Spatio-temporal distribution, photoreactivity and environmental control of dissolved organic matter in the sea-surface microlayer of the eastern marginal seas of China

[摘要] As the boundary interface between the atmosphere and ocean, the sea-surfacemicrolayer (SML) plays a significant role in the biogeochemical cycles ofdissolved organic matter (DOM) and macronutrients in marine environments. Inour study, the optical properties of DOM were compared between the sub-surface water (SSW) andthe SML during spring, summer and winter in the East China Sea (ECS) and theYellow Sea (YS). In addition, photoexposure experiments were designed tocompare photochemical degradation processes of DOM between the SML and theSSW. Chromophoric DOM (CDOM), fluorescent DOM, dissolved organic carbon,chlorophyll  a (Chl  a ), picoplankton, nutrients and bacteria were frequently enrichedin the SML. The enrichment factors (EFs) of tryptophan-like component 4 weresignificantly higher than other fluorescence components; the longerwavelength absorption values of CDOM showed higher EFs in the SML, and amore significant relationship between CDOM and Chl  a in the SML, indicatingthat autochthonous DOM was more strongly enriched in the SML than theterrestrial DOM. Higher EFs were generally observed in the SML in theoff-shore regions than in the coastal regions, and CDOM in the SML wasphotobleached more after relatively strong irradiation, as also indicated bythe lower percentages of humic-like DOM and lower specific UV absorbancevalues (SUVA 254 ) in the SML than the SSW. Comparedto the SSW, the elevated nutrients may stimulate phytoplankton growth,biological activity and then production of abundant fresh autochthonous DOMin the SML. Our results revealed a new enrichment model for exploring theair–sea interface environment, which can explain the more autochthonousproperties of DOM in the SML than the SSW.

[学科分类] 大气科学