HR: 11:50h
AN: PP12B-07    [Abstracts]
TI: High resolution Nd isotope evidence for variations in NADW circulation during interstadial intervals and Heinrich Events
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Rt. 9W, Palisades, NY 10964 United States
AU: * Piotrowski, A M
EM: apio04@esc.cam.ac.uk
AF: Dept. Earth Sci., Cambridge University, Downing Place, Cambridge, CB2 3EQ United Kingdom
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Rt. 9W, Palisades, NY 10964 United States
AB: Nd isotope ratios of Fe-Mn oxides have been used as a proxy for past changes in deep water mass mixing. Results on eastern South Atlantic sediment cores indicate glacial-interglacial changes in the relative proportion of North Atlantic Deep Water (NADW) and southern-sourced waters in the Cape Basin. Piotrowski et al. EPSL 2004 examined millennial-scale variability in NADW circulation during the last deglaciation and concluded that it was closely linked to rapid changes in North Atlantic sea ice coverage. Here we examine the high-resolution Nd isotope record from sediment core TNO57-21 during the last glacial period, focusing on millennial-scale changes during MIS 2-3 interstadial cycles and Heinrich Events. Periods of greater presence of NADW during MIS 2-3 occur during Northern Hemisphere interstadials in Greenland ice core oxygen isotopes, suggesting stronger Atlantic overturning during warm Northern Hemisphere climate conditions. Northern Hemisphere stadials containing Heinrich events are associated with higher (more Pacific-like) Nd isotope ratios. This observation argues against millennial-scale changes in the NADW endmember through sediment-seawater exchange, because North Atlantic ice rafted debris and glacially derived sediments have much lower Nd isotope ratios. The higher Nd isotope ratios during Heinrich events and stadial periods instead necessitate a strong reduction in NADW contribution to the southeastern Atlantic. The South Atlantic location of RC11-83/TNO57-21 allows our Northern Hemisphere-forced ocean circulation record to be directly compared to Southern Hemisphere climate records such as planktonic foraminiferal oxygen isotopes, which is well correlated to the D/H of Antarctic ice as shown by Ninnemann et al., 1999. Like carbon isotopes, our Nd isotope record shows a greater proportion of northern-sourced waters reached the deep South Atlantic during Southern Hemisphere cooling. Northern Hemisphere Heinrich ice rafting events appear to play an important role in reducing NADW production, and inter-hemispheric correlation suggests that a reduction in ocean circulation may be associated warming in the Southern Hemisphere. This lends additional support to the hypothesis that ocean circulation links Northern and Southern Hemisphere climate changes on millennial timescales.
DE: 1040 Radiogenic isotope geochemistry
DE: 4532 General circulation (1218, 1222)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4924 Geochemical tracers
DE: 4938 Interhemispheric phasing
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005