Most pristine air lies above Antarctica | Polarjournal
Antarctica is considered to be the last pristine wilderness on Earth. According to the results of the US-Australian research group, this statement is also true for the air. They could hardly detect bacteria from other populated regions. Photo: Michael Wenger

The human influence on Earth seems limitless. Wherever you are, there are residues of our existence. This includes not only the apparent legacies such as plastic or concrete, but also microscopic particles in the earth, in the water and in the air. But a research team from the US and Australia has now found a region where at least the air has little trace of land and man: Antarctica.

The research group, led by Professor Sonia Kreidenweis of Colorado State University, found hardly any particles, so-called aerosols, in the boundary layers of the air above the Southern Ocean and in Antarctica, which would testify to human activities from other regions further north. “We used bacteria from the air above the Southern Ocean as a diagnostic tool to determine the key properties of the lower atmosphere,” explains the study’s co-author, Thomas Hill. “We were able to show that the aerosols that control cloud formation over the Southern Ocean are very closely linked to biological processes in the sea and that Antarctica is isolated from the southward dispersion of microorganisms and nutrient deposits from Southern continents. Overall, the Southern Ocean seems to be one of the few places in the world that has been spared from human activity,” says Hill. The results of the work have been published in the journal Proceedings of the National Academy of Sciences.

In the lowest layer of the atmosphere, where sea and air meet, the greatest exchange of particles takes place. Bacteria are distributed with the water drops in the air and drifted with the wind. The particles in the water are also the basis for the formation of clouds over the sea. Photo: Michael Wenger

During a research trip by the Australian research vessel RV Investigator, samples were taken by students from the boundary layer between air and sea. The ship followed a transect from Tasmania towards the ice edge near Antarctica. The samples were then examined for DNA traces of bacteria by Jun Uetake, the lead author of the study, at a clean lab in Colorado. He and Sonia Kreidenweis had to work very carefully to avoid any contamination. Because bacteria and other particles are almost everywhere in the air and they are drifted hundreds and thousands of kilometers away with winds. The samples analyzed were then compared with wind data collected. To find out if the particles originated from land and human activity, Uetake and the researchers divided the compositions by latitudinal zones.

The bacterial communities discovered by the researchers were all of marine origin. The bacteria are brought into the air by the sea spray and drifted with the winds. But the amounts of bacteria are very small, according to the research. Photo: Michael Wenger

The results show that closer to populated continents such as Australia, bacterial and particle composition is more influenced by land, land use and pollution compared to the middle of the Southern Ocean. Plant material and soils are strong sources of particles that promote the freezing of so-called super-cold droplets. In the Southern Ocean, on the other hand, the spray, which is created by the breaking of waves, forms the starting material of liquid cloud droplets, which form small amounts of ice germ particles, unlike close to land. The amount of bacterial DNA in these marine samples has also been so small that Uetake could hardly find any evidence. This led the researchers to conclude that the air above and beyond the Southern Ocean is one of the most pristine air masses found on Earth. This fact, which had long been suspected, also had led previously to numerous atmospheric tests and measurements being carried out in Antarctica, rather than elsewhere in the world. For astronomers, too, observing the universe from Antarctica would be a worthwhile thing if only the climatic conditions were not so challenging. At least, the air is fresh in Antarctica.

Source: Colorado State University

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