Impact of Oil and Corexit on Marine Dissolved Organic Matter (DOM) Aggregation and Microgel Formation Through Dynamic Laser Scattering (DLS)

Marine dissolved organic carbon (DOC), a major reservoir of reduced carbon in the ocean, plays a critical role in marine carbon cycling. Marine microgel formation represents a critical link between more refractory DOC and POC (particulate organic carbon), an available pool of higher bioreactivity and biodegradable organic carbon accessible to the microbial community. Biopolymers (exopolymeric substances, EPS) released from marine phytoplankton or bacteria serve as important sources for the surface DOC pool that contribute to microgel formation. Here we aim to investigate the impact of oil and corexit on this critical process for surface ocean carbon dynamics. We performed mesocosm studies with four treatments: control, water accommodated oil fraction (WAF), Corexit plus WAF (CEWAF), and a diluted CEWAF (DCEWAF), in which the CEWAF and DCEWAF each match the oil concentration in the WAF tank. Our preliminary results based on dynamic laser scattering indicate that oil and Corexit can significantly change the assembly of microgels. Our observation will provide supporting evidence to help us understand the relationships shaping remineralization of these materials and the interactions with the microbial community. Further, the findings will help elucidate processes for the transport/mobilization of oil-derived carbon in the water column, and consequently its fate (sinking, dispersion or aggregation) in the ocean.

海洋溶解有机碳（DOC）是海洋中还原碳的主要储库，在海洋碳循环中发挥关键作用。海洋微凝胶的形成是难降解溶解有机碳与颗粒有机碳（POC）之间的关键纽带：颗粒有机碳是具有更高生物反应活性、可被微生物群落直接利用的可生物降解有机碳库。从海洋浮游植物或细菌中释放的生物聚合物（胞外聚合物，EPS）是表层溶解有机碳库的重要来源，而该碳库可进一步促进微凝胶的形成。本研究旨在探究石油与科思迪（Corexit）对表层海洋碳动态这一关键过程的影响。我们设置了四组围隔实验：对照组、水容石油馏分（WAF）组、科思迪联合水容石油馏分（CEWAF）组以及稀释后的CEWAF（DCEWAF）组，其中CEWAF与DCEWAF组的石油浓度均与WAF组保持一致。基于动态光散射的初步实验结果显示，石油与科思迪可显著改变微凝胶的组装过程。本研究结果将为理解调控此类物质再矿化的相关机制及其与微生物群落的相互作用提供支撑证据。此外，该研究成果还有助于阐明水柱中石油衍生碳的迁移/活化过程，进而明确其在海洋中的最终归趋（沉降、扩散或聚集）。