Abstract
The optical properties of colored dissolved organic matter (CDOM) in the Changjiang (Yangtze River) plume water were investigated during the summer of 2009 and 2010. The absorption coefficient of CDOM at 325 nm (aCDOM) increased inversely with decreasing sea-surface salinity (SSS), implying that aCDOM can be used as a natural tracer of Changjiang-diluted water (CDW). This aCDOM vs. SSS relationship, however, differed between 2009 and 2010. For mapping the CDW plume, the aCDOM was retrieved from an ocean-color satellite. Values of SSS were also derived from the satellite-retrieved aCDOM using field-based SSS vs. aCDOM relationships. Satellite observations revealed the temporary variable eastward extension of a high aCDOM, low SSS CDW plume in the central East China Sea (ECS) during the summer. The CDW plume during the summer of 2010 extended southeastward from the mouth of the Changjiang (Yangtze River) to almost 26°N. Moreover, the branch of this southeastward CDW plume was seen to extend northeastward to the eastern ECS where the Kuroshio Current flows northeastward along the shelf break. Subsequently, this branch was distributed around southern Kyushu. Satellite observations revealed this unique dispersal of the CDW plume, which illustrates that the aCDOM and SSS from ocean-color satellite data are useful for monitoring the dispersal of this river-water plume.
Highlights
Colored dissolved organic matter (CDOM) represents the fraction of the dissolved organic pool that absorbs light in the visible ranges
The objective of the present study was to identify variations in the extent and dispersal patterns of the Changjiangdiluted water (CDW) plume using the colored dissolved organic matter (CDOM) absorption coefficient derived from ocean-color satellite data
The magnitude of surface aCDOM varied inversely with sea-surface salinity (SSS), which is indicative of the presence of a freshwater source (Fig. 2a)
Summary
Colored dissolved organic matter (CDOM) represents the fraction of the dissolved organic pool that absorbs light in the visible ranges. The Changjiang (Yangtze River) is the largest river that discharges into the East China Sea (ECS; Fig. 1a). It is a major source of freshwater on the ECS shelf and supplies about 90% of the total discharge of freshwater from rivers around the ECS and the Yellow Sea (Beardsley et al 1985; Zhang 1996). Concentration (Kiyomoto et al 2001; Yuan et al 2005; Gong et al 2006; Kim et al 2009; Shi and Wang 2012) These studies showed that the CDW has profound effects on the physical and biological processes that occur on the ECS shelf. The objective of the present study was to identify variations in the extent and dispersal patterns of the CDW plume using the CDOM absorption coefficient derived from ocean-color satellite data. We focused on the distribution of the CDW in the summer of 2010 compared with 2009
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