HR: 10:45h
AN: PP22A-02    [Abstracts]
TI: Do Geochemical Proxy Records in Cape Basin Sediments Reflect Changes in Deep Ocean Circulation or Surface Ocean Productivity?
AU: * Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, P. O. Box 1000, Palisades, NY 10964 United States
AU: Fleisher, M Q
EM: martyq@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, P. O. Box 1000, Palisades, NY 10964 United States
AU: Sachs, J P
EM: jsachs@mit.edu
AF: Massassachusetts Institute of Technology, Dept. Earth, Atmospheric and Planetary Sciences 77 Massachusetts Ave., Cambridge, MA 02139 United States
AB: Recent studies have reported dramatic correlations between millennial scale variability in the carbon isotopic composition of benthic foraminifera in Cape Basin sediments and contemporary changes in the Nd isotopic composition of authigenic phases (Piotrowski et al., in press) and the Sr isotopic composition of lithogenic phases (Rutberg et al., in press) of these sediments. Factors invoked to account for these features include variability in the supply of North Atlantic Deep Water to the deep Cape Basin, regional changes in the ocean carbon cycle, and iron fertilization of local biological productivity, where the iron may have been associated with lithogenic material derived from South America. Lithogenic material from South America is characterized by non-radiogenic Sr and radiogenic Nd, and variable supply of this material may have influenced the Cape Basin records. To help sort out the relative influence on these proxies of ocean circulation and biological productivity, we compare within a single core records of Nd isotopes, C isotopes in benthic and planktonic foraminifera, concentrations of alkenones and authigenic U, and Th-normalized fluxes of lithogenic material. We find a strong correlation between paleproductivity proxies (authigenic U and alkenone concentration) and the isotopic records of authigenic Nd and of C in benthic foraminifera. The C isotopic composition of benthic foraminifera has some features correlated with the flux of lithogenic material (source of iron) and some features correlated with the C isotopic composition of planktonic foraminifera (proxy for surface nutrient concentration). We conclude that millennial variability in the supply of lithogenic material from South America had a significant influence on biological productivity in the Cape Basin, and through that on the C isotopic composition of benthic foraminifera and on the Nd isotopic composition of authigenic phases in Cape Basin sediments. Changes in supply of macronutrients seems to have been a factor as well. Increased iron supply may reflect surges in the Patagonian ice sheet, while increased surface nutrients may reflect periods of increased ventilation of deep waters. If true, then this scenario implies that the Nd isotopic composition of deep waters during the last glacial period were influenced by processes that are not found to be important today. Further work is needed to test these ideas.
DE: 3022 Marine sediments--processes and transport
DE: 3344 Paleoclimatology
DE: 4207 Arctic and Antarctic oceanography
DE: 4267 Paleoceanography
DE: 4825 Geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly