Transparent Exopolymer Particles in a Coastal Frontal Zone of the Northern South China Sea and the Associated Biogeochemical Implications

Transparent exopolymer particles (TEP) are essential for the ocean carbon cycle. However, their relationships with physical and biogeochemical processes remain inadequately understood in the coastal ocean. Here, we focus on TEP dynamics across a temperature front in the coastal waters of the Northern South China Sea (NSCS). Our results suggested that TEP concentration was relatively high across the frontal system with 35.0-160.5 mu g Xeq L-1 (mu g Gum Xanthan equivalent per liter) in the surface waters, 70.0-197.2 mu g Xeq L-1 in the bottom waters, and 12.1-16.3 mg Xeq g(-1) in the surficial sediment. In the surface layer of the front, TEP distributions appeared to be driven by cross-front physical and biogeochemical variations, as it showed significant correlations with both temperature and nutrients, as well as chlorophyll-a along with its size-fractionated components. TEP dominated on the shore side of the front with high phytoplankton biomass and intense TEP production in the surface layer. In contrast, there were much lower TEP concentrations and higher TEP production efficiencies on the seaside driven by nutrient limitation. In the bottom layer of the frontal zone, sediment resuspension associated with the front's secondary circulation was found to play a crucial role in enhancing the levels of TEP-rich aggregates with prominent distribution patterns characterized by the localized accumulation in the bottom waters at the frontal zone. Our results provide valuable insights about the controlling factors that modulate TEP dynamics in a coastal frontal system and highlighted their potential role in the carbon cycling of the NSCS shelf-sea.