Sedimentology of core PS2564-3 and GeoB2110-4

In the South Atlantic and adjoining Southern Ocean the kaolinite/chlorite-ratio in Late Quaternary sediments are an alternative deep water proxy to benthic foraminiferal proxies and carbonate preservation indices that is even suitable in regions with poor carbonate preservation. This paper shows the relationship between modern abyssal circulation and the kaolinite/chloriteratio and presents reconstructions of deep and bottom water advection based on the kaolinite/ chlorite proxy. We also discuss the limitations and future perspectives of the kaolinite/chlorite proxy. Latitudinal and water depth-related patterns of the kaolinite/chlorite-ratio in surface sediments correspond to the modern deep and bottom water mass distribution. Kaolinite originates from lowlatitudes and traces North Atlantic Deep Water (northern-source deep water) advection to the south. Chlorite from the southern high-latitudes is exported via northward advecting Antarctic Bottom Water and Circumpolar Deep Water (southern-source deep and bottom water). Deep-sea sedimentation in regions underlying the Antarctic Circumpolar Current was current-dominated throughout the Late Quaternary. Temporal variations of the kaolinite/chlorite-ratio in response to glacial-interglacial cycles reflect changing deep water mass configurations, suggesting a shallowing and northward retreat of northern-source deep water and accordingly wider expansion of southernsource deep and bottom water masses during glacial times relative to interglacial times. Submarine topography influenced the spatial and temporal patterns of deep water mass distribution.

Sedimentology and stable isotope ratios of planktonic foraminifera from two cores off Northeastern Brazil

The stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern Brazil. Stable oxygen isotope records of the planktonic foraminiferal species Globigerinoides sacculifer and Globigerinoides ruber (pink) reveal sub-Milankovitch changes in sea-surface hydrography during the last 85,000 yr. Warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high XRF intensities of Ti and Fe, and which suggest humid conditions in northeast Brazil. These tropical signals correlate with climatic oscillations recorded in Greenland ice cores (Dansgaard-Oeschger cycles) and in sediment cores from the North Atlantic (Heinrich events). Trade winds may have caused changes in the North Brazil Current that altered heat and salt flux into the North Atlantic, thus affecting the growth and decay of the large glacial ice sheets.

Paleomagnetic and stable isotope measurements and distribution of benthic foraminifera in sediment core PS1388-3 from the Antarctic continental margin in the eastern Weddell Sea

A stable isotope record from the eastern Weddell Sea from 69°S is presented. For the first time, a 250,000-yr record from the Southern Ocean can be correlated in detail to the global isotope stratigraphy. Together with magnetostratigraphic, sedimentological and micropalaeontological data, the stratigraphic control of this record can be extended back to 910,000 yrs B.P. A time scale is constructed by linear interpolation between confirmed stratigraphic data points. The benthic d18O record (Epistominella exigua) reflects global continental ice volume changes during the Brunhes and late Matuyama chrons, whereas the planktonic isotopic record (Neogloboquadrina pachyderma) may be influenced by a meltwater lid caused by the nearby Antarctic ice shelf and icebergs. The worldwide climatic improvement during deglaciations is documented in the eastern Weddell Sea by an increase in production of siliceous plankton followed, with a time lag of approximately 10,000 yrs, by planktonic foraminifera production. Peak values in the difference between planktonic and benthic d13C records, which are 0.5 per mil higher during warm climatic periods than during times with expanded continental ice sheets, also suggest increased surface productivity during interglacials in the Southern Ocean.