HR: 11:35h
AN: PP12B-06    [Abstracts]
TI: The Neodymium Isotopic Composition of Past North Atlantic Deep Water: First Results From Deep-Sea Corals
AU: * van de Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, 10964
AU: Robinson, L F
EM: laurar@gps.caltech.edu
AF: California Institute of Technology, MS100-23, 1200 E. California Boulevard, Pasadena, 91125
AU: Adkins, J F
EM: jess@gps.caltech.edu
AF: California Institute of Technology, MS100-23, 1200 E. California Boulevard, Pasadena, 91125
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, 10964
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, 10964
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, 10964
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, 10964
AB: Neodymium isotope ratios of marine authigenic phases are emerging as an important tracer for ocean circulation. However, our ability to use them to understand the role of thermohaline circulation in rapid climate change is hindered because we do not know how the Nd isotopic composition of North Atlantic Deep Water varied through time. North Atlantic ferromanganese crust records are consistent with little or no change, but their resolution is too coarse to be conclusive on glacial-interglacial time scales. On the other hand, the dispersed ferromanganese fraction in marine sediments shows great promise for continuous and high-resolution records, but most North Atlantic cores bear the problem of detrital contamination casting doubt on integrity of the seawater Nd signal. Thus in order to reliably determine the Nd isotopic composition of the North Atlantic endmember over the last glacial cycle, we need alternative archives. Here we present the first Nd isotope results on deep-sea corals, which can be precisely dated by U-series and are excellent archives of ocean history. The marine δ ²³⁴U and very low Th/U attainable in carefully cleaned samples make it a safe assumption that the Nd isotopes also reflect ambient seawater. We report data for 14 samples from the New England Seamounts in the North Atlantic. The investigated corals were recovered from 1100 to 2500 m water depth and yielded ages from modern to 92,000 years. A modern coral (318 yr) from the Gregg seamount at 1176 m water gave ε _Nd = -14.8 ± 0.4, in agreement with nearby seawater. Together with 4 other corals from intermediate water depths that grew during 11.6 - 12.7 kyr and 15.4 - 16.3 kyr, Nd isotopes trend toward slightly higher values in samples approaching the last glacial maximum (ε _{Nd = -13.1 at 16.3 kyr). Five deep water samples from the same time intervals also cover a narrow range of 2 ε units, ranging from -12.0 ± 0.3 to -13.5 ± 0.4. Four samples from various water depth between 1200 and 2400 m with ages of 50.2 kyr, 86.0 kyr, 89.7 kyr, and 91.9 kyr display a range in ε _Nd from -12.7 to -14.2. The striking conclusion from this preliminary dataset is that the Nd isotopic composition of the global endmember northern component intermediate to deep waters appears not to have changed significantly over the last glacial-interglacial cycle. This is important and encouraging news for further applications of Nd isotopes as a water mass and circulation tracer through time.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
DE: 4808 Chemical tracers
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005