NEW GEOCHEMICAL PROXIES IN PALEOC-EANOGRAPHY STUDIES
CHEN Jian fang 1,2 (1.Key Lab of Submarine Geosciences, Second Institute of Oceanography, SOA, Hangzhou 310012,China; 2.Laboratory of Marine Geology of MOE,Tongji University, Shanghai 200092,China)
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 δ 13 C fractionation during the formation of foraminifera. Recent researches show that δ 13 C fractionation of foraminifera growth depends on (ΣCO 2)δ 13 C 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 δ 13 C 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 δ 13 Corg etc. Generally, the sources of organic matter are inferred from bulk properties such as C/N, Rock Eval pyrolysis index, bulk δ 13 Corg, δ 15 N 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.
【Fund】： 国家重点基础研究发展规划项目“地球圈层相互作用中的深海过程和深海记录”(编号 :G2 0 0 0 0 785 0 0 );; 国家自然科学基金项目“UK37古温度估算的水柱校正”(编号 :40 10 60 0 4)资助
【CateGory Index】： P734
【CateGory Index】： P734