Approximately 1-6% of the surface of a glacier may be covered by “exotic” debris, which includes inorganic and organic particles that are darker than the surrounding white icy surface and thus absorb the solar radiation better than the ice. The heated debris therefore melts into the ice forming features called cryoconite holes: small, water-filled depressions that are typically < 1 m in diameter and a few centimetres deep. Life exists wherever there is water and cryoconite holes are no exception. These holes are colonized by a diverse range of microorganisms, including viruses, bacteria and microscopic plants.

Researchers from the Universities of Sheffield, Bristol and Innsbruck measured now the microbial activity associated with cryoconite holes in Greenland, Svalbard and the Alps and found that it was comparable to that found in very rich ecosystems from warmer regions. In fact, microbial activity in one gram of cryoconite was roughly the same as in one gram of soil from the Mediterranean. The colonisation of the debris by microbes subsequently leads to further darkening of the ice surface. This is because it was also found that the amount of photosynthesis (i.e. the process in which carbon dioxide is converted by plants to biomass, releasing oxygen) is much higher than the amount of respiration (i.e., the process in which oxygen is consumed and organic matter is biologically converted back to carbon dioxide). The consequence of higher photosynthesis than respiration rates is that the surface of glaciers is a self-sustained ecosystem in which organic matter can be accumulated. The result is even more enhanced absorption of solar radiation, promoting further melt and providing yet more water for microorganisms, which are then dispersed to other parts of the ice surface. This dispersal transfers the microbes, organic matter and debris to adjacent ecosystems, including those of the forefield and subglacial environments with the potential to sustaining life in other ecosystems.

The team suggests that glaciers become increasingly biological as they decay, and that glacier melting is, in part, a biologically-mediated process that initiates ecological succession long before the ice has disappeared. These hypotheses are now being tested in the current National Environment Research Council (NERC)project which started during the 2009 summer. The project aims to quantify the biological effects on glacier mass balance, and to determine fluxes and quality of organic matter exported to downstream environments during deglaciation, by examining the surfaces of Arctic valley glaciers that are retreating markedly in response to summer melt. In doing so, the researchers aim to produce the first quantification and characterisation of bio-physical effects on ice mass wastage during deglaciation.

Besides the role of being an active ecosystem, cryoconite holes are also archives of man-made material such as radionuclides. In samples of cryoconites of a temperate Austrian glacier as well as on a Svalbard Valley Glacier high activity concentrations of anthropogenic radionuclides were found, which stem from global and Chernobyl fallouts. Radionuclides identified were 137Cs, 134Cs, 238Pu, 239and240Pu, 90Sr, 241Am, 60Co, 154Eu, 207Bi, and 125Sb. Given the approximately known isotopic ratios, Cs and Pu can be separated into the contributions of either source of origin.

Further interest is given in the source of origin of microbes finally being settled in the cryoconite hole – do they origin from aeolian, terrestrial or aquatic sources? Air samples can give indication about the proportion of airborne material. One of the main aims is also to get a better understanding of these unique ecosystems and to support the idea that our adjacent glaciers are crucial habitats supporting connecting systems.

(Source and contact: Alexandre M. Anesio, Univeristy of Bristol, UK: a.m.anesio@bristol.ac.uk and Birgit Sattler, University of Innsbruck, Austria: birgit.sattler@uibk.ac.at)

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Natural cryoconite hole on Austre Brøggerbreen, Svalbard.

Cryoconite holes on Midtre Lovenbreen, Svalbard

Natural cryoconite hole on Froya Glacier, Greenland (all photos courtesy of Alexandre Anesio, University of Bristol and Birgit Sattler, University of Innsbruck)