Effects of El Nino‐Southern Oscillation and North Pacific weather patterns on interannual variability in the subarctic Bering Sea

Abstract

Extraordinary interannual variability in ice cover, air and sea surface temperatures (SST), and surface winds in the eastern Bering Sea have been observed over recent years. To investigate the causes of this interannual variability, long-term (20-30 years) time series of air, ocean, and ice parameters from the Bering Sea were cross-correlated with the southern oscillation index (SOI), an index of E1 Nino-Southern Oscillation (ENSO) events in the tropical southern hemisphere, as well as with an index of Pacific/North American (PNA) events in the north Pacific. Five to thirty percent of the interannual variability (linear regression with various smoothing) in the Bering Sea data sets, with the exception of surface winds, is explained by the SOI when the Bering Sea data lags the SOI. For comparison, 29-52% of the variability in the SST off South America can be explained by the SOI. The signs of the correlations all suggest that warming in the Bering Sea follows negative anomalies in the SOI, that is, ENSO events. Positive anomalies in the SOI, which tend to precede E1 Nino events, were found to precede cooling in the Bering Sea. Significant correlation persists for 18-20 months. Higher-order polynomial regressions between the SOI and Bering Sea data can explain up to 40% of the Bering Sea variability. The mechanism for the connection between ENSO events and Bering Sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the Aleutian low. The Aleutian low is intensified and eastward of normal in association with E1 Nino, i.e., warm events but is weaker and westward of normal during cool events. It is the regional winds associated with the variable position of the Aleutian low that cause the regional warming and cooling events. This seesaw in the Aleutian low is also used to explain the out-of-phase ice conditions between the Bering Sea and the Sea of Okhotsk. PNA events are also associated with an intensified Aleutian low as well as 700 mbar ridging over northwestern North America causing southerly flow over Alaska. However, while correlation between ENSO events and PNA was significant, the correlation between the Bering Sea and PNA was marginal except for surface winds. Here surface winds from the north were significantly correlated with the PNA. This apparent inconsistency, as well as the lack of correlation of surface winds with the SOI, is explained by the lack of preferred site of the Aleutian low during ENSO events. This lack of preferred site helps explain why the major EL Nino event of 1982-1983 had little apparent effect on the Bering Sea.As indicated by the sea ice cycle as well as the monthly mean sea surface temperature (SST) around the Pribilof Islands (Figure 1) that seasonally varies from less than iøC in April to almost 9øC in August, the Bering Sea is characterized by strong variability due primarily to its high latitude and associated seasonal variability in weather and insolation. However, in addition to the strong annual variabilit...

Recent climate variation in the Bering and Chukchi Seas and its linkages to large-scale circulation in the Pacific

“…The NPO pattern, of course, exerts a strong influence over the Pacific basin; Di Lorenzo et al (2008) found that the NPO serves as the atmospheric forcing pattern for the oceanic NPGO pattern. Previous studies also emphasized that the regional Bering Sea variability is closely related to the state of the entire Pacific climate system (Niebauer 1988;Minobe 2002). Figure 10 displays the regressed spatial patterns of SSTA and 1,000-hPa geopotential height anomalies over the tropical and North Pacific (100°E-80°W, 10°S-70°N).…”

“…In particular, its relationship with climate variability has long been the focus of attention (Grebmeier et al 2006;Overland and Stabeno 2004;Hunt et al 2002;Kruse 1998;Brodeur et al 1999). Furthermore, the Bering Sea, as a marginal section of the North Pacific Ocean, is sensitive to Pacific largescale climate phenomena such as the El Niño/Southern Oscillation (ENSO) (Niebauer 1988) and the Pacific Decadal Oscillation (PDO) (Hare and Mantua 2000;Overland et al 1999). Understanding the oceanic and atmospheric variability over the Bering Sea, therefore, is essential from both ecological and climatological perspectives.…”

“…Moreover, Minobe (2002) argued that the changes in the Bering Sea in the late-1990s are a part of the Pacificscale atmospheric and oceanic change, which is regarded as a potential climatic regime shift. The linkage between the Bering Sea and the North Pacific large-scale climate variability was supposed to be established primarily through the atmosphere; in particular, the connection between the two regions seems to vary according to the strength and position of the Aleutian Low (Niebauer 1988;Overland et al 1999;Stabeno et al 2001).…”

Variability in Bering Sea ice cover as affected by a regime shift in the North Pacific in the period 1947–1996

“…For sea ice, as well as for other environmental variables such as temperatures, winds, etc. [e.g., Niebauer, 1988], most of the interannual variability in the Bering Sea region is driven by winter conditions when there is a minimum of insolation and a maximum in atmospheric advection. Interannual variability is typically not driven by summer In summer the Aleutian low is nearly nonexistent and the Bering Sea is between the northern portions of the North Pacific high and low pressure over Asia.…”

Modeling the Effect of Environmental Factors on the Ricker Stock-Recruitment Relationship for North Pacific Albacore Using Generalized Additive Models

“…The annual mean SST in the North Pacific Ocean for each year was recalculated and compared with the mean SST from 1975SST from -2004. The Southern Oscillation Index (SOI), which is the difference in sea level pressure between Tahiti and Darwin, is an effective indicator of El Niño events in the North Pacific Ocean (Niebauer 1988). The SOI data obtained from the National Oceanic and Atmospheric Administration Climate Prediction Center (NOAA/CPC) were also transformed into anomalies as SST.…”