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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, p. 123-136Article 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.
    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.

  • 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.
    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.  

  • 4.
    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, p. 66-78Article 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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Department of Physical Geography and Quaternary Geology Annual Report 20062007Report (Other (popular science, discussion, etc.))
  • 9.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geology of Bayan Har Shan, northeastern Tibetan Plateau2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The paleoglaciology of the Tibetan Plateau is still largely unexplored, despite its importance for regional and global climate reconstructions. In this thesis a comprehensive glacial geological record is presented from an extensive part of the northeastern Tibetan Plateau centred on the Bayan Har Shan. Glacial reconstructions for this region range from restricted mountain glaciers through the intermediate-size regional-scale Huang He ice sheet to a plateau-scale Tibetan ice sheet. To provide a robust basis for glacial reconstructions, this thesis provides conclusions based on two principle methods, remote sensing and field studies. The remote sensing of a 90 m resolution digital elevation model and 15- and 30 m resolution satellite imagery renders a detailed data set with complete spatial coverage of large- and medium-scale glacial landforms, and large-scale plateau geomorphology. Observations from fieldwork campaigns add detailed point information for the distribution of glacial deposits. Geomorphological glacial traces such as glacial valleys, glacial lineations, marginal moraines, meltwater channels, and hummocky terrain occur frequently in elevated mountain areas, indicating former alpine-style glaciations. Glacial deposits in the form of till, erratic boulders, and glaciofluvial sediments are common in areas with mapped glacial landforms, but also beyond, in areas lacking large-scale glacial landforms. For extensive plateau areas in-between formerly glaciated mountain blocks, there is a striking absence of glacial landforms and sediments, indicating that these areas, perhaps, never were ice covered. Interestingly, glacial deposits occur further away from the mountain blocks than the large- and medium-scale glacial landforms, indicating insignificant erosion beneath the maximum ice covers close to their margins.

    The large-scale geomorphology of the northeastern Tibetan Plateau is characterised by a low-relief plateau surface with glacial valleys in elevated mountain blocks and marginal steep V-shaped valleys. This geographical distribution indicates a dominance of glacial erosion in the elevated mountain areas and a dominance of fluvial erosion along the steep plateau margins, dissecting a relict plateau surface. The outline of the relict plateau surface mimics the proposed outline of the Huang He ice sheet, suggesting that the inferred ice sheet may represent a misinterpreted relict surface with scattered glacial traces.

    In conclusion, the glacial geology examined in the Bayan Har Shan region is consistent with paleo-glaciers of varying extent restricted to elevated mountain areas. Even though extensive icefields/ice caps were centred on discrete mountain areas, there is no indication that these ice masses merged but rather that they were separated from each other by unglaciated plateau areas. The presented glacial geological record will be used in further studies towards a robust paleoglaciological reconstruction for the northeastern Tibetan Plateau.

  • 10.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Palaeoglaciology of the northeastern Tibetan Plateau2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This study concerns the palaeoglaciation of the northeastern Tibetan Plateau, with emphasis on the Bayan Har Shan (Shan = Mountain) in the headwaters of Huang He (Yellow River). To reconstruct past glacier development multiple techniques, including remote sensing, field investigations, cosmogenic exposure dating, and numerical modelling have been employed. Analysis of the large-scale geomorphology indicates that glacial erosion has been dominant in the elevated mountain areas on the low-relief plateau, whereas fluvial erosion outpaces glacial erosion along the plateau margin. Landform and sediment records yield evidence for multiple local glaciations, restricted to the highest mountain areas, and a maximum glaciation beyond the mountain front. Absence of data supporting the former presence of proposed ice sheets, plateau-wide or regional, tentatively indicates that no ice sheet glaciation occurred on the northeastern Tibetan Plateau. Cosmogenic exposure dating of boulders, surface pebbles, and sediment sections in central Bayan Har Shan indicates that its record of past glaciations predates the global Last Glacial Maximum (LGM). Based on a world-wide analysis, yielding that wide age disparity within apparent exposure age datasets is most likely caused by post-glacial shielding processes, the Bayan Har Shan exposure ages constrain four periods of glaciation with minimum ages of 40-65 ka, 60-100 ka, 95-165 ka, and undetermined oldest stage. Similar to Bayan Har Shan, the plateau-wide distribution of boulders with pre-LGM exposure ages close to present-day glaciers shows that its LGM glaciers were generally not much larger than today. The results of a high resolution glacier model applied to nine regions across the plateau indicates that temperature depressions of 2-4 K are enough to expand glaciers beyond their global LGM extent, implying that during periods of Northern Hemisphere glaciation the Tibetan Plateau was not much colder than today or became exceedingly dry.

  • 11.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Paleoglaciation of the Tibetan Plateau and surrounding mountains based on exposure ages and ELA depression estimates2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 91, p. 30-41Article in journal (Refereed)
    Abstract [en]

    The Tibetan Plateau holds an ample record of past glaciations, and there is an extensive set of glacial deposits dated by exposure dating. Here a compilation is presented of 10Be exposure ages from 485 glacial deposits with 1855 individual samples on the Tibetan Plateau, and ELA depression estimates for the glacial deposits based on a simple toe to headwall ratio approach. To recalculate the Tibetan Plateau exposure ages, 10Be production rates from 24 calibration sites across the world are compiled and recalibrated yielding an updated global reference 10Be production rate. The recalculated exposure ages from the Tibetan Plateau glacial deposits are then divided into three groups based on exposure age clustering, to discriminate good (well-clustered) from poor (scattered) deglaciation ages. A major part of the glacial deposits have exposure ages affected by prior or incomplete exposure, complicating exposure age interpretations. The well-clustered deglaciation ages are primarily from mountain ranges along the margins of the Tibetan Plateau with a main peak between 10 and 30 ka, indicating glacial advances during the global LGM. A large number of deglaciation ages older than 30 ka indicates maximum glaciation predating the LGM, but the exposure age scatter generally prohibits accurate definition of the glacial chronology. The ELA depression estimates scatter significantly, but the main part is remarkably low. Average ELA depressions of 337 ± 197 m for the LGM and 494 ± 280 m for the pre-LGM indicate restricted glacier expansion.

  • 12.
    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.

  • 13.
    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.

  • 14.
    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.

  • 15.
    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, p. 42-62Article 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.

  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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.

  • 20.
    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, p. 710-727Article 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.

  • 21.
    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.

  • 22.
    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.

  • 23.
    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.

  • 24.
    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.

  • 25.
    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.

  • 26.
    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.

  • 27.
    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, p. 71-80Article 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.

  • 28.
    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.

  • 29.
    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.

  • 30.
    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, p. 3815-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.

  • 31.
    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.

  • 32. Lifton, Nathaniel
    et al.
    Beel, Casey
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kassab, Christine
    Rogozhina, Irina
    Heermance, Richard
    Oskin, Michael
    Burbank, Douglas
    Blomdin, Robin
    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.
    Caffee, Marc
    Goehring, Brent M.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ivanov, Mikhail
    Li, Yanan
    Li, Yingkui
    Petrakov, Dmitry
    Usubaliev, Ryskul
    Codilean, Alexandru T.
    Chen, Yixin
    Harbor, Jon
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University, USA.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Constraints on the late Quaternary glacial history of the Inylchek and Sary-Dzaz valleys from in situ cosmogenic Be-10 and Al-26, eastern Kyrgyz Tian Shan2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 101, p. 77-90Article in journal (Refereed)
    Abstract [en]

    Paleoclimatic constraints from regions at the confluence of major climate systems are particularly important in understanding past climate change. Using geomorphic mapping based on remote sensing and field investigations, combined with in situ cosmogenic Be-10 and Al-26 dating of boulders associated with glacial landforms, we investigate the chronology of past glaciation in the Inylchek and Sary-Dzaz valleys in the eastern Kyrgyz Tian Shan, a tectonically active area with some of the highest peaks in the world outside of the Himalayas. Cosmogenic Be-10 and (26) Al exposure ages of boulders on moraines record up to five glacial advances including: Lateglacial age lateral moraine remnants and meltwater channels in the upper Inylchek Valley; Last Glacial Maximum (LGM, Marine Oxygen Isotope Stage [MIS] 2) moraines in the Sary-Dzaz Valley and in a terminal moraine complex at the west end of the Inylchek Valley, overriding older moraines; an MIS 4 or 5 moraine remnant above the Inylchek terminal moraine complex; and an older high moraine remnant down-valley from the confluence of the Inylchek and Sary-Dzaz valleys. The evidence for glacial extent in this study is consistent with a limited ice expansion hypothesis for Tian Shan glaciation. Published results from the western and central Kyrgyz Tian Shan do not show evidence for significant LGM glacier expansion, which in combination with the results presented here, indicate a spatial variation in glacier records along the Tian Shan. This may reflect either paleoclimatic gradients or the impact of local physiographic conditions on responses to regional climate change, or both.

  • 33. Margold, Martin
    et al.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Clague, John J.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Timing of terminal Pleistocene deglaciation at high elevations in southern and central British Columbia constrained by Be-10 exposure dating2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 99, p. 193-202Article in journal (Refereed)
    Abstract [en]

    The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (ILGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present Be-10 exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at elevations of 2126-2230 m a.s.l. in the Marble Range and 1608-1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting Be-10 ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 +/- 0.7 and 15.2 +/- 0.8 ka. These ages are 1.8-3.0 ka younger than the well-established ILGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the ILGM age for the Puget lobe if a snow-shielding correction to their uncertainty-weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 +/- 1.4 and 33.0 +/- 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 +/- 0.6, 10.2 +/- 0.7, 10.4 +/- 0.5, and 11.5 +/- 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 +/- 0.7 ka, consistent with deglacial C-14 ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the ILGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the ILGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations.

  • 34. Stokes, Chris R.
    et al.
    Tarasov, Lev
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Cronin, Thomas M.
    Fisher, Timothy G.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hindmarsh, Richard C. A.
    Hughes, Anna L. C.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Livingstone, Stephen J.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Murton, Julian B.
    Noormets, Riko
    Peltier, W. Richard
    Peteet, Dorothy M.
    Piper, David J. W.
    Preusser, Frank
    Renssen, Hans
    Roberts, David H.
    Roche, Didier M.
    Saint-Ange, Francky
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Teller, James T.
    On the reconstruction of palaeo-ice sheets: Recent advances and future challenges2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 125, p. 15-49Article, review/survey (Refereed)
    Abstract [en]

    Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.

  • 35.
    Stroeven, Arjen
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Harbor, Jonathan
    Purdue University.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Erosional landscapes2013In: Treatise on Geomorphology: Vol. 8, Glacial and Periglacial Geomorphology / [ed] John F. Shroder, San Diego: Academic Press, 2013, p. 100-112Chapter in book (Refereed)
    Abstract [en]

    Glacial erosion has created distinctive types of landscapes reflecting the extent, duration, and processes of the parent glaciers. Alpine landscapes are representative of pervasive erosion at the local scale. Landscapes formerly covered by larger scale glaciations display a wide range of appearances, from intensively eroded to preserved. Landscapes of selective linear erosion were formed, where subglacial melting occurred along certain corridors that were flanking regions of subglacial freezing. Landscapes of areal scouring were formed where subglacial melting on low-relief surfaces allowed spatially extensive subglacial stripping to dominate. Landscapes of little or no erosion indicate a dominance of subglacial freezing conditions.

  • 36.
    Stroeven, Arjen
    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.
    Harbor, Jon
    Zhou, Liping
    Li, Yinkui
    Caffee, Marc
    Ma, Haizhou
    Liu, Gengnian
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Paleoglaciology of the Bayan Har Mountain area, eastern Tibetan Plateau2006In: Asian Conference on Permafrost, 2006Conference paper (Refereed)
    Abstract [en]

    The glacial history of the Tibetan Plateau is a topic of considerable interest because of its significance for regional and global environmental reconstructions, and its interaction with variations in monsoon strength and plateau uplift. Published glacial reconstructions for the last glaciation range from a large ice sheet covering the entire Tibetan Plateau to extended valley glaciation forming discrete glaciated mountain blocks. Although current chronologies appear to underpin the restricted glaciation model, there appears to be enough regional variation to motivate further study, especially the glacial history predating the last glaciation. We therefore study the glacial history of a large upland section of the eastern Tibetan Plateau centered on the currently unglaciated Bayan Har Mountains (BHM), partly because chronological constraints are entirely absent, and partly because the area may once have been covered by an ice sheet of intermediate proportions. The BHM area, which houses the headwaters of the Huang He (Yellow River), contains a wide array of glacial deposits and morphologies. Moreover, it appears that superseding glaciations were ever limiting in extent and the area therefore presents optimal conditions to investigate glaciations over long time periods.

    We report from an on-going investigation into the extent and chronology of Quaternary glaciers in this region, manifested in glacial deposits and landforms (e.g., erratics, end moraines, tills and trough valleys). Previous studies have indicated the occurrence of two phases of mountain glaciation during the last glaciation (OIS 2-4), with mountain glaciers distributed around the highest summits, and two prior glaciations of ice sheet glaciation character (the penultimate glaciation, OIS 6, and the Huang He ice sheet, OIS 12).

    We mapped the glacial morphology of the area using satellite images and a DEM of 90 m resolution. Large-scale glacial landforms such as cirques, glacial troughs and U-shaped valleys indicate repeated glaciations, and so do series of moraine ridges and meltwater channels. The abundance of glacial traces detectable through remote sensing techniques diminish with decreasing elevation, and it appears that evidence for former ice sheets are based mainly on sedimentary evidence.

    In an introductory field work in 2005, surface boulders (including erratics) and boulders in till profiles have been sampled for dating using terrestrial cosmogenic nuclide (TCN) concentrations in quartz. Sampling was carried out along a 300 km stretch of the Qingkang highway, crossing the 80,000 km2 area of the Huang He ice sheet. We intend to present these first TCN results at the meeting.

    Our study will present new data for the paleoglaciology of the eastern Tibetan Plateau, and will contribute to the resolution of questions such as:

    • What glacial fluctuations occurred in the BHM area throughout the last glaciation?

    • When did glaciation pre-dating the last glaciation occur?

    • Was the area ever covered by an ice sheet?

    • What is the relation Tibetan glaciation – uplift – climate variations?

    These are questions of special significance also for former periglacial conditions, as reconstructed glaciers and ice sheets had a fundamental effect on regional paleoenvironmental conditions.

  • 37.
    Stroeven, Arjen
    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.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Geomorphology of the Huang He ice sheet area: towards a reconstruction of the glacial history of the northeastern Tibetan Plateau2006In: INQUA conference on Mountain Glaciation, 2006Conference paper (Refereed)
    Abstract [en]

    Recent terrestrial cosmogenic nuclide (TCN) studies on end moraines of the Tibetan Plateau have yielded a first synthesis of the timing of mountain glacier and ice field maximum extents at discrete times in the past. Although these allow important constraints on the presence of expanded ice on the plateau, they don’t address the question of the presence of areally more extensive ice sheet configurations where mountain ice complexes from discrete mountain blocks coalesce to form larger bodies. Two ice sheets hypothesised to have covered parts of the Tibetan Plateau are the Tibetan ice sheet and the areally much more restricted Huang He ice sheet. In this study we have focussed on the hypothesised Huang He ice sheet area in the headwaters of the Huang He and Yangtze rivers on the north-eastern margin of the Tibetan Plateau.

    Two mountain blocks from which ice might have emanated to inundate the plateau surface around it and form the ice sheet are the marginally-located Anyemaqen and centrally-located Bayan Har Mountains. Of these the Anyemaqen is located closer to the edge of the plateau, is higher, wetter, and is ornamented with glaciers today, which, according to TCN studies have been more extensive during marine oxygen isotope stages 3, 2, and 1.

    Using Landsat 7 ETM+ satellite imagery we have mapped the glacial geomorphology of the entire hypothesised Huang He ice sheet area (50,000-70,000 km2) and concentrated our TCN field sampling to its core area, the Bayan Har Mountains. The area displays widespread morphological evidence of glacial erosion and deposition, particularly around the higher mountain blocks. The erosional landforms include large-scale glacial troughs, U-shaped valleys and occasional lake basins, and small-scale lateral meltwater channels. The depositional landforms include primarily lateral and end-moraines, but also hummocky moraines and drumlins. Field inspection has yielded observations of tills and erratic boulders. Taken together, these traces comprise an impressive record of multiple large-scale erosional events as witnessed by cross-cutting relationships of glacial valleys and multiple glacier advances through the Bayan Har Mountain valleys, some of which terminated onto the plateau surface, by the presence of suites of end-moraines and associated meltwater traces.

    The mapping exercise thus far has established a clear patchiness to the erosional imprint of ice in the uplands comprising the Huang He ice sheet area. Although the integrated imprint of erosion is clear and displays a pattern of topographically-forced selective linear erosion, the rates of glacial landscape change in the absence of TCN measurements remains unknown.

    We note that except for the arguable presence of tills and the reported, but not confirmed, presence of erratics beyond the mountain fronts, we have not been able to establish firm evidence of ice coverage on the intervening plateau surfaces. Rather, many areas display a distinct non-glacial morphology with welldeveloped fluvial valley systems and basins infilled with alluvial deposits. This casts some doubt on the concept of the Huang He ice sheet, although one may argue that, if of considerable age, few glacial traces may have survived degradational processes. Moreover, we conclude that the break in slope between the youthful steep fluvial landscapes of the Huang He and Yangtze rivers and the relict gentle sloping surface of the Tibetan Plateau almost entirely coincides with the outline of the Huang He ice sheet bordering these rivers. This could be used to further question the reality of the Huang He ice sheet or, if indisputable further evidence can be uncovered in the years to come, the coincidence of borders could indicate that the ice sheet was larger but that evidence for this is now flowing down the rivers.

    Finally, an ambitious TCN and OSL sampling campaign in the Bayan Har Mountains region with our colleagues from the USA (Caffee, Harbor, Li) and China (Zhou, Liu, Ma) will likely shed light on the timing of glacial advances through the dating of end moraines, erratics and till stratigraphies and establish contemporary landscape catchment erosion rates through the analysis of river bank sediment TCN concentrations.

  • 38.
    Stroeven, Arjen
    et al.
    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).
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Harbor, Jon
    Li, Yingkui
    Zhou, Liping
    Caffee, Marc
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Ma, Haizhou
    Liu, Gengnian
    Landscape analysis of the Huang He headwaters, NE Tibetan Plateau — Patterns of glacial and fluvial erosion2009In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 103, no 2, p. 212-226Article in journal (Refereed)
    Abstract [en]

    The large-scale geomorphology of the Huang He (Yellow River) headwaters, centered around the Bayan Har Shan (5267 m asl) in the northeastern part of the Tibetan Plateau, is dominated by an uplifted remnant of a low-relief relict plateau with several mountain ranges. We have performed geomorphological mapping using SRTM topographic data and Landsat 7 ETM+ satellite imagery to evaluate landscape characteristics and patterns, and to investigate the relative importance of different erosional processes in the dissection of this plateau remnant. The distribution of valley morphologies indicates that the eastern and southern margins of the plateau remnant have been extensively dissected by the Huang He and Chang Jiang (Yangtze) rivers and associated tributaries, while the mountain ranges have valley morphologies with U-shaped cross-sections that indicate large impacts from glacial erosion during Quaternary glaciations.

    An east-west decrease in the abundance of glacial valleys in mountains above 4800 m asl suggests that the diminishing size of the mountain blocks, coupled with increased continentality, resulted in more restricted glaciations to the west. Glacial valleys in mountain blocks on the plateau remnant are wider and deeper than adjacent fluvial valleys. This indicates that, integrated over time, the glacial system has been more effective in eroding the mountains of the relict upland surface than the fluvial system. This erosion relationship is reversed, however, on the plateau margin where dramatic fluvial rejuvenation in valleys that are part of the Huang He and Chang Jiang watersheds has consumed whatever glacial morphology existed. A remarkable correspondence exists between the outline of the relict plateau remnant and the outline that has been proposed for the Huang He Ice Sheet. This coincidence could mean that the Huang He Ice Sheet was larger than originally proposed, but that evidence for this has been consumed by fluvial incision at the plateau margin. Alternatively, this coincidence could indicate that what has been described as an ice sheet border is merely the outline of a relict plateau landscape.

    In apparent support of the latter, the absence of large-scale glacial geomorphological evidence on the plains of the relict plateau surface is not consistent with the hypothesis of a Huang He Ice Sheet.

  • 39.
    Stroeven, Arjen P.
    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.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Purdue University .
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Morén, Björn M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geomorphology of the Tian Shan2013In: Journal of Maps, ISSN 1744-5647, E-ISSN 1744-5647, Vol. 9, no 4, p. 505-512Article in journal (Refereed)
    Abstract [en]

    The glacial geomorphology of the Tian Shan has been mapped, with the study area covering almost 638,000km(2). The map, designed to be printed at A0 size due to the elongated shape of the mountain range, is presented at a scale of 1:1,100,000. Five glacial landform categories are presented; glacial valleys, marginal moraines, glacial lineations, hummocky terrain and meltwater channels. These landform categories were mapped using the Shuttle Radar Topography Mission (SRTM) digital elevation model (90m resolution), Landsat 7 ETM+ satellite imagery (30m resolution), and images contained in Google Earth. The mapped landforms were created by glaciers that were restricted to mountain areas and their immediate surroundings.

  • 40.
    Stroeven, Arjen P.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kleman, Johan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Fabel, Derek
    Fredin, Ola
    Goodfellow, Bradley W.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Potsdam, Germany.
    Olsen, Lars
    Caffee, Marc W.
    Fink, David
    Lundqvist, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Rosqvist, Gunhild C.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Bergen, Norway.
    Strömberg, Bo
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Deglaciation of Fennoscandia2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, p. 91-121Article in journal (Refereed)
    Abstract [en]

    To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17-15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models.

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