近日，美国佛罗里达州立大学Heather J. Forrer团队研究了下沉海洋有机质的分子水平成岩时钟。相关论文于2025年11月24日发表在《美国科学院院刊》杂志上。

海洋生物碳泵由沉降颗粒有机物（POM）驱动。沉降速率和再矿化速率决定了中层带的通量衰减。由于所有海洋有机物的最终归宿要么是完全矿化，要么转化为更稳定的产物，因此成岩作用的改变会影响大气二氧化碳的封存时间。

为探究颗粒物在分子层面的转化过程，研究组采用超高分辨率质谱技术，对主导生物地球化学环境中沉降颗粒物的水溶性有机质（WEOM）组分进行表征。结果发现，在从沿岸上升流到寡营养条件的生产力梯度上，有机物的分子层面氮含量和转化程度（即“稳定性”）呈现出显著的负相关关系。在沿岸上升流区域观察到氮富集和低稳定性，且这一特征持续到400米以下水深。此外，碳通量与稳定WEOM（“稳定岛”分子式）的相对丰度在不同生产力区域和深度间均呈现强相关性。

这表明表层和中层带的成岩作用存在普遍规律，凸显出沉降有机物离开真光层时的分子组成在不同区域间的差异，比随深度变化的差异更为显著。这一现象归因于真光层内高度可变的沉降速率和微生物成岩作用历史。稳定性与通量的关系可视为相对于有机物形成过程的“成岩时钟”，其中“稳定岛”分子式的相对丰度描述了有机物分子组成与初始形成时的偏离程度。这一普遍存在的成岩时钟轨迹进一步支撑了全球海洋沉降颗粒有机物的分子特征。

附：英文原文

Title: The molecular-level diagenetic clock of sinking marine organic matter

Author: Forrer, Heather J., Stukel, Michael R., McKenna, Amy M., Chen, Huan, Holt, Amy D., Kranz, Sven A., Spencer, Robert G. M.

Issue&Volume: 2025-11-24

Abstract: The marine biological carbon pump is driven by sinking particulate organic matter (POM). Sinking speed and remineralization rate determine flux attenuation in the mesopelagic. Since the fate of all marine organic matter is either complete remineralization or transformation to more stable products, diagenetic modifications impact carbon dioxide sequestration time from the atmosphere. To investigate particle transformation at the molecular level, we characterize the water-extractable organic matter (WEOM) fraction of sinking particles from dominant biogeochemical environments using ultrahigh-resolution mass spectrometry. We find distinct, inverse associations in molecular-level nitrogen content and degree of transformation (i.e., “stability”) of organic matter across a productivity gradient from coastal upwelling to oligotrophic conditions. Nitrogen enrichment and low stability were observed at the coastal upwelling site and persisted to depths >400 m. Further, carbon flux is strongly correlated with the relative abundance of stable WEOM (“Island of Stability” molecular formulae) across productivity regimes and depth. This suggests emergent patterns in epi- and mesopelagic diagenesis, highlighting that the molecular composition of sinking organic matter exiting the euphotic zone varies more across regions than as a function of depth. This is attributed to highly variable sinking rates and the microbial diagenetic histories within the euphotic zone. The stability–flux relationship is considered a “diagenetic clock” relative to organic matter formation where the relative abundance of Island of Stability molecular formulae describes the degree of departure from the organic matter molecular-level composition at formation. This ubiquitous trajectory of the diagenetic clock further underpins a global ocean molecular signature of sinking POM.

DOI: 10.1073/pnas.2504769122

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2504769122