Sinking rates and export flux of Transparent Exopolymer Particles (TEPs) in an eutrophic coastal sea: a case study in the Changjiang (Yangtze River) Estuary

Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. However, the role TEPs play as a carbon sink in eutrophic coastal seas is not well studied. In order to investigate this issue, two cruises in the spring and summer of 2011 were carried out in the Changjiang (Yangtze River) estuary, a typical eutrophic coastal sea. The concentrations, sinking rates, and export flux of TEPs were studied. TEP concentrations ranged from 40.00 to 1040.00 μg Xeq L−1 (mean = 209.70 ± 240.93 μg Xeq L−1) in spring and from 56.67 to 1423.33 μg Xeq L−1 (mean = 433.33 ± 393.02 μg Xeq L−1) in summer. A significant positive correlation between TEP concentrations and chlorophyll (Chl) a concentrations was observed. TEP sinking rates ranged from 0.08 to 0.57 m d−1 (mean = 0.28 ± 0.14 m d−1) in spring and from 0.10 to 1.08 m d−1 (mean = 0.34 ± 0.31 m d−1) in summer. TEP sinking rates were always higher in the upper layers than in the deeper layers during both seasons. The export flux of TEPs was also calculated, and it ranged from 4.95 to 29.40 mg C m−2 d−1 in spring (mean = 14.66 ± 8.83 mg C m−2 d−1) and from 6.80 to 30.45 mg C m−2 d−1 (mean = 15.71 ± 8.73 mg C m−2 d−1) in summer. This study is the first study on TEP sinking in the Changjiang (Yangtze River) Estuary, and it confirmed that TEP plays a significant role as a carbon sink in the eutrophic coastal sea.