Reevaluating the carbon sink due to sedimentary carbonate formation in modern marine sediments
Reevaluating the carbon sink due to sedimentary carbonate formation in modern marine sediments
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DOI：
10.1016/j.epsl.2019.04.044
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发表时间：
2019-08-01
影响因子：
5.3
通讯作者：
Turchyn, Alexandra, V
中科院分区：
文献类型：
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作者：
Bradbury, Harold J.;Turchyn, Alexandra, V
以前量化现代海洋沉积物中沉积碳酸盐沉淀量的尝试，是通过假设稳态下由于扩散而进入沉积物的钙通量，应用菲克第一定律，然后将这些特定地点的速率外推到全球海洋沉积物柱中。然而，这种方法是有限的，因为大部分海底还没有采样。我们采用机器学习方法来更新和完善沉积碳酸盐降水的估计，并定义沉积碳酸盐降水是由有机碎屑微生物硫酸盐还原还是厌氧甲烷氧化驱动的。我们根据海洋的物理和化学性质，包括水深、温度、水深、离海岸的距离、初级生产的示踪剂，以及全球ODP/IODP数据库的数据，利用机器学习来识别沉积碳酸盐岩地层的区域。我们的研究结果表明，沉积碳酸盐岩地层的总量远低于之前的估计，为1.35 +/- 0.5 x 10(11) mol C/yr。我们认为这个比率是一个较低的估计，并讨论了为什么机器学习方法可能总是产生全局过程的下限估计。我们的计算表明，今天沉积碳酸盐的形成主要是由厌氧甲烷氧化（77%）驱动的，其余归因于有机碎屑硫酸盐还原。我们使用我们的机器学习结果来推测沉积碳酸盐降水可能对地球历史上表面溶解无机碳储层的碳同位素组成产生的影响。(C) 2019 Elsevier B.V.版权所有
Previous attempts to quantify the amount of sedimentary carbonate precipitation in modern marine sediments have been derived from the flux of calcium into the sediments due to diffusion under assumed steady state, the application of Fick's first law, and then extrapolation of these site-specific rates to the global ocean sediment column. This approach is limited, however, as much of the ocean floor has not been sampled. We take a machine learning approach to update and refine the estimate of the amount of sedimentary carbonate precipitation, as well as define whether sedimentary carbonate precipitation is driven by organoclastic microbial sulfate reduction or anaerobic methane oxidation. We identify areas where there is sedimentary carbonate formation using machine learning, based upon oceanic physical and chemical properties including bathymetry, temperature, water depth, distance from shore, and tracers of primary production, and data from the global ODP/IODP database. Our results suggest that the total amount of sedimentary carbonate formation is much lower than previous estimates, at 1.35 +/- 0.5 x 10(11) mol C/yr. We suggest that this rate is a lower estimate and discuss why machine-learning approaches may always produce lower-bound estimates of global processes. Our calculations suggest that the formation of sedimentary carbonate today is mainly driven by anaerobic methane oxidation (77%), with the remainder attributed to organoclastic sulfate reduction. We use our machine-learning results to speculate the impact that sedimentary carbonate precipitation may have had on the carbon isotope composition of the surface dissolved inorganic carbon reservoir over Earth history. (C) 2019 Elsevier B.V. All rights reserved.