Study: Warming threatens ocean life
PORTLAND – A study by Oregon State University scientists and others has confirmed that warming oceans could lead to a decline in phytoplankton, the microscopic plants that underpin the ocean’s food supply.
Scientists from OSU, NASA and four other institutions used 10 years of satellite data to determine that phytoplankton populations plummet as oceans warm and increase as they cool.
The findings suggest that if oceans continue to warm, as many climate projections predict, ocean life could decline.
A decline in the plants, which consume carbon dioxide, means more of the Earth-warming greenhouse gas would be left in the atmosphere.
“The results essentially provide us with a sneak peek of how ocean biology in the coming century might change as climate continues to change and warm,” said Michael Behrenfeld, an OSU professor of botany who led the study.
The findings appeared in Thursday’s edition of the journal Nature.
Phytoplankton, invisible to the naked eye, live in the ocean’s upper sunlit layer and account for about the same amount of photosynthesis as all land plants combined. The process converts carbon dioxide into organic carbon that fuels nearly every ocean ecosystem.
The phytoplankton multiply rapidly and only live for a day or two, “but they’re also eaten very quickly,” Behrenfeld said. “Because of that rapid turnover, they are very sensitive to changes in climate. They record very short time-scale changes in their environment, so they make a really sensitive measure of what is going on in the ocean.”
The study found that plant growth increased between 1997 and 1999 during a La Niña cooling period.
“Since then, we’ve gone through dips and bumps in the climate,” Behrenfeld said, “but the general trend has been a warming of the oceans. And we found there’s been a general decrease in the production of phytoplankton on a global scale.
“So the two – biological activity and climate – seem to be very tightly coupled in the ocean,” said Behrenfeld.
Like land plants, phytoplankton require nutrients such as phosphorus and iron to survive.
But when surface waters warm as during an El Niño, a warm upper layer of water forms that prevents nutrients to upwell from the colder, deeper water. The phytoplankton starve, and the ocean’s food supply is cut.
Gene Carl Feldman, a scientist at the Goddard Space Flight Center who was involved in the study, emphasized that the findings make no predictions about the future climate “but demonstrates what the biology would do” if climate models are correct.
Scott Doney, an oceanographer at Woods Hole Oceanographic Institution in Massachusetts, praised the satellite study because “there are very few observations that allow us to look at the globe all at once and to look at it over a long period of time.”
Doney, who was not part of the research team, said the study indicates that a “warming ocean would mean that it’s going to have very big impacts higher up in the marine food chain, including seabirds, mammals and fish.”
“It would affect all of us.”