Neogene burial of organic carbon in the global ocean

The global rate of OC burial is conventionally established by using the mass balance between inorganic and organic carbon, each with distinct isotopic values (δ¹³C). However, this method is complicated by major uncertainties associated with some key parameters. Here we report a “bottom up” approach independent from mass balance calculations, by using data from 81 globally distributed IODP/ODP/DSDP sites covering all major ocean basins and sedimentary environments, to establish regional and global history of OC burial over the Neogene (~23 – 3 million years ago). Our results show large spatiotemporal variability of OC burial, suggesting that it plays a much more important role in regulating the carbon cycle than previously thought. Globally, the burial was higher towards the early Miocene and Pliocene, but lowest during the mid-Miocene.The enriched carbonate δ¹³C during the mid-Miocene is more likely related to shifts to a volcanic-dominated source of carbon into the Earth’s surficial system,which turns the interpretation of OC burial during the Miocene on its head and demands a reconsideration of the Monterey Hypothesis and the necessity to rethink some of the fundamentals of the global carbon cycle.

有机碳（Organic Carbon, OC）埋藏的全球速率，传统上通过无机碳与有机碳之间的质量平衡法确定，二者各自具有独特的同位素数值（δ¹³C）。然而，该方法受限于若干关键参数带来的显著不确定性，流程较为复杂。本研究提出一种独立于质量平衡计算的"自下而上"研究方法：利用全球分布的81个综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）、大洋钻探计划（Ocean Drilling Program, ODP）与深海钻探计划（Deep Sea Drilling Project, DSDP）站位数据，这些站位覆盖了所有主要大洋盆地与沉积环境，以此重建新近纪（Neogene，约2300万至300万年前）有机碳埋藏的区域与全球历史。研究结果显示，有机碳埋藏具有显著的时空变异性，表明其在调控全球碳循环中的作用远高于此前认知。全球范围内，有机碳埋藏速率在中新世早期与上新世时期较高，而在中新世中期达到最低值。中新世中期碳酸盐岩δ¹³C值偏高，更可能与地球地表系统碳源向火山主导型转变相关，这一结论彻底颠覆了此前对中新世有机碳埋藏的认知，要求重新审视蒙特雷假说（Monterey Hypothesis），并重新思考全球碳循环的若干基础理论。