New research shows that ice flow from temperate glaciers is more stable than previously thought, leading to lower projections of sea level rise. [emphasis, links added]
When Neil Iverson was asked to describe a research paper on glacial ice flows that had just been published in the journal, he started with two lessons in ice physics science.
First, there are different types of ice within glaciers, said Professor Emeritus of the Department of Earth, Atmosphere and Climate at Iowa State University.
Parts of the glacier are at pressure melting temperatures and are soft and watery.
This temperate ice is like ice cubes left on a kitchen counter, with meltwater collecting between the ice and the countertop, he said. Temperate ice is difficult to study and characterize.
Second, other parts of the glacier have cold, hard ice, like ice cubes in a refrigerator. This ice is commonly studied and used as the basis for glacier flow models and predictions.
The new research paper involves the former, said Iverson, co-author and project director.
The paper describes laboratory experiments and resulting data showing that Standard values in “Empirical Basis of Glacier Flow Models” – An equation called Glen’s law of flow, named after the late British ice physicist John W. Glen – Should be changed to temperate ice.
New values when used for flow laws “There is a tendency to predict much smaller increases in flow rates in response to increases in pressure caused by ice sheet shrinkage in a warming climate,” Iverson said.
that means Models will show fewer glaciers flowing into the ocean and expect smaller sea level rises. …shear…
reset n to 1.0
Glenn's flow law can be written as: e ̇ =Atn.
This equation involves the stress on the ice, tits deformation rate, e ̇Where one is a constant for a specific ice temperature.
The results of the new experiment show the value of the stress index, nis 1.0, rather than the normally specified values of 3 or 4.
The author writes: “For genAccording to Glen's original experiments and many subsequent experiments, mainly performed on cold ice (-2 degrees Celsius and below), the value of the stress index n The value in the model has been considered as 3.0. (They also write that other studies of ice sheet cold ice have shown n higher, at 4.0.
This is to some extent, “Because conducting ice experiments at pressure melting temperatures is a challenge,” said paper co-author Lucas Zoet, the L. Morgridge Associate Professor, former postdoctoral researcher at Iowa State University and dean of the Department of Geosciences at the University of Wisconsin-Madison.
Zoet, co-director of the project, built a slightly smaller version of the ring shear device with transparent walls for his lab.
However, data from large-scale shear deformation experiments at the Iverson Laboratory raise questions about assigned values n.
Temperate ice is linearly viscous (n = 1.0) “exceeds the common range of liquid water contents and pressures expected near glacier beds and at the edges of ice flows,” the authors write.
The reason, they propose, is that melting and refreezing along the boundaries of single millimeter- to centimeter-scale ice particles should occur at a rate linearly proportional to stress.
This new data enables modelers to “Based their ice sheet model on physical relationships demonstrated in the laboratory,” Zoett said. “Improving this understanding could improve the accuracy of predictions.”
It takes some perseverance to get the data to support the new value of n.
“We've been working on this project for years,” Schon said. “It’s really hard to make this work.”
In the end, Iverson said, “Given all the failures and developments, this was about a 10-year process.”
This is a lengthy process that is critical to more accurately modeling temperate glacial ice and better predicting glacier flow and sea level rise, the researchers say.
Popular photo on Unsplash by Vince Gx
Read the full article at SciTechDaily
