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

Type Article
Acceptance Date 2020 IN PRESS
Language English
Author(s) Ma Ruifang1, 2, Sépulcre Sophie1, Licari Laetitia3, Haurine Frédéric1, Bassinot Franck5, Yu Zhaojie5, Colin Christophe1
Affiliation(s) 1 : GEOPS, Université Paris-Saclay, CNRS, Orsay, 91405, France
2 : State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
3 : CEREGE, Aix-Marseille Université-Europole de l'Arbois-BP80, Aix-en-Provence, 13545, France
4 : LSCE/IPSL, CEA CNRS UVSQ, Gif Sur Yvette, F-91190, France
5 : Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China
Source Climate of the past (1814-9332) (Copernicus GmbH) In Press
DOI 10.5194/cp-2020-143
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.

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Ma Ruifang, Sépulcre Sophie, Licari Laetitia, Haurine Frédéric, Bassinot Franck, Yu Zhaojie, Colin Christophe 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. Climate of the past IN PRESS. Publisher's official version : https://doi.org/10.5194/cp-2020-143 , Open Access version : https://archimer.ifremer.fr/doc/00659/77152/