Reply on RC1

Abstract

As the boundary interface between the atmosphere and ocean, the sea-surface microlayer (SML) plays a significant role in the biogeochemical cycles of dissolved organic matter (DOM) and macronutrients in marine environments. In our study, chromophoric DOM (CDOM), fluorescent DOM, dissolved organic carbon, chlorophyll a, picoplankton, nutrients, and bacteria were frequently enriched in the SML. We focus specifically on the optical properties in the SML, and we find that the enrichment factors (EFs) of tryptophan-like component 4 was significantly higher than other fluorescence components; the longer wavelength absorption values of CDOM showed higher EFs in the SML, and the more significant relationship between CDOM and Chl-a in the SML, indicating that autochthonous DOM was more frequently enriched in the SML than the terrestrial DOM. We find that higher EFs were generally observed in the SML in the off-shore regions than in the coastal regions, and CDOM in the SML is photobleached less after relatively strong irradiation, as also indicated by the lower percentages of humic-like DOM and lower specific UV absorbance values (SUVA254) in the SML than the subsurface water (SSW). In combination with the SSW, the elevated nutrients may stimulate phytoplankton growth, biological activity and then production of abundant fresh autochthonous DOM in the SML. Our results revealed a general enrichment model and the more autochthonous properties of DOM in the SML than the SSW for exploring the oceanic air-sea layer environment.