Geology and Seabed Morphology
The Atlantic Unit extends from Scatarie Bank off eastern Cape Breton Island to Brier Island on the west coast of Nova Scotia and includes German Bank off southwestern Nova Scotia. It is underlain by coastal extensions of Meguma bedrock, part of the Atlantic Uplands formation, and the surface is a combination of sandy/gravelly till, larger rocks and boulders, and exposed bedrock ledges. Most of the Atlantic Unit occurs on the Scotian Shelf, and bedrock slopes gradually offshore for 25 km to depths of approximately 110 m. There are significant surficial features, including gravel waves, bedrock folding, drumlins, and small glacial moraines. An extensive field of sand waves occurs on German Bank (50-100 m long). Most of the exposed coastline is rocky or in sand beaches but contains numerous protected bays and inlets, in many of which finer substrates occur.
Surface sediments are thin and represent the remnants of glacial till which was extensively modified and removed during the recent advance of the sea. What remains of the glacial deposits is coarse gravel and sands (Sable Island Sand and Gravel) confined to depressions on the bedrock surface. The bedrock contains eroded valleys filled with glacial till. These extend from shore at the mouths of many major rivers that once flowed out onto the exposed shelf. Nearshore areas can have a variety of sediments as a result of local formation. A few localized depressions such as Chedabucto Bay contain pockets of clay.
The Unit is exposed to the Atlantic Ocean and, for the most part, the influence of the coastal Nova Scotia Current. Water movement shows a predominant drift southwestwards (the Nova Scotia Current). Coastal upwelling is driven in most of the District by southwesterly summer winds; however, off Cape Sable it is apparently driven by alongshore density variations maintained by tidal mixing (see T6.1).
Conditions in the western portion overlap those in the Bay of Fundy, possibly because of cooler ocean temperatures associated with upwelling induced by tides, but this part of the District differs from the Bay of Fundy by having a reduced tidal regime.
Surface waters are relatively fresh and warm. Underneath is a cold, more saline intermediate layer, and near the bottom a slightly warmer yet more saline layer with a larger slope water component.
The Atlantic Unit has some of the most significant seaweed growth and productivity in the province owing to the availability of suitable rocky bottom and adequate wave energy. Sheltered bays and estuaries have significant Eelgrass beds and tidal marshes.
Seaweeds occur in shallow water near shore, and phytoplankton is important throughout the Unit. The dominant species of kelp are Laminaria longicruris, L. digitata, and Alaria esculenta in the shallow subtidal; and Agarum cribrosum in deeper waters. Encrusting coralline algae cover rock surfaces in the shallower parts. Eelgrass grows in soft substrates in sheltered inlets along the coast.
Similar species of lower animals (arctic-boreal in exposed areas and Virginian in sheltered situations) can be found throughout the Unit, varying according to local distributions of substrates and plants. The distribution of fish, birds, and marine mammals is more complex, reflecting long-established movement patterns and stock distributions. The spawning, summer, and larval distributions of herring coincide with the upwelling zones in southwestern Nova Scotia. Inshore concentrations of Atlantic Halibut are known off Cape Sable Island.
Bottom invertebrate communities typically include the Horse Mussel; sea cucumbers
Cucumaria frondosa and Psolus fabricii; a sea star Asterias vulgaris; the amphipods
Corophium bonelli, Ischyrocerus anguipes,
Jassa falcata, and Caprella spp.; the barnacles Balanus crenatus and B. hameri; the crabs Cancer borealis and C. irroratus; and lobsters, scallops, quahogs, and sea urchins.
Click to enlarge
Several species of seabirds occur in offshore waters and Leach's Storm-petrel breeds on coastal islands chiefly in this Unit. Grey and Harbour seals frequent coastal waters, and the small Harbour Porpoise is sparsely distributed along the coast. Several species of whale, including the Humpback, Fin, Minke, Northern Right, Pilot and Sei Whales, move through coastal waters and can be seen near the coast, though significant feeding areas are found only at the mouth of the Bay of Fundy.
Common Eider form large summer moulting concentrations offshore in the Port Mouton to Port l'Hebert area of the South Shore. Dense concentrations of Canada Geese overwinter in inlets in the above area and in the Musquodoboit to Cole Harbour area of the Eastern Shore, feeding on Eelgrass beds there.
The Atlantic Unit contains valuable resources of seaweed, lobster, herring, and mackerel. These tend to be most abundant in the southwest, but herring are important in Chedabucto Bay during the winter. Many communities have fleets of fishing vessels that make trips to Middle and Outer Shelf Districts 920 and 930 and further. Concentrations of Ocean Quahog are found mainly within a few miles of the shore,
but Sea Scallop are fished commercially on the German Bank. Seaweeds, particularly Irish Moss and rockweeds, are harvested and processed in the southwestern part of the Unit. Fisheries are regulated as part of Fishing Zone 4. Productive salt marshes, mud flats, sand beaches, and offshore islands are significant wildlife habitat and provide recreational opportunities for field naturalists and hunters. Waterfowling in the fall is
a traditional, regulated hunt for ducks and geese. Several provincial and federal wildlife management areas have been created on the coast (e.g., the Eastern Shore Island Wildlife Management Area). The coast is generally used for commercial shipping and recreational boating, and there are some military training areas (e.g., off Osborne Head).
|T2.2 The Avalon and Meguma Zones|
|T3.5 Offshore Bottom Characteristics|
|T6.1 Ocean Currents|
|T6.2 Oceanic Environments|
|T10.9 Algae||T11.7 Seabirds||
|T11.12 Marine Mammals|
|T11.14 Marine Fishes|
|T11.17 Marine Invertebrates|
|T12.6 The Ocean and Resources|
|T12.10 Plants and Resources|
|T12.11 Animals and Resources|
|T12.12 Recreational Resources||
|Associated Coastal Districts|
|810 Basalt Peninsula|
|820 Cliffs and Beaches|
|830 Beaches and Islands|
|840 Quartzite Headlands|
|850 Granite Barrens|
|860 Sedimentary Lowlands|
|870 Till Plain|