Long-Term Changes in Metocean-Ice Conditions in the Canadian Beaufort Sea

摘要

Existing long-term metocean-ice data sets are reviewed and analyzedfor estimation of trends and changes relevant to offshore oil and gasand shippingavigation activities in the Canadian Beaufort Sea (CBS).An analysis of 45 years (1968-2012) of sea ice properties fromCanadian Ice Service sea ice charts indicates that the summer and earlyfall concentrations of sea ice are decreasing by up to 7.4% per decade(September to mid-October). Old ice concentrations are decreasing at ahigher rate along the slope and deeper offshore waters of the BeaufortSea at rates of 10.5% per decade. There is also evidence of anincreasing presence of glacial ice features passing through the CanadianBeaufort Sea. In contrast to the deeper offshore waters, the reductionsin ice concentrations over the continental slope are smaller but stillstatistically significant in some subregions. The mid-outer shelf regionalso exhibits substantial reductions in mid-October with the loss of oldice and young ice being a large part of the total ice reduction. However,there have been no significant changes observed in ice thickness incontinental shelf region. The duration of the landfast ice off thecoastline of the CBS is also being reduced with a delay in formationdate of 2.8 weeks per decade and an advance in break-up date of 0.65week per decade.An analysis of long-term air temperatures reveals that the largestwarming occurs in the fall and winter corresponding to a temperatureelevation of about 4°C over the past five decades or an equivalent rateof decadal change of, approximately, 0.8°C. The regional windpatterns in the region exhibit little evidence of long-term trends incoastal zones, while cyclonic activity appears to be increasing inoffshore areas. The combination of the reduced areal extent of sea icein summer and especially in the fall, and continuing and perhapsincreased cyclonic activity in offshore areas, is leading to increasingoccurrences of large ocean waves, as seen through analyses of mooredupward looking sonar data obtained over the past decade.