The Late Pleistocene South Atlantic and Southern Ocean Surface - A Summary of Time-Slice and Time-Series Studies

Central to global climate evolution is the paleoceanographic development of the South Atlantic as it represents the passageway for inter-hemispheric heat exchange within global thermohaline circulation (THC). Processes in the adjacent Southern Ocean regulate the heat import into the South Atlantic via the Agulhas “warm water route” (WWR) and the Drake Passage “cold water route” (CWR), and amplify climate change through various feedback mechanisms and teleconnections. For paleoceanographic reconstruction an inventory of new data sets and methods is now available, allowing for the estimation of Pleistocene sea-surface water temperatures and sea-ice distribution on time-slices and time-series based on the calcareous and siliceous microfossil record. Reconstruction of the Last Glacial Maximum (LGM) reveals distinct cooling in the Southern Ocean (up to 4 – 6 °C) accompanied by an expansion of winter and summer sea ice, cooling in the African upwelling regimes (up to 10°C) and in the Equatorial Atlantic ( 4 – 5 °C), but the Subtropical Gyre region remains relatively warm and unchanged compared with the present. While the WWR was not strongly altered during the LGM, heat transport via the CWR was most probably much weaker. The reconstruction of time-slices representing a warm climate end-member at the onset of the last climate cycle documents a distinct lead of southern high-latitudes in global climate development that also affects the south-west African upwelling regions. It is at the Marine Isotope Stage (MIS) 6/MIS 5 transition when Southern Ocean surface temperatures reach maximum values and sea ice is at a minimum, marking a period of South Atlantic heat piracy. During the isotopic minimum of MIS 5.5, the tropical South Atlantic was slightly colder than at present, likely the result of an enhanced poleward heat export. Time-series studies from key areas document that climate variability related to orbital forcing is overprinted by THC changes driven by meltwater injections into the North Atlantic and the Southern Ocean, changes in atmospheric circulation and greenhouse gas concentration, as well as sea ice that amplify climate change at global, hemispheric and regional scales. The study of centennial-scale variability during interglacial optima, such as MIS 5.5 and MIS 11, suggests that the presence of large ice sheets, meltwater events, changes in greenhouse gas concentration and sea-ice distribution are not the only prerequisite to trigger millennial-centennial-scale variability, but that another external agent, changes in solar irradiance, must be considered as an important factor in climate development.