Upwelling of Atlantic Water along the Canadian Beaufort Sea Continental Slope: Favorable Atmospheric Conditions and Seasonal and Interannual Variations

Abstract

Abstract The role of wind forcing on the vertical displacement of the −1°C isotherm and 33.8 isohaline depths was examined based on snapshots of historical (1950–2013) temperature and salinity profiles along the Mackenzie continental slope (Beaufort Sea). It is found that upwelling is correlated with along-slope northeast (T59°) winds during both ice-free and ice-covered conditions, although the wind impact is more efficient during the ice-free season. One of the most important factors responsible for vertical displacements of isopycnals is sustained wind forcing that can last for several weeks and even longer. It accounts for 14%–55% of total variance in isotherm/isohaline depths, although these numbers might be underestimated. The upwelling and downwelling events are discussed in the context of the interplay between two regional centers of action—the Beaufort high and Aleutian low—that control the wind pattern over the southern Beaufort Sea. The probability of upwelling-favorable wind occurrence is closely related to the sea level pressure difference between these two centers, as well as their geographical positions. The combined effect of both centers expressed as the SLP differences is highly correlated (0.68/0.66 for summer/winter) with occurrences of extreme upwelling-favorable northeast (NE) winds over the Mackenzie slope, although the Beaufort high plays a more important role. The authors also diagnosed the predominant upwelling-favorable conditions over the Mackenzie slope in the recent decade associated with the summertime amplification of the Beaufort high. The upwelling-favorable NE wind occurrences also demonstrate the significant but low (−0.30) correlation with Arctic Oscillation (AO) during both summer and winter seasons, whereas the high correlation with North Pacific index (NPI; −0.52) is obtained only for the ice-covered period.