Submarine volcanoes may alter long-term climate: study

Volcanoes hidden under the oceans may have a greater influence on our planet's long-term climate than previously thought, a U.S. study said Friday.

The study published in the U.S. journal Geophysical Research Letters found that submarine volcanoes flare up on strikingly regular cycles, ranging from two weeks to 100,000 years and that they erupt almost exclusively during the first six months of each year.

Previously, scientists presumed underwater volcanoes are Earth' s gentle giants, oozing lava at slow, steady rates, but the new study said they produce maybe eight times more lava annually than land volcanoes.

Due to the chemistry of their magmas, the carbon dioxide they emit is currently at about 88 million tons a year, the same as, or perhaps a little less than, from land volcanoes, study author Maya Tolstoy of Columbia University's Lamont-Doherty Earth Observatory said.

If underwater volcanoes were a little bit more active, their carbon dioxide output would shoot up, Tolstoy said.

The findings suggested that models of earth's natural climate dynamics and human-influenced climate change may have to be adjusted. "People have ignored seafloor volcanoes on the idea that their influence is small -- but that's because they are assumed to be in a steady state, which they're not," said Tolstoy.

"They respond to both very large forces, and to very small ones, and that tells us that we need to look at them much more closely."

In the study, Tolstoy and colleagues closely monitored 10 submarine eruption sites using sensitive new seismic instruments.

They also created new high-resolution maps showing outlines of past lava flows and analyzed some 25 years of seismic data from ridges in the Pacific, Atlantic and Arctic oceans, plus maps showing past activity in the south Pacific.

The long-term eruption data, spread over more than 700,000 years, showed that during the coldest times, when sea levels are low, undersea volcanism surges, producing visible bands of hills.

This is because sea levels drop as water gets locked into ice, relieving pressure on submarine volcanoes and causing them to erupt more.

Tolstoy also attributed this to changes in earth's orbit that have a 100,000-year cycle. When the orbit is more elliptical, Earth gets squeezed by the sun's gravitational pull, thereby massaging undersea magma upward and opening the tectonic cracks that let it out. When the orbit is fairly circular, as it is now, the squeezing effect is minimized, and there are fewer eruptions.

Seismic data also suggested that undersea volcanoes pulse to life every two weeks. That is the schedule upon which combined gravity from the moon and sun cause ocean tides to reach their lowest points, thus subtly relieving pressure on volcanoes below.

Furthermore, Tolstoy found that all known modern eruptions occur from January through June. January is the month when Earth is closest to the sun, July when it is farthest, a period similar to the squeezing effect in longer-term cycles.

"This study ... may have a long-term feedback into our whole climate system," Tolstoy said. "If we are going to protect Earth we have to understand how the planet functions as a whole."

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