding by snow. Apparent deglaciation ages range from _14 ka at the Younger Dryas moraine to _8 ka approximately 500 km to the south in the northern Swedish Mountains. The spread of ages do not deviate from what would be expected for a regular uninterrupted retreat by the ice margin

  • 9.
    Fritzon, Ruben
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Goodfellow, Bradley
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Estholm, Madelene
    Caffee, Marc
    Evaluating geochemical evidence of earthquake periodicity, Sparta Fault, Southern GreeceManuscript (preprint) (Other academic)
    Abstract [en]

    Determining prehistoric earthquake periodicity and magnitudes is important for risk assessments in seismically active areas. We evaluate a geochemical method, which has previously been used to identify prehistoric slips on normal fault scarps through an analysis of variations in the concentration of rare earth elements and Y (REE-Y) along vertical transects. Our study object is the Sparta Fault, a normal fault in southern Greece, developed in limestone and previously documented, and dated using 36Cl, to have been last active 464 BC. From geochemical analyses of 39 fault rock samples, we conclude that REE-Y concentrations correlate strongly with the abundance of quartz and possibly other heterogeneities in the fault scarp. Because the sampled fault rock is a protocataclasite, formed at depth, variations in the abundance of quartz are not associated with prehistoric movements along the fault. We therefore conclude that geochemical evidence does not provide a reliable paleoseismic proxy for fault movement. We also present data indicating a co-variation between quartz and 36Cl concentrations, which we suggest requires a re-examination of this widely used application of the cosmogenic nuclide surface exposure dating method.

  • 10.
    Fu, Ping
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan M.
    Purdue University.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zhou, Li Ping
    Peking University.
    Glacial geomorphology and paleoglaciation patterns in Shaluli Shan, the southeastern Tibetan Plateau — Evidence for polythermal ice cap glaciation2013In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 182, 66-78 p.Article in journal (Refereed)
    Abstract [en]

    Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area on the southeastern TibetanPlateau. Our studies provide evidence for multiple glaciations, including the formation of regional ice caps andvalley glaciers. The low-relief topographywithin the Shaluli Shan, the Haizishan Plateau, and Xinlong Plateau displayzonal distributions of glacial landforms that is similar to those imprinted by Northern Hemisphere ice sheetsduring the last glacial cycle, indicating the presence of regional, polythermal ice caps. Abundant alpine glaciallandforms occur on high mountain ranges. The pattern of glaciated valleys centered on high mountain rangesand ice-scoured low relief granite plateaus with distinctive patterns of glacial lineations indicate a strong topographiccontrol on erosional and depositional patterns by glaciers and ice caps. In contrast to the Shaluli Shan,areas farther north and west on the Tibetan Plateau have not yielded similar landform evidence for regionalice capswith complex thermal basal conditions. Such spatial differences across the Tibetan Plateau are the resultof variations in climate and topography that control the extent and style of glaciations and that reinforce the importanceof detailed geomorphological mapping for understanding paleoclimate variations and characteristics offormer glaciations.

  • 11.
    Fu, Ping
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Zhou, Liping
    Department of Urban and Environmental Sciences, Peking University, China.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geomorphology of the Haizi Shan area, SE Tibetan Plateau2009Conference paper (Refereed)
    Abstract [en]

    The Haizi Shan area on the SE Tibetan Plateau is characterized by an elliptical relatively low relief plateau surrounded by steeper fluvial valleys. Glacial deposits and erosive imprints are widely distributed indicating former glacier expansions of varying extents in a presently ice-free area. We have initiated a project on the glacial history of the Haizi Shan area and we here present some initial mapping results. Glacial landforms have been mapped based on remote sensing (SRTM digital elevation model, Landsat ETM+ satellite imagery, and Google Earth) and one short reconnaissance field season. Well-preserved moraines from different stages and distinctive U-shaped glacial valleys are abundant (Fig. 1). In the Daocheng Valley southwest of the Haizi Shan Plateau we have mapped glacial deposits in the form of discontinued moraine ridges at Sangdui village. This line, which might be the maximum Quaternary glacial extent, can be traced for several kilometers along the western side of the valley as dispersed erratic boulders. This implies that during the maximum glaciation, ice from the Haizi Shan Plateau crossed the valley and reached up to the piedmont of the opposite mountain. Smaller in extent than the former, numerous large moraine ridges reach down towards valley floors along the edges of the Haizi Shan Plateau. In several locations these valleys lack cirque heads indicating former outlet glaciers emanating from a Haizi Shan ice cap. We will use TCN and OSL dates of samples collected from numerous ice marginal moraines of the Haizi Shan Plateau to determine a glacial chronology. Hence, using remote sensing, field investigations and numerical dating techniques for the Haizi Shan we aim to advance our knowledge on Quaternary glaciations of the SE Tibetan Plateau.

  • 12.
    Fu, Ping
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan M.
    Purdue University.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Caffee, Marc W.
    Purdue University.
    Complex erosion patterns produced by the Haizishan paleo-ice capManuscript (preprint) (Other academic)
    Abstract [en]

    Determining patterns and rates of glacial erosion is important in understanding landscape evolution, topographic relief production, geochemical cycles, climate change, and glacial thermal regimes of paleo glaciers and ice sheets. Combining in situ $^{10}$Be and $^{26}$Al apparent exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4 000 km$^2$ Haizishan paleo-ice cap on the southeastern Tibetan Plateau. Our results show that ice caps developed several times on the low relief Haizishan Plateau and produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with last deglaciation, complete resetting of the cosmogenic exposure age clock indicates that more than 2 m of glacial erosion occurred during the last major glaciation (which in this area correlates with the global Last Glacial Maximum (gLGM)).  However, older apparent exposure ages on bedrock and in saprolites profiles in areas known to have been covered by the paleo ice cap during gLGM indicate inheritance and thus limited or no erosion by the last ice cap in several areas, including the central zone of the paleo ice cap and at the head of an outlet glacier. Similarly, cosmogenic radionuclide depth profiles in saprolites show erosion of $>$2 m in an outlet valley bottom and in the mountains that make up the northern border of the paleo ice cap, while samples from saprolites in areas of otherwise scoured terrain have a large nuclide inheritance indicating limited erosion. As patterns of glacial erosion intensity are largely driven by basal thermal regime, our results are consistent with a hypothesis of complex thermal regimes for the paleo Haizishan ice cap during gLGM that was proposed previously on the basis of landform patterns. Future work, including glaciological modeling, is required to fully understand the implications and mechanisms of the complex thermal regime of this paleo ice cap.

  • 13.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, D.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Caffee, M.
    Bintanja, R.
    Vertically mixed and unmixed: Do surface features tell the whole story? An investigation of glacial regolith profiles using in-situ produced cosmogenic radionuclides2007In: EOS, 2007Conference paper (Refereed)
    Abstract [en]

    Whether a regolith is unmixed or mixed is critical to determining its erosion rate or age from in situ-produced cosmogenic nuclides. We use in situ-produced 10Be and 26Al in quartzite clasts extracted from depth profiles to investigate mixing of a periglacially-sorted till blanketing a plateau in the northern Swedish mountains. Our data indicate significant intra-site variations from a completely unmixed to a fully mixed regolith. We conclude that caution must be exercised in assuming that an entire regolith is either unmixed or mixed from interspersed depth profiles and that the degree of mixing may differ significantly from that indicated by observation of surface features. From the difference between the surface isotope concentration of an unmixed profile and the average isotope concentration of a fully mixed profile, we confirm that the regolith is a glacial till and that it could have been emplaced in a single event. Incorporating isotope concentrations, 26Al/10Be ratios, and an isostasy and ice sheet burial model we date the till emplacement to the Saalian glaciation (~ 200 to 130 ka).

  • 14.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fredin, Ola
    Derron, Marc-Henri
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Weathering processes and Quaternary origin of an alpine blockfield in Arctic Sweden2009In: Boreas, ISSN 0300-9483, Vol. 38, no 2, 379-398 p.Article in journal (Refereed)
    Abstract [en]

    The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigatedthrough an examination of fine matrix and clasts from two pits excavated across ridge-top sorted circles; one on asummit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorlycrystallized Al- and Fe-oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occursin the saddle. In both locations, volumes of clay-sized matrix are low, mass balance calculations indicate onlyminor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). Inaddition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sortedcircles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix-rich circle centres,and some rind development, which increases in frequency in the clast-rich rings. The dominance of physicalweathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicatethat the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developingduring interglacials, interstadials and the Holocene, primarily through subsurface weathering processes.

  • 15.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Deciphering a non-glacial/glacial landscape mosaic in the northern Swedish mountains2008In: Geomorphology, Vol. 93, no 3-4, 213-232 p.Article in journal (Refereed)
    Abstract [en]

    Relict surfaces contain information on past surface processes and long-term landscape evolution. A detailed investigation of relict non-glacial surfaces in a formerly glaciated mountain landscape of northern Sweden was completed, based on interpretation of colour infrared aerial photographs, analysis in a GIS, and fieldwork. Working backwards from landscape to process, surfaces were classified according to large- and small-scale morphologies that result from the operation of non-glacial processes, the degree of weathering, regolith characteristics, and the style of glacial modification. Surfaces were also compared in the GIS according to elevation, slope angle, and bedrock lithology. The study revealed five types of relict non-glacial surfaces but also two types of extensively weathered glacial surfaces that were transitional to relict non-glacial surfaces, illustrating spatially variable processes and rates of non-glacial and glacial landscape evolution. Rather than being static preglacial remnants, relict non-glacial surfaces are dynamic features that have continued to evolve during the Quaternary. The classification provides hypotheses for landscape evolution that can be field tested through, for example, terrestrial cosmogenic nuclide studies and geochemical analyses of fine matrix materials. The classification may be applicable to relict non-glacial surfaces in other formerly glaciated landscapes

  • 16.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Fredin, Ola
    Derron, M.-H.
    Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    Relict non-glacial surfaces occur within many formerly glaciated landscapes

    and contain important information on past surface processes and long-term landscape evolution. While cosmogenic dating has confirmed

    the antiquity of relict non-glacial surfaces, the processes that contribute to their evolution and, consequently, the time scales over which they develop remain poorly understood. Of particular importance

    is the possibility that relict non-glacial surfaces may provide geomorphic markers for the reconstruction of preglacial landscapes, which would allow subsequent glacial erosion to be quantified. Furthermore,

    relict non-glacial surfaces may also hold information on preglacial

    and interglacial environmental conditions. An investigation of relict non-glacial surfaces was undertaken through remote sensing, mapping and analysis of surfaces in a GIS, and regolith studies involving

    cosmogenic dating-, grain size-, X-ray diffraction-, and X-ray fluorescence

    analyses. On the basis of these on-going studies, we show that depending on spatial variables such as bedrock lithology, slope, regolith thickness, and the abundance of fine matrix and water some surfaces are denuding very slowly, while others display more rapid denudation. High spatial variability in denudation rates results in changing surface morphologies over time. Rather than being static preglacial

    remnants, relict non-glacial surfaces are dynamic features that have evolved during the Quaternary. While reconstructions of preglacial

    landscapes and subsequent quantifications of glacial erosion from relict non-glacial surfaces remain valid, the Quaternary evolution of these surfaces should also be considered.

  • 17.
    Goodfellow, Bradley
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Fredin, Ola
    Derron, M.-H.
    Relict non-glacial surfaces in formerly glaciated landscapes: dynamic landform systems?2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    Relict non-glacial surfaces occur within many formerly glaciated landscapes and contain

    important information on past surface processes and long-term landscape evolution

    (Goodfellow, 2007). While cosmogenic dating has confirmed the antiquity of

    relict non-glacial surfaces, the processes that contribute to their evolution and, consequently,

    the time scales over which they develop remain poorly understood. Of particular

    importance is the possibility that relict non-glacial surfaces may provide geomorphic

    markers for the reconstruction of preglacial landscapes, which would allow

    subsequent glacial erosion to be quantified. Furthermore, relict non-glacial surfaces

    may also hold information on preglacial and interglacial environmental conditions.

    An investigation of relict non-glacial surfaces was undertaken through remote sensing,

    mapping and analysis of surfaces in a GIS, and regolith studies involving cosmogenic

    dating-, grain size-, X-ray diffraction-, and X-ray fluorescence analyses. On

    the basis of these on-going studies, we show that depending on spatial variables such

    as bedrock lithology, slope, regolith thickness, and the abundance of fine matrix and

    water some surfaces are denuding very slowly, while others display more rapid denudation.

    High spatial variability in denudation rates results in changing surface morphologies

    over time. Rather than being static preglacial remnants, relict non-glacial

    surfaces are dynamic features that have evolved during the Quaternary. While reconstructions

    of preglacial landscapes and subsequent quantifications of glacial erosion

    from relict non-glacial surfaces remain valid, the Quaternary evolution of these surfaces

    should also be considered.

    Goodfellow B.W., 2007. Relict non-glacial surfaces in formerly glaciated landscapes.

    Earth-Science Reviews, 80(1-2): 47-73.

  • 18.
    Goodfellow, Bradley W.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stanford University, USA.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Martel, Stephen J.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Controls of tor formation, Cairngorm Mountains, Scotland2014In: Journal Of Geophysical Research: Earth Surface, ISSN 2169-9003, Vol. 119, no 2, 225-246 p.Article in journal (Refereed)
    Abstract [en]

    Tors occur in many granitic landscapes and provide opportunities to better understand differential weathering. We assess tor formation in the Cairngorm Mountains, Scotland, by examining correlation of tor location and size with grain size and the spacing of steeply dipping joints. We infer a control on these relationships and explore its potential broader significance for differential weathering and tor formation. We also assess the relationship between the formation of subhorizontal joints in many tors and local topographic shape by evaluating principle surface curvatures from a digital elevation model of the Cairngorms. We then explore the implications of these joints for tor formation. We conclude that the Cairngorm tors have formed in kernels of relatively coarse grained granite. Tor volumes increase with grain size and the spacing of steeply dipping joints. We infer that the steeply dipping joints largely formed during pluton cooling and are more widely spaced in tor kernels because of slower cooling rates. Preferential tor formation in coarser granite with a wider joint spacing that is more easily grusified indicates that joint spacing is a dominant control on differential weathering. Sheet jointing is well developed in tors located on relatively high convex surfaces. This jointing formed after the gross topography of the Cairngorms was established and before tor emergence. The presence of closely spaced (tens of centimeters), subhorizontal sheeting joints in tors indicates that these tors, and similarly sheeted tors elsewhere, formed either after subaerial exposure of bedrock or have progressively emerged from a regolith only a few meters thick. Key Points <list list-type=bulleted id=jgrf20195-list-0001> <list-item id=jgrf20195-li-0001>Tors form in kernels of coarse-grained granite among finer-grained granite <list-item id=jgrf20195-li-0002>Wide joint spacing in tors attributable to a slow cooling rate of the granite <list-item id=jgrf20195-li-0003>Sheet jointing discounts tor formation within a thick regolith

  • 19.
    Goodfellow, Bradley W.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Lund University, Sweden.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, D.
    Fredin, O.
    Derron, M. -H.
    Bintanja, R.
    Caffee, M. W.
    Arctic-alpine blockfields in the northern Swedish Scandes: late Quaternary - not Neogene2014In: Earth Surface Dynamics, ISSN 2196-6311, Vol. 2, no 2, 383-401 p.Article in journal (Refereed)
    Abstract [en]

    Autochthonous blockfield mantles may indicate alpine surfaces that have not been glacially eroded. These surfaces may therefore serve as markers against which to determine Quaternary erosion volumes in adjacent glacially eroded sectors. To explore these potential utilities, chemical weathering features, erosion rates, and regolith residence durations of mountain blockfields are investigated in the northern Swedish Scandes. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay / silt ratios, secondary mineral assemblages, and imaging of chemical etching of primary mineral grains in fine matrix are each used for this purpose. Secondly, erosion rates and regolith residence durations of two of the summits are inferred from concentrations of in situ-produced cosmogenic Be-10 and Al-26 in quartz at the blockfield surfaces. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite consistent variability according to slope position. In addition, average erosion rates of similar to 16.2 and similar to 6.7 mm ka(-1), calculated for the two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few metres in thickness, within a late Quaternary time frame. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. The persistence of autochthonous blockfields over multiple glacial-interglacial cycles confirms their importance as key markers of surfaces that were not glacially eroded through, at least, the late Quaternary. However, presently blockfield-mantled surfaces may potentially be subjected to large spatial variations in erosion rates, and their Neogene regolith mantles may have been comprehensively eroded during the late Pliocene and early Pleistocene. Their role as markers by which to estimate glacial erosion volumes in surrounding landscape elements therefore remains uncertain.

  • 20.
    Gribenski, Natacha
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lukas, Sven
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ivanov, Mikhail N.
    Heyman, Jakob
    Petrakov, Dmitry A.
    Rudoy, Alexei
    Clifton, Tom
    Lifton, Nathaniel A.
    Caffee, Marc W.
    Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 149, 288-305 p.Article in journal (Refereed)
    Abstract [en]

    The Southern part of the Russian Altai Mountains is recognized for its evidence for catastrophic glacial lake outbursts. However, little is known about the late Pleistocene paleoglacial history, despite the interest in such reconstructions for constraining paleoclimate. In this study, we present a detailed paleoglaciological reconstruction of the Chagan Uzun Valley, in the Russian Altai Mountains, combining for the first time detailed geomorphological mapping, sedimentological logging, and in situ cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. The Chagan Uzun Valley exhibits the most impressive glacial landforms of this sector of the Altai, with extensive lobate moraine belts deposited in the intramontane Chuja Basin, reflecting a series of pronounced former glacial advances. Observations of “hillside-scale” folding and extensive faulting of pre-existing soft sediments within the outer moraine belts, together with the geomorphology, strongly indicate that these moraine belts were formed during surge-like events. Identification of surge-related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate, but instead largely influenced by various internal and external factors. Therefore, no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the Chagan Uzun Valley/Chuja basin. In contrast, the inner (up-valley) glacial landforms of the Chagan Uzun valley were likely deposited during retreat of temperate valley glaciers, close to equilibrium with climate, and so most probably triggered by a general warming. Cosmogenic ages associated with the outermost, innermost, and intermediate stages all indicate deposition times clustered around 19 ka. However, the actual deposition time of the outermost moraine may slightly predate the 10Be ages due to shielding caused by subsequent lake water coverage. This chronology indicates a Marine Isotope Stage (MIS) 2 last maximum extent of the Chagan Uzun Glacier, and an onset of the deglaciation around 19 ka. This is consistent with other regional paleoclimate proxy records and with the Northern Hemisphere glaciation chronology. Finally, this study also highlights the highly dynamic environment in this area, with complex interactions between glacial events and the formation and drainage of lakes.

  • 21.
    Gribenski, Natacha
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lukas, Sven
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ivanov, Mikhail N.
    Heyman, Jakob
    Petrakov, Dmitry A.
    Rudoy, Alexei
    Clifton, Tom
    Lifton, Nathaniel A.
    Caffee, Marc W.
    Reply to comment received from J. Herget et al. regarding "Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai" by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-3052017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 168, 219-221 p.Article in journal (Refereed)
  • 22.
    Harbor, Jon
    et al.
    Department of Earth and Atmospheric Sciences, Purdue University.
    Fu, Ping
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Zhou, Liping
    Department of Geography, Peking University.
    Glacial Geomorphology of the Haizi Shan area, SE Tibetan Plateau2010Conference paper (Refereed)
    Abstract [en]

    The Haizi Shan area on the SE Tibetan Plateau is characterized by a relatively low relief plateau surrounded by steeper fluvial valleys. Glacial deposits and erosive imprints are widely distributed indicating former glacier expansions of varying extents in a presently ice-free area. Glacial landforms have been mapped using remote sensing (SRTM digital elevation model, Landsat ETM+ satellite imagery, and Google Earth) and field reconnaissance. Well-preserved moraines from different stages and distinctive U-shaped glacial valleys are abundant. In the Daocheng Valley southwest of the Haizi Shan Plateau we have mapped glacial deposits which likely reflect the maximum Quaternary glacial extent for several kilometers along the western side of the valley. During the maximum glaciation, we infer that ice from the Haizi Shan Plateau crossed the valley and extended in to tributary valleys. Numerous large moraine ridges also reach down towards valley floors along the edges of the Haizi Shan Plateau. In several locations these valleys lack cirque heads indicating former outlet glaciers emanating from a Haizi Shan ice cap. In ongoing work we are using TCN and OSL to determine a glacial chronology for this area and advance our knowledge of Quaternary glaciations of the SE Tibetan Plateau.

  • 23. Heyman, Jakob
    et al.
    Applegate, Patrick J.
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Boulder height - exposure age relationships from a global glacial Be-10 compilation2016In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 34, 1-11 p.Article in journal (Refereed)
    Abstract [en]

    Cosmogenic exposure dating of glacial boulders is commonly used to estimate the timing of past glaciations because the method enables direct dating of the duration a boulder has been exposed to cosmic rays. For successful dating, the boulders must have been fully shielded from cosmic rays prior to deposition and continuously exposed to cosmic rays ever since. A common assumption is that boulder height (the distance between the top of the boulder and the surrounding surface) is important, and that tall boulders are more likely to have been continuously exposed to cosmic rays than short boulders and therefore yield more accurate exposure ages. Here we test this assumption 'based on exposure age clustering for groups of glacial boulders (and single cobbles) Be-10 exposure ages that have recorded boulder heights (3741 boulders; 579 boulder groups with >= 3 boulders). Of the full set of boulder groups with >= 3 boulders, 21% fulfill a reduced chi square criterion (chi(2)(R) < 2) for well-clustered exposure ages. For boulder groups containing only tall boulders, the fraction of well-clustered exposure age groups is consistently larger. Moreover, this fraction of well-clustered exposure age groups increases with the minimum boulder height in each group. This result confirms the common assumption that tall boulders are generally better targets for cosmogenic exposure dating compared to short boulders. Whereas the tall boulder groups have a significantly larger fraction of well-clustered exposure age groups, there is nonetheless a dominant fraction (>50%) of the boulder groups with scattered exposure ages, highlighting the problem with prior and incomplete exposure for cosmogenic dating of glacial boulders.

  • 24.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hubbard, Alun
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacier mass balance modelling of the Tibetan Plateau – mesh dependence issues2008Conference paper (Refereed)
    Abstract [en]

    The Tibetan Plateau is an extraordinary topographic feature which exerts a major impact on regional and global climate. Its glacierised mountain ranges attain extreme altitudes and represent an important water resource for more than a billion people in Asia. Understanding the past glacial history of the Tibetan Plateau therefore is important to understanding global and regional climate and glacier hydrological evolution. A regional glacier modelling study has been initiated as part of an umbrella project aiming towards reconstructing the Quaternary palaeoglaciology of the Tibetan Plateau. On the basis of field studies which includes cosmogenic exposure-age dating, it is now generally recognised that former glaciers on the Tibetan Plateau, while more extensive than today, were still restricted to individual mountain areas. In contrast, a handful of previous modelling studies (Kuhle et al. 1989; Calov & Marsiat 1998; Bintanja et al. 2002; Casal et al. 2004) yield a bifurcated result with either 1) the growth of plateau-wide ice sheets (thus overshooting field evidence) or, 2) virtually no ice (which undershoots field evidence).

    We apply and test a positive degree day (PDD) model across the Tibetan Plateau to explore the parameter sensitivity and potential issues of grid-dependence. Utilising the 1km mean monthly (1950 – 2000) distributions of temperature and precipitation from the WorldClim database as a contemporary reference climatology, a suite of PDD experiments are run to predict present day ice cover. At a resolution of 1 km the algorithm nicely identifies zones of positive mass balance (accumulation) across most major contemporary glaciarised areas. Unsurprisingly increased grid resolution yields a significant decrease in the predicted accumulation area with a 40 km grid completely failing to predict accumulation across the domain. Such mesh dependence with larger grid-resolutions yielding less accumulation illustrates a major flaw in large-scale, low resolution ice modelling in areas of high topographical relief where adequate sub-grid parameterisation of accumulation/flow/melt processes have not been accounted for in a meaningful manner (e.g. Marshall & Clarke 1999). The result of the 20 km resolution PDD model can be manipulated to converge by applying extreme perturbations in temperature (c. -10 K) or precipitation (c. + 8000 %) but this yields plateau-wide accumulation areas far exceeding field evidence of glaciation. Our results indicate that the bifurcation in Quaternary ice extent identified in previous ice sheet modelling studies of the Tibetan Plateau are very likely a consequence of grid-resolution related issues implicit to the models applied.

    References

    Bintanja R., van de Wal R.S.W., Oerlemans J. 2002: Global ice volume variations through the last glacial cycle simulated by a 3-D ice-dynamical model. Quaternary International, 95-96, 11-23.

    Calov R, Marsiat I. 1998: Simulations of the Northern Hemisphere through the last glacial-interglacial cycle with a vertically integrated and a three-dimensional thermomechanical ice-sheet model coupled to a climate model. Annals of Glaciology, 27, 169-176.

    Casal T.G.D., Kutzbach J.E., Thompson L.G. 2004: Present And Past Ice-Sheet Mass Balance Simulations For Greenland And The Tibetan Plateau. Climate Dynamics, 23, 407-425.

    Kuhle M., Herterich K., Calov R. 1989: On the Ice Age Glaciation of the Tibetan Highlands and its Transformation into a 3-D Model. GeoJournal, 19, 201-206.

    Marshall S.J., Clarke G.K.C. 1999: Ice sheet inception: subgrid hypsometric parameterization of mass balance in an ice sheet model. Climate Dynamics, 15, 533-550.

  • 25.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    A glacial geomorphological map of the northeastern Tibetan plateau2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    The extent and chronology of Quaternary glaciations on the Tibetan plateau are still elusive, and reconstructions range from an ice sheet covering the entire plateau to local valley glaciers restricted to the highest mountain areas. Glacial landforms and deposits constitute the primary data set used for reconstructing the extent of former glaciers. However, this data has rarely been systematically mapped over large areas, making it problematic to evaluate proposed palaeoglaciological reconstructions. Today, detailed maps of the glacial geomorphology, such as those which form the basis for reconstructions of the North American and European ice sheets, only exist for restricted areas on the Tibetan plateau. Hence, in order to evaluate existing palaeoglaciological reconstructions, and to be able to propose alternative reconstructions, regional-scale or plateau-wide scale mapping efforts are required.

    We here present the first detailed map of the glacial geomorphology covering a large area of the northeastern Tibetan plateau, encompassing the location of a previously suggested regional-scale ice sheet – the Huang He ice sheet. The map covers an area of ~135.000 km2, is centered around the Bayan Har Mountains, and is constrained in the southwest by Chang Jiang (Yangtze River). The map is based on an interpretation of satellite images (Landsat ETM+, Landsat TM, ASTER), a digital elevation model (SRTM 90 m resolution) and Google Earth imagery. Field checks of mapped landforms have been performed during two field seasons, 2005 and 2006. Identified glacial landforms are marginal moraines, marginal moraine remnants, glacial hummocky terrain, glacial lineations and glacial meltwater channels.

    There is a clear pattern of numerous glacial landforms distributed in and around higher mountain areas, whereas glacial landforms are absent on surfaces in-between the higher mountain blocks. Upland areas such as the Bayan Har Mountains display a consistent pattern of glacial lineations in the higher central parts of the mountains, series of end moraines across glacially eroded valleys, and glacial hummocky terrain and meltwater channels mainly in the lower slopes of the mountains. The mapped glacial landforms reveal evidence of glacial advances of varying extent in and around several separate mountain areas. The presented map will be used for reconstructing the outline of former glaciation, which, together with chronological constraints from cosmogenic nuclide- and optically stimulated luminescence samples, will eventually form a new paleoglaciological reconstruction for the northeastern Tibetan plateau.

  • 26.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    A glacial geomorphological map of the northeastern Tibetan plateau2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    The extent and chronology of Quaternary glaciations on the Tibetan plateau remains elusive, despite intensified research over the past 20 years. While reconstructions of the North American and European ice sheets are fairly well established, the extent of Tibetan palaeo-glaciers range from an ice sheet covering the entire plateau to local valley glaciers restricted to the highest mountain areas. The primary data for reconstructing the outline of former glaciers are glacial landforms and glacial deposits. However, for the Tibetan plateau this data has rarely been systematically mapped over large areas, making it problematic to evaluate proposed palaeoglaciological reconstructions. In order to make well motivated reconstructions of the extent of palaeo-glaciers based on sound evidence, regional-scale or plateau-wide scale mapping efforts are required. We here present the first detailed glacial geomorphological map of the northeastern Tibetan plateau, covering an area of c. 135.000 km2 centered on the Bayan Har Mountains and encompassing a previously suggested ice sheet – the Huang He ice sheet. The landscape is characterized by a plateau surface at c. 4300 m asl, higher mountain groups reaching up to 1500 m above the plateau surface and marginal areas of fluvial incision by rivers draining the Tibetan plateau creating a steep, fluvial landscape. The map is based on interpretation of satellite images (Landsat ETM+, Landsat TM, ASTER), a digital elevation model (SRTM 90 m resolution) and Google Earth imagery. Field investigations of the mapped landforms have been performed during two field seasons, 2005 and 2006. We have identified and mapped glacial valleys and cirques, marginal moraines, marginal moraine remnants, glacial hummocky terrain, glacial lineations and glacial meltwater channels. Glacial landforms are abundant mainly in and around higher mountain blocks, whereas there is a lack of glacial landforms identifiable by remote sensing in the intervening, lower areas. Upland areas such as the Bayan Har Mountains display a consistent pattern of glacial lineations in the higher central parts of the mountains, marginal moraines across glacially eroded valleys and glacial hummocky terrain and meltwater channels mainly on the lower slopes of the mountains. The mapped landforms indicate glacial advances of varying extent in and around several mountain areas. The presented map, together with chronological constraints from cosmogenic isotope and optically stimulated luminescence dating, will eventually form the basis for a new palaeoglaciological reconstruction for the northeastern Tibetan plateau.

  • 27.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hättestrand, Clas
    Stroeven, Arjen P
    Glacial geomorphology of the Bayan Har sector of the NE Tibetan Plateau2008In: Journal of Maps, ISSN 1744-5647, Vol. 2008, 42-62 p.Article in journal (Refereed)
    Abstract [en]

    We here present a detailed glacial geomorphological map covering 136,500 km2 of the Bayan Har sector of the northeastern Tibetan Plateau - an area previously suggested to have nourished the most extensive Quaternary glaciers of the Tibetan Plateau. The map, presented at a scale of 1:650,000, is based on remote sensing of a 90 m SRTM digital elevation model and 15/30 m Landsat ETM+ satellite imagery. Seven landform types have been mapped; glacial valleys, glacial troughs, glacial lineations,marginal moraines, marginal moraine remnants, meltwater channels and hummocky terrain. A large number of glacial landforms exist, concentrated around mountain blocks protruding above the surrounding plateau area, testifying to former glacial activity. In contrast, large plateau areas of lower altitude lack glacial landforms. The mapped glacial geomorphology indicates multiple former glacial advances primarily by valley and piedmont glaciers, but lends no support to the hypothesis of ice sheet scale glaciation in the area. The presented glacial geomorphological map demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology of the Tibetan Plateau, and it will be used for reconstructing the paleoglaciology of the Bayan Har sector of the northeastern Tibetan Plateau.

  • 28.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Caffee, Marc W
    Department of Physics/Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Li, Yingkui
    Department of Geography, University of Missouri-Columbia, USA.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Zhou, Liping
    Department of Geography, Peking University, China.
    Constraining the glacial chronology of Bayan Har Shan, NE Tibetan Plateau – Cosmogenic exposure dating of boulders, surface pebbles/cobbles and sediment depth profiles2009In: Geophysical Research Abstracts: Vol. 11, EGU2009-12053, 2009, 2009Conference paper (Refereed)
    Abstract [en]

    The paleoglaciology of the Tibetan Plateau remains elusive, with important hiata regarding the style, extent, and timing of glaciations. Bayan Har Shan is a mountain region on the northeastern Tibetan Plateau, in a transition zone from the dry interior of the plateau in the west to the wetter eastern margin affected by the Asian monsoon. Bayan Har Shan hosts an ample record of glacial landforms and deposits indicating paleo-glaciers ranging from cirque and valley glaciers to ice-fields and ice caps. These glaciers, it has been suggested, also nourished a regional ice sheet. In an attempt to constrain the timing of glaciations in Bayan Har Shan, we have performed terrestrial cosmogenic nuclide (TCN) exposure dating on surface boulders and pebbles/cobbles from glacial deposits, and on pebbles in sediment depth profiles. The aim has been two-fold: to constrain the glacial chronology and to compare and evaluate the TCN ages of the three different TCN sample types.

    We present the result of 67 Be-10 measurements from 15 sites in central Bayan Har Shan (40 boulder samples, 12 surface pebbles/cobbles samples and 15 depth profile samples from four depth profiles). The obtained TCN apparent exposure ages of boulders and surface pebbles/cobbles range from 3 ka to 145 ka with wide age spreads within groups of samples collected from one glacial deposit. Our TCN results of three different sample types (boulders, surface pebbles/cobbles and depth profile pebbles) from the northeastern Tibetan Plateau form an intriguing data set that may yield different age estimates with different interpretation strategies. However, they permit the following conclusions to be advanced:

    • Pebbles/cobbles ages are broadly in agreement with boulder ages.

    • Three depth profiles yield exponential curves for Be-10 concentrations with depth, in agreement with theoretical TCN depth profiles; ages are in broad agreement with boulder and surface pebbles/cobbles samples.

    • Maximum ages (adopting an approach where the maximum ages constrain the minimum age of formation) of multiple sample sites are all c. 50 ka or older. This is underlined by the maximum ages around 50 ka from three moraines formed by glaciers just a few kilometres long, indicating that there has been no significant glaciation of central Bayan Har Shan over the last 50 ka.

  • 29.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Li, Yingkui
    Harbor, Jon
    Caffee, Marc
    Zhou, Liping
    Veres, Daniel
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial landforms and deposits of the Bayan Har Shan, NE Tibetan plateau – a dataset for reconstructing the extent of former glaciations2008Conference paper (Refereed)
    Abstract [en]

    Glacial reconstructions of the Tibetan plateau range from a plateau-scale ice sheet to restricted valley glaciers and ice caps. However, the Tibetan glacial landforms and sediments – although forming a crucial tool for paleoglaciological reconstructions – have rarely been mapped for larger areas. We here present data on the glacial landforms and deposits in the Bayan Har Shan area on the northeastern Tibetan plateau, previously suggested to have nourished the most extensive Quaternary Tibetan ice mass. Detailed geomorphological mapping based on remote sensing and extensive field studies reveal a generous array of glacial landforms and deposits, indicating former glaciers of varying extent. Large scale glacial landforms mapped from a digital elevation model and satellite imagery are abundant in elevated mountain blocks. The mapped landforms testify of alpine style glaciation but lend no support to the existence of any ice sheet. Field observations of glacial, and non-glacial, deposits further enhance the dataset concerning former glacial extent. Tills and erratic boulders are present within the glacial landscape based on remote sensing, but in several localities they also exist further down some distance outside mapped glacial landforms. There is a notable absence of glacial deposits around the Huang He valley and in the northern part of the study area, where they have previously been reported as evidence of a paleo-ice sheet. We argue for a non-glacial origin of deposits in these areas, because we have not found any indications of a glacial origin. The mapped landforms and deposits display an interesting dataset for paleoglaciological reconstructions. While the glacial landforms from remote sensing – by virtue of completeness covering extensive areas – present a good image of the more restricted glaciations, the identified most extensive glaciation is so far only recorded as point data in the form of glacial deposits.

  • 30.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Li, Yingkui
    Harbor, Jon
    Caffee, Marc
    Zhou, Liping
    Veres, Daniel
    Reconstructing former glacial extent of the NE Tibetan Plateau – combining remote sensing and field data of glacial geology2008In: Geophysical Research Abstracts, 2008Conference paper (Refereed)
    Abstract [en]

    Glacial reconstructions of the Tibetan Plateau range from a plateau-scale ice sheet to restricted valley glaciers and ice caps. However, glacial landforms and sediments – although forming a crucial fundament for paleoglaciological reconstructions – have rarely been mapped for extensive areas of the Tibetan Plateau. The NE Tibetan Plateau hosts a wide array of glacial landforms and deposits, and the area has been suggested to have nourished an extensive Quaternary ice mass on the Tibetan Plateau – the Huang He ice sheet. We here present data on the glacial geology of the Bayan Har Shan area, NE Tibetan Plateau, based on two diverse methods: remote sensing and field observations. Using the SRTM 90 m resolution digital elevation model, Landsat ETM+ satellite images and Google EarthTM imagery, a detailed mapping of the glacial geomorphology for a 135.000 km2 area has been performed. Mapped landforms include glacial valleys/troughs, marginal moraines, glacial lineations, meltwater channels and hummocky terrain. During 2005-2007 field work we have gathered data on glacial and non-glacial deposits. Deposits affirmative of glacial action occur in the form of till, glaciofluvial sediments and erratic boulders. Using a simple identification scheme, based on the abundance of erratic boulders, striated clasts and presence of diamictic sediments, we have mapped the occurrence of glacial deposits.

    The remote sensing and field data in general strongly support the presence of former glaciers centred on mountain blocks, and offers no support for the former existence of an ice sheet. However, there is a discrepancy between the glacial geomorphology mapped by remote sensing and the distribution of glacial deposits as mapped in the field. Glacial landforms mapped by remote sensing indicate former glaciers of varying extent, ranging from cirque glaciers to extended valley glacier networks, with glacial U-shaped valleys up to 60 km long. Whereas glacial deposits occur most frequently in the areas of mapped glacial landforms, they also occur up to 25 km outside mapped glacial landforms and indicate ice cap/ice field glaciation, presumably predating more restricted glaciations marked by marginal moraines and meltwater channels. The presence of glacial deposits in the absence of glacial morphology has implications for the large-scale glacial imprint, as glacial landforms of the most extensive glaciation(s) have either been eroded/degraded, or been buried by subsequent deposits, or else were never been formed. On the basis of an absence of erosional morphology, we conclude that erosion by such an enlarged ice cap/ice field beyond the mountains has been negligible.

  • 31.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Zhou, Liping
    Dong, Jianyi
    Li, Yinkui
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Caffee, Marc
    Ma, Haizhou
    Liu, Gengnian
    Landscape evolution of the northeastern Tibetan plateau - relict surfaces and fluvial margins2007In: Geophysical Research Abstracts, 2007Conference paper (Refereed)
    Abstract [en]

    The actively uplifting Tibetan plateau has a profound impact on climate and displays a landscape marked by geomorphological action. This is because the uplift is counteracted by intense fluvial incision of some of the world’s largest rivers and their tributaries that drain the plateau. Glaciers and glacial landforms occur predominantly in and around the highest elevation areas. By investigating the imprints of glacial and fluvial erosion we can enhance our understanding of the long-term landscape evolution, as well as illuminate the paleoglaciology of the Tibetan plateau. We here present an investigation of the large-scale geomorphology of the northeastern Tibetan plateau and its implication for landscape evolution and paleoenvironmental reconstructions.

    The northeastern part of the Tibetan plateau is characterized by a plateau surface at c. 4300 m asl with higher mountain groups reaching up to 1500 m above the surrounding plateau surface. We used SRTM 90 m digital elevation model, satellite images and Google Earth imagery to map the large-scale geomorphology for an area of c. 135.000 km2 centered around the Bayan Har mountains. Our mapping reveals a clear pattern of substantial glacial erosion on the highest, central parts of the mountain areas and decreasing amounts of glacial erosion with decreasing elevation and increasing distance away from these centers of glaciation. Beyond the areas of glacial erosion, there is a low-relief fluvial landscape that typifies the rest of the plateau surface. The plateau margins are formed by steep fluvial valleys which cut backwards into the gentle sloping relict plateau surface. Thus, the overall landscape may be divided into three classes; (i) glacially eroded surfaces in the highest areas, (ii) a relict, low-relief plateau surface, and (iii) a steep, fluvial landscape juxtaposing the former two classes.

    The distribution of the different landscapes indicates the following temporal evolution of the landscape. The glacial landforms indicate a repeated glaciation of the mountain areas. The steep fluvial valleys consuming the relict plateau surface represent an ongoing adjustment of the river channels to the actively uplifting plateau margin. The pattern of abandoned fluvial erosion of the northern part of the study area supports the notion of a stepwise uplift. This is because progressively younger uplift of the northern parts of the area induced a piracy of originally N-flowing rivers to currently ESE-flowing rivers along major faults (such as we infer for the Huang He river). It is noteworthy that the outline of the relict landscape, that is the pronounced break in slope between the low-relief relict landscape and the young fluvial landscape, coincides almost completely with the outline of a hypothesized former ice sheet, the Huang He ice sheet. We have not been able to confirm the presence of geomorphology or stratigraphy that would support this reconstruction. If true, however, our notion of outline conformance could indicate that the Huang He ice sheet may actually have been larger than suggested and that glacial traces are being consumed by the fluvial incision triggered by plateau uplift.

  • 32.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Li, Yingkui
    Department of Geography, University of Tennessee, USA.
    Caffee, Marc W
    Department of Physics, Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Zhou, Liping
    Department of Geography, Peking University, China.
    Veres, Daniel
    'Emil Racovita' Institute of Speleology, Romania.
    Liu, Feng
    Department of Geography, Peking University, China.
    Machiedo, Martin
    Department of Geology, University Centre in Svalbard (UNIS), Norway.
    Palaeoglaciation of Bayan Har Shan, northeastern Tibetan Plateau: glacial geology indicates maximum extents limited to ice cap and ice field scales2009In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 24, no 7, 710-727 p.Article in journal (Refereed)
    Abstract [en]

    Key locations within an extensive area of the northeastern Tibetan Plateau, centred on Bayan Har Shan, have been mapped to distinguish glacial from non-glacial deposits. Prior work suggests palaeo-glaciers ranging from valley glaciers and local ice caps in the highest mountains to a regional or even plateau-scale ice sheet. New field data show that glacial deposits are abundant in high mountain areas in association with large-scale glacial landforms. In addition, glacial deposits are present in several locations outside areas with distinct glacial erosional landforms, indicating that the most extensive palaeo-glaciers had little geomorphological impact on the landscape towards their margins. The glacial geological record does indicate extensive maximum glaciation, with local ice caps covering entire elevated mountain areas. However, absence of glacial traces in intervening lower-lying plateau areas suggests that local ice caps did not merge to form a regional ice sheet on the northeastern Tibetan Plateau around Bayan Har Shan. No evidence exists for past ice sheet glaciation.

  • 33.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Caffee, Marc W.
    Hattestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan M.
    Li, Yingkui
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zhou, Liping
    Hubbard, Alun
    Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: exposure ages reveal a missing LGM expansion2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 15-16, 1988-2001 p.Article in journal (Refereed)
    Abstract [en]

    The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined (10)Be exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40-65 ka. More extensive glaciations occurred before 60-100 ka and 95-165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Hat Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments.

  • 34.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Caffee, Marc W
    Department of Physics, Purdue Rare Isotope Measurement Laboratory, Purdue University.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University.
    Li, Yingkui
    Department of Geography, University of Tennessee, Knoxville.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Zhou, Liping
    Department of Geography, Peking University.
    Hubbard, Alun
    Institute of Geography and Earth Sciences, Aberystwyth University.
    Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: the case of a missing LGM expansionManuscript (preprint) (Other academic)
    Abstract [en]

    The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined 10Be apparent exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Apparent exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in ages for individual sites and within the recognised four morphostratigraphical groups. The age disparity is inexplicable as arising from differences in inheritance without the application of unrealistic assumptions but it can be explained as arising from differences in post-glacial shielding, yielding exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40-65 ka. More extensive glaciations occurred before 60-100 ka and 95-165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Har Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is supported by high-resolution glacier modelling experiments.

  • 35.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Caffee, Marc W
    Department of Physics/Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Li, Yingkui
    Department of Geography, University of Tennessee, USA.
    Zhou, Liping
    Department of Urban and Environmental Sciences, Peking University, China.
    Liu, Gengnian
    Department of Urban and Environmental Sciences, Peking University, China.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fu, Ping
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    An evaluation of multiple working hypotheses to explain cosmogenic exposure age data from glacial deposits in the Bayan Har Shan, NE Tibetan Plateau2009In: Proceedings, 2009Conference paper (Refereed)
    Abstract [en]

    Many questions remain unanswered regarding the Quaternary glaciations of the Tibetan Plateau. We have used terrestrial cosmogenic nuclide (TCN) exposure age dating of glacial deposits to examine the style, extent, and timing of past glaciations of the Bayan Har Shan, a mountain region on the northeastern Tibetan Plateau. This area lies within a transition zone between the dry interior of the Tibetan Plateau and the wetter eastern margin affected by the Asian monsoon. Bayan Har Shan has many glacial landforms and deposits that provide evidence for former glaciation ranging from cirque and valley glaciers to ice-fields and ice caps.

    In an attempt to constrain the timing of glaciations in Bayan Har Shan, we have performed TCN exposure dating on 65 samples in central Bayan Har Shan from glacial deposits. boulders (39 samples), on surface pebbles/cobbles (12 samples), and on pebbles in sediment depth profiles (14 samples from four profiles) allow us to examine the timing and extent of glaciations in this area. As is often the case, there are some challenges in interpreting the range of TCN apparent exposure ages that is found in data from several samples and sample types on a single deposit and from samples taken at various sites. Thus we evaluate multiple working hypotheses to explain apparent exposure ages on glacial deposits, which in this case range from 3 ka to 129 ka. We consider three different hypotheses; 1) some samples have erroneously old exposure ages due to inheritance, 2) samples have been preserved under cold-based, non-erosive ice, and 3) samples have experienced only post-glacial shielding. Only when we adopt a hypothesis that assumes no prior exposure, and thus that maximum apparent exposure ages constrain the minimum age of formation of a feature (working hypotheses 3), do we find broad consistency between apparent exposure ages from different sample types (erratic boulders, surface pebbles/cobbles and pebbles from depth profiles). This leads to the conclusion that all of the sites of former glaciations we examined are at least 50ka in age, and that there has been no large-scale expansion of glaciers in the central Bayan Har Shan over the last 50ka.

  • 36.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University.
    Caffee, Marc W
    Department of Physics, PRIME Lab, Purdue University.
    Boulder cosmogenic exposure ages as constraints for glacial chronologies2010In: Geophysical Research Abstracts, 2010Conference paper (Refereed)
    Abstract [en]

    Cosmogenic exposure dating greatly enhances our ability to define glacial chronologies spanning several global cold periods, and glacial boulder exposure ages are now routinely used to constrain deglaciation ages. However, calculating an exposure age from a measured cosmogenic nuclide concentration involves assumptions about the geological history of the sample that are difficult to test and yet have a profound effect on the inferred age.Two principal geological factors yield erroneous inferred ages: pre-depositional exposure (yielding exposure ages that are too old) and post-depositional shielding (yielding exposure ages that are too young). To evaluate the importance of these two problems we have compiled datasets of glacial boulder 10Be exposure ages from theTibetan Plateau (1099 boulders), the Northern Hemisphere palaeo-ice sheets (613 boulders), and present-day glaciers (141 boulders). All exposure ages have been recalculated with the CRONUS online calculator version 2.2 (http://hess.ess.washington.edu/) using the new 10Be half-life of 1.36 Ma. All boulders from present-day glaciers have exposure ages <3.5 ka indicating that none of these boulders experienced significant pre-depositional exposure.The palaeo-ice sheet boulders in the dataset were deposited during the last deglaciation c. 25-8 ka. By subtracting independently-derived, primarily radiocarbon-based, deglaciation ages we have quantified the inheritance of cosmogenic nuclides from pre-depositional exposure. Only 4% of the boulders from glacially modified landscapes (n = 385; dated to constrain the glacial chronology) have exposure ages >10 ka older than the deglacial age of the surface. Boulders from the Tibetan Plateau have mainly been collected from moraine ridges. We haveorganized them into boulder groups, each of which has one deglacial age. The age spread of the Tibetan Plateau boulder group dataset is significantly higher than the inheritance observed in the palaeo-ice sheet boulders. If this spread is attributed to inheritance we would conclude that on the Tibetan Plateau inheritance plays a much more prominent role than is seen in the palaeo-ice sheet areas. Alternatively, a simple exponential post-glacial landform degradation model produces exposure age distributions remarkably similar to the measured data, indicating that post-depositional shielding is likely the dominant process producing spread among boulder age distributions. Our analysis lends strong support to the argument that post-depositional shielding is the most important geological process leading to potential errors in cosmogenic exposure ages for glacial boulders older than a few thousand years. The strong recommendation emerging from this analysis of global 10Be exposure ages is to interpret sets of dates from glacial settings in terms of post-depositional shielding: i.e., that exposure ages represent minimum ages of deglaciation.

  • 37.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University.
    Caffee, Marc W
    Department of Physics, Purdue Rare Isotope Measurement Laboratory, Purdue University.
    Boulder cosmogenic exposure ages as constraints for glacial chronologiesManuscript (preprint) (Other academic)
    Abstract [en]

    Cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods, and glacial boulder exposure ages are now routinely used to constrain deglaciation ages. However, exposure dating involves assumptions about the geological history of the sample that are difficult to test and yet may have a profound effect on the inferred age. Two principal geological factors yield erroneous inferred ages: exposure prior to glaciation (yielding exposure ages that are too old) and post-glacial shielding (yielding exposure ages that are too young). Here we show that post-glacial shielding is more important than prior exposure, using datasets of glacial boulder 10Be exposure ages from the Tibetan Plateau (1123 boulders), Northern Hemisphere palaeo-ice sheets (615 boulders), and present-day glaciers (186 boulders). No boulders from present-day glaciers and very few boulders from the palaeo-ice sheets have exposure ages significantly older than independently known deglaciation ages, indicating that prior exposure is of limited significance. Further, the exposure age distribution of boulders from the Tibetan Plateau agrees with the distribution produced by a simple post-glacial landform degradation model, indicating that post-glacial shielding is important. The large global dataset demonstrates that, in the absence of other evidence, glacial boulder exposure ages should be viewed as minimum limiting deglaciation ages.

  • 38.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Caffee, Marc W
    Department of Physics/Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Cosmogenic exposure ages of glacial boulders from the Tibetan Plateau - Age distributions support boulder exhumation/erosion and indicate old glacial deposits.2009In: Geophysical Research Abstracts, : Vol. 11, EGU2009-12078-1, 2009, 2009Conference paper (Refereed)
    Abstract [en]

    Terrestrial cosmogenic nuclide (TCN) exposure dating has become the most dominant technique for constraining glacial chronologies. This is particularly true for the Tibetan Plateau because of its low frequency of organic material (limiting the possibilities to use radiocarbon dating) and high altitude (favouring TCN dating with high cosmogenic nuclide production rates), with, consequently, a large number of TCN samples processed. However, multiple samples from one glacial deposit commonly yield a wide range of TCN ages which complicates their interpretation. Two principal possibilities can cause a wide range of ages to result from one glacial deposit. First, TCN ages may exceed the true age by a varying number of years as a result of pre-depositional cosmogenic nuclide inheritance. Second, TCN ages may underestimate the true age by a varying number of years as a result of post-depositional exhumation and/or erosion. By analysing trends within a large set of TCN ages we can evaluate whether inheritance (too old TCN ages) or exhumation/erosion (too young TCN ages) has best explanatory power.

    We have thus analysed 794 Be-10 TCN ages from 211 individual groups of glacial boulders collected from 30 different areas on the Tibetan Plateau. Analysis of the 211 sample group age distributions and the relationships with their maximum and minimum ages clearly reveals that older sample groups have wider age spread. This fact indicates that if inheritance is the cause of the wide age spread, older deposits have higher cosmogenic inheritance. However, the wide age spread and distinct age spread/deposition age-trend argue against this explanation. Furthermore, there is no significant inheritance in boulders from young (late Holocene) glacial deposits of the Tibetan Plateau. Exhumation/erosion of boulders, on the other hand, may explain the age distribution as a result of post-depositional shielding of samples. With degrading moraine ridges exhuming boulders and erosion of the boulder surfaces, previous shielding of the collected samples will result in TCN ages underestimating the true age to a varying degree depending on the rate and timing of exhumation/erosion. If exhumation/erosion is a continuous process, older deposits will have wider age spread due to the longer time (higher probability) of exhumation/erosion. Thus, the age distribution within groups of boulder TCN ages from the Tibetan Plateau indicates that cosmogenic inheritance is probably not an overarching problem, and that the spread in ages in glacial deposits is generally caused by boulder exhumation and/or erosion. By inference, the oldest boulder of each sample group most reliably constrains the minimum age of glacial deposition. Because the average of the 211 maximum ages is 61 ka and half of them are older than 25 ka, an important conclusion of our trend analysis is that the glacial geological record of the Tibetan Plateau to a large extent corresponds to glaciations pre-dating the global Last Glacial Maximum. Hence, the Tibetan Plateau offers a window into glaciations significantly older than is normally found in the northern hemisphere.

  • 39.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Caffee, Marc W
    Department of Physics/Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Glacial boulder exposure ages from the Tibetan Plateau - old deposits and postglacial shielding2009Conference paper (Refereed)
    Abstract [en]

    Terrestrial cosmogenic nuclide (TCN) exposure dating is an important chronological tool in Quaternary glacial geology. For the Tibetan Plateau, with its lack of organic material (hindering radiocarbon dating) and high altitude (yielding high cosmogenic isotope production rates), TCN dating has been widely used over the last 10 years to provide evidence for limited glacial expansion during the last glacial cycle. However, for a large number of TCN samples, apparent exposure ages deviate from depositional ages as shown by wide age spreads from multiple samples. There are two principal geological explanations for the presence of incorrect and varying exposure ages; 1) pre-glacial exposure and 2) post-glacial shielding. While pre-glacial exposure results in inherited cosmogenic isotope concentrations (yielding too old exposure ages), post-glacial shielding results in reduced cosmogenic isotope concentrations (yielding too young exposure ages). To evaluate the likelihood of each explanation, and to provide guidance on how to interpret the often complex TCN exposure assemblages, we have compiled a large data set of 945 10Be TCN ages from glacial boulders on the Tibetan Plateau and 578 10Be TCN ages from glacial boulders displaced by Laurentide and European ice sheets.

    TCN ages from the Tibetan Plateau derive from 237 groups with multiple boulders. The grouping of boulders allows us to evaluate the age spread for locations of the same age. All TCN ages have been recalculated (from original publications) using the CRONUS-Earth online calculator version 2.2 (http://hess.ess.washington.edu/) which standardizes measurements using different 10Be standards (thus allowing comparison of multiple TCN age studies) and applies a new 10Be half-life of 1.36 Ma.

    TCN apparent exposure ages range from 0 to 450 ka and reveal a clear trend with wider age spread (higher uncertainty) with increasing age (valid for both minimum and maximum ages). This characteristic may be explained by shielding during post-glacial time, or, alternatively, would require very high and increasing inheritance with age if explained by pre-glacial exposure. To further evaluate these two explanatory models, we have employed two simple numerical models simulating inheritance and postglacial shielding. We have also compared the Tibetan age spreads with glacial boulder 10Be TCN ages for the Laurentide and European ice sheets, for which we have a relatively good idea of the glacial chronology.

    The outcome of our analysis is that, although we can not rule out inheritance for individual boulders, post-glacial shielding is a far more poweful explanatory model to explain the increasingly wide age spreads. By inference, the glacial boulder TCN record of the Tibetan Plateau reveals a paleoglaciological record which is significantly older than normally found in the Northern Hemisphere; with discernable glaciations up to several hundred thousand years old.

  • 40.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan M.
    Caffee, Marc W.
    Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 302, no 1-2, 71-80 p.Article in journal (Refereed)
    Abstract [en]

    Cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods, and glacial boulder exposure ages are now routinely used to constrain deglaciation ages. However, exposure dating involves assumptions about the geological history of the sample that are difficult to test and yet may have a profound effect on the inferred age. Two principal geological factors yield erroneous inferred ages: exposure prior to glaciation (yielding exposure ages that are too old) and incomplete exposure due to post-depositional shielding (yielding exposure ages that are too young). Here we show that incomplete exposure is more important than prior exposure, using datasets of glacial boulder 10Be exposure ages from theTibetan Plateau (1420 boulders), Northern Hemisphere palaeo-ice sheets (631 boulders), and present-day glaciers (208 boulders). No boulders from present-day glaciers and few boulders from the palaeo-ice sheets have exposure ages significantly older than independently known deglaciation ages, indicating that prior exposure is of limited significance. Further, while a simple post-depositional landform degradation model can predict the exposure age distribution of boulders from the Tibetan Plateau, a prior exposure model fails, indicating that incomplete exposure is important. The large global dataset demonstrates that, in the absence of other evidence, glacial boulder exposure ages should be viewed as minimum limiting deglaciation ages.

  • 41.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Caffee, Marc W
    Department of Physics, PRIME Lab, Purdue University.
    Fu, Ping
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Department of Earth And Atmospheric Sciences, Purdue University.
    Hubbard, Alun
    Institute of Geography and Earth Sciences, Aberystwyth University.
    Li, Yingkui
    Department of Geography, University of Tennessee.
    Zhou, Liping
    Department of Geography, Peking University.
    LGM Tibetan Plateau glaciers were not much larger than today2010In: Geophysical Research Abstracts, 2010Conference paper (Refereed)
    Abstract [en]

    The Tibetan Plateau is the largest and highest elevated area on Earth with consequential impacts on regional (monsoon development) and global (CO2 sequestering) climate patterns and evolution, and with its glaciers providing meltwater for some of the largest rivers of the world. The glacial history of the Tibetan Plateau is dominantly characterized by glaciers and ice caps centered on elevated mountain regions of the plateau, as evidenced by an extensive glacial geological record. Here we present the outcome of a five year project aiming towards a palaeoglaciological reconstruction for the Bayan Har Shan region of the northeastern Tibetan Plateau. We have used remote sensing, field studies and 10Be exposure ages towards a robust reconstruction of former glaciation. Glacial landforms and sediments in Bayan Har Shan, distributed around elevated mountain areas, indicate a maximum Quaternary glaciation significantly larger than today. We have dated 40 boulders, 12 surface pebbles samples, and 15 depth profile samples (in 4 depth profiles) from 15 sites (mainly moraine ridges) using 10Be exposure dating. Our boulder and pebble exposure ages range from 3 ka to 128 ka with large age spreads within populations of individual sites. Based on the premise that cosmogenic age spreads within populations are caused by post-depositional shielding which yields exposure ages younger than deglaciation ages (see Heyman et al. Abstract/Poster in session CL4.7/GM2.4/SSP2.5/SSP3.9: EGU2010-14159-1) and based on the exposure ages of the multiple sample types, all dated glacial deposits pre-date the global Last Glacial Maximum (LGM). Our results further indicate that even the innermost and highest of the dated moraines, formed by glaciers <10 km long, have minimum deglaciation ages of 45 ka. These results agree well with those sites on the Tibetan Plateau where samples close outside present-day glacier margins have yielded exposure ages significantly older than the LGM. In fact, for sites where exposure age studies have been performed on the Tibetan Plateau, it is a rule rather than an exception with pre-LGM exposure ages close outside present-day glacier margins. This indicates that during the LGM, when large ice sheets covered North America and northern Europe, glaciers on the northeastern Tibetan Plateau, and perhaps the plateau at large, did not grow much larger than today.

    To explore the climate implications of restricted Tibetan Plateau LGM glaciers, we employ a high-resolution 3D glacier model forced with static climate perturbations of the present-day climate (WorldClim data:http://www.worldclim.org/). Allowing glaciers to grow and expand to but not exceed well-dated moraines enables us to derive and present climate constraints for the Tibetan Plateau during the LGM.

  • 42.
    Heyman, Jakob
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen P
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon
    Department of Earth and Atmospheric Sciences, Purdue University, USA.
    Caffee, Marc W
    Department of Physics/Purdue Rare Isotope Measurement Laboratory, Purdue University, USA.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Li, Yingkui
    Department of Geography, University of Tennessee, USA.
    Zhou, Liping
    Department of Urban and Environmental Sciences, Peking University, China.
    Liu, Gengnian
    Department of Urban and Environmental Sciences, Peking University, China.
    Fu, Ping
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    A paleoglaciological reconstruction for Bayan Har Shan, NE Tibetan Plateau2009Conference paper (Refereed)
    Abstract [en]

    The paleoglaciology of the Tibetan Plateau has remained elusive because extensive areas still lack detailed scrutiny. We here present a paleoglaciological reconstruction for the Bayan Har Shan region, NE Tibetan Plateau, which could serve as a working model to investigate other poorly investigated regions. The reconstruction is primarily based on three methods for revealing the glacial history; 1) remote sensing (geomorphology), 2) field studies (stratigraphy), and 3) numerical dating techniques. Remote sensing (SRTM elevation data, Landsat ETM+ satellite imagery and Google Earth) of a 136 500 km2 area reveals an abundance of glacial landforms in the highest mountain areas and an absence of glacial landforms on intervening plateau surfaces. Stratigraphical data collected during three field seasons supplement the picture emerging from remote sensing. Glacial deposits (including erratic boulders and till) occur in the elevated mountain areas but are absent on the intervening plateau areas. Marginal moraines in central Bayan Har can be grouped to represent at least three separate glacial extents and scattered observations of glacial deposits indicate the presence of a fourth (and maximum) glacial extent. To tie the glacial geological record to a chronology we have employed terrestrial cosmogenic nuclide (TCN) exposure and optically stimulated luminescence (OSL) dating. Beryllium apparent exposure ages of 65 glacial boulders, surface cobbles/pebbles and depth profile samples yield minimum ages for the three youngest glacial extents of 40-65 ka, 60-100 ka, and 95-165 ka (with the wide age ranges due to TCN dating uncertainties). A preliminary OSL age of c. 160 ka from glacial sediments of the oldest of these glacial extents supports our interpretation based on TCN dating.

    The glacial extent presented here is more restricted than most previous reconstructions, most notably with very restricted glaciers over at least the last 40-65 ka. These results indicate that while continental-scale ice sheets evolved and disappeared in North America and Eurasia over the last half of the last glacial cycle, the NE corner of the Tibetan Plateau experienced relatively minor glacial fluctuations.

  • 43.
    Hättestrand, Clas
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kolka, Vasili
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The Keiva ice marginal zone on the Kola Peninsula, northwest Russia: a key component for reconstructing the palaeoglaciology of the northeastern Fennoscandian Ice Sheet2007In: Boreas, Vol. 36, 352-370 p.Article in journal (Refereed)
    Abstract [en]

    One of the key elements in reconstructing the palaeoglaciology of the northeastern sector of the Fennoscandian Ice Sheet is the Keiva ice marginal zone (KIZ) along the southern and eastern coast of Kola Peninsula, including the Keiva I and II moraines. From detailed geomorphological mapping of the KIZ, primarily using aerial photographs and satellite images, combined with fieldwork, we observed the following. (1) The moraines display ice contact features on both the Kola side and the White Sea side along its entire length. (2) The Keiva II moraine is sloping along its length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River). (3) The KIZ was partly overrun and fragmented by erosive White Sea-based ice after formation. From these observations we conclude that the KIZ is not a synchronous feature formed along the lateral side of a White Sea-based ice lobe. If it was, the moraines should have a reversed slope. Rather, we interpret it to be time transgressive, formed at a northeastward-migrating junction between a warm-based Fennoscandian Ice Sheet expanding from the west and southwest into the White Sea depression, and a sluggish cold-based ice mass centred over eastern Kola Peninsula. In contrast to earlier reconstructions, we find it unlikely that an ice expansion of this magnitude was a mere re-advance during the deglaciation. Instead, we propose that the KIZ was formed during a major expansion of a Fennoscandian Ice Sheet at a time pre-dating the Last Glacial Maximum.

  • 44.
    Hättestrand, Clas
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, Derek
    Kolka, V.V.
    The Keiva ice marginal zone on the Kola Peninsula, NW Russia – a complex marginal deposit of the Fennoscandian ice sheet2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    One of the key elements in reconstructing the palaeoglaciology of the northeastern sector of the Fennoscandian Ice Sheet is the Keiva ice marginal zone (KIZ) along the southern and eastern coasts of Kola Peninsula, including the Keiva I and II moraines. From detailed geomorphological

    mapping of the KIZ, primarily using aerial photographs and satellite images, combined with field work, we observe the following:

    (a) The moraines display ice contact features on both the Kola Peninsula- and the White Sea side along its entire length; (b) the Keiva II moraine is sloping along its 220 km length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River); (c) the KIZ was partly overrun and fragmented by erosive White Sea based ice after formation. From these observations we conclude that the KIZ is not a synchronous feature formed along the lateral side of a White Sea based ice lobe. If it was, the moraines should have a reversed slope. Rather, we interpret it to be formed time transgressively at the northeastward

    migrating junction between warm-based parts of the Fennoscandian

    ice sheet expanding from the southwest into the White Sea depression and across southeastern Kola Peninsula, and a sluggish cold-based ice mass centred over eastern Kola Peninsula. In contrast to earlier reconstructions, we find it unlikely that an ice expansion of this magnitude was a mere readvance during the deglaciation. Instead, we propose that the Keiva ice marginal zone was formed during major expansion of a Fennoscandian Ice Sheet at a time predating the LGM. Our geomorphological interpretation is consistent with new Be-10 cosmogenic isotope data of several boulders embedded in the eastern part of the Keiva II moraine, with apparent exposure ages between 250 and 420 ka. One interpretation of the data is that these boulders were deposited as an integral part of the moraine ridge, hence indicating that the KIZ, or at least sections of it, is of Middle Pleistocene age. Another interpretation is that the KIZ is younger than 250 ka (but older than LGM on the strength of the evidence of post-depositional overriding) and that all boulders sampled have considerable inheritance from previous

    exposure periods. The results are also consistent with the geomorphological

    observations indicating that the KIZ has a history far more intricate than has previously been acknowledged in most paleoglaciological

    reconstructions.

  • 45.
    Jansen, John D.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. University of Wollongong, Australia.
    Codilean, A. T.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fabel, D.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jon M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University, USA.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kubik, P. W.
    Xu, S.
    Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, 3815- p.Article in journal (Refereed)
    Abstract [en]

    The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along similar to 500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.

  • 46.
    Jansson, Krister
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alm, Göran
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dahlgren, T.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    GIS modelling of the MIS 2-8 onshore glacial erosional pattern in northern Scandinavia2007In: Quaternary International, 2007Conference paper (Refereed)
    Abstract [en]

    A 50-m cell size digital elevation dataset over northern Scandinavia has been analysed for patterns of glacial erosion using filtering techniques of the Erdas Imagine 8.6

    spatial modeller software. A maximum value filtering technique using variable neighbourhoods has been applied such that existing highpoints in the landscape have been

    used as erosional base levels for the reconstruction of past landscape relief. We assume that the highest surfaces have experienced no down-wearing (or, alternatively, an

    even down-wearing could be specified) and also that the size of the valleys rather than the direction of the valleys relative to former ice flow directions determines how

    much material has been removed by ice sheet erosion. Over multiple runs the reconstructed paleo-relief becomes increasingly dominated by the highest summits in the

    landscape and the valley pattern is smoothed by in-filling from the sides. The model was run until eroded bedrock volumes equalled bedrock equivalents of erosion

    products deposited during MIS 2, 6, 8, 10, 12, 18 and for the full glacial period offshore of northern Norway. The pattern of glacial erosion, which is mainly correlated to

    slope angles and relative relief, is characterized by: (1) An abrupt start of glacial erosion below preserved summit areas; (2) Enhanced erosion in narrow valleys; (3)

    Restricted erosion of smooth areas, independently of elevation; (4) Erosion of small scale irregularities, and; (5) Restricted erosion on isolated hills in low-relief terrain.

  • 47.
    Jansson, Krister N.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dahlgren, K. I. Torbjörn
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alm, Göran
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glasser, Neil F.
    Goodfellow, Brad W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial erosion and the evolution of relief in northern Scandinavia over the last 2.7 Myr2008In: Geophysical Research Abstracts, Vol. 10, EGU2008-A-07548, 2008Conference paper (Refereed)
  • 48.
    Jansson, Krister
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alm, Göran
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dahlgren, K. I. T.
    Glasser, N. F.
    Goodfellow, B. W.
    Using a GIS filtering approach to replicate patterns of glacial erosion2011In: Earth Surface Processes and Landforms, ISSN 0197-9337, E-ISSN 1096-9837, Vol. 36, no 3, 408-418 p.Article in journal (Refereed)
    Abstract [en]

    In order to extend our knowledge of glacial relief production in mountainous areas new methods are required for landscape reconstructions on a temporal resolution of a glacial cycle and a spatial resolution that includes the most important terrain components. A generic data set and a 50 m resolution digital elevation model over a study area in northern Sweden and Norway (the present day landscape data set) were employed to portray spatial patterns of erosion by reconstructing the landscape over successive cycles of glacial erosion. A maximum-value geographic information system (GIS) filtering technique using variable neighbourhoods was applied such that existing highpoints in the landscape were used as erosional anchor points for the reconstruction of past landscape topography. An inherent assumption, therefore, is that the highest surfaces have experienced insignificant down-wearing over the Quaternary. Over multiple reconstruction cycles, proceeding backwards in time, the highest summits increase in area, valleys become shallower, and the valley pattern becomes increasingly simplified as large valleys become in-filled from the sides. The sum of these changes reduces relief. The pattern of glacial erosion, which is to 60% correlated to slope angle and to 70% correlated to relative relief, is characterized by (i) an abrupt erosional boundary below preserved summit areas, (ii) enhanced erosion in narrow valleys, (iii) restricted erosion of smooth areas, independently of elevation, (iv) eradication of small-scale irregularities, (v) restricted erosion on isolated hills in low-relief terrain, and (vi) a valley widening independent of valley directions. The method outlined in this paper shows how basic GIS filtering techniques can mimic some of the observed patterns of glacial erosion and thereby help deduce the key controls on the processes that govern large-scale landscape evolution beneath ice sheets.

  • 49.
    Kirchner, Nina
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Greve, Ralf
    Institute of Low Temperature Sciences, Hokkaido University, Japan.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Tibetan Plateau glaciation during the last glacial cycle: widely diverging (LGM-) reconstructions of glacial extents using numerical ice sheet simulations driven by GCM-ensembles of climate forcings2009In: Geophysical Research Abstracts: Vol. 11, EGU2009-1791, 2009, 2009Conference paper (Refereed)
    Abstract [en]

    The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. Yet, the glacial history of the Tibetan Plateau is less constrained than the history of some other formerly glaciated regions, especially in the Northern Hemisphere (e.g. Laurentide Ice Sheet, Fennoscandian Ice Sheet). Nevertheless, field evidence for extensive valley glaciation indicates that ice sheet glaciation on the Tibetan Plateau did not evolve during the Last Glacial maximum (LGM). This is an important and robust result that has not been widely investigated using numerical ice sheet models, despite potentially important climate ramifications. Perhaps this is because reconstructions of the LGM glacial configurations of the Tibetan Plateau in the framework of numerical simulations covering an entire glacial cycle exhibit a pronounced variability then entire range of which is not supported by field evidence.

    Using the 3d thermomechanical ice sheet model SICOPOLIS, we simulated the evolution of Tibetan Plateau ice configurations during the last 125.000 years. Temperature and precipitation data driving the simulations have been applied in the form of a large ensemble of glacial/interglacial climate scenarios. It is observed that variations in ice sheet configuration resulting from the prescription of different present-day precipitation- and temperature data sets, on the one hand, and different paleoclimates as obtained from reconstructions based on different GCM-model outputs, on the other hand, include as extreme end members an entirely ice free Tibetan Plateau during the last glacial cycle as well as a plateau-scale Tibetan Ice sheet during the LGM. Comparison of such numerical results with available field data indicates that further refinements in the numerical simulations are required, and that these must include atmosphere-ice sheet feedback mechanisms.

    However, because mapped and simulated glacial extents are represented at different spatial scales, this task is not straightforward.

  • 50.
    Kirchner, Nina
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Greve, Ralf
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Paleoglaciological reconstructions for the Tibetan Plateau during the last glacial cycle: evaluating numerical ice sheet simulations driven by GCM-ensembles2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 1-2, 248-267 p.Article in journal (Refereed)
    Abstract [en]

    The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 kyr), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 kyr in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and regional climate data and climate reconstructions.

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