Scientists Worried Over Latest Sign of Rapid Change in the Oceans
A population boom among the ocean’s smallest organisms is the latest evidence that greenhouse gas emissions may be upsetting the balance of the world’s oceans.
In a recent study published in the journal Science, researchers report that there was a tenfold increase in the occurrence of a major group of microscopic ocean plants called coccolithophores in the North Atlantic between 1965 and 2010 and that rising carbon dioxide levels are so far the most likely reason why.
The increase is invisible to the naked eye, and 45 years sounds like half a lifetime.
But in Earth science terms, said Anand Gnanadesikan, a climate scientist at Johns Hopkins University and a study coauthor, the change is huge—it happened in the blink of an eye, and scientists didn’t see it coming.
“We do believe it a sign of rapid ocean change,” he said. “A tenfold change like this [is] a sign that the models may be too conservative in what we’re forecasting, or projecting, in terms of the impact of growth of carbon dioxide in the atmosphere on ecosystems.”
The change is troubling in part because scientists are still trying to understand what role coccolithophores play in the marine food web, Gnanadesikan said. “What does it mean for fish? What does it mean for salmon, for whales? We don’t know.”
Mak Saito, an ocean biogeochemist at the Woods Hole Oceanographic Institution, called the finding “an impressive and worrying shift that we’re seeing in ocean ecosystems.” He lauded the study for “ground-truthing the laboratory studies and models and allowing us to improve our ability to predict how the oceans will respond to CO2 emissions.”
Among the concerns raised by the findings, scientists speculate that a continued bloom of coccolithophores could increase climate instability by decreasing the amount of CO2 absorbed by seawater over the next several decades.
Oceans absorb around half the CO2 created by burning fossil fuels. Coccolithophores take up some of that carbon organically and also grow beautifully detailed calcium carbonate—chalk—shells. These phytoplankton sink when they die, taking the carbon in their bodies to the sea floor.
“This is a major way in which chalk is buried in the ocean, and the burial of that chalk is a major way that CO2, over geological time scales of hundreds to thousands of years, is removed from the atmosphere,” said Saito.
Fossil chalk deposits such as the White Cliffs of Dover are modern-day evidence of how long this cycle has gone on, he said.
But coccolithophores also “give off CO2 as they fix calcium carbonate” to make their shells, Saito added, reducing for a short while the ocean’s capacity to take up CO2 from the atmosphere.
“It’s one of the seminal concepts in chemical oceanography that we struggle to communicate,” Saito said. “They’re still moving carbon, and it’s still a long-term carbon removal.”
While there is more research to be done, Saito said he found the study’s conclusions about coccolithophore increases and their possible impacts reasonable. “If we want to have a sustainable human society, we don’t want to be having unintended changes in our large ocean ecosystems,” he said.