Trace metal evidence for a poorly ventilated glacial Southern Ocean
M. Wagner1,* and I. L. Hendy11Department of Earth and Environmental Sciences, University of Michigan, 1100 N University Ave, Ann Arbor, MI 48109, USA *now at: Department of Earth and Atmospheric Sciences, Central Michigan University, Brooks Hall 314, Mount Pleasant, MI 48859, USA
Received: 04 Dec 2014 – Accepted for review: 10 Feb 2015 – Discussion started: 11 Mar 2015
Abstract. Glacial benthic δ13C and Δ14C measurements from the Atlantic Ocean have been interpreted to indicate the existence of a poorly ventilated Southern Ocean with greater CO2 and nutrient contents compared to present. Enhanced storage of CO2 in the deep ocean predicts that oxygen concentrations should have declined at the same time, although no unequivocal evidence for glacial Southern Ocean suboxia has yet been found. Here we take a novel approach by using concentrations of redox-sensitive trace metals to show that Southern Ocean sediments from two cores in the Atlantic sector were suboxic during deglaciation and the last glacial period, implying reduced ventilation and/or elevated export production that significantly altered deep water chemistry. In the Cape Basin, high concentrations of the authigenically deposited trace metal Re coincide with oldest Δ14C values at 3.8 km water depth in the Subantarctic Zone, indicating that poorest Southern Ocean ventilation occurred during the Last Glacial Maximum (~ 23–19 ka). Furthermore, trace metal results suggest that the vertical structure of the glacial Southern Ocean differed from modern deep water mass arrangement such that Lower Circumpolar Deep Water had lower O2 concentrations, and therefore was the likely reservoir of glacial CO2.
Wagner, M. and Hendy, I. L.: Trace metal evidence for a poorly ventilated glacial Southern Ocean, Clim. Past Discuss., 11, 637-670, doi:10.5194/cpd-11-637-2015, 2015.