Where did Irish animals live during the Ice Age?
ANOTHER LIFE:THE INUIT WORD nunataq has always appealed to me – an evocative, spiky sound. Geology borrowed it from Greenland to describe peaks of mountains that stick up through the ice.
In Ireland’s big glaciations, heaped hugely over the north, some summits stayed ice free. They poked up in the Wicklows, the Knockmealdowns and the Galtees and in Connemara. Our mountain, Mweelrea, was also a nunatak – the anglicised spelling changes the Inuit slightly – leaving frost-shattered rock at the summit to clatter under one’s boots.
Nunataks were far too small to sustain the few native species that lived through the last of the ice. The Irish stoat and the Irish hare certainly were not sharing the same mountaintops. So where were they? Study of the Quaternary period, as it’s called, has focused on the last two big glaciations, the Munsterian and the Midlandian. In the Munsterian Cold Stage, most of the island seems to have been buried at some stage, right to the south coast and beyond.
In the later Midlandian Cold Stage, beginning about 80,000 years ago, a great oval ice cap was pictured reaching across to a line of moraines from the Shannon to Wicklow, with an isolated ice cap on the Cork and Kerry Mountains and dry tundra left across most of Munster.
With the level of the sea having fallen by up to 120m, its water gone to make ice, there were also great reaches of exposed seabed. Some Irish scientists thought this offshore land could have sheltered some plants and wildlife, but most argued about possible land bridges from Britain, supplying Ireland with wildlife as the ice retreated.
In the late 20th century the whole “Midlandian” picture was changed. Dr William Warren of the Geological Survey of Ireland proposed three major ice domes on Ireland, merging with the Irish Sea ice lobe to cover the island completely. Research has since been confirming his ideas. A key study by Prof Colm Ó Cofaigh and his team has the last ice covering most of Munster, with the midland moraines created in the retreat, not the advance, of the glaciers.
An important contribution on the spread of the ice has now come from the Quaternary environmental-change research group at the University of Ulster at Coleraine, led by Dr Paul Dunlop. It used the maps of the Irish National Seabed Survey to trace the edge of it through seabed marks and gravel ridges. These showed landbound ice extending westwards beyond the island for 90km or more, in places reaching the great precipice of the Atlantic continental shelf.
The shelf continues off the southwest of Ireland, curving back into the Bay of Biscay, its undersea cliff edge steep and scored by great canyons and meandering “riverbeds” carved by the westward rush of sediments.
But most of the shallower Celtic Sea fell outside the great wedge of Ireland’s seabed domain. How far south of the Munster coast the final glaciers reached is thus still deeply mysterious, though, farther east, ice seems to have crept south of the Isles of Scilly.
To the west of Ireland its edge met Atlantic waves. These followed it in as it retreated, leaving no room for any wildlife refuge.
But the shelf to the south, towards Spain, may be more accommodating. Arguments on land bridges to Britain are becoming redundant as genetic research links more and more Irish species to Iberia and Europe. The idea of some midway southern ecosystem, sheltering animals and plants through the last of the Ice Age, has been reborn.
As DNA discoveries are gathered in, excitement prompted last month’s Mind the Gap conference on postglacial colonisation to expand into a series of scientific meetings, the next on October 20th at Fota Wildlife Park, in Co Cork, and a final one in February. Its prime movers are Dr Paddy Sleeman, the University College Cork zoologist, and the archaeologist Prof Peter Woodman.
In an emergent new grouping of “native” Irish species, some with ancient and very unusual DNA profiles, the animal list runs as follows: Irish stoat, hare, otter, badger, red squirrel, wood mouse, Leisler’s bat, natterjack toad and frog, not to mention the hairy wood ant, Formica lugubris, driven to inbreeding in its lonely forest mounds. Even Connemara’s “Lusitanian” heather species, St Dabeoc’s heath, seems to have spent time in a refuge somewhere now drowned in the Bay of Biscay. Indeed, as Dr Jim Provan of Queen’s University Belfast allows: “We cannot conclusively rule out the existence of a small, more northerly refugium.”
If all the species listed above were living somewhere together, theirs would have been an elaborate Arcadia, demanding, as Sleeman admits, a coastal location with woods and fresh water. In all the shallow ocean explored for the National Seabed Survey, the scratches of grounded icebergs appear everywhere. And could a wooded “refuge” zone have retreated and advanced with the spread and withdrawal of ice? For the moment its existence can seem as conjectural as Hy Brasil. But genetic research seems to have sunk the once-inevitable bridges to Britain, and southern reaches of the Celtic Sea could hold more big surprises.
Eye on nature
We have noticed an increase in fast-moving spiders in our home. They appeared for the first time a few years ago and are about 3cm long. A friend is convinced he was bitten by one.
Aidan Hamill, Crumlin, Co Antrim
The spider is a male giant house spider (Tegenaria gigantea), judging from your photograph. It is quite common. They rarely bite, and if they do it is painless. The female spins her web in a corner; it includes a funnel through which the spider retreats.
Recently we have been invaded by hordes of goldfinches displacing all the other birds at our three nut feeders.
Robert Hill, Faithlegg, Co Waterford
They flock in late autumn and winter, travelling around in search of food.
I have twice seen what I believe is an albino hen harrier over marshy land at the back of our garden.
Gillian O’Connor, Ballinamult, Co Waterford
An albino hen harrier has been recorded near the Knockmealdown Mountains, which is close to you.
Huge numbers of swallows, swifts and sand martins are still around here at the end of September.
Shay McGuinness, Skerries, Co Dublin
They are flocking in preparation for the journey south to Africa.
Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, email firstname.lastname@example.org. Please include a postal address