A Changing Balance
Life at the bottom of a cryoconite hole is dark. The chocolate-colored bacteria inside each granule produce black or dark brown organic matter, and certain larger animals in the cryoconite holes, such as black tardigrades, are also dark. These pigments protect against the damaging effects of solar radiation, but as Cook discovered, they also give cryoconite grains impressive ice-carving powers.
On the glaciers of Svalbard, he added extra cryoconite sediment to existing holes to see what would happen. He found that the granules spread out as much as possible, forming a thin layer. The dark layer of cryoconite and the creatures in the hole absorb sunlight, warming the walls around them and melting a wider hole. “What’s really amazing is that a cryoconite hole can change its shape,” he says.
The advantages of this habitat build-out are many, Cook found in a 2010 study. With the grains more widely distributed, more of the grains’ surface area is exposed to sunlight, and the additional meltwater lets the glacier host more life.
But with the arrival of human-caused climate change, this age-old cycle now has a dark side. The very mechanisms that have allowed cryoconite organisms to thrive may be exaggerating the threat of global warming and aiding in the destruction of their own home. What’s more, dust freed from within glaciers as the ice melts can seed new cryoconite granules, says Andy Hodson, who studies glacier ecology at the University of Sheffield.
But dust is tiny, and glaciers are huge. How big of a problem can all this granule activity be in the grand scheme of things?