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

Wilson, David J. and Piotrowski, Alexander M. and Galy, Albert and Banakar, Virupaxa K. (2015) Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles. Paleoceanography. 2014PA002707. ISSN 1944-9186 DOI

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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, via NADW temperature, 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 of Northern Hemisphere ice sheets, carbon cycling in the glacial ocean was more strongly linked to Southern Ocean processes.

Item Type: Article
Uncontrolled Keywords: AREP2015; IA68;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
08 - Green Open Access
Journal or Publication Title: Paleoceanography
Page Range: 2014PA002707
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 17 May 2015 21:24
Last Modified: 22 Jul 2016 17:01

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