Seasonal Sinking rates of Transparent Exopolymer Particles (TEP) concentrations with associated Carbon flux in adjacent Bohai Seaand Yellow Sea

Abstract. To study the seasonal transparent exopolymer particles (TEP) distributions, sedimentation and its impacts on carbon cycle in north Chinese seas, a total of total 56 stations TEP samples and its sinking rate measurements by SETCOL method via water sampling cruise during autumn (2014), summer (2015) and winter (2015) in the Bohai Sea (BS), North Yellow Sea (NYS) and South Yellow Sea (SYS) at three different depths were carried out. Temperature, phytoplankton, chlorophyll-a (Chl-a) and salinity with five nutrients, phosphate (DIP), silicate (DSi), dissolved inorganic nitrate (DIN) (including nitrite, nitrate and ammonium) were also collected and measured for correlation analysis to visualize the seasonal effects on TEP concentrations (CTEP) and its sinking. Average of total CTEP (2.13 μg Xeq L⁻¹) was higher in NYS (3.32 μg Xeq L⁻¹) costal currents with highest average CTEP during winter (6.17 μg Xeq L⁻¹) specially in NYS (7.00 μg Xeq L⁻¹) through coastal current mixing zone. Average of total sinking rates (1.03 mD⁻¹) was higher in SYS (1.09 mD⁻¹) through mid-water layer than other seas, especially in autumn (1.13 mD⁻¹) with higher seasonal average sinking rates at summer (1.04 mD⁻¹). Carbon associated with TEP (TEP-C) was averagely distributed (1.47 μg C L⁻¹) at subsurface layer of study areas. Seasonal highest distribution of TEP-C was 4.44 μg C L⁻¹ during winter, mostly in NYS. Dominant phytoplankton species Paralia sulcata, Thalassisira excentrica and Rhizosolenia styliformis maintained average correspondences with CTEP which may indicate the influences of them on TEP concentration. Congregating oceanic stations in other groups, coastal stations were averagely clustered together in multivariate analysis. Average canonical correspondence analysis showed close relation of CTEP with Chl-a during autumn and with nutrient during winter.