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Geophysical Institute

GFI/BCCR Seminar | Chris R Stokes: How Ice Sheets Collapse – A Lesson from the Laurentide

Chris R Stokes (Durham University, UK)

How Ice Sheets Collapse – A Lesson from the Laurentide

Abstract:

The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely due to the thinning and retreat of rapidly-flowing outlet glaciers and ice streams. This ‘dynamic’ mass loss is a serious concern, with some numerical modelling studies suggesting that collapse of the West Antarctic Ice Sheet is imminent or potentially already underway, but others predicting a more limited response. A major problem is that observations used to initialize and calibrate numerical models typically span only a few decades and, at the ice-sheet scale, it is unclear how the entire drainage network of ice streams evolves over longer timescales. This represents one of the largest sources of uncertainty when predicting the contributions of ice sheets to sea-level rise. A key question is whether ice streams might increase and sustain rates of mass loss over centuries or millennia, beyond those expected for a given ocean–climate forcing. Drawing on almost two decades of research, this talk reconstructs ice stream activity during deglaciation of the North American Laurentide Ice Sheet (from around 22,000 to 7,000 years ago), which is a potentially powerful analogue for future ice sheet dynamics. Contrary to the established view that sees ice streams as unstable entities that can accelerate ice-sheet collapse, it is shown that ice streams exerted progressively less influence on ice sheet mass balance during deglaciation. This raises some interesting questions about the role of ice streams in ice sheet dynamics, and the source of major jumps in sea level (meltwater pulses) during the last deglaciation.