NSFGEO-NERC: Two-phase dynamics of temperate ice

Discharge of ice from the Antarctic Ice Sheet is dominated by ice-stream flow, but there is no consensus as to what controls the onset and geometry of ice streams or their evolution. Diverse observations clearly indicate the importance of water in affecting flow resistance, both within the icestream margins and at the bed. However, ice-stream models do not yet account for the necessary feedbacks among temperature, water content, and ice deformation to resolve and interrogate these processes. Specific observations highlight processes and knowledge gaps: (i) the basal hydrology of ice streams is responsible for low basal shear stresses that focus stress and strain at ice-stream margins; (ii) strain heating within ice-stream shear margins raises the temperature of the ice to the pressure melting point, causing internal dissipative melting and helping to control the distribution of temperate ice; (iii) interstitial water in ice-stream margins may significantly soften the ice, with poorly known dynamical consequences; (iv) the dependence of ice rheology on water content is itself poorly constrained; (v) the multiphase dynamics of temperate ice, including permeability and drainage rates within ice sheets, are not known; (vi) routing of meltwater to and at the bed is a primary control on ice speed. Without models that address these processes, predictions of the ice sheet's mass balance and sea-level contribution will inevitably be speculative, with incomplete physical grounding.

This study will target the dynamics of temperate ice, with the overarching goal of determining its effect on ice streaming. The project will have two components that reinforce each other: laboratory experiments in which an existing rotary device at Iowa State University will be used to study the effect of water content on the rheology and permeability of temperate ice; and development at Oxford University of a two-phase, thermo-mechanical theory for temperate ice flow-with water production, storage, and routing-that will serve at the basis for fully dynamic and multidimensional models of ice-stream motion. Results of the experiments will guide the constitutive rules and parameter ranges considered in the theory, and application of elements of the theory will improve interpretations of the experimental results. The theory and resultant models will predict the coupled distributions of temperate ice, water, stress, deformation, and basal slip that control the evolution of ice-stream speed and geometry.

This project could benefit society by contributing to efforts by the broader scientific community to assess future sea-level rise and its associated economic and environmental consequences. A laboratory apparatus to be used in this project-built with an NSF MRI grant and open to users outside Iowa State University-will be modified to allow the study of ice rheology, thereby increasing infrastructure for glaciology. Two postdoctoral researchers will be supported, trained, and mentored for academic careers (see mentoring plans), and three undergraduates, who will serve as research assistants in the experimental and modeling efforts, will be introduced to research in the geosciences. The UK PIs will use their links in the Oxford Climate Research Network and Met Office Academic Partnership to promote the research to a wide audience, and the post-docs will develop interactive material for use in existing outreach programs (e.g., http://www.oxfordsparks.net/).