Ocean Changes Could Diminish Phytoplankton’s Role as Carbon Sink

Warming seawater temperatures and ocean acidification could diminish the capacity of a critical species of phytoplankton to pull carbon dioxide from the atmosphere and store it in the deep ocean, the world’s biggest carbon sink, according to a new study. Under typical conditions, the phytoplankton Emiliania huxleyi develops plates of calcified armor called coccoliths while floating in the ocean’s upper layers before eventually sinking, a process responsible for about 80 percent of inorganic carbons trapped at the bottom of the sea. In a study published in the journal Global Change Biology, researchers at San Francisco State University found that exposure to higher levels of carbon dioxide, which makes seawater more acidic, and higher ammonium levels altered the phytoplankton’s biology and growth. Signficantly, they found that the coccoliths formed under those conditions were “incomplete or hollow,” containing lower amounts of inorganic carbon and making them less likely to sink. “Without this, the carbon is more likely to be recycled into the Earth’s atmosphere,” said Jonathon Stillman, an assistant professor of biology and lead author of the study.