Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geography

First Advisor

Konrad Steffen

Second Advisor

Waleed Abdalati

Third Advisor

Mark Serreze

Fourth Advisor

Ted Scambos

Fifth Advisor

Harihar Rajaram

Abstract

Understanding ice shelf structure and processes is paramount to future predictions of sea level rise, as nearly 75% of the ice flux from the Antarctic Ice Sheet (AIS) passes through these gates. The breakup of an ice shelf removes the longitudinal back stress acting on the grounded inland ice and leads to flow acceleration, dynamic thinning and frontal retreat, processes that can be sustained for more than a decade. Increased ice discharge to the ocean contributes to global sea level rise. This dissertation investigates basal crevasses and suture zones, two key structural components of ice shelves, in order to understand how the structure of an ice shelf influences its stability in a warming climate. Ground penetrating radar, high-resolution satellite imagery and a variety of modeling approaches are utilized to assess these features on the Larsen C Ice Shelf but in a manner that considers their influence on ice shelf stability around the AIS. Basal crevasses are largescale (~66% of ice thickness and ten’s of km in length) and abundant features that are significant structural weaknesses. The viscoplastic deformation of the ice shelf in response to the perturbed hydrostatic balance leads to the formation of both surface depressions and crevasses, hence weakening the ice shelf further. Basal crevasses increase the local ice-ocean interface by ~30%, thereby increasing basal roughness and altering ice-ocean interactions. Ice-shelf fractures frequently terminate where they encounter suture zones, regions of material heterogeneity that form at the lateral bounds of meteoric inflows to ice shelves. The termination of a 25 km-long rift in the Churchill Peninsula suture zone is investigated and found to contain ~60 m of accreted marine ice. Steady-state basal melting/freezing rates are determined for the ice shelf and applied to a flowline model to examine the along-flow evolution of ice shelf structure. The thickening surface wedge of locally accumulated meteoric ice, which likely has limited lateral variation in its mechanical properties, accounts for ~60% of the total ice thickness near the calving front. This suggests that the material heterogeneities present in the lower ~40% of the ice column are responsible for resisting fracture propagation and thereby delaying tabular calving events. This represents a highly sensitive aspect of ice-shelf stability, as changes in the oceanic forcing may lead to the loss of this heterogeneity.

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