What gives glacier algae their wild colors?

When a British expedition reported seeing pink mountain snow in 1818, the London Times said: “Our credulity is put to an extreme test upon this occasion, but we cannot learn that there is any reason to doubt the fact as stated.” Two hundred years later, we now can confirm that pink snow (“watermelon snow”) is real and it is caused by certain types of algae. But why is it that snow algae take on such distinctive red and purple colors? And how does this connect to melting glaciers or global sea level rise?

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