Multiple Indicators Track Major Ecosystem Shifts in the Bering Sea

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Observations over the previous five years show persistent warm and ice-free conditions in the southeastern Bering Sea compared to the mid-1990s, despite large variability in climate indices such as the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO). These conditions follow a major transformation around 1977 as part of the PDO, with a change from a predominantly cold Arctic climate at least back to the early 1800s to a warmer subarctic maritime climate, accompanied by a major reorganization of the marine ecosystem. Over the last decade annual fisheries surveys indicate a continued decline in recruitment to cold water stocks such as Greenland turbot and snow crab. However, walleye pollock is characterized by a large, rather stable population. Pacific Walrus is another species showing northward movement due to lack of sea ice and warmer temperatures. While it is difficult to show direct causality, the timing of reductions in other marine mammals suggests some loss of their traditional Arctic habitat. We hypothesize that the large-scale climate change occurring in the Arctic is making the Bering Sea less sensitive to the intrinsic climate variability of the North Pacific. While the ecosystem trajectory favors continued warm conditions, the alternate scenario with a return to cold state could produce rapid declines in the pelagic ecosystem. Multivariate indicators are the critical method for tracking change in the Bering Sea and should be watched closely for the next five years to confirm or reject the hypothesis of the northward movement of the cold water curtain