Hypoxia, acidification and nutrient accumulation in the Yellow Sea Cold Water of the South Yellow Sea

Abstract

Hypoxia and acidification in coastal waters are of global concern. However, the complex hydrodynamic processes and human interferences are major challenges for the diagnosis of their mechanism. The role of seasonal water masses involved still remains unknown. We herein investigated the dynamics of dissolved oxygen (DO), pH, inorganic and organic nutrients in the South Yellow Sea (SYS) in autumn, aiming for a better understanding of the biogeochemical processes of the Yellow Sea Cold Water (YSCW). Low DO, pH and organic nutrients were observed in the YSCW, while the apparent oxygen utilization and dissolved inorganic nutrients were relatively high. Quantitative assessment shows that although the water volume of the YSCW accounts for only 16.4% that of the SYS, the reservoirs of dissolved inorganic nitrogen, phosphate and silicate were 30.8%, 52.1% and 33.0%, respectively. Our results suggest that organic matter mineralization and water stratification are important driving forces for hypoxia, acidification and nutrient accumulation in the YSCW. The upwelling of the YSCW can bring abundant nutrients and stimulate the algal blooms, which are detrimental to the ecology. As global warming continues, the hypoxia and acidification in the YSCW will likely intensify in the near future in response to a projected slowdown of overturning circulation.

Keywords: Acidification; Hypoxia; Nutrients; Yellow Sea Cold Water.