Hydrographic data from the World Ocean Database 2013 and the Chinese National Arctic Research Expedition were used to investigate the summertime changes in the eastern Chukchi Sea from 1974 to 2017. Owing to the Pacific inflow and timing of the sea ice retreat, water masses and vertical thermohaline structures in the eastern Chukchi Sea have changed but with regional differences. The entire eastern Chukchi Sea warmed up with significant temperature increase in the central shelf; however, the surface and bottom salinity in the southern, central, and northern shelves exhibited different trends. The northward extension of the Pacific Summer Water after 1997 influenced the summer hydrography significantly. Moreover, the data reveal changes in the characteristics of various water masses. Both Bering Summer Water (BSW) and Pacific Winter Water in the deeper layer became saltier, whereas the Alaskan Coastal Water in the upper layer became fresher after 1997. The previous definition of the BSW should be modified to include the warming water mass in the southern Chukchi Sea in the more recent years. Furthermore, the vertical thermohaline structure over the Chukchi shelves experienced considerable changes in its characteristics due to the combined effects of the Pacific inflow and surface forcing.
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