The Last Glacial Maximum & Birth of Island Ireland
Over the last few months we have taken a look at some of the fascinating mammals which inhabited Ireland during the late Ice Age, but what should now be clear is that there was a point, centred around 24,000 years ago, when Ireland was virtually wiped clear of life as its surface was buried under a great mass of ice. The story of Ireland's Ice Age animals, then, is one with two parts – one before the ice and one after, and each of these episodes has its own distinct cast, albeit some characters occupying roles in both. Thus, to understand the nature of Ireland's late Ice Age mammals we must also understand the nature of the icy interval which separates them, that period known as the Last Glacial Maximum. Understanding this icy interlude is not only pivotal to understanding Ireland's Ice Age animals, but to understanding the very nature of Ireland itself, as the emergence of Ireland from this icy invasion would result in its birth as the island we know today.
The Last Glacial Maximum (LGM) lasted from around 26,000 to 19,000 years ago but was a culmination of a process which had begun much earlier. As we've seen in former posts, the invasion of Ireland by ice was underway by around 35,000 years ago as a great ice sheet surged southwards from southwest Scotland to occupy much of the northern half of Ireland. As the millennia passed, this invading ice sheet pressed farther and farther into the southern provinces, being joined along the way by an icy fifth column in the shape of Ireland's upland glaciers. By around 24,000 years ago (or even earlier according to some recent studies) the icy takeover of Ireland was complete, and at their greatest extent the ice sheets stretched far beyond the present southern shore and perhaps as much as 90 kilometres west of what is now the Donegal coast.
At the height of the LGM, in the thickest sections of the ice sheet covering Ireland, the land was likely buried in ice up to a depth of one-and-a-half kilometres. Some of the only forms of life to survive this episode of deep cold were extremely hardy Arctic-type plants which managed to scrape by living on exposed upland outcrops of rock called nunataks ('nunatak' is a term derived from nunataq, a word from the language of the Inuit who live in the icy wilds of Greenland). For mammals, Ireland became a forbidden land and those which had not perished with the onset of Arctic conditions had either migrated to refugia in southern Europe located in Spain, Italy, and the Balkans, or relocated to other refugia to the south of Ireland which now lie under the sea.
As tightly as the ice gripped the land, though, it could not hold Ireland in its icy grasp forever. By 19,000 years ago, the ice sheets were in retreat and much of Ireland's southern lands had emerged from the ice. Although there were subsequent readvances, the overall pattern of deglaciation continued and by around 16,000 years ago only parts of Connacht and the north of Ireland were still occupied by significant ice masses. Eventually, even these tenacious ice caps had surrendered to the inevitable and by around 14,000 years ago Ireland is thought to have become virtually ice-free.
The collapse of Ireland's ice sheet must have been a wondrous sight, especially when we consider that this ice sheet was a far more dynamic structure than once thought – not a monolithic icy sheet but a collection of separate ice domes. During deglaciation, the Irish ice sheet would have broken away from the British ice sheet and then fragmented into its component domes, each of these moving in its own particular way, resulting in all the criss-crossing glacial features seen in Ireland's landscape today. Their eventual collapse must have been a thing of catastrophic beauty as they surged out through lowland gateways in the west, including Donegal Bay, Clew Bay, the Shannon Estuary, and Bantry Bay, impregnating the surrounding seas with vast flotillas of icebergs.
Of course, the demise of Ireland's ice sheets not only marked the death of Ireland as an ice-land but its birth as an island. Around 20,000 years ago, southeast Ireland may still have been connected to southwest Britain by a narrow, low-lying landbridge, but by around 16,000–15,000 years ago, with sea levels having continued to rise as deglaciation gathered pace, this thin isthmus would have been swallowed by the waves.
Although Ireland had become isolated as an island countless times in the past up to this point, this event marks the birth of the island which still sits in wave-locked isolation today, a land born of ice and water.