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Green snow phenomenon in Antarctica worries scientists

The algae that green the white continent are spreading more and more as the planet warms up.

Study lead author Andrew Gray geotags snowy algae blooms. Credit: University of Cambridge.

Although the presence of algae in Antarctica was warned long ago by various expeditions, such as the one carried out by the British Ernest Shackleton, its full extent was unknown.

Now, a team of scientists has made the first large-scale map of microscopic algae off the coast of the Antarctic Peninsula and has warned that plant life will continue to spread across the icy continent as global temperatures rise from the change. climate.

Although each algae is microscopic, when they grow en masse, they make the snow turn bright green, a phenomenon that can be seen from space and is called “green snow.”

The scientific team, made up of researchers from the University of Cambridge and the British Antarctic Survey, have combined satellite data and field observations from two summers in Antarctica, and their findings have been published in Nature Communications.

The results of the study will represent “a significant advance in our understanding of terrestrial life in Antarctica and how it could change in the coming years as the climate warms up,” explains Matt Davey, from the Department of Plant Sciences at the University of Cambridge and director of research.

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Snow algae are a key component of the continent’s ability to capture carbon dioxide from the atmosphere through photosynthesis.

These green algae blooms are found around the Antarctic coast, particularly on islands along the western coast of the Antarctic Peninsula, “warm” areas where the average temperature is just above zero degrees Celsius in the southern summer, which in the southern hemisphere runs from November to February. The Peninsula is the part of Antarctica that experienced the fastest warming in the latter part of the last century.

The study finds that the distribution of green algae in the snow is also “strongly influenced by birds and marine mammals”, whose droppings act as a highly nutritious natural fertilizer that accelerates the growth of algae. In fact, more than 60% of the algae is less than five kilometers from a penguin colony, and close to places for bird nesting or seal landing.

No snow in summer

For this study, the team has used images from the European Space Agency’s Sentinel 2 satellite taken between 2017 and 2019 and has combined them with measurements made in Ryder Bay on Adelaide Island and on the Fildes Peninsula on King Island. George.

“We identified 1,679 separate green algae blooms on the snow surface, which together covered an area of ​​1.9 km², equivalent to a carbon sink of about 479 tons per year,” the same amount of carbon emitted for 875,000 trips on gasoline cars in the UK, Davey says.

Nearly two-thirds of the green algae blooms were on small, low-lying islands without high ground. As the Antarctic Peninsula warms due to rising global temperatures, these islands may lose their summer snow cover and with it their snowy algae. However, in terms of mass, most of the snow algae are found in a small number of larger flowers in the north of the Peninsula and the South Shetland Islands, in areas where they can spread to higher lands as the low snow melts.

“As Antarctica warms, we believe the overall mass of snow-covered algae will increase, as the spread to higher lands will significantly compensate for the loss of small patches of seaweed on the islands,” warns Andrew Gray, lead author of the paper. and researcher at the NERC Field Spectroscopy Facility in Edinburgh.

Antarctica is the southernmost continent in the world, typically known as a frozen land of snow and ice. But terrestrial life can be abundant, particularly along its coast, and is responding rapidly to climate change in the region. Mosses and lichens form the two largest visible groups of photosynthetic organisms, and have been the most studied to date.

This new study has found that microscopic algae also play an important role in the Antarctic ecosystem and its carbon cycle.

Source: University of Cambridge

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