A Year Marked by Rising Water Temperatures and Decreasing Ice Cover in the Gulf of St. Lawrence

2017-03-16

Peter Galbraith

Every year, through the Atlantic Zone Monitoring Program, Fisheries and Oceans Canada assesses the physical oceanographic conditions in the Gulf of St. Lawrence. The main facts to point out for 2016 are as follows: third lowest ice cover since 1969, warmest summer surface waters in the St. Lawrence Estuary since 1985, and warmest sub-surface waters in 100 years!

The El Niño winter of 2016 started with very mild air temperatures over the Gulf; these temperatures greatly limited sea ice cover formation to its third lowest maximum seasonal volume since 1969. Another consequence of this mild weather was that a portion of the surface waters did not reach its freezing point, as it usually does in most of the Gulf every winter. The surface waters between the western tip of Anticosti Island and Port-aux-Basques and Gros Morne National Park (in Newfoundland and Labrador) remained considerably above the freezing point (above –1°C). Ultimately, in the summer of 2016, the thickness and temperature of the cold intermediate water layer were thinner and warmer than the climate normals. Located at a depth of about 20 to 120 m, this layer includes waters that cooled during the previous winter and are now at temperatures below 1 or 2°C.

Between May and November, surface water temperatures were, on average, 0.6°C above normal for the entire Gulf, but they rose to a record level of 1.4°C above normal in the Estuary. November also set a record, the temperature for the entire Gulf exceeding the climate norm of 1.7°C. Other records were also broken in the Estuary (+1.8°C), the northwestern Gulf (+1.9°C), the Esquiman Channel (+1.8°C), the Cabot Strait (+2.2°C) and the Magdalen Shallows (+2.0°C).

Temperatures in the deep waters of the Gulf continue to rise. This is explained primarily by waters coming in from the Cabot Strait whose temperatures broke certain record highs in recent years. This is the case with the record set in 2015 at a depth of 200 m; the waters had never been so warm since record keeping began in 1915. On the whole, waters between 250 and 300 m also broke centuries-old records in 2016: 6.1°C and 6.2°C. The area of the seafloor covered by waters at temperatures above 6°C finally decreased in the Anticosti and Esquiman channels, but greatly increased in the centre of the Gulf. It also made its first appearance in the northwestern Gulf.