title: Evolution of South Atlantic density and chemical stratification across the last deglaciation.
abstract: Explanations of the glacial-interglacial variations in atmospheric pCO2 invoke a significant role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. A wealth of proxy data supports the presence of a "chemical divide" between intermediate and deep water in the glacial Atlantic Ocean, which indirectly points to an increase in deep-ocean density stratification. However, direct observational evidence of changes in the primary controls of ocean density stratification, i.e., temperature and salinity, remain scarce. Here, we use Mg/Ca-derived seawater temperature and salinity estimates determined from temperature-corrected δ(18)O measurements on the benthic foraminifer Uvigerina spp. from deep and intermediate water-depth marine sediment cores to reconstruct the changes in density of sub-Antarctic South Atlantic water masses over the last deglaciation (i.e., 22-2 ka before present). We find that a major breakdown in the physical density stratification significantly lags the breakdown of the deep-intermediate chemical divide, as indicated by the chemical tracers of benthic foraminifer δ(13)C and foraminifer/coral (14)C. Our results indicate that chemical destratification likely resulted in the first rise in atmospheric pCO2, whereas the density destratification of the deep South Atlantic lags the second rise in atmospheric pCO2 during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed.
authors.affiliation: Godwin Laboratory for Paleoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom; British Antarctic Survey, Cambridge CB3 0ET, United Kingdom; jr451@cam.ac.uk.
authors.forename: Jenny
authors.identifier: http://orcid.org/0000-0002-1098-0829
authors.initials: J
authors.lastname: Roberts
authors.affiliation: Godwin Laboratory for Paleoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom;
authors.forename: Julia
authors.identifier: http://orcid.org/0000-0002-0403-3059
authors.initials: J
authors.lastname: Gottschalk
authors.affiliation: Godwin Laboratory for Paleoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom;
authors.forename: Luke C
authors.initials: LC
authors.lastname: Skinner
authors.affiliation: British Antarctic Survey, Cambridge CB3 0ET, United Kingdom;
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Peck
authors.affiliation: Centre for Environmental Geochemistry, School of Geography, University of Nottingham, Nottingham NG7 2RD, United Kingdom; British Geological Survey, Nottingham NG12 5GG, United Kingdom;
authors.forename: Sev
authors.initials: S
authors.lastname: Kender
authors.affiliation: Godwin Laboratory for Paleoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom;
authors.forename: Henry
authors.initials: H
authors.lastname: Elderfield
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, Domaine du CNRS, 91198 Gif-sur-Yvette, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Waelbroeck
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, Domaine du CNRS, 91198 Gif-sur-Yvette, France.
authors.forename: Natalia
authors.identifier: http://orcid.org/0000-0001-7513-153X
authors.initials: N
authors.lastname: Vázquez Riveiros
authors.affiliation: Godwin Laboratory for Paleoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom;
authors.forename: David A
authors.initials: DA
authors.lastname: Hodell
keywords: South Atlantic; atmospheric CO2; density gradient; last deglaciation; ocean stratification