From: Arthur Hirsch, Johns Hopkins
Published November 27, 2015 08:04 AM

Rapid plankton growth seen as indicator of carbon dioxide loading in oceans

A microscopic marine alga is thriving in the North Atlantic to an extent that defies scientific predictions, suggesting swift environmental change as a result of increased carbon dioxide in the ocean, a study led a by Johns Hopkins University scientist has found.

What these findings mean remains to be seen, as does whether the rapid growth in the tiny plankton's population is good or bad news for the planet.

Published today in the journal Science, the study details a tenfold increase in the abundance of single-cell coccolithophores between 1965 and 2010, and a particularly sharp spike since the late 1990s in the population of these pale-shelled floating phytoplankton.

"Something strange is happening here, and it's happening much more quickly than we thought it should," said Anand Gnanadesikan, associate professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins and one of the study's five authors.

Gnanadesikan said the Science report certainly is good news for creatures that eat coccolithophores, but it's not clear what those are. "What is worrisome," he said, "is that our result points out how little we know about how complex ecosystems function." The result highlights the possibility of rapid ecosystem change, suggesting that prevalent models of how these systems respond to climate change may be too conservative, he said.

The team's analysis of Continuous Plankton Recorder survey data from the North Atlantic Ocean and North Sea since the mid-1960s suggests rising carbon dioxide in the ocean is causing the coccolithophore population spike, said Sara Rivero-Calle, a Johns Hopkins doctoral student and lead author of the study. A stack of laboratory studies supports the hypothesis, she said. Carbon dioxide is a greenhouse gas already fingered by scientific consensus as one of the triggers of global warming.

"Our statistical analyses on field data from the CPR point to carbon dioxide as the best predictor of the increase" in coccolithophores, Rivero-Calle said. "The consequences of releasing tons of CO2 over the years are already here and this is just the tip of the iceberg."

The CPR survey is a continuing study of plankton, floating organisms that form a vital part of the marine food chain. The project was launched by a British marine biologist in the North Atlantic and North Sea in the early 1930s. It is conducted by commercial ships trailing mechanical plankton-gathering contraptions through the water as they sail their regular routes.

William M. Balch of the Bigelow Laboratory for Ocean Sciences in Maine, a co-author of the study, said scientists might have expected that ocean acidity due to higher carbon dioxide would suppress these chalk-shelled organisms. It didn't. On the other hand, their increasing abundance is consistent with a history as a marker of environmental change.

Glowing plankton in the Maldives image via Shutterstock.

Read more at Johns Hopkins.

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