I started seeing snow like this high on Mt. Shasta some years in the 1970s and 1980s. I knew even then not to eat it. It usually formed above 9000 or 10,000 feet often in glaciers in the summertime on Mt. Shasta. However, the pink algae is usually only in the top 5 inches or so of snow where the sun can hit it and it can live on the water in the snow that first melts from the sun.
begin quote from:Watermelon Snow: Not Edible but Important for Climate Change
Watermelon Snow: Not Edible but Important for Climate Change
Summer
is the season to cool off with a big chunk of watermelon. But there’s
another kind of watermelon that’ll have you trading in your sandals for
hiking boots if you want to experience it. While you’re not going to
want to eat what some people call “watermelon snow,” researchers have
found that having a better understanding of it could be important in a
warming world.
In snowy places across the globe, “watermelon snow”
forms as the summer sun heats up and melts winter’s leftovers. The
colorful snow is made up of communities of algae that thrive in freezing
temperatures and liquid water, resulting in algal blooms. When these
typically green organisms get a lot of sun, they produce a natural type
of sunscreen that paints the slopes pink and red. The addition of color
to the surface darkens the snow, allowing it to heat up faster, and melt
more quickly.
“Imagine wearing black instead of a white T-shirt in the sun. It feels much hotter,” wrote Stefanie Lutz,
a geobiologist at GFZ German Research Center for Geosciences, in an
email. “It is the same for the snow: More heat means more melting.”
Dr. Lutz, together with Liane Benning and their colleagues at a number of universities, published a study
Thursday in Nature Communications that examined microbes in summer
snow, and noted that while bacterial communities differ from place to
place, the same algae that produce watermelon snow appear to be so
global that it’s time for climate models to consider their effects on
snow and ice melt.
Algae
changes snow’s albedo, or how much light, or radiation, its surface
reflects back into the atmosphere. Based on 40 samples from four
locations, the new study estimated that blooms of snow algae can lead to
an albedo decrease of 13 percent over the course of an Arctic melt
season, compared with clean snow, meaning the dark snow would absorb
much more light. Just how much melting this will account for, or how
much that may affect sea level rise, however, is still to be determined.
But algal effects on albedo are going to be important for melting
glaciers, which play a huge role in the climate system, said Dr. Lutz.
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Current
climate models take into account how soot from forest fires, dust from
the Sahara or even increased water content (which slightly darkens snow
to blue) affect albedo, but they have yet to measure biological effects,
like that of algae.
“A small amount may have a big effect,” said Joseph Cook, a glaciologist at the University of Sheffield who was not involved in the study, but is looking at bacteria’s effect on the albedo of Greenland ice sheets (where ice turns brown, purple and gray in some cases).
Dr.
Lutz worries that an interplay between today’s rising temperatures and
the snow algae could cause a “runaway effect,” whereby melting snow
would cause algae to bloom, which would darken the snow, causing more to
melt, creating more water, which also darkens the snow and feeds the
algae, and so on, in a circular pattern of cotton candy-colored surfaces
melting.
If
you’d like to cool down this summer with watermelon snow, the pink
stuff can be found nearly anywhere that has melting snow — the Arctic,
Antarctica, the Himalayas and the Rockies, among others. Logistics are
important, said Dr. Benning, because these places aren’t easy to get to,
and you’ll be hiking and camping in the cold, lonely wilderness. She
says everyone has their favorite spots, but she likes the beauty and
remoteness of a glacier in Svalbard: “A place where there are no worries
about what happens back home.”
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