Increasing Rain Events Change Dynamics of Greenland Ice Melt

August 20, 2015

Very nice video from the ice sheet edge in this report from a Chinese English News service on the effects of rain events on the speed of Greenland Ice flow. Significant because those kinds of events are happening over larger areas of the ice sheet as the climate warms. (audio slightly out of synch, but good visuals)

Not sure if this represents greater coverage of climate issues in the Chinese media, but welcome nevertheless.

The video features several scientists from the Geological Survey of Denmark and Greenland, who were co-authors of a study published in Nature, with Jason Box, and Alun Hubbard.

CCTV English:

In one of the studies published in ‘Nature,’ scientists described how lakes under the ice sheet are draining far faster than previously thought. The water released then lubricates the bottom of the sheet, accelerating its movement.

The result is increased ‘calving,’ where blocks of ice break off from the glacier’s edges. The other study points to a similar mechanism from rainfall.

“When you get rainfall occurring over the ice sheet, especially close to the end of the melt season, the water finds it hard to get out of the ice sheet. So it goes down to the bed of the glaciers of the ice sheet and it will try to find a way out anyway it can,” said Ruth Mottram, climate scientist, Danish Meteorological Institute.

“But, by the end of the melt season there isn’t very efficient drainage: it’s like the pipes that drain the ice sheet are starting to close down; they’re starting to get blocked.”

“So this means that the whole ice sheet starts to move, it starts to accelerate, because this water is lifting it up and it’s kind of lubricating the bed a little. So this has quite an important impact on the ice sheet as a whole; the whole thing starts to stretch, it starts to move a bit fast, you maybe get an increase in calving.”

Below, video from Jason Box, taken during a rain event in 2014.

Nature Geoscience: Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

 For eight days during late August and early September 2011, reanalysis data27 indicate that a cyclone (minimum surface pressure of 992hPa) centred on Baffin Bay off the west coast of Greenland advected warm, southwesterly airflow over the GIS, bringing extensive precipitation, which was especially heavy in southeast Greenland.

We find that a concomitant flow response is evident in all available velocity records from these regions, including three major marine-terminating glaciers located up to 370km north of Kangerlussuaq: ice flow increased by 9% and 95% above the preceding week at GPS sites on Store Glacier30 (S11) and Sermeq Avannarleq6 (A20) respectively.

Science Nordic:

The study began after observing exceptionally warm wet weather in late summer 2011, causing huge amounts of melt at the ice surface. At this time of the year, there was no snow on the surface of the ice to absorb and act as a buffer for all this rain and melt water, which then moved very quickly through the ice sheet.

“At first our observations of this late-August intense rainfall and melt event were met with the attitude of “hey big deal, it’s summer, it melts”,” says professor Alun Hubbard from the Center for Arctic Gas Hydrate, Environment and Climate at The Arctic University of Norway, and principle investigator of the project that led to the study.

“But this new data, shows these periods of rapid movement of the ice are in fact tied to a particular type of rainfall event, the kind of storm you would expect to see in the mid-latitudes — UK or Scandinavia — and not so much in Greenland where high pressure systems are more common.”

“We can now reinterpret these big late summer melt events to get a much better understanding of what is going on — what is affecting the ice sheet system and how it is responding” he says.

Imagine a storm drainage system after heavy rain

Hubbard uses the analogy of a storm drainage system, to explain how the rain and melted ice moves through the ice sheet so quickly.

“Imagine a big downpour in a city. You get so much rain so quickly, on to an impermeable concrete surface that the water is immediately shunted into the city’s drainage system — which due to the huge volumes of water — can’t cope. Drains back up and it floods. Basically, the same thing happens on the bare ice sheet surface, which like the city is literally comprised of pipes, conduits and cavities,” he says.

According to him, when these pipes back up the hydraulic pressure lifts the ice sheet up, like a gigantic iceberg. There is less friction at the bed and so it moves faster.

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