‘Watermelon’ snow is helping melt glaciers | Science News for Students

‘Watermelon’ snow is helping melt glaciers

Algae that paint the snow pink make it absorb more sunlight — and heat
Nov 10, 2017 — 6:45 am EST
watermelon snow

Some Arctic algae turn the snow red to pink on parts of Alaska’s Harding Icefield. This colored snow melts faster than clean, white snow, new data show.

Gerard Ganey

Certain microbes that grow on glaciers and ice sheets can paint the snow pink. Sometimes called watermelon snow, this reddish pigment makes the snow soak up more sunlight. And that makes it melt faster, data now show.

The alga Chlamydomonas nivalis (KLAM-ee-duh-MO-nus NIV-ah-lis) and its kin appear to be to blame. C. nivalis thrives in cold water. Although frozen, glaciers and snow are still watery environments, says Roman Dial. He’s a biologist at Alaska Pacific University in Anchorage. He also was an author of the new study.

These watermelon-hued algae appear in the spring and summer. At times they will proliferate dramatically. Ecologists refer to this as an algal bloom. Research had suggested a colorful blood could darken snow, fostering its melt. The reason: Dark colors absorb more sunlight. That’s why you feel hotter standing in the sun in a black shirt than in a white one. A bloom of C. nivalis is like covering snow with a dark t-shirt.

If microbes help melt the snow, that water might help even more algae grow. That could create a “feedback” cycle where increased melting creates conditions for even more melting. Or that’s what scientists suspected. But to be sure, they need to acquire some data from testing.  

“We used everything from microscopes to satellites,” Dial says. Doing so confirmed that places with extra watermelon algae melted much faster.

The researchers shared their new data September 18 in Nature Geoscience.

Little microbes, big effect

Glaciers naturally have small amounts of nutrients. These include nitrogen and phosphorus. Higher levels of those nutrients might act as fertilizer to help algae grow. So Dial and colleagues added either plain water or water with fertilizer in it to different patches of snow on Harding Icefield. This frozen expanse in southern Alaska spans 1,900 square kilometers (730 square miles).

This image shows how snow algae increased across Alaska’s Harding Icefield over the summer of 2013. Its estimated range went from low (light blue) in June to high (red) by September.
G. Ganey

In places where they added water, 50 percent more algae grew than in untouched areas. Adding fertilizer quadrupled the algal growth.

Now that the scientists knew how to boost algae growth, they did related tests. In some areas, they boosted the growth of the algae by dousing the snow in fertilizer. At other sites, they killed off such algae with bleach. Over 100 days, the scientists tracked melting at both sites.

Places with extra algae melted much faster than where the algae were wiped out. By the end of the test, snow that got extra algae was three times as likely to have melted to slush or down to a layer of ice beneath it. Exposing that ice under the snow could further boost algae’s melting. Why? Bare ice absorbs more sunlight than does clean snow.

The team collected satellite data, such as photos of the snow cover and measurements of how reflective the snow was. From this, the team then estimated the effects of algae across the whole Harding Icefield.

Algae grew on more than one-third of the ice sheet. Within that area, the microbes were responsible for almost one-sixth of the snowmelt, the team calculated. Warm temperatures caused most of the rest of the melt.

Not just Alaska

“There's a growing push to understand the impact of microorganisms on glaciers and ice sheets,” says Christopher Williamson. He’s a microbiologist in England at the University of Bristol who did not take part of this study. Scientists often do research like this — observing one area over a long time, Williamson says. But here, scientists instead altered the environment to probe directly for any direct link between algae and snowmelt.

The effect probably isn’t limited to Alaska, either. Another team sampled watermelon snow across the Arctic. They found that the reddish snow was 13 percent less reflective. And any light that is not reflected into space can be absorbed by the snow as heat. So the snow probably melted faster, although the scientists didn’t measure that directly.

Those researchers published their results last year in Nature Communications.

C. nivalis and other snow microbes like to live where the temps are just below freezing. If global warming heats up more of the Arctic into this range, those algae might expand their range.

Other microbes or pollutants might also speed the melting of Arctic ice. Williamson is part of a five-year project studying the impact of microbes on ice in Greenland. There, he’s studying both bacteria and ice algae — which are different than snow algae. These microbes have been darkening Greenland’s ice. That may help explain why ice there has been melting faster than would be expected due to climate change alone. Williamson and colleagues now want to figure investigate if microbes are part of the reason.  

Power Words

(more about Power Words)

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

Arctic     A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

biologist     A scientist who focuses on living things.

bleach     A dilute form of the liquid, sodium hypochlorite, that is used around the home to lighten and brighten fabrics, to remove stains or to kill germs.

bloom     (in microbiology) The rapid and largely uncontrolled growth of a species, such as algae in waterways enriched with nutrients.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

colleague     Someone who works with another; a co-worker or team member.

ecology     A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

feedback     (in climate science) A process or combination of processes that propel or exaggerate a change in some direction. For instance, as the cover of Arctic ice disappears with global warming, less of the sun’s warming energy will be reflected back into space. This will serve to increase the rate of Earth’s warming. That warming might trigger some feedback (like sea-ice melting) that fosters additional warming.

fertilizer     Nitrogen, phosphorus and other plant nutrients added to soil, water or foliage to boost crop growth or to replenish nutrients that were lost earlier as they were used by plant roots or leaves.

geoscience     Any of a number of sciences, like geology or atmospheric science, concerned with better understanding Earth. People who work in this field are known as geoscientists.

glacier     A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.

global warming     The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

Greenland     The world’s largest island, Greenland sits between the Arctic Ocean and North Atlantic. Although it is technically part of North America (sitting just east of Northern Canada), Greenland has been linked more politically to Europe. Indeed, Vikings arrived in Greenland around the 10th century, and for a time the island was a colony of Denmark. In June 2009, Greenland became an independent nation. Ice covers roughly 80 percent of Greenland. Indeed, the Greenland ice sheet is the world’s largest. If its frozen water were to melt, it could raise sea levels around the world by 6 meters (about 20 feet). Although this is the 12th biggest nation (based on surface area), Greenland averages the fewest people per square kilometer of its surface area.

ice sheet     A broad blanket of ice, often kilometers deep. Ice sheets currently cover most of Antarctica. An ice sheet also blankets most of Greenland. During the last glaciation, ice sheets also covered much of North America and Europe.

kin     Family or relatives (sometimes even distant ones).

link     A connection between two people or things.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiologist     A scientist who studies microbes, principally bacteria, fungi and viruses. They may study microbes and the infections they can cause or ways that they can interact with their environment.

nitrogen     A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

phosphorus     A highly reactive, nonmetallic element occurring naturally in phosphates. Its scientific symbol is P. It is an important part of many chemicals and structures that are found in cells, such as membranes, and DNA.

pigment     A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors.

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

reflective     Having the quality of reflecting light strongly. Reflective objects can produce a strong bright glare when sunlight bounces off of them. Examples of reflective objects include a mirror, a smooth metal can, a car window, a glass bottle, ice, snow or the watery surface of a lake.

satellite     A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.


Journal: G.Q. Ganey et al. The role of microbes in snowmelt and radiative forcing on an Alaskan icefield. Nature Geoscience. Published online September 18, 2017. doi: 10.1038/NGEO3027.

Journal: S. Lutz. The biogeography of red snow microbiomes and their role in melting arctic glaciers. Nature Communications. Published online June 22, 2016. doi: 10.1038/ncomms11968.