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Research Document 2016/083

Meteorological, Sea Ice and Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2015

By D. Hebert, R. Pettipas, D. Brickman, and M. Dever

Abstract

In 2015, the North Atlantic Oscillation index was above the 1981-2010 mean (+17.8 mb, +2.0 SD [standard deviation]) and was the largest value in the 121 year record. Mean annual air temperature anomalies were negative at all sites except Sable Island at +0.5°C (+0.7 SD) and slightly positive at Yarmouth, with values ranging elsewhere from slightly negative at Boston to -0.5°C (-0.7 SD) at Halifax. Positive satellite-based sea surface temperature (SST) annual anomalies prevailed throughout the region except at Cabot Strait at -0.1°C (-0.1 SD), with values ranging from +0.4 to +1.1°C (+0.4 to +1.0 SD) above the 1981-2010 mean values. Sea ice coverage on the Scotian Shelf in 2015 was above the 1981-2010 average unlike the 2010-2013 period that had extremely low coverage and volume. Long-term coastal monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded annual SST anomalies of +0.3°C (+0.3 SD) and +0.0°C (+0.0 SD), respectively, in 2015. At selected sites across the region, annual water temperature anomalies were positive in 2015: +0.9°C (+2.6 SD) for Cabot Strait at 200-300 m depth range (the third largest anomaly; 2012 was the largest); +0.9°C (+1.4 SD) for Misaine Bank at 100 m; +1.2°C (+1.3 SD) for Emerald Basin at 250 m; +1.1°C (+1.4 SD) for Lurcher Shoals at 50 m; and +1.0°C (+1.2 SD) for Georges Basin at 200 m (the warmest year was 2013). Bottom temperature anomalies in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4VWX were all positive in 2015 ranging from +0.9°C (+1.3 SD) in NAFO Division 4X to +1.9°C (+2.8 SD) in NAFO Division 4Vs. Average stratification on the Scotian Shelf continue to weakened from 2013 and was less than the 1981-2010 mean value. Since 1948, the stratification has slowly been increasing on the Scotian Shelf due mainly to one-third freshening and two-thirds warming of the surface waters. A composite index, consisting of 18 ocean temperature time series from surface to bottom across the region, indicated that 2015 was the fifth warmest of 46 years (2012 was the warmest), with an averaged normalized anomaly of +1.2 SD relative to the 1981-2010 period.

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