Mixed with this granule and melted ice are cyanobacteria, which run in sunlight. As a cryoconite hole gets deeper, its bottom moves out of direct sunlight, which means there is less energy available for the cyanobacteria that live in it. But, says Leidman, “when it rains or when a strong melt occurs, the sediment in those cryoconites is washed and washed in these supraglacial courses, where it accumulates in the floodplains.”
Now, the bacteria are exposed to all the sunlight they could ever dream of, especially given the low cloud cover over Greenland. As they proliferate, cyanobacteria have two ways of darkening that sediment. For one, they themselves produce a dark substance, a combination of humic acids and what scientists call extracellular polymeric substances. The first comes from the degradation of dead bacteria and can provide UV protection against surviving bacteria. The latter is a glue-like adhesive that helps cyanobacteria stabilize their local environments.
The second way, says Leidman, is to “change the structure of the sediment, agglomerate it so that it can more easily retain water and stick more easily to surfaces. So just the fact that it is crowded means that it can absorb more sunlight. “The accumulation accumulated in the supraglacial courses is significantly darker than the ice itself.
Flying drones around the Greenland ice sheet, Leidman and colleagues found that the sediment could cover up to 25% of a river’s bottom. (See their beautiful images below.) In addition, they estimated that without the bacteria acting to gather the seeds, only 1.2 percent of the bottom would be covered, as smaller free particles would wash away. to sit down.
Researchers are still facing many unknowns. Since cyanobacteria work in sunlight, they will probably proliferate as Greenland warms. But how hot it is also warm? “We don’t really know if these bacteria will survive with higher temperatures or higher flows or how rivers will change shape,” says Leidman. But, he adds, “as the temperature rises, there will probably be a greater growth of bacteria. So, although it is certainly not the main cause of the increase in melting rates, it is most likely a factor that is not negligible.