During ice ages, the global average sea level decreases due to the storage of large quantities of sea water in the form of huge continental glaciers. So far, mathematical models of the last ice age have not been able to reconcile the rise in sea level with the thickness of the glaciers: the so-called lost ice problem. With the new calculations taking into account the turbulence of the Earth’s crust, the gravitational pull and the rotation of the solid Earth, an international team of climate researchers has resolved the paradox, among them Dr. Paolo Stucci of the Royal Netherlands Institute for Ocean Research (NIOZ). The study now published in the journal Nature connections, It can significantly advance research into past climate and help make better predictions of sea level for the future.
Paolo Stucci: “The new reconstruction revolutionized what we had thought about the global continental ice mass during the last ice age. The total mass of glaciers in the last ice age was 20% smaller and accumulated faster than previously thought.”
Glacier cultivation and melting
As ice ages and warm ages alternate, glaciers in Greenland, North America and Europe are growing and contracting over tens of thousands of years. The more water is stored in the form of ice, the less water is in the oceans – and the lower the sea level. Climate researchers want to know how much melt glaciers can melt in the context of man-made climate change in the coming centuries and how much sea level will rise as a result. To do this, they look at the past. If one succeeds in understanding the growth and melting of glaciers during recent periods of ice and warmth, then conclusions can be drawn for the future.
The ‘lost ice problem’
But this view of the past is difficult because glacier thickness and sea level rise can no longer be directly measured at a later time. So climate researchers must effortlessly gather evidence that can be used to reconstruct the past. However, based on the clues you collect, results vary and appear to conflict with one another. Previous models and calculations have led to the so-called “lost ice” puzzle. Geological evidence from ocean areas suggests that sea level may have dropped by 120-140 meters than it is today during the last Ice Age 20,000 years ago. However, the uncertainty about this data is very large. To account for these low sea levels, up to twice the current mass of Greenland ice sheet worldwide would have to be frozen. However, these glaciers couldn’t be large at the time, according to climate models. Also, there is no geological evidence for the higher latitudes of such a large block of ice. How do we explain then that the water was not in the sea and at the same time it was not stored in the refrigerator on land either?
80,000 years of ice sheets and sea level changes meticulously rebuilt
This problem is now solved by a new method by an international team of scientists led by Dr. Evan Joan (Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, in Bremerhaven). Among them is the geophysicist Dr. Paolo Stucci of the Royal Netherlands Institute for Marine Research. Says Dr. Paolo Stucci, who helped create a new global model for ice sheets by including crustal turbulence, gravity, and solid Earth rotations. Their new model explains local sea levels that are lower than they are today by integrating the relative motion of the sea surface and the Earth’s crust. In this way, previous local sea levels that were much lower than they are today can be modeled without the need for an unrealistically large global ice mass. Hard Earth moves will do the trick!
Understand the behavior of glaciers by looking at the Earth’s cover
Using the new method, scientists were finally able to reconcile the sea level with the mass of glaciers: according to their calculations, the sea level should be about 116 meters lower than it is today at that time. There is no contradiction in terms of the mass of the glaciers. In contrast to the previous global model, the team took a closer look at geological conditions in adjacent and previously subglacial regions, rather than in remote ocean areas: How steep are the mountain slopes? Where did the glaciers reach the sea? Does friction interfere with the ice flow velocity? And how much The new paradigm includes all these local factors. It is also responsible for the cortical deformations caused by carrying ice and water. The latter is important because it alters the Earth’s topography, thus affecting the flow of ice and ultimately the size of glaciers. “Crustal deformations are regulated by hard-Earth physical factors such as viscosity,” says Paolo Stucci. Earth’s mantle, in fact, behaves like a very viscous liquid on geological time scales and deforms under the weight of a volatile mass of ice. “By assuming different viscosities of the Earth’s cover, we represent different developments of the Earth’s topography, which then lead to different glacier scenarios.” Harmony can now be achieved with marine geological evidence from ocean areas, without additional mass required.
The applicable isotope model needs revision
The technical article by Evan Joan and his team takes a closer look at the method for estimating the masses of glaciers 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 neutrons and therefore have different weights. For example, there is the isotope of 16O which is lighter and the isotope of 18O that is heavier than oxygen. The theory says that the 16O light evaporates from the sea and the heavy 18O remains in the water. Accordingly, during ice ages, when large glaciers form on the mainland and the amount of water in the sea decreases, the concentration of 18O in the oceans should be increased. But as it turns out, this consistent method produces inconsistencies when it comes to reconciling sea level with the mass of glaciers in a time 20,000 years and earlier.
“The isotope model has been used widely for years to determine the size of ice in glaciers until millions of years before our era. Our work now raises doubts about the reliability of this method,” says Paolo Stucci. His goal now is to use the new model to determine the current rates of deformation of the Earth’s crust in the North and Wadden Seas, thus revealing the actual contribution of current climate change to the relative regional changes in sea level.