Snow-dwelling microbes on an Alaskan ice field could substantially accelerate glacier melt by making the surface darker and decreasing its reflectivity, which in turn encourages the growth of more algae, according to a study published online in Nature Geoscience this week.
Although fresh snow reflects the majority of the incoming energy from the Sun, impurities such as black carbon and dust darken the surface and reduce the reflected energy. This dirty snow increases glacial melting as the darker snow surface warms more easily. The specialized algae living on glaciers have a similar effect as they change the colour of the snow surface to red, making it darker than unaffected snow.
Roman Dial and colleagues carried out experiments on the glacier in which they added nutrients and water to different areas of glacial snow. Compared to a control, which was left undisturbed, they find one and a half times more algae when water is added and almost four times more algae when nutrients are included. Using data from satellites to estimate snowmelt across the landscape, they show that red-snow algae increased melting by about 17%. As the areas of algae-covered red snow generate more meltwater, this could lead to a feedback of more algal growth and glacial melting.