Date of Award

Fall 12-2021

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Peter Koons

Second Committee Member

Gordon Hamilton

Third Committee Member

Chris Borstad

Additional Committee Members

Seth Campbell

Zoe Courville

Ellyn Enderlin

Eric Landis

Martin Truffer,

Abstract

As ice shelves are floating and lack resistive stress at their base, resistance to flow is accommodated along their lateral margins and various pinning points such as ice rises and nunataks. As such, ice shelf shear margins and their strength through time remain a critical control on ice shelf stability. Specifically, lateral shear zone destabilization is an important precursor to ice shelf collapse. In this thesis I utilize in-situ, remote sensing, and numerical modeling techniques in order to characterize the flow field and geometry of the western lateral margin of the Ross Ice Shelf as well as a region upstream of the grounding line. I first develop a method to investigate the kinematic drivers of crevasse initiation in the McMurdo Shear Zone, Antarctica through the delineation of crevasse features from ground penetrating radar observations and comparison with kinematic outputs derived from remotely-sensed ice surface velocities. I then use spatial patterns in crevasse attributes to make inferences on crevasse history and discuss implications on the current and future stability of the shear margin. Next, I estimate ice thickness within this shear margin from a combination of mid-frequency ground penetrating radar observations and Digital Elevation Models and assess the sensitivity of Ross Ice Shelf stress balance to uncertainties in ice thickness datasets within this region through numerical modeling techniques. My results suggest that previous modeling frameworks have overestimated the sensitivity of the region to melting. Finally, I perform a transient streamline analysis of a region of upstream grounded ice known as the Whillans and Ice Stream and characterize the short-term velocity fluctuations within its slowdown evolution using available remotely-sensed velocity datasets between 1997 and 2016. I incorporate these observations of velocity fluctuations as well as mass changes into a transient finite element modeling solution of ice flow. Through inversion techniques, I estimate annual changes in basal shear stress in order to force a 100-year transient model of ice slowdown for the Whillans Ice Stream and discuss the possible mechanisms that could be driving slowdown fluctuations on annual timescales such as lake drainage events, basal freeze-on and till weakening mechanisms, as well as changes to downstream boundary conditions.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share