Sea-Floor Volcanoes Play a Bigger Role in Earth's Climate Than Previously Thought

Sea-floor volcanoes — eruptions at the bottom of the ocean typically thought of as slow, steady occurrences — actually pop up in bursts and play an integral role in climate variations, new research suggests.

The eruptions — which create new sea floor along 37,000 miles of active mid-ocean ridges — flare up in cycles, in tandem with the rise and fall of sea levels, says the study, published in Geophysical Research Letters and authored by Maya Tolstoy of Columbia University's Earth Institute. Previously, said Tolstoy, such underwater activity was not factored into models of the Earth's climate system which are used to project future oceanic and atmospheric conditions.

"Mid-ocean eruptions have been thought of as a small but steady contributor to climate," she told VICE News. "They are out of sight and out of mind, but it turns out they're quite important."

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Spurts of high underwater volcanic activity correspond with periods of low sea level, found Tolstoy, who studied 10 sites where underwater seismic activity occurs. When the Earth's atmosphere and oceans are cooler, sea levels lower, since more water is trapped in ice. The lower sea levels relieve pressure on the ocean floor, which leads to more eruptions, she explained. Meanwhile, high sea levels foster a lower rate of eruptions, she said — which is what the Earth is currently experiencing.

"We need to put these pulses into the climate models," she said of the importance of using the eruptions to predict future weather patterns. She noted that sea levels and underwater eruptions impacted each other in cycles, partly because of the output of carbon dioxide.

During an ice age, for instance, more eruptions prompt greater amounts of greenhouse gases to be released, Tolstoy said. The higher atmospheric concentrations of carbon might help end the ice age because carbon dioxide warms the atmosphere and melts the ice.

But currently, despite a lower rate of eruptions, carbon dioxide levels are rising — thanks to human impacts, Tolstoy said.

"The fact that we have fewer eruptions means that less carbon dioxide should be entering the system, but what we're seeing is carbon dioxide going up," she said, noting that the evidence was just one more reason for alarm at human-induced climate change. "This definitely supports the fact that anthropogenic impacts are affecting our climate."

Tolstoy found that the eruptions also occurred mainly during the first six months of each year, as the Earth moved from its closest position to the sun in January to its farthest in June, the elliptical orbit helping to coax magma toward the surface.

The eruption data Tolstoy used — which spanned over 700,000 years — showed that during colder times, undersea eruptions surged, creating "visible bands of hills."

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Another geophysics report released this week highlighted the integral relationship between underwater volcanism and fluctuations in the atmosphere. When sea levels decreased, hills on the sea floor increased due to increased eruptions, says a study of the Antarctic-Australian mid-ocean ridge and published in the journal Science.

"People usually study what happens on the surface of the Earth and the interior of Earth totally separately, so people doing climate modeling won't include what's happening under the ground and then people under ground ignore what's on the surface," John Crowley, lead author and researcher at Harvard and Oxford universities, told VICE News. "But there's actually a strong link between the two."

Despite the link, Crowley noted that it was "unclear" how today's sea level would affect future activity.

"The only way present-day sea level would have an effect on mid-ocean range volcanism is if the sea level change continued for thousands of years," he said. "That's still unclear."

Follow Meredith Hoffman on Twitter: @merhoffman