Huge Ocean Discovered Under East Asia

Location of ocean under Earth's surface

Scientists probing the Earth's interior have found a large reservoir of water equal to the volume of the Arctic Ocean beneath eastern Asia. The left figure is a slice through the Earth, taken from the figure on the right, showing the attenuation anomalies within the mantle at a depth of roughly 620 miles. In the image, red shows unusually soft and weak rock believed to be saturated with water, and the blue  in both images shows unusually stiff rock (yellow and white show near-average values).

The discovery marks the first time such a large body of water has found in the planet's deep mantle. The finding, made by Michael Wysession, a seismologist at Washington University in St. Louis, and his former graduate student Jesse Lawrence, now at the University of California, San Diego, will be detailed in a forthcoming monograph to be published by the American Geophysical Union.

The pair analyzed more than 600,000 seismograms — records of waves generated by earthquakes traveling through the Earth—collected from instruments scattered around the planet.  They noticed a region beneath Asia where seismic waves appeared to dampen, or "attenuate," and also slow down slightly. "Water slows the speed of waves a little," Wysession explained. "Lots of damping and a little slowing match the predictions for water very well."
 
This augers well for a world which is worried about finding enough pure water to supply the planet in the future. I am assuming it is not salt water. The scientists did not specify.