Seasonal variations of suspended sediments in transport and flux in the coastal area of the northern Fujian Province

Based on the simultaneous field observation along three transects off the coastal area of the northern Fujian Province in September and December of 2015, as well as the data of sea surface temperature acquired from MODIS, seasonal variations in suspended sediment concentration (SSC) and transport flux are examined. The results show that the nearshore SSC in winter is much higher than that in summer, and vertical mixing is obviously enhanced in winter due to the intensification of the winter-monsoon. The offshore SSC has low seasonal variability. Because of the strong wind and Min-Zhe coastal current in winter, the nearshore sediment transport flux is much higher than that offshore, and as the result, the sediment is transported southwestward in both summer and winter seasons. However, in the offshore area the sediment is transported northeastward in winter and southwestward in summer. At the stations around 50-m in depth there is no significant seasonal differences in both SSC and sediment flux observed. The distribution of thermal front derived from the sea surface temperature indicates that the interaction between Min-Zhe coastal current and Taiwan Warm Current will join and form a banded transition zone along the 50-m isobath. Facts show that the thermal front plays an important role in the tempo-spatial distribution pattern of SSC in the coastal area of the study area. It may constrain the cross-isobath transportation of suspended matter, as indicated by the higher SSC in the nearshore side of thermal front.