The University of British Columbia

About my work

I am a mathematical / physical glaciologist whose main interest is the dynamics of ice sheets, such as those found in Antarctica and Greenland. My work focuses on fundamental aspects of ice sheet dynamics. Some of the questions that motivate my work are: what drove the retreat of the West Antarctic Ice Sheet following the Last Glacial Maximum? How can large ice sheets such as the Laurentide disintegrate as quickly as they are known to have done? What caused the massive discharges of sediment-laden ice known as Heinrich events? What is the likely future behaviour of West Antarctica and Greenland?

In order to answer these questions, the flow behaviour of ice sheets must be understood. Ice sheets accumulate snow in their interior where surface elevations are high. They lose mass at their margins, either through melting or through calving. Ice is transported between these regions by ice flow, and generally, the faster the rate of flow, the greater the rate of mass loss. Much of my work has concentrated on processes that can speed up ice flow and can potentially contribute to the rapid and irreversible disintegration of ice sheets. My main contributions to date have been in ice stream and marine ice sheet dynamics, and in the role of meltwater drainage in speeding up ice sheet flow.

A word about mathematics...

Some of the methods I use are mathematical. In the mathematical sphere, I have a particular interest in partial differential equations, free boundary problems, applied complex analysis, nonlinear dynamics, perturbation methods and scientific computing, and in fluid dynamics in general.

A word about field work...

I also conduct field work on glacier dynamics, with the aim of understanding processes that affect ice sheets by observing them in the logistically simpler setting of a mountain glacier. In collaboriation with Gwenn Flowers at Simon Fraser University I have been developing a project in the St Elias Mountains, Yukon Territory, aimed at understanding the dynamics of a small valley glacier.

Prospective graduate and undergraduate research students

I currently have three graduate students and one co-advised postdoc, which is about the right group size for my mode of working. However, I may consider new graduate students or postdocs who are interested in a field-based component or a theoretical project. I will post any openings I have for undergraduate assistans.

The Canadian funding system makes supporting graduate students financially difficult, so external funding through NSERC or similar sources is a bonus. Note that NSERC funding applications for graduate studies are ideally submitted in October of your last year as an undergraduate (you have to be Canadian or a permanent resident to qualify for most NSERC programs). In addition, there are internal scholarships at UBC; these are awarded competitively so a strong performance in your most recent degree is essential, as is an early application to the EOS graduate program (for a scholarship application to get full consideration, your application to EOS usually has to be complete with references by mid-February).

That said, the most important qualities I look for in a graduate student are inquisitiveness, a willingness to explore (and therefore to admit that there is something still to be learnt!) and initiative (e.g., can you come up with a research idea of your own? Find something out about the field you want to study? Or maybe fix a propane-powered pump on a glacier with whatever tools and spare parts are on hand?).

For the theoretical side, strong mathematics and physics skills are also essential. My publications page gives a good impression of the type of work you may find yourself involved in if you are interested in taking that route, and supervision through the Institute of Applied Mathematics is possible.

For the fieldwork-oriented side of my work, engineering skills and experience with instrumentation are ideal, as is a willingness to spend weeks camping in a cold and wet place while never getting to climb any of the surrounding peaks. Basic outdoor and mountaineering skills (glacier travel, backcountry travel) are also very useful, but bear in mind that we don't go into the field in order to climb! And above all, common sense is a great asset in the field.

Marine ice sheet dynamics

The Western half of Antarctica contains enough ice to raise sea levels by about 6 m. It also rests on bedrock below sea level, which leaves it vulnerable to irreversible shrinkage if the rate of ice flow from the grounded ice sheet into the surrounding ice shelves were to increase, causing partial flotation and hence retreat of the grounded ice sheet. A hotly debated hypothesis in glaciology asserts that a marine ice sheet is susceptible to such irreversible shrinkage if its grounding line rests on an upward-sloping bed, because a small retreat in grounding line position should lead to increased discharge, which leads to further retreat and so on.

The key to this hypothetical positive feedback is that discharge through the grounding line - where grounded ice lifts off the bed to become an ice shelf - must increase with water depth there. The assertion that this is the case has been around for over thirty years, but has not previously been proven. In two theoretical papers (Marine ice sheet dynamics. Part 1: the case of rapid sliding, Marine ice sheet dynamics. Part 2: a Stokes flow contact problem), I have been able to use boundary layer theory to show that the positive feedback does indeed exist. My third paper on the subject (Ice sheet grounding line dynamics: steady states, stability and hysteresis) explores the implications of this for large-scale ice sheet dynamics, and demonstrates that the behaviour of West Antarctica can be understood in simple terms as a hysteresis loop driven for instance by sea level changes, providing a teleconnection to ice sheets in the Northern Hemisphere: a transition to a large ice sheet in West Antarctica occurs when sea levels drop below a critical level, while the reverse transition occurs when they rise again beyond a second critical level that is higher than the first. Such variations in sea level can of course be driven by the growth and shrinkage of the Laurentide or Fennoscandian ice sheets.

The main outstanding issues in marine ice sheet dynamics are to understand the effect of lateral confinement of ice shelves on the dynamics of the grounding line, and to incorporate ice stream dynamics (see below) into the picture. The activation of ice streams could cause a marine ice sheet to destabilize. Conversely, a marine ice sheet can potentially be stabilized if it is fringed by a confined ice shelf, as is the case in West Antarctica. Recent work (Grounding line movement and ice shelf buttressing in marine ice sheets) shows that the precise geometry of the shelf becomes important if stabilization is to occur. In order to understand the evolution of ice shelf geometry through calving and basal melting, a better understanding of ice shelf-ocean interactions and of fracturing processes will be required. Recent observations of ocean warming and ice shelf collapse around Antarctica make this a topic of pressing concern.

MISMIP

Richard Hindmarsh, Frank Pattyn and I have devised an intercomparison exercise aimed at exploiting recent advances in marine ice sheet modelling. The project has now been launched. Full details can be found on the MISMIP website.

Ice stream dynamics and glacier sliding

Ice streams are the main arteries through which ice can flow rapidly in an ice sheet. They are narrow bands of rapidly flowing ice in an ice sheet whose high velocities are caused by sliding at the bed, and this sliding motion is often unsteady on a wide range of timescales, to the extent that ice streams can shut down completely and subsequently re-activate. Much of the physics driving ice stream flow is poorly understood.

My work has focused on

• using first-principles physics to derive friction parameterizations (e.g. The effect of cavitation on glacier sliding, Bed topography and surges in ice streams)
• incorporating modern understanding of sliding into large-scale ice sheet models (A variational appraoch to ice-stream flow, Variational methods for glacier flow over plastic beds)
• Higher order glacier flow models as means of representing fast and slow sliding in a single mathematical description (Thin film flows with wall slip: an asymptotic analysis of higher order glacier flow models,Coulomb friction and other sliding laws in a higher order glacier flow model)
• improving models of subglacial meltwater drainage, and relating these to temporal changes in ice stream geometry and flow velocities (Drainage through subglacial water sheets, Ice sheet acceleartion driven by melt supply variability)
• Understanding the thermomechanics of ice stream shear margins, and tracking them as an internal free boundary in ice sheets (On the mechanics of ice-stream shear margins)

The ultimate goal of this work is to explain the spatial patterning and likely oscillatory behaviour of ice streams, and to incorporate ice stream physics into predictive ice sheet models. I also have an observational angle to my work on subglacial sliding and glacier hydrology: our field program is providing data for testing of some of our theoretical work.