© NOAAEvery year, billions of gallons of ocean water fall into the Earth at tectonic plate boundaries, then gush back out at hydrothermal vents like the one seen here. A new study shows that this deep water cycle may contribute to hundreds of feet of sea level loss over time.
The ocean is a big bathtub full of
326 million cubic miles (1.3 billion cubic kilometers) of water, and somebody has unplugged the drain.
Every day, hundreds of millions of gallons of water stream from the bottom of the ocean into Earth's mantle as part of a very wet recycling program that scientists call the deep water cycle. It works like this: First, water soaked up in the crust and minerals at the bottom of the sea both get shoved into Earth's interior at the undersea boundaries where tectonic plates collide. Some of that water stays trapped (
some studies estimate that two to four oceans' worth of water are sloshing through the mantle), but large amounts of that water get spewed back to the surface via
underwater volcanoes and hydrothermal vents. [
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It's not a perfect system; scientists think there's currently a lot more water plunging into the mantle than spewing out of it - but that's OK. Overall, this cycle is just one cog in the machine that determines whether the
world's oceans rise or fall.
Now, in a study published May 17 in the journal
Geochemistry, Geophysics and Geosystems, researchers report that this cog may be more important than previously thought. By modeling the fluxes in the deep water cycle over the last 230 million years, the study authors found that there were times in Earth's history when the gargantuan amount of water sinking into the mantle played an outsize role in sea level; during those times, the deep water cycle alone may have contributed to 430 feet (130 meters) of sea-level loss, thanks to one world-changing event: the breakup of the
supercontinent Pangaea.
"The breakup of Pangaea was associated with a time of very rapid tectonic plate subduction," lead study author Krister Karlsen, a researcher at the Centre for Earth Evolution and Dynamics at the University of Oslo, told Live Science. "This led to a period of large water transport into the Earth, causing associated sea-level drop."
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