Science is more stable
Glacier ice flow rates are more sensitive to stress than previously calculated, according to a new study by MIT researchers that modified a method, according to a new study by MIT researchers. Decades are used to describe the flow of ice.
This is a new article in communications earth and environment
The viscosity of ice is more sensitive to commonly assumed stress
Earth & Environment Communication Chap 3Number of Posts: 57 (2022)
abstract
Accurate representation of the viscous flow of ice is fundamental to understanding glacier dynamics and predicting sea level rise. Ice viscosity is often described by a simple but largely untested and uncorrected constitutive relation, Glen’s Law of Flow, in which strain rate is proportional to stress increased capacity. n. Value n = 3 is often specified in ice flow models, although observations and experiments support a wide range of values for stresses and temperatures found on Earth. Here, we utilize recent remote sensing observations of Antarctic ice shelves to show that Glen’s Law of Flow approximates the viscous flow of ice with n = 4.1 ± 0.4 in fast-moving water. Consequently, the viscosity and flow rate of ice are more sensitive to changes in stress than most ice flow models allow. By correcting the adjusted equation of ice strain, our results represent a path towards improving projections of future glacial change.
And the conclusion: It’s worse than we thought.
Conclusion
Results that n≈ 4 long-standing practical challenges when assuming the exponent of the flow law is n= 3 anywhere and anytime, in large-scale ice flow models. While our observations focused on specific regions in the extended flow regime on ice shelves subjected to 100 kPa order stress (Supplementary Fig. S6)Additional laboratory studies show that n= 4 is appropriate at higher stresses15 extended support to our conclusion that n≈ 4 to other dynamic regions in Antarctica. In addition, our conclusions complement a growing body of work advocating the use of n> 3 in other areas of the cryosphere19,26. Taken together, this work calls for a broader community effort to quantify the uncertainty in flow law parameters and the consequences of these uncertainties on glacial dynamics models. . The higher value of nincreases the sensitivity of the viscosity to changes in stress, but the effect of n= 4 on large-scale ice flow models used to predict sea level rise, and the evolution of ice sheets is still unclear because several sensitivity analyzes have been performedten and nnot a parameter explored in the current meta-model analysesfirst,2. Value n= 4 is likely to increase the susceptibility of ice mass loss to ongoing climate change significantly compared with n= 3 due to the stronger dependence of the flow rate on the change in resistive stress.
By applying continental-scale satellite observations to standard models in glacial dynamics, we validated Glen’s Law of Flow, a constitutive relationship that helps form the ice’s foundation modern glaciation and stress exponential correction in Antarctic ice shelves. This work serves as a roadmap towards a standard calibration framework for the community using publicly available remote sensing data. Our conclusion that n≈ 4 through most of Antarctica’s ice shelf is a step towards re-evaluating the dominant equations of runoff in the satellite age and shows the increased sensitivity of flow rates to applied stresses compared with the commonly used equation n= 3. Therefore, future sea level rise is likely to be more sensitive to climate changes than predicted by current models using prevailing assumptions of flow laws.
Here is the press release from EurekAlert!
Research: Ice flow is more sensitive to stress than previously thought
Changes to a key ice discharge equation can refine estimates of sea level rise.Peer-reviewed publications
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
Glacier ice flow rates are more sensitive to stress than previously calculated, according to a new study by MIT researchers that modified a method, according to a new study by MIT researchers. Decades are used to describe the flow of ice.
Tension in this case refers to the forces acting on the glaciers of Antarctica, which are mainly influenced by gravity pulling the ice down with lower altitudes. Joanna Millstein, a doctoral student in the Glacier Dynamics and Remote Sensing Group and lead author of the study, explains. “If you squeeze honey in the middle of a piece of toast, and the honey accumulates there before it flows out, then that’s exactly what motion happens to ice.”
The modification of the equation proposed by Millstein and her colleagues will improve the models for making predictions about the flow of glaciers. This could help glaciologists predict how the flow of Antarctic ice could contribute to future sea-level rise, although Millstein said the change in the equation is unlikely to increase estimates of sea level rise exceed the maximums predicted in climate change models.
“Most of our uncertainty about sea level rise from Antarctica is related to the physics of ice flow, so this will hopefully be a limit to that uncertainty,” she said. .
Other authors on the paper, published in Nature Communication Earth and Environmentincluding Brent Minchew, the Cecil and Ida Professor of Green Career Development in MIT’s Department of Earth, Atmosphere and Planetary Sciences, and Samuel Pegler, an undergraduate research fellow at the University of Leeds.
Benefits of big data
The equation in question, known as Glen’s Law of Flow, is the most widely used equation to describe the flow of viscous ice. It was developed in 1958 by British scientist JW Glen, one of the few glaciologists to study the physics of ice flow in the 1950s, according to Millstein.
With relatively few scientists working in the field until recently, coupled with the remoteness and inaccessibility of most large glaciers, there has been little effort to correct the Law of the River. flow of Glen outside the lab until recently. In recent work, Millstein and her colleagues leveraged numerous new satellite images of Antarctic ice shelves, the floating extension of the continental ice sheet, to modify the stress exponent of the process. flow law.
“In 2002, this great ice shelf [Larsen B] crashed in Antarctica, and all we have from that collapse are two satellite images a month apart,” she said. “Now, on that same area, we can get [imagery] every six days. ”
The new analysis shows that “ice flows in the most dynamic, fastest-changing regions of Antarctica – the ice shelves, which essentially hold and embrace the interior of the continental ice – are sensitive to stress.” than is often assumed,” says Millstein. She is optimistic that the growing profile of satellite data will help capture rapid changes in Antarctica in the future, providing insights into the underlying physical processes of glaciers.
But stress isn’t the only thing that affects the flow of ice, the researchers note. Other parts of the flow law equation represent differences in the temperature, size and orientation of the ice particles, as well as the impurities and water contained in the ice – all of which can alter the flow velocity. Factors such as temperature could be especially important in understanding how ice flow impacts future sea level rise, Millstein said.
Crack under tension
Millstein and colleagues are also studying the mechanism of ice sheet collapse, which involves physical models that are different from those used to understand the problem of ice flow. “The cracking and breaking of ice is what we are working on, using strain rate observations,” says Millstein.
The researchers use InSAR, a radar image of the Earth’s surface collected by satellites, to observe the deformations of the ice sheets that can be used to make precise deformation measurements. By observing areas of ice with high strain rates, they hope to better understand the rate at which cracks and rifts propagate to cause collapse.
The research was supported by the National Science Foundation.
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Written by Becky Ham, MIT News reporter
Paper: “The viscosity of ice is more sensitive to stress than what is generally assumed”
https://www.nature.com/articles/s43247-022-00385-x
DOI
ARTICLE TITLE
“The viscosity of ice is more sensitive to stress than what is generally assumed”
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