Spatial and temporal variability of suspended sediment fronts over the Yangtze Bank in the Yellow and East China Seas

Abstract

Suspended sediment fronts (SSFs) are an important sub-mesoscale phenomenon prevalent in estuaries, coasts, and continental shelf seas, affecting ocean hydrodynamics, fisheries, and ecology. Using archived (2011–2021) Geostationary Ocean Color Imager (GOCI) data, the spatial distributions and long-term variations in SSFs over the Yangtze Bank were quantitatively investigated by calculating frontal probability (FP). The findings indicate that the majority of SSFs occurred in regions inside the 50-m isobath. Their distributions were considerably limited by depth gradients. The FP values were divided into three main levels according to their statistical characteristics. The boundaries of moderate-FP zones (FP = 3%) were aligned with the locations of tidal mixing fronts. Empirical orthogonal function (EOF) analysis revealed that frontal activity exhibited strong seasonal cycles, together with large interannual variations. Its spatio-temporal pattern was associated with multiple factors. Among them, topographic effects combined with tidal mixing dominated frontogenesis. The seasonal development of SSFs was mainly controlled by stratification and wind waves associated with monsoons and was partially affected by wind-driven regional circulations. The direct impact of the Yangtze River sediment discharge was restricted to waters inside the 30-m isobath. The El Niño-Southern Oscillation affected interannual frontal dynamics to a large extent. After El Niño years, due to weakening winter winds and warmer sea surfaces, frontal activity was suppressed by the intensification of stratification and weakening of vertical mixing. In contrast, frontal activity increased after La Niña years. These findings will broaden the understanding of SSF variability and its ecological effects over the Yangtze Bank and in other systems.