Iodine to calcium ratios in marine carbonate as a paleo-redox proxy during oceanic anoxic events
Iodine to calcium ratios in marine carbonate as a paleo-redox proxy during oceanic anoxic events
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DOI：
10.1130/g31145.1
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发表时间：
2010-12-01
期刊：
影响因子：
5.8
通讯作者：
Rickaby, Rosalind E. M.
中科院分区：
文献类型：
--
作者：
Lu, Zunli;Jenkyns, Hugh C.;Rickaby, Rosalind E. M.
在中生代地质记录中已经确认了全球分布的极端缺氧时期，即所谓的海洋缺氧事件（OAE），并且似乎是极端温暖时期的特征。在这里，我们探讨了应用碘/钙比（I/Ca）在海洋碳酸盐作为一个新的地球化学指标，以限制海水氧化还原变化，并提供额外的见解海洋化学响应古代气候变暖。碘是一种氧化还原敏感的亲生物元素，在海水中主要以碘酸盐和碘化物的形式存在，碘酸盐在缺氧条件下转化为碘化物。实验室实验从掺有碘酸盐的溶液中生长方解石晶体表明，这是结合到碳酸盐结构中的离子种类，可能取代CO（3）（2-）离子。在早期Toarcian和Cenomanian-Turonian OAE期间，在浅水中由海洋钙化物形成的碳酸盐中测量的I/Ca比的下降被解释为对海洋沃茨中碘酸盐/碘化物比下降和加速有机物埋藏条件下全球碘库存下降的响应。结果表明，在碳酸盐中的I/Ca比可用于监测整个地球历史的海水氧化水平。
Periods of globally distributed extreme oxygen depletion, so-called oceanic anoxic events (OAEs), have been recognized in the Mesozoic geological record and appear to be characteristic of episodes of extreme warmth. Here we explore the application of iodine/calcium ratios (I/Ca) in marine carbonate as a new geochemical proxy to constrain seawater redox change, and provide additional insights into the response of ocean chemistry to ancient climatic warming. Iodine has long been known as a redox-sensitive and biophilic element, mainly present as iodate and iodide in seawater, iodate converting to iodide under anoxic conditions. Laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure, likely substituting for the CO(3)(2-)ion. A fall in the I/Ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early Toarcian and Cenomanian-Turonian OAEs is interpreted both as a response to a decrease in the iodate/iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic-matter burial. The results suggest that I/Ca ratios in carbonates may be used to monitor seawater oxidation levels throughout Earth history.