Winds of change
Palmer LTER team report suggests link between physical conditions and wildlife
Posted July 11, 2014
A long-term study of the links between climate and marine life along the rapidly warming western Antarctic Peninsula reveals how changes in physical factors such as wind speed and sea-ice cover send ripples through the food web, with impacts on everything from single-celled algae to penguins.
Grace Saba at Rutgers University is lead author of the study, published this month in Nature Communications , along with members of the Palmer Long-Term Ecological Research (LTER) program, which conducts annual shipboard surveys along the western side of the Antarctic Peninsula, as well as out of the U.S. Antarctic Program’s coastal Palmer Station .
The National Science Foundation has funded the Palmer LTER program since 1990.
Photo Credit: Kyle Hoppe/Antarctic Photo Library
The team’s research shows that populations of photosynthetic algae – the tiny drifting plants that support the polar food web – peak every four to six years in the waters along the western Antarctic Peninsula. These blooms correlate with a negative phase of the Southern Annular Mode , or SAM, a seesaw shift in atmospheric pressure between mid-latitudes and Antarctica.
In winter during a negative phase of SAM, cold southerly winds blow across the peninsula, increasing the extent of winter ice. From spring into summer, winds are significantly reduced, delaying ice retreat.
“The combination of a 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,” Saba said in a press release from the Virginia Institute of Marine Science , where several of the co-authors of the paper work.
This stable, or stratified water column, with a layer of fresher, less-dense ice-melt floating atop a saltier layer below, encourages phytoplankton growth, likely by keeping the tiny plants nearer the sunlit surface and in proximity to the iron-rich glacial meltwater they need to thrive.
The team’s sampling reveals that the area’s periodic, climate-driven phytoplankton blooms are a key to krill “recruitment” – the addition of new, young individuals into the krill population.
When SAM is positive, warm northwesterly winds blow over the peninsula region, bringing less sea ice and a less-stable water column – factors that discourage the large blooms of phytoplankton on which krill rely.
“Penguins then have to forage further, and thus end up delivering less food to their chicks. That can decrease their reproductive success,” Saba said.
Adélie penguins and other top predators in the Antarctic food web rely on a robust population of krill prey for their own health and reproductive success. Ongoing work by Palmer LTER scientists shows that the population of Adélie penguins near Palmer Station has fallen 85 percent since 1974.
The western Antarctic Peninsula is one of the fastest warming regions on Earth, with the average annual temperature rising a half-degree Celsius per decade since the 1950s.
“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,” Saba said. “If even one positive SAM episode lasted longer than the krill lifespan – four to six years with decreased phytoplankton abundance and krill recruitment – it could be catastrophic to the krill population.”
NSF-funded research in this article: Hugh Ducklow, Columbia University, Award No. 1344502 . Co-authors of the study include William R. Fraser, Vincent S. Saba, Richard A. Iannuzzi, Kaycee E. Coleman, Scott C. Doney, Hugh W. Ducklow, Douglas G. Martinson, Travis N. Miles, Donna L. Patterson-Fraser, Sharon E. Stammerjohn, Deborah K. Steinberg and Oscar M. Schofield.