Ireland's ice age uncovered
Scientists are revealing clues about climate change by looking at the movement of Ireland’s glaciers during the last ice age, writes DICK AHLSTROM
MAPS OF THE seabed, ancient plankton and particles from outer space are all helping to explain how the glaciers that blanketed Ireland waxed and waned during the last ice age. This in turn helps paeleoglaciologists learn more about the climate change that drives ice ages.
Dr Paul Dunlop is head of the Quaternary Environmental Change Research Group at the University of Ulster, Coleraine. The Quaternary Period covers the past 1.5 million years, but his group is particularly interested the past 120,000 years, when the last ice age came and went.
“The real goal for the team here is to study climate change,” he says. They do this by finding ways to track changes over time in the ice sheet that covered Ireland in a kilometre-deep blanket of ice.
“The Quaternary is characterised by climate change, and this caused changes in the ice sheets,” says Dunlop. These come and go in a fairly regular way with a period of 100,000 years of cold typically followed by an interglacial period, perhaps 10,000 years long. The changes can set in quickly with a rapid slide into a new ice age, he says.
“The problem with the ice sheets is they are so destructive they destroy all the evidence of past glaciations. It is very difficult to get information on previous ice sheets. The deeper you go back in geological time the more vague it becomes.” Even so his group is finding ways to retrieve this information.
He was at NUI Galway when Ireland’s comprehensive seabed survey was underway, an ambitious mapping programme that included all of Ireland’s extensive continental shelf out to the edge of the deep Atlantic waters and beyond.
As a glaciologist he was aware of studies of ice-sheet grounding points off Antarctica. These occur where the heavy ice resting on the ground reaches its furthest limits and the floating ice shelf begins. While the shelf ice leaves no mark, the sheet ice presses into the seabed and deposits a continual supply of rock and overbear, scraped off by the slowly moving ice flow.
Dunlop had moved up to Coleraine at this stage and began studying some of the seabed mapping data for Donegal and over the Malin continental shelf. It didn’t take long before he started to find underwater gravel ridges, formed in a succession of long arcs.
“The big unknown question was: how far out did the ice sheet extend?” he says. The research team found it extended for many kilometres, in come cases out to the edge of the continental shelf. He concentrated on the Malin shelf region. “The most striking features we see are the ridges, 10km long. We have definitely mapped the western extent of the ice sheet,” Dunlop says.