A three-day ship journey off the Mexican coast brought Maya Tolstoy to a part of an ocean known only by its map coordinates.
Below was the East Pacific Rise, a point in the ocean floor where continents move apart, causing magma contained in the Earth’s core to rise to the surface and spew from underwater volcanoes. Into these depths, Tolstoy, a marine geophysicist with the Lamont-Doherty Earth Observatory of Columbia University, dropped 12 seismographs. They would help her track volcanism at the seabed.
Her quest was driven by an attempt to measure the contribution such underwater volcanoes make to the global climate over thousands of years. They spew lava, carbon dioxide and other elements into the deep oceans. The carbon gets trapped in circulating water, cycled to different regions of the ocean, where it gets caught up in upwelling currents and emitted to the atmosphere. The process can take up to 2,000 years and adds a fraction of the 88 million metric tons of carbon belched out by the volcanoes to the atmosphere.
Tolstoy wanted to figure out how often these volcanoes erupt and what causes their eruption. Her ocean voyage happened in 2005, and five years later, her research was published this week in Geophysical Research Letters.
In it, she finds that the Earth’s volcanism is tied to minute shifts in motion of the Earth around the sun, as well as to sea levels, in a chain of events that scientists have never before envisioned. The elegance of the theory surprised Edward Baker, a scientist at the Joint Institute for the Study of Atmosphere and Ocean at the National Oceanic and Atmospheric Administration.
"We don’t usually think of eruptions as being affected by very small changes — astronomical changes — and sea levels rising and falling, and the Earth spinning around the sun at different distances," Baker said in a phone interview. "It’s another way of understanding how the Earth works."
The cusp of Tolstoy’s work depended on real-time monitoring of underwater volcanoes that lie along the 37,000 miles of ocean ridges on this planet. She had data from 10 volcanoes, from the East Pacific as well as historical information collected from a few other ridges.
The devices she dropped into the depths in 2005 were seismographs that could measure the rumblings in deep Earth associated with volcanic activity. The plates there are quickly spreading apart, the fastest in the planet, making them a hot spot for volcanism.
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Next summer, she picked up the devices and found that eight were stuck in lava.
"It was interesting to see my instruments stuck in it, and the lava is very shiny when it first comes out, and actually very pretty," she said in a phone interview.
She recovered four, and then colleagues at Woods Hole Oceanographic Institution used an unmanned underwater vehicle (UUV) to pry two more out. Illuminated by ghostly light, the robotic arm of the UUV freed the yellow-capped seismograph from encrusted lava, allowing the devices to bob to the surface.
The data helped her understand patterns in the planet’s volcanism. Volcanoes seem to erupt when ocean tides are at their lowest point due to the gravitational pull of the moon and the sun. The timing corresponds to the six months of the year when the planet is drawing away from the sun, which loses its influence on the tides.
The implication of this finding is that as sea levels rise due to climate change, they could mimic high tides and suppress underwater volcanic activity, and thousands of years hence, it would affect future climate.
Tolstoy went a step further and linked volcanism to tiny shifts in the Earth’s orbit around the sun, as well, that occur every 100,000 years. These shifts would trigger ice ages and warm periods, both of which affect global sea levels. That, in turn, would increase or suppress volcanic activity, Tolstoy said.
Such linkages between volcanoes and planetary alignments could be better represented in climate models, Tolstoy said. Present-day models do represent underwater volcanoes, but they assume that volcanoes have a constant effect on the planet’s carbon cycle. But Tolstoy’s study suggests that, if anything, volcanism happens in spurts dictated by astronomical events.
Baker of NOAA cautioned that this does not mean that present-day climate change is not driven by human activity, because humans far outstrip the fractional contribution of prehistorical volcanoes to global warming.
"It’s important to keep in mind that, even on a 1,000-year time scale, human emissions of CO2 will continue to dominate climate change," he said. "That is, we cannot blame seafloor eruptions for the ongoing increase in atmospheric and oceanic CO2 concentrations."