Irish Sea
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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 (the
Celtic Sea) 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 50 mile (80 km) rail tunnel to link Britain and Ireland; annual traffic between the two islands amounts to over 12 million passengers and 17
megatonnes of trade. Curiously, whilst territorial ownership of waters of the "Irish" Sea is in fact divided between
Britain and
Ireland, there appears to be no objection to the term within the UK (cf. controversy over the term
British Isles).
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
[Port Statistics, (Link), Mersey Docks Website]. Holyhead port handles most of the passenger traffic from Dublin and Dun Laoghaire port, as well as 3.3 million tonnes of freight.
[UK Port Traffic Highlights: 2002, (pdf), UK Maritime Statistics, Dept of Transport]Ports in the Republic handle 3,600,000 travelers crossing the Irish sea each year, amounting to 92% of all sea travel
[ Direct Passenger Movement by Sea from and to Ireland (Republic), (link), Central Statistics Office of Ireland]. This has been steadly 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.
See also: Transport in Ireland, Transport in the United Kingdom, Transport on the Isle of ManThe 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 (now closed) 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.
Despite the pollution, there is still plenty of interesting flora and fauna to be seen.
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.
[U-Boat Alley by Roy Stokes, published by Compuwreck, ISBN 0-9549186-0-6][The War in Maps: The Irish Sea, (Link), UBoat.net]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.
["Petroleum prospectivity of the principal sedimentary basins on the United Kingdom Continental Shelf" (pdf), Dept Trade and Industry, 2003][Liverpool Bay, UK, (Link), BHP Oil Ltd]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 detailsThe Liverpool Bay development comprises:
Four offshore platforms. Offshore storage and loading facilities. The onshore gas processing terminal at Point of Ayr.
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.
["An Irishman's Diary" by Wesley Boyd, (Link), The Irish Times, Feb 2004 (subscription required)]. A tunnel project has been discussed several times in the Irish Parliament,
[Written Answers. - Sea Transport, (Link), Dáil Éireann - Volume 384 - 16 November, 1988][Written Answers. - Irish Sea Railway Ferry, (Link), Dáil Éireann - Volume 434 - 19 October, 1993][Written Answers. - Ireland-UK Tunnel, (Link), Dáil Éireann - Volume 517 - 29 March, 2000][Written Answers - Transport Projects, (Link), Dáil Éireann - Volume 597 - 15 February, 2005]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 Vision of Transport in Ireland in 2050, IEI report (pdf), The Irish Academy of Engineers, 21/12/2004] [Tunnel 'vision' under Irish Sea, (link), BBC news, Thursday, 23 December, 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 [Largest Car Ferry, (Link), Guinness Book of Records]. 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 recent 15 km
Oresund Bridge between
Malmo,
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.
[Closing the gap with £1.5bn road-and-rail link, by Walt Kilroy, (Link), The Irish Times, Mon, Dec 29, 97] 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 "Ulster Gauge" not "standard gauge" in 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.
One of the world's largest wind farms is being developed on Arklow Bank
[Arklow Bank Project, (Link), Airtricity], 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:
* The North Hoyle] site off the coat of north
Wales, containing thirty 2 MW turbines.
[North Hoyle Offshore Wind Farm, (Link), NPower Renewables]* A site in the
Solway Firth is being developed
* Turbines are being erected off the coast of
Walney Island
