Ancient ice age valleys offer clues to future ice sheet change
Research by the British Antarctic Survey suggests ancient ice age valleys can provide clues to future ice sheet changes
Deep valleys buried under the seafloor of the North Sea record how the ancient ice sheets that used to cover the UK and Europe expelled water to stop themselves from collapsing.
A new study published this week has surprised the British Antarctic Survey (BAS) research team, who discovered that the valleys took just hundreds of years to form as they transported vast amounts of meltwater away from under the sheets and out into the sea.
This new understanding of when the vast ice sheets melted 20,000 years ago has implications for how glaciers may respond to climate warming today.
Tunnel valleys are enormous channels, sometimes up to 150km long, 6km wide and 500m deep (each several times larger than Loch Ness), that drain water from beneath melting sheets.
There are thousands buried beneath the seafloor of the North Sea that record the melting of ice sheets that have covered the UK and western Europe over the last two million years.
Lead author James Kirkham, from BAS and the University of Cambridge, said: “This is an exciting discovery. We know that these spectacular valleys are carved out during the death throes of ice sheets.
“By using a combination of state-of-the-art subsurface imaging techniques and a computer model, we have learnt that tunnel valleys can be eroded rapidly beneath sheets experiencing extreme warmth.”
See also: Models show climate history ‘more complex than previously thought’
last ice age
The team analysed ‘jaw-droppingly detailed’ seismic images that provide a 3D scan of the Earth’s buried layers.
Informed by delicate clues discovered within the valleys, the authors performed a series of computer modelling experiments to simulate valley development, and test how quickly they formed as the last ice sheet to cover the UK melted away at the end of the most recent ice age about 20,000 years ago.
The research suggests that this process is quick by geological timescales, with the meltwater forming giant tunnel valleys within hundreds of years, expelling water that could otherwise accelerate rates of ice loss.
Traditionally, the drainage of water from beneath the sheets is thought to stabilise ice flow, a process that could potentially buffer modern sheets from collapse in a warming climate.
But while inspecting the detailed seismic scans, the authors began to find tell-tale signatures of both stagnant and rapid ice movement within the valleys, complicating the picture of how these rapidly forming channels might affect future ice sheet behaviour.
What is certain, is that the surprisingly fast rate at which these tunnels form means that scientists need to start considering their effects in models of how today’s sheets will evolve in the coming decades to centuries.
There are no modern analogues for this rapid process, but these ancient valleys, now buried hundreds of metres beneath the muds of the North Sea seafloor, record a mechanism for how ice sheets respond to extreme warmth that is missing from present-day models.
Such models do not currently resolve fine-scale water drainage processes, despite them appearing to be an important control on future ice loss rates and ultimately sea level rise.
Kirkham added: “The pace at which these giant channels can form means that they are an important, yet currently ignored, mechanism that may potentially help to stabilise ice sheets in a warming world.
“As climate change continues to drive the retreat of the modern-day Greenland and Antarctic ice sheets at ever increasing rates, our results call for renewed investigation of how tunnel valleys may help to stabilise contemporary ice losses, and therefore sea level rise, if they switch on beneath the Earth’s ice sheets in the future.”
The work highlights a currently overlooked process that can rapidly switch on beneath melting sheets. Whether these channels will act to stabilise or destabilise the Earth’s contemporary ice sheets in a warming world remains an important and open question.
The study is published in the journal Quaternary Science Reviews.
Image: Graphic shows deep channel under the North Sea.
Credit: James Kirkham @ BAS.