Abstract Dark carbon fixation (DCF) by chemoautotrophic microorganisms can sustain food webs in the seafloor by local production of organic matter independent of photosynthesis. The process has received considerable attention in deep sea systems, such as hydrothermal vents, but the regulation, depth distribution, and global importance of coastal sedimentary DCF have not been systematically investigated. Here we surveyed eight coastal sediments by means of stable isotope probing (13C‐DIC) combined with bacterial biomarkers (phospholipid‐derived fatty acids) and compiled additional rates from literature into a global database. DCF rates in coastal sediments range from 0.07 to 36.30 mmol C m−2 day−1, and there is a linear relation between DCF and water depth. The CO2 fixation ratio (DCF/CO2 respired) also shows a trend with water depth, decreasing from 0.09 in nearshore environments to 0.04 in continental shelf sediments. Five types of depth distributions of chemoautotrophic activity are identified based on the mode of pore water transport (advective, bioturbated, and diffusive) and the dominant pathway of microbial sulfur oxidation. Extrapolated to the global coastal ocean, we estimate a DCF rate of 0.04 to 0.06 Pg C year−1, which is less than previous estimates based on indirect measurements (0.15 Pg C year−1), but remains substantially higher than the global DCF rate at deep sea hydrothermal vents (0.001–0.002 Pg C year−1).

中文翻译：

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沿海沉积物中暗碳固定的跨系统比较


摘要：化能自养微生物的暗碳固定（DCF）可以通过不依赖于光合作用的局部有机物生产来维持海底的食物网。该过程在深海系统（例如热液喷口）中受到了相当多的关注，但沿海沉积 DCF 的调节、深度分布和全球重要性尚未得到系统研究。在这里，我们通过稳定同位素探测 (13C-DIC) 结合细菌生物标志物（磷脂衍生脂肪酸）对八个沿海沉积物进行了调查，并将文献中的其他比率编译到全球数据库中。沿海沉积物中的 DCF 率范围为 0.07 至 36.30 mmol C m−2 day−1，DCF 与水深之间存在线性关系。 CO2固定比（DCF/呼吸CO2）也呈现出随水深变化的趋势，从近岸环境中的0.09下降到大陆架沉积物中的0.04。根据孔隙水输送模式（平流、生物扰动和扩散）和微生物硫氧化的主要途径，确定了化学自养活性的五种深度分布。外推到全球沿海海洋，我们估计 DCF 率为 0.04 至 0.06 Pg Cyear−1，低于之前基于间接测量的估计值（0.15 Pg Cyear−1），但仍远高于全球 DCF 率在深海热液喷口（0.001–0.002 Pg C 年−1）。