Interannual to interdecadal changes in the Bering Sea and concurrent 1998/99 changes over the North Pacific

Sea-Surface Temperatures (SSTs), upper water Heat Storage (HS), Sea-Level Displacements (SLDs), Sea-Ice Concentration (SICs) in the Bering Seas and associated atmospheric circulations are analyzed to identify dominant interannual to interdecadal variations. As a representative time series of the SST variations, Principal Component (PC) of the first mode of a seasonally combined Empirical Orthogonal Function (EOF) is employed. The corresponding EOF (spatial pattern) exhibits the smallest amplitudes in winter and largest in summer. PC1 is characterized by a warming trend throughout the record (1921-2001) with the warmest year in 1997, which is followed by rapid cooling until 1999. The warming from 1995-1997 and cooling from 1997-1999 are commonly found in HS along the southern rim of the Bering Sea, and also accompanied by SLD rise and fall, respectively. The SIC variability corresponding to SST PC1 is prominent in the eastern Bering Sea in spring with correlations as high as 0.7, but good correlations were mainly observed prior to 1990. The correlations between the SST PC1 and sea-level pressures (SLPs) also suggest that the spring atmospheric circulation anomalies play an important role in the variations of the SST and sea-ice in the Bering Sea. The cooling and SLD fall in the late 1990s in the Bering Sea might be related with a possible major regime shift in 1998/1999, which was discussed by Minobe (2000), Hare and Mantua (2000), and Schwing and Moore (2000). In the 1998/99 change over the North Pacific, SSTs and HS increased abruptly both in the Kuroshio/Oyashio Extension region and the central North Pacific, accompanied by cooling in the eastern North Pacific. At the same time, SLDs rose from Japan to 160 W roughly along Kuroshio Extension path with a tongue-like structure. The tongue-like SLD rise is likely forced by wintertime atmospheric anomalies associated with SLP increase in the eastern North Pacific. (C) 2002 Elsevier Science Ltd. All rights reserved.