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Gulf Waters Carefully Scrutinized

R. Pigeon

Each year, as part of the Atlantic Zone Monitoring Program, teams from Fisheries and Oceans Canada's Maurice Lamontagne Institute scrutinize the Gulf of St. Lawrence by sea and by air to determine its physical oceanographic conditions. During the analysis, which is conducted four times a year and covers the entire gulf, these teams collect various samples that are used to make observations and predictions, particularly about the water's conditions, temperature and salinity.

In summer, one of the gulf's key features is its cold intermediate layer, which is made up of cold water from the preceding winter. Its analysis is very useful to biologists who evaluate fish stocks because the core of the cold intermediate layer is a vital habitat for many organisms and provides an essential route for others. For most commercially fished species, the time spent living in the cold intermediate layer is a crucial phase. The analysis results are used as a marine resource management tool and contribute, for example, to recommendations for setting fishing quotas that are better adapted to the environmental conditions.

Results for 2011

In 2011 the physical oceanographic conditions in the Gulf of St. Lawrence were generally characterized by above-normal temperatures on the surface and in the intermediate layers, and near-normal temperatures in deep water.

The average air temperatures from January to March were higher than usual after a warm December 2010, which broke a 65-year-old record for high temperatures. Furthermore, a large portion of the ocean's surface layer had temperatures from 0.5 to 1oC above the freezing point in March 2011. This was the second time in 16 years of winter monitoring that such conditions were observed, greatly limiting the formation of sea ice. The ice cover in 2010–11 was in fact thinner than usual, very close to the record low established one year earlier.

Moreover, during summer 2011, the conditions of the intermediate cold layer were comparable to those noted in 2006, which had been the warmest year since 1983. On the Magdalen Shallows in September 2011, the water temperature near the bottom did not drop below 0°C. This was the third consecutive summer that this occurred.

In general, deep water temperatures were close to normal, but very warm waters were recorded in Cabot Strait at a depth of 250 metres, while the estuary had very cold water. It is predicted that in two or three years, the warm anomaly in Cabot Strait will propagate into the estuary.

The analyses also showed that the freshwater input measured in Quebec City during the spring flooding was the highest it had been in 35 years. The St. Lawrence Estuary's surface salinity was also the lowest it had been since at least 1991.

Further details on the results of this research will soon be available on the Canadian Science Advisory Secretariat Web site.

Canadian Science Advisory Secretariat

Peter S. Galbraith
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