Mineral dust is driving increasingly large algal blooms on the Greenland Ice Sheet. Researchers at the University of Leeds have found that the blooms have created a “Dark Zone” on the western margin of the ice sheet where sunlight is not properly reflected, which causes the ice to melt faster.
Across the Greenland Ice Sheet, surface melting and water runoff has increased by about 40 percent in the last 25 years. The new research indicates that algae living on the melting ice surfaces are contributing to this phenomenon, and that phosphate mineral dust is helping the algal blooms thrive.
According to study co-author Professor Jim McQuaid, mineral dust can be transported thousands of miles by wind, but the dust examined by the researchers was from local sources.
“As dryland areas in northerly latitudes become even drier under climate change, we can expect to see more dust transported and deposited on the Greenland Ice Sheet, further fuelling algal blooms,” said Professor McQuaid.
“As an atmospheric scientist, it’s exciting to see how wind-blown mineral dust is linked to algal bloom development and impacts ice sheet melting.”
The algae blooms darken the ice as they spread out. This decreases the ice sheet’s albedo, or its ability to reflect sunlight.
The Leeds team analyzed samples from the southwestern margin of the Greenland ice sheet over two years. By examining the surface dust, the experts determined that phosphorus is used as a key nutrient to help the algae grow.
The researchers identified the phosphorus-containing mineral hydroxylapatite as the source of fuel for the algal blooms in the Dark Zone. The hydroxylapatite was blown onto the ice from neighboring rock outcrops.
“The photosynthesis rate of the ice algae improved significantly when we provided them with a source of phosphorus,” said study lead author Dr. Jenine McCutcheon. “Our mineralogy results revealed that the phosphorus used by ice algae may be coming from the hydroxylapatite we identified in the mineral dust.”
“It’s important to understand the controls on algal growth because of their role in ice sheet darkening. Although algal blooms can cover up to 78% of the bare ice surfaces in the Dark Zone, their abundance and size can vary greatly over time.”
“From one season to the next, algal blooms may change and vary in intensity, making them difficult to model year-to-year.”
Previous studies have shown that for the last two decades, the melt season in the Dark Zone has started progressively earlier and lasted longer, reducing the ice sheet’s ability to reflect solar radiation.
“The glacier ice algae bio-mine the phosphorus from the minerals fueling the blooms that cover larger and larger areas each year, leading to more melting and faster rising sea levels,” said Professor Liane G. Benning, who is the principal investigator of the Natural Environment Research Council project Black and Bloom.
“As current ice sheet and climate models do not include this phenomena, this research will advance these models and give us a greater understanding of the annual lifecycle of algal blooms.”
The study is published in the journal Nature Communications.