Are underwater volcanoes causing global warming? Oceanic eruptions may have a greater effect on climate than first thought
- Geophysicists at Columbia University have found underwater volcanoes erupt in regular cycles that range from a fortnight to 100,000 years
- They claim that volcanoes on the sea floor are currently experiencing a lull
- They warn an increase in eruptions will contribute more to climate change
- Some climate models have assumed they erupt at a steady rate over time
- The new research shows they change with the seasons and Earth's orbit
Volcanoes lurking hidden under the world's oceans may play a far greater role in climate change than previously thought, according to a new study.
Scientists have found that underwater volcanoes, which were long assumed to ooze lava at relatively steady rates, in fact erupt in pulses.
A new study has shown that these submarine eruptions follow regular cycles that can range from just a couple of weeks to 100,000 years.
The researchers claim these
eruptions appear to be linked to changes in the Earth's orbit that occur over time.
Surprisingly the researchers also found that these eruptions also appear to be clustered during the first six months of each year.
The findings may now mean that
models predicting how human activity will change the climate will need to be adjusted.
Volcanic eruptions are known to throw huge amounts of gas into the atmosphere, including carbon dioxide that are thought to increase global warming.
However, volcanoes also release aerosol gases that are now known to reduce global warming by creating a reflective barrier against the sun.
Dr Maya Tolstoy, a marine geophysicist at the Lamond-Doherty Earth Observatory at Columbia University, said: '
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.
'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.'
Underwater volcanoes are known to be widespread on the floor of the world's oceans at joins in the tectonic plates.
Most are located in the deep ocean, where their activity can be difficult to measure, although some in shallow water can erupt with enough lava to create new islands. Others erupt with explosive results.
One of the most intriguing findings by the new study of
underwater volcanic eruptions is that they appear to follow a seasonal pattern.
Data collected by Dr Maya Tolstoy from Columbia University showed that
almost all undersea eruptions recorded in the past 25 years occur in the first six months of the year.
This may be because January is the month when the Earth is closest to the sun and July is when it is at it's farthest,
creating slight squeezing and unsqueezing as it moves.
This may be similar to the effect that Dr Tolstoy
detected on longer timescales as the shape of the Earth's orbit changes.
There may also be some affect caused by changes in sea level as water trapped in the ice around the Arctic and then melts.
Dr Tolstoy said: 'If you look at the present-day eruptions,
volcanoes respond even to much smaller forces than the ones that might drive climate.'
In the deep ocean, the high pressures there mean the surrounding water do not boil and instead forms supercritical fluids.
In some cases hydrothermal vents that
spew clouds of sulphur and soot under water appear, known as black smokers.
The new research by Dr Tolstoy, which is published in the journal Geophysical Research Letters, found that the undersea volcanoes, which mainly appear along the growing edges of the tectonic plates beneath the ocean, are currently in a relatively weak phase.
She believes that despite this they may produce maybe eight times more lava than volcanoes on land but
similar levels of carbon dioxide - about 88 million metric tons a year.
However, she warns that as the cycle of undersea eruptions change, this could mean more of this gas being produced.
Dr Tolstoy and her colleagues monitored 10 submarine eruptions using seismic instruments placed on the sea floor.
They also used underwater mapping to produce high-resolution maps providing evidence of past lava flows and analysed seismic data from the ocean ridges in the Pacific, Atlantic and Arctic oceans.
She found that during the coldest periods when ice ages occur, undersea volcanism seems to surge, producing visible bands of hills.
This, she says, is because sea levels drop as water becomes locked up on the land in glaciers, relieving pressure on the undersea volcanoes and allowing them to erupt more often.
Changes in the gravitational pull on the Earth as it orbits the sun is also thought to influence these eruptions.
The planet gets squeezed and squashed as it travels on its elliptical orbit around the solar system.
Over time the Earth's orbit changes shape, altering the pressure placed on the tectonic plates and so the rate of eruptions.
These changes in the rate of eruption can occur over hundreds of thousands of years.
Dr Tolstoy said
similar affects can also be seen in shorter time frames due to the gravitational pull of the moon, causing undersea volcanoes to pulse into life roughly every two weeks.
She found that seismic signals that indicated eruptions coincided with fortnightly low tides in eight out of nine study sites.
Daniel Fornari, a senior scientist at Woods Hole Oceanographic Institution not involved in the research, said the findings could have important implications for
understanding how underwater volcanoes influence the climate.
However, he warned that seismic activity could be due to rumbles and cracking on the sea floor and not actual eruptions of lava.
Edward Baker, a senior ocean scientist at the National Oceanic and Atmospheric Administration, added: 'The most interesting takeaway from this paper is that it provides further evidence that the solid Earth, and the air and water all operate as a single system.'
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