Evolution of South Atlantic density and chemical stratification across the last deglaciation

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Roberts, J, Gottschalk, J, Skinner, LC, Peck, VL, Kender, S, Elderfield, H, Waelbroeck, C, Riveiros, NV, Hodell, DA
• Format: Article in Journal/Newspaper
• Language: English
• Published: National Academy of Sciences 2016
• Subjects: Antarc*; Antarctic; British Antarctic Survey
• Online Access: http://hdl.handle.net/10871/34406; https://doi.org/10.1073/pnas.1511252113

This is the author accepted manuscript. The final version is available from the National Academy of Sciences via the DOI in this record Explanations of the glacial-interglacial variations in atmospheric pCO2invoke 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 CO2in 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 δ18O 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 δ13C and foraminifer/coral14C. 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 pCO2during the late deglacial period. Our findings emphasize that the physical and chemical destratification of the ocean are not as tightly coupled as generally assumed. J.R. was funded jointly by the British Geological Survey/British Antarctic Survey (Natural Environment Research Council) and the University of Cambridge. J.G. was funded by the Gates Cambridge Trust. L.C.S. acknowledges support from the Royal Society and NERC Grant NE/J010545/1. ...