Irish Sea
The Irish Sea is a body of water that separates the islands of Ireland and Great Britain. It is linked to the Celtic Sea in the south by St George's Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Channel. Anglesey, North Wales, is the largest island in the Irish Sea, followed by the Isle of Man. The term Manx Sea may occasionally be encountered.
On its shoreline are Scotland to the north, England to the east, Wales to the southeast, Northern Ireland and the Republic of Ireland to the west. The Irish Sea is of significant economic importance to regional trade, shipping and transport, as well as fishing and power generation in the form of wind power and nuclear power plants. Annual traffic between Great Britain and Ireland is over 12 million passengers and of traded goods.
Topography
The Irish Sea joins the North Atlantic at both its northern and southern ends. To the north, the connection is through the North Channel between Scotland and Northern Ireland and the Malin Sea. The southern end is linked to the Atlantic through the St George's Channel between Ireland and Pembrokeshire, and the Celtic Sea. It is composed of a deeper channel about long and wide on its western side and shallower bays to the east. The depth of the western channel ranges from to.Cardigan Bay in the south, and the waters to the east of the Isle of Man, are less than deep. With a total water volume of and a surface area of, 80% is to the west of the Isle of Man. The largest sandbanks are the Bahama and King William Banks to the east and north of the Isle of Man and the Kish Bank, Codling Bank, Arklow Bank and Blackwater Bank near the coast of Ireland. The Irish Sea, at its greatest width, is and narrows to.
The International Hydrographic Organization defines the limits of the Irish Sea as follows,
The Irish Sea has undergone a series of dramatic changes over the last 20,000 years as the last glacial period ended and was replaced by warmer conditions. At the height of the glaciation, 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.
History
The Irish Sea was formed in the Neogene era. The Irish Sea was called Mare Hibernicus in the Roman Empire. Notable crossings include several invasions from Britain. The Norman invasion of Ireland took place in stages during the late 12th century from Porthclais near St. Davids, Wales, in Hulks, Snekkars, Keels and Cogs to Wexford Harbour, Leinster. The Tudors crossed the Irish Sea to invade in 1529 in caravels and carracks.Shipping
Because Ireland has neither tunnel nor bridge to connect it with Great Britain, the vast majority of heavy goods trade is done by sea. Northern Ireland ports handle of goods trade with the rest of the United Kingdom annually; the ports in the Republic of Ireland handle, representing 50% and 40% respectively of total trade by weight.The Port of Liverpool handles of cargo and 734,000 passengers a year. Holyhead port handles most of the passenger traffic from Dublin and Dún Laoghaire ports, as well as of freight.
Ports in the Republic handle 3,600,000 travellers crossing the sea each year, amounting to 92% of all Irish Sea travel.
Ferry connections from Wales to Ireland across the Irish Sea include Fishguard Harbour and Pembroke to Rosslare, Holyhead to Dún Laoghaire and Holyhead to Dublin. From Scotland, Cairnryan connects with both Belfast and Larne. There is also a connection between Liverpool and Belfast via the Isle of Man or direct from Birkenhead. The world's largest car ferry, Ulysses, is operated by Irish Ferries on the Dublin Port–Holyhead route; Stena Line also operates between Britain and Ireland.
"Irish Sea" is also the name of one of the BBC's Shipping Forecast areas defined by the coordinates:
The British ship LCT 326 sank in the Irish sea and was discovered in March 2020. In September 2021, the British Navy ship HMS Mercury was discovered; it sank in 1940. The British ship SS Mesaba was sunk by the Imperial German Navy U-118 in 1918 and discovered in 2022. This ship is well known for sailing near the Titanic and for attempting to warn the Titanic about dangerous icebergs.
Oil and gas exploration
Caernarfon Bay Basin
The Caernarfon Bay basin contains up to 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 mudstone 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. 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. 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 southeast 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.
Cardigan Bay Basin
The Cardigan Bay Basin forms a continuation into British 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 southwest. Permian to Triassic syn-rift sediments are less than 3 km thick and overlain by up to 4 km of Jurassic strata, and locally up to 2 km of Paleogene fluvio-deltaic sediments. The basin has a proven petroleum system, with potentially producible gas at the Dragon discovery and oil shows in three other wells. Reservoir targets include Lower Triassic Sherwood Sandstone, Middle Jurassic shallow marine sandstones and limestones, and Upper Jurassic fluvial sandstone.The most likely hydrocarbon source rocks are Early Jurassic marine mudstones. These are fully mature for oil in the west of the UK sector and gas-mature in the adjacent Irish sector. Gas-prone Westphalian pre-rift coal measures may also exist locally at depth. The basin underwent two phases of Tertiary compressive uplift; maximum burial ended by the Late Cretaceous, or earlier if Cretaceous strata were never deposited. The Dragon discovery proves hydrocarbons were locally retained despite Tertiary deformation. Untested stratigraphic trap potential also exists near synsedimentary faults in the Middle Jurassic interval.
Liverpool Bay
The Liverpool Bay Development was BHP’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 km to an oil storage barge. Gas is produced from the Hamilton, Hamilton North and Hamilton East reservoirs. After initial processing at the Douglas Complex the gas is piped to the Point of Ayr terminal. It is then piped to PowerGen’s CCGT station at Connah’s Quay. PowerGen is the sole purchaser of gas from Liverpool Bay.
The Liverpool Bay Development comprises four offshore platforms, offshore storage and loading facilities, and the Point of Ayr terminal. Production started as follows: Hamilton North, Hamilton, Douglas, Lennox, Hamilton East. First contract gas sales were in 1996.
The quality of water in Liverpool Bay was historically affected by sewage sludge dumping, which became illegal in December 1988.