Late slowdown of the Atlantic Meridional Overturning Circulation during the Last Glacial Inception: New constraints from sedimentary (231Pa/230Th) |
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| Authors: | Abel Guihou Sylvain Pichat Sìlvia Nave Aline Govin Laurent Labeyrie Elisabeth Michel Claire Waelbroeck |
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| Institution: | 1. Aix Marseille Univ, CNRS, IRD, Coll France, CEREGE, Aix-en-Provence, France;2. Laboratoire de Météorologie Dynamique, École Polytechnique, Palaiseau, France;3. ENSTA ParisTech, Université Paris-Saclay, 828 bd des Maréchaux, 91762 Palaiseau cedex, France;4. IFREMER, Unité de Recherche Géosciences Marines, F-29280 Plouzané, France;5. Université de Lille, CNRS, Université du Littoral Côte d''Opale, UMR8187, LOG, Laboratoire d''Océanologie et de Geéosciences, F-59000 Lille, France;6. Laboratoire Geosciences Paris-Sud (GEOPS), Université de Paris Sud, Université Paris-Saclay, 91405 Orsay, France;7. Laboratoire des Sciences du Climat et de l''Environnement LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France;8. Institute of Environmental Physics, University of Heidelberg, 69120 Heidelberg, Germany;9. Université Grenoble Alpes, ISTerre, CS 40700, 38058 Grenoble Cedex 9, France;10. LEGOS (Université de Toulouse/CNRS/CNES/IRD/UPS), Observatoire Midi-Pyrénées, Toulouse, France;11. Equipe de Géochimie-Cosmochimie, Institut de Physique du Globe de Paris – Sorbonne Paris Cité, Université Paris Diderot, UMR CNRS 7154, 1 rue Jussieu, 75005 Paris, France;12. ISMAR-CNR, via Gobetti 101, 40129 Bologna, Italy;13. Department of Earth Sciences, University of Cambridge, Cambridge, UK;14. Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK;15. UMR CNRS 6282 Biogéosciences, 6 Bd. Gabriel, 21000 Dijon, France |
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| Abstract: | Our study gives new constraints on the response of Atlantic Meridional Overturning Circulation (AMOC) export to various forcings during the Last Glacial Inception. The decay corrected excess sedimentary (231Pa/230Th) activity ratio (hereafter referred to as (Pa/Th)) has been measured over that period in two deep cores from the Western (SU90-11, 44°04′N, 40°01′W, 3645 m) and Eastern (MD01-2446, 39°03′N, 12°37′W, 3547 m) basins of the North Atlantic. Both records display significant changes despite the relatively short half-life of 231Pa (～ 32 kyr) compared to the period we investigate. The (Pa/Th) variability does not correlate to changes in local opal flux normalized to 230Th. Moreover, the (Pa/Th) profiles display a high degree of coherency with indirect proxies of AMOC activity such as the benthic foraminifera δ13C and the mid-latitude summer Sea Surface Temperature in nearby reference cores. These additional pieces of evidence support our interpretation of the (Pa/Th) as reflecting AMOC export. The (Pa/Th) repeatedly underwent rapid changes during the Last Glacial Inception associated with the extension of ice rafted detritus in the North Atlantic, highlighting the control of ice-sheet dynamics through freshwater forcing on AMOC export. AMOC export remains large during periods of ice-sheet growth and its decreases lag the Northern Hemisphere summer insolation forcing. AMOC modulation appears driven by ice-sheet dynamics, itself driven by the seasonal insolation gradient between low and high Northern Hemisphere latitudes and the associated intensity of the meridional oceanic and atmospheric circulation. |
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