Changes in Intermediate Circulation in the Bay of Bengal Since the Last Glacial Maximum as Inferred From Benthic Foraminifera Assemblages and Geochemical Proxies

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 20; no. 3; pp. 1592 - 1608
• Main Authors: Ma, Ruifang, Sépulcre, Sophie, Licari, Laetitia, Bassinot, Franck, Liu, Zhifei, Tisnérat‐Laborde, Nadine, Kallel, Nejib, Yu, Zhaojie, Colin, Christophe
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.03.2019; AGU and the Geochemical Society
• Subjects: Bay of Bengal; benthic foraminiferal assemblages; Benthos; Bottom water; B‐P 14C age; carbon and oxygen stable isotopes; Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide exchange; Deep water; Deglaciation; Earth Sciences; Eutrophication; Evolution; Foraminifera; Geochemistry; glacial Holocene; Glaciation; Holocene; Intermediate water; Intermediate water masses; Last Glacial Maximum; Meltwater; Ocean circulation; Oceans; Oxygen; Relative abundance; Sciences of the Universe; Tracers; Upwelling; Ventilation; Water masses; Bay of Bengal; Southern Ocean
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2018GC008179

Benthic foraminiferal assemblages and geochemical tracers (δ18O, δ13C and 14C) have been analyzed on benthic and planktonic foraminifera from core MD77‐176, located in the northern Bay of Bengal, in order to reconstruct the evolution of intermediate circulation in the northern Indian Ocean since the last glaciation. Results indicate that during the Last Glacial Maximum (LGM), Southern Sourced Water masses were dominant at the core site. A high relative abundance of intermediate and deep infaunal species during the LGM reflects low oxygen concentration and/or mesotropic to eutrophic deep water conditions, associated with depleted benthic δ13C values. During the Holocene, benthic foraminiferal assemblages indicate an oligotropic to mesotrophic environment with well‐ventilated bottom water conditions compared with LGM. Higher values for benthic foraminifera δ13C and B‐P 14C age offsets suggest an increased contribution of North Atlantic Deep Water to the northern Bay of Bengal during the Late Holocene compared to the LGM. Millennial‐scale events punctuated the last deglaciation, with a shift in the δ13C and the ɛNd values coincident with low B‐P 14C age offsets, providing strong evidence for an increased contribution of Antarctic Intermediate Water at the studied site. This was associated with enhanced upwelling in the Southern Ocean, reflecting a strong sea‐atmospheric CO2 exchange through Southern Ocean ventilation during the last deglaciation. Key Points We produced high‐resolution records of benthic foraminiferal assemblages, 14C ages, oxygen, and carbon stable isotopes since 40 kyr BP Hydrological changes of the intermediate water in Bay of Bengal since LGM, were influenced by SSW during the LGM and NADW during the Holocene During the last deglaciation, geochemical records indicate increased northward flow of AAIW and enhanced upwelling in the Southern Ocean