Growth,dynamics and deglaciation of the last British–Irish ice sheet: the deep-sea ice-rafted detritus record |
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| Authors: | James D Scourse Anna I Haapaniemi Elena Colmenero-Hidalgo Victoria L Peck Ian R Hall William EN Austin Paul C Knutz Rainer Zahn |
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| Institution: | 1. School of Ocean Sciences, College of Natural Sciences, Bangor University, Askew Street, Menai Bridge, Anglesey, LL59 5AB, UK;2. Department of Geology, Box 64, FIN-00014, University of Helsinki, Helsinki, Finland;3. School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3YE, UK;4. British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK;5. School of Geography and Geosciences, University of St. Andrews, Irvine Building, North Street, St Andrews, Fife KY16 9AL, UK;6. Department of Geophysics, Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark;7. Institució Catalana de Recerca i Estudis Avançats (ICREA), Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain;8. Institut de Ciència i Tecnologia Ambientals, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain;9. Departament de Geologia, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain;1. Department of Geography, College of Science, Swansea University, Singleton Park, Swansea, SA2 8PP, UK;2. School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, UK;3. Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK;1. Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK;2. Department of Geography, Durham University, Durham DH1 3LE, UK;3. BP Norway, Godesetdalen 8, Postboks 197, 4065 Stavanger, Norway;4. Department of Geography, Loughborough University, Loughborough LE11 3TU, UK;5. The University Centre in Svalbard (UNIS), Postboks 156, 9171 Longyearbyen, Norway;1. Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany;2. University of Bremen, Department of Geosciences, Klagenfurter Straße, 28359 Bremen, Germany;3. TGS, Lensmannslia 4, P.O. Box 154, N-1371, Asker, Norway;4. MARUM, Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, 28359 Bremen, Germany;1. Department of Geography, Durham University, Durham, DH1 3LE, UK;2. School of Geography and Environmental Sciences, Ulster University, Coleraine, BT52 1SA, Ireland;3. Department of Geography, University of Liverpool, Liverpool, UK;4. School of Ocean Sciences, Bangor University, Menai Bridge, UK;5. University of Plymouth, School of Biological and Marine Sciences, Drake Circus, Plymouth, PL4 8AA, UK;6. Department of Geography, University of Sheffield, Sheffield, S10 2TN, UK;7. Scottish Universities Environmental Research Centre, University of Glasgow, East Kilbride, G75 0QF, UK;8. Natural Environment Research Council, Radiocarbon Facility, East Kilbride, Scotland, G75 OQF, UK;1. Department of Earth Science, University of Bergen, N-5007 Bergen, Norway;2. Department of Geography, University of Sheffield, Sheffield S10 2TN, UK;3. British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;1. School of Environmental Sciences, University of Ulster, Cromore Road, Coleraine, BT52 1SA, Northern Ireland, UK;2. Department of Geography, Durham University, Durham, DH1 3LE, UK |
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| Abstract: | The evolution and dynamics of the last British–Irish Ice Sheet (BIIS) have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data. This reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary. In order to enhance BIIS reconstruction, we present a compilation of new and previously published ice-rafted detritus (IRD) flux and concentration data from high-resolution sediment cores recovered from the NE Atlantic deep-sea continental slope adjacent to the last BIIS. These cores are situated adjacent to the full latitudinal extent of the last BIIS and cover Marine Isotope Stages (MIS) 2 and 3. Age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera Neogloboquadrina pachyderma sinistral (% Nps) to the Greenland GISP2 ice core record. Multiple IRD fingerprinting techniques indicate that, at the selected locations, most IRD are sourced from adjacent BIIS ice streams except in the centre of Heinrich (H) layers in which IRD shows a prominent Laurentide Ice Sheet provenance. IRD flux data are interpreted with reference to a conceptual model explaining the relations between flux, North Atlantic hydrography and ice dynamics. Both positive and rapid negative mass balance can cause increases, and prominent peaks, in IRD flux. First-order interpretation of the IRD record indicates the timing of the presence of the BIIS with an actively calving marine margin. The records show a coherent latitudinal, but partly phased, signal during MIS 3 and 2. Published data indicate that the last BIIS initiated during the MIS 5/4 cooling transition; renewed growth just before H5 (46 ka) was succeeded by very strong millennial-scale variability apparently corresponding with Dansgaard–Oeschger (DO) cycles closely coupled to millennial-scale climate variability in the North Atlantic region involving latitudinal migration of the North Atlantic Polar Front. This indicates that the previously defined “precursor events” are not uniquely associated with H events but are part of the millennial-scale variability. Major growth of the ice sheet occurred after 29 ka with the Barra Ice Stream attaining a shelf-edge position and generating turbiditic flows on the Barra–Donegal Fan at ～27 ka. The ice sheet reached its maximum extent at H2 (24 ka), earlier than interpreted in previous studies. Rapid retreat, initially characterised by peak IRD flux, during Greenland Interstadial 2 (23 ka) was followed by readvance between 22 and 16 ka. Readvance during H1 was only characterised by BIIS ice streams draining central dome(s) of the ice sheet, and was followed by rapid deglaciation and ice exhaustion. The evidence for a calving margin and IRD supply from the BIIS during Greenland Stadial 1 (Younger Dryas event) is equivocal. The timing of the initiation, maximum extent, deglacial and readvance phases of the BIIS interpreted from the IRD flux record is strongly supported by recent independent data from both the Irish Sea and North Sea sectors of the ice sheet. |
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