Glacial troughs – Shelf valleys at high latitudes incised by glacial erosion during the Pleistocene ice ages form elongate troughs, typically trending across the continental shelf and extending inland as fjord complexes (Hambrey, 1994).  The largest of these features are glacial troughs, characterised by depths of over 100 m (often exceeding 1,000 m depth) and are distinguished from shelf valleys by an over-deepened longitudinal profile that reaches a maximum depth inboard of the shelf break, thus creating a perched basin on the shelf with an associated sill (Hambrey, 1994; Anderson, 1999).

Glaciation of the continents during the last ice age extended across what are now the continental shelves of Antarctica, western and northeastern North America (eg. Barrie et al., 2012), western Europe, Greenland, Iceland, South America, and New Zealand. U-shaped glacial valleys that exist as fjords along the coast extend in places across the full width of the continental shelf.  The Arctic Ocean has the largest absolute area of glacial troughs although they are more common in the Antarctic as a percentage of shelf area, covering more than 40% of the Antarctic shelf (see Table).

Geomorphic features of the continental margin off central-northern Norway showing banks, glacial troughs and submarine canyons (after Buhl-Mortenson et al., 2012).

Statistics on glacial troughs (after Harris et al., 2014). Note some glacial troughs extend onto the slope and so are not confined wholly to the shelf. As their name suggests, glacial troughs are formed by glacial erosion of the shelf during ice ages when continental ice sheets extended over what is now the submerged continental shelf.  They are on average 40 times larger than other shelf valleys, having an average size of 16,960 km2.  The 214 glacial troughs mapped here are more abundant in the northern hemisphere where 146 of them are found.  Glacial troughs cover 24% and 40% of shelf area of the Arctic and Antarctic shelf environments, respectively, but they are also found on shelves in Chile, British Columbia, Alaska New Zealand and northern Europe.

OceanGlacial Troughs Area km2Glacial Trough Area%% Shelf that is Glacial TroughGlacial trough numberAverage Glacial Trough Size km2
Arctic Ocean1,634,77012.624.35728,680
Indian Ocean00000
Mediterranean & Black Sea 00000
North Atlantic 740,0901.6510.15613,220
North Pacific 134,7100.1642.19334,080
South Atlantic 200.000040.0008120
South Pacific 27,3600.03141.08102,740
Southern Ocean1,091,7905.3740.26217,610
All Oceans3,628,7301.0011.321416,960

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

Barrie, J.V., Greene, H.G., Conway, K.W., Picard, K., 2012. Ch. 44: Inland Tidal Sea of the Northeastern Pacific. 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. 623-634.

Buhl-Mortensen, L., Bøe, R., Dolan, M.F.J., Buhl-Mortensen, P., Thorsnes, T., Elvenes, S., Hodnesdal, H., 2012. Ch. 51: Banks, Troughs, and Canyons on the Continental Margin off Lofoten, Vesterålen, and Troms, Norway. 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. 703-715.

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

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

Harris, P.T., O’Brien, P.E., 1996. Geomorphology and sedimentology of the continental shelf adjacent to Mac.Robertson Land, East Antarctica: a scalped shelf. Geo-Marine Letters 16, 287-296.