Ephemeral grounding as a signal of ice-shelf change
Abstract:Interferometric synthetic aperture radar (InSAR) observations of iceshelf tidal deformation reveal the wide transition between grounded and floating ice as well as local areas where the ice shelf is only grounded at low tide, a condition that we call ephemeralgrounding. Ephemeralgrounding creates a subtle, localdisturbance on the vertical motion field of the ice-shelf surface in response to changes in oceanic tide which is detected with millimetric precision using InSAR. These ice-shelf features are, however, not expected to produce a noticeable disturbance on the ice-shelf velocity field. To illustrate the influence of ephemeral grounding on ice-shelf creep flow, we use a finite-element modelin which ephemeralgrounding is incorporated through a variable basalfriction coefficient. The results show that while ice rises (permanently grounded areas) have a pronounced influence on the ice-shelf velocity field, areas of ephemeral grounding have a vanishingly small influence. What is thus of most interest is the capacity for observations of ephemeral grounding to reveal subtle changes in ice-shelf thickness over time. We discuss an example in the Thwaites Glacier area, West Antarctica, where multi-year data show how ice rises become ephemeralgrounding and subsequently disappear. This result is consistent with the grounding-line retreat and ice thinning of Thwaites Glacier.
Document Type: Research Article
Publication date: January 1, 2001
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