Marine deoxygenation has received more and more attention, which can impact on the marine carbon and nitrogen cycling. Previous studies about the dynamics of dissolved organic matter (DOM) during this process were mainly conducted in the deep coastal and open ocean waters. In this study, the production of DOM was investigated during summertime deoxygenation in the bottom water in a shallow coastal sea (Bohai Sea), China. DOM in this region was mainly biological origin indicated by the humification and biological indices (HIX and BIX). Persistent production of DOC, CDOM and FDOM were observed from June to early August in the bottom water, during which duration, dissolved oxygen was gradually consumed. The results again demonstrated particulate organic matter (POM) degradation dominated summertime deoxygenation in bottom water in such a shallow coastal ecosystem. Notably, the newly produced DOM in bottom water contains more CDOM and FDOM, with higher molecular weight and aromaticity. Further analysis suggested about 7% of POC was transformed to DOC, with the remaining fraction directly mineralized to CO₂.

Dissolved organic carbon,chromophoric dissolved organic matter,fluorescent dissolved organic matter,net production,deoxygenation,Bohai Sea