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.