| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 95 === The δ44Ca, δ18O, and Mg/Ca ratios of fossil G. sacculifer over the past 20 ka extracted from a Caribbean core, TT9108-1GC, have been measured in order to examine the possibility of using δ44Ca as a proxy for paleoceanography. Our results indicate that the δ44Ca 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 δ18O 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 δ44Ca 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 δ44Ca and seawater [CO3=]. Moreover, variation of G. sacculifer δ44Ca 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++ in G. sacculifer, resulting in different δ44Ca 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 δ44Ca reflects the adjustments of temperature, salinity, and pH of seawater isolated in vacuoles during the growth of G. sacculifer.
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