HR: 08:45h
AN: PP31B-04    [Abstracts]
TI: Glacial Nd Isotope Composition of Equatorial Atlantic Bottom Water
AU: * Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Piotrowski, A M
EM: arcturus@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Franzese, A M
EM: franzese@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Broecker, W S
EM: broecker@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964 United States
AU: Curry, W B
EM: wcurry@whoi.edu
AF: Woods Hole Oceanographic Institution, Mailstop 23, Woods Hole, MA 02543 United States
AB: Atmospheric and oceanic circulation together redistribute heat and moisture around the Earth. The parallel behavior of climate proxies in ice core and marine sediment records demonstrates that these changes are globally represented. Results from general circulation models attest to the instability of the thermohaline system and its capacity for rapid changes. Nevertheless, the origin of thermohaline instabilities and their relationship to rapid global scale climate events remain unresolved. NADW turnover is expected to dramatically decrease when a sudden flux of fresh water is injected into the North Atlantic. Models differ in detail, but have in common the sensitivity of Atlantic overturning to freshwater injections, and they also produce a cooling of air and sea surface temperatures in the eastern North Atlantic when overturning is slowed or halted. The relative importance of atmospheric teleconnections and changes in the meridional overturning in the North Atlantic require multiple observational and modeling approaches. The approach presented here is the application of Nd isotopes in the ferromanganese fraction of marine sediment cores. Nd isotope ratios in modern Atlantic water profiles follow temperature-salinity variations, indicating that Nd isotope ratios in these waters conserve the characteristics of major water masses. Nd isotope ratios of leached extractions of the authigenic ferromanganese components of core top samples are consistent with modern water values, although the Sr isotope compositions are generally elevated relative to seawater in North Atlantic samples. We present here new data from the western tropical Atlantic. Samples from the last glacial maximum yield significantly more radiogenic values of -7.6 to -8.2 compared to modern values of approximately -12. This approximately 4 epsilon difference is consistent with published Nd isotope evidence from the southeastern Atlantic (Cape Basin) that there was a significant reduction in the NADW contribution to the Atlantic basin during glacial times. Although causes and effects from changing meridional overturning remain open questions, the evidence is mounting for a significant difference in the deep water mixing processes during glacial times compared to today, and is consistent with substantially reduced NADW production.
DE: 4825 Geochemistry
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting