The effect of low oxygen conditions on biogeochemical cycling of nutrients in a shallow seasonally stratified bay in southeast Korea (Jinhae Bay).

The formation and distribution of oxygen-deficient water mass (ODW) in Jinhae Bay exhibited seasonal patterns similar to those of the summer thermocline, indicating a close mutual relationship, and the influence of ODW formation conditions appeared prominently in the bottom water. The principal factors analysis indicate that dissolved oxygen and NO2 in the bottom water during the time of ODW formation were highly correlated with NH3 and dissolved inorganic phosphorus. The findings clearly illustrate the effects on ODW of seasonal physical and chemical changes. ODW that formed in the bottom water of Jinhae Bay during summer produced high concentrations of nutrients in the bottom water; since the growth of phytoplankton was limited by the strong stratification and low concentrations of dissolved oxygen (<3mg/L) in the bottom layer, these nutrients (especially NH3 and DIP) were retained and accumulated, serving as a major source of nutrients during the dry winter.