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Climate of the Past An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  06 Mar 2020

06 Mar 2020

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A revised version of this preprint is currently under review for the journal CP.

Dynamics of primary productivity in the northeastern Bay of Bengal over the last 26 000 years

Xinquan Zhou1, Stéphanie Duchamp-Alphonse1, Masa Kageyama2, Franck Bassinot2, Luc Beaufort3, and Christophe Colin1 Xinquan Zhou et al.
  • 1Université Paris-Saclay, Géosciences Paris Sud, UMR 8148, CNRS, Rue du Belvédère, 91405 Orsay, France
  • 2Laboratoire des Sciences du Climat et de l'Environnement, UMR8112, CEA/CNRS/UVSQ, Université Paris-Saclay, Centre CEA-Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
  • 3Centre de Recherche et d’Enseignement de Géosciences de l’Environnement, UMR 7330, CNRS/IRD/Aix-Marseille Université, Av. Louis Philibert, BP80, 13545, Aix-en-Provence, France

Abstract. At present, variations of primary productivity (PP) in the Bay of Bengal (BoB) are responding to salinity-related-stratification which is controlled by the Indian Summer Monsoon (ISM). The relationships between PP, ISM, and to a broader scale, North Atlantic climate rapid variability in the past, are not clearly understood. Here, we present a new record of PP based on the examination of coccolithophore assemblages in a 26 000 years sedimentary record, retrieved in the northeastern BoB (core MD77-176). Comparisons with published climate and monsoon records, as well as outputs from the transient climate simulation TraCE-21 and experiments run with the Earth System Model IPSL-CM5A-LR, including marine biogeochemical components, helped us interpret our PP records in the context of ISM and Atlantic Overturning Meridional Circulation (AMOC) changes. We demonstrate that PP is influenced by vertical stratification in the upper water column over the last 26 000 years (26 kyr BP). It is controlled by wind-driven mixing from 26 to 19 kyr BP, i.e., when dry climate conditions and reduced freshwater inputs occurred, and by salinity-related-stratification over the last 19 kyr BP (since the Last Glacial Maximum), i.e., when humid conditions prevailed. During the deglaciation, salinity and stratification are related to monsoon precipitation dynamics, which are chiefly forced by both, insolation and the strength of the AMOC. The collapse (recovery) of the AMOC during Heinrich Stadial 1 (Bølling Allerød) weakened (strengthened) ISM and diminished (increased) stratification, thus enhancing (subduing) productivity.

Xinquan Zhou et al.

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Xinquan Zhou et al.

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Publications Copernicus
Short summary
We provide a high-resolution PP record of the Bay of Bengal over the last 26 000 years. Combined with climate model outputs, we demonstrate that since the Last Glacial Maximum, PP at both orbital- and millennial-scales are controlled by upper seawater salinity-stratification related to monsoon precipitation, a mechanism different from that working for the Arabian Sea. During the deglaciation the Atlantic Meridional Overturning Circulation is the main forcing factor.
We provide a high-resolution PP record of the Bay of Bengal over the last 26 000 years. Combined...