HR: 0800h
AN: PP21B-1564    [Abstracts]
TI: Relationships between Deep Ocean Circulation and Carbonate Preservation in the South Atlantic
AU: * Zylberberg, D R
EM: davidz@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 64 Route 9W, Palisades, NY 10964 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 64 Route 9W, Palisades, NY 10964 United States
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 64 Route 9W, Palisades, NY 10964 United States
AU: Piotrowski, A M
EM: apio04@esc.cam.ac.uk
AF: University of Cambridge Department of Earth Sciences, Downing Street, Cambridge, CB2 3EQ United Kingdom
AB: The concentration of carbonate in deep sea sediment is controlled by multiple factors including carbonate production in the surface ocean, water column dissolution, post-depositional preservation, and dilution by non-carbonate phases. Cape Basin cores from very deep sites TNO57-21(41°S, 10°E, 4981m) and ODP Site 1089, (41°S, 8°E, 4621m) have been interpreted to show a ``Pacific-type'' carbonate abundance pattern on Milankovich timescales, with peaks of maximum carbonate at deglacial terminations and minimum carbonate at glacial inceptions (Hodell 2001, EPSL). These workers have suggested that the high variability (>50%) mainly reflects carbonate preservation and dissolution at glacial terminations and inceptions respectively. In contrast, the nearby and shallower Site 1090 (43°S, 9°E, 3702m) exhibits an ``Atlantic-type'' pattern of greater carbonate preservation during interglacials and reduced preservation during glacial periods. The opposing trends of carbonate variability at sites 1089 and 1090 indicate that productivity is a minor factor in controlling the carbonate records. Alternative controls include variation in sedimentation rates of diluting phases and changes in deep ocean circulation. The importance of deep ocean circulation changes in carbonate preservation can be evaluated by directly comparing the carbonate record to paleo-circulation proxies from the same core. The Nd isotope ratios of the leachable Fe-Mn oxide component of TNO57-21 reflect changes in the relative balance of NADW and CDW overlying the core site (Piotrowski et al. 2004, EPSL and 2005, Science). Site 1089 and its companion core, TNO57-21, currently abut the boundary between North Atlantic Deep Water (NADW) and CaCO₃ under-saturated, corrosive Circumpolar Deep Water (CDW). The high sedimentation rate of these cores allows comparison of millennial-scale Nd isotope and carbonate preservation records. On millennial timescales the patterns of percent carbonate and Nd isotope variability are strongly correlated, and can be interpreted to indicate more carbonate dissolution during periods of weaker NADW flux to the deep Cape Basin compared to periods of stronger NADW influence. This short-wavelength signal is overprinted upon the long-wavelength glacial-interglacial variability. Thus, while the larger magnitude, glacial-interglacial variability in percent carbonate is controlled by variations in the carbonate saturation of Pacific waters, the correlation with Nd isotopes implies that the rapid variability at millennial timescales reflects changes in meridional overturning circulation.
DE: 1040 Radiogenic isotope geochemistry
DE: 4283 Water masses
DE: 4806 Carbon cycling (0428)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005