Data of Seasonal Dynamics of Surface Dissolved Organic Matter in the South China Sea and the Straits of Malacca: Implications for Biogeochemical Province Delineation of Marginal Seas

Biogeochemical provinces are an important aid to identify homogeneous biogeochemical characteristics and underlying ecosystem dynamics in the open ocean. This approach based on macroscale considerations does not appear to be applicable to marginal seas owing to their complex hydrodynamics and biogeochemical processes. Here, we adopted two observation schemes with continuous surface-water sampling throughout the South China Sea (SCS) and Straits of Malacca (MS) during March and May 2018. Dissolved organic matter (DOM) properties were investigated and applied to biogeochemical province delineation. The results showed that the seasonal variability of DOM pools in the SCS was modulated by biological activities and abiotic process (e.g., photodegradation). The western SCS seasonally received terrestrial DOM under monsoon regulation. The MS served as an efficient source to export terrestrial DOM to the northern Indian Ocean during the Northeast Monsoon, enriched in high-molecular-weight humic-like substances, likely attributable to intense human perturbations. We successfully identified five biogeochemical provinces by employing k-means cluster analysis based on a combination of chromophoric DOM index a325 and classical parameters (temperature, salinity, chlorophyll-a, and bathymetry), which allowed us to integrate distinct biogeochemical processes on seasonal timescales. The delineation obtained in this study will be of great value for the management framework of the SCS and MS, and a325 has been shown to be crucial for biogeochemical province delineation of marginal seas. The manuscript has been published by Journal of Geophysical Research - Biogeosciences.生物地球化学省（biogeochemical provinces）是识别开阔海洋中均一生物地球化学特征与潜在生态系统动态的重要工具。这种基于大尺度考量的方法似乎不适用于边缘海，因后者拥有复杂的水动力与生物地球化学过程。本研究于2018年3月及5月，在南海（South China Sea, SCS）与马六甲海峡（Straits of Malacca, MS）范围内采用两套观测方案，开展连续表层海水采样。本研究针对溶解有机物（dissolved organic matter, DOM）的属性展开调查，并将其应用于生物地球化学省的划分工作。研究结果表明，南海海域溶解有机物库的季节变化受生物活动与非生物过程（photodegradation）所调控。南海西部在季风调控下，季节性接收陆地来源的溶解有机物。马六甲海峡在东北季风期间，作为高效载体将陆地来源的溶解有机物输送至北印度洋，其输送的溶解有机物富含高分子量类腐殖质物质，这一现象可能与强烈的人类活动扰动有关。本研究基于有色溶解有机物（chromophoric DOM）的a325指数与经典参数（温度、盐度、叶绿素a及水深）的组合，采用k-means聚类分析（k-means cluster analysis），成功识别出五个生物地球化学省，这一方法可整合季节尺度下的不同生物地球化学过程。本研究得到的生物地球化学省划分结果，对南海与马六甲海峡的管理框架具有重要价值，且a325指数已被证实对边缘海的生物地球化学省划分工作至关重要。本研究论文已发表于《地球物理研究杂志-生物地球科学分册（Journal of Geophysical Research - Biogeosciences）。