Vast ecosystem of microalgae accelerates ice melt on Antarctic ice cap
For the first time, researchers investigated an algal bloom on an Antarctic ice cap and discovered an astonishing diversity of microbial life. However, the coloration accelerates the melting.
The vast majority of Antarctica is covered in snow and ice – but you won’t find snow-white areas everywhere. As on ice caps and glaciers in the northern hemisphere, there are also regions in Antarctica where snow and ice are reddish or purple in color.
Studies in alpine regions and in Greenland have shown that these colorations are caused by cold-tolerant microorganisms – bacteria, cyanobacteria, algae, fungi and microscopic animals.
An international research team led by the Scottish Association for Marine Science (SAMS) has now also discovered such communities in the Antarctic – on the ice cap of Robert Island northwest of the tip of the Antarctic Peninsula. Their findings were published in Nature Communications on March 18.
An overlooked ecosystem
The researchers spent two months on the island to study the microorganisms in their habitat. For the first time, they found direct evidence for the existence of photosynthetic communities on ice caps in the maritime Antarctic. These differ from other cryoflora communities that have already been researched, such as the red and green snow algae on snow surfaces near the coast.
“This is the first time these ice-cap communities in Antarctica have been mapped and studied in detail,” said Dr. Alex Thomson, algal researcher at SAMS and lead author of the study, in a SAMS press release. “We know that ice-free areas in Antarctica serve as oases for life, but discovering this extent and diversity of life on the ice itself was like finding forests in a desert.”
With an area of around 2.7 square kilometers, the algal bloom on Robert Island covered around 6 % of the terrestrial photosynthetic areas mapped to date in Antarctica – a remarkable proportion. The researchers assume that similar communities also occur on other Antarctic ice caps, which could make them one of the largest photoautotrophic ecosystems in the maritime Antarctic in terms of area.
Different from the north – and uniquely diverse
Microscopic and genetic analyses revealed that the composition of the algae communities on Robert Island differs significantly from comparable communities on glaciers in the northern hemisphere.
While they are dominated by species of the genus Ancylonema in the north, the researchers found a mixed community here with unusually high proportions of green algae, more specifically Chlorophyceae and Trebouxiophyceae. Particularly noteworthy: the genetic analyses show a great diversity within the genus Ancylonema – including previously unknown variants that only occur in the Antarctic.
Algae make a measurable contribution to ice melt
The research team also investigated the influence of the algal bloom on the albedo of the ice surface and found that the bright red and purple pigments produced by the algae absorb sunlight.
According to the researchers’ calculations, the resulting local warming increases the melting rate by up to 5 millimetres per day. This corresponds to a contribution of up to 2.4 percent to the total ice loss in the study region.
Even if these values are below those of severely affected areas such as Greenland, the biologically enhanced melting contributes significantly to the overall melting of the ice cap on Robert Island given its extent.
“Now that we know there are large glacial algal communities in Antarctica, the goal is to see how extensive they are, how they contribute to Antarctica’s wider biodiversity and what role they play in influencing glacial melt rates there,” says Dr. Andrew Gray, researcher at the Norwegian Institute for Nature Research and co-author of the study, in the press release.
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