Arctic buildings, highways and services all are specially designed to cope with extremely cold weather as well as permafrost affected ground.  One of the key things is to prevent permafrost degradation and frost heave.  Frost heave happens in frozen soil because as water freezes in soil, it draws more unfrozen water towards it which then freezes.  This ‘ice lense’ expands and causes the soil to ‘heave’.  For many Canadians, we experience this when our house shifts during the winter. The key to preventing frost heave is that the soil needs to be porous and there should be little liquid water present.

The term ‘liquid water‘ sounds strange but it refers to water that is still in liquid phase below zero degrees centrigrade.  The majority of water will be present as ice but a small fraction, <20% is present as liquid and can still move through the soil. We term this water as liquid water to differentiate this water from the ice present in the soil or from water vapour.

Recently, our group has found that diesel spills in Antarctic soils increases the amount of liquid water present in frozen soils.  We think that the diesel is increasing the liquid water content because it is decreasing the free energy of the liquid water present in the soil.  I know that this sounds even stranger.  But when you are thinking about phase changes, you need to think about the relative energy of the two phases.  So in this case, we have the environment at a specific energy and then the liquid water at another energy.  As the environment cools, at some point it will be more energically favourable for the liquid water to be in the solid phase.  Thus, if diesel decreases the free energy of liquid water, then the environment will have to be colder to before the water undergoes phase transition to solid state (i.e. ice).

This increase in liquid water by diesel is a good news/bad news story.  The bad news is that it is possible that the presence of diesel will make certain soils more susceptible to frost heave because more water will be available to move and form ice lenses.  These ice lenses could cause frost heaving and topple existing infrastructure.  The good news is that degradation of diesel is more dependent on liquid water than temperature in Arctic soils.  Thus, diesel contamination may make it easier for microbes to eat the diesel because there is more liquid water around that microbes need to eat.

If you find this interesting, you can find the detailed technical publication of these results in an upcoming issue of Environmental Science and Technology.