SOURCE: American Geophysical Union (AGU)

DATE: December 20, 2017

SNIP: New research shows algae growing on the Greenland ice sheet, the Earth’s second-largest ice sheet, significantly reduce the surface reflectivity of the ice sheet’s bare ice area and contribute more to its melting than dust or black carbon. The new findings could influence scientists’ understanding of ice sheet melting and projections of future sea level rise, according to the study’s authors.

The new study quantitatively assessed how surface ice algae contribute to darkening of the ice sheet, and found the algae reduce the ice sheet’s albedo significantly more than non-algal materials, like mineral particles and black carbon. Algal darkening is responsible for 5 percent to 10 percent of the total ice sheet melt each summer, according to the new research published in Geophysical Research Letters, a journal of the American Geophysical Union.

Absorption of sunlight is responsible for most of the ice melt in Greenland, according to Jason Box, a climatologist at The Geological Survey of Denmark and Greenland and the other lead author of the new study.

Microbes such as algal cells colonize the ice and can accumulate over time given enough sunlight, water and nutrients. Surface ice algae produce dark pigments to protect themselves from high intensity radiation, further darkening the sheet surface, Marek Stibal, a cryosphere ecologist at Charles University in Prague, Czech Republic and one of the lead authors of the new study, said.

The new study didn’t estimate how much more ice could melt in the future due to algal darkening. But the results can lay the groundwork to devise more accurate projections of sea level rise scenarios due to melting ice from Greenland and other ice sheets, Stibal said.

He also believes a warming climate could be a boon to algal populations, potentially increasing their darkening influence.

“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. “Additionally, the growing season will lengthen, so the contribution of algae to melting of the ice will probably increase over time.”