Irish Sea

2007 Schools Wikipedia Selection. Related subjects: Geography of Great Britain

Relief map of the Irish Sea. Major ports shown as red dots. Freight only ports as blue dots.
Relief map of the Irish Sea. Major ports shown as red dots. Freight only ports as blue dots.

The Irish Sea ( Irish: Muir Éireann) separates the islands of Ireland and Great Britain. It is connected to the Atlantic Ocean by St George's Channel between the Republic of Ireland and Wales and Cornwall to the south and by the North Channel between Northern Ireland and Scotland to the north-east. The Isle of Man lies in the middle of the Irish Sea. The sea is of high economic importance to regional trade, shipping and transport, fishing and power generation in the form of wind power and nuclear plants. There has been long discussion of building a 80 km (50 mile) rail tunnel to link Britain and Ireland; annual traffic between the two islands amounts to over 12 million passengers and 17 megatonnes of trade.


Ireland has no tunnel or bridge connection to a continent. Thus the vast majority of heavy goods trade is done by sea. Northern Irish ports handle 10 megatonnes of goods trade with Britain annually, while ports in the south handle 7.6 Mt, representing 50% and 40% respectively of total trade by weight.

Liverpool and Birkenhead port handles 32 Mt cargo and 734 thousand passengers a year . Holyhead port handles most of the passenger traffic from Dublin and Dun Laoghaire port, as well as 3.3 million tonnes of freight.

Ports in the Republic handle 3,600,000 travelers crossing the Irish sea each year, amounting to 92% of all sea travel . This has been steadily dropping for a number of years (20% since 1999), probably as a result of low cost airlines.

Ferry connections between Britain to Ireland via the Irish Sea include the routes from Swansea to Cork, Fishguard and Pembroke to Rosslare, Holyhead to Dún Laoghaire, Stranraer to Belfast and Larne, and Cairnryan to Larne. There is also a connection between Liverpool and Belfast via the Isle of Man. The world's largest car ferry, Ulysses, is operated by Irish Ferries on the Dublin–Holyhead route.


The Irish Sea has undergone a series of dramatic changes over the last 20,000 years as the last ice age ended and was replaced by warmer conditions. At the height of the ice age the central part of the modern sea was probably a long freshwater lake. As the ice retreated 10,000 years ago the lake reconnected to the sea, becoming brackish and then fully saline once again.


The Irish Sea has been subject to heavy radioactive contamination by the first British weapons grade 239Pu nuclear production plant and power station at Sellafield, also known as Windscale. (See the Sellafield page about the naming of this site.) An estimated 250 kg of plutonium have been deposited in marine sediments during the first decades of production. Another source of radioactive pollution may be the Dundrennan Range on the Solway Firth. Further north are the Holy Loch (the location of a United States Navy base [1960 to 1991]) and Faslane bases, where nuclear submarines were serviced during the cold war. After the Chernobyl disaster, rain containing Cs-137 and other radioactive material fell in the area. The area of the Beaufort's Dyke has been used as a dump for chemical weapons and possibly more nuclear waste.

The Irish Sea Forum is an environmental forum concerned with the Irish Sea. Some elements of the Irish Sea fishery are subject to collapse, due to overfishing from worldwide population growth, and also due to marine pollution. In response, the UK government has created Biodiversity Action Plans related to the solea solea and other fishes.

U-boat Alley

During the Great War the Irish Sea became known as “ U-boat Alley”. After the United States entered the war in 1917, the U-boats moved their emphasis from the Atlantic to the Irish Sea.

Oil and gas exploration

East Irish Sea Basin

With 7.5 trillion cubic feet (210 km³) of gas and 176 million barrels (28,000,000 m³) of oil estimated by the field operators as initially recoverable reserves from eight producing fields (DTI, 2001), the East Irish Sea Basin is at a mature exploration phase. Early Namurian basinal mudstones are the source rocks for these hydrocarbons. Production from all fields is from fault-bounded traps of the Lower Triassic formation, principally aeolian Sherwood Sandstone reservoir, top-sealed by younger Triassic continental mudstones and evaporites. Future exploration will initially concentrate on extending this play, but there remains largely untested potential also for gas and oil within widespread Carboniferous fluvial sandstone reservoirs. This play requires intraformational mudstone seal units to be present, as there is no top-seal for reservoirs subcropping the regional base Permian unconformity in the east of the basin, and Carboniferous strata crop out at the sea bed in the west.

Caernarfon Bay Basin

The Caernarfon Bay Basin contains up to 7 km of Permian and Triassic syn-rift sediments in an asymmetrical graben that is bounded to the north and south by Lower Paleozoic massifs. Only two exploration wells have been drilled so far, and there remain numerous undrilled targets in tilted fault block plays. As in the East Irish Sea Basin, the principal target reservoir is the Lower Triassic, Sherwood Sandstone, top-sealed by younger Triassic mudstones and evaporites. Wells in the Irish Sector to the west have demonstrated that pre-rift, Westphalian coal measures are excellent hydrocarbon source rocks, and are at peak maturity for gas generation (Maddox et al., 1995). Seismic profiles clearly image these strata continuing beneath a basal Permian unconformity into at least the western part of the Caernarfon Bay Basin. The timing of gas generation presents the greatest exploration risk. Maximum burial of, and primary gas migration from, the source rocks could have terminated as early as the Jurassic, whereas many of the tilted fault blocks were reactivated or created during Paleogene inversion of the basin. However, it is also possible that a secondary gas charge occurred during regional heating associated with intrusion of Paleogene dykes, such as those that crop out nearby on the coastline of north Wales. (Floodpage et al., 1999) have invoked this second phase of Paleogene hydrocarbon generation as an important factor in the charging of the East Irish Sea Basin’s oil and gas fields. It is not clear as yet whether aeromagnetic anomalies in the south-east of Caernarfon Bay are imaging a continuation of the dyke swarm into this area too, or whether they are instead associated with deeply buried Permian syn-rift volcanics. Alternatively, the fault block traps could have been recharged by exsolution of methane from formation brines as a direct result of the Tertiary uplift (cf. Doré and Jensen, 1996).

The Cardigan Bay Basin

The Cardigan Bay Basin forms a continuation into UK waters of Ireland’s North Celtic Sea Basin, which has two producing gas fields. The basin comprises a south-easterly deepening half-graben near the Welsh coastline, although its internal structure becomes increasingly complex towards the south-west. Permian to Triassic, syn-rift sediments within the basin are less than 3 km thick and are overlain by up to 4 km of Jurassic strata, and locally also by up to 2 km of Paleogene fluvio-deltaic sediments. The basin has a proven petroleum system, with potentially producible gas reserves at the Dragon discovery near the UK/Ireland median line, and oil shows in a further three wells. The Cardigan Bay Basin contains multiple reservoir targets, which include the Lower Triassic (Sherwood Sandstone), Middle Jurassic shallow marine sandstones and limestone (Great Oolite), and Upper Jurassic fluvial sandstone, the reservoir for the Dragon discovery. The most likely hydrocarbon source rocks are early Jurassic marine mudstones (Lias Group). These are fully mature for oil generation in the west of the UK sector, and are mature for gas generation nearby in the Irish sector. Gas-prone, Westphalian pre-rift coal measures may also be present at depth locally. The Cardigan Bay Basin was subjected to two Tertiary phases of compressive uplift, whereas maximum burial that terminated primary hydrocarbon generation was probably around the end of the Cretaceous, or earlier if Cretaceous strata, now missing, were never deposited in the basin. Despite the Tertiary structuration, the Dragon discovery has proved that potentially commercial volumes of hydrocarbons were retained at least locally in Cardigan Bay. In addition to undrilled structural traps, the basin contains untested potential for stratigraphic entrapment of hydrocarbons near synsedimentary faults, especially in the Middle Jurassic section.

The Liverpool Bay Development is BHP Billiton Petroleum's largest operated asset. It comprises the integrated development of five offshore oil and gas fields in the Irish Sea:

  • Douglas oil field
  • Hamilton gas field
  • Hamilton North gas field
  • Hamilton East gas field
  • Lennox oil and gas field

Oil is produced from the Lennox and Douglas fields. It is then treated at the Douglas Complex and piped 17 kilometres to an oil storage barge ready for export by tankers.

Gas is produced from the Hamilton, Hamilton North and Hamilton East reservoirs. After initial processing at the Douglas Complex the gas is piped by subsea pipeline to the Point of Ayr gas terminal for further processing. The gas is then sent by onshore pipeline to PowerGen's combined cycle gas turbine power station at Connah's Quay. PowerGen is the sole purchaser of gas from the Liverpool Bay development.

First production

  • Hamilton North 1995
  • Hamilton 1996
  • Douglas 1996
  • Lennox (oil only) 1996
  • First contract gas sales 1996
  • Hamilton East 2001

Facility details The Liverpool Bay development comprises:

Four offshore platforms. Offshore storage and loading facilities. The onshore gas processing terminal at Point of Ayr.

Proposed tunnel projects

Discussions of linking Britain to Ireland began in 1895, with an application £15,000 towards the cost of carrying out borings and soundings in the North Channel to see if a tunnel between Ireland and Scotland was viable. Sixty years later Harford Montgomery Hyde, Unionist MP for North Belfast, called for the building of such a tunnel. . A tunnel project has been discussed several times in the Irish Parliament,

Several potential Irish Sea tunnel projects have been proposed, most recently the "Tusker Tunnel" between the ports of Rosslare and Fishguard proposed by The Institute of Engineers of Ireland in 2004. . A different proposed route is between Dublin and Holyhead, proposed in 1997 by a leading British engineering firm, Symonds, for a rail tunnel from Dublin to Holyhead. Either tunnel, at 80 km, would be by far the longest in the world, and would cost an estimated €20,000,000,000.

There could be an economic case for such a link. The Irish sea is one of the busiest shipping regions in the world and has the world's largest car ferry— Irish Ferries Ulysses . In addition, half of the air traffic at Dublin Airport is to Britain, with 8,300,000 passengers per annum. The Dublin-London air route is the busiest in the European Union and the second busiest in the world, with about 50 daily flights and 4.5 million journeys per annum. The success of the 15 km Oresund Bridge, inaugurated in 2000 and linking Malmö, Sweden and Copenhagen, Denmark, which has led to important economic integration between the two cities, suggests that the Dublin–Holyhead route may be the most promising. With the addition of high speed rail, such a tunnel could cut journey times from the northern English cities of Liverpool and Manchester to Dublin to under an hour. The combined population of the three metropolitan areas is over 5 million. The question would have to be raised over what gauge to build a rail link as Ireland uses a different gauge to the UK.

Despite this, and possibly due to the failure of the Channel Tunnel to generate adequate passenger numbers, various Irish government studies have concluded that an Irish Sea tunnel is, as yet, economically unfeasible.

Wind power

The North Hoyle] site 4 - 5 miles off the coast from Rhyl and Prestatyn in north Wales, containing thirty 2 MW turbines.Built in 2003 , about 10 km off the coast of County Wicklow in the south Irish Sea. The site currently has seven GE 3.6 MW turbines, each with 104 m rotor diameters, the world's first commercial application of offshore wind turbines over three megawatts in size. The operating company, Airtricity, has indefinite plans for nearly 100 further turbines on the site.

Further wind turbine sites include:

  • (Link), NPower Renewables</ref>
  • A site in the Solway Firth is being developed
  • Turbines are being erected off the coast of Walney Island
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