Long-term changes in thermal conditions on the surface of the Far-Eastern Seas and North-West Pacific and their relationship with large-scale climate processes

Previously published results of the study [Khen et al., 2019b] are continued. Long-term changes of the sea surface temperature (SST) in the Far-Eastern Seas and North-West Pacific (NWP) are described for 1950–2019 and their relationship with large-scale climate processes described by climatic indices (AO, Nino 3.4, PDO, ALPI, NPI, PNA, SHI, and WP) is analyzed. SST has increased in all seasons, with higher rate in winter and autumn and less significant trend in summer. A prominent shift to warmer regime occurred in the Bering Sea in 1977 that coincided with a sharp change in dynamics of PDO, ALPI, NPI, and PNA indices. Such shifts were observed in the Okhotsk Sea in 1981 and in the Japan Sea in 1990, one year after the shifts in the time-series of AO, PDO, and PNA indices. Smaller shifts to warming happened in NWP in 2008 and 2018. Pacific Decadal Oscillation is the main contributor to temperature variability in the Bering Sea in all seasons, though the contribution of ALPI and PNA variation is considerable in winter and spring. Arctic Oscillation is the most important for the Okhotsk Sea. Variations of AO, SHI and WP are significant for the SST variability in the Japan Sea. Any single climatic index does not determine the SST variability in NWP, in all seasons. The set of climatic indices can be divided into two categories: western and eastern ones, according to their contribution to SST variability in certain regions. The western group includes AO, SHI, and WP, which contribute mostly to the variations in the western regions, westward from the longitude of Kamchatka. The most important indices in the eastern group are PDO, PNA and ALPI.