Characteristics | Geology | Seabed Morphology | Climate Oceanography | Sediments | Plants | Animals Cultural Environment | Topics & Habitats

Regional Characteristics
The continental shelf extends from 125-230 km offshore to depths of about 200 metres. Major offshore areas that make up the shelf are the Northumberland Strait, southeastern Gulf of St. Lawrence, Sydney Bight, Scotian Shelf, Georges Bank, Gulf of Maine, and Bay of Fundy. The landscape is that of a submerged coastal plain, and the structure reflects long periods of terrestrial erosion, the passage of continental ice sheets, and the influence of the ocean. Features include basins up to 280 m deep on the central shelf; fishing banks; channels; and Sable Island (District 890), on Sable Island Bank, extending 26 m above sea level. Waters from the Gulf of St. Lawrence and from further offshore (the slope water) mainly influence biological processes on the shelf; and the animals and plants, and seasonal cycles of productivity and abundance, follow patterns typical of cool temperate regions.

Beyond the shelf break (200 m) the bottom slopes steeply to a depth of 2,000 metres, reaching a maximum of 5,000 metres at the edge of the Region. The area experiences full oceanic conditions.

Geology
Various geological or bedrock provinces are represented on the continental shelf (see T3.5). Inshore, the bedrock is usually a seaward extension of rock formations on the adjacent land. Areas of complex geology may have different subtidal bedrock than on the coast. Patterns and variations of bedrock geology are not as easily identified in the offshore but are probably as varied as on land.

Four major geological or bedrock units are represented: (1) the Acadian Basin, an area of Triassic rocks in the Bay of Fundy and northern Gulf of Maine, (2) terrestrial bedrock extending to 25 km off-shroe along the Atlantic coast of Nova Scotia and into basins on the south side of the Gulf of Maine, (3) an outer area comprising the Middle and Outer Scotian Shelf, consisting of Jurrasic, Cretaceous, and Tertiary rocks and including Georges Bank, the outer Gulf of Maine, and the outer part of the Laurentian Channel, and (4) Sydney Basin, an area of carboniferous rocks northeast of Cape Breton Island. Northumberland Strait is underlain in places by Ordovician to Middle Carboniferous rocks of the Antigonish and Cape Breton highlands, and by horizontal or gently folded Upper Carboniferous and Permian sedimentary rocks.

Seabed Morphology
The basic features of the marine "landscape" were formed during long periods of terrestrial erosion of ancient bedrock surfaces. This topography was subsequently modified by the passage of glaciers and, on a smaller scale, by the action of the sea. The large features (e.g., banks and basins) are not unlike uplands, peneplains, and valley systems on the modern mainland surface, sharing their elevation and extent, although the continental shelf lacks priminent geological features like those found on land (e.g., Cape Breton highlands, North Mountain). Where ancient drainage systems reached the edge of the continental shelf, dramatic, steep-sided submarine valleys reach down the continental slope. Glacial features create more localized variations in landscape and include moraines and other features, such as pockmarks and iceberg scours (see T3.4). The surface sediment patterns on the continental shelf result from the action of the ocean and its interaction with retreating Holocene glaciers. The finest surface features are caused by waves and currents, and include sand ridges, waves, and ripples. Sable Island (Region 890) is a unique offshore feature derived from glacial material on top of early bedrock features

Climate
The climate of the Offshore/Continental Shelf Region follows the general pattern found on land but does not show the same degree of local variation. In addition to atmospheric factors, the temperature of the ocean and distance from land influence climate at sea. The ocean can hold heat and tends to moderate the temperature of the air above it.

In general, wind speeds are higher over the sea than over land because of reduced wind resistance. However, offshore winds are reduced within a few kilometres of the shore because of the shielding effect of the land. Further out to sea, wind is virtually unhindered and assumes a speed which more closely resembles the velocity of the wind tens of metres above the surface.

The temperatures of water masses influence air temperatures, significantly in some cases. In early spring the water is cold and cools the air above it, frequently forming fog. As the season progresses, the surface waters are heated by sunlight and grow gradually warmer. This rise is punctuated by periods when storms bring cold water to the surface and bring temporary declines in temperature. The annual peak water temperature occurs in the fall in the Atlantic (Unit 911) and the Outer Bay of Fundy (Unit 912), but warmer temperatures are observed in late summer in the Northumberland Strait (Unit 914), Minas Basin (sub-Unit 913a), and shallow coastal bays and inlets (District 460) where water is shallower and less influenced by colder, deeper water. The resulting warmer water temperatures make these areas popular for tourists.

Areas where warm and cold water masses meet are also marked by abrupt changes in air temperature. Just beyond the outer edge of the continental shelf, a warmer water mass (slope water) meets the shelf water and results in a sudden temperature change for ships passing across the boundary. Further offshore, the edge of the Gulf Stream heralds a sudden jump in temperatures to near tropical conditions. Even in winter, sailors can work comfortably here in shirt sleeves. In both cases, fog frequently occurs along the boundaries as warmer humid air flows over cooler water and condensation (fog) develops.

The waters of the Outer Bay of Fundy seldom have a chance to warm at the surface because of the significant mixing caused by tidal movements. Consequently, the water is cool most of the year. Just outside the Bay of Fundy, however, the water is more stable and can warm up more. The contrast in the temperatures of these water masses is one of the causes of the frequent fogs in southwest Nova Scotia, particularly near Yarmouth.

Oceanography
Tides, winds, buoyancy, and remote forcing are important oceanographic factors on the continental shelf (see T6.1). The large ocean currents include the extension of the Gaspé Current in Northumberland Strait, and the Nova Scotia Current along the continental shelf. The Gulf Stream comes closest to the Canadian continental shelf off East Georges Bank (sub-Unit 931a). Other oceanographic features include coastal upwelling, estuarine circulation, tidal fronts, tidal gyres, shelf-break fronts, and warm-core rings.

Temperature and salinity are important components of oceanic climate and influence biological productivity. In February, upper layer temperatures in some areas are at or near freezing, while temperatures on the South Shore of Nova Scotia and in the Bay of Fundy are considerably warmer. August temperatures are highest in Northumberland Strait and become cooler southwestwards from Cape Breton along the Atlantic Coast (Region 800). At the sea surface on the Scotian Shelf, temperature and salinity increase as one moves southeastwards from land.

Sediments
Most sediments on the continental shelf originated as glacial deposits. Glacial till was deposited in some places, while silt from glacial meltwater extended widely. Following glaciation, glacial till on the shallower parts was exposed to the action of the ocean, which washed and sorted it and spread a layer of clays to the deep basins and a fringe of sand to the offshore banks, resulting in the general pattern observed today. Unlike the land, the ocean bottom has not been modified significantly by the growth of plants and soil formation, and in many cases is being continually altered, at least in surface layers, by ocean processes.

The tops of banks and shallow coastal areas throughout the Region are generally sandy to gravelly in character and occasionally have large boulders like the glacial erratics found on land, thus making bad trawling ground. Below a depth of 100-120 m, the sediments have more sand and finer material but still contain boulders and gravel. These deeper sediments were never reworked by rising sea levels at the end of the last glaciation and consequently have retained more fine sediment components. In contrast, near the Atlantic coast of Nova Scotia and up to 25 km offshore, the bottom is rough and rocky - part of the bedrock of the coastal land mass. The relatively steep slope, in combination with rising sea levels, led to the scouring of most of the surface sediment, leaving only bedrock.

In the deeper basins, clays occur, because water motion is low enough to permit fine particles to settle. Deep channels and submarine canyons frequently have strong currents and usually contain coarse sediments. The bottom of the continental slope has thick surficial sediments of clay and sand.

Plants
Beds of kelp and other marine algae grow on the seabed close to shore, and microscopic phytoplankton occur both nearshore and in most other waters. Most anchored marine plants can occur only to a depth of about 30 m and generally fall into two types: those attached to rocks and those in soft bottom. The main attached species of the Nova Scotia coast are the kelps and rockweeds, but more than 300 species of seaweed occur around Nova Scotia coasts.

Marine seaweed growth is most abundant on exposed rocky shores typical of the Atlantic coast, where there are sites for attachment and adequate water movements to supply nutrients. Seaweeds generally grow less and their shapes change in sheltered environments. In areas with ice cover through part of the year, profuse algal growth can develop only beneath the depth of winter ice scour, even on a suitable substrate. These areas - the Northumberland Strait (Unit 914), Inner Bay of Fundy (Unit 913), and Bras d'Or Lake (Unit 916) - have a characteristic intertidal zone scraped clean of algae every year but upon which a carpet of algae can develop seasonally. Irish Moss develops in the subtidal zone beneath the ice in western and northern P.E.I.

Particularly in the Northumberland Strait but also in protected inlets and bays throughout Nova Scotia, soft bottoms, usually just below tide level, are populated by Eelgrass. This flowering plant grows the world over and is important in marine food chains. Eelgrass beds support a diverse invertebrate fauna as well as the young stages of a variety of fish and shellfish species.

Phytoplankton, notably diatom growth, occurs throughout the offshore and creates the main food source for planktonic animals and bottom-dwelling filter feeders. It eventually reaches and supports the extensive offshore fisheries resource. Areas of enhanced phytoplankton growth occur where ocean conditions bring nutrients to the surface, such as along the Atlantic coast, off southwest Nova Scotia, on the northern margin of Georges Bank (upwellings), and in a band stretching along the outer edge of the Scotian Shelf, where shelf and slope water meet and nutrients come to the surface. Water column activity peaks from spring to summer.

Plants in the Nova Scotia offshore are generally typical of the boreal cold-water species which occur throughout much of the North Atlantic. Plant production of both seaweeds and phytoplankton in these areas is typically among the highest in the world. Occasional warmer-water species occur, often introduced by shipping. A suite of warm-water algae occurs in the Gulf of St. Lawrence in estuaries and lagoons where water temperatures are higher.

Animals
Oceanic food chains are based on phytoplankton primary production. Most organisms in the ocean feed on phytoplankton, if only in their juvenile stages. Microscopic phytoplankton is consumed directly by grazing vertebrates, invertebrates and by suspension feeders such as mussels, scallops and oysters. Seaweeds also form the basis for food chains involving grazers such as sea urchins, or a wide variety of detritivores, upon death. Invertebrate communities are much more in evidence in these ecosystems, within the water column, on substrate surfaces as well as within the sediments.

The major commercial fish species are groundfish that live on or near the bottom and include cod, haddock, pollock, halibut, and various species of flatfish. These feed on seabed invertebrates as adults but consume zooplankton as they develop from eggs and larvae.

Principal pelagic fish species on the continental shelf (herring, mackerel, Bluefin Tuna, capelin, and some smaller species) feed on zooplankton or smaller fish all their lives (herring can use gill structures to filter the water). Deep water beyond the shelf break has an oceanic fauna with characteristic zooplankton and mesopelagic fish, cephalopods, and crustaceans. Baleen whales such as the Humpback feed on zooplankton, and toothed whales, including the endangered Northern Right Whale, another common Nova Scotia species, feed on fish and squid. Nova Scotia has a summer population of rare Bottlenose Whales near Misaine Bank that feeds on squid concentrated there.

Seabirds include common species associated with land and coastal areas (Herring and Black Back gulls, Great and Double-crested cormorants) and truly oceangoing birds such as shearwaters, terns, jaegers, phalaropes, and Storm-petrels, which migrate seasonally into Nova Scotia waters. Nesting colonies of gannets, puffins, petrels, and kittiwakes use offshore waters as a food source, with certain species sometimes flying daily to outer parts of the continental shelf. Waters off Nova Scotia are resting places for more northerly species and for overwintering waterfowl such as geese and seaducks.

Cultural Environment
For thousands of years the waters off Nova Scotia have been important for coastal transportation and their marine resources have been used by aboriginal peoples and later immigrants. The abundance of marine fisheries was noted by early European explorers. Excellent harbours provided sites for European settlement, commerce, and strategic naval and military bases (e.g., Louisbourg 1712 and Halifax 1749). The wide range of seaweed, shellfish, groundfish, pelagic fish, and marine mammal resources are now regulated to compensate for overuse and the effects of coastal pollution. Closure of the ground fisheries in 1992 had a severe economic impact. Hydrocarbon (oil and gas) and other mineral resources of the seabed are under development. Several marine locations have been used as dumping areas, particularly for munitions, and many submarine cables have been laid throughout the Region.

Associated Topics T2.7 Offshore Geology T3.5 Offshore Bottom Characteristics T5.1 The Dynamics of Nova Scotia's Climate T5.2 Nova Scotia's Climate T6.2 Oceanic Environments T6.3 Coastal Aquatic Environments T10.9 Algae T11.5 Freshwater Wetland Birds and Waterfowl T11.7 Seabirds and Birds of Marine Habitats T11.12 Marine Mammals T11.14 Marine Fishes T11.17 Marine Invertebrates T12.3 Geology and Resources T12.6 The Ocean and Resources

Associated Habitats H1.1 Offshore Open Water H1.2 Offshore Benthic H2 Coastal