Recent warming and sea ice reduction in the Bering Sea and its possible relationship to the central Pacific El Nino

The thermal state of the Bering Sea exhibits interdecadal variations, with distinct changes occurred in 1997-1998. After the unusual thermal condition of the Bering Sea in 1997-1998, we found that the recent warming signal (1999-2010) in the Bering Sea is closely related to Pacific basin-scale atmospheric and oceanic circulation patterns. The melting of the sea ice in the Bering Sea involves energy transfer from the ocean to atmosphere, which acts a forcing mechanism for the atmosphere. The atmospheric response to the recent warming in the Bering Sea includes the mid-latitude North Pacific Oscillation (NPO) pattern in winter, which is characterized by a southward shift of the atmospheric center of action from its climatological position. This NPO pattern potentially links the mid-latitude atmospheric variability to the El Ni–o events by affecting air-sea interaction in the subtropical and the tropical Pacific. Furthermore, several recent studies argued that the initial establishment of SST anomalies in the tropical central Pacific is intimately tied to mid-latitude NPO pattern [Furtado et al., 2011; Kim et al., 2012; Yu and Kim, 2011]. Indeed, we find that the NPO-related El Ni–o features the sea surface temperature anomalies centered in the equatorial central Pacific—the so-called central Pacific (CP) El Ni–o. Here, the physical connection between the Bering Sea variability, the NPO pattern and the CP El Ni–o is investigated via cyclostationary empirical orthogonal function (CSEOF) analysis. An additional model experiment using the NCAR Community Atmospheric Model, version 3 (CAM3), supports the conclusion that the recent warming over the Bering Sea can induce the NPO-like atmospheric response. In conclusion, the results presented in this study suggest that the recent warming in the Bering Sea can exert an indirect influence on the CP El Ni–o development by altering the mid-latitude NPO pattern.