Penguin poop is melting Antarctic snow by keeping algae green

Penguin poop is fertilizing snow algae blooms along the Antarctic Peninsula, feeding dense green algae patches along the coastline, a new study shows. These expanding stretches of green snow melt faster than clean, white snow, potentially speeding up the spread of snow- and ice-free areas of Antarctica.

As temperatures rise across Antarctica, snow algae habitats are expanding along the coasts, darkening the surface and leading to even more warming and snowmelt. By tracking their poop across the snow, penguins are inadvertently supplying the algae with vital nutrients that keep the blooms green and make the melting effect even stronger.

"The link between wildlife, nutrients, and snow algae is a critical missing component in projections of expansion of ice-free areas in Antarctica," said Alia Khan, a cryosphere biogeochemist at the University of Colorado Boulder and senior author of the study who began this research while at Western Washington University.

"Without accounting for these biological darkening effects, we are likely underestimating how rapidly coastal snowpacks are melting and how fast ice-free terrain will expand across Antarctica."

The study appears in Journal of Geophysical Research: Biogeosciences.

Green means grow

Khan and her team focused on color-changing Antarctic snow algae, which grow densely enough in some areas to make the snow itself look red or green. When nutrients are abundant, the algae can stay active, packing their cells with green pigments like chlorophyll to ramp up photosynthesis as the algae race to grow as much as possible during the short Antarctic summer.

When nutrients are scarce or conditions are harsh, the algae hunker down, producing sunscreen-like red pigments to protect themselves from the sun while putting growth on hold.

Red snow absorbs about 20% more energy from sunlight than clean, white snow. This extra energy heats up the snow, leading to more snowmelt. Where nutrients fuel more green pigment and more algae cells overall, green snow absorbs 40% more energy than clean snow—twice the increase seen in red snow—amping up the melt rate even further.

Stinky samples

Traveling by boat across the rough seas of the Drake Passage, the team gathered samples of both red and green snow algae along the coast of the West Antarctic Peninsula, covering five degrees of latitude and areas with and without penguin colonies.

Taking samples near penguin colonies is not a glamorous job, requiring the team to get close to smelly bird droppings to gather algae-tinted snow in bags with ceramic spoons.

"[Penguin] poop can visually look similar to the red snow algae," Khan said. "It's very stinky working near penguins. They're just waddling around in their poop and tracking it all over the snow."

Fortunately, the difference between poop, known as guano, and snow algae is clearer in the lab. Elise Ryan, the study's lead author, and other members of Khan's lab counted the number of algae cells in each snow sample under a microscope and extracted the pigments and nutrients in each sample.

Where algae cells had predominantly green pigments, the researchers found that the snow had far more phosphate, a critical nutrient found in guano, than where the algae had predominantly red, sunscreen-like pigments.

"This finding links the marine food web to snow ecology," Khan said. After feasting on marine creatures at sea, she explained, penguins and seabirds like skuas spread the resulting nutrients (including phosphate) over coastal snowpack in the form of their poop. "The penguin guano acts as a fertilizer ... that fuels these dense green snow algae blooms."

Polar projections

As penguins waddle their way closer to the South Pole in response to changing conditions, there's potential for guano-fertilized snow algae habitats to expand and spread their melt-enhancing effects over a larger area. But scientists' projections of Antarctic melting don't yet account for this phenomenon.

Khan's team is the first to show a direct link between penguin poop and the different-colored stages of snow algae's life cycle, and more data is needed before guano-fueled greening can be added to snowmelt projections for the Antarctic Peninsula.