Blue!
Blue Ice. Patagônia, 2014.
This is the most common answer, but
there is also green ice, black (dark) ice, red ice, yellow ice.
Many factors can
change the ice colors: the amount of air that ice contains, the light
incidence, the ice age, the matter inside them: rock sediments, algae or other
organisms.
Blue and Green Ice. Antarctica, 2018.
Ice, such as water,
behaves like a weak blue filter, absorbing red and orange light more strongly
than green and blue light. The thicker the ice, the bluer it will look, as more
red and orange light is absorbed.
Blue Ice. Patagônia, 2014.
Icebergs and glaciers
can contain large amounts of air. The air-ice interface reflects white sunlight
before it has the chance to penetrate and be absorbed. Thus, the snow and the
surface of the glaciers appear with a bright white color. However, some light
penetrates deeper into the glacier where much of the air has been squeezed to
form ice, leaving only a few air bubbles that reflect the light back. At that
point is where most of the absorption happens. The result is a deep dispersion
of blue light within the glacier.
Blue Ice. Antarctica, 2018.
Nevertheless, the
older the ice, the higher the pressure of water on the air inside it, making it
harder to incident light, performing it darker with a vitreous appearance.
Black Ice. Antarctica, 2018.
Is there a relationship between colors and climate
change?
Ice and snow can also
act as a microorganisms habitat (such as red snow algae, green snow algae,
brown ice algae, bacterias etc.) whose coloration will dye the surface of large
ice sheets in Antarctica.
Lutz et al., 2016.
One of the problems
caused by the snow coloration, given by the proliferation of microorganisms on
its surface, is the albedo reduction. Albedo (whiteness or reflected sunlight)
is the reflectivity or the power of reflection of a surface. White reflects
more light, while darker colors absorb light. The more algae there is in the
snow, the darker it becomes and the less sunlight it reflects.
Red Ice. Antarctica, 2018.
The darkening of the
ice sheet surface is one of the responsible for the thaw. This phenomenon plays
an important role in climate change and the process of ice melting.
In the Arctic, for
example, Lutz, S. et al. (2016) found was that the same algal species was
responsible for causing the pink snow across the Arctic. This creates a sort of
snowball effect: the more glaciers and snowmelt, the more algae forms. The more
algae forms, the more sunlight it absorbs, causing more melting.
During the months that
it’s warm in the Arctic, a thin layer of meltwater forms on ice and snow. The
sunlight and the water are ideal growing conditions for algae and they begin to
thrive. (Lutz, et al., 2016).
The phenomenon can
also be observed in other polar regions of the planet and its study can
contribute to the understanding of the melting and climate changes.
References
Lutz, S. et al. The
biogeography of red snow microbiomes and their role in melting arctic glaciers.
Nature Communications. Vol.
7. 22 jun.2016
Acknowledgments: Thanks to my friend Claudineia Lizieri for inspiring
me to write this text. Clau, I keep hoping to write that article about the colors of
the ice.
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