A land bridge never formed between Ireland and Scotland, according to controversial new research, writes Dick Ahlstrom.
Ireland was always an island and a land bridge never formed to connect it to Britain, according to new research from the University of Ulster. Contrary to the general view, sea levels never fell far enough to allow dry land to emerge between the two landmasses.
This controversial new theory is proposed by Dr Andrew Cooper of UU Coleraine's Centre for Coastal and Marine Research. Working in co-operation with US colleagues from the University of Maine, the team has found compelling evidence the bridge never formed.
There is no doubt there was a land bridge between Britain and the Continent 10,000 years ago, at the end of the last Ice Age. There was also a universal assumption that a second land bridge connected Ireland to Britain, but Cooper's "seismic stratography" data, which makes it possible to visualise layers of sediments below the seafloor, suggests otherwise. This seismic work indicates that sea levels never dropped far enough to produce a land bridge to Scotland, says Cooper.
The last Ice Age tied up huge volumes of water in glaciers that covered the land, as a consequence dropping sea levels globally by as much as 130 metres, he explains. This should have been more than enough to connect us up to Britain and through it to continental Europe, but Cooper's work suggests the sea level fall around Ireland was only about 30 metres.
The weight of ice here and in Scotland was enough to depress both land masses, pushing them down and keeping us separated by water. When the ice retreated and sea levels rose, the land rebounded, maintaining the waterway between us.
"Our geophysical surveys suggest that 10,000 years ago the sea level drop was 30 metres and 30 metres isn't enough to form a land bridge between Ireland and Scotland," he says. "For a land bridge between Ireland and Scotland you would have to drop water levels by 60 metres."
The two universities are hoping that seabed sediment cores retrieved during the summer will help prove their theory. Last June they used coring equipment brought in from the US and carried by the Northern Ireland Department of Agriculture's research vessel, Lough Foyle to retrieve a series of seabed core samples from Belfast Lough and from along the northern coast near Portrush, Co Antrim. The team plans to open the first cores later this month.
"The submerged landscapes were dry land about 10,000 years ago, at about the same time as the first humans arrived in Ireland. People most likely lived and hunted on these ancient coastal plains," says Cooper. "As the sea level dropped, land plants colonised the land. If we are really lucky we will pick up some peat horizons or other organic horizons showing dry land." Over these areas he also expects to see clear signs of the sea's return, when the land was first disturbed by the waves and then overtaken to be covered in sand and later sediments.
"It forms a very distinctive layer in the stratography," he says, a feature known as a "transgressive unconformity".
In the initial coring runs they intentionally targeted sites in the hope they would penetrate submerged land surfaces. By the same token, he expects these layers to be absent in cores retrieved from deeper waters, an indication that there was no dry land there 10,000 years ago.
This raises questions about how animals such as the great Irish elk could have made it to Ireland without a land bridge, but the team believes it can answer this. There are plenty of sandbanks and shoals known today in the Irish Sea's north channel, and a 30 metre fall in sea level would have been more than enough to lift many of them out of the water to become islands. Movement from island to island "would have made passage by sea much easier", he says.
The elk could well have reached these islands and ultimately Ireland by swimming between them according to the University of Maine researchers. "They have observations of moose swimming out five or six miles to reach islands in large lakes," says Cooper. "It is conceivable that the elk could have done this across the islands, using them like stepping stones."