Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles

• Published in: Paleoceanography
• Main Authors: Wilson, David, Piotrowski, Alexander, Galy, Albert, Banakar, Virupaxa
• Other Authors: University of Cambridge UK (CAM), Department of Earth Science and Engineering Imperial College London, Imperial College London, Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), CSIR National Institute of Oceanography India (NIO)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: Circumpolar Deep Water; glaciation; orbital forcing; ocean circulation; carbon cycle; neodymium isotopes; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; [SDU]Sciences of the Universe [physics]; Antarctic; Indian; Southern Ocean; Antarc*; NADW; North Atlantic Deep Water; North Atlantic; Sea ice
• Online Access: https://hal.univ-lorraine.fr/hal-01770017; https://hal.univ-lorraine.fr/hal-01770017/document; https://hal.univ-lorraine.fr/hal-01770017/file/2014PA002707.pdf; https://doi.org/10.1002/2014PA002707

International audience Changes in ocean circulation structure, together with biological cycling, have been proposed for trapping carbon in the deep ocean during glacial periods of the Late Pleistocene, but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles. In this study, we use neodymium (Nd) and carbon isotopes from a deep Indian Ocean sediment core to reconstruct water mass mixing and carbon cycling in Circumpolar Deep Water over the past 250 thousand years, a period encompassing two full glacial cycles and including a range of orbital forcing. Building on recent studies, we use reductive sediment leaching supported by measurements on isolated phases (foraminifera and fish teeth) in order to obtain a robust seawater Nd isotope reconstruction. Neodymium isotopes record a changing North Atlantic Deep Water (NADW) component in the deep Indian Ocean that bears a striking resemblance to Northern Hemisphere climate records. In particular, we identify both an approximately in‐phase link to Northern Hemisphere summer insolation in the precession band and a longer‐term reduction of NADW contributions over the course of glacial cycles. The orbital timescale changes may record the influence of insolation forcing, for example via NADW temperature and/or Antarctic sea ice extent, on deep stratification and mixing in the Southern Ocean, leading to isolation of the global deep oceans from an NADW source during times of low Northern Hemisphere summer insolation. That evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions. However, mid‐depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods, and a return to an interglacial‐like circulation state during marine isotope stage (MIS) 6.5 was accompanied by only minor changes in atmospheric CO2. Although a gradual reduction of NADW export through glacial periods may have produced slow climate feedbacks linked to the growth ...