Ephemeral grounding as a signal of ice-shelf change

• Published in: Journal of Glaciology
• Main Authors: Schmeltz, Marjorie, Rignot, Eric, MacAyeal, Douglas R
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2001
• Subjects: Physical Geography and Environmental Geoscience; Meteorology & Atmospheric Sciences; Thwaites Glacier; West Antarctica; Antarc*; Antarctica; Ice Shelf; Journal of Glaciology
• Online Access: https://escholarship.org/uc/item/2q0462j8; https://escholarship.org/content/qt2q0462j8/qt2q0462j8.pdf; https://doi.org/10.3189/172756501781832502

Interferometric synthetic aperture radar (InSAR) observations of ice-shelf 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 ephemeral grounding. Ephemeral grounding creates a subtle, local disturbance on the vertical motion field of the ice-shelf surface in response to changes in occanic 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 model in which ephemeral grounding is incorporated through a variable basal friction 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 ephemeral grounding and subsequently disappear. This result is consistent with the grounding-line retreat and ice thinning of Thwaites Glacier.