Opportunities

Research Opportunities

PhD opportunity in ice-atmosphere interaction (modeling)

The Geophysical Institute of the University of Alaska Fairbanks is seeking a PhD student for the recently funded NSF project "Feedbacks between Orographic Precipitation and Ice Dynamics". The overall goal of this project is to study the interaction between ice flow, orographic precipitation and, to some degree, landscape evolution. The interdisciplinary project is co-led by Andy Aschwanden (UAF), Erin Pettit (UAF) and G. Roe (UW).
We seek motivated candidates with a degree (preferably a M.Sc. or equivalent) 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) or Erin Pettit (ecpettit@alaska.edu).

Project description

The interactions between prevailing winds and mountain topography give rise to order-of-magnitude variations in precipitation and create the strongest climatic gradients on Earth. For mountain ranges in which ice overtops the bedrock to form ice sheets (such that ice dynamics controls the position of the topographic divide), these orographically driven feedbacks between precipitation and surface topography occur on timescales much shorter than for normal mountain building. For meso-scale ice sheets (100's km) the ice-dynamic response time may be of the same order of magnitude as climate change (hundreds to thousands of years) resulting in rapid feedback adjustment. The Antarctic Peninsula is an archetype of these feedbacks. It is aligned perpendicular to the prevailing winds and precipitation ranges from as high as 10 m/yr on the wet side of the mountain range to 10 cm/yr on dry side over less than 50 km. Despite the low snowfall on the dry side, the northern Antarctic Peninsula hosts large trunk glaciers like Crane, Flask and Leppard.

We hypothesize that the feedbacks between orographic precipitation, ice dynamics, and thermodynamics drive asymmetry in the topography and behavior of the ice sheet. On longer timescales, these feedbacks also include glacial erosion and uplift. In particular, we suggest that several aspects of the behavior of the northern Antarctic Peninsula ice sheet are important to understand within the context of these feedbacks, including, but not limited to: (1) the asymmetric response of the ice sheet to sudden change in backstress due to the loss of an ice shelf (decadal to century timescale response); (2) the stability of peripheral ice domes as local topographic highs flanking a central large ice sheet (glacial-interglacial timescale response); and (3) development of large troughs due to the advance and retreat of large trunk glaciers on the dry side over multiple glacial cycles.

The PIs propose to use the framework of the Parallel Ice Sheet Model coupled with an orographic-precipitation model. By using idealized geometries as well as the geometry of the northern Antarctic Peninsula during the Last Glacial Maximum and today, we will explore the impact of these feedbacks on the evolution of ice-sheet geometry. We target the Antarctic Peninsula as the ideal case study, in the context of its rapid modern and future change as well as its deflation since the Last Glacial Maximum.

PhD opportunity in ice-ocean interaction (modeling)

The Geophysical Institute of the University of Alaska Fairbanks is seeking a PhD student for the recently funded 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 PhD 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 degree (preferably a M.Sc. or equivalent) 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.