NSFGEO-NERC: Two-phase dynamics of temperate ice

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences


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.

Planned Impact

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/).


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Haseloff M (2019) Englacial Pore Water Localizes Shear in Temperate Ice Stream Margins in Journal of Geophysical Research: Earth Surface

Description We have developed theory and models of temperate ice in ice stream margins. These models show that englacial viscous dissipation can cause melting and that that melt can drain to the bed as a substantial flux. Water retained in the pores of the temperate ice can reduce the shear viscosity of the margins, leading to sharp localisation of shear there. This helps to explain observations of very sharp margins of Antarctic ice streams. The model predictions are sensitive to two poorly constrained material parameters of temperate ice: its permeability and viscosity as a function of pore-water content.
Exploitation Route We are following up with a meso-scale, pseudo-3D model of ice stream margins that will incorporate our findings from the first publication. These calculations will help to better contextualise the physics of the margin and hence help to devise parameterisations that can be injected into large-scale ice sheet models. These calculations are now being written up into a manuscript. This progress has been severely delayed by COVID-related workload and caring responsibilities by the former PDRA, Marianne Haseloff.
Sectors Environment

Title Data supporting 'Complex motion of Greenland Ice Sheet outlet glaciers with basal temperate ice' 
Description Data in support of the article 'Complex motion of Greenland Ice Sheet outlet glaciers with basal temperate ice'. This includes final model outputs from finite-element modelling in ParaView .vtu format, Elmer/Ice solver input files (.sif format) and user solver files in Fortran 90, and some workflow scripts. For full description of data collection and processing methods please see the associated paper. Contents: ~/run_outputs/ contains subdirectories for each of RESPONDER, S5, and SAFIRE sites, which are then named in accordance with table S1 in the associated paper. ~/scripts/boundary_conditions/ contains scripts to extract boundary information from .vtu files in a .xyz text files (edge_extractor_shift_v3.m and surface_extractor_shift_v2.m). This is done as the free surface runs use cuboid mesh elements whereas thermomechanical runs use METIS generated meshes. See associated paper for full information. ~/scripts/DEMs/ contains scripts to generate geostatistical topography (Conditional_simulations_Sermeq.ipynb) and manipulate data for inclusion in Elmer/Ice model runs (DEM_taper_gauss_from_matv_detrendv3-0.py and npy_to_xyz_simple.m). ~/sifs/ contains user solver files to calculate basal sliding under the relationship of Helanow et al. (2021) and basal melting (USF_Sliding.F90 and USF_basal_melt.F90 respectively), mesh generation script for Gmsh and example mesh (8k_4k_lc25.geo and 8k_4k_lc25.msh respectively), DummySolver.F90 to be used when obtaining outputs from Elmer but with not solver specified, enth_output.sif to simply obtain the enthalpy field from specified parameters without conducting a full model run, and NS_b_variable_output.sif to obtain other specified variables without a full model run. NS_a.sif is the first .sif for generating results and is used to give FS.sif (free surface runs) a sensible initial velocity field. NS_b.sif is for the final thermomechanical run calculating temperate ice variation and with a fixed surface. As above, see associated paper for further details. references: 1. C. Helanow, N. R. Iverson, J. B. Woodard, L. K. Zoet, A slip law for hard-bedded glaciers derived from observed bed topography. Sci. Adv. 7, eabe7798 (2021). 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/345186
Description NSF/NERC collaboration partnership 
Organisation National Science Foundation (NSF)
Country United States 
Sector Public 
PI Contribution This is a NSF/NERC partnership grant. The NSF side of the award was granted to Prof. Neal Iverson (Iowa State University) and Prof. Luke Zoet (University of Minnesota). The Oxford team is contributing the modelling research while the US team is contributing the laboratory experiments.
Collaborator Contribution They are conducting large-scale ring-shear experiments on temperate ice to measure the influence of inter granular water content on ice viscosity.
Impact None yet.
Start Year 2017