Advances in Earth Science ›› 2002, Vol. 17 ›› Issue (3): 402-410. doi: 10.11867/j.issn.1001-8166.2002.03.0402

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NEW GEOCHEMICAL PROXIES IN PALEOC-EANOGRAPHY STUDIES 

CHEN Jian-fang 1,2   

  1. 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
  • Received:2001-04-23 Revised:2001-07-06 Online:2002-12-20 Published:2002-06-01

CHEN Jian-fang. NEW GEOCHEMICAL PROXIES IN PALEOC-EANOGRAPHY STUDIES [J]. Advances in Earth Science, 2002, 17(3): 402-410.

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 δ13Corg etc. Generally, the sources of organic matter are inferred from bulk properties such as C/N, Rock-Eval pyrolysis index, bulk δ13Corg, δ15Norg 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.

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