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Research Document 2021/040

Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2019

By Hebert, D., Layton, C., Brickman, D. and Galbraith, P.S.

Abstract

In 2019, the North Atlantic Oscillation index was above normal (+0.6, +1.1 SD [standard deviation]) but much smaller than in 2015, which had the largest value in the 70-year record. Mean annual-air-temperature anomalies ranged from -0.4°C (-0.6 SD) below climatology to near normal for most stations except for Boston, which was above normal (+1.2°C [+1.7 SD]). Satellite-based Sea Surface Temperature (SST) annual anomalies ranged from -0.8°C (-1.5 SD) in Northwest Atlantic Fisheries Organization (NAFO) Division 4Vn to +0.1°C (+0.2 SD) in the eastern Gulf of Maine/Bay of Fundy. Long-term coastal-monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded annual SST anomalies of +0.4°C (+0.6 SD) and +0.1°C (+0.2 SD), respectively. At other selected sites across the region, annual water-temperature anomalies were positive: +1.6°C (+4.8 SD) for Cabot Strait at 200-300 m depth range (the warmest anomaly; four of the last five years were the warmest on record); -0.2°C (-0.3 SD) for Misaine Bank at 100 m; +1.8°C (+2.2 SD) for Emerald Basin at 250 m (the warmest anomaly; the last six years were the warmest on record); +1.7°C (+3.2 SD) for Georges Basin at 200 m (the second warmest); near-normal conditions for Eastern Georges Bank at 50 m; and +0.3°C (+0.4 SD) for Lurcher Shoals at 50 m. The average bottom-temperature anomaly in NAFO Division 4Vn was +1.0°C (+2.4 SD), the second warmest on record. Divisions 4Vs, 4W, and 4X were +0.8°C (+1.2 SD), +0.9°C (+1.2 SD), and +1.2°C (+1.6 SD), respectively. Stratification in 2019 was significantly greater than in 2018 due to the surface freshening that had a greater effect than the surface cooling. 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 22 ocean-temperature time series from surface to bottom across the region, indicated that 2019 was the 14th warmest of 50 years of observations (2012 was the warmest), with an averaged normalized anomaly of +0.9 SD relative to the 1981-2010 period.

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