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Research Document - 2012/055

Meteorological, Sea Ice and Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2011

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

Abstract

In 2011, the North Atlantic Oscillation (NAO) index remained below the 1981-2010 mean (-10.2 mb, -1.2 SD [standard deviation]). In 2010, the NAO index was at its lowest value in the entire record analyzed, -25.1 mb, 2.9 SD below normal.  Mean annual air temperatures were from 0.6°C (Sydney, Nova Scotia, and Saint John, New Brunswick)  to 1.1°C (Yarmouth, Nova Scotia), approximately 1 to 2 SD, above normal in 2011 but lower than those found in 2010. There has been essentially no ice on the Scotian Shelf from December 2009 until the end of the season in May 2011. The ice volume during 2011 was the third lowest since 1969 and not significantly different from the lowest volume of the 43 year record. Positive sea surface temperature (SST) anomalies prevailed throughout the region during 2011, with representative values of about +0.1 to 0.8°C (+0.1 to 0.7 SD). Long-term coastal monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded positive annual SST anomalies, 0.9°C (+1.6 SD) and 0.6°C (+0.8 SD) in 2011 and were similar to those observed in 2010. At selected sites across the region, annual water temperature anomalies were positive in 2011:  +0.6°C (+1.6 SD) for Cabot Strait 200-300 m (the 2nd warmest in 60 years), +0.8°C (+1.2 SD) for Misaine Bank 100 m, +0.9°C (+1.1 SD) for Emerald Basin 250 m, +1.3°C (+1.7 SD) for Lurcher Shoals 50 m, and +0.8°C (+1.5 SD) for Georges Basin 200 m the 2nd highest anomaly with last year being the highest.  Bottom temperature anomalies in Northwest Atlantic Fisheries Organization areas 4VWX were all positive in 2011 and ranged from +0.2°C (+0.3 SD) in 4W to +0.8°C in 4Vn (+1.6 SD). Average stratification on the Scotian Shelf weakened significantly compared to 2010, reaching a low value not seen since 2002. This decrease in stratification from 2010 to 2011 was due mainly to a decrease in surface temperature. Surface salinity was also the lowest in more than a decade. Since 1950, the stratification has slowly been increasing on the Scotian Shelf due mainly to a freshening of the surface waters. A composite index consisting of ocean temperatures from surface to bottom across the region indicated that 2011 was the 6th warmest of 42 years, with an averaged normalized anomaly of +0.9 SD relative to the 1981-2010 period.

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