Continental Slope

Overview

The continental slope marks the transition between the continental shelf and the deeper waters of the North Atlantic. The edge, or shelf break, generally occurs at ~200 m. in most places. At this depth the bottom falls away relatively steeply until it meets the continental rise, which slopes gradually to the deepest areas of the North Atlantic.1

Surface area

9,392 mi2 (24,325.17 km2)

Depth

~100 to ~2000 m (the shallowest depth occurs in a few places where the most rapid change in slope occurs at 100 m)

Bathymetry including key features

The upper slope has a gradient of 7-8 degrees; it flattens with depth as it meets the continental rise.2 More than fifteen canyons mark the continental slope where it passes along the southern edge of Georges Bank.3 The larger canyons are as deep as 400 m and as wide as 5 km.4 These canyons provide habitat for a variety of species not found on the smoother portions of the continental slope.5

Substrate

In general, the substrate of the continental slope is comprised of sandy and clayey silt.6 Shallower portions of the slope are sandy. Below a line found at 250 m – 300 m sediments are characterized by silt and clay. The canyons are characterized by coarse sediments and rock outcrops. Occasional boulders occur that were deposited by glaciers and pockets of sand are found that are formed as a result of slumping of slope sediments.7

Relationship to large-scale circulatory patterns of the Gulf of Maine

Currents in the vicinity of the continental slope are isolated from the Gulf of Maine by Georges Bank, the eastern coastal shelf and the Scotian shelf. Dense, warmer and more saline water from the continental slope outside of the Gulf enters the Gulf through the Northeast Channel. Surface waters from the Gulf exit the Gulf through the Great South Channel and the Northeast Channel. The clockwise gyre that occurs on Georges Bank creates a front between the waters of the Bank and the shallower waters of the continental slope.

Information on average (seasonal/annual) oceanographic conditions

The oceanography of the continental slope is characterized by three vertical layers. A deep cold layer comprises two thirds of the water column. A middle warmer layer comprises the majority of the remainder of the water column. Seasonal warming creates a still warmer third layer during the summer months. This layer penetrates no more than 200 m of slope waters. Eddies of the Gulf Stream are the principle source of variability in slope waters. Eddies take the form of either warm or cold core rings, which persist for several months. Ranging in size from 150 m to 230 m in diameter at the surface, such rings extend, in the shape of a funnel, as much as 2000 m in depth. The exchange of water by means of Gulf Stream rings has a significant impact on the oceanography of the continental slope and shelf.8

1 New England Seabirds, Undated
2 U.S. Geological Survey GLORIA Mapping Program, Undated
3 Dorsey and Pederson, 1998
4 U.S. Geological Survey GLORIA Mapping Program, Undated
5 Dorsey and Pederson, 1998
6 Ibid.
7 New England Fisheries Management Council, 2003
8 Ibid.