HR: 0800h
AN: PP31B-0423    [Abstracts]
TI: Assessing the potential of paired Mg/Ca and d18O to resolve millennial-scale SST variability in the Holocene North Atlantic
AU: * Almasi, P
EM: palmasi@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, Rt 9W, Palisades, NY 10964, United States
AB: The potential of paired Mg/Ca and d18O measurements to resolve 1-2 C SST variability in the Holocene North Atlantic was evaluated in G. bulloides and N. pachyderma (d). Mg/Ca and d18O were measured in core-top samples, down-core series from nearby cores, and across the faunally-defined Younger Dryas/Pre-Boreal climate transition. Both oxidative and reductive cleaning steps were necessary for acceptable picked replicate reproducibility (3.15%). Mg/Ca and d18O were measured in G. bulloides and N. pachyderma (d.) samples from 7 core tops containing post-1950 radiocarbon located across a modern 4 C SST gradient. An exponential fit to Mg/Ca vs. d18O-derived calcification temperature for G. bulloides yielded the relation Mg/Ca=0.93±0.15e(0.07±0.01T). Mg/Ca from N. pachyderma (d.) did not show a relation to calcification temperature in these core top samples, an unexpected result given the comparable d18O measured for each species. This result may reflect sample dissolution during intense trace metal cleaning procedures. Mg/Ca and d18O measurements from G. bulloides from 800-14000 BP were compared between two cores located 68 km apart on the Reykjanes Ridge. While d18O is comparable between the two cores, baseline Mg/Ca from core V23-43 is on average 30% higher than in samples from adjacent core KN158-4-63GGC. Plotting independently calculated Mg/Ca and d18O calcification temperatures along a 1:1 line for both cores shows agreement within 1.5 C (1 sigma) for KN158-4-63GGC, but unrealistically high Mg/Ca-derived temperature for V23-43. The elevated Mg/Ca in V23-43 is reproducible and unlikely a result of contamination. To assess the Mg/Ca-temperature relations across abrupt climate changes that cause large shifts in faunal abundance, down-core Mg/Ca measurements from G. bulloides were compared with lithic grain and faunal assemblage counts during the YD/Pre-boreal transition. Faunal and lithic counts clearly resolve the YD interval in both cores, while Mg/Ca does not. This suggests Mg/Ca from a single species is not a reliable indicator of ocean temperature across climate transitions associated with large shifts in species relative abundance. These comparisons indicate that while existing calibrations may suggest robust Mg/Ca-temperature relation, they do not address all sources of variability in down-core records.
DE: 4870 Stable isotopes (0454, 1041)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting