Study explores Southern Ocean nutrient cycle
FRISCO — Melting Antarctic glaciers are adding nutrients to the Southern Ocean, potentially boosting the entire food chain. The Southern Ocean could become a more productive ecosystem as a result of climate change, scientists suggested in a new study accepted for publication in Journal of Geophysical Research: Oceans, an American Geophysical Union journal.
“Coastal Antarctica is likely to become a more productive place in the future,” said Kevin Arrigo, a biological oceanographer with the Department of Earth System Science at Stanford University in California, and lead author of the new study.
Specifically, the research found that the melting glaciers are adding iron to areas of open water, called polynyas, where it stimulates growth of phytoplankton, ocean algae that form the base of the marine food chain. Krill and fish thrive on phytoplankton, and these smaller animals support penguins, seals and whales that feed and breed in the polynyas that ring the Antarctic coast.
“These coastal polynyas are sensitive to inputs from adjacent glaciers, and these glaciers are probably going to accelerate their melting in the future, which is certainly going to have implications for these polynyas,” Arrigo said.
Winds blowing off the Antarctic Ice Sheet in summer push sea ice away from the shore, creating the polynas, which can be as large as the great lakes. The polynyas are “hotspots” for phytoplankton and, in turn, the entire ocean food chain, according to Arrigo.
“When you look at satellite images of ocean color, these areas just light up [green] compared to the [blue] waters around them,” he said, explaining that the study suggests that melting Antarctic glaciers are the biggest factor in phytoplankton abundance.
The study is based on satellite data that helps explain the Antarctic marine foodweb. But the observed changes could be offset by other, as-yet unknown environmental shifts, Arrigo added. Most marine organisms, including phytoplankton, will be negatively affected warming and increasingly acidic oceans, he said.
Increased phytoplankton productivity is likely to increase carbon uptake through photosynthesis.
“These polynyas appear to be disproportionately important, for their size, as sinks of carbon. And the reality is that they really are not included in anyone’s carbon budget,” said Arrigo.
The researchers used satellite images from 1997 to 2014 to calculate the amount of phytoplankton growing in 46 polynyas that ring the coast of Antarctica, finding that phytoplankton were most abundant in polynyas near glaciers pumping out large amounts of water.
Higher temperatures also enhanced phytoplankton growth but not nearly as much as Arrigo originally believed. The algae evolved to thrive at low temperatures, and the small differences in temperature between polynyas – from 1 degree to 2 degrees Celsius (34 to 36 degrees Fahrenheit) – does not make a large difference in the amount of phytoplankton, said Arrigo.
Field measurements could help confirm the findings from the satellite data, said Peter Sedwick, a chemical oceanographer with Ocean, Earth & Atmospheric Sciences at Old Dominion University in Norfolk, Virginia, who was not associated with the study.
Those observations could help shed further light on how phytoplankton productivity — and food for fish, penguins and seals — could change as a result of climate change, Sedwick added.