Distribution and influencing factors of dissolved manganese in the Yellow Sea and the East China Sea

The distribution of dissolved manganese (dMn) was studied in the Yellow Sea (YS) and East China Sea (ECS) onboard the GEOTRACES GP06-CN cruise in October 2015. Dissolved Mn samples were collected by both NiskinX and CTD-Niskin systems at 8 clean stations and collected by the CTD-Niskin system at all 27 grid stations. There was no significant difference in dMn between the two systems (r = 0.98, p < 0.01, n = 39) from the results of the 8 clean stations. We used the "towed fish" system to collect high-resolution surface samples. The range and mean concentrations of dMn were 0.9-16.9 nM and 5.7 +/- 2.5 nM in the ECS and 5.4-42.5 nM and 12.5 +/- 5.3 nM in the YS. Dissolved Mn concentration decreased with increasing distance from the coast, with high concentrations (similar to 42.5 nM) occurring around Jiaozhou Bay and the Zhe-Min coast and low concentrations (< 3.0 nM) appearing in the shelf break, which was affected by Kuroshio Water (KW) intrusion. Vertical distributions of dMn in the PN and QT sections showed that dMn concentrations were relatively high in the surface and near-bottom layers. Based on simplified two end-members mixing model calculations, we found that water mass mixing between the Changjiang Diluted Water (CDW) and KW, upward diffusion of dMn from the porewater, and release of dMn during sediment resuspension were the major influencing factors controlling the dMn behavior in the ECS. According to the positive correlation between the subsurface dMn maximum and apparent oxygen utilization (AOU) below 400 m in the shelf break, organic matter remineralization in the OMZ also affected dMn behavior in the ECS. Dissolved Mn was nearly conservative in the subsurface layers of the southern ECS. The presence of a dMn plume indicated cross-shelf transport at the subsurface at a potential density of 23.0-24.0 kg/m(3). The plume was over the QT section, accompanied by a reduction in the dMn concentration to 12.2% of the concentration adjacent to the 50 m isobath and an output flux of 1.9 x 10(-8) mol Mn/yr. These results indicated that the ECS is highly efficient in pumping Mn-rich coastal waters to the Kuroshio region and western Pacific in autumn.