Water-mass controls on the distribution and production of transparent exopolymer particles in the continental shelf of the East China Sea.

Transparent exopolymer particles (TEP) play important roles in marine aggregation dynamics and carbon cycling, yet the influence of water masses on their distribution and production remains poorly understood. In this study, we investigated TEP concentration and production rate in the continental shelf of the East China Sea (ECS) during spring 2024 under three water masses: coastal water (CW), shelf mixed water (SMW), and Kuroshio water (KW). Surface TEP concentrations ranged from 55 to 346 μg Xeq L-1 (mean 144 ± 82 μg Xeq L-1), with the highest values in CW (190 ± 69 μg Xeq L-1), followed by SMW (170 ± 104 μg Xeq L-1), and the lowest in KW (91 ± 31 μg Xeq L-1). In contrast, the relative contribution of TEP-associated carbon to particulate organic carbon (TEP-C/POC) was highest in KW (44% ± 12%), followed by CW (38% ± 9%), and lowest in SMW (28% ± 3%), indicating that TEP concentration and its relative importance in the POC pool do not necessarily vary in parallel. Surface TEP production rates ranged from 5.61 to 21.53 μg Xeq L-1 d-1 (mean 13.78 ± 4.83 μg Xeq L-1 d-1), and showed the same spatial pattern as TEP concentration, with the highest rate in CW (17.87 ± 3.36 μg Xeq L-1 d-1), intermediate values in SMW (14.10 ± 2.98 μg Xeq L-1 d-1), and the lowest in KW (10.10 ± 3.74 μg Xeq L-1 d-1). Correlation analysis showed that TEP production rate was positively related to nutrient concentrations and phytoplankton biomass, suggesting that enhanced nutrient supply and biological production in CW promoted active TEP formation, whereas the lower nutrient availability and biological activity in KW limited in situ TEP production. These results demonstrate that water-mass differentiation strongly regulates both the distribution and production of TEP across the continental shelf of the ECS, which have important implications for carbon cycling and TEP-mediated aggregation processes in different hydrographic regimes.