[vc_row][vc_column][vc_column_text]Continental slope – The slope is “the deepening sea floor out from the shelf edge to the upper limit of the continental rise, or the point where there is a general decrease in steepness” (IHO, 2008). Compared with the relatively flat surface and gentle inclination of the continental shelf, the continental slope dips steeply into the ocean basins at an average angle of around 4° although it may be much steeper locally (35 to 90°). The continental slope (often referred to simply as “the slope”) is commonly dissected by submarine canyons; faulting, rifting and slumping of large blocks of sediment can form steep escarpments, relatively flat terraces and (under certain conditions) basins perched on the slope.
On average, the slope is a narrow band ~41 km wide that encircles all continents and islands. The passive margin slopes of the South Atlantic Ocean are the widest on average (73 km), although the slope attains its greatest width of 368 km in the North Atlantic, where the slope protrudes south of Newfoundland. The most narrow, active margin, slopes are in the Mediterranean and Black Seas (25.8 km). The average width of active slopes (35.6 km) is somewhat less than the average width of passive margin slopes (45.7 km).[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]
The continental slope extends from the shelf break to water depths typically of around 3,000–4,000 m where an abrupt change in gradient delimits the foot of slope. It may be bounded on its seaward margin by thick deposits comprising the continental rise or basin-filling deposits of the (essentially flat) abyssal plains. The seaward limit of the continental slope is denoted by a general reduction in slope, tending toward the horizontal.
A first-order control on continental slope morphology is the tectonic setting of the margin. Emery (1980) and Uchupi and Emery (1991) noted that active and passive continental margin types exhibit differences in morphology that can be attributed to the processes governing their formation. Passive margin morphology is controlled by deposition and erosion processes, whereas active margin morphology is controlled by tectonic/magmatic processes. Thus, passive margins generally are less steep and are likely to have adjacent sedimentary continental rises and abyssal plains. In contrast, active margins are thinly draped by sediments and may have an adjacent ocean trench or trough.
Depth is found in many studies to be a fundamental (biome-defining) parameter that correlates with the occurrence of biota (McArthur et al., 2010), and continental slopes span a great range of depths, from the shelf break to ~4,000 m. For these reasons, associations between benthic communities and geomorphic features on the continental slope must be considered in the context of their depth of occurrence. Althaus et al. (2012) conclude that “while some (slope) geomorphic features have high potential to act as surrogates for biodiversity at intermediate spatial scales, a hierarchical context is necessary to define and validate them within a larger, biogeographical context.”[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_column_text]
Althaus, F., Williams, A., Kloser, R.J., Seiler, J., Bax, N.J., 2012. Ch. 48: Evaluating geomorphic features as surrogates for benthic biodiversity on Australia’s western continental margin. In: Harris, P.T., Baker, E.K. (Eds.), Seafloor geomorphology as benthic habitat: GeoHAB Atlas of seafloor geomorphic features and benthic habitats. Elsevier, Amsterdam, pp. 665-679.
Emery, K.O., 1980. Continental margins; classification and petroleum prospects. AAPG Bulletin 64, 297-315.
Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4-24.
IHO, 2008. Standardization of Undersea Feature Names: Guidelines Proposal form Terminology, 4th ed. International Hydrographic Organisation and Intergovernmental Oceanographic Commission, Monaco, p. 32.
McArthur, M.A., Brooke, B.P., Przeslawski, R., Ryan, D.A., Lucieer, V.L., Nichol, S., McCallum, A.W., Mellin, C., Cresswell, I.D., Radke, L.C., 2010. On the use of abiotic surrogates to describe marine benthic biodiversity Estuarine, Coastal and Shelf Science 88, 21-32.
Uchupi, E., Emery, K.O., 1991. Genetic global geomorphology: a prospectus, in: Osborne, R.H. (Ed.), From shoreline to abyss: contributions in marine geology in honor of Francis Parker Shepard. SEPM Special Publication, Tulsa, Oklahoma, pp. 273-290.