Colliding tectonic plates under the ocean drag three times more water into the Earth than previously expected, according to a new seismic study that spans the entire Marianas Trench.
“People knew that subduction zones could bring down water, but they didn’t know how much water,” said Chen Cai, who recently completed his doctoral studies at Washington University. Cai is the first author of the study published in the Nov. 15 issue of the journal Nature.
Over millions of years rupturing tectonic plates on the ocean floor draw cold, wet layers of the upper mantle down in to the Earths molten core. This eventually leads to a pole shift from the disequilibrium of temperature beneath the mantle. Oceanic cycles are a growing subject of concern among scientists who want to build more accurate climate models. Understanding water fluctuation can help us more accurately distinguish man-made from natural climate change. For example, all of these variables needs to be considered before making claims about the amount of flooding caused by glacial meltdown.
“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 the National Science Foundation’s Division of Ocean Sciences, which funded the study. “The results highlight the important role of subduction zones in Earth’s water cycle.”
“Previous estimates vary widely in the amount of water that is subducted deeper than 60 miles,” said Doug Wiens, the Robert S. Brookings Distinguished Professor in Earth and Planetary Sciences in Arts & Sciences and Cai’s research advisor for the study. “The main source of uncertainty in these calculations was the initial water content of the subducting uppermost mantle.”
Researchers poured through a years worth of Earthly sounds – from simple ambience to the reverberating echo of earthquakes in action by utilizing a network of 19 passive, ocean-bed seismographs strewn across the Marianas Trench, and seven above water, island-based seismographs.
“Previous conventions were based on active source studies, which can only show the top 3-4 miles into the incoming plate,” Cai said.
Seismic photographs depict an area of hydrated rock stretching almost 20 miles beneath the Marianas trench.
Based on these new findings the amount water going in to the Earth far exceeds the amount of water vapor steaming out of volcanoes, which is how scientists previously thought it was escaping. What this means is that water must be finding another way out of the Earth.
“The estimates of water coming back out through the volcanic arc are probably very uncertain,” said Wiens, who hopes that this study will encourage other researchers to reconsider their models for how water moves back out of the Earth. “This study will probably cause some re-evaluation.”
Due to recent findings under the southernmost continent of Antarctica it’s likely that there is some sort of honeycomb like cave system of aquatic reservoirs beneath the surface of the Earth causing all of these anomalies to manifest. For example, they’ve already discovered 120 000 cubic miles of freshwater beneath North America, Australia and China, 100 time greater than all of the fresh water used since the start of the twentieth century. Another study claims that “Earth’s mantle is so vast, that if 1% of the material in the transition zone is actually water, it would represent a reservoir three times larger than all of Earth’s oceans combined.”
Of course that all has serious implications for the economy as well, in the case of the former nations may not have to resort to conflict over freshwater in the future after all, if they can co-operate to extract it from beneath those 3 continents. There’s also research potential if they can establish permanent stations within each cave system we may even find new forms of aquatic life.