18 Nov 2020
18 Nov 2020
Status: a revised version of this preprint is currently under review for the journal CP.

Changes in productivity and intermediate circulation in the northern Indian Ocean since the last deglaciation: new insights from benthic foraminiferal Cd / Ca records and benthic assemblage analyses

Ruifang Ma1,2, Sophie Sépulcre1, Laetitia Licari3, Frédéric Haurine1, Franck Bassinot4, Zhaojie Yu5, and Christophe Colin1 Ruifang Ma et al.
  • 1GEOPS, Université Paris-Saclay, CNRS, Orsay, 91405, France
  • 2State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
  • 3CEREGE, Aix-Marseille Université-Europole de l'Arbois-BP80, Aix-en-Provence, 13545, France
  • 4LSCE/IPSL, CEA CNRS UVSQ, Gif Sur Yvette, F-91190, France
  • 5Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China

Abstract. We have measured Cd / Ca ratios of several benthic foraminiferal species and studied benthic foraminiferal assemblages on two cores from the northern Indian Ocean (Arabian Sea and northern Bay of Bengal, BoB), in order to reconstruct variations in intermediate water circulation and paleo-nutrient content since the last deglaciation. Intermediate water Cdw records estimated from the benthic Cd / Ca reflect past changes in surface productivity and/or intermediate-bottom water ventilation. The benthic foraminiferal assemblages are consistent with the geochemical data. These results suggest that during the last deglaciation, the Heinrich Stadial 1 and Younger Dryas (HS1 and YD, respectively) millennial-scale events were marked by a decrease in Cdw values, indicating an enhanced ventilation of intermediate-bottom water masses. Benthic foraminifer assemblages indicate that surface primary productivity was low during the early Holocene (from 10 to 6 cal kyr BP), resulting in low intermediate water Cdw at both sites. From ~ 5.2 to 2.4 cal kyr BP, the benthic foraminiferal assemblages indicate meso- to eutrophic intermediate water conditions, which correspond to high surface productivity. This is consistent with a significant increase in the intermediate water Cdw in the southeastern Arabian Sea and the northeastern BoB. The comparison of intermediate water Cdw records with previous reconstructions of past Indian monsoon evolution during the Holocene suggests a direct control of intermediate water Cdw by monsoon-induced changes in upper water stratification and surface primary productivity.

Ruifang Ma et al.

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Ruifang Ma et al.

Ruifang Ma et al.


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