Concentration and Characterization of Colored Dissolved Organic Matter in the Surface Microlayer and Subsurface Water of the Yellow Sea and the East China Sea

The distribution and chemical properties of colored dissolved organic matter (CDOM) in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated. The input of freshwater and biological activities had an evident influence on the CDOM levels (characterized by the light absorption coefficient at the wavelength of 355 nm a(355)) in the study area. The spatial distribution of CDOM levels displayed a gradually decreasing trend from the coastal waters (0.37 m(-1)) to the open sea (0.18 m(-1)). The spectral slope ratio (the slope ratio S-R defined as S275-295:S350-400) during the cruise was correlated with salinity, and exhibited a large variation from inshore (average of 2.515) to offshore sites (average of 5.327) compared with the distribution of a(355). The values of S-R were related to CDOM molecular weight (MW). The a(355), S-R, and chlorophyll a in 37 samples collected from the surface microlayer were significantly correlated with those in the corresponding subsurface water samples, implying a strong exchange action between the microlayer and bulk water. The a(355) and SR of CDOM exhibited significant microlayer enrichment, with mean enrichment factors (EFs) of 1.72 and 1.62, respectively.