古海洋研究中的地球化学新指标

有机地球化学与微量元素地球化学古环境指标及其相关的同位素指标已成为追溯古全球变化与古海洋生物地球化学演化的有力工具。从古环境替代指标的示踪原理和应用的角度，综述了有孔虫碳同位素、有机地球化学整体指标、生物标志化合物、单体有机分子同位素、微量元素等在古海洋古环境研究中的应用及相关的研究动态与进展。指出古海洋研究正从以恢复古海洋的物理参数（温度、盐度、古洋流等）为主，向着揭示古水团演化、古生产力、古营养状况、碳贮库及碳循环等古生物地球化学演化过程方向纵深发展。

NEW GEOCHEMICAL PROXIES IN PALEOC- EANOGRAPHY STUDIES

Organic geochemistry and trace metal geochemistry provide a variety of indicators, or proxies, that can be used to reconstruct records of paleo-global changes as well as paleo-biogeochemical cycles. Here in this review paper the author introduces and outlines some important progresses in paleo-proxies on organic geochemistry and trace metal geochemistry with focusing on principals and applications of these proxies. Usually, the carbon isotope and oxygen isotope of foraminifera can simultaneously be analyzed, but few carbon isotope data were presented and interpreted, because we did not clearly know the mechanism of δ¹³C  fractionation during the formation of foraminifera. Recent researches show that δ¹³C fractionation of foraminifera growth depends on （ΣCO₂）δ¹³C  in the sea water, which is controlled by photosynthesis, decomposition of organic matter, air-sea exchanges and fresh water input. These progresses lead to the multiple applications of foraminifera δ¹³C  on estimating forest-vegetation area, indicating fresh water input during the transit of glacial to interglacial period, reflecting paleo-productivity, monitoring deep waters evolution etc. Organic matter constitutes a minor fraction of marine sediments, yet it is the residue of past biota, so the amounts and types of organic matter present in sediments consequently reflect different biota source of organic matter and environmental conditions that impacted ecosystems at different past time. These organic paleo-indicators include bulk parameters of organic geochemistry, molecular biomarkers, compound-specific δ¹³C_org etc. Generally, the sources of organic matter are inferred from bulk properties such as C/N, Rock-Eval pyrolysis index, bulk δ¹³C_org, δ¹⁵N_org etc., while details of specific organic matter origins are refined by analyses of molecular compositions. Source changes of organic matter reflect the fluctuations in oceanic environment such as sea level, currents and climates. Compound-specific carbon isotope analysis provides a powerful source of paleoenvironmental information. This analytical combination of gas chromatography and isotope ratio mass spectrometry offers ways to explore the origins of organic matter, the effects of diagenesis, and the types of depositional settings that neither bulk organic matter parameters nor traditional biomarker can individually provide. Following the enormous success of carbonate oxygen isotope paleoclimatology, several other tracers in calcareous micro-fossils have been explored. In particular, foraminiferal Cd/Ca was used as an indicator of past nutrient levels. With the development of geochemical analysis technology, paleoceanograpy will not only reconstruct physical parameter such as paleo-temperature and salinity, but also study paleo-biogeochemical proxies such as paleo-pH, paleo-nutrients, paleo-prodctivity, paleo-oxygen condition etc.