DURHAM, N.C. -- Warming waters and shrinking sea ice along the Western Antarctic Peninsula have altered the makeup of microscopic sea life there, causing changes in the region’s plankton communities that may have important climate implications, according to a study led by scientists at Duke University and Duke Kunshan University in China.

Plankton are small organisms that float at or near the surface of the ocean. They help combat climate change by absorbing vast quantities of carbon dioxide (CO2) from the atmosphere through photosynthesis and transforming it into organic carbon, some of which ultimately sinks into the ocean’s depths.

The new study, which appears Aug. 16 in Nature Communications, finds that the diversity of plankton communities in the Western Antarctic Peninsula’s coastal waters has declined and they have become less evenly distributed in response to the warming conditions.

In the wake of these changes, CO2 absorption has also declined, the researchers’ analysis shows.

“Our findings suggest that as climate change continues to affect coastal Antarctic regions, there could be substantial declines in plankton biodiversity and biological carbon drawdown, impacting the Southern Ocean’s capacity to mitigate carbon emissions in the atmosphere,” said Yajuan Lin, assistant professor of biogeochemistry at Duke Kunshan.

“Understanding the feedbacks between ocean biology and climate is particularly important in the Southern Ocean because it contributes disproportionately to the global oceanic heat gain and CO2 uptake,” said Nicolas Cassar, professor of biogeochemistry at Duke University’s Nicholas School of the Environment, who, along with Lin, was a corresponding author of the study. Lin conducted much of the study as a postdoctoral researcher in Cassar’s lab.

The Western Atlantic Peninsula has been warming rapidly with significant loss of sea ice since the middle of the last century, but scientists have lacked sufficient data to quantify the long-term impacts these changes may be having on plankton biodiversity and carbon cycling at a regional scale.

To resolve that data gap, Lin and her colleagues collected and analyzed plankton DNA samples from coastal waters around the peninsula over a five-year period in the Antarctic region.

Their study, which was funded by a National Science Foundation grant to Cassar, strongly suggests that water temperature and the extent of sea-ice cover are dominant factors influencing the composition and CO2 uptake of plankton communities in the region.

Lin likens the plankton communities to an underwater forest.

“This invisible forest in the ocean sucks up carbon dioxide from the atmosphere, so changes to it are incredibly important,” she said. “The research suggests that forest may be doing less of this in the Western Antarctic Peninsula.”

To conduct the study, researchers collected DNA samples of microbial sea life, including algae and microzooplankton, on annual trips to the Western Antarctic Peninsula from 2012 to 2016. They used a mass spectrometer to monitor carbon sequestration levels on each trip. The work was conducted primarily aboard the research vessel Laurence M. Gould with short spells at the U.S. Antarctic base Palmer Station and the British Antarctic Survey base Rothera.

Following each trip, members of the team, which included scientists from the University of North Carolina at Chapel Hill, Rutgers University, Columbia University and the British Antarctica Survey, spent months at Duke and at the University of Nantes analyzing the samples using a high-throughput DNA sequencing technology. This allowed them to measure species numbers, community composition, carbon levels and other features in the samples, despite the organisms’ microscopic size.

The study comes on the heels of a report by the UN Intergovernmental Panel on Climate Change earlier this month that documented the dangers climate change will pose to Earth’s oceans, ice caps and land in coming decades.

Lin hopes the new study will add to our understanding of those dangers and help inform discussions at the UN Convention on Biological Diversity in October and the UN Climate Change Conference (COP26) in November.

“Our results add to the data about climate change and biodiversity and could help to provide a clearer picture of what’s happening,” she said.  “However, a longer study will be needed to confirm the pattern.”

CITATION: “Decline in Plankton Diversity and Carbon Flux with Reduced Sea Ice Extent Along the Western Antarctic Peninsula,” Yajuan Lin, Carly Moreno, Adrian Marchetti, Hugh Ducklow, Oscar Schofield, Erwan Delage, Michael Meredith, Zuchuan Li, Damien Eveillard, Samuel Clarkson and Nicolas Cassar; Aug. 16, 2021, Nature Communications. DOI: https://doi.org/10.1038/s41467-021-25235-w

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