Using data from ESAs Copernicus Sentinel-2 mission and two field campaigns, a team of UK scientists has identified 1,679 blooms of Antarctic green snow algae, seasonally covering 1.95 km2 and equating to 1,300 tons total dry biomass.
A photograph showing a snow algae bloom dominated by green algae on Anchorage Island. Image credit: Gray et al, doi: 10.1038/s41467-020-16018-w.
Blooms of snow algae in Antarctica were first described by expeditions in the 1950s and 1960s.
They host a diverse range of algal species and are found around the Antarctic coastline, particularly on islands along the west coast of the Antarctic Peninsula. They grow in warmer areas, where average temperatures are just above zero degrees Celsius during the austral summer (November to February).
Dr. Matt Davey, a researcher in the Department of Plant Sciences at the University of Cambridge, and colleagues attempted to estimate the distribution, size and biomass of snow algal blooms across the entire the Antarctic Peninsula.
The scientists used images from ESAs Sentinel-2 satellite taken between 2017 and 2019, and measurements they made on the ground in Antarctica at Ryder Bay, Adelaide Island, and the Fildes Peninsula, King George Island.
We identified 1,679 separate blooms of green algae on the snow surface, which together covered an area of 1.95 km2, equating to a carbon sink of around 479 tons per year, Dr. Davey said.
Put into context this is the same amount of carbon emitted by about 875,000 average petrol car journeys in the UK.
Antarctic green snow algae distribution and modeled cell density: (a) overview of the locations of individual blooms of green-dominant snow algae identified across the Antarctic Peninsula using modeled data from satellite imagery and ground data (circles); circle color scale represents the mean cell density of each bloom; red triangles indicate the location of ground validation sites; cyan triangles show the location of our Adelaide Island and King George Island field sites; (b) RGB Sentinel 2A image of green snow algae blooms at one of our validation sites, Anchorage Island (February, 2020); (c) output of IB4; pixel values are converted to cell density with the color scale showing the resultant cell density for each pixel identified as containing green snow algae. Image credit: Gray et al, doi: 10.1038/s41467-020-16018-w.
Dr. Davey and co-author found that the distribution of green snow algae is strongly influenced by marine birds and mammals, whose excrement acts as a highly nutritious natural fertilizer to accelerate algal growth.
Over 60% of blooms were found within 5 km of a penguin colony. Algae were also observed growing near the nesting sites of other birds, including skuas, and areas where seals come ashore.
Almost two thirds of the green algal blooms were on small, low-lying islands with no high ground.
As the Antarctic Peninsula warms due to rising global temperatures, these islands may lose their summer snow cover and with it their snow algae.
However, in terms of mass, the majority of snow algae is found in a small number of larger blooms in the north of the Peninsula and the South Shetland Islands, in areas where they can spread to higher ground as low-lying snow melts.
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, said Dr. Andrew Gray, a researcher in the Department of Plant Sciences at the University of Cambridge and NERC Field Spectroscopy Facility.
The teams paper was published in the journal Nature Communications.
A. Gray et al. 2020. Remote sensing reveals Antarctic green snow algae as important terrestrial carbon sink. Nat Commun 11, 2527; doi: 10.1038/s41467-020-16018-w