Oceans and seas

Gulf of St. Lawrence

May 13, 2013, 9:42 pm
Content Cover Image

Regional view of the Gulf of St. Lawrence. Source: P. Saundry and Demis World Maps

The Gulf of Saint Lawrence (in French: Golfe du Saint-Laurent), situated in southeastern Canada, is the most extensive estuary on Earth, having a volume of around 35,000 cubic kilometers. Notable bird colonies are found around the perimeter of the Gulf of Saint Lawrence; as an example, prolific breeding colonies of the common murre (Uria aalge) and northern gannet (Morus bassanus) exist at Cape St. Marys, one of the southern extremities of Newfoundland. 

caption Gooseberry Cove, Newfoundland along a northern arm of the Gulf of St. Lawrence. Source: C.Michael Hogan


The Gulf of St. Lawrence is fed chiefly by the St. Lawrence River, which is the only oceanic outlet of the North American Great Lakes. Other notable tributaries to the Gulf include the Restigouche River, Miramichi River, Natashquan, Margaree River, and Newfoundland's Humber River.

The surface area of the Gulf of St. Lawrence approximates an area of about 236,000 square kilometers. Significant sized arms of the Gulf of St. Lawrence include Miramichi Bay, Chaleur Bay, St. George's Bay, Newfoundland's Bay of Islands and Northumberland Strait.

The three connections of the Gulf leading to the Atlantic Ocean are:

  • Cabot Strait lying in between Newfoundland and Cape Breton Island (approximately 105 kilometers in width and 480 meters in maximum depth

  • Strait of Belle Isle separating Labrador from Newfoundland; this water body is around 17 kilometers in width and attains a maximum depth of about sixty meters..

  • Strait of Canso located between Cape Breton Island and the peninsula of Nova; this water body is only about 1000 meters wide and sixty meters deep; however, since the advent of the Canso Causeway in the year 1955, this strait does not allow free exchange of waters between the Atlantic Ocean water and the Gulf of St. Lawrence.

caption Gulf of Saint Lawrence. Source: National Aeronautics and Space Administration

Water quality

At the western extemity of the Gulf of St. Lawrence, surface waters seasonably vary from a salinity level of about 25.2 to 30.0 (parts per thousand);  the lower salinities generally track the late spring/summer months, subsequent to snowmelt and peak runoff. Lower depth variation is more subtle, with a seasonal variation from about 34.0 to 34.4, at the maximum depths of 200 to 300 metres. Correspondingly, at the outlet to the Atlantic Ocean, the salinity of the Gulf varies from 31.3 to 32.0 for surface waters, to a high of 34.2 to 34.8 at depths of 200 to 500 metres.

The Gulf's western extremity surface water temperature minimum is 0.9 degreees Celsius, attained in January; the corresponding temperature peak of surface waters is 8.7 degrees Celsius. At the bottom of the western extremity waters the seasonal variation is a more modest 3.3 to 5.1 degree range. At the mouth of the Gulf where it joins the Atlantic, the surface temperature minimum attains its low in February, at a value of - 0.7 degrees Celsius; the surface water maximu is reached in September at a level of 14.5 degrees Celsius. At depths of 300 to 500 metres, the mouth waters vary a more limited extent, ranging seaonally from 4.5 to 5.7 degrees Celsius.


The Gulf of St. Lawrence  is delimited at the north by the Labrador Peninsula, at its eastern edge by Newfoundland, at the south by the Nova Scotia peninsula and Cape Breton Island, and at the west by the Gaspé Peninsula and New Brunswick. Significant islands within the Gulf are Anticosti, Prince Edward Island, and the Magdalen Islands. Five of the ten Canadian provinces border the Gulf: the Canadian Maritimes provinces of New Brunswick, Nova Scotia, and Prince Edward Island, as well as Quebec and the province of Newfoundland and Labrador. The official boundaries of the Gulf as set forth by the International Hydrographic Organization are:

  • At the northeast. A line running from Cape Bauld (North point of Quirpon Island, (|51|40|N|55|25|W)to the eastern extremity of Belle Isle and on to the Northeast Ledge (52|02|N|55|15|W|. Thence a line joining this ledge with the eastern extremity of Cape Saint Charles (52°13'N) Labrador.

  • At the southeast: A line from Cape Canso (45|20|N|61|0|W|) to Nova Scotia's Red Point (45|35|N|60|45|W) on Cape Breton Island, through said island to Cape Breton (Nova Scotia) (45|57|N|59|47|W) and thence to Pointe Blanche (46|45|N|56|11|W) on the Island of Saint-Pierre, Saint Pierre, and thence to the southwestern tip of Morgan Island (46|51|N|55|49|W).

  • At the west: The meridian of 64°30'W, but the whole of Anticosti Island is included within the Gulf.

Aquatic species

The largest native demersalAn organism living at the bottom of a surface water system. species in the Gulf of St.Lawrence are the 430 centimetre (cm) Atlantic sturgeon (Acipenser oxyrinchus) and the 275 cm lake sturgeon (Acipenser fulvescens). The cisco (Coregonus artedi) is a 57 cm native pelagic-neritic fish species found in the Gulf. Note that the length of species is the maximum expected adult length of the respective taxon.

On the Quebec side, the chief fish species taken are snow crab, shrimp, lobster, Atlantic and Greenland halibut and cod, as well as scallop. Seal hunting has been an important activity in the Magdalen Islands.

Terrestrial ecoregions

The terrestrial ecoregions that rim the Gulf of St. Lawrence include:

  1. Eastern Canadian forests
  2. Gulf of St. Lawrence lowland forests
  3. New England-Acadian forests

Source: World Wildlife Fund.

The Gulf of St. Lawrence lowland forests ecoregion includes the entirety of Prince Edward Island, Isles de la Madeleine, Quebec, the majority of east-central New Brunswick, the Annapolis Valley and the Northumberland Strait coast of Nova Scotia. Prince Edward Island, Iles de la Madeleine, and the maritime lowlands of New Brunswick and Nova Scotia are underlain by Carboniferous sandstones, shales, and conglomerates and rise inland from sea level to 200 meters above sea level. The closed mixed forests of this ecoregion are strongly influenced by a maritime climate, in which warm summers engender robust growth of hardwoods, which are often dominated by red spruce (Picea rubens) and balsam fir (Abies balsamea). Eastern hemlock (Tsuga canadensis) and eastern white pine (Pinus strobus) are found in the maritime lowlands of New Brunswick and the Annapolis-Minas Lowlands of Nova Scotia. Sugar maple (Acer saccharum), yellow birch (Betula allegheniensis) and beech (Fagus grandifolia) are more common on the well-drained higher elevation areas. Bogs and fens are significant in the Minas Lowlands, while mesic locations support white elm (Ulmus americana), black ash (Fraxinus nigra), and red maple (A. rubrum). The Prince Edward Island original mixedwood forest was characterised by red oak (Quercus rubra), sugar maple, yellow birch and beech while abandoned fields are more recently returning to forests of white spruce (P. glauca)

caption Stand of mixed conifers, Eastern Canadian lowland forest, western Newfoundland. Source: C.Michael Hoganna The Eastern Canadian forests ecoregion cover much of the forested land in eastern Quebec, most of the Newfoundland coast, and disjunctive areas on Cape Breton Island, Nova Scotia. Anticosti Island stands out in this ecoregion, as it is a south-dipping cuesta of Paleozoic carbonate strata, and relief rarely reaches 150 meters above mean sea level. The boreal forest in this ecoregion is dominated by a mixture of balsam fir (Abies balsamea) and black spruce (Picea mariana).  Paper birch (Betula papyrifera), aspen (Populus tremuloides), and black spruce are typical of disturbed sites. White spruce (Picea glauca) dominates in coastal areas where sea salt spray affects plant distributions. Moss-heath vegetation or barrens are also common in coastal areas affected by high winds. The warmer Lac St. Jean valley is dominated by mixed woods more typical of southern climates, with sugar maple (Acer saccharum), beech (Fagus grandifolia) and yellow birch (Betula alleghaniensis) on upland sites while eastern hemlock (Tsuga canadensis), balsam fir, eastern white pine (Pinus strobus), and white spruce prevailing in the valleys.

The New England-Acadian forests form a mosaic of forest types and nonforest habitats covering the Eastern Townships and Beauce regions of Quebec, approximately 50 percent of New Brunswick, most of Nova Scotia, northwestern Massachusetts and extreme northwestern Connecticut, and all but the southwestern corner of Maine, the Champlain Valley of Vermont and the coastal plain of New Hampshire.

See also


  • International Hydrographic Organization. 1953. Limits of Oceans and Seas, Third edition
  • Parks Reserves and Natural Sites. Tourisme Îles de la Madeleine
  • Galbraith, P.S., Pettipas, R.G., Chassé, J., Gilbert, D., Larouche, P., Pettigrew, B., Gosselin, A., Devine, L. and Lafleur, C. 2009. Physical Oceanographic Conditions in the Gulf of St. Lawrence in 2008. DFO Can. Sci. Advis. Sec. Res. Doc.
  • Gilbert, D., B. Sundby, C. Gobeil, A. Mucci and G.-H. Tremblay. 2005. A seventy-two-year record of diminishing deep-water oxygen in the St. Lawrence estuary: The northwest Atlantic connection. Limnol. Oceanogr., 50(5): 1654-1666
  • World Wildlife Fund. 2011. Eastern Canadian forests


Hogan, C. (2013). Gulf of St. Lawrence. Retrieved from http://www.eoearth.org/view/article/153203


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