大洋缺氧事件金属稳定同位素研究进展

Advances in Research on Stable Metal Isotopes in Oceanic Anoxic Events

白垩纪大洋缺氧事件记录了地球气候和古海洋环境的显著变化,是全球碳循环的主要扰动事件,受到了国内外学者的广泛关注。近20年来,随着金属稳定同位素测试技术的发展,越来越多的金属稳定同位素(例如钼同位素、锌同位素、铀同位素、铬同位素、镉同位素和钙同位素等)被用于研究大洋缺氧事件期间的环境变化。通过系统总结钼同位素(δ^(98)Mo)、锌同位素(δ^(66)Zn)和铀同位素(δ^(238)U)的地球化学性质以及在大洋缺氧事件中的研究进展,发现钼同位素主要用于指示局部海洋硫化和非硫化环境的转变过程;锌同位素多用于区分局部海洋对初级生产力、大陆风化以及沉积物埋藏/分解等过程的不同响应情况;铀同位素可以估算全球海底缺氧面积占海底总面积的比例,同时可以结合碳—磷—铀耦合模型模拟全球海洋对大火成岩省形成、大陆风化、生物活动等过程的响应机制。但目前这些金属稳定同位素在海洋体系中的循环分馏机制尚未完善,且研究对象主要聚焦于大洋缺氧事件OAE2的沉积记录,未来还需要更系统全面的研究。

Cretaceous Oceanic Anoxic Events(OAEs)have recorded significant changes in the climatic and paleoceanographic states of the planet and represent major carbon cycle perturbations.In the past two decades,analytical techniques for stable metal isotopes,such as molybdenum,zinc,uranium,chromium,cadmium,and calcium isotopes,have been developed to study OAEs.By systematically summarizing the geochemical characteristics of molybdenum isotopes(δ^(98)Mo),zinc isotopes(δ^(66)Zn),and uranium isotopes(δ^(238)U),and research advances on Cretaceous OAEs,we found that molybdenum isotopes mainly reflect the transformation between sulfide and non-sulfide in the regional marine environment during OAEs.Zinc isotopes can reflect different responses of regional marine environments to different processes,such as primary productivity,continental weathering,and sediment burial/decomposition.Uranium isotopes can be used to estimate the global extent of seafloor euxinia.The coupled global C-P-U cycle model can simulate the response mechanism of the global ocean to different processes,such as the formation of large igneous provinces,continental weathering,and biological activities.However,the cyclic fractionation mechanism of these isotopes in marine systems is still in progress,and most research has only focused on the deposition record of OAE2.In the future,it will be necessary to conduct more systematic research on OAEs.