Postdoc opportunity in ice-ocean interaction (modeling) Fall 2019

The Geophysical Institute of the University of Alaska Fairbanks is seeking a Postdoc for the NSF project "Understanding the controls on spatial and temporal variability in ice discharge using a Greenland-wide ice sheet model". The overall goal of this project is to develop novel parametrizations of ice-ocean interaction that are suitable for large scale ice-sheet modeling. The interdisciplinary project is co-led by Andy Aschwanden (UAF; ice sheet modeling) and Patrick Heimbach (U Texas at Austin, ocean modeling) and comprises two Postdoc positions, one focussing on the ocean side (see separate announcement) and the other on the ice sheet side (this posting). The student here at UAF will implement and test parameterizations within the framework of the Parallel Ice Sheet Model (PISM) but will closely collaborate with U Texas, including mutual visits.

We seek motivated candidates with a PhD in geosciences, physics, mathematics, engineering or related fields. Basic experience in numerical modeling, good oral and written communication skills are a prerequisite.

For more information, please contact Andy Aschwanden (aaschwanden@alaska.edu).

Project description

Over the past decades, the Greenland Ice Sheet (GrIS) has been delivering fresh water in solid and liquid form to the subpolar North Atlantic at an accelerating rate, thereby raising global mean sea level. This acceleration is thought to be triggered by large-scale circulation changes in both the atmosphere and ocean, yet their individual contributions are not well constrained. Ice discharge to the ocean mainly occurs through Greenland's 200+ outlet glaciers, fast-flowing (>200 m/yr) topographically-controlled features terminating in narrow fjords. Improving our understanding of the controls on outlet glacier system dynamics is essential to improve projections of 21st century GrIS ice discharge.

Interaction between ice and ocean in fjords is complex and highly variable in space and time. Four possible controls on outlet glacier systems dynamics have been identified: (1) Warming subsurface ocean water and/or increased subglacial runoff may increase submarine ice melting. (2) Rigid sea ice and ice melange (a mixture of sea ice and ice bergs) can suppress calving, allowing for terminus advance. (3) The terminus position relative to subglacial topography (e.g., overdeepenings or sills) influences rates of retreat. (4) Changes in the resistive stress caused by contact with the fjord walls and/or glacier bed can lead to terminus advance, retreat, and/or thinning.

Previous simulation efforts have been limited by the insufficient resolution of models and observational data, which prevented whole-ice sheet simulations to faithfully capture outlet glacier flow. Results to date are either obtained from regional models or from highly idealized flow line models that were upscaled to ice-sheet scale. Recent advances in ice sheet modeling, and the availability of high-resolution subglacial topography, now allow to resolve individual outlet glacier flow in ice sheet-wide simulations. This proposal will use the framework of the open-source Parallel Ice Sheet Model (PISM), uni-directionally coupled to new high-resolution hindcasts of the atmosphere and ocean. Within this framework, the researchers will develop and apply novel parameterizations of ice-ocean interaction, including fjord and drainage basin transfer functions, suitable for continental-scale ice sheet modeling, to provide a test bed for the following research questions: On a glacier-by-glacier basis, (1) what is the relative present-day contribution of the four controls to outlet glacier flow, and thus ice discharge; (2) what is the potential for a substantial increase in 21st century ice discharge; (3) what conditions would precipitate large changes (e.g., spatio-temporal distribution of ocean warming, enhanced surface runoff); and (4) what observations are required in support of a Greenland Ice Sheet Ocean Observing System to capturing the forcing or onset of large changes?

Available remotely-sensed and in-situ observations, including, but not limited to, time-series of surface velocities, surface elevation and mass changes will serve as metrics of success. Simulations of the 21st century evolution of the GrIS will then be performed, based on available atmosphere-ocean scenario calculations, to provide the most realistic estimates of ice discharge. A highly efficient ice sheet model allows the exploration of many scenarios and will result in a better assessment of forecasting accuracy of ice discharge on the centennial time scale.

For questions, please contact Andy Aschwanden at aaschwanden@alaska.edu.