10Be/9Be Ratios Reveal Marine Authigenic Clay Formation
10Be/9Be Ratios Reveal Marine Authigenic Clay Formation
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DOI：
10.1029/2019gl086061
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发表时间：
2020-02-28
影响因子：
5.2
通讯作者：
Wittmann, H.
中科院分区：
文献类型：
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作者：
Bernhardt, A.;Oelze, M.;Wittmann, H.
由于反向风化已被证明会影响大气中二氧化碳水平的长期变化，因此开发定量工具来重建海洋自生粘土的形成是至关重要的。我们探索了海洋粘土大小沉积物中记录的铍(Be)同位素比值(Be-10/Be-9)追踪自生粘土新形成的潜力。这种替代品的威力依赖于大陆Be和Be溶解在海水中的Be-10/Be-9比值的数量级差异。在沿智利边缘断面采集的海洋沉积物中，我们化学提取了反应相，并分离出粘土大小的组分，以比较该组分的河流和海洋Be-10/Be-9比值。从河流沉积物到海洋沉积物，Be-10/Be-9比值增加了4倍。我们将这一增长归因于溶解的生物蛋白石中Be-10/Be-9的高含量，这也是海洋自生粘土降水的硅源。因此，Be-10/Be-9比值可以灵敏地跟踪形成海洋自生粘土的逆风化反应。当粘土在海洋中形成时，二氧化碳就会释放出来。到目前为止，还没有一种方法可以轻松地测量海洋中形成的粘土矿物的数量。我们使用了同一元素的两个同位素铍(Be)，原子质量分别为9和10，以测试该同位素系统是否可以用于测量海相粘土的形成。这些同位素的丰度在陆地和海洋上有很大的不同。我们测量了智利近海河流沉积物和海底沉积物中的铍同位素，并比较了它们的比值(Be-10/Be-9)。与河流沉积物相比，海洋沉积物中的这一比例高出四倍。我们解释说，这种增长是由于海洋中粘土矿物的形成，其中包括形成过程中高的Be-10/Be-9比值。我们得出结论，铍同位素体系可以用来测量极少量(小于2%)的海相粘土矿物的形成。这一点很重要，因为粘土形成的化学反应会释放出对全球气候有长期影响的二氧化碳。
As reverse weathering has been shown to impact long-term changes in atmospheric CO2 levels, it is crucial to develop quantitative tools to reconstruct marine authigenic clay formation. We explored the potential of the beryllium (Be) isotope ratio (Be-10/Be-9) recorded in marine clay-sized sediment to track neoformation of authigenic clays. The power of such proxy relies on the orders-of-magnitude difference in Be-10/Be-9 ratios between continental Be and Be dissolved in seawater. On marine sediments collected along a Chilean margin transect we chemically extracted reactive phases and separated the clay-sized fraction to compare the riverine and marine Be-10/Be-9 ratio of this fraction. Be-10/Be-9 ratios increase fourfold from riverine to marine sediment. We attribute this increase to the incorporation of Be high in Be-10/Be-9 from dissolved biogenic opal, which also serves as a Si-source for the precipitation of marine authigenic clays. Be-10/Be-9 ratios thus sensitively track reverse-weathering reactions forming marine authigenic clays.Plain Language Summary Clay minerals can form on land by the chemical breakdown of rock-forming minerals, but clays can also form in the ocean. When clay formation takes place in the ocean, CO2 is released. To date, there is no method that can easily measure the amount of clay minerals formed in the ocean. We used two isotopes of the same element, beryllium (Be), with the atomic mass of 9 and 10 to test whether this isotope system can be used to measure marine clay formation. The abundance of these isotopes differs majorly on land and in the ocean. We measured beryllium isotopes in river sediment and ocean-bottom sediment offshore the Chile coast and compared the ratios of the isotopes (Be-10/Be-9). The ratio is four times higher in ocean sediment, when compared to river sediment. We interpret this increase to be due to the formation of clay minerals in the ocean, which include the high Be-10/Be-9 ratio during their formation. We conclude that the beryllium-isotope system can be used to measure the formation of even very small amounts (less than 2%) of marine clay minerals. This is important, as the clay-forming chemical reactions release CO2 which has a long-term effect on global climate.