Controls on the Distribution, Enrichment, and Degradation of Dissolved Organic Matter in the Sea Surface Microlayer of the Yellow Sea and East China Sea

Abstract

The concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), total dissolved carbohydrates (TDCHO), and total hydrolyzable amino acids (THAA) in the sea surface microlayer (SML) and subsurface water (SSW) were measured in the Yellow Sea and East China Sea. Concentrations of DOC and TDCHO in the SML were correlated with their respective concentrations in the SSW (Pearson's correlations: DOC, r2 = 0.17, n = 45, p < 0.01; TDCHO, r2 = 0.32, n = 45, p < 0.01). In contrast, DON and THAA concentrations in the SML and SSW were not correlated, suggesting that processes other than exchange with SSW dominated their loss or gain in the SML. Both THAA and TDCHO were significantly enriched in the SML, with mean enrichment factors (EFs) of 2.24 ± 1.17 and 1.98 ± 1.08, respectively. The EFs of dissolved organic matter (DOM) were not correlated with wind speed under the influence of complex processes (e.g., bubbling and turbulence). THAA‐C% and TDCHO‐C% in the SML were 3.38 ± 1.71% and 8.49 ± 4.81%, respectively, which were significantly higher than those in the SSW (Mann‐Whitney U test, p < 0.05), suggesting that DOM in the SML was fresher than that in the SSW. While the high bioavailability of DOM in the SML should be conducive to neuston proliferation in this unique environment, no significant correlations were observed between degradation indicators and neuston abundances. In contrast, the changes of temperature and pH may have an important impact on the degradation of DOM.