Environmental influence on transparent exopolymer particles and the associated carbon distribution across northern South China Sea

Microgels are plankton-derived transparent exopolymer particles (TEP) and have a significant impact on global marine carbon cycle. We investigated the influence of biogeochemical variables on the pattern of TEP abundance and its associated carbon (TEPC) distribution through a vertical transect of the northern South China Sea (nSCS) during summer, 2014. The average TEP concentration was 58.32±30.56 μg Xeq./L. Vertically, it was higher in the subsurface water column and lower at 200-m water depths. As chlorophyll a (chl a), TEP, and TEPC were highly concentrated at the bottom of the study transect, mainly on the continental shelf bottom and slope regions. Among biotic factors, cyanobacteria, especially Trichodesmium thiebautii showed significant positive correspondences with TEP through studied water columns in nSCS. In addition, TEP showed a positive correlation with chl-a distribution and clustered closely with diatom as well. It indicates a combined contribution of them on TEP sourcing accordingly. Nutrient concentrations were also high due to estuarine diluted water from Zhujiang (Pearl) River in the season that may intrigue those scenarios. Significant positive correlation (P < 0.05) among biotic and abiotic parameters also supported the statement. Furthermore, mentionable contribution of TEP-derived TEPC was found after comparing the particulate organic carbon data, which may signify the importance of TEP in local carbon cycle in the nSCS.