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Earth is "drinking" more seawater through the Mariana Trench than previously thought

Earth is "drinking" more seawa...
Seismic activity at the Mariana plate is dragging far more water into the Earth's mantle than previously thought
Seismic activity at the Mariana plate is dragging far more water into the Earth's mantle than previously thought
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Seismic activity at the Mariana plate is dragging far more water into the Earth's mantle than previously thought
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Seismic activity at the Mariana plate is dragging far more water into the Earth's mantle than previously thought

The Earth's surface is famously a pretty wet place, but a new study suggests that the mantle is home to much more water than was previously believed. Observations of seismic activity around the Mariana Trench have revealed that subducting tectonic plates are dragging more water deeper into the Earth, which could change our understanding of the global water cycle.

The Mariana Trench is best known for being the deepest part of the ocean, plunging all the way down almost 11,000 m (36,000 ft) at its lowest known point. That's because the trench is the meeting place of two tectonic plates – the tiny Mariana Plate and the huge Pacific Plate. Being denser and older, the latter is actually sliding under the former, which lets vast amounts of seawater pour down through the cracks into the Earth's crust and the upper mantle.

But it's not just as a liquid. Under the higher temperature and pressure at that depth, the water can be locked into the lower plate's rocks as hydrous minerals, which then sink deeper into the mantle as the plate does. So just how much water ends up down there?

"Previous estimates vary widely in the amount of water that is subducted deeper than 60 miles (97 km)," says Douglas A. Wiens, research adviser for the study. "The main source of uncertainty in these calculations was the initial water content of the subducting uppermost mantle."

To get a better understanding, researchers from Washington University in St. Louis used a network of 19 seismographs deployed on the bottom of the ocean around the Mariana Trench, backed up by seven land-based ones on the nearby Mariana Islands. With those instruments, the team listened to over a year's worth of seismic movements to get a closer look at the structure and speed of the plates.

The team found that the hydrated rock in the area extends almost 32 km (20 mi) below the seafloor. Previous studies imaged underground structures by firing sound waves from air guns from research vessels, but these could only peer a fraction of that distance down.

"Previous conventions were based on active source studies, which can only show the top 3-4 miles into the incoming plate," says Chen Cai, first author of the study. "They could not be very precise about how thick it is, or how hydrated it is. Our study tried to constrain that. If water can penetrate deeper into the plate, it can stay there and be brought down to deeper depths."

The observations suggest that in the Mariana Trench, four times more water is captured and dragged down than previous studies estimate. If this trend applies to other similar regions around the world, then there could be about three times more water in the deep mantle than we thought. That lines up well with the recent discovery of exotic forms of ice trapped in diamonds, which are also evidence of a wetter mantle.

So where does all that water end up? It's commonly believed that most of it is ejected back to the surface through volcanic eruptions, sometimes hundreds of miles away. But, the team says the new findings suggest that far more water is going in than is coming out, which may prompt a closer look at our understanding of the global water cycle.

The research was published in the journal Nature.

Source: Washington University in St. Louis

10 comments
MD
Hydrology is settled.. oops nope.
Dziks
Does it mean that polar caps must melt to keep the water level? And that the greenhouse effect could be also indirectly caused by this water sucking and need for new water in the oceans?
amazed W1
It might be happening on Mars as well, so take your drills with you when you go!
Observer101
Well, I guess we won't have to worry about Global Flooding (due to "Global warming")...... LOL
ljaques
Yet more proof that Earth scientists don't even know what's going on under their noses while they try to convince us that WereAllGonnaDieAgain from global warming/climate change/tipping point stuff. Keep studying, folks. You'll get up to a 1% knowledge level yet! And the more you know, the less you'll be trying to pawn off this AGWK stuff on us. P.S: I still haven't heard your take on all the new volcanoes under Antarctica, or your apology about the ice shelf breakoff misread.
Jean Lamb
Stephen Baxter has a lovely book called FLOOD which hypothesizes this, though he points to the mid-Atlantic rift as a possible source for upwelling, too.
Towerman
@ljaques What you say disproves absolutely nothing, expect the evidence for human induced climate change to grow even larger as time passes and the dire consequences it has on the earth not just because it's getting hotter, but because of the effects it has on so many eco systems, the world as a whole life sustaining planet balancing in the wake of unnatural change. Simply barking out shallow snarky comments with absolutely nothing backing your claims will not change Scientific Facts !
Colt12
AmazedW1, There is a probe on Mars right now that NASA reported had it's drill stuck at the 6" level. It was designed to drill 15 feet deep which is where I believe it will be a game changer. No information has been released since the drill became stuck about 6 months ago. Makes me wonder what was found at 6 inches.
Brian M
@Towerman What ljaques says is not without some validity. Man made global warming might well be occurring, but nature also has its own sources of warming (and cooling) actions. The earth is one big dynamic system that has gone through lots of changes without any intervention by man, but more worryingly one we still understand little of. That's not to say moving towards 'renewables' is not a bad thing but its not the real issue, over population is!
EUbrainwashing
If the upper mantel is absorbing vast quantities of sea-water what happens to all the organic material in that water? Perhaps we do not fully understand the origins of oil anything like as well as most folk think!