Tiny Ocean Creatures Tell of Global Warming

Sediment cores collected from the seafloor off Southern California suggest that plankton populations in the Northeastern Pacific have changed significantly since the early 1900s. Scientists say these changes parallel a general warming trend starting at that time.

Subtropical and tropical species of small marine organisms called foraminifera seemed to become more abundant as ocean temperatures increased, researchers said. At the same time, similar species living in cooler waters seemed to become less abundant. Changes in the last 30 years are unlike anything found in sediment evidence from the past 1,400 years, the scientists said.

"These data show that ocean warming has affected foram populations prior to the late twentieth century," said study co-author David Field of the University of California, San Diego.  "However, changes since the 1970s have been particularly unusual, and show that ocean ecosystems in the northeastern Pacific have passed some threshold of natural variability."

The foraminifera studied are small, amoeba-like organisms that live inside tiny shells called "tests," several of which might fit on the head of pin. Most forams live near the surface of the ocean, with different species living in ocean waters of different temperatures. When they die, their shells sink to the seafloor, often mixing with the sediment there to form distinct annual layers similar to growth rings in a tree. In some areas those annual layers remain relatively intact for millennia.

This study provides the kind of long-term data needed to clarify whether the warming trend and ecosystem changes are within the range of natural variability, or are the result of human activities.

This research is detailed in the Jan. 6 issue of the journal Science.