Temporal and spatial variations of the cross-shelf cold tongue in the southern yellow sea and its influencing factors

The cross-shelf cold tongue extending from northern Jiangsu to the northern East China Sea is one of the typical hydrological phenomena in the southern Yellow Sea during winter. It not only indicates a cross-shelf transport pathway but also plays a significant role in heat exchange, material transport, and ecological environment regulation. However, there is currently a lack of quantitative research on the spatiotemporal response characteristics and driving mechanisms of the cold tongue against the background of global warming.Based on the ERA5 reanalysis sea surface temperature and heat flux data from the European Centre for Medium-Range Weather Forecasts (ECMWF) for January from 2005 to 2025, the surface geostrophic current field data from the Copernicus Marine Environment Monitoring Service (CMEMS) in Europe, and the PN section observation station information from the Japan Meteorological Agency (JMA) in Okinawa, Japan, this paper quantifies the spatial position, frontal curvature and temperature front intensity of the southern Yellow Sea cold tongue by extracting the 15 ℃ characteristic isotherm, and further analyzes its intensity variations using methods such as Empirical Orthogonal Function (EOF) analysis. It also analyzes the impacts of factors such as wind stress, net sea surface heat flux, intensity of the Yellow Sea Warm Current, and intensity of the Kuroshio Current on its variations.The results show that over the past 21 years, the cold tongue and its leading temperature front have retreated towards the northwest, with a strengthening trend in the temperature front. Atmospheric forcing exerts an overall controlling effect on regional sea temperature, followed by the regulation of the Yellow Sea Warm Current and the Kuroshio Current on the temperature field. The intensity of the Yellow Sea Warm Current is the primary dominant factor for the advance and retreat of the cold tongue, with a significant negative correlation: the warm current intrudes northward while the cold tongue retreats. Meridional wind stress serves as a secondary independent influencing factor, mainly controlling the north-south oscillation of the cold tongue. The intensity of the Kuroshio Current and wind stress play secondary roles overall, while the direct impact of net sea surface heat flux and zonal wind stress is not significant. In addition, there is a periodicity of approximately 2-3 years and 7 years in the changes in the cold tongue's position, indicating a teleconnection between regional water temperature variations and El Niño events. This study reveals the response pattern of the shelf hydrological environment to global climate change and tropical Pacific sea temperature anomalies.