HR: 0800h
AN: PP31B-0412    [Abstracts]
TI: Can d44Ca be a Proxy for Paleoceanography? - A Case Study of Globigerinoides Sacculifer from Western Equatorial Atlantic
AU: * Yang, S
EM: r94224204@ntu.edu.tw
AF: Institute of Earth Science, Academia Sinica, 128 Academia Road Sec. 2, Taipei, 115, Taiwan
AU: Wei, K
EM: weiky@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, 1 Rosveld Road Sec. 4, Taipei, 106, Taiwan
AU: Shen, J J
EM: mountain@earth.sinica.edu.tw
AF: Institute of Earth Science, Academia Sinica, 128 Academia Road Sec. 2, Taipei, 115, Taiwan
AB: The δ ⁴⁴Ca, δ ¹⁸O, and Mg/Ca ratios of fossil Globigerinoides sacculifer over the past 20 ka extracted from a Caribbean core, TT9108-1GC, have been measured in order to examine the possibility of using δ ⁴⁴Ca as a proxy for paleoceanography. Our results indicate that the δ ⁴⁴Ca of G. sacculifer varies as a function of sea surface temperature (SST) and sea surface salinity (SSS). The Caribbean Sea SSS, reconstructed by combining the δ ¹⁸O and Mg/Ca ratios of G. sacculifer and sea level change data, shows significant fluctuations between 36.5 and 39.5 psu during the last 20 ka. After isolating the temperature effect, the δ ⁴⁴Ca of G. sacculifer exhibits a positive correlation with SSS, ca 0.27±0.02 ‰ per 1 psu. On the other hand, no significant relationship is observed between δ ⁴⁴Ca and seawater [CO₃ ^-2]. Moreover, variation of G. sacculifer δ ⁴⁴Ca can also be explained using a Rayleigh fractionation model. As a function of temperature and salinity, the metabolic rate may influence the utilization of vacuole Ca⁺² in G. sacculifer, resulting in different δ ⁴⁴Ca values. The results of this study are inconsistent with the "rate-controlled fractionation model" of Lemarchand et al. (2004), instead, the results are more in-line with the foraminiferal biomineralization model of Erez (2003), where δ ⁴⁴Ca reflects the adjustments of temperature, salinity, and pH of seawater isolated in vacuoles during the growth of G. sacculifer.
DE: 0419 Biomineralization
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting