The width, depth, strength of an ice stream's bed would have controlled ice loss to the ocean as the ice sheet retreated. The impact of these underlying factors on ice-sheet retreat are almost certain to be enhanced under global warming scenarios.
The new paper published today in Science Advances forms part of the wider BRITICE-CHRONO project – led by Professor Chris Clark, at the University of Sheffield – which used a range of onshore and offshore dating techniques and digital mapping methods to reconstruct the complete deglaciation history of the entire British-Irish Ice Sheet from 30,000 to 15,000 years ago.
Ice streams are ‘flow corridors’ within an ice sheet that move significantly faster – up to 1,000 metres a year – than the surrounding ice. They are to 10 to 100 km wide, and hundreds of kilometres in length. They transport vast amounts of ice from inland to the oceans and account for most of the ice leaving the ice sheet.
Dr Bradwell’s team identified a “major step change” in ice stream behaviour around 18,500 to 16,000 years ago – with the collapse of ice shelves in NW Scotland followed by rapid ‘runaway’ ice-front retreat.
“This behavioural change was out of tune with climate forcing,” Dr Bradwell explained. “Instead, we attribute it to variability in the seabed landscape – most importantly the width and depth of the ice stream trough and changes in the geology, or strength, of the underlying bed. In a glacial climate, these factors would have controlled ice loss to the ocean as the ice sheet retreated – at certain times causing it to accelerate via ice-shelf collapse and rapid iceberg calving.
“The impact of these underlying factors on ice-sheet retreat are almost certain to be enhanced under global warming scenarios.”
The study included a 30-day science cruise and two onshore fieldwork campaigns. The research team combines marine and terrestrial geologists, geochronologists, glaciologists and ice-sheet modellers from a number of institutions: The Universities of Stirling, Sheffield, Durham, Liverpool, Bangor, Aberystwyth, and Glasgow, as well as the Scottish Universities Environment Research Centre, and the British Geological Survey.
The BRITICE-CHRONO project was conducted between 2013 and 2018 and is funded by the Natural Environment Research Council (NERC), part of UKRI (UK Research and Innovation).
The new paper, Ice-stream demise dynamically conditioned by trough shape and bed strength, is published in Science Advances. For more information, see a short interview with lead author Dr Bradwell below, including footage from the marine cruise, captured by videographer Alex Ingle.