Phytoplankton forms an important base to a number of food webs in the ocean, and in a balanced ecosystem, they provide food for a wide range of sea creatures, including whales, shrimp, snails, and jellyfish.
However, with increased ocean acidification, along with increases in carbon dioxide levels in the atmosphere, the calcification mechanisms of a particular phytoplankton, coccolithophores, may be affected. It is believed that this causes an increase in coccolithophore populations.
Researchers at Johns Hopkins University conducted a study that has shown a tenfold increase in the number of coccolithophores throughout the world’s oceans between 1965 and 2010, and a particularly sharp spike since the late 1990s.
One of the study’s five authors, Anand Gnanadesikan, associate professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins, said, “Something strange is happening here, and it’s happening much more quickly than we thought it should.”
Continuous Plankton Recorder data used in study
The research team analysed data from the Continuous Plankton Recorder (CPR) measurements from the North Atlantic Ocean and the North Sea since the mid-1960s. The study revealed that higher carbon dioxide levels in the Earth’s oceans may be causing an increase in coccolithophore populations.
“Our statistical analyses on field data from the CPR point to carbon dioxide as the best predictor of the increase in coccolithophores,” Sara Rivero-Calle, a Johns Hopkins doctoral student and lead author of the study, said. “The consequences of releasing tons of CO2 over the years are already here and this is just the tip of the iceberg.”
William M. Balch of the Bigelow Laboratory for Ocean Sciences in Maine, and a co-author of the study, said it had long been expected that ocean acidification due to increases in carbon dioxide would suppress the chalk-like organisms, but the study showed just the opposite effect, according to the CS Monitor.
“Coccolithophores have been typically more abundant during Earth’s warm interglacial and high CO2 periods,” said Balch. “The results presented here are consistent with this and may portend, like the ‘canary in the coal mine,’ where we are headed climatologically.”
A clear shift in marine ecosystem – What does it mean?
Coccolithophores are photosynthetic organisms, meaning they use some carbon dioxide in the calcification reaction for photosynthesis. But because they produce calcium carbonate, this drives the surface alkalinity of the ocean’s water down.
This creates higher acidity levels and CO2 ends up being released back into the atmosphere. However, many scientists believe the large blooms of coccolithophores we are seeing may be a short-term effect in the increase in global warming.
The more accepted idea is that coccolithophores contribute to an overall decrease in atmospheric CO2 concentrations. Why is this? A little chemistry is needed. During calcification, two carbon atoms are taken up, with one of them becoming trapped as calcium carbonate. This sinks to the ocean floor, becoming part of the sediment. So, coccolithophores provide a sink for emitted carbon, mediating the effects of greenhouse gas emissions.
In July 2015, a study showed that the balance of the plankton in the oceans is going to shift over the next 85 years because of changing ocean water acidity. The Christian Science Monitor reported, “By 2100, ocean acidification will have grown to such an extent that some species of phytoplankton ‘will die out while others will flourish.’”
According to the latest study, “These clearly represent major shifts in ecosystem type,” Gnanadesikan said. “But unless we understand what drives coccolithophore abundance, we can’t understand what is driving such shifts. Is it carbon dioxide?”
This interesting study, “Multidecadal increase in North Atlantic coccolithophores and the potential role of rising CO2,” was published in the journal Science, AAAS on November 26, 2015.
