Surprise! Greenland Ice Sheet Melting
From the American Geophysical Union and the “but we’ll still find a way to blame CO2, just you wait” department. It seems this is a frustrating day for climate-ice researchers, earlier, it was found that ice cores used to determine ancient CO2 levels are likely contaminated by microbes, and they altered the gas mixture balance.
Algae growth reduces reflectivity, enhances Greenland ice sheet melting
WASHINGTON D.C. — 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.
Glaciologists have long known materials such as mineral dust and black carbon can darken the surface of large ice sheets. Scientists study these impurities because they reduce the sheet’s albedo, or the extent to which it reflects light, which increases melting of the ice and affects projections of sea level rise. But few studies had examined the darkening effect of algal cells, which naturally grow on the ice sheet.
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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.
Microphotographs of ice algae (mostly the species Ancylonema nordenskioldii). CREDIT Marian Yallop
The findings sharpen the way glaciologists think about melting of ice sheets and how ice reflects light, according to Marek Stibal, a cryosphere ecologist at Charles University in Prague, Czech Republic and one of the lead authors of the new study. A warming climate could also increase algal growth in the future, potentially boosting algae’s influence on ice sheet melting, he said.
“The novel aspect of our study is that we discover biological processes play an important role in ice sheet behavior,” Stibal said. “Glaciologists usually only look at inorganic materials when studying light reflectance and ice melt because biological processes are often too complicated to capture. But we find organisms can have a large-scale effect on a system that was previously studied in an abiotic context.”
Studying algae in the field
Previous studies suggested impurities such as black carbon and dust drive melting of bare ice on the lower part of the ice sheet. Impurities darken the surface of the sheet, reducing its albedo and allow it to absorb more light. The increased absorption of solar radiation raises the temperature of the ice sheet and accelerates the melting process.
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, Stibal said.
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.
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