Similar glacial and interglacial export bioproductivity in the Atlantic sector of the Southern Ocean:: Multiproxy evidence and implications for glacial atmospheric CO2

We present time series of export productivity proxy data including Th-230(ex)-normalized deposition rates train rates) of Be-10, dissolution-corrected biogenic Pa, and biogenic opal as well as authigenic U concentrations which are complemented by rain rates of total (detrital) Fe and sea ice indicating diatom abundances from five sediment cores across the Atlantic sector of the Southern Ocean covering the past 150,000 years. The results suggest that Be-10 rain rates and authigenic U concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of Be-10 and bulk sedimentation rates (sediment focussing) and deep water oxygenation: in the case of U.The combined results of the remaining productivity proxies of this study train rates of biogenic opal and biogenic Pa in those sections without authigenic U) and other previously published proxy data from the Southern Ocean (Pa-231/Th-230 and nitrogen isotopes) suggest that a combination of sea ice cover, shallow remineralization depth, and stratification of the glacial water column south of the present position of the Antarctic Polar Front and possibly Fe fertilization north of it have been the main controlling factors of export paleoproductivity in the Southern Ocean over the last 150,000 years. An overall glacial increase of export paleoproductivity is not supported by the data, implying that bioproductivity variations in the Southern Ocean are unlikely to have contributed to the major glacial atmospheric CO2 drawdown observed in ice cores.