The researchers, led by the Woods Hole Oceanographic Institution, uncovered evidence of explosive volcanic eruptions deep beneath the ice-covered surface of the Arctic Ocean. The scientists said evidence of violent eruptions of splintered, fragmented rock -- known as pyroclastic deposits -- weren't thought possible at great ocean depths because of the intense weight and pressure of water and because of the composition of sea floor magma and rock.

Researchers found jagged, glassy rock fragments spread over a 4-square-mile area around a series of small volcanic craters about 2 1/2 miles below the sea surface.

"These are the first pyroclastic deposits we've ever found in such deep water, at oppressive pressures that inhibit the formation of steam, and many people thought this was not possible," said WHOI geophysicist Rob Reves-Sohn. "This means that a tremendous blast of CO2 was released into the water column during the explosive eruption."

The study, co-authored by 22 investigators from nine institutions in four nations, appears in the journal Nature.