Sea Change

Ecosystems along the continental shelf waters of the Northwest Atlantic Ocean, from the Labrador Sea south of Greenland all the way to North Carolina, are experiencing large, rapid changes. While some scientists have pointed to the decline of cod from overfishing as the main reason for the shifting ecosystems, a recent paper emphasizes that climate changes are also playing a big role.

"It is becoming increasingly clear that Northwest Atlantic shelf ecosystems are being tested by climate forcing from the bottom up and overfishing from the top down," said Charles Greene, director of the Ocean Resources and Ecosystems Program in Cornell's Department of Earth and Atmospheric Sciences and the paper's lead author. Andrew Pershing, an oceanographer at the University of Maine and Gulf of Maine Research Institute, co-authored the article. "Predicting the fate of these ecosystems will be one of oceanography's grand challenges for the 21st century."

Most scientists believe the planet is being warmed by greenhouse gases emitted in the burning of fossil fuels, and by changing land surfaces. Early signs of this warming have appeared in the Arctic: Since the late 1980s, scientists have noticed that pulses of fresh water from increased precipitation and melting of ice on land and sea in the Arctic have flowed into the North Atlantic Ocean and made the water less salty.

At the same time, climate-driven shifts in Arctic wind patterns have redirected ocean currents. The combination of these processes has led to a freshening of seawater along most of the Northwest Atlantic shelf.

"We suggest that, with or without the collapse of cod, a bottom-up, climate driven regime shift would have taken place in the Northwest Atlantic during the 1990s," Greene said.

This research was published in this week's issue of Science.

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