Change search
Refine search result
1 - 46 of 46
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 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. 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.

  • 3. 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.

  • 4. 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.

  • 5. 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.

  • 6.
    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.

  • 7.
    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.

  • 8. 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.

  • 9.
    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.

  • 10.
    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.

  • 11.
    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.

  • 12. 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.

  • 13.
    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.

  • 14. 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.

  • 15. Garcia, Marga
    et al.
    Dowdeswell, Julian A.
    Ercilla, Gemma
    Jakobsson, Martin
    Recent glacially influenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 49, p. 64-81Article in journal (Refereed)
    Abstract [en]

    This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of landform development points to a predominantly glacial origin of the sediment supplied to the continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led to the development of scarps and channels on the slope and debris flows on the continental rise. The more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin. (C) 2012 Elsevier Ltd. All rights reserved.

  • 16.
    Hanslik, Daniela
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Backman, Jan
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Björck, Svante
    Sellén, Emma
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    O'Regan, Matt
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Fornaciari, Eliana
    Univ Padua, Dept Geosci, I-35100 Padua, Italy..
    Skog, Göran
    Lund Univ, Dept Earth & Ecosyst Sci, Div Geol, Radiocarbon Dating Lab, Lund, Sweden..
    Quaternary Arctic Ocean sea ice variations and radiocarbon reservoir age corrections2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3430-3441Article in journal (Refereed)
    Abstract [en]

    A short sediment core from a local depression forming an intra basin on the Lomonosov Ridge, was retrieved during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). It contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. The Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Calibration of the radiocarbon ages, using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core, results in marine reservoir ages of 1400 years or more, at least during the last deglaciation. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Lateglacial to the Holocene, suggesting circulation and ventilation changes. (C) 2010 Elsevier Ltd. All rights reserved.

  • 17. Hogan, K. A.
    et al.
    Dowdeswell, J. A.
    Noormets, R.
    Evans, J.
    Cofaigh, C. O.
    Jakobsson, M.
    Submarine landforms and ice-sheet flow in the Kvitoya Trough, northwestern Barents Sea2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, SI, p. 3545-3562Article in journal (Refereed)
    Abstract [en]

    High-resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in Kvitoya Trough, northwestern Barents Sea. A new swath-bathymetric dataset identifies three types of submarine landform in the study area (streamlined landforms, meltwater channels and cavities, iceberg scours). Subglacially produced streamlined landforms provide a record of ice flow through Kvitoya Trough during the last glaciation. Flow directions are inferred from the orientations of streamlined landforms (drumlins, crag-and-tail features). Ice flowed northward for at least 135 km from an ice divide at the southern end of Kvitoya Trough. A large channel-cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice-sheet base. Modest landform elongation ratios and a lack of mega-scale glacial lineations suggest that, although ice in Kvitoya Trough was melting at the bed and flowed faster than the likely thin and cold-based ice on adjacent banks, a major ice stream probably did not occupy the trough. Retreat was relatively rapid after 14-13.5 C-14 kyr B.P. and probably progressed via ice sheet-bed decoupling in response to rising sea level. There is little evidence for still stands during ice retreat or of ice-proximal deglacial sediments. Relict iceberg scours in present-day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat. (C) 2010 Elsevier Ltd. All rights reserved.

  • 18. Hubberten, Hans W
    et al.
    Julian A. Dowdeswell, Mona Henriksen
    Martin Jakobsson, Svetlana Kuzmina
    Jan Mangerud, Per Möller
    Christine Siegert, Martin J. Siegert
    The periglacial climate andenvironment in northern Eurasia during the Last Glaciation2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, p. 1333-1357Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the results of studies of the Late Weichselian periglacial environments carried out in key areas of northern Eurasia by several QUEEN teams (European Science Foundation (ESF) programme: ‘‘Quaternary Environment of the Eurasian North’’). The palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the EU funded project ‘‘Eurasian Ice Sheets’’. These data prove beyond any doubt, that with the exception of the northwestern fringe of the Taymyr Peninsula, the rest of the Eurasian mainlandand Severnaya Zemlya were not affectedby the Barents–Kara Sea Ice Sheet during the Last Glacial Maximum (LGM). Inversedmod elling basedon these results shows that a progressive cooling which startedaround30 ka BP, causedice growth in Scandinavia and the northwestern areas of the Barents–Kara Sea shelf, due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets. In the rest of the Eurasian Arctic extremely low precipitation rates (less than 50mmyr 1), did not allow ice sheet growth in spite of the very cold temperatures. Palaeoclimatic and palaeoenvironmental conditions for the time prior to, during, and after the LGM have been reconstructed for the non-glaciated areas around the LGM ice sheet with the use of faunal and vegetation records, permafrost, eolian sediments, alluvial deposits and other evidences. The changing environment, from interstadial conditions around 30 ka BP to a much colder and drier environment at the culmination of the LGM at 20–15 ka BP, andthe beginning of warming around15 ka BP have been elaboratedfrom the fieldd ata, which fits well with the modelling results.

  • 19. Jakobsson, M.
    et al.
    Nilsson, J.
    O'Regan, M.
    Backman, J.
    Löwemark, L.
    Dowdeswell, J. A.
    Mayer, L.
    Polyak, L.
    Colleoni, F.
    Anderson, L. G.
    Björk, G.
    Darby, D.
    Eriksson, B.
    Hanslik, D.
    Hell, Benjamin
    Marcussen, C.
    Sellén, Emma
    Wallin, T.
    An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3505-3517Article in journal (Refereed)
    Abstract [en]

    The hypothesis of floating ice shelves covering the Arctic Ocean during glacial periods was developed in the 1970s. In its most extreme form, this theory involved a 1000 m thick continuous ice shelf covering the Arctic Ocean during Quaternary glacial maxima including the Last Glacial Maximum (LGM). While recent observations clearly demonstrate deep ice grounding events in the central Arctic Ocean, the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions. Here we present new data from previously inaccessible, unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials. These data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the Chukchi Borderland, southern Lomonosov Ridge north of Greenland, Morris Jesup Rise, and Yermak Plateau. Sediment cores from the mapped areas provide age constraints on the glaciogenic features. Combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex, including an ice shelf, existed in the Amerasian Arctic Ocean during Marine Isotope Stage (MIS) 6. From a conceptual oceanographic model we speculate that the cold halocline of the Polar Surface Water may have extended to deeper water depths during MIS 6 inhibiting the warm Atlantic water from reaching the Amerasian Arctic Ocean and, thus, creating favorable conditions for ice shelf development. The hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central Arctic Ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor.

  • 20. Jakobsson, Martin
    et al.
    Anderson, John B.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Kirshner, Alexandra E.
    Kirchner, Nina
    O’Regan, Matthew
    Mohammad, Rezwan
    Eriksson, Bjorn
    Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 38, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream’s dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73 degrees S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only similar to 80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric “bottle neck”. (C) 2011 Elsevier Ltd. All rights reserved.

  • 21. Jakobsson, Martin
    et al.
    Andreassen, Karin
    Bjarnadottir, Lilja Run
    Dove, Dayton
    Dowdeswell, Julian A.
    England, John H.
    Funder, Svend
    Hogan, Kelly
    Ingolfsson, Olafur
    Jennings, Anne
    Larsen, Nikolaj Krog
    Kirchner, Nina
    Landvik, Jon Y.
    Mayer, Larry
    Mikkelsen, Naja
    Moller, Per
    Niessen, Frank
    Nilsson, Johan
    O’Regan, Matt
    Polyak, Leonid
    Norgaard-Pedersen, Niels
    Stein, Ruediger
    Arctic Ocean glacial history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, no SI, p. 40-67Article in journal (Refereed)
    Abstract [en]

    While there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the Arctic Ocean, a holistic view on the Northern Hemisphere’s late Quaternary ice-sheet extent and their impact on ocean and sea-ice dynamics remains to be established. Here we aim to provide a step in this direction by presenting an overview of Arctic Ocean glacial history, based on the present state-of-the-art knowledge gained from field work and chronological studies, and with a specific focus on ice-sheet extent and environmental conditions during the Last Glacial Maximum (LGM). The maximum Quaternary extension of ice sheets is discussed and compared to LGM. We bring together recent results from the circum-Arctic continental margins and the deep central basin; extent of ice sheets and ice streams bordering the Arctic Ocean as well as evidence for ice shelves extending into the central deep basin. Discrepancies between new results and published LGM ice-sheet reconstructions in the high Arctic are highlighted and outstanding questions are identified. Finally, we address the ability to simulate the Arctic Ocean ice sheet complexes and their dynamics, including ice streams and ice shelves, using presently available ice-sheet models. Our review shows that while we are able to firmly reject some of the earlier hypotheses formulated to describe Arctic Ocean glacial conditions, we still lack information from key areas to compile the holistic Arctic Ocean glacial history. (C) 2013 The Authors. Published by Elsevier Ltd.

  • 22. Jakobsson, Martin
    et al.
    Ingolfsson, Olafur
    Long, Antony J.
    Spielhagen, Robert F.
    The dynamic Arctic Introduction2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, no SI, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of Arctic cryosphere and climate change over a range of time scales. As a consequence, rather than seeing the Arctic as a near static environment in which large scale changes occur slowly, we now view the Arctic as a system that is typified by frequent, large and abrupt changes. The traditional focus on end members in the system - glacial versus interglacial periods - has been replaced by a new interest in understanding the patterns and causes of such dynamic change. Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets. Recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different Arctic systems, on their interactions and the driving mechanisms of change. Future Arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on. (C) 2014 The Authors. Published by Elsevier Ltd.

  • 23. Jakobsson, Martin
    et al.
    Ingólfsson, Ólafur
    Long, Antony J.
    Spielhagen, Robert F.
    The dynamic Arctic2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Abstract Research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of Arctic cryosphere and climate change over a range of time scales. As a consequence, rather than seeing the Arctic as a near static environment in which large scale changes occur slowly, we now view the Arctic as a system that is typified by frequent, large and abrupt changes. The traditional focus on end members in the system – glacial versus interglacial periods – has been replaced by a new interest in understanding the patterns and causes of such dynamic change. Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets. Recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different Arctic systems, on their interactions and the driving mechanisms of change. Future Arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on.

  • 24.
    Jakobsson, Martin
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Long, Antony
    Univ Durham, Dept Geog, Durham DH1 3LE, England..
    Ingolfsson, Olafur
    Univ Iceland, Fac Earth Sci, IS-101 Reykjavik, Iceland..
    Kjaer, Kurt H.
    Univ Copenhagen, Nat Hist Museum, Ctr GeoGenet, DK-1350 Copenhagen, Denmark..
    Spielhagen, Robert F.
    IFM GEOMAR, Leihniz Inst Marine Sci, D-24148 Kiel, Germany.;Acad Sci Humanities & Literature, Mainz, Germany..
    New insights on Arctic Quaternary climate variability from palaeo-records and numerical modelling2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3349-3358Article in journal (Refereed)
    Abstract [en]

    Terrestrial and marine geological archives in the Arctic contain information on environmental change through Quaternary interglacial-glacial cycles. The Arctic Palaeoclimate and its Extremes (APEX) scientific network aims to better understand the magnitude and frequency of past Arctic climate variability, with focus on the "extreme" versus the "normal" conditions of the climate system. One important motivation for studying the amplitude of past natural environmental changes in the Arctic is to better understand the role of this region in a global perspective and provide base-line conditions against which to explore potential future changes in Arctic climate under scenarios of global warming. In this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning Arctic palaeo-records and natural variability, including spatial and temporal variability of the Greenland Ice Sheet, Arctic Ocean sediment stratigraphy, past ice shelves and marginal marine ice sheets, and the Cenozoic history of Arctic Ocean sea ice in general and Holocene oscillations in sea ice concentrations in particular. The combined sea ice data suggest that the seasonal Arctic sea ice cover was strongly reduced during most of the early Holocene and there appear to have been periods of ice free summers in the central Arctic Ocean. This has important consequences for our understanding of the recent trend of declining sea ice, and calls for further research on causal links between Arctic climate and sea ice. (C) 2010 Elsevier Ltd. All rights reserved.

  • 25.
    Kirchner, Nina
    et al.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Hutter, Kolumban
    Swiss Fed Inst Technol, Lab Hydraul Hydrol & Glaciol, CH-8092 Zurich, Switzerland..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Gyllencreutz, Richard
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Capabilities and limitations of numerical ice sheet models: a discussion for Earth-scientists and modelers2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 25-26, p. 3691-3704Article in journal (Refereed)
    Abstract [en]

    The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The 'zero order' (Shallow Ice Approximation, SIA)-, 'higher order'-, and 'full Stokes' ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheet-ice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model. (C) 2011 Elsevier Ltd. All rights reserved.

  • 26.
    Kirshner, Alexandra E.
    et al.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    O'Regan, Matthew
    Cardiff Univ, Sch Earth & Ocean Sci, Cardiff, S Glam, Wales..
    Majewski, Wojciech
    Polish Acad Sci, Inst Paleobiol, PL-00818 Warsaw, Poland..
    Nitsche, Frank O.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA..
    Post-LGM deglaciation in Pine Island Bay, West Antarctica2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 38, p. 11-26Article in journal (Refereed)
    Abstract [en]

    To date, understanding of ice sheet retreat within Pine Island Bay (PIB) following the Last Glacial Maximum (LGM) was based on seven radiocarbon dates and only fragmentary seafloor geomorphic evidence. During the austral summer 2009-2010, restricted sea ice cover allowed for the collection of 27 sediment cores from the outer PIB trough region. Combining these cores with data from prior cruises, over 133 cores have been used to conduct a detailed sedimentological facies analysis. These results, augmented by 23 new radiocarbon dates, are used to reconstruct the post-LGM deglacial history of PIB. Our results record a clear retreat stratigraphy in PIB composed of, from top to base; terrigenous sandy silt (distal glacimarine), pebbly sandy mud (ice-proximal glacimarine), and till. Initial retreat from the outer-continental shelf began shortly after the LGM and before 16.4 k cal yr BP, as a likely response to rising sea level. Bedforms in outer PIB document episodic retreat in the form of back-stepping grounding zone wedges and are associated with proximal glacimarine sediments. A sub-ice shelf facies is observed in central PIB and spans similar to 12.3-10.6 k cal yr BR It is possible that widespread impingement of warm water onto the continental shelf caused an abrupt and widespread change from sub-ice shelf sedimentation to distal glacimarine sedimentation dominated by widespread dispersal of terrigenous silt between 7.8 and 7.0 k cal yr BP. The final phase of retreat ended before similar to 1.3 k cal yr BP, when the grounding line migrated to a location near the current ice margin. (C) 2012 Elsevier Ltd. All rights reserved.

  • 27. Larocque, I.
    et al.
    Hall, R. I.
    Holocene temperature estimates and chironomid community composition in the Abisko Valley, northern Sweden2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 23, p. 2453-2465Article in journal (Refereed)
    Abstract [en]

    Multi-proxy paleoenvironmental reconstructions are useful to determine the various factors affecting the biological communities of a lake, but to assess if changes in community composition of one indicator organism accurately reconstructs climatic changes through time, it may be more useful to compare temperature reconstructions using the same indicator in several lakes. Here, we compare reconstructions of mean July air temperature using chironomid-based transfer functions from Holocene records at three nearby lakes in the Abisko Valley of northern Sweden to assess if chironomids can be used as indicators of regional temperature changes. The three study lakes experience the same regional climatic conditions, but are located along gradients of elevation (348-999m a.s.l), temperature (8.1-12°C) and terrestrial vegetation (coniferous to alpine). Chironomid-temperature reconstructions from the three sites indicate a general pattern of temperature decrease (1.5-2.4°C) during the Holocene, consistent with decreases observed from analyses of other proxies in this area, and from other alpine regions in Europe and North America. Similarities between these reconstructions suggest that chironomids can adequately record general patterns of temperature changes through the Holocene, although effects of site-specific factors such as variations in lake water pH can cause deviations in inferred temperature among sites during some periods.

  • 28.
    Larocque, I.
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Halla, R.I.
    Holocene temperature estimates and chironomid community composition in the Abisko Valley, northern Sweden2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 23-24, p. 2453-2465Article in journal (Refereed)
    Abstract [en]

    Multi-proxy paleoenvironmental reconstructions are useful to determine the various factors affecting the biological communities of a lake, but to assess if changes in community composition of one indicator organism accurately reconstructs climatic changes through time, it may be more useful to compare temperature reconstructions using the same indicator in several lakes. Here, we compare reconstructions of mean July air temperature using chironomid-based transfer functions from Holocene records at three nearby lakes in the Abisko Valley of northern Sweden to assess if chironomids can be used as indicators of regional temperature changes. The three study lakes experience the same regional climatic conditions, but are located along gradients of elevation (348–999 m a.s.l), temperature (8.1–12°C) and terrestrial vegetation (coniferous to alpine). Chironomid-temperature reconstructions from the three sites indicate a general pattern of temperature decrease (1.5–2.4°C) during the Holocene, consistent with decreases observed from analyses of other proxies in this area, and from other alpine regions in Europe and North America. Similarities between these reconstructions suggest that chironomids can adequately record general patterns of temperature changes through the Holocene, although effects of site-specific factors such as variations in lake water pH can cause deviations in inferred temperature among sites during some periods.

  • 29. Larsen, Nicolaj K.
    et al.
    Funder, Svend
    Linge, Henriette
    Möller, Per
    Schomacker, Anders
    Fabel, Derek
    Xu, Sheng
    Kjær, Kurt H.
    A Younger Dryas re-advance of local glaciers in north GreenlandIn: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArticle in journal (Refereed)
    Abstract [en]

    Abstract The Younger Dryas (YD) is a well-constrained cold event from 12,900 to 11,700 years ago but it remains unclear how the cooling and subsequent abrupt warming recorded in ice cores was translated into ice margin fluctuations in Greenland. Here we present 10Be surface exposure ages from three moraines in front of local glaciers on a 50 km stretch along the north coast of Greenland, facing the Arctic Ocean. Ten ages range from 11.6 ± 0.5 to 27.2 ± 0.9 ka with a mean age of 12.5 ± 0.7 ka after exclusion of two outliers. We consider this to be a minimum age for the abandonment of the moraines. The ages of the moraines are furthermore constrained using Optically Stimulated Luminescence (OSL) dating of epishelf sediments, which were deposited prior to the ice advance that formed the moraines, yielding a maximum age of 12.4 ± 0.6 ka, and bracketing the formation and subsequent abandonment of the moraines to within the interval 11.8–13.0 ka ago. This is the first time a synchronous YD glacier advance and subsequent retreat has been recorded for several independent glaciers in Greenland. In most other areas, there is no evidence for re-advance and glaciers were retreating during YD. We explain the different behaviour of the glaciers in northernmost Greenland as a function of their remoteness from the Atlantic Meridional Overturning Circulation (AMOC), which in other areas has been held responsible for modifying the YD drop in temperatures.

  • 30. Larsen, Nicolaj K.
    et al.
    Kjaer, Kurt H.
    Funder, Svend
    Moller, Per
    van der Meer, Jaap J. M.
    Schomacker, Anders
    Linge, Henriette
    Darby, Dennis A.
    Late Quaternary glaciation history of northernmost Greenland - Evidence of shelf-based ice2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, SI, p. 3399-3414Article in journal (Refereed)
    Abstract [en]

    We present the mapping of glacial landforms and sediments from northernmost Greenland bordering 100 km of the Arctic Ocean coast. One of the most important discoveries is that glacial landforms, sediments, including till fabric measurements, striae and stoss-lee boulders suggest eastward ice-flow along the coastal plain. Volcanic erratic boulders document ice-transport from 80 to 100 km west of the study area. We argue that these findings are best explained by local outlet glaciers from the Greenland Ice Sheet and local ice caps that merged to form a shelf-based ice in the Arctic Ocean and possibly confirming an extensive ice shelf in the Lincoln Sea between Greenland and Ellesmere Island. It is speculated that the shelf-based ice was largely affected by the presence of thick multiyear sea ice in the Arctic Ocean that prevented it from breaking up and forced the outlet glaciers to flow eastwards. During the initial retreat the coastal area was dammed by the shelf-based ice and kame and glaciolacustrine sediments were deposited up to 50 m above the marine limit before the final deglaciation and marine transgression. The timing of the shelf-based ice is constrained on land by dating glaciolacustrine sediments with OSL and marine molluscs with radiocarbon and by re-evaluating IRD events in cores from the Fram Strait. Results show that the shelf-based ice started to build-up as early as 30 cal ka BP and reached a maximum during the Last Glacial Maximum (LGM). The shelf-based ice began to retreat ca 16 ka to 10.3 cal ka BP before the final break-up, which took place ca 10.1 cal ka BP probably as a combined result of increased inflow of warm Atlantic water through the Fram Strait, a shallower halocline and higher summer temperatures, corresponding to orbital maximum solar insolation at this time. The existence of extensive shelf-based ice north of Greenland provides an important contribution to the understanding of the LGM glaciation history of the Arctic Ocean. (C) 2010 Elsevier Ltd. All rights reserved.

  • 31.
    Larter, Robert D.
    et al.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Graham, Alastair G. C.
    British Antarctic Survey, Cambridge CB3 0ET, England.;Univ Exeter, Coll Life & Environm Sci, Exeter EX4 4RJ, Devon, England..
    Gohl, Karsten
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Hillenbrand, Claus-Dieter
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Johnson, Joanne S.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Kuhn, Gerhard
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Nitsche, Frank O.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY USA..
    Smith, James A.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Witus, Alexandra E.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Bentley, Michael J.
    Univ Durham, Dept Geog, Durham DH1 3LE, England..
    Dowdeswell, Julian A.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Ehrmann, Werner
    Univ Leipzig, Inst Geol & Geophys, D-04103 Leipzig, Germany..
    Klages, Johann P.
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-27568 Bremerhaven, Germany..
    Lindow, Julia
    Univ Bremen, Dept Geosci, D-28359 Bremen, Germany..
    Cofaigh, Colm O.
    Univ Durham, Dept Geog, Durham DH1 3LE, England..
    Spiegel, Cornelia
    Univ Bremen, Dept Geosci, D-28359 Bremen, Germany..
    Reconstruction of changes in the Amundsen Sea and Bellingshausen Sea sector of the West Antarctic Ice Sheet since the Last Glacial Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 55-86Article in journal (Other academic)
    Abstract [en]

    Marine and terrestrial geological and marine geophysical data that constrain deglaciation since the Last Glacial Maximum (LGM) of the sector of the West Antarctic Ice Sheet (WAIS) draining into the Amundsen Sea and Bellingshausen Sea have been collated and used as the basis for a set of time-slice reconstructions. The drainage basins in these sectors constitute a little more than one-quarter of the area of the WAIS, but account for about one-third of its surface accumulation. Their mass balance is becoming increasingly negative, and therefore they account for an even larger fraction of current WAIS discharge. If all of the ice in these sectors of the WAIS were discharged to the ocean, global sea level would rise by ca 2 m. There is compelling evidence that grounding lines of palaeo-ice streams were at, or close to, the continental shelf edge along the Amundsen Sea and Bellingshausen Sea margins during the last glacial period. However, the few cosmogenic surface exposure ages and ice core data available from the interior of West Antarctica indicate that ice surface elevations there have changed little since the LGM. In the few areas from which cosmogenic surface exposure ages have been determined near the margin of the ice sheet, they generally suggest that there has been a gradual decrease in ice surface elevation since pre-Holocene times. Radiocarbon dates from glacimarine and the earliest seasonally open marine sediments in continental shelf cores that have been interpreted as providing approximate ages for post-LGM grounding-line retreat indicate different trajectories of palaeo-ice stream recession in the Amundsen Sea and Bellingshausen Sea embayments. The areas were probably subject to similar oceanic, atmospheric and eustatic forcing, in which case the differences are probably largely a consequence of how topographic and geological factors have affected ice flow, and of topographic influences on snow accumulation and warm water inflow across the continental shelf. Pauses in ice retreat are recorded where there are "bottle necks" in cross-shelf troughs in both embayments. The highest retreat rates presently constrained by radiocarbon dates from sediment cores are found where the grounding line retreated across deep basins on the inner shelf in the Amundsen Sea, which is consistent with the marine ice sheet instability hypothesis. Deglacial ages from the Amundsen Sea Embayment (ASE) and Eltanin Bay (southern Bellingshausen Sea) indicate that the ice sheet had already retreated close to its modern limits by early Holocene time, which suggests that the rapid ice thinning, flow acceleration, and grounding line retreat observed in this sector over recent decades are unusual in the context of the past 10,000 years. (C) 2014 The Authors. Published by Elsevier Ltd. All rights reserved.

  • 32. Loader, N. J.
    et al.
    Young, G. H. F.
    Grudd, H.
    McCarroll, D.
    Stable carbon isotopes from Torneträsk, northern Sweden provide a millennial length reconstruction of summer sunshine and its relationship to Arctic circulation2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 62, no Supplement C, p. 97-113Article in journal (Refereed)
    Abstract [en]

    Abstract This paper presents results from the first 1100 years of a long stable carbon isotope chronology currently in development from Scots Pine (Pinus sylvestris L.) trees growing in the Torneträsk region of northern Sweden. The isotope record currently comprises a total of 74 trees with a mean annual replication of >12, thereby enabling it to be compared directly with other tree-ring based palaeoclimate reconstructions from this region. In developing the reconstruction, several key topics in isotope dendroclimatology (chronology construction, replication, CO2 adjustment and age trends) were addressed. The resulting carbon isotope series is calibrated against instrumental data from the closest meteorological station at Abisko (AD1913-2008) to provide a record of June-August sunshine for northern Fennoscandia. This parameter is closely linked to the direct control of assimilation rate; Photosynthetically Active Radiation (PAR) and the indirect measures; mean July-August temperature and percent cloud cover. The coupled response of summer sunshine and temperature in this region permits a multi-parameter comparison with a local reconstruction of past temperature variability based upon tree growth proxies to explore the stability of this coupling through time. Several periods are identified where the temperature (X-ray density) and sunshine (stable carbon isotope ratio) records diverge. The most significant and sustained of these occur between c AD1200-1380 and c AD1550-1780, providing evidence for a cool, sunny, two-phase "Little Ice Age". Whilst summer sunshine reconstructed for the 20th century is significantly different from the mean of the last 1100 years (P < 0.01), conditions during the early mediaeval period are similar to those experienced in northern Fennoscandia during the 20th century (P > 0.01), so it is the 17th–18th, and to a lesser extent, the 13th centuries rather than the early mediaeval period that appear anomalous when viewed within the context of the last 1100 years. The observed departures between temperature and sunshine are interpreted as indicating a change in large-scale circulation associated with a southward migration of the Polar Front. Such a change, affecting the Northern Annular Mode (Arctic Oscillation) would result in more stable anticyclonic conditions (cool, bright, summers) over northern Fennoscandia, thus providing a testable mechanism for the development of a multi-phase, time-transgressive "Little Ice Age"€ across Europe.

  • 33. Löwemark, L.
    et al.
    Marz, C.
    O'Regan, M.
    Gyllencreutz, R.
    Arctic Ocean Mn-stratigraphy: genesis, synthesis and inter-basin correlation2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92Article in journal (Refereed)
    Abstract [en]

    Across the Arctic Ocean, late Quaternary deep marine sediments are characterized by the occurrence of brownish layers intercalated with yellowish to olive gray sediments. These layers show enhanced levels of bioturbation, peaks in Mn content, and typically contain elevated abundances of planktonic and benthic micro-and nannofossils. It was early surmised that these layers were deposited under interglacial conditions and that their cyclical downcore occurrence could be correlated to the global benthic oxygen isotope curve. However, the synchronicity of Mn layers with interglacial conditions and the underlying mechanisms responsible for their formation remain controversial. Here we compile and synthesize findings of the last decades with several recent studies that shed light on issues such as the sources of Mn to the Arctic Ocean, the processes and pathways for Mn to the deep sea, the chemical processes active in the sediment, and the spatial and temporal distribution of Mn-rich layers in Arctic deep marine sediments. Budget calculations show that about 90% of Mn input to the Arctic Ocean originates from Arctic rivers or coastal erosion, two sources effectively shut down during mid-to late Quaternary glacial intervals by continental ice sheets blocking or redirecting the rivers and vast subaerial exposure of the shelf areas. Thus, the strong late Quaternary interglacial-glacial cyclicity in Mn content is clearly an input-related signal, and only secondarily influenced by chemical processes in the water column and in the sediment. On the shelves, the Mn undergoes repeated geochemical recycling caused by the high organic carbon content in the sediments before it is ultimately exported to the deep basins where scavenging processes in the water column effectively bring the Mn to the sea floor in the form of Mn (oxyhydr)oxides. The close synchronicity with enhanced bioturbation and elevated micro and nannofossil abundances shows that the Mn peaks are preserved at a stratigraphic level closely corresponding to the interglacial intervals. However, under certain biogeochemical conditions, Mn (oxyhydr)oxides may diagenetically become both dissolved and re-precipitated deep in the sediments, as shown by pore water analyses and X-ray radiograph studies. Dissolution is particularly conspicuous in late Quaternary sediments from the Lomonosov Ridge, where in rapidly deposited coarse grained intervals (diamictons) with elevated total organic carbon (TOC) contents, Mn appears almost completely removed from within the glacial sediments, and also the surrounding interglacial sediments. Correspondingly, bundles of closely spaced, mm-thick, Mn-rich horizontal bands are observed in sediment otherwise devoid of indicators for interglacial conditions, suggesting that these bands were purely formed by diagenetic processes redistributing the Mn from deeper sediment layers. This type of diagenetic Mn redistribution within the sediment can be recognized in XRF-core scanner data combined with sedimentological information from X-ray radiographs, while pore water data are highly promising if clear diagenetic features in the sediment are missing. With this increasing ability to recognize intervals where a diagenetic overprint exists in the Mn record, the recently improved understanding of the Mn cycle in the Arctic Ocean provides a conceptual paleoenvironmental framework in which carefully applied Mn stratigraphy can provide a powerful correlation tool, when combined with other paleoceanographic proxies and sedimentological data. (C) 2013 Elsevier Ltd. All rights reserved.

  • 34. Löwemark, Ludvig
    et al.
    Chao, Weng-Si
    Gyllencreutz, Richard
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Hanebuth, Till J. J.
    Chiu, Pin-Yao
    Yang, Tien-Nan
    Su, Chih-Chieh
    Chuang, Chih-Kai
    Leon Dominguez, Dora Carolina
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, p. 164-177Article in journal (Refereed)
    Abstract [en]

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<< 5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10 -20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MISS appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a sedimentary regime shift previously identified in the Eurasian Basin and may be an indicator for the growth of larger ice sheets on the Eurasian landmass during the penultimate glacial period.

  • 35. Möller,
    Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to late Quaternary (vol 25, pg 21)2007In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, no 7-8, p. 1148-1191Article in journal (Refereed)
    Abstract [en]

    Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79 degrees N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS C-14, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of >2000m only 200km from the deep Arctic Ocean, consistent with published evidence of ice grounding at similar to 1000m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula. (c) 2007 Elsevier Ltd. All rights reserved.

  • 36. Möller, P.
    et al.
    Alexanderson, H.
    Funder, S.
    Hjort, C.
    The Taimyr Peninsula and the Severnaya Zemlya archipelago, Arctic Russia: a synthesis of glacial history and palaeo-environmental change during the Last Glacial cycle (MIS 5e-2)2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107Article in journal (Refereed)
    Abstract [en]

    We here suggest a glacial and climate history of the Taimyr Peninsula and Severnaya Zemlya archipelago in arctic Siberia for the last about 150 000 years (ka). Primarily it is based on results from seven field seasons between 1996 and 2012, to a large extent already published in papers referred to in the text and on data presented by Russian workers from the 1930s to our days and by German colleagues working there since the 1990s. Although glaciations even up here often started in the local mountains, their culminations in this region invariably seems to have centred on the shallow Kara Sea continental shelf - most likely due to expanding marine ice-shelves grounding there, as a combined effect of thickening ice and eustatically lowered sea-levels. The most extensive glaciation so far identified in this region (named the Taz glaciation) took place during Marine Isotope Stage 6 (MIS 6), i.e. being an equivalent to the late Saale/Illinoian glaciations. It reached c. 400 km southeast of the Kara Sea coast, across and well beyond the Byrranga Mountain range and ended c. 130 ka. It was followed by the MIS 5e (Karginsky/Eemian) interglacial, with an extensive marine transgression to 140 m above present sea level - facilitated by strong isostatic downloading during the preceding glaciation. During the latest (Zyryankan/Weichselian/Wisconsinan) glacial cycle followed a series of major glacial advances. The earliest and most extensive, culminating C. 110-100 ka (MIS 5d-5e), also reached south of the Byrranga mountains and its post-glacial marine limit there was c. 100 m a.s.l. The later glacial phases (around 70-60 ka and 20 ka) terminated at the North Taimyr Ice Marginal Zone (NTZ), along or some distance inland from the present northwest coast of Taimyr. They dammed glacial lakes, which caused the Taimyr River to flow southwards where to-day it flows northwards into the Kara Sea. The c. 20 ka glacial phase, contemporary with the maximum (LGM) glaciation in NW Europe, was this glacial cycle's least extensive one up here probably an effect of precipitation shadow caused by the major glaciations to the west. From the Kara Sea shelf this advance only reached c. 100 km inland, over some limited parts of NW Taimyr. The Severnaya Zemlya islands were only locally glaciated at this time. The lowlands south of the Byrranga Mountains have been a terrestrial "Mammoth steppe" environment during the last c. 50 ka and periglacial permafrosted sediments here have preserved excellent information on its megafauna and vegetation. The latter, according to new DNA-data, had considerably more (for grazing animals nourishing) flowering plants growing than earlier pollen-based (grass dominated) spectra have suggested. (C) 2014 Elsevier Ltd. All rights reserved.

  • 37. Möller, Per
    et al.
    Lubinski, D.
    Ingólfsson, Ó.
    Forman, S. L
    Siedenkrantz, M-S
    Bolshiyanov, D. Yu.
    Lokrantz, H.
    Antonov, O.
    Pavlov, ´M.
    Ljung, Karl
    Zeeberg, J. J.
    Andreev, A.
    Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary2006In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 25, no 21-22, p. 2894-2936Article in journal (Refereed)
    Abstract [en]

    Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79 degrees N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS C-14, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of > 2000m only 200km from the deep Arctic Ocean, consistent with published evidence of ice grounding at similar to 1000m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula.

  • 38.
    O'Regan, Matthew
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Kirchner, Nina
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Glacial geological implications of overconsolidated sediments on the Lomonosov Ridge and Yermak Plateau2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3532-3544Article in journal (Refereed)
    Abstract [en]

    With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (similar to 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf. (C) 2010 Elsevier Ltd. All rights reserved.

  • 39.
    Rosqvist, G.
    et al.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Jonsson, C.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Yam, R.
    Karlén, W.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Shemesh, A.
    Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 7-8, p. 851-859Article in journal (Refereed)
    Abstract [en]

    We use a pro-glacial oxygen isotope record of diatom silica (δ18Odiatom) and a sedimentary proxy for glacier flutuations to determine centennial-millennial scale climate change during the last 5000 yeras in northern Sweden. We show that the lake water isotopic composition åredominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (> 1‰ excursions) during four occasions centered at 4400, 3000, 2000 and, after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, taht caused the catchment glacier to advance. A peristan cgange in the atmopheric circulation pattern could potentially have caused the registered chnages in the δ18Odiatom because different air masses hold characteristics δ18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded chnages in both these proxies is a steadily increasing but fluctuating dominance of colder and δ18O depleted air masses from the north/northeast during the past 5000 years. Theδ18Odiatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlanic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominace of north/northeasterly winds occured at these time intervals.

  • 40. Rousseau, Denis-Didier
    et al.
    Boers, Niklas
    Sima, Adriana
    Svensson, Anders
    Bigler, Matthias
    Lagroix, France
    Taylor, Samuel
    Antoine, Pierre
    (MIS3 & 2) millennial oscillations in Greenland dust and Eurasian aeolian records - A paleosol perspective2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 169, p. 99-113Article in journal (Refereed)
    Abstract [en]

    Since their discovery, the abrupt climate changes that punctuated the last glacial period (similar to 110.6-14.62 ka) have attracted considerable attention. Originating in the North-Atlantic area, these abrupt changes have been recorded in ice, marine and terrestrial records all over the world, but especially in the Northern Hemisphere, with various environmental implications. Ice-core records of unprecedented temporal resolution from northern Greenland allow to specify the timing of these abrupt changes, which are associated with sudden temperature increases in Greenland over a few decades, very precisely. The continental records have, so far, been mainly interpreted in terms of temperature, precipitation or vegetation changes between the relatively warm “Greenland Interstadials” (GI) and the cooler “Greenland Stadials” (GS). Here we compare records from Greenland ice and northwestern European eolian deposits in order to establish a link between GI and the soil development in European mid latitudes, as recorded in loess sequences. For the different types of observed paleosols, we use the correlation with the Greenland records to propose estimates of the maximum time lapses needed to achieve the different degrees of maturation and development. To identify these time lapses more precisely, we compare two independent ice-core records: 6180 and dust concentration, indicating variations of atmospheric temperature and dustiness in the Greenland area, respectively. Our method slightly differs from the definition of a GI event duration applied in other studies, where the sharp end of the 8180 decrease alone defines the end of a Gl. We apply the same methodology to both records (i.e., the GIs are defined to last from the beginning of the abrupt 6180 increase or dust concentration decrease until the time when 6180 or dust recur to their initial value before the GI onset), determined both visually and algorithmically, and compare them to published estimates of GI timing and duration. The duration of the GI and consequently the maximum time for paleosol development varies between 200 and 4200 years when visually determined and between 200 and 4800 years when estimated algorithmically for GI 17 to 2, i.e. an interval running from 60 ka to 23 ka b2k (age before 2000 AD). Furthermore, we investigate the abruptness of the transition from stadial to interstadial conditions, which initiates the paleosol development. The average transition duration is 55.4 +/- 16.1 (56.8 +/- 19.6) years when determined visually, and 36.4 +/- 13.4 (60.00 +/- 21.2) years when determined algorithmically for the delta O-18 (dust concentration). The 6180 increases correspond to a mean temperature difference of 11.8 degrees C on the top of the Greenland ice sheet, associated with substantial reorganizations of the ecosystems in mid-latitude Europe. (C) 2017 Elsevier Ltd. All rights reserved.

  • 41. Sellen, E.
    et al.
    O’Regan, M.
    Jakobsson, M.
    Spatial and temporal Arctic Ocean depositional regimes: a key to the evolution of ice drift and current patterns2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, SI, p. 3644-3664Article in journal (Refereed)
    Abstract [en]

    Sediment physical properties measured in cores from all the major ridges and plateaus in the central Arctic Ocean were studied in order to analyze the spatial and temporal consistency of sediment depositional regimes during the Quaternary. In total, six physiographically distinct areas are outlined. In five of these, cores can be correlated over large distances through characteristic patterns in sediment physical properties. These areas are (1) the southern Mendeleev Ridge, (2) the northern Mendeleev Ridge and Alpha Ridge, (3) the Lomonosov Ridge, (4) the Morris Jesup Rise and (5) the Yermak Plateau. Averaged downhole patterns in magnetic susceptibility, bulk density and lithostratigraphy were compiled to establish a composite stratigraphy for each area. In the sixth physiographic area, the Chukchi Borderland, repeated ice-grounding during recent glacial periods complicates the stratigraphy and prevents the compilation of a composite stratigraphy using the studied material. By utilizing published age models for the studied cores we are able to show that the northern Mendeleev Ridge and Alpha Ridge have the lowest average late Quaternary sedimentation rates, while intermediate sedimentation rates prevail on the southern Mendeleev Ridge and the Morris Jesup Rise. The second highest sedimentation rate is observed on the Lomonosov Ridge, whereas the average sedimentation rate on the Yermak Plateau is more than twice as high. The close correlation of physical properties within each area suggests uniform variations in sediment transport through time, at least throughout the later part of the Quaternary. The unique stratigraphic characteristics within each area is the product of similar past depositional regimes and are key for furthering our understanding of the evolution of ice drift and current patterns in the central Arctic Ocean. (C) 2010 Elsevier Ltd. All rights reserved.

  • 42.
    Sparrenbom, Charlotte J.
    et al.
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Bennike, Ole
    Geol Survey Denmark & Greenland, DK-1350 Copenhagen, Denmark..
    Fredh, Daniel
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Randsalu-Wendrup, Linda
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Zwartz, Dan
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington 6140, New Zealand..
    Ljung, Karl
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Björck, Svante
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Lambeck, Kurt
    Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200, Australia..
    Holocene relative sea-level changes in the inner Bredefjord area, southern Greenland2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 69, p. 107-124Article in journal (Refereed)
    Abstract [en]

    In this paper we present new relative sea-level data from southern Greenland, a key area for understanding the Greenland Ice Sheet (GIS) response to climate change. Within fourteen lakes and marine lagoons from the inner part of Bredefjord (Nordre Sermilik) in southern Greenland, isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed. Due to coastal emergence caused by the GIS retreat within the area, the relative sea-level fell rapidly in the early Holocene between at least c. 9600 and c. 7300 cal. yrs BP attaining a rate of 2 cm per year between 9600 and 8000 cal. yrs BP. Spatial variability in relative sea-level changes is show for southern Greenland from a comparison with the Nanortalik and the Qagortoq areas. The regression occurred about 2000 years later in the inner Bredefjord area, compared to the Nanortalik area, and about 1000 years later compared to the Qaqortoq area. This is a consequence of earlier deglaciation in areas located at the outer coast. Between c. 8000 cal. yrs BP and the present day, relative sea level was lower than today. The lowest relative sea level in the Inner Bredefjord area of between -5.4 and -15 m a.h.a.t. (above highest astronomical tide) was reached between 7000 and 1000 cal. yrs BP. The neoglacial readvance together with the collapse of the Laurentide peripheral bulge is probably responsible for the transgression in the Inner Bredefjord area, as has been indicated from the nearby sites Qagortoq and Nanortalik. Our relative sea-level reconstructions showing spatial variability within southern Greenland have implications for Glacial Isostatic Adjustment (GIA) modelling and the understanding of the GIS ice sheet dynamics. The early Holocene regression is consistent with the recession of the southern sector of the GIS from the shelf edge at c. 22 000 cal. yrs BP, reaching inland of the present day outer coast by c. 12 000 cal. yrs BP, and its present margin by c. 10 500 cal. yrs BP. (c) 2013 Elsevier Ltd. All rights reserved.

  • 43.
    Stranne, Christian
    et al.
    Univ Gothenburg, Dept Earth Sci, S-41320 Gothenburg, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Bjork, Goran
    Univ Gothenburg, Dept Earth Sci, S-41320 Gothenburg, Sweden..
    Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 123-132Article in journal (Refereed)
    Abstract [en]

    Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (similar to 6000-10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere sea ice ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bolling Allerod period (c. 12,700-14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

  • 44.
    Unkel, Ingmar
    et al.
    GeoBiosphere Sci Ctr, SE-22362 Lund, Sweden..
    Björck, Svante
    GeoBiosphere Sci Ctr, SE-22362 Lund, Sweden..
    Wohlfarth, Barbara
    Stockholm Univ, Dept Geol & Geochem, SE-10691 Stockholm, Sweden..
    Deglacial environmental changes on Isla de los Estados (54.4 degrees S), southeastern Tierra del Fuego2008In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, no 15-16, p. 1541-1554Article in journal (Refereed)
    Abstract [en]

    The island of Isla de los Estados is situated at 54.5 degrees S, 64 degrees W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16-10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 kin further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age-depth modeling based on AMS-C-14 dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data Suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene. (C) 2008 Elsevier Ltd. All rights reserved.

  • 45.
    Witus, Alexandra E.
    et al.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Branecky, Carolyn M.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Szczucinski, Witold
    Adam Mickiewicz Univ, Inst Geol, PL-61606 Poznan, Poland..
    Schroeder, Dustin M.
    Univ Texas Austin, Inst Geophys, Austin, TX USA..
    Blankenship, Donald D.
    Univ Texas Austin, Inst Geophys, Austin, TX USA..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Meltwater intensive glacial retreat in polar environments and investigation of associated sediments: example from Pine Island Bay, West Antarctica2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 85, p. 99-118Article in journal (Refereed)
    Abstract [en]

    Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are among the fastest changing portions of the cryosphere and the least stable ice streams in Antarctica. Here we show that the uppermost sediment unit in Pine Island Bay was deposited from a meltwater plume, a plumite, during the late stages of ice sheet retreat similar to 7-8.6 k cal yr BP and argue that this deposit records episodes of meltwater intensive sedimentation. The plumite is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glaci-marine sediments and thickens towards the modern grounding line. The uppermost sediment unit is interpreted as a product of non-steady-state processes in which low background sedimentation in large bedrock-carved basins alternates with episodic purging of sediment-laden water from these basins. The inner part of Pine Island Bay contains several basins that are linked by channels with a storage capacity on the order of 70 km(3) of stagnant water and significant sediment storage capacity. Purging of these basins is caused by changes in hydraulic potential and glacial reorganization. The sediment mobilized by these processes is found here to total 120 km3. This study demonstrates that episodes of meltwater-intensive sedimentation in Pine Island Bay occurred at least three times in the Holocene. The most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit. We note that the final phase of ice stream retreat in Marguerite Bay was marked by a similar sedimentary event and suggest that the modern Thwaites Glacier is poised for an analogous meltwater-intensive phase of retreat. (C) 2013 Elsevier Ltd. All rights reserved.

  • 46. Xuan, Chuang
    et al.
    Channell, James E. T.
    Polyak, Leonid
    Darby, Dennis A.
    Paleomagnetism of Quaternary sediments from Lomonosov Ridge and Yermak Plateau: implications for age models in the Arctic Ocean2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 32, p. 48-63Article in journal (Refereed)
    Abstract [en]

    Inclination patterns of natural remanent magnetization (NRM) in Quaternary sediment cores from the Arctic Ocean have been widely used for stratigraphic correlation and the construction of age models, however, shallow and negative NRM inclinations in sediments deposited during the Brunhes Chron in the Arctic Ocean appear to have a partly diagenetic origin. Rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite. Thermal demagnetization of the NRM indicates that shallow and negative inclination components are largely “unblocked” below similar to 300 degrees C, consistent with a titanomaghemite remanence carrier. Following earlier studies on the Mendeleev Alpha Ridge, shallow and negative NRM inclination intervals in cores from the Lomonosov Ridge and Yermak Plateau are attributed to partial self-reversed chemical remanent magnetization (CRM) carried by titanomaghemite formed during seafloor oxidation of host (detrital) titanomagnetite grains. Distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western (Mendeleev Alpha Ridge) and central Arctic Ocean (Lomonosov Ridge) and, to a lesser extent, near the ice edge (Yermak Plateau). On the Yermak Plateau, magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6, implying that magnetic grain size is sensitive to glacial interglacial changes in bottom-current velocity and/or detrital provenance. (C) 2011 Elsevier Ltd. All rights reserved.

1 - 46 of 46
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf