Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2021

Abstract

In 2021, the North Atlantic Oscillation index was near normal (−0.1, −0.2 SD [standard deviation]). Mean annual air temperature anomalies relative to 1991–2020 climatology were positive for all sites, with anomalies ranging from +1.0 °C (+1.3 SD) for Saint John to +1.2 °C (+1.7 SD) at Sydney. Valid data for Boston are only for the last three months of year. Satellite based Sea Surface Temperature (SST) annual anomalies were above normal (1991–2020 average temperature) with values ranging from +0.6 °C (+1.3 SD) in 4Vn to +1.3 °C (+1.9 SD) in the eastern Gulf of Maine/Bay of Fundy, the warmest year in the record. It was the 2nd warmest year for 4Vs, 4W and 4X on the Scotian Shelf and 3rd warmest for 4Vn. Long-term coastal monitoring at Halifax (Nova Scotia) recorded annual SST anomalies of +1.7 °C (+2.8 SD), the 2nd warmest temperature in the record. At other selected sites across the region, annual water temperature anomalies were above normal. Cabot Strait at 200–300 m depth range was the second largest anomaly with 2020 being record high, +1.2°C (+1.9 SD); five of the last six years survived the warmest on record. Emerald Basin at 250 m was the sixth warmest anomaly, +1.6 °C (+1.1 SD); the last six years were the warmest on record with 2019 a high record. Georges Basin at 200 m was the third warmest year, +1.1 °C (+1.6 SD) with 2018 as the warmest. Also, the last nine years were the warmest. Stratification in 2021 was higher than in 2020 due to the surface becoming fresher. 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 17 ocean temperature time series from surface to bottom across the region, indicated that 2021 was mainly above normal by at least one standard deviation.