Observations of the warm-tongue circulation in the northern East China Sea

Abstract

A subsurface thermohaline front semi-permanently formed in association with near-bottom cyclonic circulation in the northern east china Sea was newly found from detailed hydrographic data collected during two cruises in February 2017 (winter) and April 2018 (spring) along with supplementary satellite remote sensing and historical hydrographic data. An alternate intruding frontal structure in water properties was observed across the cyclonic circulation in both seasons as formed by two contrasting water masses-low-temperature and low-salinity (i.e., low spiciness) water transported by the East China Sea Current and high-temperature and high-salinity (i.e., high spiciness) water transported by the Tsushima Warm Current. Consistent structures were confirmed from current observations during the two cruises, historical hydrographic observations, and satellite altimetry-derived sea surface height and surface frontal structure, indicative of retroflection of the Cheju Warm Current as deemed by the seasonal development of thermal stratification in spring. Our results reveal significant heat and material exchanges between the open Pacific and the broad shelf, particularly via diapycnal mixing and cross-front transports associated with across-front flow and cyclonic circulation, in the northern East China Sea. Understanding the structure of the thermohaline front and associated circulation in the northern East China Sea is of great importance because the northern East China Sea is located in the middle of heat and material exchange between the open Pacific and the neighbouring marginal seas such as the Yellow Sea, East China Sea, and coastal waters around Korea 1-3. The formation and dissipation of the thermohaline front in the northern East China Sea are very closely linked with the variation of the seasonal currents 2. The currents and circulation of the northern East China Sea are driven and modified by four factors: the Kuroshio main stream, northeast Asian Monsoon, tides, and the buoyancy formed by surface solar heating and freshwater discharge 4. Among these factors, the northeast Asian Monsoon has the prominent effect on the currents and circulation of the northern East China Sea 4,5. The northeast Asian Monsoon is dominated by northerly winds in winter and southerly winds in summer 1. During the winter monsoon, the Korea Coastal Current (KCC) and the China Coastal Current (CCC) transport relatively low-temperature and low-salinity waters southward along the west coast of Korea and the east coast of China, respectively 4. In contrast, the Yellow Sea Warm Current (YSWC) intermittently transports high-temperature and high-salinity water of Tsushima Warm Water (TWW) origin northward toward the west trough of the Yellow Sea when the northerly wind bursts 6,7. The YSWC branches from the Tsushima Warm Current (TWC) to the west of Cheju Island. The divergence formed by the southward wind-driven CCC and the northward YSWC drives the CCC to move in the southeast direction, creating an offshore East China Sea Current (ECSC) 8...

Identifying Priority Conservation Areas of Largehead Hairtail (Trichiurus japonicus) Nursery Grounds in the East China Sea

“…The CMEMS was used to act as our data for modeling because CMEMS assimilates a number of observation data sources, and previous findings indicated that the data assimilation technique can produce a reliable dataset (Edwards et al, 2015;Martin et al, 2015). Indeed, numerous studies employed the CMEMS to evaluate their observational data or produced ocean model in ECS and South China Sea (Lin et al, 2017;Lee et al, 2020;Sun et al, 2020b;Kok et al, 2021;Wu et al, 2021). Three topographic variables and six oceanographic variables were extracted for each position and date of the survey dataset, all variables were downscaled using a bilinear interpolation to match our fisheries data.…”