Shelf valleys –  Valleys incised more than 10 m into the continental shelf and greater than 10 km in length overall are mapped as shelf valleys.  Only features that had a definite elongate shape were included as valleys, nominally more than 4 times greater in length than width.  Features that intersected the shelf break and extended both onto the shelf and down-slope (where they become submarine canyons) were also included.  Shelf valleys of glacial origin incised >100 m into the shelf are mapped here as glacial troughs.

Shelf valleys are most common in polar areas where valleys have formed by glacial erosion (Hambrey, 1994; Anderson, 1999).  Non-glacial shelf valleys were formed mainly during the Pleistocene ice ages by fluvial erosion when rivers flowed across what is now the submerged continental shelf, and also by the erosive effects of tidal and other ocean currents.  Other non-glacial shelf valleys have formed in some tropical carbonate provinces, where valleys appear as inter-reef channels formed when sea level changes have left submerged banks (drowned reefs) stranded offshore, delimiting inter-bank channels that are a type of shelf valley (Harris et al., 2005).

False colour, 3D bathymetyric image of tidally incised shelf valleys in the Gulf of Papua (Papua New Guinea), showing dunes (yellow area) and patches of coral reef growth (red areas).  The image was produced using multibeam sonar echo-sounding data (reported by Harris et al., 2005).

False colour bathymetyric map of the Timor Sea region of northern Australia showing shelf valleys (indicated by arrows) incised into a 800 km long, shelf-edge, raised carbonate rim around Bonaparte Gulf.

The complexity of the seabed associated with incised shelf valleys (including rocky exposures along valley walls with soft sediments and sometimes bedforms on valley floors) gives rise to high biodiversity associated with these features.  In the English Channel (located between the UK and France) a shelf valley complex described by James et al. (2012) is characterized by comparatively rich macrofaunal communities comprising infaunal and epifaunal species such as interstitial polychaetes, pea urchins, barnacles and the creeping anemone Epizoanthus couchii.   In the adjacent North Sea, the walls of glacially incised tunnel valleys are colonized by bioherm-forming worms Sabellaria spinulosa documented by Pearce et al. (2012).

Statistics on shelf valleys (from Harris et al., 2014).

OceanShelf Valleys Area km2Shelf Valleys Area%% Shelf that is Shelf Valleys Shelf Valleys NumberAverage Shelf Valley Size km2
Arctic Ocean189,9201.462.82394480
Indian Ocean120,4300.1692.97289420
Mediterranean & Black Sea 25,4900.8433.5980320
North Atlantic 354,2000.7914.841,146310
North Pacific 249,4600.3044.06441570
South Atlantic 83,9200.2084.10114740
South Pacific 60,9800.07002.41346180
Southern Ocean43,1500.2121.5986500
All Oceans1,127,5600.3113.502,879390

Anderson, J.B., 1999. Antarctic Marine Geology. Cambridge University Press, Cambridge, UK.

James, J.W.C., Pearce, B., Coggan, R.A., Morando, A.  2012.  Ch. 41 Open shelf valley system, Northern Palaeovalley, English Channel, U.K., in: P. T. Harris, E. K. Baker (Eds.), Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitats, Elsevier, Amsterdam,

Hambrey, M.J., 1994. Glacial Environments. UCL Press, London.

Harris, P.T., Heap, A., Passlow, V., Hughes, M., Daniell, J., Hemer, M., Anderson, O., 2005. Tidally-incised valleys on tropical carbonate shelves: an example from the northern Great Barrier Reef, Australia. Marine Geology 220, 181-204.

Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4-24.

Pearce, B., Tappin, D.R., Dove, D., Pinnion, J., 2012. Ch. 42 Benthos supported by the tunnel-valleys of the southern North Sea, 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. 597-610.