We use benthic foraminiferal assemblages and benthic δ13C to interpret glacial-to-interglacial contrasts in two gravity cores from the lower bathyal Antarctic continental margin at 69°S, and the abyssal Agulhas Basin at 43°S. As a recent analogue, sediment surface samples from an eastern Atlantic Ocean and Weddell Sea transect between 20°–70°S are discussed. In the investigated area, benthic foraminiferal assemblages reflect both ocean circulation and surface productivity. Also at most stations from a belt with seasonally high surface productivity between 48°S–55°S, the δ13C values of epibenthic Cibicidoides spp., including F. wuellerstorfi are depleted relative to the bottom water δ13C∑CO2 and hence do not follow the 1:1 relationship established for more northern areas. This bears implications for the interpretation of large glacial-interglacial 513C shifts from the Southern Ocean: Significant parts of this shift can be caused by a northward migration of high productivity belts associated with the Polar Front and the winter sea-ice limit rather than indicating nutrient-rich glacial Southern Ocean deep and bottom water.During interglacial climatic optima, seasonally open surface water accompanied by relatively high opal and very low carbonate accumulation characterises the Antarctic continental margin environment. The recent benthic foraminiferal fauna indicates moderate productivity, but during peak warm periods (oxygen isotope Stages: 11, 9, 7.5, 7.3, 5.5 and 1.1) very low numbers of benthic foraminifera are inferred to represent maximum organic matter fluxes with severe calcite dissolution on the sea floor. Equally high δ13C values in surface and bottom water as inferred from planktic and benthic foraminifera, may indicate deep convection and bottom water formation during interglacials. In contrast, during glacials, very low opal accumulation, moderate carbonate accumulation, a benthic fauna that is presently associated with low productivity, as well as different benthic and planktic δ13C values are consistent with both a reduced primary productivity and a stratified water column, suggesting suppressed bottom water generation.In the Agulhas Basin high carbonate and low organic carbon (Corg) accumulation reflect the late Holocene position of the site investigated well north of the present-day Polar Front. Low Holocene δ13C values of 0.3‰ and a benthic foraminiferal fauna that indicates a southern bottom water mass which is corrosive to carbonate is in agreement with the injection of North Atlantic Deep Water into Circumpolar Deep Water at intermediate depths, which does not affect bottom waters of this basin. During glacial periods, a specific southern fauna, associated with high productivity today, low carbonate, high sediment and Corg accumulation, and by 1.1‰ lower δ13C values indicate a bottom water mass of southern origin, a northward shift of the high productivity belt by 7°, and strongly diminished injection of NADW into the Southern Ocean.
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- Benthic Foraminiferal Assemblages and the δ13C-Signal in the Atlantic Sector of the Southern Ocean: Glacial-to-Interglacial Contrasts
- Springer Berlin Heidelberg