Concentrations and sinking rates of transparent exopolymer particles (TEPs) in a coastal sea: the Changjiang River (Yangtze River) Estuary

Abstract

Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. To investigate the role of coastal TEPs in sinking carbon from the upper layer, samples were collected in the spring and summer of 2011 in the Changjiang River (Yangtze River) Estuary, a typical coastal water. The concentrations and sinking rates of TEPs were measured, and potential sedimentation flux of TEPs was estimated. TEPs concentrations ranged from 40.00 µg/L to 1 040.00 µg/L (mean=(209.70±240.93) µg/L) in spring and 56.67 µg/L to 1 423.33 µg/L (mean=(433.33±393.02) µg/L) in summer, and they were higher at bloom stations than at non-bloom stations during both cruises. A significant positive correlation between TEPs concentration and chlorophyll a (Chl a) concentration was detected, suggesting that phytoplankton was the primary source of TEPs in this area. TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of (0.28±0.14) m/d in spring and 0.10 m/d to 1.08 m/d with a mean of (0.34±0.31) m/d in summer. The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d) to 29.40 mg/(m2·d) with a mean of (14.66±8.83) mg/(m2·d) in spring and 6.80 mg/(m2·d) to 30.45 mg/(m2·d) with a mean of (15.71±8.73) mg/(m2·d) in summer, which was ∼17.81% to 138.27% (mean=65.15%±31.75%) of sedimentation flux of phytoplankton cells in the study area. Due to the increase of TEPs concentrations and their sinking rates, sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises. This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary, especially during bloom events, and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.