Excerpt from "Seismic study reveals huge amount of water dragged into Earth’s interior," posted on NSF News, November 14, 2018.
Slow-motion collisions of tectonic plates under the ocean drag about three times more water down into the deep Earth than previously estimated, according to a first-of-its-kind seismic study that spans the Mariana Trench, a crescent-shaped trench in the Western Pacific that measures 1,500 miles long and is the deepest ocean trench in the world.
The observations from the trench have important implications for the global water cycle, according to researchers at Washington University in St. Louis whose work is supported by the National Science Foundation (NSF).
"People knew that subduction zones could bring down water, but they didn't know how much water," said Chen Cai, lead author of the study, which was published in this week's issue of the journal Nature.
"This research shows that subduction zones move far more water into Earth's deep interior -- many miles below the surface -- than previously thought," said Candace Major, a program director in NSF's Division of Ocean Sciences . "The results highlight the important role of subduction zones in Earth's water cycle."
Researchers listened to more than a year's worth of Earth's rumblings, from ambient noise to actual earthquakes, using a network of 19 ocean-bottom seismographs deployed across the Mariana Trench, along with seven island-based seismographs.
"Previous estimates vary widely on the amount of water that is subducted deeper than 60 miles," said Doug Wiens, a geoscientist at Washington University and co-author of the paper. "The main source of uncertainty in these calculations was the initial water content of the subducting uppermost mantle."
The Mariana Trench is where the western Pacific Ocean plate slides beneath the Mariana Plate and sinks deep into the Earth's mantle as the plates slowly converge.
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