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  • 1. Abbott, P. M.
    et al.
    Davies, S. M.
    Steffensen, J. P.
    Pearce, N. J. G.
    Bigler, M.
    Johnsen, S. J.
    Seierstad, I. K.
    Svensson, A.
    Wastegard, S.
    A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36Article in journal (Refereed)
    Abstract [en]

    Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval: the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grimsvotn, Grimsvotn-Kverkfjoll and either Reykjanes or Veidivotn-Bardarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICCO5 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences. (C) 2011 Elsevier Ltd. All rights reserved.

  • 2. Abbott, Peter M.
    et al.
    Davies, Siwan M.
    Steffensen, Jorgen Peder
    Pearce, Nicholas J. G.
    Bigler, Matthias
    Johnsen, Sigfus J.
    Seierstad, Inger K.
    Svensson, Anders
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36, p. 59-77Article in journal (Refereed)
    Abstract [en]

    Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval: the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grimsvotn, Grimsvotn-Kverkfjoll and either Reykjanes or Veidivotn-Bardarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICCO5 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.

  • 3.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Parducci, Laura
    Unneberg, Per
    Ågren, Rasmus
    Schenk, Frederik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rattray, Jayne E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Han, Lu
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences. Columbia University, USA.
    Pedersen, Mikkel W.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Afrifa Yamoah, Kweku
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Slotte, Tanja
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Archaeal community changes in Lateglacial lake sediments: Evidence from ancient DNA2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 181, p. 19-29Article in journal (Refereed)
    Abstract [en]

    The Lateglacial/early Holocene sediments from the ancient lake at Hasseldala Port, southern Sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present Interglacial. The existing multi-proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes. Yet, it remains unclear how microorganisms, such as Archaea, which do not leave microscopic features in the sedimentary record, were affected by these climatic shifts. Here we present the metagenomic data set of Hasseldala Port with a special focus on the abundance and biodiversity of Archaea. This allows reconstructing for the first time the temporal succession of major Archaea groups between 13.9 and 10.8 ka BP by using ancient environmental DNA metagenomics and fossil archaeal cell membrane lipids. We then evaluate to which extent these findings reflect physical changes of the lake system, due to changes in lake-water summer temperature and seasonal lake-ice cover. We show that variations in archaeal composition and diversity were related to a variety of factors (e.g., changes in lake water temperature, duration of lake ice cover, rapid sediment infilling), which influenced bottom water conditions and the sediment-water interface. Methanogenic Archaea dominated during the Allerod and Younger Dryas pollen zones, when the ancient lake was likely stratified and anoxic for large parts of the year. The increase in archaeal diversity at the Younger Dryas/Holocene transition is explained by sediment infilling and formation of a mire/peatbog.

  • 4.
    Ahmed, Engy
    et al.
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden.;Sci Life Lab, Tomtebodavagen 23A, SE-17165 Solna, Sweden..
    Parducci, Laura
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
    Unneberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Evolution.
    Ågren, Rasmus
    Chalmers Univ Technol, Dept Chem & Biol Engn, Sci Life Lab, SE-41296 Gothenburg, Sweden..
    Schenk, Frederik
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden..
    Rattray, Jayne E.
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden.;Univ Calgary, Biol Sci, 2500 Univ Dr NW, Calgary, AB, Canada..
    Han, Lu
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics. Jilin Univ, Coll Life Sci, Ancient DNA Lab, Changchun, Jilin, Peoples R China..
    Muschitiello, Francesco
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden.;Columbia Univ, Lamont Doherty Earth Observ, 61 Route 9NW, Palisades, NY USA..
    Pedersen, Mikkel W.
    Univ Cambridge, Dept Zool, Downing St, Cambridge CB2 3EJ, England..
    Smittenberg, Rienk H.
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden..
    Yamoah, Kweku Afrifa
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden..
    Slotte, Tanja
    Stockholm Univ, Dept Ecol Environm & Plant Sci, SE-10691 Stockholm, Sweden.;Sci Life Lab, Tomtebodavagen 23A, SE-17165 Solna, Sweden..
    Wohlfarth, Barbara
    Stockholm Univ, Dept Geol Sci, SE-10691 Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, SE-10691 Stockholm, Sweden..
    Archaeal community changes in Lateglacial lake sediments: Evidence from ancient DNA2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 181, p. 19-29Article in journal (Refereed)
    Abstract [en]

    The Lateglacial/early Holocene sediments from the ancient lake at Hasseldala Port, southern Sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present Interglacial. The existing multi-proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes. Yet, it remains unclear how microorganisms, such as Archaea, which do not leave microscopic features in the sedimentary record, were affected by these climatic shifts. Here we present the metagenomic data set of Hasseldala Port with a special focus on the abundance and biodiversity of Archaea. This allows reconstructing for the first time the temporal succession of major Archaea groups between 13.9 and 10.8 ka BP by using ancient environmental DNA metagenomics and fossil archaeal cell membrane lipids. We then evaluate to which extent these findings reflect physical changes of the lake system, due to changes in lake-water summer temperature and seasonal lake-ice cover. We show that variations in archaeal composition and diversity were related to a variety of factors (e.g., changes in lake water temperature, duration of lake ice cover, rapid sediment infilling), which influenced bottom water conditions and the sediment-water interface. Methanogenic Archaea dominated during the Allerod and Younger Dryas pollen zones, when the ancient lake was likely stratified and anoxic for large parts of the year. The increase in archaeal diversity at the Younger Dryas/Holocene transition is explained by sediment infilling and formation of a mire/peatbog. (C) 2017 Elsevier Ltd. All rights reserved.

  • 5. Alexanderson, Helena
    et al.
    Backman, Jan
    Cronin, Thomas M.
    Funder, Svend
    Ingolfsson, Olafur
    Jakobsson, Martin
    Landvik, Jon Y.
    Lowemark, Ludvig
    Mangerud, Jan
    Maerz, Christian
    Moller, Per
    O’Regan, Matt
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, no SI, p. 9-31Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required, not least for correlation to extra-Arctic records. In this paper we discuss, from an Arctic perspective, methods and correlation tools that are commonly used to date Arctic Pleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, with focus on factors that affect the possibility and quality of dating, and support this overview by examples of application of modern dating methods to Arctic terrestrial and marine sequences. Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided by radiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning. Recent advances in dating technology, calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material (i.e. foraminifera for C-14, and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolution of most dating methods. Consequently improving the accuracy and precision (analytical and geological uncertainty) of dating methods through technological advances and better understanding of processes are important tasks for the future. Another challenge is to better integrate marine and terrestrial records, which could be aided by targeting continental shelf and lake records, exploring proxies that occur in both settings, and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers. (C) 2013 Elsevier Ltd. All rights reserved.

  • 6. Alexanderson, Helena
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Funder, Svend
    Ingólfsson, Ólafur
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Landvik, Jon Y.
    Löwemark, Ludvig
    Mangerud, Jan
    März, Christian
    Möller, Per
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 9-31Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.

  • 7.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bigler, Christian
    Department of Ecology and Environmental Science, Umeå University.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lotter, André F.
    Institute of Environmental Biology, Laboratory of Palaeobotany and Palynology, Utrecht University.
    Veres, Daniel
    “Emil Racovita” Speleological Institute, Clinicilor 5, 400006 Cluj-Napoca, Romania.
    Modest summer temperature variability during DO cycles in western Europe2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 11-12, p. 1322-1327Article in journal (Refereed)
    Abstract [en]

    Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.

  • 8. Ampel, Linda
    et al.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wohlfarth, Barbara
    Risberg, Jan
    Lotter, André F
    Veres, Daniel
    Modest summer temperature variability during DO cycles in western Europe2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 11/12, p. 1322-1327Article in journal (Refereed)
    Abstract [en]

    Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.

  • 9. Anchukaitis, Kevin J.
    et al.
    Wilson, Rob
    Briffa, Keith R.
    Buntgen, Ulf
    Cook, Edward R.
    D'Arrigo, Rosanne
    Davi, Nicole
    Esper, Jan
    Frank, David
    Gunnarson, Björn E.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hegerl, Gabi
    Helama, Samuli
    Klesse, Stefan
    Krusic, Paul J.
    Stockholm Univ, Dept Phys Geog, Stockholm, Sweden.
    Linderholm, Hans W.
    Myglan, Vladimir
    Osborn, Timothy J.
    Zhang, Peng
    Rydval, Milos
    Schneider, Lea
    Schurer, Andrew
    Wiles, Greg
    Zorita, Eduardo
    Last millennium Northern Hemisphere summer temperatures from tree rings: Part II, spatially resolved reconstructions2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 163, p. 1-22Article, review/survey (Refereed)
    Abstract [en]

    Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regional scale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation changes, radiative forcing, and large-scale modes of ocean-atmosphere variability, and provide spatiotemporal targets for climate model comparison and evaluation. Here we use a multiproxy network of tree-ring chronologies to reconstruct spatially resolved warm season (May August) mean temperatures across the extratropical Northern Hemisphere (40-90 degrees N) using Point-by-Point Regression (PPR). The resulting annual maps of temperature anomalies (750-1988 CE) reveal a consistent imprint of volcanism, with 96% of reconstructed grid points experiencing colder conditions following eruptions. Solar influences are detected at the bicentennial (de Vries) frequency, although at other time scales the influence of insolation variability is weak. Approximately 90% of reconstructed grid points show warmer temperatures during the Medieval Climate Anomaly when compared to the Little Ice Age, although the magnitude varies spatially across the hemisphere. Estimates of field reconstruction skill through time and over space can guide future temporal extension and spatial expansion of the proxy network.

  • 10. Anderson, J. B.
    et al.
    Conway, H.
    Bart, P. J.
    Witus, A. E.
    Greenwood, S. L.
    McKay, R. M.
    Hall, B. L.
    Ackert, R. P.
    Licht, K.
    Jakobsson, M.
    Stone, J. O.
    Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100Article in journal (Refereed)
    Abstract [en]

    Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by similar to 13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by similar to 11 ka BP, just north of Ross Island by similar to 7.8 ka BP, and near Hatherton Glacier by similar to 6.8 ka BP. Farther south, Be-10 exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after similar to 13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis. (C) 2014 The Authors. Published by Elsevier Ltd. All rights reserved.

  • 11. Anderson, John B.
    et al.
    Conway, Howard
    Bart, Philip J.
    Witus, Alexandra E.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McKay, Robert M.
    Hall, Brenda L.
    Ackert, Robert P.
    Licht, Kathy
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stone, John O.
    Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 31-54Article in journal (Refereed)
    Abstract [en]

    Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by similar to 13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by similar to 11 ka BP, just north of Ross Island by similar to 7.8 ka BP, and near Hatherton Glacier by similar to 6.8 ka BP. Farther south, Be-10 exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after similar to 13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.

  • 12. Andresen, Camilla S.
    et al.
    Björck, Svante
    Jessen, Catherine
    Rundgren, Mats
    Early Holocene terrestrial climatic variability along a North Atlantic Island transect: palaeoceanographic implications2007In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, no 15-16, p. 1989-1998Article in journal (Refereed)
    Abstract [en]

    A synthesis of the early Holocene climatic development in the North Atlantic region is presented, based on three previously published lake records from southern Greenland (Lake N14), Iceland (Lake Torfadalsvatn) and the Faroe Islands (Lake Lykkjuvotn). The interval 11500-8500 cal BP has been divided into five phases with respect to the inferred strength of the North Atlantic Current (NAC) and Irminger Currents (IC). Phase 1 (11 500-10 750 cal BP) was characterised by the first establishment of the NAC and IC in the vicinity of the studied sites, interrupted by the Preboreal Oscillation around 11 200cal BP. Phase 2 (10 750-10 100 cal BP) was marked by a further warming step in southern Greenland rather concordant with a change into colder and more variable winters on the Faroe Islands. It is proposed that this could partly be related to a series of melt water outbursts disturbing the thermohaline circulation in the eastern Atlantic Ocean, resulting in a warming trend in the western region. During Phase 3 (10 100-9400cal BP) the strength of the IC reaching northwestern Iceland intensified. A more stable regime in surface circulation was established at the onset of Phase 4 (9400-8900 cal BP) in southern Greenland and was followed by a change towards further warm conditions on Iceland at the onset of Phase 5 (8900-8500 cal BP). (C) 2007 Elsevier Ltd. All rights reserved.

  • 13. Backman, J
    et al.
    Jakobsson, M
    Lovlie, R
    Polyak, L
    Febo, L A
    Is the central Arctic Ocean a sediment starved basin?2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 11-13, p. 1435-1454Article in journal (Refereed)
    Abstract [en]

    Numerous short sediment cores have been retrieved from the central Arctic Ocean, many of which have been assigned sedimentation rates on the order of mm/ka implying that the Arctic Basin was starved of sediments during Plio-Pleistocene times. A review of both shorter-term sedimentation rates, through analysis of available sediment core data, and longer-term sedimentation rates, through estimates of total sediment thickness and bedrock age, suggests that cm/ka-scale rates are pervasive in the central Arctic Ocean. This is not surprising considering the physiographic setting of the Arctic Ocean, being a small land-locked basin since its initial opening during Early Cretaceous times. We thus conclude that the central Arctic Ocean has not been a sediment starved basin, either during Plio-Pleistocene times or during pre-Pliocene times. Rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of similar to2600 km, from the northwestern Amerasia, Basin to the northwestern Eurasia Basin via the Lomonosov Ridge, using paleomagnetic, biostratigraphic, and cyclostratigraphic data. (C) 2004 Elsevier Ltd. All rights reserved.

  • 14.
    Baker, Andrea
    et al.
    University of Stellenbosch, South Africa.
    Pedentchouk, Nikolai
    University of East Anglia, England.
    Routh, Joyanto
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Roychoudhury, Alakendra N.
    University of Stellenbosch, South Africa.
    Climatic variability in Mfabeni peatlands (South Africa) since the late Pleistocene2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 160, p. 57-66Article in journal (Refereed)
    Abstract [en]

    It has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the late Pleistocene. A key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions. Southern Africas contemporary C-3 and C-4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones; however, the region is generally archive poor due to its overall semi-arid climate and high relief topography. The Mfabeni peatland, with a basal age of c. 47 k yrs calibrated before present (kcal yr BP), is one of the oldest continuous coastal peat deposits in Southern Africa. Molecular leaf wax isotopes (delta C-13(wax)) were generated for a 810 cm long core, and combined with previously published bulk geochemical (delta C-13(bulk), %TOC), palynological, and stratigraphic data, to reconstruct the late Pleistocene and Holocene palaeoenvironments. We interpreted environmental shifts associated with the Heinrich 4, Last Glacial Maximum, deglacial and Holocene periods, which are consistent with adjacent Indian Ocean sea surface temperature records. However, the other shorter climate perturbations during the Heinrich 5, 3, 2, 1, Antarctic cold reversal and Younger Dryas, were muted, most likely due to local hydrological overprinting on the Mfabeni record. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene. (C) 2017 Elsevier Ltd. All rights reserved.

  • 15.
    Bentley, Michael J.
    et al.
    Univ Durham, Dept Geog, Sci Labs, Durham DH1 3LE, England..
    Cofaigh, Colm O.
    Univ Durham, Dept Geog, Sci Labs, Durham DH1 3LE, England..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Conway, Howard
    Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA..
    Davies, Bethan
    Aberystwyth Univ, Dept Geog & Earth Sci, Ctr Glaciol, Aberystwyth SY23 3DB, Dyfed, Wales..
    Graham, Alastair G. C.
    Univ Exeter, Coll Life & Environm Sci, Exeter EX4 4RJ, Devon, England..
    Hillenbrand, Claus-Dieter
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Hodgson, Dominic A.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Jamieson, Stewart S. R.
    Univ Durham, Dept Geog, Sci Labs, Durham DH1 3LE, England..
    Larter, Robert D.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Mackintosh, Andrew
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington, New Zealand..
    Smith, James A.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Verleyen, Elie
    Univ Ghent, Dept Biol, Lab Protistol & Aquat Ecol, B-9000 Ghent, Belgium..
    Ackert, Robert P.
    Harvard Univ, Dept Earth & Planetary Sci, Cambridge, MA 02138 USA..
    Bart, Philip J.
    Louisiana State Univ, Dept Geol & Geophys, Baton Rouge, LA 70803 USA..
    Berg, Sonja
    Univ Cologne, Inst Geol & Mineral, D-50674 Cologne, Germany..
    Brunstein, Daniel
    Univ Paris 01, CNRS, Lab Geog Phys, F-92195 Meudon, France..
    Canals, Miguel
    Univ Barcelona, Fac Geol, Dept Stratig Paleontol & Marine Geosci, CRG Marine Geosci, E-08028 Barcelona, Spain..
    Colhoun, Eric A.
    Univ Newcastle, Sch Environm & Life Sci, Callaghan, NSW 2308, Australia..
    Crosta, Xavier
    Univ Bordeaux 1, UMR 5805, F-33405 Talence, France..
    Dickens, William A.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Domack, Eugene
    Univ S Florida, Coll Marine Sci, St Petersburg, FL 33701 USA..
    Dowdeswell, Julian A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Dunbar, Robert
    Stanford Univ, Stanford, CA 94305 USA..
    Ehrmann, Werner
    Univ Leipzig, Inst Geol & Geophys, D-04103 Leipzig, Germany..
    Evans, Jeffrey
    Univ Loughborough, Dept Geog, Loughborough LE11 3TU, Leics, England..
    Favier, Vincent
    UJF CNRS, UMR5183, LGGE, F-38402 St Martin Dheres, France..
    Fink, David
    Australian Nucl Sci & Technol Org, Inst Environm Res, Menai, NSW 2234, Australia..
    Fogwill, Christopher J.
    Univ New S Wales, Climate Change Res Ctr, Sydney, NSW, Australia..
    Glasser, Neil F.
    Aberystwyth Univ, Dept Geog & Earth Sci, Ctr Glaciol, Aberystwyth SY23 3DB, Dyfed, Wales..
    Gohl, Karsten
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Golledge, Nicholas R.
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington, New Zealand..
    Goodwin, Ian
    Macquarie Univ, Dept Geog & Environm, N Ryde, NSW 2109, Australia..
    Gore, Damian B.
    Macquarie Univ, Dept Geog & Environm, N Ryde, NSW 2109, Australia..
    Greenwood, Sarah L.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Hall, Brenda L.
    Univ Maine, Sch Earth & Climate Sci, Orono, ME USA..
    Hall, Kevin
    Univ No British Columbia, Geog Programme, Prince George, BC V2N 479, Canada..
    Hedding, David W.
    Univ S Africa, Dept Geog, ZA-1710 Florida, South Africa..
    Hein, Andrew S.
    Univ Edinburgh, Sch Geosci, Edinburgh EH8 9XP, Midlothian, Scotland..
    Hocking, Emma P.
    Northumbria Univ, Dept Geog, Newcastle Upon Tyne NE1 8ST, Tyne & Wear, England..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Johnson, Joanne S.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Jomelli, Vincent
    Univ Paris 01, CNRS, Lab Geog Phys, F-92195 Meudon, France..
    Jones, R. Selwyn
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington, New Zealand..
    Klages, Johann P.
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Kristoffersen, Yngve
    Univ Bergen, Dept Earth Sci, N-5014 Bergen, Norway..
    Kuhn, Gerhard
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Leventer, Amy
    Colgate Univ, Dept Geol, Hamilton, NY 13346 USA..
    Licht, Kathy
    Indiana Univ Purdue Univ, Dept Earth Sci, Indianapolis, IN 46202 USA..
    Lilly, Katherine
    Univ Otago, Dept Geol, Dunedin, New Zealand..
    Lindow, Julia
    Colgate Univ, Dept Geol, Hamilton, NY 13346 USA.;Univ Bremen, Dept Geosci, D-28359 Bremen, Germany..
    Livingstone, Stephen J.
    Univ Sheffield, Dept Geog, Sheffield S10 2TN, S Yorkshire, England..
    Masse, Guillaume
    Univ Paris 06, CNRS, IRD, MNHN,LOCEAN,UMR7159, F-75252 Paris, France..
    McGlone, Matt S.
    Landcare Res, Lincoln 7640, New Zealand..
    McKay, Robert M.
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington, New Zealand..
    Melles, Martin
    Univ Cologne, Inst Geol & Mineral, D-50674 Cologne, Germany..
    Miura, Hideki
    Natl Inst Polar Res, Tokyo 1908518, Japan..
    Mulvaney, Robert
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Nel, Werner
    Univ Ft Hare, Dept Geog & Environm Sci, ZA-5700 Alice, South Africa..
    Nitsche, Frank O.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY USA..
    O'Brien, Philip E.
    Macquarie Univ, Dept Geog & Environm, N Ryde, NSW 2109, Australia..
    Post, Alexandra L.
    Geosci Australia, Canberra, ACT 2601, Australia..
    Roberts, Stephen J.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Saunders, Krystyna M.
    Univ Bern, Inst Geog, CH-3012 Bern, Switzerland.;Univ Bern, Oeschger Ctr Climate Change Res, CH-3012 Bern, Switzerland..
    Selkirk, Patricia M.
    Macquarie Univ, Dept Biol Sci, N Ryde, NSW 2109, Australia..
    Simms, Alexander R.
    Univ Durham, Dept Geog, Sci Labs, Durham DH1 3LE, England.;Univ Calif Santa Barbara, Dept Earth Sci, Santa Barbara, CA 93106 USA..
    Spiegel, Cornelia
    Univ Bremen, Dept Geosci, D-28359 Bremen, Germany..
    Stolldorf, Travis D.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Sugden, David E.
    Univ Edinburgh, Sch Geosci, Edinburgh EH8 9XP, Midlothian, Scotland..
    van der Putten, Nathalie
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    van Ommen, Tas
    Australian Antarctic Div, Hobart, Tas 7001, Australia.;Antarctic Climate & Ecosyst Cooperat Res Ctr, Hobart, Tas 7001, Australia..
    Verfaillie, Deborah
    UJF CNRS, UMR5183, LGGE, F-38402 St Martin Dheres, France..
    Vyverman, Wim
    Univ Ghent, Dept Biol, Lab Protistol & Aquat Ecol, B-9000 Ghent, Belgium..
    Wagner, Bernd
    Univ Cologne, Inst Geol & Mineral, D-50674 Cologne, Germany..
    White, Duanne A.
    Univ Canberra, Inst Appl Ecol, Canberra, ACT 2601, Australia..
    Witus, Alexandra E.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Zwartz, Dan
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington, New Zealand..
    A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 1-9Article in journal (Refereed)
    Abstract [en]

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community. (C) 2014 The Authors. Published by Elsevier Ltd.

  • 16. Bentley, Michael J.
    et al.
    Cofaigh, Colm O.
    Anderson, John B.
    Conway, Howard
    Davies, Bethan
    Graham, Alastair G. C.
    Hillenbrand, Claus-Dieter
    Hodgson, Dominic A.
    Jamieson, Stewart S. R.
    Larter, Robert D.
    Mackintosh, Andrew
    Smith, James A.
    Verleyen, Elie
    Ackert, Robert P.
    Bart, Philip J.
    Berg, Sonja
    Brunstein, Daniel
    Canals, Miguel
    Colhoun, Eric A.
    Crosta, Xavier
    Dickens, William A.
    Domack, Eugene
    Dowdeswell, Julian A.
    Dunbar, Robert
    Ehrmann, Werner
    Evans, Jeffrey
    Favier, Vincent
    Fink, David
    Fogwill, Christopher J.
    Glasser, Neil F.
    Gohl, Karsten
    Golledge, Nicholas R.
    Goodwin, Ian
    Gore, Damian B.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hall, Brenda L.
    Hall, Kevin
    Hedding, David W.
    Hein, Andrew S.
    Hocking, Emma P.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johnson, Joanne S.
    Jomelli, Vincent
    Jones, R. Selwyn
    Klages, Johann P.
    Kristoffersen, Yngve
    Kuhn, Gerhard
    Leventer, Amy
    Licht, Kathy
    Lilly, Katherine
    Lindow, Julia
    Livingstone, Stephen J.
    Masse, Guillaume
    McGlone, Matt S.
    McKay, Robert M.
    Melles, Martin
    Miura, Hideki
    Mulvaney, Robert
    Nel, Werner
    Nitsche, Frank O.
    O'Brien, Philip E.
    Post, Alexandra L.
    Roberts, Stephen J.
    Saunders, Krystyna M.
    Selkirk, Patricia M.
    Simms, Alexander R.
    Spiegel, Cornelia
    Stolldorf, Travis D.
    Sugden, David E.
    van der Putten, Nathalie
    van Ommen, Tas
    Verfaillie, Deborah
    Vyverman, Wim
    Wagner, Bernd
    White, Duanne A.
    Witus, Alexandra E.
    Zwartz, Dan
    A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 1-9Article in journal (Refereed)
    Abstract [en]

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

  • 17. Björck, Jonas
    et al.
    Andrén, Thomas
    Wastegård, Stefan
    Possnert, Göran
    Schoning, Kristian
    An event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden: results from investigations of varved clay and terrestrial sequences2002In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 21, no 12/13, p. 1489-1501Article in journal (Refereed)
    Abstract [en]

    This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the time-span from ca 12,900 to 10,200 cal yr BP. The local event stratigraphy has been linked to the GRIP isotopic event stratigraphy by different correlations. The onset of the Younger Dryas is dated to 12,650 cal yr BP. This cold event lasted for ca 1125 cal yr in the area. The Vedde Ash (ca 12,000 cal yr BP) has been recorded in two terrestrial sequences, which makes it possible to exactly link the event stratigraphy to the GRIP ice-core and to marine cores in the North Atlantic region. The final drainage of the Baltic Ice Lake has been dated to ca 11,560 cal yr BP, which predates the Younger Dryas/Preboreal climatic boundary with ca 35 yr. An early Holocene cold event has been detected both in terrestrial and varved clay sequences at ca 11,305-11,185 cal yr BP. This cold event coincides almost exactly with a brackish water phase in the Baltic Sea. A previously unrecorded early Holocene tephra horizon has been found in lacustrine sediments at ca 10,200 cal yr BP.

  • 18.
    Björck, Svante
    et al.
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Rundgren, Mats
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Ljung, Karl
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Unkel, Ingmar
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Wallin, Åsa
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Multi-proxy analyses of a peat bog on Isla de los Estados, easternmost Tierra del Fuego: a unique record of the variable Southern Hemisphere Westerlies since the last deglaciation2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 42, p. 1-14Article in journal (Refereed)
    Abstract [en]

    We have analyzed an almost 14,000 year old peat sequence on the island of Isla de los Estados (55 degrees S. 64 degrees W), east of Tierra del Fuego, in the core of the Southern Hemisphere Westerlies. A multitude of methods have been used: high resolution C-14 dating; detailed lithologic descriptions including humification degree; loss on ignition; magnetic susceptibility; bulk density; pollen and spore analysis and determination of Aeolian sand influx. By combining proxies for wind and precipitation we have been able to reconstruct how the westerlies have varied over time in the Atlantic sector of the Southern Ocean. It shows that this westerly wind belt was most intense at the onset of the record, 13,600-13,200 cal BP, coinciding with the mid to late part of the Antarctic Cold Reversal, followed by a gradual decline. At 12,200 cal BP the westerlies seem to have shifted to a position south of Tierra del Fuego and this phase, the calmest and driest period on the island throughout the sequence, ended at 10,000 cal BP when the westerlies moved equatorward again. Since then the westerlies have been present but with a variable impact on the 55 degrees S latitude of the Atlantic. Mostly conditions have been fairly similar to today, but occasionally with a wider or narrower and/or weaker or stronger wind belt. At 7200 cal BP wind intensity began to increase and between 4500 and 3500 cal BP these southern latitudes experienced a distinct wind and precipitation maximum, both in terms of perseverance and intensity. Our results show a both wide and strong wind belt, with possible niveo-aeolian activity in Tierra del Fuego in winter, and possibly creating milder summers around the Antarctic Peninsula. In the later part of the Holocene, expansion contraction phases of the wind belt, especially in winter, seem to have been a common phenomenon. (C) 2012 Elsevier Ltd. All rights reserved.

  • 19. Björkman, L.
    et al.
    Feurdean, A.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Cinthio, K.
    Wohlfarth, B.
    Possnert, G.
    Lateglacial and early Holocene vegetation development in the Gutaiului Mountains, NW Romania2002In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 21, no 8-9, p. 1039-1059Article in journal (Refereed)
  • 20. Blockley, Simon
    et al.
    Blaauw, Maarten
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Bronk Ramsey, Christopher
    van der Plicht, Johannes
    Building and testing age models for radiocarbon dates in Lateglacial and Early Holocene sediments2007In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, no 15-16, p. 1915-1926Article in journal (Refereed)
    Abstract [en]

    The growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives. This has in turn led to attempts at significant improvements in the required precision at which records can be dated. Radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives, and as such many of the recent developments in improving precision have been aimed at this technique. These include: (1) selection of the most suitable datable fractions within a record, (2) the development of better calibration curves, and (3) more precise age modelling techniques. While much attention has been focussed on the first two items, testing the possibilities of the relatively new age modelling approaches has not received much attention. Here, we test the potential for methods designed to significantly improve precision in radiocarbon-based age models, wiggle match dating and various forms of Bayesian analyses. We demonstrate that while all of the methods can perform very well, in some scenarios, caution must be taken when applying them. It appears that an integrated approach is required in real life dating situations where more than one model is applied, with strict error calculation, and with the integration of radiocarbon data with sedimentological analyses of site formation processes.

  • 21.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jon M.
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Lifton, N. A.
    Heyman, J.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Petrakov, D. A.
    Caffee, M. W.
    Ivanov, M. N.
    Hättestrand, Clas
    Stockholm Univ, Dept Phys Geog, Geomorphol & Glaciol, Stockholm, Sweden.
    Rogozhina, I.
    Usubaliev, R.
    Evaluating the timing of former glacier expansions in the Tian Shan: A key step towards robust spatial correlations2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 153, p. 78-96Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Blomdin, Robin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Harbor, Jonathan M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lifton, Nathaniel A.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gribenski, Natacha
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Petrakov, Dmitry A.
    Caffee, Marc W.
    Ivanov, Mikhail N.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Rogozhina, Irina
    Usubaliev, Ryskul
    Evaluating the timing of former glacier expansions in the Tian Shan: a key step towards robust spatial correlationsIn: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArticle in journal (Refereed)
    Abstract [en]

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

  • 23. Bourne, A. J.
    et al.
    Cook, E.
    Abbott, P. M.
    Seierstad, I. K.
    Steffensen, J. P.
    Svensson, A.
    Fischer, H.
    Schupbach, S.
    Davies, S. M.
    A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25-45 ka b2k2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 118, p. 122-141Article in journal (Refereed)
    Abstract [en]

    Tephra layers preserved within the Greenland ice-cores are crucial for the independent synchronisation of these high-resolution records to other palaeoclimatic archives. Here we present a new and detailed tephrochronological framework for the time period 25,000-45,000 a b2k that brings together results from 4 deep Greenland ice-cores. In total, 99 tephra deposits, the majority of which are preserved as cryptotephra, are described from the NGRIP, NEEM, GRIP and DYE-3 records. The major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from Iceland. Specifically, 43 originate from Grimsvotn, 20 are thought to be sourced from the Katla volcanic system and 17 show affinity to the Kverkfjoll system. Robust geochemical characterisations, independent ages derived from the GICCO5 ice-core chronology, and the stratigraphic positions of these deposits relative to the Dansgaard-Oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the North Atlantic region between GS-3 and GI-12. Of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period. This framework of well-constrained, time-synchronous tie-lines represents an important step towards the independent synchronisation of marine, terrestrial and ice-core records from the North Atlantic region, in order to assess the phasing of rapid climatic changes during the last glacial period. (C) 2014 Elsevier Ltd. All rights reserved.

  • 24. Buylaert, J. -P
    et al.
    Murray, A. S.
    Gebhardt, A. C.
    Sohbati, R.
    Ohlendorf, C.
    Thiel, C.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zolitschka, B.
    Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 70-80Article in journal (Refereed)
    Abstract [en]

    We have measured and tested a luminescence chronology for the PASADO core 5022-1D from the maar lake of Laguna Potrok Aike. Because of unsuitable quartz OSL characteristics, sand-sized K-feldspar extracts were chosen as a dosimeter and the dose was measured using a post-IR IRSL (pIRIR(290)) measurement protocol. Using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of feldspar signal instability. Extensive laboratory tests show that the chosen pIRIR(290) protocol is applicable to these samples. We also developed a new criterion based on known relative bleaching rates of the conventional IRSL signal (IR50) and the pIRIR(290) signal and the relationship between resulting equivalent doses; this is used to identify and reject poorly bleached samples. Eighteen samples out of 47 were rejected based on this criterion, without reference to absolute doses or stratigraphy; the resulting age-depth profile is self-consistent, increases smoothly with depth and is in agreement with independent age control based on volcanic ash layers (Reclus, Mt Burney and Hudson tephras) at the top and middle of the core. Our new luminescence chronology suggests that the 5022-1D core reaches back to similar to 65 ka at similar to 96 m below lake floor.

  • 25. Capraro, L.
    et al.
    Massari, F.
    Rio, D.
    Fornaciari, E.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Channell, J. E. T.
    Macri, P.
    Prosser, G.
    Speranza, F.
    Chronology of the Lower-Middle Pleistocene succession of the south-western part of the Crotone Basin (Calabria, Southern Italy)2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 9-10, p. 1185-1200Article in journal (Refereed)
    Abstract [en]

    Biostratigraphy based on calcareous nannofossils, integrated by magnetostratigraphic, geochronological and isotopic data, allowed establishing a precise chronological framework for the Pleistocene succession within the south-western sector of the Crotone Basin (Calabria, Southern Italy), where the Pliocene-Pleistocene global stratotype section and point is defined, thus demonstrating that sedimentation was quasi-continuous during most of the Lower and Middle Pleistocene. At a large scale, the Pleistocene succession in this sector of the Crotone Basin is characterized by an evident shallowing-upwards trend, showing facies changes from bathyal to shelfal to littoral/continental. However, comparison between adjacent sectors within the investigated area demonstrates that stratigraphic architectures change vastly on very short distances. Our chronological constraints indicate that such changes in sedimentation styles probably occurred in response to differential subsidence rates, which originated tectonically-controlled synsedimentary structures where accommodation space and sediment yield were allotted unevenly. This articulated physiography led to striking differences in the overall thicknesses and organization of Pleistocene stratigraphies and, eventually, to a distinct diachroneity in the first appearance of shallow-marine deposits. In addition, superimposed are complex interplays between regional and local tectonics, eustasy and orbitally-forced climate changes. These interactions have been highlighted by the oxygen isotope stratigraphy established for a part of the studied succession, which is likely to document almost continuously the interval from Marine Isotope Stage (MIS) 26 to MIS 17. In its younger part (post-MIS 17), chronological ties are poor, as the succession is dominated by shallow-water to continental deposits showing a prominent organization into cyclothems. Nevertheless, based on the chronology of the underlying units, it is feasible that basin infill ended during MIS 15-MIS 14 times.

  • 26.
    Chauhan, T.
    et al.
    Univ Ctr Svalbard UNIS, Dept Arct Geol, N-9171 Svalbard, Norway.;Univ Tromso, Dept Geol, NO-9037 Tromso, Norway..
    Rasmussen, T. L.
    Univ Tromso, Dept Geol, NO-9037 Tromso, Norway..
    Noormets, R.
    Univ Ctr Svalbard UNIS, Dept Arct Geol, N-9171 Svalbard, Norway..
    Jakobsson, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Hogan, K. A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Glacial history and paleoceanography of the southern Yermak Plateau since 132 ka BP2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 155-169Article in journal (Refereed)
    Abstract [en]

    The southern Yermak Plateau (YP) is situated at the entrance to the Arctic Ocean in the narrow Marginal Ice Zone (MIZ) between the Polar and Arctic Fronts, north-west of Svalbard. A gravity core JM10-02GC has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the Svalbard-Barents Sea Ice Sheet (SBIS) during the Last Interglacial Glacial cycle. The distribution of planktic and benthic foraminifera, planktic and benthic oxygen and carbon isotopes and variations in ice-rafted debris (IRD) has been investigated. The sediment core covers the time interval from the Marine Isotope Stage (MIS) 6/5e transition (Termination II, c. 132 ka BP) to the early Holocene. During Termination II (TII), the SBIS retreated and the sea ice margin was in distal position whereas during MIS 5 to MIS 4 the sea ice margin was close to the core site. Several core intervals interpreted as representing MIS 5e, MIS 5c, MIS 5a, MIS 3 and MIS 1 were barren of calcareous microfossils whereas the intervals representing MIS 4 and MIS 2 were characterised by high productivity (HP) of planktic and benthic foraminifera. These "glacial" HP zones were associated with the open water conditions resulting from the advection of Atlantic Water (AW) and retreat of the sea ice margin. The barren zones during MIS 5, MIS 3 and MIS 1 resulted from the proximity of the sea ice margin whereas during MIS 2 the likely cause was an advance of the SBIS. (C) 2013 Elsevier Ltd. All rights reserved.

  • 27. Chauhan, T.
    et al.
    Rasmussen, T. L.
    Noormets, R.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogan, K. A.
    Glacial history and paleoceanography of the southern Yermak Plateausince 132 ka BP2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 155-169Article in journal (Refereed)
    Abstract [en]

    The southern Yermak Plateau (YP) is situated at the entrance to the Arctic Ocean in the narrow MarginalIce Zone (MIZ) between the Polar and Arctic Fronts, north-west of Svalbard. A gravity core JM10-02GChas been analysed in order to reconstruct paleoceanographic conditions and the movement of the seaice margin as well as the glacier ice conditions of the SvalbardeBarents Sea Ice Sheet (SBIS) during theLast InterglacialeGlacial cycle. The distribution of planktic and benthic foraminifera, planktic and benthicoxygen and carbon isotopes and variations in ice-rafted debris (IRD) has been investigated. The sedimentcore covers the time interval from the Marine Isotope Stage (MIS) 6/5e transition (Termination II, c.132 ka BP) to the early Holocene. During Termination II (TII), the SBIS retreated and the sea ice marginwas in distal position whereas during MIS 5 to MIS 4 the sea ice margin was close to the core site. Severalcore intervals interpreted as representing MIS 5e, MIS 5c, MIS 5a, MIS 3 and MIS 1 were barren ofcalcareous microfossils whereas the intervals representing MIS 4 and MIS 2 were characterised by highproductivity (HP) of planktic and benthic foraminifera. These “glacial” HP zones were associated with theopen water conditions resulting from the advection of Atlantic Water (AW) and retreat of the sea icemargin. The barren zones during MIS 5, MIS 3 and MIS 1 resulted from the proximity of the sea icemargin whereas during MIS 2 the likely cause was an advance of the SBIS.

  • 28.
    Chawchai, Sakonvan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Chabangborn, Akkaneewut
    Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
    Fritz, Sherilyn
    Valiranta, Minna
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lowemark, Ludvig
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 111, p. 62-71Article, review/survey (Refereed)
    Abstract [en]

    The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, delta C-13, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS C-14 ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35 degrees N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17 degrees N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.

  • 29.
    Chawchai, Sakonvan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chabangborn, Akkaneewut Nut
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Loewemark, L.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, M.
    Klubseang, W.
    Reimer, P. J.
    Fritz, S. C.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, p. 59-75Article in journal (Refereed)
    Abstract [en]

    The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new C-14-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400-5200 cal yr BP. The driest interval in Kumphawapi's history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important palaeoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail.

  • 30. Clark, Chris D.
    et al.
    Hughes, Anna L. C.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jordan, Colm
    Sejrup, Hans Petter
    Pattern and timing of retreat of the last British Irish ice sheet2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 44, p. 112-146Article in journal (Refereed)
    Abstract [en]

    During the last glacial the ice sheet that subsumed most of Britain, Ireland and the North Sea attained its maximum extent by 27 ka BP and with an ice volume sufficient to raise global sea level by ca 2.5 m when it melted. We reconstruct the demise of this British-Irish Ice Sheet (BIIS) and present palaeo-glaciological maps of retreat stages between 27 and 15 ka BR The whole land area was investigated using remote sensing data and we present maps of moraines, meltwater channels, eskers, and drumlins and a methodology of how to interpret and bring them together. For the continental shelf, numerous large moraines were discovered recording an extensive pattern of retreat stretching from SW Ireland to the Shetland Isles. From an integration of this new mapping of glacial geomorphology (>26,000 landforms) with previously published evidence, compiled in the BRITICE database, we derive a pattern of retreat for the whole BIIS. We review and compile relevant dates (881 examples) that constrain the timing of retreat. All data are held within a Geographic Information System (GIS), and are deciphered to produce a best-estimate of the combined pattern and timing of retreat. Pattern information reveals an ice sheet mainly comprised of a shelf-parallel configuration from SW Ireland to NE Scotland but it spread far enough to the south to incorporate outlying ice domes over Wales, the Lake District and Kerry. Final disintegration was into a number of separate ice caps, rather than reduction as a single mass, and paradoxically, retreat was not always back to high ground. By 23 ka BP ice withdrew along its northern boundaries at the same time as the southern margins were expanding, including transient ice streaming down the Irish Sea and advances of lobes in the Cheshire Basin, Vale of York and east coast of England. Ice divides migrated south. By 19 ka the ice sheet was in crisis with widespread marine-based ice losses, particularly in the northern North Sea and the Irish Sea. Considerable dynamic-thinning occurred during this phase. Final collapse of all marine sectors occurred by 17 ka BP and with most margins beginning to back-step onshore. Disintegration of the North Sea 'ice bridge' between Britain and Norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted. The North Channel and Irish Sea ice streams had finally cleaved the ice sheet into separate Irish and Scottish ice sheets by 16 ka BP. Rates of ice loss were found to vary widely over space and time (e.g., 65-260 km(3) per year). The role of ice streams and calving losses of marine-based sectors are examined. Retreat rates of up to ca 150 ma(-1) were found for some ice stream margins. That large parts (2/3) of the BIIS were marine-based, drained by ice streams, and possibly with fringing ice shelves in places, makes it a useful analogue for the West Antarctic Ice Sheet (WAIS). This is especially so because the BIIS deglaciated in response to rising temperatures and a rising sea level (driven by melting of other ice masses) which are the current forcings that might cause collapse of the WAIS. Our reconstruction, when viewed from the opposite perspective, documents when fresh land became exposed for exploitation by plants, animals and Man, and records for how long such land has been available for soil and geochemical development and ecological succession.

  • 31. Cohen, T. J.
    et al.
    Nanson, G. C.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gliganic, L. A.
    May, J. -H.
    Larsen, J. R.
    Goodwin, I. D.
    Browning, S.
    Price, D. M.
    A pluvial episode identified in arid Australia during the Medieval Climatic Anomaly2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 56, p. 167-171Article in journal (Refereed)
    Abstract [en]

    Optically stimulated luminescence (OSL) ages from a relict shoreline on Lake Callabonna record a major pluvial episode in southern central Australia between 1050  70 and 1100  60 Common Era (CE), within the Medieval Climatic Anomaly (MCA). During this pluvial interval Lake Callabonna filled to 10e12 times the volume of the largest historical filling (1974) and reached maximum depths of 4e5 m, compared to the 0.5e1.0 m achieved today. Until now there has been no direct evidence for the MCA in the arid interior of Australia. A multi-proxy, analogue-based atmospheric circulation reconstruction indicates that the pluvial episode was associated with an anomalous meridional atmospheric circulation pattern over the Southern extratropics, with high sea-level pressure ridges in the central Indian Ocean and Tasman Sea, and a trough extending from the Southern Ocean into central Australia. A major decline in the mobility of the Australian aboriginal hunter-gatherer coincides with this MCA period, in southern central Australia.

  • 32.
    Colleoni, F.
    et al.
    CNRS, Lab Glaciol & Geophys Environm, UJF, F-38402 St Martin Dheres, France.;Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Krinner, G.
    CNRS, Lab Glaciol & Geophys Environm, UJF, F-38402 St Martin Dheres, France.;Alfred Wegener Inst Polar & Marine Res, D-14473 Potsdam, Germany..
    Jakobsson, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    The role of an Arctic ice shelf in the climate of the MIS 6 glacial maximum (140 ka)2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3590-3597Article in journal (Refereed)
    Abstract [en]

    During the last decade, Arctic icebreaker and nuclear submarine expeditions have revealed large-scale Pleistocene glacial erosion on the Lomonosov Ridge, Chukchi Borderland and along the Northern Alaskan margin indicating that the glacial Arctic Ocean hosted large Antarctic-style ice shelves. Dating of sediment cores indicates that the most extensive and deepest ice grounding occurred during Marine Isotope Stage (MIS) 6. The precise extents of Pleistocene ice shelves in the Arctic Ocean are unknown but seem comparable to present existing Antarctic ice shelves. How would an Antarctic-style ice shelf in the MIS 6 Arctic Ocean influence the Northern Hemisphere climate? Could it have impacted on the surface mass balance (SMB) of the MIS 6 Eurasian ice sheet and contributed to its large southward extent? We use an Atmospheric General Circulation Model (AGCM) to investigate the climatic impacts of both a limited MIS 6 ice shelf covering portions of the Canada Basin and a fully ice shelf covered Arctic Ocean. The AGCM results show that both ice shelves cause a temperature cooling of about 3 degrees C over the Arctic Ocean mainly due to the combined effect of ice elevation and isolation from the underlying ocean heat fluxes stopping the snow cover from melting during summer. The calculated SMB of the ice shelves are positive. The ice front horizontal velocity of the Canada Basin ice shelf is estimated to approximate to 1 km yr(-1) which is comparable to the recent measurements of the Ross ice shelf, Antarctica. The existence of a large continuous ice shelf covering the entire Arctic Ocean would imply a mean annual velocity of icebergs of approximate to 12 km yr(-1) through the Fram Strait. Our modeling results show that both ice shelf configurations could be viable under the MIS 6 climatic conditions. However, the cooling caused by these ice shelves only affects the Arctic margins of the continental ice sheets and is not strong enough to significantly influence the surface mass balance of the entire MIS 6 Eurasian ice sheet. (C) 2010 Elsevier Ltd. All rights reserved.

  • 33. Colleoni, Florence
    et al.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Niessen, Frank
    Quiquet, Aurelien
    Liakka, Johan
    An East Siberian ice shelf during the Late Pleistocene glaciations: Numerical reconstructions2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, p. 148-163Article in journal (Refereed)
    Abstract [en]

    A recent data campaign in the East Siberian Sea has revealed evidence of grounded and floating ice dynamics in regions of up to 1000 m water depth, and which are attributed to glaciations older than the Last Glacial Maximum (21 kyrs BP). The main hypothesis based on this evidence is that a small ice cap developed over Beringia and expanded over the East Siberian continental margin during some of the Late Pleistocene glaciations. Other similar evidence of ice dynamics that have been previously collected on the shallow continental shelves of the Arctic Ocean have been attributed to the penultimate glaciation, i.e. Marine Isotopes Stage 6 (approximate to 140 kyrs BP). We use an ice sheet model, forced by two previously simulated MIS 6 glacial maximum climates, to carry out a series of sensitivity experiments testing the impact of dynamics and mass-balance related parameters on the geometry of the East Siberian ice cap and ice shelf. Results show that the ice cap developing over Beringia connects to the Eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m SLE, depending on the climate forcing. This ice cap generates an ice shelf of dimensions comparable with or larger than the present-day Ross ice shelf in West Antarctica. Although the ice shelf extent strongly depends on the ice flux through the grounding line, it is particularly sensitive to the choice of the calving and basal melting parameters. Finally, inhibiting a merging of the Beringia ice cap with the Eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the Eurasian ice sheet.

  • 34.
    Colleoni, Florence
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Joseph Fourier University, France.
    Krinner, G.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The role of an Arctic ice shelf in the climate of the last glacial maximum of MIS 6 (140 ka)2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3590-3597Article in journal (Refereed)
    Abstract [en]

    During the last decade, Arctic icebreaker and nuclear submarine expeditions have revealed large-scale Pleistocene glacial erosion on the Lomonosov Ridge, Chukchi Borderland and along the Northern Alaskan margin indicating that the glacial Arctic Ocean hosted large Antarctic-style ice shelves. Dating of sediment cores indicates that the most extensive and deepest ice grounding occurred during Marine Isotope Stage (MIS) 6. The precise extents of Pleistocene ice shelves in the Arctic Ocean are unknown but seem comparable to present existing Antarctic ice shelves. How would an Antarctic-style ice shelf in the MIS 6 Arctic Ocean influence the Northern Hemisphere climate? Could it have impacted on the surface mass balance (SMB) of the MIS 6 Eurasian ice sheet and contributed to its large southward extent? We use an Atmospheric General Circulation Model (AGCM) to investigate the climatic impacts of both a limited MIS 6 ice shelf covering portions of the Canada Basin and a fully ice shelf covered Arctic Ocean. The AGCM results show that both ice shelves cause a temperature cooling of about 3 °C over the Arctic Ocean mainly due to the combined effect of ice elevation and isolation from the underlying ocean heat fluxes stopping the snow cover from melting during summer. The calculated SMB of the ice shelves are positive. The ice front horizontal velocity of the Canada Basin ice shelf is estimated to ≈ 1 km yr−1 which is comparable to the recent measurements of the Ross ice shelf, Antarctica. The existence of a large continuous ice shelf covering the entire Arctic Ocean would imply a mean annual velocity of icebergs of ≈12 km yr−1 through the Fram Strait. Our modeling results show that both ice shelf configurations could be viable under the MIS 6 climatic conditions. However, the cooling caused by these ice shelves only affects the Arctic margins of the continental ice sheets and is not strong enough to significantly influence the surface mass balance of the entire MIS 6 Eurasian ice sheet.

  • 35. Croke, Jacky
    et al.
    Jansen, John D.
    School of Physical, Environmental and Mathematical Sciences, University of New South Wales @ADFA, Canberra ACT 2600, Australia.
    Amos, Kathryn
    Pietsch, Timothy J.
    A 100 ka record of fluvial activity in the Fitzroy River Basin, tropical northeastern Australia2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 13-14, p. 1681-1695Article in journal (Refereed)
    Abstract [en]

    This study reports the nature and timing of Quaternary fluvial activity in the Fitzroy River basin, which drains a diverse 143,000 km(2) area in northeastern Queensland, before discharging into the Great Barrier Reef Marine Park. The catchment consists of an extensive array of channel and floodplain types that we show have undergone large-scale fluvial adjustment in-channel planform, geometry and sinuosity. Optically stimulated luminescence (OSL) dating of quartz sediments from fifteen (3-18 m) floodplain cores throughout the basin indicates several discrete phases of active bedload activity: at similar to 105-85 ka in Marine Isotope Stage (MIS) 5, at similar to 50-40 ka (MIS 3), and at similar to 30-10 ka (MIS 3/2). The overall timing of late Quaternary fluvial activity correlates well with previous accounts from across Australia with rivers being primarily active during interstadials. Fluvial activity, however, does not appear to have been synchronous throughout the basin's major sub-catchments. Fluvial activity throughout MIS 2 (i.e. across the Last Glacial Maximum) in the meandering channels of the Fitzroy correlates well with regional data in tropical northeastern Queensland, and casts new light on the river response to reduced rainfall and vegetation cover suggested by regional palaeoclimate indicators. Moreover, the absence of a strong Holocene signal is at odds with previous accounts from elsewhere throughout Australia. The latitudinal position of the Fitzroy across the Tropic of Capricorn places this catchment at a key location for elucidating the main hydrological drivers of Quaternary fluvial activity in northeastern Australia, and especially for determining tropical moisture sources feeding into the headwaters of Cooper Creek, a major river system of the continental interior.

  • 36. Cronin, T. M.
    et al.
    Gemery, L.
    Briggs, W. M.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Polyak, L.
    Brouwers, E. M.
    Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3415-3429Article in journal (Refereed)
    Abstract [en]

    Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25–45 ka), minimal sea ice during the last deglacial (16–11 ka) and early Holocene thermal maximum (11–5 ka) and increasing sea ice during the mid-to-late Holocene (5–0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon.

  • 37.
    Cronin, T. M.
    et al.
    US Geol Survey, MS 926A, Reston, VA 20192 USA..
    Gemery, L.
    US Geol Survey, MS 926A, Reston, VA 20192 USA..
    Briggs, W. M., Jr.
    Univ Colorado, Inst Arctic & Alpine Res INSTAAR, Boulder, CO 80309 USA..
    Jakobsson, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Polyak, L.
    Ohio State Univ, Byrd Polar Res Ctr, Columbus, OH 43210 USA..
    Brouwers, E. M.
    US Geol Survey, MS 406, Denver Fed Ctr, Denver, CO 80225 USA..
    Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3415-3429Article in journal (Refereed)
    Abstract [en]

    Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon. Published by Elsevier Ltd.

  • 38.
    Czymzik, Markus
    et al.
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Adolphi, Florian
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Muscheler, Raimund
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Mekhaldi, Florian
    Lund Univ, Dept Geol, Quaternary Sci, S-22362 Lund, Sweden..
    Martin-Puertas, Celia
    GEZ German Res Ctr Geosci, Sect Climate Dynam & Landscape Evolut 5 2, D-14473 Potsdam, Germany..
    Aldahan, Ala
    United Arab Emirates Univ, Dept Geol, Al Ain 15551, U Arab Emirates..
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandem Laboratory.
    Brauer, Achim
    GEZ German Res Ctr Geosci, Sect Climate Dynam & Landscape Evolut 5 2, D-14473 Potsdam, Germany..
    A varved lake sediment record of the Be-10 solar activity proxy for the Lateglacial-Holocene transition2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 153, p. 31-39Article in journal (Refereed)
    Abstract [en]

    Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on Be-10 records from ice cores and C-14 time-series from tree rings, all including archive-specific limitations. We present the first Be-10 record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, Be-10 deposition using a new approach based on regression analyses between our Be-10 record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our Be-10 record, but cannot be the main explanation for major Be-10 excursions. Corrected for these environmental influences, our Be-10 record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in Be-10 from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.

  • 39. Davies, S. M.
    et al.
    Abbott, P. M.
    Meara, R. H.
    Pearce, N. J. G.
    Austin, W. E. N.
    Chapman, M. R.
    Svensson, A.
    Bigler, M.
    Rasmussen, T. L.
    Rasmussen, S. O.
    Farmer, E. J.
    A North Atlantic tephrostratigraphical framework for 130-60 ka b2k: new tephra discoveries, marine-based correlations, and future challenges2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 106Article in journal (Refereed)
    Abstract [en]

    Building chronological frameworks for proxy sequences spanning 130-60 ka b2k is plagued by difficulties and uncertainties. Recent developments in the North Atlantic region, however, affirm the potential offered by tephrochronology and specifically the search for cryptotephra. Here we review the potential offered by tephrostratigraphy for sequences spanning 130-60 ka b2k. We combine newly identified cryptotephra deposits from the NGRIP ice-core and a marine core from the Iceland Basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time-interval. Forty-three tephra or cryptotephra deposits are incorporated into this framework; twenty three tephra deposits are found in the Greenland ice-cores, including nine new NGRIP tephras, and twenty separate deposits are preserved in various North Atlantic marine sequences. Major, minor and trace element results are presented for the new NGRIP horizons together with age estimates based on their position within the ice-core record. Basaltic tephras of Icelandic origin dominate the framework with only eight tephras of rhyolitic composition found. New results from marine core MD99-2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits. Tephra-based correlations in the marine environment provide independent tie-points for this time-interval and highlight the potential of widening the application of tephrochronology. Further investigations, however, are required, that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes, in order to trace coeval events between the two depositional realms. (C) 2014 The Authors. Published by Elsevier Ltd.

  • 40. Davies, Siwan M.
    et al.
    Abbott, Peter M.
    Pearce, Nicholas J. G.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Blockley, Simon P. E.
    Integrating the INTIMATE records using tephrochronology: rising to the challenge2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36, p. 11-27Article in journal (Refereed)
    Abstract [en]

    Little has challenged our understanding of climate change more so than the abruptness with which large-scale shifts in temperature occurred during the Late Quaternary. The causal mechanisms driving these rapid changes are poorly understood, largely due to the inherent difficulties of integrating palaeoclimate records which represents the key focus of the INTIMATEI project. Tephrochronology has become central to the synchronisation goals of INTIMATE, the overall aim of which is to test the degree of climatic synchroneity in relation to these rapid climatic events. Here we present a European framework of 12 volcanic events that hold considerable promise for achieving the INTIMATE goals and effecting precise correlation of widespread palaeoarchives. These tephras are widespread and fall stratigraphically in close association to rapid climatic changes. We believe that these represent the most valuable tephras for the European INTIMATE project, but also highlight those that require urgent investigation to refine their geochemical signatures, eruptive context and chronological and stratigraphical uncertainties. For instance, new data are presented for the Saksunarvatn Ash that question the sole reliance on major-element analysis for tephra characterisation and highlights some of the challenges that remain for tephra studies. Accordingly, we outline a number of key recommendations relating to geochemical characterisation, data comparison, assessing the depositional integrity of tephra horizons as well as methods for improving age estimates - all of which will optimise the application of tephrochronology to meet the INTIMATE goals.

  • 41. de Boer, Erik J.
    et al.
    Hooghiemstra, Henry
    Florens, F. B. Vincent
    Baider, Claudia
    Engels, Stefan
    Dakos, Vasilis
    Blaauw, Maarten
    Bennett, Keith D.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Rapid succession of plant associations on the small ocean island of Mauritius at the onset of the Holocene2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, p. 114-125Article in journal (Refereed)
    Abstract [en]

    The island of Mauritius offers the opportunity to study the poorly understood vegetation response to climate change on a small tropical oceanic island. A high-resolution pollen record from a 10 m long peat core from Kanaka Crater (560 m elevation, Mauritius, Indian Ocean) shows that vegetation shifted from a stable open wet forest Last Glacial state to a stable closed-stratified-tall-forest Holocene state. An ecological threshold was crossed at similar to 11.5 cal ka BP, propelling the forest ecosystem into an unstable period lasting similar to 4000 years. The shift between the two steady states involves a cascade of four abrupt (<150 years) forest transitions in which different tree species dominated the vegetation for a quasi-stable period of respectively similar to 1900, similar to 1100 and similar to 900 years. We interpret the first forest transition as climate-driven, reflecting the response of a small low topography oceanic island where significant spatial biome migration is impossible. The three subsequent forest transitions are not evidently linked to climate events, and are suggested to be driven by internal forest dynamics. The cascade of four consecutive events of species turnover occurred at a remarkably fast rate compared to changes during the preceding and following periods, and might therefore be considered as a composite tipping point in the ecosystem. We hypothesize that wet gallery forest, spatially and temporally stabilized by the drainage system, served as a long lasting reservoir of biodiversity and facilitated a rapid exchange of species with the montane forests to allow for a rapid cascade of plant associations.

  • 42. Dehnert, Andreas
    et al.
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Evolution of an overdeepened trough in the northern Alpine Foreland at Niederweningen, Switzerland.2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArticle in journal (Refereed)
    Abstract [en]

    Quaternary deposits in the overdeepened Wehntal, Switzerland, were investigated using both seismicprofiling and the analysis of 93.6 m long drill core using sedimentology, geochemistry, palynology,magnetic properties, and luminescence dating. The sediments reveal evidence for two glacial advancesthat reached the area during Marine Isotope Stage (MIS) 6. The first advance (w185 ka) may have carvedout the basin or at least removed the entire previous Quaternary sediment filling. This first advance likelyreached far beyond the limit of the maximum of the Last Glaciation. The second advance (w140 ka) wasof smaller extent, possibly of cold-based nature, and likely reached only slightly beyond the limits of theLast Glaciation.

  • 43. Delmonte, B.
    et al.
    Andersson, P. S.
    Schoeberg, H.
    Hansson, M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Petit, J. R.
    Delmas, R.
    Gaiero, D. M.
    Maggi, V.
    Frezzotti, M.
    Geographic provenance of aeolian dust in East Antarctica during Pleistocene glaciations: preliminary results from Talos Dome and comparison with East Antarctic and new Andean ice core data2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 02-jan, p. 256-264Article in journal (Refereed)
    Abstract [en]

    The strontium and neodymium isotopic signature of aeolian mineral particles archived in polar ice cores provides constraints on the geographic provenance of dust and paleo-atmospheric circulation patterns. Data from different ice cores drilled in the centre of the East Antarctic plateau such as EPICA-Dome C (EDC, 75 degrees 06'S: 123 degrees 21'E) and Vostok (78 degrees 28'S, 106 degrees 48'E) suggested a uniform geographic provenance for dust during Pleistocene glacial ages, likely from southern South America (SSA). In this work the existing dust isotopic data from EDC have been integrated with new data from Marine Isotopic Stage (MIS) 14 (about 536 ka before 1950AD) and in parallel some first results are shown for the new TALDICE ice core which was drilled on the edge of the East Antarctic Plateau (Talos Dome, 72 degrees 48'S, 159 degrees 06'E) on the opposite side with respect to SSA. Interestingly, the isotopic composition of TALDICE glacial dust is remarkably similar to that obtained from glacial dust from sites located in the East Antarctic interior. Overall, the glacial dust isotopic field obtained from six East Antarctic ice cores matches well South American data obtained from target areas. In this respect, it was recently suggested that dust exported long-range from South America originates from Patagonia and from the Puna-Altiplano plateau. To test this hypothesis, we analysed the isotopic composition of dust from an ice core drilled on the Illimani glacier (Bolivia, 16 degrees 37'S, 67 degrees 46'W; 6350 m a.s.l.) in order to obtain information on the isotopic composition of regional mineral aerosol uplifted from the Altiplano area and likely transported over a long distance. Altogether, ice core and source data strongly suggest that the westerly circulation pattern allowed efficient transfer of dust from South America to the East Antarctic plateau under cold Quaternary climates. Isotopic data support the hypothesis of a possible mixing of dust from Patagonia and from the Puna-Altiplano plateau. Interestingly, high glacial dust inputs to Antarctica are characterized by less radiogenic Nd values, an issue suggesting that enhanced dust production in Patagonia was associated with the activation of a secondary source. Still, Patagonia was the most important supplier for dust to central East Antarctica during Quaternary glaciations.

  • 44.
    Delmonte, B
    et al.
    University Milano-Bicocca, Milano, Italy.
    Paleari, C. I.
    University Milano-Bicocca, Milano, Italy.
    Andò, S
    University Milano-Bicocca, Milano, Italy.
    Garzantini, E
    University Milano-Bicocca, Milano, Italy.
    Andersson, Per Sune
    Swedish Museum of Natural History, Department of Geology.
    Petit, J.R.
    University of Grenobles, Grenoble, France.
    Crosta, X
    Unversity of Bordeaux, St Hilaire, France.
    Narcisi, B
    ENEA, Rome, Italy.
    Baroni, C
    University of Pisa, Pisa, Italy.
    Salvatore, M.C.
    University of Pisa, Pisa, Italy.
    Baccolo, G.
    University Milano-Bicocca, Milano, Italy.
    Maggi, Valter
    University Milano-Bicocca, Milano, Italy.
    Causes of dust size variability in central East Antarctica (Dome B):Atmospheric transport from expanded South American sources during Marine Isotope Stage 22017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 168, p. 55-68Article in journal (Refereed)
    Abstract [en]

    We here investigate the spatial and temporal variability of eolian dust particle sorting recorded in the Dome B (77 05 S, 94 55 E) ice core, central East Antarctica, during Marine Isotope Stage (MIS) 2. We address the question whether such changes reflect variable transport pathways from a unique source area or rather a variable apportionment from diverse Southern Hemisphere sources transported at different elevation in the troposphere. The Sr-Nd radiogenic isotope composition of glacial dust samples as well as single-particle Raman mineralogy support the hypothesis of a single dust provenance both for coarse and fine mode dust events at Dome B. The southern South American provenance of glacial dust in Antarctica deduced from these results indicate a dust composition coherent with a mixture of volcanic material and minerals derived from metamorphic and plutonic rocks. Additionally, Dome B glacial samples contain aragonite particles along with diatom valves of marine benthic/epiphytic species and freshwater species living today in the northern Antarctic Peninsula and southern South America. These data suggest contribution from the exposed Patagonian continental shelf and glacial outwash plains of southern Patagonia at the time when sea level reached its minimum. Our results confirm that dust sorting is controlled by the relative intensity of the two main patterns of tropospheric dust transport onto the inner Plateau, i.e. fast low-level advection and long-range high-altitude transport including air subsidence over Antarctica.

  • 45.
    Dowdeswell, J. A.
    et al.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Jakobsson, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Hogan, K. A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    O'Regan, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Backman, J.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Evans, J.
    Univ Loughborough, Dept Geog, Loughborough LE11 3TU, Leics, England..
    Hell, B.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Löwemark, L.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Marcussen, C.
    Geol Survey Denmark & Greenland, DK-1350 Copenhagen, Denmark..
    Noormets, R.
    Univ Ctr Svalbard, N-9171 Longyearbyen, Norway..
    Cofaigh, C. O.
    Univ Durham, Dept Geog, Durham DH1 3LE, England..
    Sellen, E.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Sölvsten, M.
    Royal Danish Adm Nav & Hydrog, DK-1023 Copenhagen K, Denmark..
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: implications for ice-sheet grounding and deep-keeled icebergs2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3518-3531Article in journal (Refereed)
    Abstract [en]

    High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79 degrees 20' and 81 degrees 30'N and 5 degrees and 22 degrees E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal. (C) 2010 Elsevier Ltd. All rights reserved.

  • 46. Dowdeswell, J. A.
    et al.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogan, K. A.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evans, J.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Noormets, R.
    O'Cofaigh, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sölvsten, M.
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3518-3531Article in journal (Refereed)
    Abstract [en]

    High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.

  • 47. Dutton, Andrea
    et al.
    Webster, Jody M.
    Zwartz, Dan
    Lambeck, Kurt
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107, p. 182-196Article in journal (Refereed)
    Abstract [en]

    In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between similar to 129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 +/- 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require similar to 5-8 m of polar ice sheet contribution, relative to today's volume, of which only similar to 2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 +/- 1.7 m eustatic sea level position by 128.6 +/- 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

  • 48. Edwards, Thomas W. D.
    et al.
    Hammarlund, Dan
    Newton, Brandi W.
    Sjolte, Jesper
    Linderson, Hans
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Amour, Natalie A. St.
    Bailey, Joscelyn N. -L.
    Nilsson, Anders L.
    Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 165, p. 102-110Article in journal (Refereed)
    Abstract [en]

    Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.

  • 49. Esper, Jan
    et al.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Luterbacher, Jürg
    Carrer, Marco
    Cook, Ed
    Davi, Nicole K.
    Hartl-Meier, Claudia
    Kirdyanov, Alexander
    Konter, Oliver
    Myglan, Vladimir
    Timonen, Mauri
    Treydte, Kerstin
    Trouet, Valerie
    Villalba, Ricardo
    Yang, Bao
    Büntgen, Ulf
    Ranking of tree-ring based temperature reconstructions of the past millennium2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 145, p. 134-151Article in journal (Refereed)
    Abstract [en]

    Tree-ring chronologies are widely used to reconstruct high-to low-frequency variations in growing season temperatures over centuries to millennia. The relevance of these timeseries in large-scale climate reconstructions is often determined by the strength of their correlation against instrumental temperature data. However, this single criterion ignores several important quantitative and qualitative characteristics of tree-ring chronologies. Those characteristics are (i) data homogeneity, (ii) sample replication, (iii) growth coherence, (iv) chronology development, and (v) climate signal including the correlation with instrumental data. Based on these 5 characteristics, a reconstruction-scoring scheme is proposed and applied to 39 published, millennial-length temperature reconstructions from Asia, Europe, North America, and the Southern Hemisphere. Results reveal no reconstruction scores highest in every category and each has their own strengths and weaknesses. Reconstructions that perform better overall include N-Scan and Finland from Europe, E-Canada from North America, Yamal and Dzhelo from Asia. Reconstructions performing less well include W-Himalaya and Karakorum from Asia, Tatra and S-Finland from Europe, and Great Basin from North America. By providing a comprehensive set of criteria to evaluate tree-ring chronologies we hope to improve the development of large-scale temperature reconstructions spanning the past millennium. All reconstructions and their corresponding scores are provided at www.blogs.uni-mainz.de/fb09climatology.

  • 50. Esper, Jan
    et al.
    Krusic, Paul J.
    Ljungqvist, Fredrik C.
    Luterbacher, Jürg
    Carrer, Marco
    Cook, Ed
    Davi, Nicole K.
    Hartl-Meier, Claudia
    Kirdyanov, Alexander
    Konter, Oliver
    Myglan, Vladimir
    Timonen, Mauri
    Treydte, Kerstin
    Trouet, Valerie
    Villalba, Ricardo
    Yang, Bao
    Büntgen, Ulf
    Ranking of tree-ring based temperature reconstructions of the past millennium2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 145, p. 134-151Article in journal (Refereed)
    Abstract [en]

    Abstract Tree-ring chronologies are widely used to reconstruct high-to low-frequency variations in growing season temperatures over centuries to millennia. The relevance of these timeseries in large-scale climate reconstructions is often determined by the strength of their correlation against instrumental temperature data. However, this single criterion ignores several important quantitative and qualitative characteristics of tree-ring chronologies. Those characteristics are (i) data homogeneity, (ii) sample replication, (iii) growth coherence, (iv) chronology development, and (v) climate signal including the correlation with instrumental data. Based on these 5 characteristics, a reconstruction-scoring scheme is proposed and applied to 39 published, millennial-length temperature reconstructions from Asia, Europe, North America, and the Southern Hemisphere. Results reveal no reconstruction scores highest in every category and each has their own strengths and weaknesses. Reconstructions that perform better overall include N-Scan and Finland from Europe, E-Canada from North America, Yamal and Dzhelo from Asia. Reconstructions performing less well include W-Himalaya and Karakorum from Asia, Tatra and S-Finland from Europe, and Great Basin from North America. By providing a comprehensive set of criteria to evaluate tree-ring chronologies we hope to improve the development of large-scale temperature reconstructions spanning the past millennium. All reconstructions and their corresponding scores are provided at www.blogs.uni-mainz.de/fb09climatology.

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