A warmer climate and an increased Yellow River runoff weakened the barrier effect of ocean fronts on the transport of terrestrial suspended sediment and nutrients in the Chinese Bohai Sea

The barrier effect of ocean fronts (OFs) was generally acknowledged but rarely quantified. This study aimed to quantify this barrier effect in the Chinese Bohai Sea under climate changes. Firstly, with the help of GOCI-based remotely sensed retrieval and ancillary data products, we verified this barrier effect based on the contrast of contribution rate of different hydrodynamic factors (temperature, salinity, precipitation, runoff and wind speed) on suspended sediment concentration (SSC) and fluorescence line height (FLH). Secondly, sliding window threshold algorithm (SWTA) was used to obtain the areas of OFs, suspended sediment fronts (SSFs), and fluorescence fronts (FFs) from 2011 to 2020. Thirdly, we obtained outer boundaries of OFs based on morphological opening filter, and to generate closed areas involving coastline. At last, SSC and FLH in the whole Bohai Sea were divided into three categories: high-value, transition, and low-value. Percentages of three categories involved in the closed areas were further used to quantify the barrier effect. The results showed that the barrier effect was weakened due to: 1) the area of OFs decreased by 3.17 × 10³ km², while that of FFs increased by 9.67 × 10³ km²; 2) centroid of SSFs moved away from the Yellow River estuary, while that of FFs moved offshore; 3) percentages of transition, and low-value categories of SSC and FLH involved in the closed areas increased (41.45 %, 37.58 %). The warmer SST and the increased Yellow River runoff jointly led to the weakened barrier effect of OFs in the Chinese Bohai sea from 2011 to 2020.