Sources and mixing behavior of chromophoric dissolved organic matter in the Taiwan Strait

Abstract

The distribution and dynamics of chromophoric dissolved organic matter (CDOM) in the Taiwan Strait were in- vestigated throughan examination ofthe seasonal and geographic variations ofits optical properties. The absorp- tion coefficient a280 showed higher values in the onshore area occupied by the low salinity Min-Zhe Coastal Current and river plumes, and decreased toward offshore waters dominated by the South China Sea seawater and Kuroshio Current. The spectral slope over wavelengths of275–295 nm(s275–295) also increasedwith increas- ing distance from the coastline. The seasonal variations of a280 and s275–295 were closely related to the salinity, where high a280 and low s275–295 were associated with low salinity. Three fluorescent components, including two protein-like and one humic-like, were further identified with the application ofparallel factor analysis to ex- citation-emissionmatrix spectra. The seasonal variations offluorescent components were similar to a280, and the marine autochthonous fluorescent component increased from 38 to 44% along with the increasing fraction of South China Sea seawater and the Kuroshio Current in the Taiwan Strait. The spatial and seasonal distribution ofbulk CDOM and fluorescent components suggested the important contribution of terrestrial input and the hy- drological control ofCDOMdynamics in the Taiwan Strait. A mixing model of three end-members, coastal water, river plumes and offshore seawater, was applied to estimate the CDOM removal or addition in the Taiwan Strait. The results revealed moderate addition ofbulk CDOM to the Taiwan Strait in summer, likely contributed by the primary production and input from ungauged small coastal rivers. During winter, CDOM was conservatively mixed in the northern Taiwan Strait but showed up to 50% removal in the southern Taiwan Strait. ©