Global synchronous changes in the carbon isotopic composition of carbonate sediments unrelated to changes in the global carbon cycle
Global synchronous changes in the carbon isotopic composition of carbonate sediments unrelated to changes in the global carbon cycle
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DOI：
10.1073/pnas.0802841105
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发表时间：
2008-09
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影响因子：
--
通讯作者：
P. Swart
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作者：
P. Swart
在巴哈马、马尔代夫、昆士兰高原和大澳湾四个碳酸盐台地/斜坡体系边缘沉积的散体碳酸盐沉积物的碳同位素(δ13C)组成在过去0-1000万年间显示出同步变化。然而，这些变化与在同一时间段在公海测量的δ13C的既定全球模式不同。例如，从10 Ma到现在，开阔大洋碳酸盐的δ~(13)C呈下降趋势，而台地边缘沉积物则呈上升趋势。结果表明，台地边缘沉积物中的δ13C模式是富含文石的沉积物与δ13C值较低的远洋物质混合而形成的。由于更具同位素正值的浅水碳酸盐沉积物只有在平台被淹没时才会产生，因此全球海平面的变化与边缘环境中沉积物的δ13C之间存在联系。这些数据表明，δ13C的全球同步变化可以发生，与全球碳循环的变化完全无关。在以前的地质时期测量的碳酸盐沉积物δ13C的波动也可能受到类似过程的影响，δ13C的全球同步性不再一定被认为是这种变化与有机碳埋藏变化有关或由其引起的指标。关于从δ13C记录中得出的有机碳循环变化的解释的推论，应该根据这里提出的发现重新考虑。
The carbon isotopic (δ13C) composition of bulk carbonate sediments deposited off the margins of four carbonate platforms/ramp systems (Bahamas, Maldives, Queensland Plateau, and Great Australian Bight) show synchronous changes over the past 0 to 10 million years. However, these variations are different from the established global pattern in the δ13C measured in the open oceans over the same time period. For example, from 10 Ma to the present, the δ13C of open oceanic carbonate has decreased, whereas platform margin sediments analyzed here show an increase. It is suggested that the δ13C patterns in the marginal platform deposits are produced through admixing of aragonite-rich sediments, which have relatively positive δ13C values, with pelagic materials, which have lower δ13C values. As the more isotopically positive shallow-water carbonate sediments are only produced when the platforms are flooded, there is a connection between changes in global sea level and the δ13C of sediments in marginal settings. These data indicate that globally synchronous changes in δ13C can take place that are completely unrelated to variations in the global carbon cycle. Fluctuations in the δ13C of carbonate sediments measured during previous geological periods may also be subject to similar processes, and global synchroniety of δ13C can no longer necessarily be considered an indicator that such changes are related to, or caused by, variations in the burial of organic carbon. Inferences regarding the interpretation of changes in the cycling of organic carbon derived from δ13C records should be reconsidered in light of the findings presented here.