Wintertime high-resolution features of sea surface temperature and chlorophyll-α fields associated with oceanic fronts in the southern East China Sea

The southern East China Sea (ECS) and the sea north of Taiwan comprise an important transit area between the coastal waters of mainland China and the open water of the western North Pacific. Their wintertime dynamical features were examined using long-term high-resolution satellite-derived sea surface temperature (SST) and chlorophyll-α (Chl-a) images. Along the Chinese coast, a cold-water tongue with an SST of less than 15°C extended southwestwards from the ECS in December, intruded into the Taiwan Strait (TS) in January, and extended further southwestwards in February. Conforming with the cold SST development, the Chl-a concentration starts to increase along the 50-m isobath. However, in the sea north of Taiwan, the SST and the Chl-a front between the shelf region and the eastern open ocean was semicircular in shape, left the shelf break and extended northeastwards. It was found that, along the semicircular Kuroshio front in the sea north of Taiwan, alternative cold and warm fronts appeared in the geographically fixed area in January and February. Based on the investigation of the snapshot SST images, their systematic appearance is attributed to an SST pattern similar to frontal eddies at the Kuroshio northern front. High concentrations of Chl-a (>2.0 mg/m³) were found at the warm front and the offshore cold front patch.