Don’t Eat The Pink Snow: Watermelon Snow Microbiomes in the Arctic and Glacial Melt
By Cai McCann
Imagine you’re standing on the frozen ground of the Arctic, peering out at a harsh, barren tundra. Only it’s not white, it’s an explosion of pearly pink and red hues, so vibrantly stark and raw that the tundra is bleeding. You approach gingerly, your boots biting into the icy rind of the ground, and peer into this pink bank of snow. Say hello to the snow algae species of Chlamydomonas nivalis and Chlorophyta species.
Snow algae, such as Chlorophyta and Chlamydomonas nivalis, represent a phenomenon known as watermelon snow (a.k.a. “red snow,” “pink snow,” or “blood snow”). These patches found in the snowy regions circling the Arctic comprise a plethora of different cryophilic (“cold-loving”) bacteria, archaea, and eukarya species. Moreover, these snow microbiomes represent both an exciting new field of research in glacial microbiology and the salient and concerning climate change considerations.
In a 2016 study, scientists investigated the functional genetics of the microbiota in these watermelon snow “patches” in over 40 geochemically distinct sites across the Arctic regions, including glaciers and snowfields located in Svalbard, Northern Sweden, Greenland, and Iceland. They discovered that these algal blooms commonly proliferate during the melting season, resulting in pockets of immense bacterial and microbial diversity. However, genetic sequencing of specifically the algae in these patches demonstrated that there was very little genetic diversity between algae populations in different sites.
They also discovered that these snow algae have unintended consequences for climate change. For example, when the snow algae form extensive blooms in the spring and summer, they synthesize specific pigments to provide protection against radiation. This immense biomass has the unfortunate effect of darkening the surface of the glaciers. As a result, measured albedo, or the ability of the snow surface to reflect the solar energy, decreases. Think about it like this: this snow algal effect functions to increase the ground temperature the same way as wearing dark-colored clothing on a sunny day warms you up. Locally and across sites containing these snow algae, the albedo values ranged between ~0.5-0.75, which translate to a measured decrease in albedo! This result was also independent of the local environment—that is, the negative effects of snow algae on the albedo were ubiquitous.
So what does this decrease in albedo mean? With an over 13% overall decrease in snow albedo due to snow algal blooms during the melt season, we observe accelerated glacial and snow melt as the land with long-lasting snow is more apt to absorb (instead of reflecting) the solar energy of the sun. If you have more heat and solar energy-absorbing surfaces, exposed for a longer time, you will have higher glacial melt rates--this effectively exhibits a snowball effect (albeit in the opposite direction). This “bio-albedo” effect represents another layer to the multifaceted and unpredictable nature of one of the defining issues of the 21st century— climate change. It is crucial to factor these algal-albedo interactions and quantification of additional melting in future climate models.
Lutz, S. et al. The biogeography of red snow microbiomes and their role in melting arctic glaciers. Nature Communications 7, 11968 (2016).