What is Watermelon Snow?
Watermelon Snow, exactly as the name suggests, is a pink colored watermelon slushy like snow. It has been spotted in a number of snow covered regions of the earth which are permanently covered with snow. Although the pink color may look like it comes from some sort of a mineral deposit, or some other inorganic source such as meteorite debris, interestingly it is due to living organisms – Algae. Its other names are – snow algae, pink snow, red snow, or blood snow.
How does it get that color?
One of the widely found algae species in these pink snow patches contains a red pigment (called carotenoids) in addition to the green chlorophyll component. The alage itself is called Chlamydomonas nivalis.
When it is young, the same species of algae is green as well. However, to protect its food producing pigments, chlorophyll, from the UV radiation they develop this sunscreen like red pigment on top of it.
Since the top part of the snow is exposed directly to UV rays there’s that red algae there. If you dig around there’s a chance you might find the green snow. Like in the picture below we see a mix of both pink and green snow.[Scientific American]
The job of the red pigment is a lot like beta carotene in our eyes. It protects the retina from getting damaged due to exposure to UV radiation. The same carotenoids also make those vibrant colors of the Grand Prismatic spring (Rainbow colored lake) at Yellowstone national park.
Where does the algae come from?
The spores from which it blooms are present almost everywhere. It is just that they lie dormant as long as the environment is dry around them. Once the top part of the snow starts melting during the spring, the algae blooms and starts coloring the snow pink (red and white mixed appears pink).
The problem it is causing
If you notice the details in the picture above, you will see that the parts that appear in a darker shade of pink (indicating more biomass of algae in that region), those local areas of snow has melted more. Thus there are these holes formed in the snow. Clearly indicating that the snow with this algae in it melts more easily. Here’s why…
When snow is fresh it reflects about 90 % of the radiation, just because white reflects a almost all the visible light and more. This defines something called the “albedo.” So the albedo for fresh snow is the ratio of incident radiation to the reflected radiation – 90/100 = 0.9. This kind of snow, that has red algae blooming in it, due to its relatively darker color than pure white, reflects about 20% less light. The reduced albedo called the algal-albedo in this case, results in more energy absorbed, and faster melting.
The effect is a lot like those cryoconite holes
The study published in a major journal
The effect of this red algae contributing towards reduced albedo and faster melting of ice has so far been studied by geobiologists from Germany and Britain in a sweeping study carried out in several regions of the Arctic circle. Samples collected from about 40 sites in Svalbard, Northern Sweden, Greenland and Iceland show this 20% reduced albedo.
Another striking thing that the study suggests is that this algae has the ability to grow in all places of permanent snow cover, irrespective of the local geographical mineralogy. It is alarming because faster melting snow is never good. And that happening in about 50% of all the snow covered regions on earth is a disaster waiting to happen.[Nature Communications]
The snowball effect
Call it an evil feedback loop, or avalanche or a snowball effect. The red algae needs water to grow initially. So, first there’s partial surface melting of glaciers which encourages these to grow first. As it grows, it helps the snow melt more and then more algae grows. More biomass of algae means the albedo is lower (see figure 4 in the article above). More energy is absorbed. As the albedo vs. biomass corelation in the article above shows, makes the snow melt faster.
Can you eat it?
Certainly you can. But please don’t sue me if you get poisoned. Plus they say it has a laxative effect. But then some also say that it does taste like watermelon slushy. I hope Wonderbland wasn’t lying in the comments section of this Gizmodo article.
Now you find a way to wipe this algae off the earth’s face without any ecological side-effects and take your Nobel prize home.