Dark Snow Project Fieldwork Findings Published

After a long and arduous path to publication, results of Marek Stibal’s observations of ice algae, which I documented in the 2014 Dark Snow field work, have been published.
I plan to interview co-authors Marek Stibal and Jason Box next week.

Scientific American:

Algae growth as a result of climate change is making the Greenland ice sheet, a primary contributor to sea-level rise, melt faster, according to a new study.

Algae grows naturally on the ice sheet, but it thrives under a warmer climate. It makes the Greenland ice sheet, which is the second-largest ice sheet on Earth, less reflective of the sun, which means the ice absorbs more of the sun’s heat. This, in turn, drives more rapid melting, according to the paper published yesterday in Geophysical Research Letters.

Researchers found that algae accounts for about 5 to 10 percent of total ice sheet melt each summer. That means algae plays a greater role in melting than previously believed, said Marek Stibal, a cryosphere ecologist at Charles University in the Czech Republic and one of the lead authors of the new study.

“As the climate warms, the area that the algae can grow in will expand, so they’ll colonize more of the ice sheet,” he said in a statement. “Additionally, the growing season will lengthen, so the contribution of algae to melting of the ice will probably increase over time.”

Black carbon and dust have been tracked by researchers as contributors to melting of the Greenland ice sheet. Like algae, the dark particles cut down on the albedo, or reflectivity, of the otherwise white surface. The particles absorb the sun’s rays and warm the Earth underneath. Stibal said typically researchers have only looked at inorganic materials when studying ice sheet behavior, but the new research suggests that biological factors also play a significant role.

“Our analysis reveals that the impact of algae on bare (snow-free) ice darkening was greater than that of other impurities and, therefore, that algal growth was a crucial control of bare ice darkening in the study area,” the authors wrote. “Incorporating the darkening effect of algal growth is expected to improve future projections of the Greenland ice sheet melting.”

Since the Greenland ice sheet is a major contributor to sea-level rise, the study has implications for future projections of the rate of expected rise, the study found. Further study is needed to determine how sea levels could be affected by more rapid growth of algae that is expected as a result of global warming. The study also has implications outside of the Arctic, the authors found. Other areas of the world covered in ice, including the Himalayas, also have algae on the ice, which could affect rates of melting there.

American Geophysical Union:

The authors of the new study headed into the Greenland ice sheet in the summer of 2014 to quantify the contribution of algae to the darkening effect. Several members of their team camped at a study site in the southwestern region of the ice sheet for 56 days while gathering data on the sheet’s reflectivity and algal population.

Stibal and his colleagues used portable spectrometers and albedometers to measure the reflectivity spectrum of the bare ice surface each day. They also collected samples of surface ice and used a field microscope to characterize the algae and count the number of algal cells in each sample. They analyzed the relationship between the growth of the algae and the amount of light being reflected by the ice sheet surface.

The authors found the ice sheet reflected significantly less light as the algal population grew. They calculated algal growth accounted for approximately 70 percent of the variation in the light reflectance data, making it the dominant contributor to the phenomenon. The rest of the variation was due to rain and how much time had passed, and non-algal impurities weren’t significant in their analysis.