Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes
Significant increases in global weathering during Oceanic Anoxic Events 1a and 2 indicated by calcium isotopes
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DOI：
10.1016/j.epsl.2011.06.029
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发表时间：
2011-09-01
影响因子：
5.3
通讯作者：
Henderson, Gideon M.
中科院分区：
文献类型：
--
作者：
Blaettler, Clara L.;Jenkyns, Hugh C.;Henderson, Gideon M.
测定了大洋缺氧事件1a(阿普提亚早期)和海洋缺氧事件2(塞诺曼-都罗纪)期间沉积的富碳酸盐沉积剖面的钙同位素比值(Ca-44/42)。在中太平洋山脉的Resolve Guyot、意大利的科皮特拉和英国伊斯特本和南费里比的英国白垩纪的剖面中，观察到这两个事件的Ca-44/42三角洲的负漂移类似于千分之0.20和类似于0.10%。这些三角洲Ca-44/42漂移与定义事件的碳同位素漂移发生在同一地层水平，但与碳酸盐溶解或岩性变化的证据无关。成岩作用和温度对钙同位素比值的影响可以忽略不计，全球海水组成的变化是四个不同碳酸盐剖面中三角洲Ca-44/42变化的最可能解释。一个具有锶和钙同位素耦合系统的海洋盒子模型表明，全球风化作用的增加很可能是钙同位素比率瞬时漂移的主要驱动因素。该模型表明，热液活动和碳酸盐溶解的贡献太小和太短暂，不能对海洋钙库产生可测量的影响。模拟的风化通量增加约为现代通量的三倍，再加上由于Ontong-Java高原(OAE1a)和加勒比高原(OAE2)的形成而导致的热液活动增加，可以产生与碳酸盐部分中记录的信号相匹配的钙和锶同位素的趋势。这项研究首次记录了大洋缺氧事件的风化响应。(C)2011爱思唯尔B.V.保留所有权利。
Calcium-isotope ratios (delta Ca-44/42) were measured in carbonate-rich sedimentary sections deposited during Oceanic Anoxic Events 1a (Early Aptian) and 2 (Cenomanian-Turonian). In sections from Resolution Guyot, Mid-Pacific Mountains; Coppitella, Italy; and the English Chalk at Eastbourne and South Ferriby, UK, a negative excursion in delta Ca-44/42 of similar to 0.20 parts per thousand and similar to 0.10% is observed for the two events. These delta Ca-44/42 excursions occur at the same stratigraphic level as the carbon-isotope excursions that define the events, but do not correlate with evidence for carbonate dissolution or lithological changes. Diagenetic and temperature effects on the calcium-isotope ratios can be discounted, leaving changes in global seawater composition as the most probable explanation for delta Ca-44/42 changes in four different carbonate sections. An oceanic box model with coupled strontium- and calcium-isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium-isotope ratios. The model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short-lived to affect the oceanic calcium reservoir measurably. A modelled increase in weathering flux, on the order of three times the modern flux, combined with increased hydrothermal activity due to formation of the Ontong-Java Plateau (OAE1a) and Caribbean Plateau (OAE2), can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections. This study presents the first major-element record of a weathering response to Oceanic Anoxic Events. (C) 2011 Elsevier B.V. All rights reserved.