Glacier melting accelerated by dark microbial life

Scientists previously viewed glaciers as “lifeless lumps of ice” but an Aberystwyth University-led study has demonstrated how microbes that appear on their icy surface  may contribute to glacier melting.

Glacier surfaces are irregular and are almost always covered with a fine dusting of a material called ‘cryoconite’- made from a combination of small rock particles, dust and microbes that are blown onto the glacier from surrounding mountains or deposited with precipitation.

Glaciologist Dr Tristram Irvine-Fynn, the study’s lead author, said: “For several years now, I have been particularly intrigued how this cryoconite is formed and how it is then transported across a glacier surface by the flow of melt water. When I used time-lapse photography I found the dust’s movement was very complex, and I wondered if the microbes get washed away from the surface or not.”

The group set out to measure the ‘microbial budget’ of a glacier in the Norwegian High-Arctic archipelago of Svalbard by counting the number of microbes entering, leaving and being stored on the glacier’s surface using flow cytometry.

Samples of glacier melt water and surface ice were collected and analysed along with results from dust traps made from upside-down Frisbees.

The researchers discovered that every hour, about 10 million cells are washed away by melt water from a square metre of the glacier’s surface. These transported microbes contain a volume of carbon.

“Amazingly, the volume of carbon that is exported from the studied glacier each summer is similar to a bag or two of sugar from your local supermarket,” said Irvine-Fynn.

These findings mean that if the glacier studied is representative of glaciers everywhere, they would lose at least 3.5 thousand trillion cells each summer – roughly the same amount of cells estimated to be living on and in three billion people.

But what the team found particularly concerning was that the export of cells is dwarfed by the number of microbes retained within the glacier structure meaning that many of the cells landing on the ice are simply being trapped there.

The researchers found that during the Arctic summer, the total mass of microbial carbon captured across the glacier’s surface is equivalent to a sack of compost. Microbes glue together the dust, carbon and tiny rock particles and darken the ice surface, increasing the amount of the sun’s energy that melts the glacier.

“We are calling the phenomenon ‘biological darkening’ and it appears to be a significant factor which may accelerate the rate at which glaciers melt away,” said Irvine-Fynn.

Reference: Irvine-Fynn, T. D. L., Edwards, A., Newton, S., Langford, H., Rassner, S. M., Telling, J., Anesio, A. M. and Hodson, A. J. (2012), Microbial cell budgets of an Arctic glacier surface quantified using flow cytometry. Environmental Microbiology, 14: 2998–3012. doi: 10.1111/j.1462-2920.2012.02876.x