Melting Permafrost - A Purely Arctic Problem?

Last week we looked at the potential consequences of melting Arctic permafrost, so this week - that's right, you guessed it - we'll be taking a trip down south to examine the future of Antarctic permafrost. 

Not how you usually think of Antarctica? These are the McMurdo Dry Valleys,
located in Southern Victoria Land. Source: https://thelastdegrees.wordpress.com.
Credit: INSTAAR, University of Colorado.

That's better, we were definitely due a beautiful Antarctic landscape photograph. After all, we have to remind ourselves what we're talking about. Importantly, however, this image shows the McMurdo Dry Valleys, one of the places where permafrost can be found on the continent.

Compared to the Arctic equivalent, Antarctic permafrost hasn't received much attention. Indeed, until recently there was little concern about its future. However, a study conducted by researchers at the University of Texas has suggested that permafrost dynamics may not be as stable as originally thought (Levy et al., 2013). Levy and his team used the "natural laboratory" of the Garwood Valley to investigate thermokarst formation, focusing specifically on the behaviour of one particular ice cliff (Levy et al., 2013). (As previously discussed, thermokarst landforms are unstable structures created through the melting of ground ice.) The ice cliff provides a useful study site - rate of erosion can be calculated relatively easily here, by measuring retreat with respect to a set reference point, and research has shown that the exposed ice is of an identical composition to that found within the valley floor (Levy et al., 2013). Through a combination of time-lapse imaging, ground-based LiDAR (a laser scanning technology), and a monitoring station positioned ~8 metres from the ice cliff, erosion rate was measured over a number of years (Levy et al., 2013). 

These were found to increase over time: between 2001-2002 and January 2012, erosion occurred at a rate of 5000±100m^3 per year; between January 2011 and January 2012 this had risen to 11,300±230m^3 per year, which is ten times the rate estimated for the late Holocene (1150±20m^3 per year) (Levy et al., 2013). So what's caused this increase in melt rate? Although increasing air temperatures may seem like an obvious answer, between 1986 and 2000 the Dry Valleys actually experienced a cooling of 0.7°C per decade (Doran et al., 2002). Instead, Levy et al. (2013) attribute the acceleration in melt rate to an increase in solar radiation, thought to be a result of changing weather patterns. Nevertheless, future temperature increase in the Antarctic would likely lead to a similar permafrost response.

While permafrost melt in Antarctica is arguably less of a concern to the general public than that taking place in the Arctic (where the infrastructure of communities is under immediate threat), this study highlights that it is an avenue of research that should be pursued. Levy et al. (2013) point out that thermokarst structure "down-valley" showed little - if any - change between 2009 and 2012; it would therefore be interesting to see if the Garwood Valley ice cliff is in fact representative of a wider region of permafrost, or whether it is responding to increased solar radiation in an unusual way.  

Right, after all that, here's another lovely picture (just because it's lovely):

This is the Canada Glacier, found in the McMurdo Dry Valleys (specifically, the
Wright Valley). Source: www.nsf.gov. Credit: Peter Doran; National Science Foundation.

Oh, and in case you were wondering, it looks like methane release from Antarctica might be an issue too...

Wadham et al. (2012) propose that Antarctic sedimentary basins contained approximately 21,000Pg of organic carbon when the ice sheets were forming. This knowledge, combined with the relatively recent discovery of microorganisms beneath the ice sheets (see Lanoil et al., 2009), shows the potential of this environment for methanogenesis (Wadham et al., 2012). A model produced by Wadham et al. (2012) suggests there could be a methane hydrate reserve beneath the East Antarctic Ice Sheet of 70 to 390Pg of carbon (equivalent to 1.31 to 7.28x10^14 cubic metres of methane) and "some tens" of Pg of carbon (equivalent to ~2x10^13 cubic metres of methane) underneath the West Antarctic Ice Sheet. Not much imagination is required to think what might happen to all this methane if the ice sheets recede...  

Interestingly therefore, in terms of permafrost melt and methane release, the Arctic and Antarctic share a lot more similarities than I originally thought.