Study suggests warmer and more acidic oceans will inhibit carbon capture by phtyplankton
By Summit Voice
SUMMIT COUNTY — An elaborate lab experiment done by a San Francisco State University research team shows that warmer increasingly acidic oceans may fundamentally change the role some phytoplankton have in capturing carbon from the atmosphere.
The study published this week in the journal Global Change Biology suggests that at least one species of ubiquitous phytoplankton — Emiliania huxleyi — forms incomplete or hollow coccoliths in high carbon and high ammonium conditions, resulting in less carbon sinking to the ocean floor.
Coccoliths are elaborate plates of calcified armor that form as the phytoplankton floats free in the sunny top layers of the oceans. The coccoliths form a hard and heavy shell that eventually sinks to the ocean depths.
“About 80 percent of inorganic carbon trapped down there is from coccoliths like these,” said SF State assistant professor Jonathon Stillman, one of the study’s co-authors.”The ratio of inorganic to organic carbon is important,” Stillman said. “As inorganic carbon increases, it adds more ballast to the hard shell, which makes it sink and makes it more likely to be transported to the deep ocean. Without this, the carbon is more likely to be recycled into the Earth’s atmosphere.”
“Our results suggest in the future there will be overall lower amounts of calcification and overall lower amount of transport of carbon to the deep ocean,” he added.
To measure the impacts of warmer temperatures and increasing acidification, the scientists raised more than 200 generations of Emiliania huxleyi in the lab, adjusting carbon dioxide levels and the type of nitrogen in the phytoplankton’s seawater bath.
Changes to this massive carbon sink could have a critical effect on the planet’s future climate, Stillman said, especially as atmospheric carbon dioxide levels continue to rise sharply as a result of fossil fuel burning and other human activities.
The shell-building capacity of the phytoplankton could also be inhibited by thickening layers of warm water that prevent upwelling of nitrate-rich water. Emiliania huxleyi typically use nitrates to make proteins, but this form of nitrogen may be in shorter supply as ocean temperatures change.
At the same time, the warmer temperatures favor bacteria that turn recycled nitrogen from surface waters and the atmosphere into ammonium, and acidification inhibits the bacteria that turn ammonium into nitrate.
“It is likely that in the future, the ocean surface will contain more ammonium,” which the phytoplankton will assimilate instead of nitrates, Stillman said. “Metabolizing nitrogen as ammonium versus nitrates requires different biochemical constituents that impact how well the cells make their coccoliths. They will survive just fine, but their biology will be different as a result.”
The study by Stillman and colleagues is the first to look at the intertwined effects of ocean acidification and changes in nitrogen on phytoplankton like Emiliania huxleyi. It’s also one of the first studies to observe these effects continuously over a long time scale, “so the responses of the phytoplankton are likely what we’ll see in the ocean itself,” Stillman said.
Stephane Lefebrve, the SF State postdoctoral student who developed the experiments for the study, said he is now looking for phytoplankton genes that “will help us to build the genetic blueprint of their responses to elevated carbon dioxide and a nitrogen source”
Filed under: climate and weather, Environment, global warming, Marine biology, Summit County news Tagged: | carbon cycle, Carbon sink, climate change, Coccolith, Emiliania huxleyi, Environment, global warming, ocean acidification, phtyoplankton, San Francisco State University, Summit County News