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Research Document - 2013/058

Meteorological, Sea Ice and Physical Oceanographic Conditions on the Scotian Shelf and in the Gulf of Maine during 2012

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

Abstract

In 2012, the North Atlantic Oscillation index was above the 1981-2010 mean (+11.8 mb, +1.3 SD [standard deviation]) reaching its 4th highest value two years after its record low.  Mean annual air temperatures were from +1.3°C (Saint John, New Brunswick) to +1.7°C (Shearwater (Halifax), Sable Island and Sydney, Nova Scotia), +1.8 to +2.5 SD, above normal in 2012 and higher than those observed in 2011.  There has been essentially no ice on the Scotian Shelf from April 2009 until the end of the season in May 2012. The ice volume during 2012 was the fourth lowest in the 51 year long record.  Only 1969, 2010 and 2011 had lower coverage and volume. Positive sea surface temperature (SST) anomalies prevailed throughout the region during 2012, with representative values of about +1.7 to +2.5°C (+1.4 to +3.2 SD).  Long-term coastal monitoring sites at St. Andrews (New Brunswick) and Halifax (Nova Scotia) recorded positive annual SST anomalies of +1.8°C (+3.2 SD) and +1.0°C (+1.4 SD) in 2012 and +1°C and +0.5°C above those observed in 2011.  At selected sites across the region, annual water temperature anomalies were positive in 2012: +0.9°C (+2.7 SD) for Cabot Strait 200-300 m (the warmest in 61 years), +1.3°C (+2.0 SD) for Misaine Bank 100 m (2nd warmest year), +0.7°C (+0.9 SD) for Emerald Basin 250 m, +3.4°C (+4.3 SD) for Lurcher Shoals 50 m (warmest year), and +0.5°C (+0.9 SD) for Georges Basin 200 m (the previous two years had the highest temperatures).  Bottom temperature anomalies in Northwest Atlantic Fisheries Organization areas 4VWX were all positive in 2012 and ranged from +0.5°C (+1.2 SD) in 4Vn to +2.1°C (+3.0 SD) in 4X.  Average stratification on the Scotian Shelf strengthened significantly compared to 2011, reaching a value similar to 2010 and the fourth strongest stratification in the record.  This increase in stratification from 2011 to 2012 was due mainly to an increase in surface temperature.  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 2012 was the warmest of 43 years, with an averaged normalized anomaly of +2.8 SD relative to the 1981-2010 period.

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