Satellite Data Reveal 20,000 Previously Unknown Deep-Sea Mountains (sciencenews.org) 17
The number of known mountains in Earth's oceans has roughly doubled. Global satellite observations have revealed nearly 20,000 previously unknown seamounts, researchers report in the April Earth and Space Science. From a report: Just as mountains tower over Earth's surface, seamounts also rise above the ocean floor. The tallest mountain on Earth, as measured from base to peak, is Mauna Kea, which is part of the Hawaiian-Emperor Seamount Chain. These underwater edifices are often hot spots of marine biodiversity. That's in part because their craggy walls -- formed from volcanic activity -- provide a plethora of habitats. Seamounts also promote upwelling of nutrient-rich water, which distributes beneficial compounds like nitrates and phosphates throughout the water column. They're like "stirring rods in the ocean," says David Sandwell, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego.
More than 24,600 seamounts have been previously mapped. One common way of finding these hidden mountains is to ping the seafloor with sonar. But that's an expensive, time-intensive process that requires a ship. Only about 20 percent of the ocean has been mapped that way, says Scripps earth scientist Julie Gevorgian. "There are a lot of gaps." So Gevorgian, Sandwell and their colleagues turned to satellite observations, which provide global coverage of the world's oceans, to take a census of seamounts. The team pored over satellite measurements of the height of the sea surface. The researchers looked for centimeter-scale bumps caused by the gravitational influence of a seamount. Because rock is denser than water, the presence of a seamount slightly changes the Earth's gravitational field at that spot. "There's an extra gravitational attraction," Sandwell says, that causes water to pile up above the seamount.
More than 24,600 seamounts have been previously mapped. One common way of finding these hidden mountains is to ping the seafloor with sonar. But that's an expensive, time-intensive process that requires a ship. Only about 20 percent of the ocean has been mapped that way, says Scripps earth scientist Julie Gevorgian. "There are a lot of gaps." So Gevorgian, Sandwell and their colleagues turned to satellite observations, which provide global coverage of the world's oceans, to take a census of seamounts. The team pored over satellite measurements of the height of the sea surface. The researchers looked for centimeter-scale bumps caused by the gravitational influence of a seamount. Because rock is denser than water, the presence of a seamount slightly changes the Earth's gravitational field at that spot. "There's an extra gravitational attraction," Sandwell says, that causes water to pile up above the seamount.
Stirred (Score:2)
So they're good for making martinis the right way rather than shaking [preview.redd.it].
Probably old news to NAVOCEANO (Score:2)
Some of the highest guarded secrets in the US military are the Navy's maps of the sea floor.
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Some of the highest guarded secrets in the US military are the Navy's maps of the sea floor.
Some of the most important maps are of the Arctic floor which is between North America and Russia. This technique doesn't work there.
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Clever (Score:2)
so.. (Score:3)
Which one is Atlantis?
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Contrary to Youtube's opinion, Atlantis was a work of the imagination of Plato.
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"Atlantis was a work of the imagination of Plato."
Like geology then, to Wegener at least?
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Now, those prospectors and miners didn't produce a lot of detailed reports on their finds. But they did generate plenty of records with the tax department - which is the sort of thing historians love to dig through. Unless you're a History Channel pseudohistorian, in which case speculating groundlessly about invasions
So ... Sonar mapping is better. (Score:3)
By implication, they've extended these numbers to cover most of the (submerged) globe. So either the areas covered by sonar tracks had about 4-* the density of seamounts of the average bit of ocean, or this more inclusive survey only detects about 1-in-4 of the seamounts down there.
How much the distribution varies from random would be the interesting question. But it's not likely to be vastly different to what has already been detected from seismic and sonar work. They might pick up a few traces of "detached" segments of transform faults. which don't have seismic expression. But other than that ... not a lot expected.
The Friendly Paper. (Score:4, Informative)
The method (VGG - Vertical Gravity Gradient) has been used since 2011 (Kim & Wessel, 2011, https://doi.org/10.1111/j.1365... [doi.org]). This is an improvement on the method down to smaller gradients.
As pointed out, at least one submarine has "bumped into" a seamount. (Which also means that they weren't using a forward-looking sonar.) FTFAbstract, "we show that VGG can be used to estimate the height of small seamounts to an accuracy of â¼270 m." - which isn't going to help a huge amount, since most submarines are going to spend as little time as possible putting 270+m of loading on their missile and torpedo ports, and so still may bump into these seamounts unexpectedly.
Unfortunately, TFP doesn't itself give a map of these seamounts, their distribution, or indeed, the combined 40-odd kilo-mount catalogue. The Supplemental Data [wiley.com] for the paper includes a map of ~3 Mm by 1.5 Mm area of the South Atlantic. (31~39 deg S, 2~20 deg W "-ish"), but it is hard to recognise the old (or new) seamounts in this section.
My GIS tells me that the 2011 data set contains about 125 examples in this area, with a typical spacing of about 100 km; so the new dataset should add about another 100, and reduce the spacing to more like 60km. Which is fine enough. But as for it's utility ... a different question. This area - probably by choice - contains some Mid-Atlantic ridge, and a couple of significant transforms which also separate a part of the ridge of different character to those north and south ; in the area swept out between the transforms but closer to the African continental slope. Which raises genuine, interesting (well, I'm a geologist ; your interests may differ) questions about why there is a change in character at the ridge, and how this relates to the relatively high elevation section of seabed stretching from this area to the approximate border of Namibia and Angola. Well all very interesting geologically - it may relate to the different levels of hydrocarbon deposits on the Namibian contra Angolan coasts. But I'll save that for the next time I'm negotiating an exploration contract in West Africa - always good stuff to drop into the interview. However, that structure has been evident in datasets that have been available for years (I haven't updated my system over a year.)
New data is always welcome, but this is an incremental improvement, not the earth-shattering upheaval that the press release makes it sound like. Which is very often the case.
But ...
Why the hell is that high elevation seabed block at about 45 deg to the line of the transform faults and seabed age contours? That's odd. I don't recall any significant discussion of that, but I've only worked areas 2000 km to the NE and studied for areas 5000km to the SW. Definitely something to remember if there's any new work in that area.
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"Which also means that they weren't using a forward-looking sonar."
The point of a sub is to stay hidden. Using active sonar lets everyone know where you are.
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This is not good for concealment, which is, as you say, a significant factor for submarines.
You can't have everything, all the time, at once.
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Navy maps are supposed to be good enough to allow non-sonar running. We spent a lot to get 5 meters.
It's most likely the crash was due to disorientation.
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Since we don't have a "global positioning system" (note : generic noun phrase, not a proper noun phrase) that works below a few 10s of cm of water (including the water in the atmosphere, clouds, leaves and the raindrops upon them) because the signals from space get absorbed by the water, then submerged submarines navigate by "dead reckoning" on compass and distance log. If the log (time plus speed of movement) is inaccurate (say, there is a curren
Sea Level (Score:1)
We tend to think of sea level as an abdolutely flat (ok spherical) constant.
I was surprised to learn that it can vary by more than a hundred feet due to gravity fluctuations, atmospheric pressure, currents, tides, etc.
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Don't include the scientific community in your "we".
"We", the scientific community, have been unavoidably aware of the temporal and secular variation of sea level since ... probably the 1870s or so, when Darwin (fils, not pere) established the mathematical basis for understanding astronomical tidal interactions while the first round of systematic geological mapping was leading to an understanding of isostatic and eustatic variations in the deposition of sea-level controlled