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

Abstract

We applied ocean color algorithms and a primary production model to a 13‐year ocean color data set to assess interannual variations of Changjiang‐influenced water (CIW) dispersion, with an emphasis on the unusual CIW dispersion during July 2010. The characteristics of the CIW offshore dispersion were primarily driven by alongshore winds and secondarily by the Changjiang discharge, the interannual variations of which were linked to the El Niño/La Niña. The unusual southeastward dispersion of CIW in July 2010 was attributed to a relatively weak southwesterly wind (with southwesterly wind anomalies) and high Changjiang discharge (after the El Niño peak in winter). In July 2010, the CIW, which is characterized by low‐salinity, high‐gelbstoff, and high‐primary production, intruded into the Kuroshio Current axis to form a rare band of CIW that flowed toward an area south of Japan. The southeastward dispersion of CIW in July 2003 was also unusual, but it did not extend as far as in July 2010, perhaps because of the relatively strong southwesterly winds and low Changjiang discharge in July 2003. During La Niña events, the dispersion of CIW retreated toward the coast due to prevailing northeasterly wind anomalies. 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.

Temporal Variation of Summer Hypoxia off Changjiang Estuary During 1997–2014 and Its Association With ENSO

“…The El Niño-Southern Oscillation (ENSO), the strongest interannual air-sea signal in low latitudes, can impact hydrographical conditions in the ECS through modification of monsoon and precipitation (Zhou and Yu, 2005), sea surface temperature (SST) (Park et al, 2011), Changjiang Diluted Water (CDW) dispersion (Siswanto et al, 2018), and chlorophyll-a distribution (He et al, 2013;Park et al, 2015). As a result, ENSO is likely to have an indirect effect on the hypoxia in the ECS.…”

DataSheet_1.pdf

“…The El Niño-Southern Oscillation (ENSO), the strongest interannual air-sea signal in low latitudes, can impact hydrographical conditions in the ECS through modification of monsoon and precipitation (Zhou and Yu, 2005), sea surface temperature (SST) (Park et al, 2011), Changjiang Diluted Water (CDW) dispersion (Siswanto et al, 2018), and chlorophyll-a distribution (He et al, 2013;Park et al, 2015). As a result, ENSO is likely to have an indirect effect on the hypoxia in the ECS.…”