What are cryoconites?

The name comes from “cryo” = ice et “conite” = dust (Nordenskjöld, Greenland 1870. These formations can be observed on both poles and in glaciers of mountains. When dark matter (rocks, sediments...) falls on the white surface of ice, it takes up the heat of the Sun in summer and melts locally the ice. The dark matter goes down, as more ice is melting. The hole can vary very much in length and depth, Zorigto tells us that he has found 5 m long ones, for example.
www.people.cornell.edu/pages/bhk8/undergrad1.htm

In summer, when the hole is open, microorganisms can fall in it, and a small living community can develop. In winter, an ice lid is formed, enclosing the inhabitants but some liquid water can remain. In summer, the lid is melting and the community can continue to slowly grow, years after years. It is now realised that, if cryoconites are very numerous in glacial regions (difficult to survey), that could change the nutrient balance of these biotopes as there would be more carbon, nitrogen, etc.. than thought.
The Canada glacier (Mc Murdo Dry Valleys is melting, and shows a kind of 'transversal section' through the cryoconites (A. Fountain)

The ice is flowing to the sea or following the glacial streams. When the cryoconites arrive at a zone where the whole glacier is melting, they melt away and disappear. However, the microbial communities are then released and act like a 'seed population' to colonize the soil that has just been deglaciated. Zorigto was this summer in Svalbard with the Czech colleagues and Josef, and he could witness how a cryoconite that he spotted and into which he had inserted a sensor, vanished within a few days, due to the high melting speed in the Arctic.