Seasonal dynamics of dissolved organic matter bioavailability coupling with water mass circulation in the South Yellow Sea.

As a typical shelf-marginal sea, the South Yellow Sea (SYS) is significantly influenced by various factors such as land-based inputs and water mass movements, leading the complex biogeochemical processes of dissolved organic matter (DOM) to become highly dynamic. However, the bioavailability of dissolved organic matter (DOM) coupled with water mass circulation has not been accurately assessed, despite being crucial for understanding the source-sink pattern of organic carbon in marginal sea. In this study, four cruises were conducted in the SYS to analyze the spatial and temporal distribution characteristics of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and total dissolved amino acids (TDAA). Combined with the bioassay experiments, TDAA carbon normalized yield [TDAA (%DOC)] and TDAA degradation index (DIAA) were used as indicators to explore the bioavailability of DOM across different water masses. Results show that the DOC of the SYS exhibits higher average value in late autumn and early winter, and lower value in spring and summer due to the seasonal alternation of water mass and biological activities. The collective results indicate that DOM bioavailability is higher in the Changjiang River diluted water (CDW) and lower in the Yellow Sea warm current (YSWC) and the Yellow Sea cold water mass (YSCWM). Approximately 20 % of DON can be degraded in the YSCWM during autumn. Notably, although the YSCWM constitutes merely constitutes 10 % of the SYS volume, it stores 18.1 % dissolved inorganic nitrogen (DIN) and 23.9 % PO43- of total nutrients, indicating that the YSCWM is a significant nutrient reservoir within the SYS.

Impact of ocean waves on transport of underwater spilled oil in the Bohai Sea.

To investigate the impact of ocean waves on transport of underwater spilled oil, a wave action module is developed and embedded into an underwater oil spill model. Combined with a validated hydrodynamic background data, the model is applied to a short-term numerical simulation of the 2011 Penglai 19-3 oil spill event in the Bohai Sea. Numerical result shows that the model result is rationally consistent with the field observation. In addition, waves can influence surface oil slick in both horizontal and vertical directions: in horizontal direction, Stokes drift tends to make oil slick spread more widely under the action of wind-waves; in vertical direction, breaking waves tend to entrain the surface oil into water column, and then affects the vertical distribution of spilled oil. Furthermore, sensitivity study shows that using different parameterizations of wave entrainment can make some difference to the model output, but the effect is limited. Besides, the impact of input wave errors varies on different model outputs. This study is expected to provide offshore oil spill emergency responders and researchers with useful information on oil spill monitoring, emergency plans and environmental damage assessment.