Could deep sea volcanic eruptions be linked to the Earth's orbit and, in turn, have an influence on changes in climate?
New research suggests these underwater volcanoes flare up in regular cycles (usually exclusively in the first six months of every year) ranging from every two weeks to 100,000 years, and the phenomenon is tied to both long and short-term changes in the Earth's orbit, the Earth Institute at Columbia University reported. These patterns of activity are also linked to changes in sea levels and the triggering of natural climate swings.
Past climate studies have looked at the influence of carbon dioxide from land-based volcanoes on the climate, but the effect of marine volcanoes has been largely overlooked. The findings suggest models of earth's natural climate dynamics and the impact of human activity need 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 the study's author, marine geophysicist Maya Tolstoy of Columbia University's Lamont-Doherty Earth Observatory. "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."
Some scientists believe volcanoes flare up in unison with Milankovitch cycles (changes in the shape of the earth's orbit from round to elliptical and its tilt), producing "seesawing" periods of warmer and cooler climates. The major one of these cycles occurs every 100,000 years, and recent ice ages have appeared to build up through this cycle with warmer climates coming at its peak eccentricity.
Researchers have also suggested that as icecaps build up on land the pressure from underlying volcanoes also builds, holding back eruptions. Once this ice melts the eruptions begin, releasing loads of carbon dioxide into the atmosphere, producing even more warming. This creates a "self-feeding effect" that can launch the Earth into a sudden warm period.
On the other hand, one would believe undersea volcanoes would do the opposite. As the Earth cools it would lock more water into the ice, lowering sea levels and relieving pressure on these volcanoes to allow for more eruptions. This phenomenon could increase carbon dioxide levels, and researchers have been wondering if this is what prompts the warming that melts the ice in the first place.
In the past undersea eruptions have been difficult to observe, but the research team was able to monitor 10 eruption sites using new seismic instruments. This has allowed them to produce new high-resolution seismic maps outlining past lava flows. They also looked at 25 years of seismic data from ridges in the Pacific, Atlantic and Arctic oceans and maps showing past activity in the south Pacific.
"If you look at the present-day eruptions, volcanoes respond even to much smaller forces than the ones that might drive climate," Tolstoy said.
Long-term eruption data spanning 700,000 years showed during the coldest times on Earth (when the sea level was extremely low) there were increases in underwater volcanism. The researchers believe this is not only related to sea level, but also to changes in the Earth's orbit as the planet was "squeezed and unsqueezed" by the Sun's gravitational pull. When the Earth's orbit is relatively circular (as it is now) it can minimize this effect and decrease eruptions.
"[The findings] clearly could have important implications for better quantifying and characterizing our assessment of climate variations over decadal to tens to hundreds of thousands of years cycles," said Daniel Fornari, a senior scientist at Woods Hole Oceanographic Institution who was not involved in the research.
The findings were published in a recent edition of the journal Geophysical Research Letters
