Radio-echo sounding of Crary Ice Rise reveals abundant marine ice in former ice shelf rifts and basal crevasses
Abstract
Crary Ice Rise (CIR) is a grounded promontory within the Ross Ice Shelf that substantially resists ice shelf and ice stream flow, thereby increasing the buttressing effect of the ice shelf on the West Antarctic Ice Sheet. CIR is thought to have formed as the Ross Ice Shelf re-grounded on the seafloor ~1 kyr BP, but little is known about the processes by which the ice shelf became a grounded ice rise. We present data from ground-based ice-penetrating radar systems operated at 7 MHz and 750 MHz center frequencies, respectively, that shed light on the evolution of the ice rise and the state of the ice shelf at the time of grounding. Our data confirm that CIR is composed largely of former shelf ice, and they show for the first time that the ice shelf was highly fractured and deformed when it grounded. Numerous diffraction hyperbolae hundreds of meters above the bed overlie areas where the bed echo is absent, indicating that the ice rise contains large amounts of marine ice that accreted inside basal crevasses and rifts in the former shelf. The upper limit of marine ice deposition corresponds to a prominent internal reflection horizon, which we interpret to be the result of horizontal percolation of seawater that accessed permeable firn through basal crevasses and rifts. This layer lies sub-parallel to the surface on the deep southwest ridge of the ice rise, and it is absent on the shallow northeast ridge. The layer is strongly deformed in the central plain of CIR, likely due to the large stress gradients near the former grounding line. This area may be a former shear margin or rift zone — like those that surround the ice rise today — that was subsequently incorporated into the grounded ice rise. Marine ice deposited within basal crevasses and rifts may have strengthened the coupling between the ice shelf and the nascent grounded ice rise, and thus could have played a critical role in allowing CIR to grow laterally after the initial grounding event.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C52B..05H
- Keywords:
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- 0728 Ice shelves;
- CRYOSPHERE;
- 0774 Dynamics;
- CRYOSPHERE;
- 0776 Glaciology;
- CRYOSPHERE;
- 0798 Modeling;
- CRYOSPHERE