Why Is Antarctica’s Snow Turning Green?

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Something strange is happening in the world’s most snowy-white continent. Maybe it is time to get crayons and add some color to the maps, because the coasts of the northern Antarctic Peninsula are seasonally turning green, orange, and red – all thanks to microscopic algae.

Sensationalism aside, algal blooms on the snow-covered Antarctic coasts are not a new phenomenon. They have been observed for a long time in the areas where average temperatures rise above freezing point during the summer. Still, the phenomenon had not been analyzed and mapped in great detail before. 

Now, a crew of researchers from the University of Cambridge and the British Antarctic Survey have created the first large-scale map of green algae blooms, and have made predictions on their future spread.  Their results were published this May in the journal Nature Communications

The study included two field campaigns of measuring and sampling algae at the site; however, the main part of data was the imagery provided by the European Space Agency’s Copernicus Sentinel 2 satellite mission.  The research has revealed 1679 snow algae blooms, estimated to hold 1.3 × 103 tons of total dry biomass. 

A photograph showing a snow algae bloom dominated by green algae starting to melt out from beneath seasonal snow cover.  Photo: Gray et al., 2020.  CC BY 4.0.
A photograph showing a snow algae bloom dominated by green algae starting to melt out from beneath seasonal snow cover. Photo: Gray et al., 2020. CC BY 4.0.

The team points out that the estimate is “conservative” since the Sentinel 2 was set on picking up the wavelengths of chlorophyll present in green algae. The orange and red microscopic algae were also abundant, but wavelengths at which these are registered (“broad absorbance below 500 nm”) overlaps with that of mineral dust in the snow. It is safe to say that algal colonies are even more numerous than the study suggests – and also more colorful.

Another interesting fact revealed by the study is the relation of algae patches and birdlife– with 60 percent of blooms found less than 5 km (3 miles) away from penguin colonies. To grow and spread, algae need water originating from the melted snow, but also require nutrients. The runoff from bird droppings is able to provide just that.

The Color of Climate Change

Undoubtedly, global warming is the force behind the increase in algal blooms in Antarctica. On February 6 of this year, the northern tip of the peninsula became the record holder for the hottest Antarctic temperature ever measured – 18.3 °C, or 64.9 °F – only to be beaten days later on February 9 by a now-standing record of 20.75 °C (69.3 °F),measured at Comandante Ferraz Antarctic Station.

The loss of snow cover and bird colonies on small, low-lying northern Antarctica islands could seemingly curb the spread of snow algae blooms. However, more heating will open up higher latitudes to colonization by algae. 

The co-lead author of the study, Dr Andrew Gray of the University of Cambridge and the University of Edinburgh, confirms the notion that the blooms will become more numerous in the future. “As Antarctica warms, we predict the overall mass of snow algae will increase, as the spread to higher ground will significantly outweigh the loss of small island patches of algae.

How the algae bloom itself may affect climate change remains a mystery for now. These events represent a major carbon-dioxide sink. The researchers say that photosynthesis from this amount of algae can absorb 500 tons of carbon from the atmosphere per year – the equivalent of about 875,000 average car rides in the UK. But at the same time, the algae-induced darkening of the snow cover decreases the surface albedo, leading to greater absorbance of warmth from the sun and hence – more warming.

Surely, the scientist will have an opportunity to further study the snow algae role in climate change as the patches of these microscopic creatures that are visible from outer space grow and expand.

Resources

The Study

Gray, A. et al. (2020) Remote sensing reveals Antarctic green snow algae as important terrestrial carbon sink. Nature Communications 11, Article number: 2527 https://www.nature.com/articles/s41467-020-16018-w

Articles

Garget, J. (2020, May 19). Climate Change Will Turn Coastal Antarctica Gree, Says Scientists. University of Cambridge. https://www.cam.ac.uk/stories/antarctica-turning-green

Climate change will turn coastal Antarctica green. British Antarctic Survey. 20 May 2020.

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