Deep sea not immune to climate change.

Stability breeds success, or so say scientists who study the teeming creatures of the deep sea. Life in many forms thrives near the ocean bottom, according to ecological theory, because thousands of kilometers of water protect organisms there from the vicissitudes of climate at Earth's surface. Now, a new study of fossil crustaceans sinks that stability theory.

Deep-sea communities suffered dramatic declines during the ice ages, two scientists report in the Feb. 13 Nature. Thomas M. Cronin of the U.S. Geological Survey in Reston, Va., and Maureen E. Raymo of the Massachusetts Institute of Technology studied a group of tiny crustaceans called ostracods. By analyzing cores of sediments drilled from the floor of the North Atlantic Ocean, the researchers could track how the deep-sea ostracod community fared as the ice ages waxed and waned between 2.85 and 2.40 million years ago.

Contrary to the theory of ocean floor stability, the diversity of species rose and fell in sync with the glacial cycle. While 15 to 20 ostracod species inhabited the depths during warm times, only 2 or 3 species remained during the ice ages.

Cronin and Raymo surmise that food, rather than temperature, forced the changes in the ostracod community. Ice age conditions inhibited the growth of plankton at the sea surface, reducing the amount that sank to the deep sea. Ostracods may have spent the ice ages in shallower waters and then returned to the deep sea for the warm interglacial periods.

The scientists conclude that the abyssal ocean may not be immune to the effects of future global warming, as some researchers have suggested. "It really says there's nowhere on this Earth where you will be insulated from the effects of global climate change," says Raymo.