By promoting the aggregation of sediments, the bacteria present in the Greenland sea ice accelerate the melting of the ice. A discovery that forces us to revise upwards forecasts linked to global warming.
If from a distance, the Greenland sea ice can appear immaculate, looking a little closer it is possible to distinguish long lines a little darker and quite problematic. This is what a team of American researchers discovered who detailed their find in the review Geophysical Research Letters December 6.
« We had already seen that these traces contained sediment during drone overflights., tells Numerama lead author Sasha Leidman of Rutgers University in New Jersey. But we didn’t know there were so many sediments, much more than they needed to be. »
Before talking about sediments, you should know that the traces themselves have been widely studied for a few years. These are cracks in the ice when it melts. Water passes through it and forms small rivers. The peculiarity is that their albedo is lower: in light, they are darker than the ice itself and absorb more light, which further accentuates global warming since the heat remains on Earth instead of being thoughtful.
But the story does not end there since in addition, sediments (sand and dust in particular) accumulate in these currents. The ice thus soiled has an even lower albedo, which further accelerates the melting of the pack ice.
Bacteria found guilty
In this study, the authors looked further at the dust grains, as well as the water current, through in situ analyzes in southwest Greenland where the currents are numerous. It is also a practical place, because it has been well studied before by other teams and its characteristics are well known. Scientists focused on a single current, 137 meters long, but reconnaissance missions around it confirmed that it was representative of the others.
Their verdict? The grains of sand are far too small. They should be washed away by the current of the water, so why are they standing there? ” There are bacteria in the sediment, reveals Sasha Leidman. They hold the grains together to form balls that are 91 times larger and that are not washed away by the water. »
The presence of these bacteria changes everything since now, the sediments are linked together, agglutinate and are all the more difficult to evacuate with the current of water. This dirty ice melts even more easily, says Sasha Leidman: “ We do not know exactly how quickly melting accelerates with these accumulations. Since it is very dark, we know that the heat is absorbed even more, but it is difficult to know what role this plays in global warming. ».
For Marie Dumont, director of the Center d’Etudes de la Neige, it is these bacteria that change everything: “ Studies on albedo are old, she tells Numerama. But the aspect related to these microorganisms is currently much less treated in the scientific literature. ».
Snowball effect on ice
Yet these bacteria were there long before the industrial era: this growth began before the appearance of humanity. The problem is that it is accelerating with global warming. ” Current conditions are more favorable for the development of bacteria, confirms Sasha Leidman. With the temperatures getting milder, they proliferate and cluster in holes in the ice, cryoconites, where they become even more difficult to dislodge.. »
The phenomenon is observed elsewhere, especially in Alaska and the Himalayas. But in Greenland, the phenomenon is even more problematic since the sea ice is thicker there, allowing more significant deposits of bacteria and therefore more sediment and always the inevitable consequence: more intense ice melting.
A snowball effect, in short, in which global warming promotes the concentration of bacteria, which leads to even greater global warming. ” There are several factors that can melt snow or ice faster, adds Marie Dumont. The presence of rain, the internal microstructures which make the materials less fine and therefore more fragile, but also these sediments which pose a serious problem. »
The researcher is also currently studying the effect of sediments from the Sahara in early February on snow in the Alps. Early research has shown grains buried under fresh snow, which could speed up melting.
This study casts a dark shadow on the models around global warming. ” Our next step, says Sasha Leidman, it is to find the link between environmental change and the growth of the number of bacteria. This will tell us how they impact climate change. »
Indeed, if the temperatures are caused to rise even more, the bacteria may become more numerous and more problematic. It is now a question of predicting the magnitude of this development to know what the impact will be on future warming and on sea level rise.
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Source: Numerama by www.numerama.com.
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