HR: 0800h
AN: PP41A-0632    [Abstracts]
TI: Late Quaternary Variability in the Deep Water Exchange Between South Atlantic, Southern and Indian Oceans
AU: * Leuschner, D C
EM: dcleu@uni-leipzig.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstr. 35, Leipzig, 04103 Germany
AU: Krueger, S
EM: skrueger@uni-leipzig.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstr. 35, Leipzig, 04103 Germany
AU: Ehrmann, W
EM: ehrmann@uni-leipzig.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstr. 35, Leipzig, 04103 Germany
AU: Schmiedl, G
EM: schmiedl@uni-leipzig.de
AF: Institute for Geophysics and Geology, University Leipzig, Talstr. 35, Leipzig, 04103 Germany
AU: Kuhn, G
EM: gkuhn@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstr., Bremerhaven, 27568 Germany
AU: Mackensen, A
EM: amackensen@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstr., Bremerhaven, 27568 Germany
AU: Diekmann, B
EM: bdiekmann@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegraphenberg, Potsdam, 14473 Germany
AB: The Southern Ocean, south of Africa, is an important mixing region for northern and southern derived deep-water masses. In this region, the North Atlantic Deep Water (NADW) extends southward into the Circumpolar Deep Water (CDW) dividing it into an upper (UCDW) and a lower (LCDW) layer. Thus, marine sediments from this area are a sensitive recorder for changes of the paleocirculation and relative variations in the deep-water formation in both, the northern Atlantic and Antarctic regions. Here we present results from the EXCHANGE Project which is located in this transition zone of the South Atlantic, the Southern Ocean and the Indian Ocean. In this project we investigate six sediment cores taken along a transect from continental slope at the southern tip of Africa towards the Conrad Rise. Pronounced glacial/interglacial variations in the dominance of NADW and LCDW across the transect are reflected in the clay mineral assemblage and carbon isotope composition of benthic foraminifera. High kaolinite/chlorite-ratios associated with high stable carbon isotope ratios indicate stronger influence of NADW during interglacials. In contrast, glacials are dominated by southern-derived LCDW. Our results suggest a fast southward advance of NADW-dominance during the last two terminations while the northward retreat of NADW, with the onset of glacial conditions, is more gradual. In general, interglacial sediments are also characterized by higher mean grain size diameters in the terrigenous silt fraction (10 to 63 microns), thus indicating stronger bottom currents. However, maximum grain size and sortable silt values are reached at the early stages of the last two glacial periods. Due to the generally weakened bottom current strength, as a result of reduced deep water formation, we would expect smaller values when compared with interglacial conditions. We therefore assume that eolian dust input from the Patagonian region plays a significant role especially in the early glacial periods. The exposure of large continental areas with the low glacial sea level and desertification in the hinterland may increase the amount of dust prone for eolian transport. Moreover, the more vigorous westerly winds during glacials are capable of transporting larger grain sizes. As the amount of material prone to wind transport diminishes towards the end of the glacial, eolian influx and grain sizes decrease significantly. Then the grain size distribution is again mainly controlled by the transport through bottom currents.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 3022 Marine sediments: processes and transport
DE: 3675 Sedimentary petrology
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005