Seafloor spreading has been slowing down

Sluggish spreading rates could mean a drop in greenhouse gas emissions from volcanoes

Peer-Reviewed Publication

AMERICAN GEOPHYSICAL UNION

WASHINGTON—A new global analysis of the last 19 million years of seafloor spreading rates found they have been slowing down. Geologists want to know why the seafloor is getting sluggish.

New oceanic crust forms continuously along rifts thousands of miles long on the seafloor, driven by plate tectonics. As subduction pulls old crust down, rifts open up like fissures in an effusive volcano, drawing hot crust toward the surface. Once at the surface, the crust begins to cool and gets pushed away from the rift, replaced by hotter, younger crust.

This cycle is called seafloor spreading, and its rate shapes many global processes, including sea level and the carbon cycle. Faster rates tend to cause more volcanic activity, which releases greenhouse gases, so deciphering spreading rates helps contextualize long-term changes in the atmosphere.

Today, spreading rates top out around 140 millimeters per year, but peaked around 200 millimeters per year just 15 million years ago in some places, according to the new study. The study was published in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

The slowdown is a global average, the result of varying spreading rates from ridge to ridge. The study examined 18 ridges, but took a particularly close look at the eastern Pacific, home to some of the globe’s fastest spreading ridges. Because these slowed greatly, some by nearly 100 millimeters per year slower compared to 19 million years ago, they dragged down the world’s average spreading rates.

It’s a complex problem to solve, made more difficult by the seafloor’s slow and steady self-destruction.

“We know more about the surfaces of some other planets than we do our own seafloor,” said Colleen Dalton, a geophysicist at Brown University who led the new study. “One of the challenges is the lack of perfect preservation. The seafloor is destroyed, so we’re left with an incomplete record.”

The seafloor is destroyed in subduction zones, where oceanic crust slides under continents and sinks back into the mantle, and is reforged at seafloor spreading ridges. This cycle of creation and destruction takes about every 180 million years, the age of the oldest seafloor. The crust’s magnetic record tracks this pattern, producing identifiable strips every time the Earth’s magnetic field reverses.

Dalton and her co-authors studied magnetic records for 18 of the world’s largest spreading ridges, using seafloor ages and their areas to calculate how much ocean crust each ridge has produced over the last 19 million years. Each ridge evolved a little differently: some lengthened, some shrank; some sped up, but almost all slowed down. The overall result of Dalton’s work is that average seafloor spreading slowed down by as much as 40% over that time.

The driver here might be located at subduction zones rather than spreading ridges: for example, as the Andes grow along the western edge of the South American continent, the mountains push down on the crust.

“Think of it as increased friction between the two colliding tectonic plates,” Dalton said. “A slowdown in convergence there could ultimately cause a slowdown in spreading at nearby ridges.”  A similar process could have operated underneath the Himalaya, with the rapidly growing range slowing spreading along the ridges in the Indian Ocean.

However, Dalton points out, this added friction can’t be the only driver of the slowdown, because she found slowing rates globally and mountain growth is regional. Larger-scale processes, like changes in mantle convection, could also be playing a role. In all likelihood, she concludes, it’s a combination of both. To learn more, Dalton hopes to collect absolute plate speeds, rather than the relative speeds used in this study, which will better allow her to determine the cause of the slowdown.

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*****

Notes for Journalists:
This research study is freely available until the end of the month. Download a PDF copy of the paper here. Neither the paper nor this press release is under embargo.

Paper title:

“Evidence for a Global Slowdown in Seafloor Spreading Since 15 Ma”

Author information:      

  • Colleen Dalton (corresponding author), Timothy Herbert, Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
  • Douglas S. Wilson, Marine Science Institute, University of California-Santa Barbara, CA, USA

JOURNAL

Geophysical Research Letters

DOI

10.1029/2022GL097937 

ARTICLE TITLE

Evidence for a Global Slowdown in Seafloor Spreading Since 15 M

ARTICLE PUBLICATION DATE

28-Mar-2022

From EurekAlert!

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Ron Long
April 16, 2022 2:16 am

A typical article from the AGU, partly good data and truth and partly missing the mark. The more-dense oceanic plate descends into a subduction zone partly because it is more dense and partly because the spreading ridge is pushing it. Some of these oceanic plates collide with continental plates and obduct, they ride up over the continental plate, like the Klamath Terrain, which is partly accreted and partly obducted. The increase or decrease of volcanism where subduction creates volcanic processes is greatly controlled by how flat or steep the subduction angle is and by how direct or oblique the convergent angle is. The famous Carlin Gold Deposits, in northern Nevada, were formed by south migrating volcanism that started in British Columbia when a flat-subducting event rolled over into a steeper event, this event migrating south (at 80 million years in BC, at 60 million years in Idaho, at 40 million years in northern Nevada, and terminating at 20 million years in south-central Nevada) until the steepening roll-over was terminated by a change to oblique subduction. This topic of spreading rate is interesting as presented, by omits important considerations in the overall process.

Last edited 4 months ago by Ron Long
Rich Davis
Reply to  Ron Long
April 16, 2022 5:51 am

Since this is presented to us by YouReekAlot!, I was just waiting to hear that the reason the climate models are running hot is that there’s less CO2 coming from volcanoes than had been expected.

I mean, 40% reduction over 15 million years, why that’s 0.000107% less CO2 in the past 40 years. No wonder the models are off!

Robertvd
Reply to  Rich Davis
April 16, 2022 11:29 am

Or maybe if it had been running at the same speed we would not have been in the current Ice Age. Of course if you believe CO2 controls climate.

Ron Long
Reply to  Robertvd
April 16, 2022 3:20 pm

Yea, Robertvd, the speed is the question. The answer is we don’t know for sure because the speed is measured mostly by the magnetic reversal anomaly striping, and the reversal timing is very irregular and the spreading center is also irregular, and nobody has any actual idea about the speed of the spreading.

TonyL
Reply to  Ron Long
April 16, 2022 6:19 am

As Ron Long points out, this is another YouReekAlert posting. These are always broad-brush outlines devoid of any detail. Near as I would guess, they seem to be written for an audience with about a High School level of science education. Really they are just advertisements for a new paper. Read the paper if interested, ignore if not.

Rich Davis
Reply to  TonyL
April 16, 2022 8:54 am

Yeah, YouReekAlot! press releases are written, I suspect, by arts majors steeped in the Climastrology faith. Possibly they passed their high school science classes, mostly because they don’t teach actual science in that curriculum any longer. It’s easy to parrot the Climastrology catechism.

hiskorr
Reply to  Ron Long
April 16, 2022 8:17 am

I wonder at the causes and magnitudes of the forces involved in the subduction and obduction described. If slight differences in plate density, and gravity, account for subduction, then wouldn’t we see the continents settle, displacing the lighter oceans up and over the land?

Emily Daniels
Reply to  hiskorr
April 21, 2022 10:34 am

I know this is an old thread now, but ocean crust is denser than continental crust (more iron content vs. more granite content), so ocean plates always subduct under continental plates. When you get two of the same kind of plates colliding, they buckle and form mountains (for example, India moved north and collided with Asia, forming the Himalayas)

Reply to  Ron Long
April 16, 2022 8:20 am

I came across a website by a geologist several years ago but lost the address…he has a theory on how geology controls the climate…maybe a book or just a website. I don’t remember the details.

Clyde Spencer
Reply to  Anti_griff
April 16, 2022 12:13 pm

When a mountain range rises (orogeny), it blocks and lifts transverse wind. The atmospheric lapse rate creates different temperature differences up the mountains, with orographic precipitation providing rain and snow. As the mountains erode over tens of millions of years, the higher, colder temperature zones are removed until the range is ultimately reduced to a peneplain. At that point, the temperatures are close to sea surface temperatures, with orographic precipitation no longer occurring.

Yes, geology controls the climate.

Gregory Woods
April 16, 2022 2:23 am

WASHINGTON—A new global analysis of the last 19 million years of seafloor spreading rates found they have been slowing down. Geologists want to know why the seafloor is getting sluggish.

The reason is obvious: Global Warming….

Chaswarnertoo
Reply to  Gregory Woods
April 16, 2022 2:39 am

Trump, Brexit and the evil Putin, surely?

fretslider
Reply to  Chaswarnertoo
April 16, 2022 3:43 am

Wouldn’t it be funny if Le Pen were to be added to the list.

Robertvd
Reply to  Gregory Woods
April 16, 2022 11:35 am

That is why we are in an Ice Age right now. If you look at the last 200My the recent 3My have been the coldest including today.

Vuk
April 16, 2022 2:41 am

No idea if they are right or wrong about data going back 20 million years ago.
However, slowdown is expected due to the natural process of outer liquid core cooling, which may be to a degree reflected in falling in the intensity of the Earth’s magnetic field, which is far more rapid and by far more critical for the maintenance of the planet’s biosphere.

John VC
Reply to  Vuk
April 16, 2022 10:32 am

I was thinking much along the same lines. The core has been cooling since the start of things, and once the movement does stop–bingo another dead planet.

fretslider
April 16, 2022 3:42 am

If the tectonic plates are moving over ‘hot spots’ and this is slowing down there is an ‘alarming’ explanation for it…

“Earth’s core cooling faster than previously thought, researchers say

The planet’s core has been cooling for billions of years but perhaps “more rapidly than expected,” which could expedite the end of life on Earth — though not for quite a while.

“Results suggest the mantle is more efficiently cooled, which would ultimately weaken many tectonic activities driven by the mantle convection more rapidly than expected from conventionally believed thermal conduction behavior.”

https://www.nbcnews.com/science/science-news/earths-core-cooling-faster-previously-thought-researchers-say-rcna12732

Always good to get a ‘more than previously thought’ or even a ‘worse than we thought’ in there.

Rich Davis
Reply to  fretslider
April 16, 2022 5:56 am

Oh noes! The only solution is more socialism!!

Robertvd
Reply to  Rich Davis
April 16, 2022 11:37 am

More money printing.

MarkW
Reply to  Robertvd
April 16, 2022 3:18 pm

I thought the solution was E15 gasoline?

Observer
Reply to  fretslider
April 16, 2022 10:08 am

Oh, but this is good news…if Earth’s core cools enough, the magnetic field will vanish and all that bad carbon dioxide will get blown away into space by the solar wind. Global warming solved! Maybe that’s the next geo-engineering task, ha, ha.

Geoff Sherrington
April 16, 2022 4:22 am

Using their figures, I calculated roughly that there have been 3-4 cycles in the Pacific in those 180 million years, when a block from a ridge has travelled half the Pacific , been subducted, then cycled back to the seafloor spreading center.
It has always had me wondering why this process happens (if it does) in the broad but important sense of what the driver is. It is easier to imagine one cycle, but several cycles starts to gain impossibility objections. Geoff S

fretslider
Reply to  Geoff Sherrington
April 16, 2022 5:15 am

why this process happens (if it does)”

A model will put your mind at rest.

Smart Rock
Reply to  Geoff Sherrington
April 16, 2022 11:44 am

why this process happens (if it does) in the broad but important sense of what the driver is

It does, and the driver is heat, produced by radioactive decay of potassium, uranium and thorium in the mantle and crust, and by phase changes in the core. The earth is a giant, slow-moving heat engine. The global mean heat flow is only 0.09 W/m², miniscule compared with the heat received by the earth from solar radiation, but it is the sole driver of all the plate tectonics and associated volcanic activity. The earth has to shed that heat, and geology as we know it, is the result. Without that heat flow, we would have a static planet like Mars, where nothing happens other than meteorite strikes.

Because radioactive isotopes have half-lives, the global heat flow continues to decline. In the Archean, when the world was hot, young and headstrong, there were continents the size of France slopping around and crashing into each other like fairground dodgem cars. Gradually the heat flow waned and they started to stick together and form the cores of the big continents that we have today.

The rate of decline of radiogenic heat flow is too low to account for the slowdown in plate motion claimed by the head post. It may be only an apparent slowdown resulting from incomplete sampling (less and less older oceanic crust to study). It may be a case of part of a very long term cycle being indistinguishable from a secular trend. It may be many things.

Clyde Spencer
Reply to  Smart Rock
April 16, 2022 12:19 pm

And, during the Precambrian, there were natural nuclear reactors adding even more heat to the crust and atmosphere than produced by radioactive decay alone.

https://en.wikipedia.org/wiki/Oklo_Mine

Bill Rocks
Reply to  Smart Rock
April 17, 2022 7:25 am

SR,

Thanks for your useful and colorful words about the earth and internal heat including this gem: “…there were continents the size of France slopping around and crashing into each other like fairground dodgem cars.”

The subject study of 19 million years of seafloor spreading, a small part of 4.5 billion years of earth history, is presumptuous to claim that the study has revealed a change in dynamic earth processes. The 19 million years, if accurately understood, may be only the noise in a chaotic process.

It seems to me that the authors’ claim is similar to the many studies of short-term phenomena that have been claimed to be important long-term changes. Weather vs climate, temperature studies, ozone, polar bears, sea level, CO2, glaciers, butterflies, rainfall and drought, wildland fires, bark beetles.

Bruce Cobb
April 16, 2022 4:57 am

The reason the sea floor is sluggish is due to a lack of fiber.

Felix
Reply to  Bruce Cobb
April 16, 2022 9:11 am

There have been a whole lot of new optical fiber internet connections in the last few years.

VOWG
April 16, 2022 6:06 am

I would venture a guess that as the planet cools, and it has been cooling for millions of years, something like that would happen. The core is not self generating, it will and is cooling.

Robert of Texas
Reply to  VOWG
April 16, 2022 1:14 pm

The core is not self generating”

I assume you mean the core-heat? Radioactive materials are responsible for the Earth core to have remained partially liquid for so long a time. Without radioactive elements, the core would have solidified by now – so at least to some degree the core is able to generate it’s own internal heat thus slowing down the cooling.

RealityCheck
April 16, 2022 6:07 am

If seafloor spreading is real, then why is the crust near the northwest pacific coast the newest according to magnetic maps of the seafloor? Why does the east coast of the US not have subduction, being that it has older crust with the associated earthquakes? Why do maps showing areas of subduction in general have newer crust?
https://www.ck12.org/earth-science/Magnetic-Evidence-for-Seafloor-Spreading/lesson/Magnetic-Evidence-for-Seafloor-Spreading-HS-ES/

Clyde Spencer
Reply to  RealityCheck
April 16, 2022 12:22 pm

Because the older oceanic rocks have been over-ridden by continental crust in those particular areas.

Agamemnon
Reply to  RealityCheck
April 16, 2022 1:26 pm

New oceanic crust being subducted happens all the time. We have plenty of examples where you can subduct entire oceanic plate with their spreading ridge all together (e.g., Nazca plate and part of the Pacific plate on the western coast of Central America). This happened when you have forced subductions in which a very young oceanic plate can be subducted providing you have the right plate velocities. Usually, the subducted plate has a very low plunging angle. This can happen to small marginal sea oceanic crust or to much bigger oceanic domain.

GregK
Reply to  RealityCheck
April 17, 2022 2:53 am

If you are using the referenced article for your information I think you are mis-reading it..
It clearly shows older crust along the Atlantic seaboard of the northern US.

In the Atlantic the map shows younger [red] crust along the mid-ocean ridges, spreading zones, and not associated with subduction zones.

On the NW Pacific coast of the US seafloor on the eastern side of the spreading ridge is being sub-ducted before it gets old [Ref The Who https://www.youtube.com/watch?v=qjN5uHRIcjM%5D. What is happenning to that seafloor? A lot of it is getting turned into the volcanoes of Washington, Oregon and California

william Johnston
April 16, 2022 6:11 am

So does this mean we must decommission all geothermal heat pumps? In that they are removing heat from the earth core?

Robert of Texas
Reply to  william Johnston
April 16, 2022 1:16 pm

If we are worried about containing the heat of the Earth we need to be dumping much more CO2 into the atmosphere, thus creating a “blanket”. Of course this only works until a new equilibrium is reached, so more and more CO2 is needed over time.

Matthew Sykes
April 16, 2022 6:23 am

Must mean less earth quakes. So, thats due to climate change? 🙂

Robert W Turner
April 16, 2022 6:50 am

Sea floor spreading rates likely have cycles and are the reason for the Ice Age – Hot House cycle. Spreading rates coincide with hydrothermal cycling rates and correlates to changes in global marine chemistry – the aragonite/calcite sea cycle. These chemistry cycles correlate to the Ice Age – Hot House cycles. Increased “greenhouse gases” during hot house periods is due to warmer oceans, not the other way around.

Richard Hill
Reply to  Robert W Turner
April 17, 2022 11:11 am

Is anyone measuring the current sea floor spreading rate, and if so where, and is the data available somewhere?

Gordon A. Dressler
April 16, 2022 7:39 am

Just one more thing to blame on climate change™.

Felix
April 16, 2022 9:10 am

19 million years from the tail end of several billion years seems pretty meaningless. How does this short episode compare to the entire previous history? Have there been similar slowings? Corresponding speedups?

For all they know, this 19 million years could be a return to normal slow spreading, and the period 19-30 million years ago was a hot rod by comparison.

Agamemnon
April 16, 2022 9:52 am

There have always been strong variations in plate velocities across the geological time. We have a pretty good idea of what they were as far as thé Paleoproterozoic 2.4 billion years ago. There are period of maximum velocities, usually when a supercontinent break up and period of relative quiescence (usually after a supercontinent assembled).
if the mid-oceanic ridge in the Atlantic really slows down, we may see subduction zones appear near the eastern coast of North America. This is where the oceanic crust is the thickest, coldest and densest which means that subductions can spontaneously be initiated.

Cam
April 16, 2022 11:18 am

I wonder if it has to do with the fact that the moon is getting further away from the earth by 1.5″ a year. In 19 million years, that’s almost 450 miles. Further away would mean less gravitational influence which might cause less tectonic stresses. Just speculating.

Bob Close
Reply to  Cam
April 16, 2022 12:07 pm

Of course gravity may have something to do with rates of change in subduction in relation to an expanding Earth as canvassed by some. However I thought that if the eastern Pacific subduction zones are generally reaching maturity as has the NE sector, re California and the trans current movement via the San Andrius Fault system; then resistance to further slab sinking may be increasing as a normal process before the whole process shuts itself off, or moves elsewhere. Good topic for further research, but not in relation to a token climate change argument!

Robert of Texas
Reply to  Cam
April 16, 2022 1:34 pm

450 miles represents an extremely small change of the distance to the moon – 0.188 percent if I did my math right. That would make the mantle have to be extremely sensitive to change.

Robert of Texas
April 16, 2022 1:10 pm

This is just a guess – but I expect the sea-floor spreading increases in rate after a large disturbance shakes things up and then gradually slows down (on average) as a new equilibrium between the forces is reached.

For example, it would not surprise me that after the asteroid strike about 65 million years ago the sea-floor started spreading faster and after a suitable amount of time for things to settle in, it begins slowing down again.

Think of a pot of boiling stew forming some kind of froth on top…it seems to reach a point where there is little change. Stick in a spoon and stir it and change occurs rapidly for a short time until once again reaching a point of little change over time.

Anything that can ring Earth like a bell would likely have the ability to “stir things up”.

Again – pure speculation.

Pat from kerbob
Reply to  Robert of Texas
April 17, 2022 10:02 am

Change causes change
Not idle speculation at all

MarkW
April 16, 2022 3:12 pm

Since they are using magnetic reversals as their clock, how did they manage to rule out the possibility that magnetic reversals aren’t happening more frequently now, compared to 18 million years ago?

Last edited 4 months ago by MarkW
Myron
April 16, 2022 5:51 pm

It’s man made! All the anchors from all the sunk ships are grabbing onto the ocean floor and slowing things down.

Geoff Sherrington
April 16, 2022 10:09 pm

By good fortune, our group of mineral exploration professionals became quite close to Prof S Warren Carey from the University of Tasmania in the 1970-90 era, after he had done most of his research on the Expanding Earth Hypothesis, about which he was a World leader. His works often compare this hypothesis to others including plate tectonics.
PII: 0012-8252(75)90097-5 (ualberta.ca)
Carey did not favor one mechanism over another – he merely reported what was observed and deduced. One of his quotes from 1975 was “A second wave … (of scientists) … ran against the orthodox tide, which, in geology, is lethal.” So much for modern gatekeeping complaints!
Some of the measurements critical to the Expanding Earth were unfinished when we last met. Several involved satellite observations that were either planned or would later happen. The theory is presently held to be unsupported by adequate evidence, though the topic can get quite deep.
Those interested in plate tectonics should find an abundance of material by following the Carey references and writings. He lived 1911-2002.

Geoff Sherrington
April 16, 2022 10:15 pm

The problem of global heat balance.
Yes, it is entirely credible that radioactive decay is a heat source. Yes, it is probable that we know the main isotopes causing decay heat. Yes, we know their decay energetics.
No, we do not know their abundance – far too deep to drill – so we cannot even start to model how much heat is produced over time. No, we do not know the thermal conductivity properties of the materials in the Earth that conduct some heat to the surface.
Various authors do make models, but they are highly dependent on assumptions for which we currently have no means of proof. Geoff S

J. R.
April 16, 2022 11:04 pm

Sea floor spreading is slowing down, but the expansion of the universe is speeding up. I wonder if that has to do with conservation of momentum or energy or something.

Kevin kilty
April 17, 2022 7:05 am

This cycle is called seafloor spreading, and its rate shapes many global processes,

Its rate shapes the ocean floor profile and thus the available volume of the ocean basins. If this slowdown has been going on long enough then in the absense of other factors (like thermal expansion or acceleration of groundwater or river flow into oceans) then sea level should fall.

Pat from kerbob
April 17, 2022 9:59 am

I see no one is addressing the real problem.
The core is cooling, naturally.

If the adoption of geothermal takes off we will accelerate the freeze up of the earths core because there is no free lunch, and then, yes indeed, we all die.

Once again

Partial /sarc

Last edited 4 months ago by Pat from kerbob
RoHa
April 17, 2022 11:14 pm

I’m sure man-made CO2 is responsible.

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