Chain Reaction Of Draining Lakes Is Undermining The Greenland Ice Sheet's Stability

These supraglacial lakes are beautiful, but bad news. NASA/ESO

It’s nothing but bad news for the disintegrating Greenland Ice Sheet (GIS), the second-largest agglomeration of landlocked ice in the world.

Although stable a quarter of a century ago, between 1992 and 2014, it cumulatively lost a staggering 3.6 trillion tonnes of ice, with the rate of ice lost increasing rapidly over time. Now, a team led by Cambridge University report in Nature Communications that a series of lakes at the surface are exacerbating its instability.

These beautiful-looking pools sit atop the GIS and absorb sunlight, unlike the reflective ice around them. They warm up, and far from just melting more ice around them, they occasionally drain downwards in what were assumed to be isolated events.

Siphoning this much warm water down to the bottom of the colossal ice sheet has consequences. It’s often trapped down there under thick ice, causing it to spread out over large areas.

This vast zone of meltwater chips away at and lubricates massive sections at the base of the GIS, causing it to move faster. This puts stress on the ice sheet, which creates new drainage cracks, as a positive feedback cycle begins.

Far from just draining individually, then, this paper concludes that these lakes almost always simultaneously cascade downwards, a phenomenon the researchers refer to as a “chain reaction drainage”. Strikingly, the team’s models and day-to-day observations of ice flow suggest that, in some instances, these chain reactions can temporarily accelerate the ice flow rate by as much as 400 percent.

If confirmed, this is nothing less than an unexpected, ominous discovery.

The chain reaction drainage model, from a to d. Christoffersen et al./Nature Communications

In the Intergovernmental Panel on Climate Change's (IPCC) fifth and latest assessment report, the authors explain that abundant surface meltwater on the GIS “does not seem to be driving significant changes in basal lubrication that impact on ice sheet flow.”

According to lead author Dr Poul Christoffersen, from Cambridge’s Scott Polar Research Institute, this was based on a series of assumptions – most importantly, “that surface meltwater produced at higher elevations farther inland, where ice is much thicker, stays on the surface,” because there are no escape fractures available there.

“Our findings… show that this assumption is incorrect,” Christoffersen told IFLScience. Instead, their work points to the drainage of these lakes through networks that, according to the paper, can be found “farther inland than previously considered possible.”

These supraglacial lakes happen to be growing in number as time ticks on and the atmosphere continues to warm, as do their drainage networks. This points to a future where these chain reactions become more severe or commonplace.

All in all, this means that “the interior ice sheet may respond more sensitively to climate change than indicated by observations made closer to the margin,” Christoffersen explained.

It is worth pointing out, however, that although the lakes and crevasses are real, the way in which they drain and affect the base of the GIS is based on a 3D model. Rigid though the data may be, additional fieldwork is required to confirm its validity, but at least it sheds light on a perhaps underappreciated phenomenon.

Just last November, a separate mapping study concluded that the GIS is exposed to warming ocean waters far more extensively than previously thought too. Make no mistake: this reservoir of ice is under attack, from above and below. Considering that its climate change-led collapse into the sea is driving global sea level rise, the implication here is that we’re in – to understate things – a spot of bother.

If anything, this new study reminds us that climate change, and ice, is deeply complex – and there are certainly plenty more scientific surprises to come.

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