Researchers show that high ancient shorelines do not necessarily reflect ice sheet collapse millions of years ago
From the Canadian Institute for Advanced Research:
For decades, scientists have used ancient shorelines to predict the stability of today’s largest ice sheets in Greenland and Antarctica. Markings of a high shoreline from three million years ago, for example – when Earth was going through a warm period – were thought to be evidence of a high sea level due to ice sheet collapse at that time. This assumption has led many scientists to think that if the world’s largest ice sheets collapsed in the past, then they may do just the same in our modern, progressively warming world.
However, a new groundbreaking study now challenges this thinking.
Using the east coast of the United States as their laboratory, a research team led by David Rowley, CIFAR Senior Fellow and professor at the University of Chicago, has found that the Earth’s hot mantle pushed up segments of ancient shorelines over millions of years, making them appear higher now than they originally were millions of years ago.
“Our findings suggest that the previous connections scientists made between ancient shoreline height and ice volumes are erroneous and that perhaps our ice sheets were more stable in the past than we originally thought,” says Rowley. “Our study is telling scientists that they can no longer ignore the effect of Earth’s interior dynamics when predicting historic sea levels and ice volumes.”
The study, published online in Science on May 16, was a collaboration that included CIFAR Senior Fellows Alessandro Forte (Université du Québec à Montréal) and Jerry Mitrovica (Harvard), and a former CIFAR-supported post-doctoral fellow Rob Moucha (Syracuse).
“This study was the culmination of years of work and deep collaboration by researchers in CIFAR’s program in Earth System Evolution,” explains Rowley. “For this study, each of us brought our individual expertise to the table: Rob and Alex worked on simulations of Earth’s mantle dynamics, Jerry provided calculations on how glaciers warp Earth’s surface, and I shaped our understanding of the geology of the landscape we were looking at. This study would not have been possible without CIFAR.”
The team studied the coast from Virginia to Florida, which has an ancient scarp tens of metres above present-day sea level. Until now, many research groups have studied this shoreline and concluded that during a warm period three million years ago, the Greenland, West Antarctic and a fraction of East Antarctic ice sheets collapsed, raising the sea level at least 35 metres. But the new findings by Rowley and his team suggest that these ice sheets, particularly the East Antarctic Ice Sheet (the world’s largest), were probably more stable.
To do their study, the team used computer simulations to follow the movement of mantle and tectonic plates that occurred over time. Their prediction of how the ancient shoreline would have developed over millions of years matched what geologists mapping this ancient coast have observed. The next steps for the team are to try to make accurate predictions in other locations around the world.
“The paper is important because it shows that no prediction of ancient ice volumes can ever again ignore the Earth’s interior dynamics,” explains Rowley. “It also provides a novel bridge between two disciplines in Earth science that rarely intersect: mantle dynamics and long-term climate. It is the kind of study that changes how people think about our past climate and what our future holds.”
Source: http://www.cifar.ca/ancient-shorelines-ice-sheets-stability
h/t Dennis Wingo
===============================================================
Dynamic Topography Change of the Eastern United States Since 3 Million Years Ago
David B. Rowley, Alessandro M. Forte,Robert Moucha, Jerry X. Mitrovica,
Nathan A. Simmons, Stephen P. Grand
Abstract
Sedimentary rocks from Virginia through Florida record marine flooding during the mid-Pliocene. Several wave-cut scarps that at the time of deposition would have been horizontal are now draped over a warped surface with a maximum amplitude of 60 m. We modeled dynamic topography using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial isostatic adjustment, account for the current architecture of the coastal plain and proximal shelf. This confounds attempts to use regional stratigraphic relations as references for longer-term sea-level determinations. Inferences of Pliocene global sea-level heights or stability of Antarctic ice sheets therefore cannot be deciphered in the absence of an appropriate mantle dynamic reference frame.
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“To do their study, the team used computer simulations……. Sorry, lost interest there.
Small question do they get Earth Quakes in the Arctic and Antartic.Might explain the ice breaking up.And are there Under Water Volcaoes.
The estimates of ice sheet volumes and sealevels during the earlier Pleistocene is done by balancing ‘water’ isotopes, mostly 18O, since heavy water evaporates less easily. For the last glacial maximum we have sealevel indicators some 120 meters below the surface in several areas around the equator. However if you crunch the numbers you end up with way too much ice.
And then there is this forgotten study (forgotten maybe because it’s compromising the current scholar view?).
http://geology.gsapubs.org/content/30/4/379.abstract
Beijing inundated by the sea within the past 80 k.y.: Nannofossil evidence
Beijing was to be more than a hundred meter above sealevels in the current ice age model, not below. That would have been ‘impossible’ and also glacial rebound/isostacy has nothing to do with that.
I’d say this study deserves a duplication attempt and if so, we should toss away all our conclusions about the Pleistocene and vertical earth movements.
“However, a new groundbreaking study now challenges this thinking.”
Hmmm, groundbraking? We structural geologists have never taken shorelines in a particular geographic location as reference points for eustatic sealevel rise or fall. Only when a globally correlated rise or fall can be established one may use this methodology.
Just mentioned this in tips but appropriate here also.
Interesting paper on the oldest sea level gauge in the world. Well above sea level now due to rebound.
http://www.historicalgeophysics.ax/sp/01.pdf
Another paper for John Cook to ignore.
Let’s keep a little perspective: this is only one paper. I’d like to see a bit of confirmation before we go off the deep end. (Pun not intended) 🙂
This sounds interesting and certainly deserves more attention, but haste makes
wastebad research.Ok, I’ll put my twopenneth worth in – just for the heck of it.
In essence, all geologists know full well that the idea of fixed ‘ground level’ is a non starter. But what we do not have is any ‘fixed’ point of reference. We know full well that mountain ranges got built, plates moved, subductions zones occurred, etc, etc. and the most important bit – is that this movement has been going on for 4.6 billion years. what was the start point? – we dunno!
what are we actually looking at when we look at the ‘current’ earths crust? – we dunno for sure!(but we can and do deduce things, like what kind of conditions sediments were laid down in, ages of rocks, etc)
FWIW, my personal take on crustal movement (or perhaps more accurately – ‘crustal volume’) – is that the total crustal volume is essentially ‘static’ but in a constant state of flux or movement. But consider if this is reasonably true, when a mountain range is getting built – somewhere else on the planet, the crustal volume must be going down (by an equal and opposite amount).
Thought experiment/imagination time:
If we consider the earth as having a molten or semi-molten mantle – then it is not unreasonable to assume that, in complete equilibrium (i.e. no movement and everything ‘levelled out’ over time due to gravity), the crustal rocks would be an even ‘volume’ laying as a ‘skin’ evenly spread over the mantle. Consider then, that the total ocean volume sits on top of this ‘skin’ – which would be at a given water depth (i.e. estimated oceanic volume spread over the entire globe).
Now, lets introduce some tectonic movement….what happens? – the crust rises in some part of the globe and correspondingly falls at another part (making a mountain range in the rising part, and a deeper ocean in the falling part). The net crustal volume hasn’t actually changed – neither has the net ocean volume – they just shifted about!
Ignoring (for the minute) any glacial ice content variation (and isostatic rebound) – we then have to ask, what is the starting point for any sea level observations? Answer – there isn’t one!
Logically, if the crust moves, the sea must move too – hence we will be unlikely to reconcile sea level observations around the world without detailed knowledge of the crustal movement and volumetric changes thereof.
If we have a rising volcanic mountain range – where has that material come from? It comes from the mantle, which is replenished by subducted material somewhere else. The mid-atlantic oceanic spread is widening the ocean, making its ‘volume’ greater – but the pushing together of other plates is making the available ‘volume’ in those areas smaller. If the oceans were not physically connected – you would see the Atlantic dropping and the Pacific rising, in such a scenario. Neither would be due to Glaciation/Ice melt/CAGW or whatever – just the natural volumetric change/flux of the planets crust.
Having said the above – now add in the NATURAL climatic ‘glacial’ variations – and I defy anyone to come up with a start point for where sea level should be – or even what an imaginary ‘equilibrium’ level might possibly be. From that it follows that any observed sea level variation (up/down/static) are in NO WAY indicative of a simple man-made cause. End of.
Gosh. Real science.
How on Earth did they get funding ? Someone must have made a slip up there.
No redundant thread-bombing intended, but this subject has been mentioned before, and judging by the comments, need to be mentioned again. From Wiki on “Earth Tide”….
“The Earth tide encompasses the entire body of the Earth and is uninhibited by the thin crust and land masses of the surface, on scales that make the rigidity of the rock irrelevant.”
As a civil engineer, I dealt with surveyors who were jubilant over the potential of converting the Texas State Plane Coordinate system from the cumbersome, line of sight, triangulation system of the USGS to a satellite GPS system. The initial results for horizontal control were encouraging, but there was a vertical anomaly. This was assumed to be corrected as more satellites were in orbit, giving greater satellite triangulation signals. Instead, the anomaly had a consistent VERTICAL daily variation of, on average 18″ per day. The Moon lifts the oceans, on average 6 ft per day. This moving mass unloads the ocean floor, and when coupled with the same tidal force lifting the plastic, molten rock below, causes this daily Earth tide.
Suddenly there was a good explanation for Plate Tectonics, as the Lunar gravity exerted an upward and westward pull, creating cracks along the sea floor rift lines, which were instantly in-filled with molten rock from below. This molten rock fill instantly solidified in contact with with deep ocean 4C water, causing a daily, but irregular ‘ratchet’ effect on the plates, resulting in uplift and subduction zones. This movement is only possible because deep Earth fission heat, which is also not constant, provides the movable mass of molten mantle rock, and the rift fill material. Restating correctly from above….
“In this Universe, nothing is constant and equilibrium is an illusion.” This includes our silly notion of fixed atomic decay rates and decay products, as well as any notion of Terra Firma. The poorly measured watts/meter square of geothermal heat flow is also an inaccurate measure of the extent of this fission energy. For more on that, see “Earth’s Missing Geothermal Flux”.
NASA are well aware of the problem that we currently have no real frame of reference in order to separate out sea level rise and fall from isostatic variations. And so a number of satellites are planned to establish this.
I think there was an article about NASA’s plans for this on WUWT a little while ago. Maybe a WUWT mod can find the link and add it here;
I suppose I should add my take on isostatic rebound too – which is that this is also compensated for in the ‘volume balance’. if a massive load of ice sits on the crust – it pushes it down – which correspondingly pushes the crust (including the ocean floor) UP somewhere else. The net volume of oceanic water has reduced (to make the ice) – but the ice (frozen water) is still ‘in the system’ as weight on the land!
Theoretically, if this was an experiment in a bucket of water and a floating block of wood (as a closed system), and you froze some of the water and put it onto the block of wood, the water level would remain exactly the same! (Archimedes and all that!).
consider the crustal rocks as floating on the mantle and you have the same principle!
Isostatic adjustment can go both ways. NE Scotland is sinking slightly despite being covered in ice 12000 years ago. The west of Scotland is rising so somewhere between the two is a tipping point.
Where have I heard that term used before?
The ‘team climate scientists’ and their sycophants remind me of a school of fish in a tight bait ball … they know their number is up but pack in closer and closer in the hope that any other fish than themselves gets picked off by the pelagics.
should have added that the reverse is true – i.e. if you melt the ice, the land rises, but the ocean floors will drop to compensate – ergo, no significant sea level change.
Of course, what we can see – is that the time it takes for the crust to adjust is much longer than the time it takes for ice to melt and reform – so that is why we see actual sea level variation! It’s basically due to the time lag in the whole ‘adjustment’ process.
Hope all that made sense – or I’ve wasted everyones time!
regards
Kev
I don’t understand. Are you saying that when people previously checked the geological record for past sea levels, they failed to consider the possibility that the ground may have moved? I am possibly stating the obvious here but that’s a bit surprising isn’t it? I mean geology is a bit to do with the fact that the ground does move – over geological time frames. That’s why they call it geology, isn’t it?
(Also, where do virgins fit in…?)
markx says:
May 18, 2013 at 9:05 pm
Otter says: May 18, 2013 at 7:11 pm
………. there are a huge number of adjustments and jerry rigging going on to make satellite figures work.
http://en.wikipedia.org/wiki/Permanent_Service_for_Mean_Sea_Level
http://ilrs.gsfc.nasa.gov/docs/GRASP_COSPAR_paper.pdf
I wonder if gravitational waves would affect the height of the geostationary orbit?
To do their study, the team used computer simulations …
What’s sauce for the goose is sauce for the gander.
Found it.
http://wattsupwiththat.com/2012/12/03/why-ice-loss-and-sea-level-measurements-via-satellite-and-the-new-shepard-et-al-paper-are-highly-uncertain-at-the-moment/
This new satellite system could be “game changing”.
Many first year university geology students are taught to measure height differences in raised beach levels to determine rates of tectonic uplift. Movements in the earths crust can be much more substantial and occur over shorter time frames than sea level changes due to a warming climate.
Why is this not taken into account by climate change models when predicting sea level rises? Most of the worlds ocean floor is moving both horizontally and vertically by continental drift. These movements are commonly several millimetres a year. This has been known for many decades and can often be measured.
Compare the water level in a half full plastic water bottle when it is squeezed with the water bottle when the water is warmed. Note that the water level changes dramatically in the squeezed bottle. Now apply both slow warming and slow squeezing to the bottle at the same time. Can you tell which makes the water level change the most – squeezing or heating?
Kelvin Vaughan says:
May 19, 2013 at 3:31 am
“I wonder if gravitational waves would affect the height of the geostationary orbit?”
That would make it rather easy to detect them, and scientists are still trying to do that with extremely sensitive equipment. So probably not.
As we have seen before , on the very long term , geology & climate are usually tightly interlocked.
And yet climatologist routinely dismiss the geologic record as unimportant in their research …. probably because they can’t support alarming hypotheses if they do include a geologic perspective.
For those of you who aren’t geologists, sea level changes over geologic time has been a topic of significant research as sea level changes have a fundamental influence over how & where sedimentary rocks types are distributed, which in turn is fundamentally important in finding & developing oil & gas deposits. A subject for debate is always if a given change in the stratigraphic reocord is global or regional, whether it is tectonically driven or whether it is climatologically driven. This article is just one of many which looks at this issue. If you are interested is seeing what sea level changes look like over geologic time , see this link:
http://en.wikipedia.org/wiki/File:Phanerozoic_Sea_Level.png
J Martin says:
May 19, 2013 at 2:59 am
Gosh. Real science.
How on Earth did they get funding ? Someone must have made a slip up there.
The geologists must have been getting peeved at all the funding going to the climatologists, so they used the magic words Climate Change in the grant application and hey presto! they got their project funded.