沉积物单/多壳体底栖有孔虫稳定氧碳同位素组成、比较及其指示意义

SINGLE/MULTI-SHELL BENTHIC FORAMINIFERAL STABLE OXYGEN AND CARBON ISOTOPIC COMPOSITION,DIFFERENCE AND ITS SIGNIFICANCE

提要底栖有孔虫壳体稳定氧碳同位素在古海洋学研究中发挥了重要作用,获得可靠的稳定氧碳同位素数据是研究的关键。但同位素数据的精度通常受有孔虫属种个体差异的影响,用多少壳体进行测试可忽略个体差异带来的影响是个值得研究的问题。本研究对位于葡萄牙岸外的IODP U1391站位顶部~10 m岩心的多个沉积物样品中的底栖有孔虫Uvigerina mediterranea,Cibicidoides pachyderma,Cibicidoides wuellerstorfi和Uvigerina peregrina parva进行单个和多个壳体的稳定氧碳同位素测试。测试结果显示,U.mediterranea个体间δ13C差异高达0.74‰,而δ18O相对稳定,差异不超过0.26‰。C.pachyderma和C.wuellerstorfi则与之相反,两属种的个体间δ13C差异分别不超过0.20‰和0.23‰,而个体间δ18O差异分别高达0.76‰和0.60‰。生命效应、微生境异质性和底层水环境变化可能是造成个体差异的主要因素。以U.peregrina parva为例,用6枚壳体进行测试可以显著降低这些因素对稳定氧碳同位素尤其是对δ13C的干扰。用4枚C.pachyderma或C.wuellerstorfi壳体可以保证获得较为稳定可靠的δ18O值。

Benthic foraminiferal stable oxygen and carbon isotopes play an important role in paleoceanographic studies,so obtaining reliable stable isotopes is the key.The precision of isotopic data is often affected by differences among foraminiferal individuals.It is worth investigating how many tests used can ignore the effects of individual differences.In this study,benthic foraminifera Uvigerina mediterranea,Uvigerina peregrina parva,Cibicidoides pachyderma and Cibicidoides wuellerstorfi picked from the top~10 m-long sucession of IODP U1391 drilled off the Portuguese margin were used for single-shell and multi-shell stable oxygen and carbon isotope measurements.The results show thatδ13C varied up to 0.74‰among individuals of Uvigerina mediterranea,whileδ18O was relatively stable with differences less than 0.26‰.For Cibicidoides pachyderma and Cibicidoides wuellerstorfi,the situation was reversed.Theδ13C differences among individuals of the two species did not exceed 0.20‰and 0.23‰,respectively,while the differences inδ18O were as high as 0.76‰and 0.60‰,respectively.Vital effect,microenvironmental heterogeneity and bottom water environmental changes may be the main factors responsible for individual isotopic differences.Taking Uvigerina peregrina parva as an example,the measurement with six shells could reduce the effect of these factors on stable oxygen and carbon isotopes,especiallyδ13C.Four shells of Cibicidoides pachyderma or Cibicidoides wuellerstorfi measured could produce stable and reliableδ18O data.