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Research Document 2021/070

Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2020

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

Abstract

In 2020, the North Atlantic Oscillation index was above normal (+1.2, +2.0 SD [standard deviation]) but much smaller than in 2015, which had the largest value in the 71-year record. Mean annual air temperature anomalies were positive for all sites, with anomalies ranging from +0.6°C (+0.7 SD) for Sydney to +1.2°C (+1.8 SD) at Boston. Satellite-based Sea Surface Temperature (SST) annual anomalies were above normal (1982–2010 average temperature), except at the eastern Gulf, +0.7°C (+1.3 SD), for 4W, +0.5°C (+0.8 SD) and for 4Vs, +0.7°C (+1.2 SD). Long-term coastal monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded annual SST anomalies of +1.3°C (+2.2 SD), the 3rd warmest temperature in the record and +0.9°C (+1.3 SD), respectively. At other selected sites across the region, annual water temperature anomalies were near normal to well above normal. Cabot Strait at 200–300 m depth range was a record high, +2.1°C (+6.3 SD); four of the last five years were the warmest on record. Emerald Basin at 250 m was the fourth warmest anomaly, +1.6°C (+1.9 SD); the last six years were the warmest on record with 2019 a high record. Georges Basin at 200 m was the sixth warmest year, +1.1°C (+2.2 SD) with 2018 as the warmest. Also, the last eight years were the warmest. The average bottom temperature anomaly in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4Vn, 4Vs, 4W, and 4X were above the 1981–2010 average values. The anomalies ranged from +0.9°C (+1.2 SD) at 4X to +1.6°C (+2.1 SD) at 4W, fourth warmest, and +0.9°C (+2.3 SD) at 4Vn, third warmest. Stratification in 2020 was significantly lower than in 2019 due to the surface becoming saltier and warmer. Since 1948, the stratification has slowly been increasing on the Scotian Shelf due 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 2020 was the 3rd warmest of 51 years of observations (2012 was the warmest; 2016, 2017, and 2018 were the 2nd, 4th, and 5th warmest), with an averaged normalized anomaly of +2.0 SD relative to the 1981–2010 period.

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