Changing Antarctic Climate Linked to Marine Food Web: Penguins in Peril?

Climate may have more of an impact on the Antarctic than we thought. A long-term study between climate and marine life along the West Antarctic Peninsula reveals that changing conditions can greatly impact species that range from single-celled algae to penguins.

Scientists first began studying the fast-changing region of the West Antarctic Peninsula in 1990. Since then, they've gathered data on climate and the species that live there. This, in turn, gave researchers a dataset of sufficient length to reveal how climate signals can reverberate through a food web.

In this case, the researchers found that populations of photosynthetic algae, which are tiny, drifting marine plants, peak every four to six years in the waters along the West Antarctic Peninsula. These blooms correlate with a negative phase of the "Southern Annular Mode," or SAM. This is a seesaw shift in atmospheric pressure between mid-latitudes and Antarctica.

During a negative phase of SAM in the winter, cold southerly winds blow across the Peninsula, which increases the extent of winter ice. From spring into summer, these winds are significantly reduced and delay ice retreat.

"The combination of windy winter with heavy sea ice followed by a calm spring favors the development and persistence of a stable water column in the summer along the West Antarctic Peninsula," said Vincent Saba, one of the researchers, in a news release. The stratified and stable water column that results encourages phytoplankton growth.

These periodic phytoplankton blooms are crucial for the entire polar food web. They're key to krill "recruitment," which is the addition of new, young individuals into the krill population. When climate conditions lead to peaks in the abundance of phytoplankton and krill, Adelie penguins don't have to go far in order to forage. But when SAM is positive, warm winds bring less sea ice and a less-stable water column, which means the penguins have to forage further afield. In fact, researchers have found that Adelie penguin populations near Palmer Station have fallen by 85 percent since 1974.

"Projections from global climate models under 'business-as-usual' emission scenarios up to the year 2100 suggest a further increase in temperature and in the occurrence of positive-SAM conditions," said Saba. "If even one positive SAM episode lasted longer than the krill lifespan-four or six years with decreased phytoplankton abundance and krill recruitment-it could be catastrophic to the krill population."

The findings are published in the journal Nature Communications.