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Things that live in glaciers

During my first ever field season, I studied a small drainage basin on Devon Island in the High Arctic of Canada. There was a glacieret, a tiny glacier, in the upper part of the basin, and it was mostly pink. As I had been taught that glaciers are whitish or brownish, depending on how much sediment they contain, this pinkness surprised me.

Later I learned that coloured ice is not all that unusual. Glacier ice can be intensely blue if it is free of air bubbles, which are the source of the whiteness. It can be black, or at least look black, if it is floating on water and is transparent. But pink? In northwest Greenland there is a 70-km stretch of the margin of the ice sheet called the Crimson Cliffs. It turns out that the pink colour comes from the carotene manufactured by bacteria that contrive to get a living from the glacier surface. Relatives of this bacterial carotene explain the pinkness of flamingos (they will insist on eating shrimps, which eat the pink bacteria), and the carrotiness of carrots.

Biologists are a bit like glaciologists in that they are willing to study almost anything, so bacteria on glaciers are not new to science. But are they any more than an arresting curiosity?

In recent years, microbiologists have become quite excited about evidence for a so-called deep biosphere. The distribution and abundance of hydrocarbon molecules in deep environments suggest that there must be organisms manufacturing some of the molecules. These deep environments include the beds of glaciers. From the Arctic, the Alps and elsewhere, strong circumstantial evidence has accumulated for ecosystems consisting of distinctive subglacial microbes. Last year D’Elia and colleagues showed photomicrographs of bacteria and possible fungi from ice that had accreted from the water of Subglacial Lake Vostok in Antarctica. The microbiologists seem to be satisfied that they are not looking at samples contaminated by near-surface organisms.

Apart from provoking us to rethink the meaning of “life”, subglacial microbes have implications. Wadham and colleagues explore the question of what they might have done to the climate if they were active beneath the ice sheets of the last ice age. There was plenty for them to eat, in the form of overridden rotting vegetation, which some of them would have converted to methane. When the ice sheets waned, the methane, a greenhouse gas, could have had substantial climatic impact when released to the atmosphere. Apparently the release would have had to be episodic to have made a big difference. This is pure, though constrained, conjecture – but what fascinating conjecture it is.

There is a potentially enormous payoff if we can develop an understanding of how organisms can thrive at the beds of glaciers. They may help to stretch the envelope of hospitability yet further, because the most impressive glacier in the known universe is one that is not on the Earth’s surface at all.

Europa, one of the Galilean satellites of Jupiter, has an outer shell consisting mainly of water ice. We cannot be sure of the thickness of the shell, but it is probably a few tens of kilometres and may be as little as just a few kilometres. The most interesting things about this lithospheric glacier may be that, firstly, it is undoubtedly floating on an ocean of what is almost certainly liquid water, and secondly, that there is compelling evidence of resurfacing. That is, images of the surface of Europa show features that make sense only if the underlying ocean has on occasion managed to rupture its ice cover and spill out onto the surface of the satellite. So Subglacial Lake Vostok, and the beds of glaciers generally, are intensely interesting from the standpoint of the search for extraterrestrial life.

Remember that oxygen, a deadly poison, is irrelevant, and the one so-far-universal common denominator of known life-hosting environments is liquid water. Ice will not do, and nor will steam. The beds of glaciers have what is needed, and they host life. The first of these two assertions appears to be as true on Europa as it is on Earth.

Posted by Graham Cogley on October 5, 2009 3:00 PM | Permalink