900 Offshore/Continental Shelf
The following physiographic featuers are the basis for the division of the Districts of Region 900:
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.
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.
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.
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.
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.
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.
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.