Characteristics and Mechanisms of Ocean Fronts-Induced Decomposition of Particulate Organic Matter and Its Implication for Marine Carbon Burial

Abstract

Ocean fronts are dynamic regions that significantly influence marine biogeochemical processes and climate change. Despite their importance, there is limited research on the dynamics of particulate organic matter (POM) at these fronts, limiting our understanding of carbon burial mechanisms in such environments. Here, we investigated the seasonal physicochemical parameters and stable isotopes of POM in the Beibu Gulf to explore how ocean fronts affect POM fate. During non-frontal periods, notably summer and fall, microbial consumption of POM is minimal due to strong stratification, resulting in partial mineralization in middle and deep waters only. In contrast, frontal formations during winter enhance the decomposition of POM. In the northern frontal region with shallower water, intense vertical mixing induces upwelling of nutrient-rich deeper water, stimulating phytoplankton growth and enhancing the production of fresh POM. This is accompanied by significant decomposition (94%) of fresh POM, driven by oxygen replenishment from photosynthesis and vertical mixing. In the eastern frontal region, with its deeper waters, restricted nutrient availability limits phytoplankton growth, resulting in more aging POM. However, decomposition still reaches 73% due to active vertical mixing. Therefore, regardless of the occurrence of phytoplankton blooms within frontal areas, decomposition is identified as a prevailing process, reducing the potential for marine carbon burial and challenging traditional theories that depict ocean fronts solely as carbon sinks. This comprehensive study sheds light on the biological pump mechanisms active within ocean fronts and highlights their potential role as significant carbon sources.