浮游有孔虫个体大小对硼同位素分析的影响

The influence of the size of marine planktonic foraminifers on the boron isotopic analysis

对比分析了太平洋(Site 806)、大西洋(Site 664)和加勒比海地区(Site 999)末次冰期最盛期和全新世钻孔顶部不同尺寸大小的浮游有孔虫Globigerinoides sacculifer(500～600μm和300～355μm)和Globi-gerinoides ruber(300～355μm和250～300μm)的硼同位素组分变化,发现个体相对较小的有孔虫样品由于受到样品量以及样品前处理过程的影响,其硼同位素在末次冰期最盛期出现异常,浮游有孔虫硼同位素分析,尤其是冰期-间冰期时间尺度上的硼同位素分析,适合用个体相对较大的有孔虫。末次冰期最盛期太平洋和加勒比海地区溶解作用可能加强,其G.sacculifer的硼同位素偏低,但G.ruber的硼同位素不受溶解作用的影响,能够反映末次冰期海水pH值的变化。三个钻孔末次冰期最盛期G.ruber的硼同位素比全新世的硼同位素平均高(1.3±1.2)‰(2s.e.),与理论预测值1.6‰一致。

We have measured the boron isotopic compositions in marine planktonic foraminifers Globigerinoides sacculifer （500-600 μm and 300-355 μm） and Globigerinoides ruber （300-355 μm and 250-300 μm） from three tropical ODP sites （Pacific Site 806, Atlantic Site 664 and Carribean Sea Site 999） during the last glacial maximum and the Holocene. Due to the limits of available sample amounts and unexpected boron loss during sample preparation, boron isotopic compositions of small size foraminifers are susceptible and large size foraminifers are better to be used for boron isotopic analysis, especially on glacial-interglacial timescales, Because of the possible enhanced dissolution effects during the last glacial maximum, δ^11 B in G. sacculifer from both Site 806 and Site 999 are much lower than the expected values. Whereas δ^11B in G. ruber are free of the dissolution effects, and can record the changes of seawater pH. The δ^11B in G. tuber from the three sites during the last glacial maximum is averagely （1.3±1.2）‰（2 s. e. ） higher than the Holocene values and comparable to the theoretical values （1.6 ‰）.