Celtic Sea

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The sea off Cork Harbour

The Celtic Sea is a posited area of the western Atlantic Ocean around the southern British Isles. Broadly the area so named is the sea off the south coast of Ireland bounded to the east by St George's Channel[1] and encompassing that shoulder of the ocean between Ireland and Cornwall, up into the Bristol Channel. However it is not a defined term; the seas around Brittany and even the Bay of Biscay have been included by some definitions. The southern and western boundaries may be delimited by the continental shelf, which drops away sharply.


The Celtic Sea takes its name from the Celtic heritage of the bounding lands to the north and east.[2] The name was first proposed by in 1921 by Ernest William Lyons Holt at a meeting of fisheries experts held in Dublin, which included representatives from across the British Isles and France.[2] The northern portion of this proposed sea had long been considered as part of St George's Channel and the southern portion as an undifferentiated part of the "Southwest Approaches" to Great Britain.

A common name was seen as of assistance because of the common marine biology, geology and hydrology.[2] The name ‘Celtic Sea’ was adopted in France before being common in the English-speaking countries.[2] It was adopted by marine biologists and oceanographers, and later by petroleum exploration firms.[3] It is named in a 1963 British atlas,[4] but a 1972 article states "what British maps call the Western Approaches, and what the oil industry calls the Celtic Sea [...] certainly the residents on the western coast [of Great Britain] don't refer to it as such."[5] The name is not much used, if at all, by fishmen on the coasts in question.


There are no land features to divide the Celtic Sea from the open Atlantic Ocean to the south and west. For these limits, Holt suggested the 200 fathom (366 m) marine contour and the island of Ushant off the tip of Brittany.

The definition approved by 1974 by the Hydrographer of the Royal Navy for use in Admiralty Charts was "bounded roughly by lines joining Ushant, Land's End, Hartland Point, Lundy Island, St. Govan's Head and Rosslare, thence following the Irish coast south to Mizen Head and then along the 200-metre isobath to approximately the latitude of Ushant."[6]

International definitions

The International Hydrographic Organization defines the limits of the Celtic Sea as follows:[7]

On the North. The Southern limit of the Irish Sea [a line joining St David's Head to Carnsore Point], the South coast of Ireland, thence from Mizen Head a line drawn to a position 51°0’0"N, 11°30’0"W.

On the West and South. A line from the position 51°0’0"N, 11°30’0"W South to 49°N, thence to latitude 46°30'N on the Western limit of the Bay of Biscay [a line joining Cape Ortegal to Penmarch Point], thence along that line to Penmarch Point.

On the East. The Western limit of the English Channel [a line joining Île Vierge to Land's End] and the Western limit of the Bristol Channel [a line joining Hartland Point to St Govan's Head].


The seabed under the Celtic Sea is called the Celtic Shelf, part of the continental shelf of Europe. The northeast portion has a depth of between 50 fathoms and 55 fathoms, increasing towards St George's Channel. In the opposite direction, sand ridges pointing southwest have a similar height, separated by troughs approximately 27 fsathoms deeper. These ridges were formed by tidal effects when the sea level was lower. South of 50° the topography is more irregular.[8]

Oil and gas exploration in the Celtic Sea has had limited commercial success. The Kinsale Head gas field supplied much of the Republic of Ireland in the 1980s and 1990s.

Outside links

("Wikimedia Commons" has material
about Celtic Sea)


  1. C.Michael Hogan. 2011. Celtic Sea. eds. P.saundry & C.Cleveland. Encyclopedia of Earth. National Council for Science and the /environment. Washington DC.
  2. 2.0 2.1 2.2 2.3 Haslam, D. W. (Hydrographer of the Royal Navy) (29 March 1976). "It's the Celtic Sea—official". The Times (59665): p. 15 (Letters to the Editor), col G. 
  3. Cooper, L. H. N. (2 February 1972). "In Celtic waters". The Times (58391): p. 20; col G (Letters to the Editor). 
  4. The Atlas of Great Britain and Northern Ireland. Clarendon Press. 1963. pp. 20–21. ; cited in
    Shergold, Vernon G. (27 January 1972). "Celtic Sea: a good name". The Times (58386): p. 20 (Letters to the Editor); col G. 
  5. Vielvoye, Roger (24 January 1972). "Industry in the regions Striking oil in Wales and West Country". The Times (58383): p. 19; col A. 
  6. Parliamentary Debates, House of Commons, 16 December 1974 , column 317W
  7. "Limits of Oceans and Seas, 3rd edition + corrections". International Hydrographic Organization. 1971. p. 42 [corrections to page 13]. http://www.iho-ohi.net/iho_pubs/standard/S-23/S23_1953.pdf. Retrieved 6 February 2010. 
  8. Hardisty, Jack (1990). The British Seas: an introduction to the oceanography and resources of the north-west European continental shelf. Taylor & Francis. pp. 20–21. ISBN 0-415-03586-4.