Multiple Timescale Variations in Water Transparency in the Eastern China Seas over the Period 1997–2019

Abstract

The detection of water transparency (Zsd) changes over multiple timescales is an important task that has wide implications from water quality to climate change research. However, to date, the understanding of Zsd variations and their driving factors in the Eastern China Seas is fairly limited. Using the Data Interpolating Empirical Orthogonal Functions (DINEOF) method and a semi‐analytic algorithm, monthly cloud‐free Zsd products over the period 1997–2019 are retrieved from the European Space Agency Ocean Color Climate Change Initiative datasets. Significant Zsd variations on seasonal, interannual, and long‐term timescales, as well as their spatial discrepancies, are quantified in the Eastern China Seas. The first EOF mode of Zsd accounts for 57.46% of the total variance, which is dominated by a seasonal cycle in response to seasonal changes in oceanic and atmospheric factors (e.g., surface winds, sea surface temperature and ocean stratification). The second and third EOF modes are likely associated with seasonal phytoplankton blooms and ocean circulations, respectively. Factors that affect the interannual variation in Zsd, including sea surface temperature, wind speed, river discharge, and the Oceanic Niño Index, are quantitatively evaluated. The long‐term trends suggest different potential driving forces for the Zsd patterns at a regional scale, such as climate‐driven increased sea surface temperatures, weakened surface winds, reduced sediment discharge, and eutrophication of coastal waters. Overall, this study presents the first comprehensive investigation of Zsd variations in the Eastern China Seas at multiple timescales and an analysis of their underlying physical and environmental drivers.

Variations of Remote-Sensed Forel-Ule Index in the Bohai and Yellow Seas during 1997–2019

“…In the shallow waters of the Bohai and Yellow Seas, inorganic suspended sediment is the most significant optically active constituent [41]. Disturbances caused by winds and tides lead to the resuspension of benthonic sediments to the surface [41][42][43][44]. Seasonal variations in the wind field, SST, and ocean stratification, under the influence of the East Asian Monsoon, act as the primary driving forces behind sediment resuspension in the Bohai and Yellow Seas.…”