2013: What’s New in the Gulf of St. Lawrence?
Every year, through the Atlantic Zone Monitoring Program, Fisheries and Oceans Canada assesses the physical oceanography conditions in the Gulf of St. Lawrence. Here are a few highlights for 2013.
The winter of 2013 was warm, with the sea ice maximum seasonal volume at its the sixth lowest since 1969 (45 years ago). Also, a large percentage of the surface mixed layer was largely above the freezing point in March, preventing ice from being formed in these areas. This mixed layer is the precursor to the summertime cold intermediate layer. The volume of the cold intermediate layer (temperature <1°C) was at its third lowest level since the beginning of the series in 1985 and the minimum temperature of the layer was at its warmest temperature since 1980. From May to November, near-surface water temperatures were near normal. Deep water temperature and salinity values remained high. The bottom temperature even exceeded the 6°C threshold in Esquiman Channel and in the centre of the Gulf. In 2012, record high levels were reached in Cabot Strait at 200 m in terms of temperature and at 300 m in terms of salinity (both since 1915). However in 2013, salinity at 300 m in Cabot Strait decreased to normal levels, accompanied by a significant drop in temperature. This major change in the water masses entering the Gulf will affect the Gulf in the coming years.
In 2013, the St. Lawrence River runoff was near normal, but the spring freshet was above normal, starting early in March, probably caused by the early melting of snow associated with above-normal air temperatures. It persisted much longer than usual, with peak runoff in May and an average runoff nearly as high in June.
A LITTLE HELPING HAND
Here are a few definitions of expressions used in the text regarding ice and various water layers found in the Gulf of St. Lawrence.
Sea ice: Ice formed on the surface of a body of salt water.
Surface mixed layer: The surface layer that is mixed by wind and waves, which averages 20 m in thickness in summer and can reach 100 m in winter.
Cold intermediate layer: The layer that stays cold after the end of winter, with an average thickness of 20 m to 100 m.
Deep waters: From 100 m to 300 m, this layer is pulled upstream by the estuarial flow of the St. Lawrence River, from the Cabot Strait to the mouth of the Saguenay.
Peter S. Galbraith