Atlantic Coastal Biome
249
into Acadian, Virginian, and Carolinian provinces, but this does not fully respond to
the variety of habitat included in NWCS and a more useful arrangement would be the
following:
(i) Newfoundland shelf, including the Grand Banks and Flemish Cap
(ii) Gulf of St. Lawrence
(iii) Northeast shelf and Gulf of Maine, from Cabot Strait to Cape Hatteras
(iv) South Atlantic Bight, from Cape Hatteras to the Florida Keys
It will be useful in this account to recognize this partition for some of the issues to be
discussed; the fourth compartment is required on account of its transitional character
with the CARB province to the south.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The continental shelf of eastern North America is a typical trailing-edge shelf and was
glaciated as far south as Cape Hatteras during the Pleistocene. The shelf shoals progressively southward from the anomalously deep regions off Labrador until, beyond Cape
Hatteras, it merges with the coastal plain ashore. In the northern regions, two entrants
greatly extend the area of shelf-depth water: (i) the Gulf of St. Lawrence that lies behind
Newfoundland, opening eastward above the glaciated deep trough of the Cabot Strait
and (ii) the more open Gulf of Maine, lying behind Georges Bank, and including the Bay
of Fundy.
The continental shelf is of great width (∼500 km) at the Grand Banks, which are isolated
from coastal processes by the Avalon Channel along the eastern coast of Newfoundland.
The sediments and topography of the Grand Banks reflect the effects of ice formation,
and extensive gravel beds represent the terminations of the continental glaciers of North
America. Lying further to the east is the isolated shallow water of the Flemish Cap.
Northeast of Newfoundland and north of the Grand Banks, a large flat area with depths
exceeding 200 m is often miscalled the Newfoundland Shelf.
Below Saguenay, the St. Lawrence River follows the deeply glaciated Laurentian Trough
that is the largest deep re-entrant on the American coastline. This trough continues
across the Gulf and passes out across the shelf through the Cabot Strait (45–47
N) as
the Laurentian Channel, which is both deep (<400 m) and wide (<100 km); this has
consequences for circulation and also for shelf-edge upwelling.
The topography on the Scotian Shelf is irregular, resembling that of the Grand Banks,
and there are several unusually deep (<200 m) basins at midshelf, whereas shallow
sandbanks are widespread on the outer shelf, of which one forms Sable Island. The Gulf of
Maine continues the glaciated topography and deposits, including the ice-cut Northeast
Channel between Georges Bank and the Scotian Shelf. Georges Bank, seaward of the Gulf,
is a large, shallow feature surrounded by deeper water and bears parallel sand ridges that
are sufficiently shallow as to force linear wave trains at the sea surface.
The Middle Atlantic Bight, between Cape Cod and Cape Hatteras, at all depths
shallower than the shelf break, bears terrigenous sediments of rather homogenous grade.
The flat, linear shelf of the South Atlantic Bight is dominated by the input of sediments
from many rivers and is quite unusually shallow, the break of slope occurring at only
80 m. The existence of a coastal frontal zone inhibits cross-shelf transport, so riverine
sediment accumulates inshore, while coarse-grained sediments dominate the outer shelf.
Tidal streams may be sufficiently rapid in some places, and water sufficiently shoal, that
stratification is rarely or never achieved; this may occur both inshore and also offshore,
as on the top of Georges Bank. The well-mixed shallow region of central Georges Bank
is separated from the surrounding stratified water in summer by an annular tidal front
that passes around the bank and has important consequences for the general productivity
of the bank ecosystem (Loder and Greenberg, 1986). Other tidally mixed areas occur
249
into Acadian, Virginian, and Carolinian provinces, but this does not fully respond to
the variety of habitat included in NWCS and a more useful arrangement would be the
following:
(i) Newfoundland shelf, including the Grand Banks and Flemish Cap
(ii) Gulf of St. Lawrence
(iii) Northeast shelf and Gulf of Maine, from Cabot Strait to Cape Hatteras
(iv) South Atlantic Bight, from Cape Hatteras to the Florida Keys
It will be useful in this account to recognize this partition for some of the issues to be
discussed; the fourth compartment is required on account of its transitional character
with the CARB province to the south.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The continental shelf of eastern North America is a typical trailing-edge shelf and was
glaciated as far south as Cape Hatteras during the Pleistocene. The shelf shoals progressively southward from the anomalously deep regions off Labrador until, beyond Cape
Hatteras, it merges with the coastal plain ashore. In the northern regions, two entrants
greatly extend the area of shelf-depth water: (i) the Gulf of St. Lawrence that lies behind
Newfoundland, opening eastward above the glaciated deep trough of the Cabot Strait
and (ii) the more open Gulf of Maine, lying behind Georges Bank, and including the Bay
of Fundy.
The continental shelf is of great width (∼500 km) at the Grand Banks, which are isolated
from coastal processes by the Avalon Channel along the eastern coast of Newfoundland.
The sediments and topography of the Grand Banks reflect the effects of ice formation,
and extensive gravel beds represent the terminations of the continental glaciers of North
America. Lying further to the east is the isolated shallow water of the Flemish Cap.
Northeast of Newfoundland and north of the Grand Banks, a large flat area with depths
exceeding 200 m is often miscalled the Newfoundland Shelf.
Below Saguenay, the St. Lawrence River follows the deeply glaciated Laurentian Trough
that is the largest deep re-entrant on the American coastline. This trough continues
across the Gulf and passes out across the shelf through the Cabot Strait (45–47
N) as
the Laurentian Channel, which is both deep (<400 m) and wide (<100 km); this has
consequences for circulation and also for shelf-edge upwelling.
The topography on the Scotian Shelf is irregular, resembling that of the Grand Banks,
and there are several unusually deep (<200 m) basins at midshelf, whereas shallow
sandbanks are widespread on the outer shelf, of which one forms Sable Island. The Gulf of
Maine continues the glaciated topography and deposits, including the ice-cut Northeast
Channel between Georges Bank and the Scotian Shelf. Georges Bank, seaward of the Gulf,
is a large, shallow feature surrounded by deeper water and bears parallel sand ridges that
are sufficiently shallow as to force linear wave trains at the sea surface.
The Middle Atlantic Bight, between Cape Cod and Cape Hatteras, at all depths
shallower than the shelf break, bears terrigenous sediments of rather homogenous grade.
The flat, linear shelf of the South Atlantic Bight is dominated by the input of sediments
from many rivers and is quite unusually shallow, the break of slope occurring at only
80 m. The existence of a coastal frontal zone inhibits cross-shelf transport, so riverine
sediment accumulates inshore, while coarse-grained sediments dominate the outer shelf.
Tidal streams may be sufficiently rapid in some places, and water sufficiently shoal, that
stratification is rarely or never achieved; this may occur both inshore and also offshore,
as on the top of Georges Bank. The well-mixed shallow region of central Georges Bank
is separated from the surrounding stratified water in summer by an annular tidal front
that passes around the bank and has important consequences for the general productivity
of the bank ecosystem (Loder and Greenberg, 1986). Other tidally mixed areas occur