The marine carbon cycle has a central role in biogeochemical cycling and a close interaction with the climate system. Here, we use the stable carbon isotope (δ13C) of particulate inorganic carbon (PIC) and particulate organic carbon (POC) in marine particles to diagnose carbonate dissolution and organic matter respiration processes in the ocean water column. We show PIC dissolution both in the euphotic zone, potentially driven by POC remineralization, and a preferential dissolution of coccoliths compared to foraminifera below the saturation horizon in the water column. Within the oxygen deficient zone (ODZ), POC remineralization and consequent respiration-driven PIC dissolution are both significantly diminished. We also demonstrate that POC remineralization preferentially removes a 13C-enriched component compared to isotopically-light bulk POC in both the large size fraction (LSF, > 51μ m) and small size fraction (SSF, 0.5 – 51μ m) of the pump particles, but exhibits a greater impact on the large particles because of its smaller inventory. Simultaneously, addition of a 13C-enriched heterotrophic or chemoautotrophic component to the SSF further increases the isotopic offset between SSF and LSF POC. Overall, this study uses δ13C to provide novel evidence for different biogeochemical processes in marine particles, and demonstrates carbonate dissolution in the ocean water column, both driven by bulk seawater chemistry and organic matter respiration within particles. The absence of O2 in the ODZ likely protects carbonate from dissolving by severely limiting organic matter respiration, thus reducing shallow PIC dissolution within the ODZs.

中文翻译：

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基于无机和有机稳定同位素的海洋颗粒中的碳循环


海洋碳循环在生物地球化学循环中起着核心作用，并与气候系统密切相关。在这里，我们使用颗粒物无机碳 （PIC） 和颗粒有机碳 （POC） 的稳定碳同位素 （δ13C） 来诊断海水柱中的碳酸盐溶解和有机物呼吸过程。我们显示了 PIC 在真光区的溶解，这可能是由 POC 再矿化驱动的，与水柱中饱和水平以下的有孔虫相比，球石的优先溶解。在缺氧区 （ODZ） 内，POC 再矿化和随之而来的呼吸驱动的 PIC 溶解都显着减少。我们还证明，与同位素轻体 POC 相比，POC 再矿化优先去除泵颗粒的大尺寸分数（LSF，> 51μ m）和小尺寸分数（SSF，0.5 – 51μ m）中富含 13C 的成分，但由于其库存较小，对大颗粒的影响更大。同时，向 SSF 中添加富含 13 C 的异养或化学自养成分进一步增加了 SSF 和 LSF POC 之间的同位素偏移。总体而言，本研究使用 δ13C 为海洋颗粒中的不同生物地球化学过程提供新证据，并证明了碳酸盐在海水柱中的溶解，这两者都是由大量海水化学和颗粒内的有机物呼吸驱动的。ODZ 中不存在 O2 可能通过严重限制有机物呼吸来保护碳酸盐不溶解，从而减少 ODZ 内的浅层 PIC 溶解。