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Research Document 2020/036

Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2018

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

Abstract

In 2018, the North Atlantic Oscillation index was above normal when compared to the 1981 to 2010 mean (+6.7 mb, +0.8 SD [standard deviation]) but smaller than in 2015, which had the largest value in the 145 year record. Mean annual air temperature anomalies ranged from +0.2°C (+0.2 SD) to +0.8°C (+1.3 SD) above the climatology. Satellite-based sea surface temperature (SST) annual anomalies ranged from -0.4°C (-0.3 SD) at Cabot Strait to +1.3°C (+2.0 SD) in the Bay of Fundy. Long-term coastal monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded annual SST anomalies of +1.0°C (+1.0 SD) and +0.6°C (+0.8 SD), respectively. At other selected sites across the region, annual water temperature anomalies were positive: +0.9°C (+2.7 SD) for Cabot Strait at 200–300 m depth range (the third largest anomaly; 2016 was the largest); +0.7°C (+1.2 SD) for Misaine Bank at 100 m; +1.6°C (+1.9 SD) for Emerald Basin at 250 m (the second largest anomaly after the record high of 2016); +2.0°C (+3.7 SD) for Georges Basin at 200 m (a record high surpassing 2017) and +2.0°C (+2.5 SD) for Lurcher Shoals at 50 m (the second highest). The average bottom temperature anomaly in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4X was +1.6°C (+2.2 SD). Due to vessel unavailability, the other Scotian Shelf divisions were not sampled. Stratification on the Scotian Shelf in 2018 was significantly less than in 2017 when surface freshening and warming had occurred. Since 1948, the stratification has slowly been increasing on the Scotian Shelf due mainly to half freshening and half warming of the surface waters. A composite index, consisting of 19 ocean temperature time series from surface to bottom across the region, indicated that 2018 was the fourth warmest of 49 years of observations (2012 was the warmest), with an averaged normalized anomaly of +1.7 SD relative to the 1981–2010 period.

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