The spatial and temporal changes of chlorophyll-a and suspended matter in the eastern coastal zones of China during 1997–2013

In this study, the spatial and temporal changes of chlorophyll-a and suspended matter (denoted using the back-scattering coefficient of suspended matter at 555 nm, bb(555)) in China’s eastern coastal zones (CECZ) over a 16 year period, using remote sensing technology, are explored. It was found that chlorophyll-a concentration and bb(555) gradually decrease from the northeastern to the southeastern CECZ due to global warming. The monthly average bb(555) slowly decreased in the CECZ from September, 1997 to September, 2013. The decreases of bb(555) led to decreases of nutrient supports and the diffuse attenuation coefficient, because the CECZ fell into the TSM-dominated coastal water category. However, the phytoplankton growth was not only limited by the nutrients provided, but also depended on the environmental temperatures, as well as some other factors. As a result, the chlorophyll-a concentration gradually increased in the Bohai and Yellow Seas, but slowly decreased in the East China Sea. Since a large amount of the river around the CECZ discharged suspended matter into the global oceanic system, there was a strong co-variation of bb(555) between the CECZ and the global oceans. The use of bb(555) in the CECZ can account for 59% of the variations of bb(555) in the global oceanic system, which is much higher than that of the chlorophyll-a concentration, due to the variables impacting the spatial distribution of phytoplankton being much more complicated than those of the suspended matter.