On Light Absorption Properties Off Southeastern China-From Estuarine To Shelf Water

Absorption properties off southeastern China were investigated, including several kinds of regimes such as the Pearl River Estuary (PRE), the southern Taiwan Strait (TWS) and the northeastern South China Sea (NSCS)—a continental shelf water. In addition, a time series of absorption properties as well as algal pigments were measured in the western Xiamen Bay in order to assess temporal variations in absorption properties of various constituents associated with bloom development.In general, de-pigmented particles dominate the total absorption at 440 nm both in the spring and the winter in the PRE, while phytoplankton dominate in the NSCS. During summer, phytoplankton are the major absorption component in the southern TWS, but the contributions of de-pigmented particles and CDOM can't be neglectable.The mean absorption spectral slope of de-pigmented particles (Sd, determined between 350-700 nm) in the NSCS is 0.0099 nm-1, similar to that in the southern TWS (0.00912 nm-1), and much smaller than that in the PRE (~0.00126 nm-1).Absorption properties of CDOM are different in the PRE and the southern TWS, depending on the different sources. Over a 0-33 salinity range, CDOM absorption coefficients at 355 nm, ag(355) decreased from 1.93 to 0.24 m-1 in the PRE in the winter, relatively lower than those in the other American and European estuaries. ag(355) showed a linear, inverse relationship with salinity, suggesting a freshwater source. High ag(355) in the vicinity of four outlets demonstrated multiple sources of CDOM. Absorption spectral slopes (Sg), determined between 300-500 nm, ranged from 0.0138 to 0.0184 nm-1. No apparent pattern of Sg for most stations was observed except lower values in the transition zone between the estuary and the South China Sea shelf, where a marine humic-like fluorophore (M) was encountered by fluorescence EEMs analysis. This phenomenon can be interpreted as a mixing process of involving upstream estuarine water and adjacent seawater with different Sg values. In the southern TWS, ag(355) varied from 0.033 to 0.456 m-1 in the summer, a little...