Why the last snow on Earth may be red – ”Snow-dwelling microbes increase glacier melt directly in a bio-geophysical feedback by lowering albedo”
By Alan Burdick
21 September 2017
(The New Yorker) – Every spring, in alpine regions around the world, one of Earth’s tiniest migrations takes place. The migrants are single-celled green algae; they are kin to seaweed, but instead of living in the sea they live in snow. (Snow weed, maybe?) They spend the winter deep in the snowpack, atop last summer’s snow, as dormant cysts. In the spring, they wake and swim up through the trickle of snowmelt to the surface, dividing and photosynthesizing as they go. Then, at the top, they turn red. This creates what scientists call pink snow or watermelon snow—drifts and glaciers that look like Slush Puppies and eventually reduce to rivulets of crimson.The color comes from astaxanthin, a molecular cousin of the chemical that makes carrots orange. The algae produce it seemingly as a sunscreen; it absorbs UV light, warming the organisms, and, critically, melting the surrounding snow. “The melting helps them a lot,” Roman Dial, a biologist at Alaska Pacific University, told me recently. “The surface of a snowfield can be a very dry place; the liquid water drains away. And life just can’t use frozen water. It’s like if you were out camping and your water bottle was frozen, you’d be thirsty until it melted.”Watermelon snow is a perfectly natural phenomenon, but in an age of disappearing glaciers it is also problematic. Last year, scientists discovered that the algae had reduced the amount of sunlight reflected by some glaciers in Scandinavia—and increased the amount of sunlight absorbed—by thirteen per cent. The result, as Dial and his colleagues demonstrated in this month’s issue of Nature Geoscience, is faster melting. As in other parts of the warming planet—particularly the Arctic, where scientists fear that thawing permafrost may be triggering a climatic feedback loop—the effect is likely self-perpetuating. Ice sheets are already being darkened by dust, soot, and ash, which hasten melting and add nutrients on which algae can flourish. As the organisms proliferate, they melt even more snow, which allows them to proliferate again. “It spreads more rapidly than people realize, once it gets established,” Dial said. [more]
Why the Last Snow on Earth May Be Red
28 September 2017 (APU) – Prominent newspapers, magazines, and journals across the country, including The New Yorker, Business Insider, and Nature Geoscience, have picked up MSES student Gerard Ganey’s research paper on “watermelon snow” in recent weeks.
In his study, done with Professor Roman Dial, Ganey discussed how an algae species found in glaciers can tint the snow crimson and cause the surrounding ice to melt faster.The paper explained that the red hue, which is found in alpine and polar settings around the world during spring and summer months, comes from a class of pigments in the algae. The more that are packed together, the redder the snow, and subsequently, the faster the ice melts. While the melt is good for the microbes that need the liquid water to survive and thrive, it’s bad for glaciers that are already melting from a myriad of other causes.To further test their theory, the researchers grew the pink snow with water or fertilizer in experimental plots in Harding Icefield and compared the growth response of the algae to control plots where nothing was added (they also sprayed some algae-destroying bleach on a few plots to make up for it). Adding water, they found, led to a 50 percent growth compared to the control regions. Adding fertilizer quadrupled the growth.They then tracked how much the areas melted over the course of 100 days. As they thought, places with more algae melted at a faster rate than where algae had been removed. They also employed satellite imagery to find that the algae grew on more than a third of the entire icefield (270 of 730 square miles).Dial said it’s too early to tell just yet what the melting means for Alaskans.“We need to know how widespread the effects of snow algae are on melt,” Dial explained. “If they are widespread, then it means algae could contribute substantially to glacier melting, sea level rise, and even warming, since they absorb solar energy that further melts glaciers that reflect light that generally cools the atmosphere. If they are not widespread, then it’s just an interesting fact.”The next step in the process in seeing just how widespread the melt is will using satellite imagery. Professor Jason Geck’s Remote Sensing class is currently doing a class project on that right now.Though Dial has been involved with snow algae studies for 15 years, he said MSES student Gerard Ganey was the lead author on the paper and did all of the work.Over the course of the study, Ganey made dozens of trips up to Harding Icefield, none of the using helicopters or airplanes, rather all by foot and skiing. He enlisted APU Ski Team members and professional climbers to help him, as they were the only ones who could keep up.“He weathered storms, wind, and rain,” Dial said. “He literally used data from the microscope to the satellite. He learned glaciology, microbiology, spectrometry, remote sensing, statistical analysis, GIS, and modeling on top of hiking from near sea level to 4,000 feet to undertake experiments in one of the harshest environments in Alaska: rainy, windy icefields.”Dial added, “From my point of view he represented what an APU grad student is all about: physically tough, intellectually capable, persistent, and inter-disciplinary.”
ABSTRACT: A lack of liquid water limits life on glaciers worldwide but specialized microbes still colonize these environments. These microbes reduce surface albedo, which, in turn, could lead to warming and enhanced glacier melt. Here we present results from a replicated, controlled field experiment to quantify the impact of microbes on snowmelt in red-snow communities. Addition of nitrogen–phosphorous–potassium fertilizer increased alga cell counts nearly fourfold, to levels similar to nitrogen–phosphorus-enriched lakes; water alone increased counts by half. The manipulated alga abundance explained a third of the observed variability in snowmelt. Using a normalized-difference spectral index we estimated alga abundance from satellite imagery and calculated microbial contribution to snowmelt on an icefield of 1,900 km2. The red-snow area extended over about 700 km2, and in this area we determined that microbial communities were responsible for 17% of the total snowmelt there. Our results support hypotheses that snow-dwelling microbes increase glacier melt directly in a bio-geophysical feedback by lowering albedo and indirectly by exposing low-albedo glacier ice. Radiative forcing due to perennial populations of microbes may match that of non-living particulates at high latitudes. Their contribution to climate warming is likely to grow with increased melt and nutrient input.
The role of microbes in snowmelt and radiative forcing on an Alaskan icefield
