Unique Dispersal of the Changjiang-Diluted Water Plume in the East China Sea Revealed from Satellite Monitoring of Colored Dissolved Organic Matter (CDOM)

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 Changjiangdiluted 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 oceancolor satellite data are useful for monitoring the dispersal of this river-water plume.

Large-Scale Retrieval of Coloured Dissolved Organic Matter in Northern Lakes Using Sentinel-2 Data

“…Several sensors for environmental monitoring have been developed for marine applications (e.g., MODerate resolution Imaging Spectroradiometer, MODIS), but their coarse spatial resolutions, ranging from 250 m to 1200 m, are not suitable for most inland waters bodies [15,18,19]. Recently, the potential for inland water applications has been enhanced by the development of sensors with higher spatial and radiometric resolution [20][21][22][23][24]. The Sentinel-2 multispectral instrument (MSI) is a state-of-art sensor with freely available images at a spatial resolution of 10 m in the visible range that was designed for land applications, but with promising utility for monitoring regional lake water quality [25][26][27].…”

A Rare Dispersion of Low‐Salinity, High‐Gelbstoff, High‐Primary Production Water in the East China Sea During the Summer of 2010: Possible Influence of the ENSO

“…In addition, southerly wind-driven upwelling, mixing, and sea surface currents shape the eastward dispersion of low SSS (Lie et al, 2003;Xuan et al, 2012) and nutrients (Gao et al, 2015) into patches rather than a continuous, tongue-like protrusion. south of Kyushu Island, Japan, and has been attributed in part to high Changjiang discharge (Sasaki et al, 2014). The annual maximum of the monthly average discharge of the Changjiang in 2010 occurred in July and was about 65,000 m 3 s 21 (Sasaki et al, 2014), much higher than the July climatological monthly peak of 50,000-52,500 m 3 s 21 (e.g., Moon et al, 2012;Siswanto et al, 2008).…”

“…Recently, based on satellite ocean color observations, Sasaki et al () have reported a rare dispersion of low‐SSS and high‐gelbstoff water during the summer of 2010 in the ECS. This low‐SSS and high‐gelbstoff water extended in an elongated protrusion from the ECS continental shelf edge northeastward to the area south of Kyushu Island, Japan, and has been attributed in part to high Changjiang discharge (Sasaki et al, ). The annual maximum of the monthly average discharge of the Changjiang in 2010 occurred in July and was about 65,000 m 3 s −1 (Sasaki et al, ), much higher than the July climatological monthly peak of 50,000–52,500 m 3 s −1 (e.g., Moon et al, ; Siswanto et al, ).…”

“…south of Kyushu Island, Japan, and has been attributed in part to high Changjiang discharge (Sasaki et al, 2014). The annual maximum of the monthly average discharge of the Changjiang in 2010 occurred in July and was about 65,000 m 3 s 21 (Sasaki et al, 2014), much higher than the July climatological monthly peak of 50,000-52,500 m 3 s 21 (e.g., Moon et al, 2012;Siswanto et al, 2008).…”

“…We confirmed that the CIW in July 2010 was characterized by low-salinity, abundant phytoplankton biomass, and high biological production. The fact that high biological production and the peak of Changjiang discharge occurred in the same month (July) in 2010 indicated that biogeochemical production stimulated by nutrients from the Changjiang was higher than during normal summer conditions.Recently, based on satellite ocean color observations, Sasaki et al (2014) have reported a rare dispersion of low-SSS and high-gelbstoff water during the summer of 2010 in the ECS. This low-SSS and high-gelbstoff water extended in an elongated protrusion from the ECS continental shelf edge northeastward to the area Key Points: Offshore dispersion of Changjianginfluenced water (CIW) was primary (secondarily) controlled by alongshore winds (Changjiang discharge) Unusual southeastward dispersion of CIW in July 2010 was due to weak southwesterly winds and high discharge related to El Niño A band of CIW toward the south of Japan was characterized by high phytoplankton standing stock and primary production…”