大洋有孔虫微量元素研究

The most novel aspect of this thesis is the combination analysis of the boron isotopes and trace elements. What’s more, it also provides a reliable analytical technique, which is suitable for both boron isotopes and trace elements. Al/Ca values can be used to monitor the clay removal during the sample preparation. It is found that when Al/Ca>100 mol/mol, the measured boron isotopic compositions are always several permil lower than those properly cleaned. B/Ca ratios can be used to calculate the exact boron loaded for each sample. Otherwise, too much loading will lead to too long time for the whole analytical sequence, and too less loading might incur serious blank problem. One other benefit besides those discussed above is that the combination analysis of boron isotopes and trace elements on the same sample allows reconstruction of the marine carbonate system and atmospheric pCO2 without assumption of the other parameter. In the marine carbonate system, with the seawater pH from the foraminiferal 11B, one has to make an assumption on the other variable to obtain the rest four variables. A series studies found that U/Ca and B/Ca are potential proxies for seawater [CO32-]and [HCO3-], respectively. Since they are measured on the same sample with boron isotopes, hence, there is no spatial or temporal ambiguity in the incorporation of the two controlling parameters. With 11B and U/Ca, the reconstructed atmospheric pCO2 variations match the atmospheric pCO2 record from the Vostok ice core within ±20 ppm. The incorporations of U and B into foraminiferal carbonates are controlled by the overall growth rate of individual foraminifers and other possible factors. The reliable application of these proxies still require further calibrations. In a similar fashion, the combination analysis of boron isotopes and Mg/Ca also has great advantages. Mg/Ca has been proved to be a reliable proxy for the surface seawater temperature. With the combination analysis, one can determine the phase between changes in atmospheric pCO2 and surface seawater temperature, thus explore the cause and mechanism of the changes in atmospheric pCO2. .