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Research Document 2020/022

Meteorological, Sea Ice and Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine During 2017

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

Abstract

In 2017, the North Atlantic Oscillation index was nearly normal when compared to the 1981 to 2010 mean (+2.7 mb, +0.3  SD [standard deviation]) but significantly much smaller than in 2015 which had the largest value in the 122 year record. Mean annual air temperature anomalies were positive at all sites examined with values ranging from +0.5°C (+0.8 SD) to +1.0°C (+1.4 SD) above the climatology. Positive satellite-based Sea Surface Temperature (SST) annual anomalies prevailed throughout the region with values ranging from +0.7°C (+1.2 SD) at Cabot Strait to +1.9°C (+3.0 SD) for the Western Scotian Shelf. After above-average conditions in 2015, sea ice in 2016 and 2017 returned to similar conditions found in 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 +0.8°C (+1.5 SD) and +0.7°C (+1.0 SD), respectively, in 2017. At other selected sites across the region, annual water temperature anomalies were positive in 2017: +1.1°C (+3.3 SD) for Cabot Strait at 200–300 m depth range (the second largest anomaly; 2016 was the largest); +0.4°C (+0.7 SD) for Misaine Bank at 100 m; +1.5°C (+1.8 SD) for Emerald Basin at 250 m (the second largest anomaly where 2016 was a record high) and +1.6°C (+3.0 SD) for Georges Basin at 200 m (a record high surpassing 2016). Bottom temperature anomalies in Northwest Atlantic Fisheries Organization (NAFO) Divisions 4VWX were all positive in 2017 ranging from +0.7°C (+1.6 SD) in Division 4Vn to +1.6°C (+2.2 SD) in Division 4X. Stratification on the Scotian Shelf was nearly the same as in 2016 where surface freshening was offset by 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 18 ocean temperature time series from surface to bottom across the region, indicated that 2017 was the third warmest of 48 years (2012 was the warmest) of observations, with an averaged normalized anomaly of +1.7 SD relative to the 1981–2010 period.

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