A new global ice sheet reconstruction for the past 80,000 years
ROYAL NETHERLANDS INSTITUTE FOR SEA RESEARCH
During ice ages, the global mean sea level falls because large amounts sea water are stored in the form of huge continental glaciers. Until now, mathematical models of the last ice age could not reconcile the height of the sea level and the thickness of the glacier masses: the so-called Missing Ice Problem. With new calculations that take into account crustal, gravitational and rotational perturbation of the solid Earth, an international team of climate researchers has succeeded in resolving the discrepancy, among them Dr. Paolo Stocchi from the Royal Netherlands Institute for Sea Research (NIOZ). The study, now published in the journal Nature Communications, could significantly advance research into the climate of the past and help to make better sea-level predictions for the future.
Paolo Stocchi: “Our new reconstruction revolutionizes what we thought about the global continental ice mass during the Last Ice Age. The total mass of the Last Ice Age glaciers was 20% smaller and accumulated faster than previously thought.”
Growing and melting glaciers
With the alternation of ice ages and warm ages, the glaciers on Greenland, North America and Europe grow and shrink over the course of tens of thousands of years. The more water is stored in the form of ice, the less water there is in the oceans – and the lower the sea level. Climate researchers want to find out how much the glaciers could melt in the course of man-made climate change in the next centuries and how much the sea level will rise as a result. To do this, they look into the past. If one succeeds in understanding the growth and melting of the glaciers during the last ice and warm periods, then conclusions can be drawn for the future.
The “problem of the missing ice”
But this look into the past is difficult because the thickness of the glaciers and the height of the sea level can no longer be measured directly in retrospect. Climate researchers therefore have to laboriously collect clues that can be used to reconstruct the past. However, depending on which clues you collect, the results are different and seem to contradict one another. Previous models and calculations led to the so-called “missing ice” riddle. Geological evidence from ocean areas suggest that sea level might have been 120-140 m lower than today during the last Ice Age 20,000 years ago. The uncertainty of these data is quite large, though. To account for these low sea levels, as much as twice the current mass of the Greenland ice sheet would have to have been frozen worldwide. However, these glacier masses could not possibly have been that large at the time, according to climate models. Also, there is no geological evidence at higher latitudes for such a large mass of ice. How to explain then that the water wasn’t in the sea and at the same time it wasn’t stored in the freezer on land either?
80,000 years of ice sheets and sea level changes accurately reconstructed
This problem has now been solved with a new method by an international team of scientists led by Dr. Evan Gowan (Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, in Bremerhaven). Among them the geophysicist Dr Paolo Stocchi from The Royal Netherlands Institute for Sea Research. “We have found a way to accurately reconstruct the last 80,000 years of ice sheets and sea level changes,” says Dr. Paolo Stocchi, who has contributed to the creation of the novel global ice sheet model by including crustal, gravitational and rotational perturbation of the solid Earth. Their new model explains past local sea levels that are lower than today by incorporating the relative motion of the sea surface and Earth’s crust. In this way, past local sea levels that are much lower than today, can be modelled without requiring an unrealistically large global ice mass. The solid Earth motions would do the trick!
Understanding the behavior of glaciers by looking at the Earth’s mantle
With the new method, the scientists have eventually reconciled sea level and glacier mass: According to their calculations, the sea level must have been around 116 meters lower than today at the time. There is no discrepancy in terms of glacier mass. Unlike the previous global model, the team took a closer look at the geological conditions in the proximity and underneath the formerly glaciated areas, and not in the far-field ocean areas: How steep were the mountain slopes? Where did glaciers reach the sea? Did friction interfere with ice flow velocity? And how much? The new model includes all these local factors. It also accounts for ice- and water-load-induced crustal deformations. The latter are important because they alter the topography of the land, thus affecting the ice flow and eventually the volume of glaciers. “Crustal deformations are regulated by solid Earth physical parameters such as viscosity,” says Paolo Stocchi. The Earth’s mantle, in fact, behaves like a highly viscous fluid on geological time scales and deforms under the weight of a fluctuating ice mass. “By assuming different viscosities of the earth’s mantle, we model different evolutions of the land topography, which then result in different scenarios for the ice masses.” These can now be brought into harmony with the marine geological evidence from the ocean areas, without the need for extra mass.
The established isotope model needs to be revised
The technical article by Evan Gowan and his team takes a critical look at the method for estimating glacier masses that has been the standard in science for many years: the method of measuring oxygen isotopes. Isotopes are atoms of the same element that differ in the number of their neutrons and therefore have different weights. For example, there is the lighter 16O isotope and the heavier 18O isotope of oxygen. The theory says that the light 16O evaporates from the sea and the heavy 18O remains in the water. Accordingly, during ice ages, when large mainland glaciers form and the amount of water in the sea decreases, the 18O concentration in the oceans must increase. But as it turns out, this established method results in discrepancies when it comes to reconciling sea level and glacier mass for the time 20,000 years ago and before.
“The isotope model has been used widely for years to determine the volume of ice in glaciers up to many millions of years before our time. Our work now raises doubts about the reliability of this method,” says Paolo Stocchi. His goal now is to use the new model to quantify the current rates of crustal deformation in the North Sea and Wadden Sea, thus revealing the actual contribution of current climate change to the regional relative sea-level changes.
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Meh, models. Even if it’s an honest model, how can anyone trust modellers anymore, especially those working in socialist academia?
This paper says that the oxygen kinetic isotope effect is problematic. That is a very big statement with vast implications for many things including climate science.
How valid is their claim about the oxygen isotope problem? What is the problem and how does it work? This should be much more important than the ice volume conundrum?
“By assuming different viscosities of the earth’s mantle, we model different evolutions of the land topography, which then result in different scenarios for the ice masses.”
They simply updated that 1976 work…
https://sites.physics.utoronto.ca/peltier_wr/selected-publications/pubs_highestimpact/w-r-peltier-w-e-farrell-j-a-clark-glacial-isostasy.pdf
Another self satisfaction fantasy model modified until it surrenders and supplies what the designers/programmers believe.
Start with a gross assumption. Use plenty of scientific words to imply knowledge and experience.
Introduce additional assumptions that complicates the scenario.
Adjust the new introduced factors until model results match researcher desires.
N.B. This is not a case where independent researchers/users validate and verify the results of a new model. It is a case of the researchers who built the model claim their new model solves all of the missing ice/sea level problems and validates their research group’s confirmation bias…
Caveat Emptor.
Now I would like to know the effect of all the volcanic venting in all the earths oceans. How much is the ocean temperature rising, if any?
Does a bear forage (or whatever) in the woods?
I should think they could have resolved this by positing that the Arctic Ocean was frozen solid with extra ice heaped on top. No crustal shifting required.
You’ll pardon my amateur confusion, after being told, for years, that ice age sea level was 394ft (120m) lower than it is today … https://iceagenow.com/Sea_Level_During_Last_Ice_Age.htm
Comes today these learned boffins who tell us that today, according to this new modeling that the sea was 380ft lower back then..”According to their calculations, the sea level must have been around 116 meters lower than today..”
Granted, 14ft around the globe would add up, but being that far off the mark for decades while the climate ‘science is settled’ leads one to wonder about just how ‘settled’ it is..
DENIER!!!!!!!
I presume that the glaciers are salt free, which means the remaining ocean will have increased salinity (assuming the absolute amount of salt in the ocean has been roughly constant over the period in question). I wondered how significant this would be but my back of the envelope calculations suggest it would be only a 3% increase in salinity. My guess is that this would not be enough to affect the life in the sea but I don’t have very much knowledge in this area. Is that correct?
I don’t know, but I would expect that difference to be detectable in the geologic record.
There seem to be a lot of unknowns in trying to estimate what the maximum ice volume and minimum sea level would have been during an ice age.
Geologists can estimate the amount of land area which could have been glaciated by noticing the positions of glacial debris left behind when the glacier retreated from its maximum extent. But the maximum thickness of the ice is harder to measure–how do you measure the height of ice that is no longer there?
The problem is more complex for the two existing large ice caps in Antarctica and Greenland, both of which are still more than 90% covered by ice. Their surface area was probably not much higher during the ice age than now, but how can we measure the thickness of ice that has long since melted and is no longer there? During a period of ice accumulation, one can drill ice cores and measure concentrations of gas isotopes trapped in the ice, but once a layer of ice melts and flows into the sea, those isotopes either mix with sea water or are emitted to the atmosphere, and the record is lost.
If the sea level was really 120 meters lower during the last ice age than it is now, how can one measure the location of an ancient shoreline now under 100 meters of water? We can sometimes observe evidence of higher past sea levels by finding fossils of marine animals inland, but do we have to try to find fossils of land animals at the sea bottom? What if these animals didn’t actually live where they are now buried, but may have been swept away to sea and drowned by a flooding river?
The writers of this article may have found a theoretical model that yields a converged mass balance, but lack the evidence to show whether or not it is correct.
We can see where corals are located that lived a when sea level was lower.
The lowest we can find such remnants gives some indication of where sea level was.
That is one way.
There are others.
It can be calculated how thick a ice sheet would need to be to gouge out rock to the depth of Lake Superior, given the known hardness of the rocks gouged out.
I suspect we will never know much of anything if the people organizing our bases of accumulated knowledge erase any parts they do not like, as was done when these guys declared that accepted values should be discarded because their models say it was impossible.
Models only say what they are programmed to say. They are not by themselves evidence of anything:
“To account for these low sea levels, as much as twice the current mass of the Greenland ice sheet would have to have been frozen worldwide. However, these glacier masses could not possibly have been that large at the time, according to climate models.”
So they took better account of the fact that our planet is a molten iron liquid balloon of fixed volume, with a thin insulating silicate scum floating on top. On top of that silicate scum over 3/4 of the planet is a layer of water and sometimes ice, that combined with the silicate scum, all obey Archimedes principle. But I think we’ve known this for a while already.
The report refers to the negligible ‘man made climate change’. Not off to a good start.
“Negligible”
Do have a link to the evidence that supports that opinion Brian?
How much did the ocean floor rise when the continents were depressed?
There are reasons to doubt the accuracy of the delta-Oxygen-18 method for sea level studies.
The method, in brief, is here.
“Delta-O-18 changes directly as a result of temperature fluctuations, so it provides a very good record of the climate. Oceanic delta-O-18 values that are high represent cold climates, while lower values indicate a warm climate. This trend occurs because of the effects of precipitation and evaporation. Since it is lighter than 18O, 16O evaporates first, so in warm, tropical areas, the ocean is high in 18O. Additionally, as water vapor condenses to form rain, water droplets rich in 18O precipitate first because it is heavier than 16O. Thus, the cold, polar regions are depleted in 18O as it all precipitates out in the lower latitudes, but they are high in 16O. On the other hand, the Tropics possess a large amount of 18O but have little 16O. This state is not permanent, however, because evaporation and precipitation are highly correlated with temperature. Changes in the climate can greatly affect the ratio of 18O and 16O and can alter their distribution throughout the globe.”
https://www.seas.harvard.edu/climate/eli/research/equable/isotope.html
The overall complication is because both are stable isotopes. The method above looks at changes in the ratio, but a change (say positive) in one pace has to be balanced by a change (say negative) in another place. These measurements are done on water and ice. +Water is mixing all of the time, so there is a probability that water from the +ve places will mix in a largely undefined way with the -ve.
In short, there does not seem to be a stable reference point to which other measurements can be related. It all floats around.
When ice is analysed, it has been formed from water evaporated usually elsewhere, then transported. In most cases, one does not know the source of the water, nor its temperature, accurately enough to relate to temperatures.
I have never used this method, so please shoot me down if I am wrong. Geoff S
Um, oxygen’s atomic mass is 16, and its isotopes are 11 through 26. Tantalum and Hafnium have isotopes with atomic mass of 180, but oxygen…no, sorry, there are none.
What about Antarctica? There is absolutely no way we can know how high the ice was piled up on Antarctica during the last glaciation. So how can we possibly know that there was ‘missing ice’ in the first place?
Where did the water go? Each glacial period represents a major issue with respect to the reconciliation of the water budget. If we use the last glacial event then the following become apparent from the USGS:
So we have a huge conundrum. The rate of ice accumulation of the permanent ice as represented by the ever-increasing ice thicknesses in Greenland and Antarctica on the one hand regardless of sea level and weather changes elsewhere around the world and the fluctuating sea levels.
So where did the water go?
Perhaps we should look at the expanding and contracting earth theory as espoused by Dr R Wilson at the University of Illinois, Urbana campus, IL in 1993.