Glacier ice is composed of individual grains, or crystals. These grains can have different orientations, similar to how a pile of snow has many flakes all pointing in different directions. When ice accumulates as snowfall, the grains point in approximately random directions. However, as glaciers move, the orientation of the grains is changed, leading to characteristic "fabrics," where the grains tend to point in distinctive directions. Here, we try to understand how one could work backwards, from the orientation of the grains, to determine how the ice flowed in the past. We use an ice-flow model to understand whether instabilities in ice streams, "rivers" of fast flowing ice in Greenland and Antarctica, would be recorded in the fabric. We find that changes in ice-stream flow could indeed be seen in the fabric for thousands or tens of thousands of years, depending on the exact type of change. We then show that these changes to fabric are large enough that they could be measured in ice cores or with specialized ice-penetrating radars. This helps lay the groundwork for better understanding of long-term changes to ice flow, which is important but hard-to-measure context for modern ice-stream retreat.
Read more: Lilien, D. A., N. M. Rathmann, C. S. Hvidberg and D. Dahl-Jensen, 2021. Modeling ice-crystal fabric as a proxy for ice-stream stability. Journal of Geophysical Research: Earth Surface, 126, e2021JF006306, doi: 10.1029/2021JF006306
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