HR: 1340h
AN: PP33A-0907    [Abstracts]
TI: Glacial - Interglacial Changes in the Provenance and Flux of Sediment to the Cape Basin, South Atlantic: Implications for Indian-Atlantic Ocean Exchange
AU: * Franzese, A M
EM: franzese@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Broecker, W S
EM: broecker@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: Deep sea sediment cores have been widely used to study changes in sea surface conditions and ocean circulation on glacial-interglacial timescales, using faunal and floral analyses, stable isotope and trace element contents of carbonate shells, and more recently subtle compositional variations in organic compounds. Radiogenic isotope ratios can be sensitive tracers of sediment provenance, and have been interpreted in terms of changes in circulation patterns. Another tool that has seen growing application for studying the past oceans is $^{230}$Th$_{xs}$$\deg$. The excess $^{230}$Th measured in the sediment is useful as a constant-flux proxy, and puts additional constraints on the lateral transport and redistribution of sediments. Until now provenance and flux measures have been applied to separate problems, and this study is unique in using the combination of these two tracers. The combined measurements of sediment provenance and flux has great potential for determining sediment transport patterns, and how they have changed through time. The southeast Atlantic is an important study site because it is a region where thermocline and intermediate waters are exchanged with the Indian Ocean by the "Agulhas Leakage". This leakage is thought to be an important source of heat and salt to the Atlantic Ocean, possibly acting as a positive feedback for the formation of North Atlantic Deep Water (NADW). Changes in the strength of NADW formation and the intensity of global thermohaline circulation (THC) have been called upon as major amplifiers for climate change during the Pleistocene glacial cycles, with the hypothesis that NADW formation was weaker during the cold periods of the glacial cycles, particularly during the Last Glacial Maximum (LGM), approximately 18,000 years ago. $^{87}$Sr/$^{86}$Sr, \epsilon $_{Nd}$ and $^{230}$Th- normalized terrigenous flux measurements from Holocene and LGM sediment samples support the Agulhas Current as a major source of sediment to the Cape Basin drift deposit. The results are consistent with 3 end- member mixing between sediment carried by the Agulhas Current, the South Atlantic or Antarctic Circumpolar Current (SAC or ACC) and a local source. A comparison of the two time- slices implies that a smaller proportion of sediment deposited in the Cape Basin is derived from the Agulhas Current during the LGM. The results are consistent with a strengthened and more sediment-laden ACC during the LGM, and possibly a reduced Agulhas leakage, and hence less interocean exchange. Further investigation is needed to constrain whether the Agulhas Current was different during the LGM.
DE: 4825 Geochemistry
DE: 4860 Radioactivity and radioisotopes
DE: 4267 Paleoceanography
DE: 3022 Marine sediments--processes and transport
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting