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  • 1.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip
    Hornibrook, Edward
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Morth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic2012In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 27, no 6, p. 545-552Article in journal (Refereed)
    Abstract [en]

    A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (similar to 2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss-dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. delta 15N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in delta 13C values appear to reflect mainly changes in plant assemblages. Positive shifts in both delta 15N and delta 13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N-enrichment.

  • 2.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Leng, Melanie J
    NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham NG12 5GG, UK.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Blaauw, Maarten
    School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, BT7 1NN Belfast, UK.
    Late Holocene climate change in central Sweden inferred from lacustrine stable isotope dataIn: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417Article in journal (Other academic)
    Abstract [en]

    Stable isotopes (18O and 13C) of lacustrine carbonates (Chara spp algae and Pisidium spp molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (18O and 2H) show that Lake Blektjärnen water isotope composition is responsive to the water balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara 18O values we infer that conditions were dry and warm between 4400-4000 cal yr BP whereas more negative values indicate that conditions were wetter and probably cooler between 4000-3000 cal yr BP. A drier climate is inferred from more positive values between 2500-1000 cal yr BP. However, a successive depletion after ca 1750 cal yr BP, also detected in several other 18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased zonal flow.

  • 3.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Leng, Melanie
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Blaauw, Maarten
    Late Holocene humidity changes inferred from stable isotopes in Chara encrustations and Pisidium shells in a lacustrine sediment sequence from central Sweden2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 8, no 25, p. 1305-1316Article in journal (Refereed)
    Abstract [en]

    Stable isotopes (δ18O and δ13C) of lacustrine carbonates (Chara spp. algae and Pisidium spp. molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (δ18O and δ2H) show that Lake Blektjärnen water isotope composition is responsive to the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration probably enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara δ18O values we infer that conditions were dry and warm between 4400 and 4000 cal. a BP, whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal. a BP. A drier climate is inferred from more positive values between 2500 and 1000 cal. a BP. However, a successive depletion after ca. 1750 cal. a BP, also detected in several other δ18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased strength of the zonal flow.

  • 4. Bigg, Grant R.
    et al.
    Levine, Richard C.
    Clark, Chris D.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Haflidason, Haflidi
    Hughes, Anna L. C.
    Nygard, Atle
    Sejrup, Hans Petter
    Last glacial ice-rafted debris off southwestern Europe: the role of the British-Irish Ice Sheet2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 5, p. 689-699Article in journal (Refereed)
    Abstract [en]

    Ice-rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short-lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short-lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka.

  • 5. Blaauw, M.
    et al.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Christen, J.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Veres, Daniel
    Hughen, K. A.
    Preusser, F.
    Svensson, A.
    Were last glacial climate events simultaneous between Greenland and France?2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 3, p. 387-394Article in journal (Refereed)
    Abstract [en]

    Several large abrupt climate fluctuations during the last glacial have been recorded in Greenland ice cores and archives from other regions. Often these Dansgaard–Oeschger events are assumed to have been synchronous over wide areas, and then used as tie-points to link chronologies between the proxy archives. However, it has not yet been tested independently whether or not these events were indeed synchronous over large areas. Here, we compare Dansgaard–Oeschger-type events in a well-dated record from southeastern France with those in Greenland ice cores. Instead of assuming simultaneous climate events between both archives, we keep their age models independent. Even these well-dated archives possess large chronological uncertainties that prevent us from inferring synchronous climate events at decadal to multi-centennial time scales. If possible, comparisons between proxy archives should be based on independent, non-tuned time-scales.

  • 6.
    Borgmark, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Schoning, Kristian
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    A comparative study of peat proxies from two eastern central Swedish bogs and their relation to meteorological data2006In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 21, no 2, p. 109-114Article in journal (Refereed)
    Abstract [en]

    Analyses of peat humification, testate amoebae, carbon and nitrogen content have been carried out on a peat sequence from Ältabergsmossen. At Gullbergbymossen testate amoebae and peat humification were analysed. Both bogs are located in eastern central Sweden. The longest sequence, Ältabergsmossen, covers the last 150 yr and the data from Gullbergbymossen covers the last 60 yr, both with a time resolution of ca. 2–4 yr cm−1. The different proxies were compared to each other and were also compared to instrumental meteorological data. Correlation between peat humification and C/N ratios is high whereas the correlation is low between these physical/chemical parameters and reconstructed water tables inferred from the testate amoebae assemblages. High peat humification values and C/N ratios greater than 50 indicate aerobic decay and are thought to reflect the thickness of the acrotelm. High humification values and low C/N ratios are recorded in peat deposited between 1965 and 1980, whereas the dry period starts in the early 1970s according to instrumental meteorological data and inferred water-table depth. The difference in the timing of the onset of a dry-shift between the physical/chemical proxies and meteorological data and testate amoebae derived water table changes is interpreted as renewed decay of already deposited peat. The term secondary decomposition is used for this process. The secondary decomposition process has implications for interpreting physical/chemical and biological parameters in peat as they may be out of phase during the beginning of a dry-shift.

  • 7.
    Chabangborn, Akkaneewut
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Climate over mainland Southeast Asia 10.5–5 ka2014In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 29, no 5, p. 445-454Article in journal (Refereed)
    Abstract [en]

    We assembled and evaluated Holocene palaeo-vegetation records regarding semi-quantitative precipitation and temperature for mainland Southeast Asia and compared these with precipitation reconstructions for the Indian Ocean (IOM) and East Asian (EAM) monsoon sub-systems. Our results indicate that temperatures and precipitation in mainland Southeast Asia generally exceeded 18 °C and 1100 mm a−1 during the Holocene. Mainland Southeast Asia experienced cool/wet climatic conditions between 10.5 and 10 ka BP, a warmer/drier climate between 10 and 9 ka BP, cooler/wetter conditions between 9 and 7 ka BP, and moderately warmer/drier conditions since 7 ka BP. The reconstructed summer monsoon intensity compares well with the reconstructed hydroclimate for the EAM region, but diverges from that of the IOM region between 10.5 and 9 ka BP and 7–6.5 ka BP. This discrepancy is explained by differences in land–sea configuration, and regional sea-level history. A strengthening/weakening of the Asian summer monsoon between 9 and 7 ka BP and after 6.5 ka BP, respectively, is observed across the whole Asian monsoon region. Our new data sets support an asynchronous onset of the Asian summer monsoon optimum.

  • 8. Davies, Siwan D.
    et al.
    Larsen, Gudrun
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Turney, Chris S. M.
    Hall, Valerie A.
    Coyle, Lisa
    Thordarson, Thor
    Widespread dispersal of Icelandic tephra: how does the Eyjafjöll eruption of 2010 compare to past Icelandic events?2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 5, p. 605-611Article in journal (Refereed)
  • 9. Delmonte, Barbara
    et al.
    Baroni, Carlo
    Andersson, Per S.
    Schoberg, Hans
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Aciego, Sarah
    Petit, Jean-Robert
    Albani, Samuel
    Mazzola, Claudia
    Maggi, Valter
    Frezzotti, Massimo
    Aeolian dust in the Talos Dome ice core (East Antarctica, Pacific/Ross Sea sector): Victoria Land versus remote sources over the last two climate cycles2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 8, p. 1327-1337Article in journal (Refereed)
    Abstract [en]

    A new ice core (TALDICE) drilled at Tabs Dome (East Antarctica, Ross Sea sector) preserves a ca. 250 ka long record of palaeoclimate and atmospheric history. We investigate dust variability and provenance at the site during glacial periods and the Holocene through the Sr-Nd isotopic composition of ice core dust and potential source areas (PSA). We provide new isotopic data on dust sources from Victoria Land such as regoliths, glacial drifts, aeolian sands and beach deposits. Some of these sources are located at high altitude and are known to have been ice free throughout the Pleistocene. The major features of the TALDICE dust record are very similar to those from central East Antarctica. During glacial times, South America was the dominant dust supplier for Tabs Dome as well as for the entire East Antarctic plateau. Conversely, during the Holocene the principal input of mineral dust at Tabs Dome probably derives from proximal sources which are the ice-free areas of northern Victoria Land, located at similar altitude with respect to the drilling site. Atmospheric mobilisation of dust from these neighbouring areas and transport inland to Tabs Dome can be ultimately associated with advection of maritime air masses from the Pacific/Ross Sea region. Copyright (C) 2010 John Wiley & Sons, Ltd.

  • 10. Esper, Jan
    et al.
    Duethorn, Elisabeth
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Timonen, Mauri
    Buentgen, Ulf
    Northern European summer temperature variations over the Common Era from integrated tree-ring density records2014In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 29, no 5, p. 487-494Article in journal (Refereed)
    Abstract [en]

    Tree-ring chronologies of maximum latewood density are most suitable to reconstruct annually resolved summer temperature variations of the late Holocene. The two longest such chronologies have been developed in northern Europe stretching back to the 2nd century BC, and the 5th century AD. We show where similarities between the two chronologies exist, and combine portions of both into a new summer temperature reconstruction for the Common Era. To minimize the transfer of potential biases, we assess the contribution of the candidate reconstructions' measurements, and exclude data (i) from exceptionally young and old trees, and (ii) produced by different laboratory technologies. Our new composite reconstruction reveals warmer conditions during Roman, Medieval and recent times, separated by prolonged cooling during the Migration period and Little Ice Age. Twentieth century warmth, as indicated in one of the existing density records, is reduced in the new reconstruction, also affecting the overall, millennial-scale, cooling trend over the late Holocene (-0.30 degrees C per 1000 years). Due to the reduced biological memory, typical for tree-ring density measurements, the new reconstruction is most suitable for evaluating the rate and speed of abrupt summer cooling following large volcanic eruptions.

  • 11.
    Feurdean, A.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Bennike, O.
    Late Quaternary palaeocological and paleoclimatological reconstruction in the Gutaiului Mountains, NW Romania2004In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 19, no 8, p. 809-827Article in journal (Refereed)
    Abstract [en]

    Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss-on-ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus-Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13 400 and 13 200 cal. yr BP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13 400 cal. yr BP. A distinct decrease in temperature and humidity between 12 900 and 11 500 cal. yr BP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11 800 cal. yr BP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11 500 cal. yr BP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11 250 cal. yr BP. Larix pollen was not found, but macrofossil evidence indicates that Larix was an important forest constituent at the onset of the Holocene. Moister conditions were followed by a dry period starting about 10 600 cal. yr BP, which was more pronounced between 8600 and 8200 cal. yr BP, as inferred from aquatic macrofossils. The maximum expansion of Tilia, Quercus, Fraxinus and Acer between 10 700 and 8600 cal. yr BP may reflect a more continental climate. A drier and/or cooler climate could have been responsible for the late expansion (10 300 cal. yr BP) and late maximum (9300 cal. yr BP) of Corylus. Increased water stress, and possibly cooler conditions around 8600 cal. yr BP, may have caused a reduction of Ulmus, Tilia, Quercus and Fraxinus. After 8200 cal. yr BP moisture increased and the forests included Picea, Tilia, Quercus and Fraxinus.

  • 12. Fransner, O.
    et al.
    Noormets, R.
    Flink, A. E.
    Hogan, K. A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden, northern Nordaustlandet, Svalbard2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 3, p. 437-455Article in journal (Refereed)
    Abstract [en]

    Observations of subglacial landforms yielding the configuration and dynamics of former ice-flows have for the first time been made in Rijpfjorden and Duvefjorden, Nordaustlandet, Svalbard, using sub-bottom acoustic, swath-bathymetric data and sediment cores. Five acoustic-stratigraphic units were distinguished suggesting the presence of a complete glacial-postglacial succession in the central fjord basins. C-14 ages from the sediments indicate that the inner Rijpfjorden and central Duvefjorden were deglaciated before ca. 10.6 cal ka BP and 11.0 cal ka BP, respectively. Maximum sediment thickness in Rijpfjorden and Duvefjorden is 26 m, resulting in sediment accumulation rates of ca. 66 cm ka(-1). The landform record suggests that the ice streaming in both fjords was topographically controlled. The considerably deeper basin and higher elongation ratios of the crag-and-tails in Duvefjorden are linked to the faulted bedrock and possibly to somewhat larger ice stream and/or more focused ice-flow compared to that in Rijpfjorden. De Geer moraines suggest slower retreat of a grounded ice margin from shallow areas of Rijpfjorden. In deeper areas of the fjords, the glaciers were probably floating, resulting in the lack of ice-marginal transverse landforms. The ice margin retreat from these areas was probably relatively rapid and dominated by calving.

  • 13.
    Goehring, Brent, M.
    et al.
    Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University.
    Lohne, Öystein S.
    Department of Earth Science, University of Bergen.
    Mangerud, Jan
    Department of Earth Science, University of Bergen.
    Svendsen, John Inge
    Department of Earth Science, University of Bergen.
    Gyllencreutz, Richard
    Univ Bergen, Dept Earth Sci, Bergen, Norway.
    Schaefer, Joerg
    Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University.
    Finkel, Robert
    Earth and Planetary Science Department, University of California-Berkeley.
    Late Glacial and Holocene 10Be production rates for western Norway2012In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 27, no 1, p. 89-96Article in journal (Refereed)
    Abstract [en]

    We present a new regional calibration of the 10Be production rate from two well-dated surfaces insouthern Norway: a rock avalanche with 14C-dated wood and a precisely dated Younger Dryas moraine. Calculated10Be production rates are 4.260.13 and 4.650.14 at g1 a1 for the Lal/Stone and Lifton scaling models,respectively. Our regional production rate for southern Norway is 5% lower than the canonical global 10Be productionrate with lower uncertainties. Our 10Be production rate agrees with regional 10Be production rates from north-easternNorth America and New Zealand. The 10Be production rate estimate presented here can be used to improve theprecision and accuracy of exposure-dated ice-marginal features, as well as other surfaces, in northern Europe.

  • 14.
    Gribenski, Natacha
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Leibniz Institute for Applied Geophysics, Germany.
    Jansson, Krister N.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Preusser, Frank
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Trauerstein, Mareike
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Caffee, Marc W.
    Lifton, Nathaniel A.
    Zhang, Wei
    Re-evaluation of MIS 3 glaciation using cosmogenic radionuclide and single grain luminescence ages, Kanas Valley, Chinese Altai2018In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 33, no 1, p. 55-67Article in journal (Refereed)
    Abstract [en]

    Previous investigations observed a period of major glacial advances in Central Asia during marine oxygen isotope stage (MIS) 3 (57-29 ka), out of phase with global ice volume records. We have re-examined the Kanas moraine complex in the Altai Mountains of Central Asia, where an MIS 3 glaciation had been previously inferred. New and consistent cosmogenic exposure and single-grain luminescence ages indicate that the Kanas complex was formed during MIS 2 (29-12 ka), which brings its timing in line with the global ice volume record. We also identified a lateral moraine from a more extensive ice extent that dates to late MIS 5/MIS 4. To place our results in a wider contextual framework, we review the chronologies of another 26 proposed major MIS 3 glacial advances in Central Asia. For most of these sites, we find that the chronological data do not provide an unequivocal case for MIS 3 glaciation.

  • 15.
    Hall, Adrian M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Binnie, Steven A.
    Sugden, David
    Dunai, Tibor J.
    Wood, Christina
    Late readvance and rapid final deglaciation of the last ice sheet in the Grampian Mountains, Scotland2016In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 31, no 8, p. 869-878Article in journal (Refereed)
    Abstract [en]

    Towards the end of the last glaciation, ice sourced from the western Grampian Mountains of Scotland flowed down Strath Spey to encroach on the northern flanks of the Cairngorm Mountains. The maximum of this late advance and its subsequent retreat is recorded by moraines, ice-marginal meltwater channels, and kame terraces that can be traced for 60 km along Strath Spey. New cosmogenic Be-10 exposure ages from moraines indicate deglaciation at 15.1 +/- 1.1 ka. This timing matches closely the recalibrated mean ages of 14.7 +/- 0.7 and 15.2 +/- 0.7 ka for the Wester Ross Readvance in the North-West Highlands. A synchronous readvance of the British-Irish Ice Sheet (BIIS) towards the end of Greenland Stadial 2a (GS-2a) (16.9-14.7 ka) is indicated. Thereafter active ice retreat from the flanks of Strath Spey was rapid, occurring within the similar to 1 ka uncertainty of the cosmogenic exposure ages. We suggest the advance followed the collapse of the marine parts of the BIIS at similar to 16 ka due to conditions of increased precipitation occurring at a time of low temperatures. The rapidity of deglaciation may reflect enhanced Fohn effects caused by the ice dome in the western Grampians.

  • 16.
    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.

  • 17.
    Jonsson, C. E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rosqvist, G. C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Leng, M. J.
    NERC Isotope Geosciences Laboratory, BGS, UK.
    Bigler, C.
    Umeå universitet.
    Bergman, J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kaislahti Tillman, P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sloane, H.
    NERC Isotope Geosciences Laboratory, BGS, UK.
    High-resolution diatom d18O records from two sub-Arctic high-altitude lakes in the Swedish ScandesIn: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417Article in journal (Refereed)
    Abstract [en]

    Waters from high altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature, and relatively short hydraulic residence times, most high altitude lakes have lake water isotopic compositions (δ18Olake) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water d18O. Here we compare two high resolution δ18Odiatom records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900 to AD 1990 is characterized by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ18Odiatom as decreasing trends. Lowest δ18Odiatom values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 years the main factor affecting the δ18Odiatom signal in these sub-Arctic high altitude lakes with short residence times has been changes in amount of winter precipitation and that δ18Odiatom derived from high altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy.

  • 18.
    Jonsson, Christina E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Rosqvist, Gunhild C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Leng, Melanie J.
    Bigler, Christian
    Bergman, Jonas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Tillman, Päivi Kaislahti
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Sloane, Hilary J.
    High-resolution diatom delta O-18 records, from the last 150 years, reflecting changes in amount of winter precipitation in two sub-Arctic high-altitude lakes in the Swedish Scandes2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 6, p. 918-930Article in journal (Refereed)
    Abstract [en]

    Waters from high-altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature and relatively short hydraulic residence times, most high-altitude lakes have lake water isotopic compositions (delta O-18(lake)) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water delta O-18. Here we compare two high-resolution delta O-18(diatom) records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900-1990 is characterised by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in delta O-18(diatom) as decreasing trends. Lowest delta O-18(diatom) values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 a the main factor affecting the delta O-18(diatom) signal in these sub-Arctic high-altitude lakes with short residence times has been changes in amount of winter precipitation and that delta O-18(diatom) derived from high-altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy.

  • 19. Kalliokoski, Maarit
    et al.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Saarinen, Timo
    Rhyolitic and dacitic component of the Askja 1875 tephra in southern and central Finland: first step towards a Finnish tephrochronology2019In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 34, no 1, p. 29-39Article in journal (Refereed)
    Abstract [en]

    Tephra from Icelandic volcanic eruptions is frequently dispersed to northern Europe, but so far tephra has not been detected in Finnish sedimentary records. We report the first finding of a cryptotephra layer in southern and central Finland. Sediment samples from five lakes and 10 peatlands, most of them located in the tephra fallout zone of the Hekla 1947 eruption, were investigated for the presence of cryptotephra to assess the potential for tephrochronology in Finland. Tephra shards were extracted from their host matrix and electron probe microanalysis was conducted on single shards for geochemical characterization. Our results confirm the presence of Askja 1875 tephra in Finland, thus extending the known dispersal area of the Askja 1875 tephra eastwards. Most of the shards are rhyolitic, but a minor concentration of tephra with dacitic composition forms a narrow dispersal zone extending from Sweden to southern Finland. This zone possibly represents the main dispersal axis of the tephra in the distal area. Our results suggest that Finnish environmental research could benefit greatly from adding tephrochronology to the array of dating methods commonly used. Additionally, the absence of Hekla 1947 tephra in the previously inferred fall-out zone is an important result indicating the complexity of tephra deposition and preservation.

  • 20. Kokfelt, U.
    et al.
    Muscheler, R.
    Mellström, A.
    Struyf, E.
    Rundgren, M.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hammarlund, D.
    Diatom blooms and associated vegetation shifts in a subarctic peatland: responses to distant volcanic eruptions?2016In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 31, no 7, p. 723-730Article in journal (Refereed)
    Abstract [en]

    We test the hypothesis that rich occurrences of diatoms observed at transitions between major peat units representing different vegetation communities in a peat sequence from subarctic northern Sweden reflect responses to acid deposition from the Samalas AD 1257 and Laki AD 1783/1784 eruptions. We observe sudden changes in the mire ecosystem and thereby in the trophic status and biogeochemical cycling of the peatland. Both the eruptions are known to have been associated with significant acid deposition events and climatic anomalies, as recorded in polar ice cores. To test the hypothesis, new chronological analyses and age modelling were applied to existing biogeochemical and biological records from the peat sequence. This approach yielded modelled age ranges of AD 1239-1284 (1s)/AD 1210-1303 (2s) (median: AD 1260) and AD 1674-1795 (1s)/AD 1665-1875 (2s) (median AD 1743), respectively, for the stratigraphic transitions. Hence, the modelled age ranges bracket the ages of the eruptions in question and the hypothesis could therefore not be rejected. Impacts of acid deposition from the eruptions are assumed to have caused instant acidification, vegetation damage, increased nutrient cycling and blooms of opportunistic epiphytic diatoms. In addition, cooling may have contributed to vegetation changes through permafrost inception, frost heave and thereby altered hydrological conditions.

  • 21.
    Larsson, Simon A.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The Laacher See Tephra discovered in southernmost Sweden2018In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 33, no 5, p. 477-481Article in journal (Refereed)
    Abstract [en]

    We present the first geochemically confirmed finding of the Laacher See Tephra (LST) on the Swedish mainland, now the northernmost extension of the LST. Sediments were sampled at the Korslattamossen fen, southernmost Sweden, and a high-concentration cryptotephra occurrence (>65000shardscm(-3)) of the LST was found in a sequence of calcareous gyttja. Tephra identification was confirmed by geochemical analysis using field-emission electron probe microanalysis and through comparison of the results with published LST data from proximal sites and distal sites north-east of Laacher See. The LST has previously been divided into eruption phases suggested to have spread in several dispersal fans, but it was not possible to confidently determine the phase of the tephra here closer than to the MLST or ULST. The finding of the LST presented here further strengthens the potential of tephrochronological studies in the south Scandinavian region.

  • 22.
    Lind, Ewa
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wastegard, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Larsen, Jeppe J.
    Univ Copenhagen, Dept Geosci & Nat Resource Management.
    A Late Younger Dryas-Early Holocene tephrostratigraphy for Fosen, Central Norway2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 8, p. 803-811Article in journal (Refereed)
    Abstract [en]

    A number of rapid climate oscillations occur during the Lateglacial-Early Holocene, 15-8 ka BP period and a well-developed tephrostratigraphy in association with these oscillations increases the possibilities to correlate climate archives around the North Atlantic. This paper presents a tephrostratigraphy for Fosen peninsula, Central Norway. Both the Vedde Ash ca.12.1 ka BP and the Saksunarvatn Ash approximate to 10.3 ka BP are important isochrones for correlations of Late Quaternary palaeoenvironmental records in the North Atlantic region and have been assigned ages in GICC05. Beside these tephras we have also identified a new tephra, the Fosen Tephra, with a Borrobol-type geochemistry that occurs above both the Vedde Ash and the Saksunarvatn Ash with an age approximate to 10.2 ka BP. Several tephras with Borrobol-type geochemistry have been identified around the North Atlantic. One group is the Borrobol/Penifiler tephras dated to Greenland Interstadial-1 and another group is dated to the Early Holocene. We suggest that some of the Early Holocene Borrobol-type tephras and the Fosen Tephra may actually be the same layer. If so, the Fosen Tephra is spread over a large area of the North Atlantic and has the potential to become an important marker for short-term climate variability in Scandinavia and in the northern hemisphere.

  • 23. Lindholm, M.
    et al.
    Aalto, T.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    McCarroll, D.
    Ogurtsov, M.
    Jalkanen, R.
    Common temperature signal in four well-replicated tree growth series from northern Fennoscandia2012In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 27, no 8, p. 828-834Article in journal (Refereed)
    Abstract [en]

    Four Nordic temperature proxies based on tree growth at the northern timberline ring-width from Sweden and Finland, maximum latewood density from Sweden, and height increment from Finland were compared. Three indexing methods were used to enhance the low (centennial and above), medium (decadal-to-multidecadal) and high (decadal-to-interannual) frequencies. The proxies are shown to have a strong temperature signal (common variance) at the interannual-to-multidecadal scale, while the multidecadal-to-centennial trends are less coherent, perhaps reflecting intra-regional differences in growing conditions but more likely due to the more noisy regional curve standardization method used to retain the longest trends. Various methods of combining the four proxy series were explored and tested by comparison with four long temperature records from northern Fennoscandia. Only relatively high-frequency, spline-indexed series produced consistently positive verification statistics as a reconstruction model for summer temperature using all four proxies.

  • 24. Loader, Neil J.
    et al.
    Jalkanen, Risto
    McCarroll, Danny
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Spring temperature variability in northern Fennoscandia AD 1693–20112011In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 26, no 6, p. 566-570Article in journal (Refereed)
    Abstract [en]

    A reconstruction of spring (April–May) temperature for northern Fennoscandia developed from the Tornionjoki (Tornio river) long cryophenological record of ice break-up dates, back to AD 1693, is presented. The record is strongly climatically sensitive and explains 67% of the variance in the instrumental data over the last 150 years. The record exhibits a stepped decrease in the duration of the river's ice cover by 14 days, equivalent to an increase in April–May mean temperature of approximately 2.5°C over the last three centuries. The relationship between the date of ice break-up, and accumulated daily mean temperatures (>0°C) is investigated. Uncertainty in the observation of ice break-up is also considered in addition to the potential of this time series for regional climate model validation.

  • 25. Macleod, A.
    et al.
    Brunnberg, L.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hang, T.
    Matthews, I. P.
    Lateglacial cryptotephra detected within clay varves in Ostergotland, south-east Sweden2014In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 29, no 7, p. 605-609Article in journal (Refereed)
    Abstract [en]

    Here we present a 710-year-long floating varve record from south-east Sweden. Tephra analyses confirm the presence of the rhyolitic Vedde Ash preserved within two consecutive varve years, confirming the Younger Dryas age of the varve series. This permits, for the first time, direct correlation of Swedish varved clay with other records of equivalent resolution which also preserve the Vedde Ash and demonstrates that the potential exists to independently date the Swedish Timescale. This discovery will allow direct comparison of rates, timing and duration of key climatic events across Europe and the North Atlantic region in records of equivalent resolution.

  • 26.
    Margold, Martin
    et al.
    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.
    Kleman, Johan
    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.
    Lateglacial ice dynamics of the Cordilleran Ice Sheet in northern British Columbia and southern Yukon Territory: retreat pattern of the Liard Lobe reconstructed from the glacial landform record2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 2, p. 180-188Article in journal (Refereed)
    Abstract [en]

    The Liard Lobe formed a part of the north-eastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that comprises glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and south-west across the Hyland Highland from its local Last Glacial Maximum position in the south-eastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. Retreat across the Liard Lowland is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and further up-valley in an eastern-facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation played a minor role in the deglaciation of this region.

  • 27. Mccarroll, Danny
    et al.
    Tuovinen, Mervi
    Campbell, Rochelle
    Gagen, Mary
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Loader, Neil J.
    Robertson, Iain
    A critical evaluation of multi-proxy dendroclimatology in northern Finland2011In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 26, no 1, p. 7-14Article in journal (Refereed)
    Abstract [en]

    Twentieth-century summer (July-August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (delta(13)C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r(2)), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, delta(13)C performs best, followed by maximum density. Combining delta(13)C and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X-ray densitometry, is shown to perform similarly. Multi-proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub-fossil chronologies where replication may be episodically low.

  • 28. Merritt, Jon W.
    et al.
    Connell, E. Rodger
    Hall, Adrian M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Middle to Late Devensian glaciation of north-east Scotland: implications for the north-eastern quadrant of the last British-Irish ice sheet2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 2, p. 276-294Article, review/survey (Refereed)
    Abstract [en]

    We present a review of over 175 years of research into the Middle to Late Devensian (Weichselian) glaciation of NE Scotland based crucially on both its lithostratigraphic and geomorphic records. The location of the region, and surrounding seabed, makes this unusually detailed record significant for deciphering the former interactions and dynamics of Scottish and Scandinavian ice within the North Sea Basin (NSB), which continue to be controversial. A 12-stage event stratigraphy is proposed based on a parsimonious interpretation of stratigraphic relationships, till lithology and regional clast fabrics, striae, subglacial bedforms, ice-marginal features and published geochronometry at critical sites. The record of regional glaciation supports converging evidence that the north-eastern quadrant of the last British and Irish Ice Sheet reached its maximum spatial extent in the late Middle to early Late Devensian and later re-expanded following widespread internal glacial reorganizations, marine transgression and partial retreat from the central NSB. Retreat was interrupted by several glacial readvances of limited extent. Field-captured data help to identify important events that are not clearly resolved from remote sensing alone, particularly regarding growth phases of the last glaciation.

  • 29. Monteath, Alistair J.
    et al.
    Teuten, Alex E.
    Hughes, Paul D. M.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Effects of the peat acid digestion protocol on geochemically and morphologically diverse tephra deposits2019In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 34, no 4-5, p. 269-274Article in journal (Refereed)
    Abstract [en]

    Tephra shards for electron probe microanalysis are most efficiently extracted from peat using acid digestion, which removes organic material that hinders density separation methods. However, strong acids are known to alter glass chemical compositions, and several studies have examined how acid digestion affects rhyolitic volcanic glass. The focus on rhyolitic tephra in these studies leaves considerable uncertainty, as the dissolution rates of natural glasses (including tephra) are determined by the chemical composition and surface area/volume ratio, both of which vary in tephra deposits. Here, we use duplicate samples of basaltic, trachydacitic and rhyolitic tephra to examine physical and geochemical alteration following acid digestion. Scanning electron microscope imagery reveals no discernible degradation of glass surfaces, and electron probe microanalysis results from duplicate samples are statistically indistinguishable. These findings suggest the acid digestion protocol for organic peats does not significantly alter glass geochemistry regardless of shard morphologies or geochemical compositions.

  • 30.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Navarino Environmental Observatory, Greece.
    Katrantsiotis, Christos
    Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
    Finné, Martin
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bjursäter, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Biomarker hydrogen isotope composition (D) as proxy for Holocene hydroclimatic change and seismic activity in SW Peloponnese, Greece2018In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 33, no 5, p. 563-574Article in journal (Refereed)
    Abstract [en]

    We present a 6000-year-long record tracing hydroclimate changes in SW Greece, based on hydrogen isotope composition of aquatic plant-derived n-C-23 alkanes (D-C23) in a sediment core from the Messenian plain, Peloponnese. The D-C23 record co-varies with other eastern Mediterranean records, suggesting relatively wetter conditions c. 6-4.5ka, followed by progressively drier conditions leading up to maximum aridity c. 2.8 ka. This arid phase was interrupted by a shift in D-C23 between 3.3 and 3.1ka inferring wetter conditions and/or tentative responses to anthropogenic water regulating activities during the Late Bronze Age. After 2.7ka, a return to more humid conditions was followed by increased dryness and stronger seasonality contrasts from c. 2.0ka. The D-C23 record shows three short-lived excursions (5.7, 5.3, 2.8ka), where isotope values dropped by >20 parts per thousand and immediately stabilized again. The events were paralleled by abrupt increases in sedimentation rates. We hypothesize that the isotopic shifts represent a response to mixing of ground water systems during tectonic events, followed by sealing of seismically derived cracks in the active fault. The outcome of the study is promising for future expansion of isotope-based proxies on sediments in the region, to reconstruct both hydroclimate and past seismic activity.

  • 31. Rasmussen, Tine L.
    et al.
    Thomsen, Erik
    Nielsen, Tove
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Atlantic surface water inflow to the Nordic seas during the Pleistocene-Holocene transition (mid-late Younger Dryas and Pre-Boreal periods, 12 450-10 000 a BP)2011In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 26, no 7, p. 723-733Article in journal (Refereed)
    Abstract [en]

    The inflow of Atlantic Water to the Nordic seas from mid-late Younger Dryas to earliest Holocene (12 450-10 000 a BP) is reconstructed on the basis of a high-resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice-rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid-late Younger Dryas and Pre-Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east-west temperature gradient across the Faroe-Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near-continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level.

  • 32. Salonen, J. Sakari
    et al.
    Helmens, Karin F.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Seppa, Heikki
    Birks, H. John B.
    Pollen-based palaeoclimate reconstructions over long glacialinterglacial timescales: methodological tests based on the Holocene and MIS 5dc deposits at Sokli, northern Finland2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 3, p. 271-282Article in journal (Refereed)
    Abstract [en]

    Palaeoclimatic reconstructions over long glacialinterglacial timescales present major methodological challenges, as calibration methods based on modern climate and vegetation patterns may yield biased reconstructions from non-analogue palaeoclimates, such as severely continental glacial periods. In this work, we present pollen-based summer temperature reconstructions based on Holocene and early Weichselian (Marine Isotope Stages (MIS) 5dc) deposits at Sokli, northern Finland. We attempt to improve the robustness of reconstructions of continental palaeoclimates by using two calibration sets, with one located in the region surrounding the fossil site and another in a more continental region in northwestern Russia. We assess the reliability of the reconstructions by estimating the compositional fit between fossil and calibration samples and by comparison with independent, plant macrofossil-based reconstructions. We find the fossil samples to fit the extra-regional, high-continentality calibration set better during the early Holocene and MIS 5dc. Especially in MIS 5dc, however, even the high-continentality calibration set fits the fossil samples poorly compared to the fit achieved in the mid and late Holocene. Thus our results highlight the problem of finding applicable calibration data for pre-Holocene periods. We finally discuss the relative strengths and vulnerabilities of different calibration methods in reconstruction of non-analogue palaeoclimates.

  • 33. Stivrins, Normunds
    et al.
    Wulf, Sabine
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lind, Ewa M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Alliksaar, Tiiu
    Galka, Mariusz
    Andersen, Thorbjørn Joest
    Heinsalu, Atko
    Seppä, Heikki
    Veski, Siim
    Detection of the Askja AD 1875 cryptotephra in Latvia, Eastern Europe2016In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 31, no 5, p. 437-441Article in journal (Refereed)
    Abstract [en]

    We report the first geochemically confirmed findings of the Askja volcano (Iceland) AD 1875 eruption cryptotephra in Eastern Europe. The cryptotephra finding in Latvia is the easternmost finding of the Askja AD 1875 so far, providing an important time marker in the sediments. Although low concentrations of Askja AD 1875 rhyolitic glass shards were recorded, our findings suggest the possibility of also tracing other historical cryptotephras in lacustrine and peat sediments in Eastern Europe. We use the Askja AD 1875 tephra isochrone to synchronize pollen data of human activities, i.e. rye (Secale cereale) cultivation. Our comparison of Secale pollen from two sites reveals that there were minor dissimilarities in the timing of highest rye cultivation, and that a synchronous decrease of rye cultivation occurred at both sites few years after the Askja eruption at AD 1875.

  • 34. van der Bilt, Willem G. M.
    et al.
    Bakke, Jostein
    Werner, Johannes P.
    Paasche, Øjvind
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Bergen, Norway.
    Solheim Vatle, Sunniva
    Late Holocene glacier reconstruction reveals retreat behind present limits and two-stage Little Ice Age on subantarctic South Georgia2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 6, p. 888-901Article in journal (Refereed)
    Abstract [en]

    Observational data show that climate in the Southern Ocean region is rapidly changing. However, past the instrumental period, our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records. Alpine glaciers, present on many Southern Ocean islands, may provide such data because changes in their mass balance, extent and erosion rates often mark a response to climate shifts. Rock flour, the fine-grained fraction of the glacial erosion process, is suspended in meltwater streams and transferred into the sediments of downstream lakes, continuously recording glacier variations. Here, we utilize this relationship to present a reconstruction of the Late Holocene glacier history of subantarctic South Georgia, using sediments from the glacier-fed Middle Hamberg Lake. To fingerprint a glacial erosion/size signal, we used titanium counts, validated against changes in sediment density and grain size, allowing a continuous reconstruction of glacier variations over the past similar to 1250 years. Together with local moraine evidence and supporting evidence from other Southern Hemisphere glaciers on New Zealand and in Patagonia, our findings reveal a series of consecutively diminishing Late Holocene advances. In addition to a glacier maximum before 1250 cal a BP, these include a twostage Litle Ice Age with advances around 300 and 120 cal a BP, in line with evidence from southern Patagonia. In addition, we present evidence for an unreported retreat behind present limits around 500 cal BP.

  • 35.
    Wagner-Cremer, Friederike
    et al.
    Institute of Environmental Biology, Utrecht University.
    Finsinger, Walter
    University of Montpellier.
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Tracing growing degree-day changes in the cuticle morphology of Betula nana leaves: a new micro-phenological palaeo-proxy2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 6, p. 1008-1017Article in journal (Refereed)
    Abstract [en]

    Changing growing-season properties in the northern latitudes are among the most obvious consequences of ongoing global change. Available techniques including satellite monitoring and phenological observations enable the detection of changes over the last few decades to centuries, but the full range of natural variability is still difficult to capture. Here we introduce a new approach to reconstruct growing season properties, by studying imprints of prolonged growing season on epidermal cell growth in Betula nana. A high correlation between cell expansion determined in annually collected B. nana leaves and subfossil leaf fragments collected from recent peat sections in northern Scandinavia, and climatic indices such as budburst date, growing-season degree-days and May–September mean temperatures, enable the establishment of a new micro-phenological proxy for growing season characteristics. The applicability of the epidermal cell undulation index (UI) is tested by comparison with historical instrumental records of growing-season degree-days for the last 200 a. The results demonstrate the potential of the new leaf-morphology-based technique to reconstruct and quantify past changes in growing degree-days beyond instrumental data series. Applied to abundant B. nana leaf remains from peat and lake sediments, the UI may enable a reconstruction of growing degree-days throughout the Holocene and other parts of the late Quaternary.

  • 36.
    Wang, Jianglin
    et al.
    Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China.
    Yang, Bao
    Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Zhao, Yan
    Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China.
    The relationship between the Atlantic Multidecadal Oscillation and temperature variability in China during the last millennium2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 7, p. 653-658Article in journal (Refereed)
    Abstract [en]

    Using a large number of temperature-sensitive proxy records, we investigated the relationship between the Atlantic Multidecadal Oscillation (AMO) and temperature variability in China during the last millennium. The results indicate a relatively homogeneous pattern of cold/warm anomalies in East, West and the whole of China (EC, WC and WOC). The six major AMO cold phases coincided with cold conditions over EC, WC and WOC, while warm conditions across China occurred during the two major AMO warm phases. This close similarity between the AMO and multi-decadal temperature variability in China is supported by climate model simulations and emphasizes the critical role of surface heating over the Asian continent in linking the AMO and the Indian summer monsoon. The mid-latitude westerly anomalies and the propagation of Rossby waves related to the AMO may be two channels linking sea surface temperature anomalies in the North Atlantic and temperature variability over East Asia. Additionally, the Atlantic Meridional Overturning Circulation may play an important role in transmitting the AMO signal over the globe. We recommend further climate model studies on the mechanisms responsible for the connection between the AMO and regional to global climate changes.

  • 37.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Davies, Siwan M.
    An overview of distal tephrochronology in northern Europe during the last 1000 years2009In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 24, no 5, p. 500-512Article in journal (Refereed)
    Abstract [en]

    Several tephra layers from the last millennium have been identified in distal peat and lake sediment sequences in northern Europe, forming a framework of volcanic events of great value for palaeoenvironmental investigations. Most of the tephras within this framework have an origin in Iceland, but distal layers from Jan Mayen have also been identified. The predominant transport pathway, in an easterly-southeasterly direction, has led to the deposition of these tephras in a number of terrestrial deposits in northern Europe. Ash from silicic eruptions (>63% SiO2) dominate at these sites, even though many of the documentary records in distal areas report tephra fall from several basaltic eruptions. Here we provide an overview of the distribution, shard concentration and geochemistry of these tephras to highlight the most important isochrones for addressing key dating issues. In particular, three horizons - Hekla-1 (AD 1104), Öræfajökull (AD 1362) and Askja (AD 1875) - are found at a number of different locations in northern Europe and as such are valuable tie-points for improving and validating chronological models and for synchronisation of records spanning the last 1000 years. In addition, we present new data identifying tephra from the Grímsvötn volcanic system within the Lomonosovfonna ice cap on Svalbard, demonstrating that some tephras have been transported 2000 km to as far north as 79° N along a northeasterly trajectory. This discovery highlights the potential for utilising tephrochronology as a correlation tool for palaeoarchives located in more northerly areas and the complex nature of fall-out from different eruptions.

  • 38. Watson, E. J.
    et al.
    Swindles, G. T.
    Lawson, I. T.
    Savov, I. P.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The presence of Holocene cryptotephra in Wales and southern England2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 4, p. 493-500Article in journal (Refereed)
    Abstract [en]

    There have been few detailed studies into the tephrostratigraphy of southern Britain. We report the tephrostratigraphy of two sites, one in southern England (Rough Tor, Cornwall) and one in Wales (Cors Fochno, west Wales). Our study extends the known southernmost reach of Icelandic cryptotephra in northern Europe. Given the large distance between sites in southern England and eruptive sources (e.g. Iceland 1500-1700km distant), most of the cryptotephra layers consist of sparse numbers of shards, even by the standards of distal tephrostratigraphy (as low as 3 shards cm(-1)), each layer spanning only 1 or 2cm in depth. We identify multiple cryptotephra layers in both sites, extending the known distribution of several tephra layers including the MOR-T4 tephra (approximate to AD 1000) most probably of Icelandic origin, and the AD 860 B tephra correlated to an eruption of Mount Churchill, Alaska. The two sites record contrasting tephrostratigraphies, illustrating the need for the inclusion of multiple sites in the construction of a regional tephrostratigraphic framework. The tephra layers we describe may provide important isochrons for the dating and correlation of palaeoenvironmental sequences in the south of Britain.

1 - 38 of 38
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