16 July 2012

The wet side of Greenland

An Arctic Sea Ice blog crosspost

When writing The dark side of Greenland, a recent blog post on decreasing reflectivity of the Greenland ice sheet, with images comparing the southwest of Greenland with satellite images from previous years, I of course realized that when that ice sheet becomes less reflective, it will soak up more solar energy and thus melt faster. But the practical aspect of this theory never really dawned on me, until I saw this video:

More videos here and here.

Levels in the Akuliarusiarsuup Kuua river, also knows as the Watson river, have reached such heights that they have smashed the two bridges connecting the north and south of Kangerlussuaq, a small settlement in southwestern Greenland, located at the head of the fjord of the same name. The river water stems from different meltwater outflow streams from Russell Glacier (an outflow of the Greenland ice sheet), and is a tributary of Qinnguata Kuussua, the main river in the Kangerlussuaq area.
     Of course the local media are covering the story. Here are a few excerpts from different news articles from Sermitsiaq (via Google translate):
What has happened in detail over the inland ice, which caused this incident, is not yet known, but the fierce heat has certainly been an important player. And unfortunately it looks like the weather will not come to the Greenlanders' rescue, as the air temperatures over the ice sheet are expected to remain warmer than normal at least the next 7-10 days, writes Greenland meteorological Jesper Eriksen at dmi.dk.
However, it's not only hot on the icecap at Kangerlussuaq. Deep in the ice, there are also plus degrees: In Greenland, it has been very hot over the inland ice in comparison to normal conditions. On July 11th at 15 UTC the recorded temperature at the Summit Camp weather station, which is located at the ice cap's highest altitude (3200 metres), was 2.2 degrees Celsius. That is quite high for this height, particularly in light of the fact that ice has a relatively high albedo.
Just 2.2 °C doesn't sound like much (although it looks to be a new record for July), until one realises that we are talking Summit Camp here. At an altitude of 3200 metres. In the middle of the Greenland ice sheet. Nothing but ice.
3.5 million liters of water pressed through the narrow river every second. It's almost a doubling of previous records. It's no wonder that a 20 ton wheel loader was torn away from the bridge in Kangerlussuaq like a toy.
It's difficult for me to assess whether this is correct, flipping through this research paper by Van As et al: Large surface meltwater discharge from the Kangerlussuaq sector of the Greenland ice sheet during the record-warm year 2010 explained by detailed energy balance observations. I'll get back on this.
     Quote from the conclusion:
Due to the early onset of melt in 2010, combined with lower winter accumulation, surface albedo was below the 2000–2010 average as determined from calibrated MODIS imagery. This in turn allowed for larger solar radiation absorption, resulting in higher melt (melt-albedo feedback). As a consequence, energy available for surface melt was larger in 2010 than in 2009, particularly in the upper ablation zone. While the warmer atmosphere caused increased melt over the entire elevation domain, in the upper ablation zone the relatively low albedo allowed for higher solar radiation absorption rates, contributing over half to the melt increase...
     During warm episodes in the future, a melt response of at least this magnitude should be expected unless large wintertime snowfall offsets the melt-albedo feedback.
Albedo of the Greenland ice sheet wasn't so great this year, judging from these regularly updated graphs on the Meltfactor blog, particularly at higher elevations:

There's another first-hand report near Kangerlussuaq, written by Ben Linhoff on the Scientific American blog:
From the mess tent, we can hear huge boulders crashing through rapids half a kilometer away. The boulders sometimes sound like approaching footsteps, and as we’re all just a tiny bit nervous about an unlikely polar bear visit, conversations trail off and we listen.
Ben Linhoff sampling the stream formed by glacial melt early in the season.
In the four years our camp has existed on this glacial river, more meltwater is spilling out from beneath Leverett Glacier than we’ve ever seen. What’s more, the river has spilled over its banks and is now eroding a glacial moraine near our camp that was likely pushed there in the 1700’s during the Little Ice Age. It’s only June and the river is still rising.
The Greenland Ice Sheet is the most impressive thing I’ve ever seen. Looking out over its seemingly endless expanse of white, grey, and black textures of crevasses and rolling hills of ice, one feels close to infinity. On my last trail run, I ran to the top of a small mountain surrounded on three sides by the ice sheet. I was wearing running shorts and a tee shirt; the sun was bright and a steady wind coming off the ice kept the mosquitoes away. I sat down on a slab of granitic gneiss and leaned against a warm boulder. The wind was surprisingly balmy and humid, despite having just crossed the Greenland Ice Sheet. I closed my eyes and soaked in the heat and sun. Later that day I reformatted my air temperature graphs from last year’s season to fit the data collected this June. The y-axis had to be expanded by 10 degrees.
I'm sure we'll hear more about this in the weeks to come.