Gulf of St. Lawrence

The gulf flows into the Atlantic Ocean through the following outlets:

• The Strait of Belle Isle between Labrador and Newfoundland: between 15 kilometres (9.3 miles) and 60 kilometres (37 miles) wide and 60 metres (200 feet) deep at its deepest.
• The Cabot Strait between Newfoundland and Cape Breton Island: 104 km (65 mi) wide and 480 m (1,575 ft) deep at its deepest.

The Strait of Canso between Cape Breton Island and the Nova Scotia peninsula had been an outlet 1.0 km (0.6 mi) wide and 60 m (200 ft) deep at its deepest. Due to the construction of the Canso Causeway across the strait in 1955, it no longer permits exchange of water between the Gulf of Saint Lawrence and the Atlantic Ocean.

The limits of the Gulf of Saint Lawrence vary between sources.

The International Hydrographic Organization defines the limits of the Gulf of Saint Lawrence as follows:[2]

On the Northeast.
A line running from Cape Bauld (North point of Kirpon Island, 51°40′N 55°25′W) to the East extreme of Belle Isle and on to the Northeast Ledge (52°02′N 55°15′W). Thence a line joining this ledge with the East extreme of Cape St. Charles (52°13'N) in Labrador.

On the Southeast.
A line from Cape Canso (45°20′N 61°0′W) to Red Point (45°35′N 60°45′W) in Cape Breton Island, through this Island to Cape Breton [45°57′N 59°47′W] and on to Pointe Blanche (46°45′N 56°11′W) in the Island of St. Pierre, and thence to the southwest point of Morgan Island (46°51′N 55°49′W).

On the West.
The meridian of 64°30'W from Pointe-Jaune (49°04′N 64°30′W) to Magpie (50°19′N 64°30′W), but the whole of Anticosti Island is included in the Gulf.

Fisheries and Oceans Canada places the western limit at Pointe-des-Monts, approximately 138 km (85.8 mi) west of the 64°30'W meridian.[3]

St. Paul Island in Nova Scotia off the northeastern tip of Cape Breton Island, is known as the "Graveyard of the Gulf" because of its many shipwrecks.[4] Access to this island is controlled by the Canadian Coast Guard.[5]

In 1919 the first Migratory Bird Sanctuaries (MBS) in Canada were established under the Migratory Birds Convention Act on Bonaventure Island, on the Bird Rocks of the Magdalen Islands, and on the Percé Rock. These migratory bird sanctuaries are administered by the Canadian Wildlife Service.[6]

The Federal Government of Canada manages the National Parks of Canada along the Gulf of Saint Lawrence at Forillon National Park on the eastern tip of the Gaspé Peninsula, Prince Edward Island National Park on the northern shore of the island, Kouchibouguac National Park on the northeastern coast of New Brunswick, Cape Breton Highlands National Park on the northern tip of Cape Breton Island, Gros Morne National Park on the west coast of Newfoundland, and a National Park Reserve in the Mingan Archipelago on the Côte-Nord of Quebec.

The five provinces bordering the Gulf of Saint Lawrence have several provincial parks with protected coasts.

Bathymetry of the gulf, with the Laurentian Channel visible

The Laurentian Channel is a feature of the floor of the Gulf that was formed during previous ice ages, when the Continental Shelf was eroded by the Saint Lawrence River during the periods when the sea level plunged. The Laurentian Channel is about 290 m (950 ft) deep and about 1,250 km (780 mi) long from the Continental Shelf to the mouth of the Saint Lawrence River. Deep waters with temperatures between 2 and 6.5 °C (36 and 44 °F) enter the Gulf at the continental slope and are slowly advected up the channel by estuariane circulation.[7] Over the 20th century, the bottom waters of the end of the channel (i.e. in the Saint Lawrence estuary) have become hypoxic.[8]