大洋缺氧事件的碳稳定同位素响应

从碳稳定同位素组成及其分馏机理出发 ,系统探讨了大洋缺氧事件与海相碳酸盐和有机碳稳定同位素分馏之间的关系。缺氧事件期间 ,由于生物大批死亡和快速埋藏 ,其分解消耗海水中大量的溶解氧 ,引起大洋水体缺氧 ,富含 1 2 C的有机质从而得以大量保存 ;相应地大气和海水中富 1 3 C,同期海相碳酸盐岩碳同位素 δ值 (δ1 3C)正偏。在世界各地缺氧事件层内 ,无一例外地碳酸盐岩碳稳定同位素出现了不同程度的正偏 ,Cenomanian- Turonian 界线偏幅达～2‰。海相碳酸盐与有机质碳稳定同位素变化不仅可以提供地质历史中有机碳埋藏量的记录。研究全球碳循环变化 ,还可能追溯有机碳风化和埋藏速率的变化 ,定性地恢复大气 p CO2 变化。

STABLE CARBON ISOTOPE RESPONSE TO OCEANIC ANOXIC EVENTS

Based on discussion of isotope compositions and fractio nations of mari ne carbonate and organic carbon, this paper studies the relationship between oce anic anoxic events and changes in the carbon isotope fractionation of both c arbo nate and organic matter. During the oceanic anoxic events, a great number of o rg anisms were rapidly buried, which caused a kind of anoxic conditions by their decomposition consuming dissolved oxygen. Since 12C-rich organ ism preserv ed, atmosphere-ocean system will enrich relatively of 13C. As a resul t, simultan eous marine carbonate will record the positive excursion of carbon isotope. Ther e is a distinctive δ13C excursion during oceanic anoxic events in the world thro ughout the geological time. In the Cenomanian-Turonian anoxic event, this p ositive exc ursion arrived at ～2‰ of marine carbonate and at ～4‰ of organic matter, respec tively. Variations in the carbon isotopic compositions of marine carbonate and o rganic carbon record the changes in the fraction of organic carbon buri ed throughout the geological time and may provide clues to the changes in ra tes of weathering and burial of organic carbon. This will provide a possibility of interpreting not onl y the changes in the global carbon cycle throughout the geological time, but als o that in atmospheric pCO2.