I'm a bit slow catching up on articles these days, but it was interesting to see this article and its findings.
Ice stream activity scaled to ice sheet volume during Laurentide Ice Sheet deglaciation
C. R. Stokes, M. Margold, C. D. Clark & L. Tarasov
Nature 530,322–326(18 February 2016)
Published online 17 February 2016
The contribution of the Greenland and West Antarctic ice sheets to sea level has increased in recent decades, largely owing to the thinning and retreat of outlet glaciers and ice streams1, 2, 3, 4. This dynamic loss is a serious concern, with some modelling studies suggesting that the collapse of a major ice sheet could be imminent5, 6 or potentially underway7 in West Antarctica, but others predicting a more limited response8. A major problem is that observations used to initialize and calibrate 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 rise8, 9, 10. 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 forcing5, 6, 7, 8, 9, 10. Here we reconstruct the activity of 117 ice streams that operated at various times during deglaciation of the Laurentide Ice Sheet (from about 22,000 to 7,000 years ago) and show that as they activated and deactivated in different locations, their overall number decreased, they occupied a progressively smaller percentage of the ice sheet perimeter and their total discharge decreased. The underlying geology and topography clearly influenced ice stream activity, but—at the ice-sheet scale—their drainage network adjusted and was linked to changes in ice sheet volume. It is unclear whether these findings can be directly translated to modern ice sheets. However, contrary to the view that sees ice streams as unstable entities that can accelerate ice-sheet deglaciation, we conclude that ice streams exerted progressively less influence on ice sheet mass balance during the retreat of the Laurentide Ice Sheet.
The authors admit that there are big differences between the Laurentide Ice Sheet and the modern ice sheets of Antarctica and Greenland -- both of which evacuate large quantities of ice via calving into the sea. But there are similarities with the British and Irish Ice Sheet or BIIS (which Henry Patton is now calling the Celtic Ice Sheet) which was of course diminishing at the same time as the Laurentide Ice Sheet. I'm particularly interested in the extent to which this new work calls into question the "binge-purge" model of ice sheet collapse as described by Hubbard et al in their seminal paper of 2009.
This is from one of my earlier posts, in 2011 (seems a long time ago):
The British - Irish ice sheet almost melted away around 27,000 BP, and then (because there was a relatively prolonged period of increased accumulation without any major interruptions) the ice sheet grew and grew until it reached its maximum volume and extent around 20,000 BP. There was a phenomenal rate of growth over 7,000 years, followed by a catastrophic collapse. The authors refer, over the whole lifetime of the ice sheet, to "binge-purge cycles" of gradual accumulations followed by rapid ice evacuations.....................
I have always been rather sceptical about the strange "surge lobe" described in a number of papers as occurring at the peak of the Devensian glaciation. The assumption seems to be that this lobe represented the final "purge" which evacuated so much ice from the centre of the ice sheet that its demise was then inevitable. Catastrophic ice sheet collapse then followed, with the whole ice sheet disappearing in just a few thousand years. I have argued that this lobe, which supposedly brought ice from the NE all the way south the the Isles of Scilly, is glaciologically improbable, since according to the model it penetrated for 400 km southwards with hardly any lateral spreading, in a landscape devoid of any lateral constraints. It was not flowing in a well defined trough, and there were no bounding hill masses or mountain walls such as those seen in Norwegian fjords or even on the flanks of current Antarctic and Greenland ice streams.
So does this new work question the "binge-purge" hypothesis at a fundamental level? Could it be that the BIIS actually disintegrated through surface melting, with rapid ice stream evacuations switched OFF? All comments welcome!