Jeremy N. Bassis
Photo Mosaic showing the `Loose Tooth' rift system.
Photograph taken from a helicopter over a large crack in the Amery Ice Shelf, East Antarctica. Photo by Jim Behrens.
Current position:
Assistant Professor
Geological Sciences
University of Michigan
Former position at University of Chicago:
Postdoctoral Researcher
Email: jbassis at umich.edu
CV (dated Spring, 2009) (pdf)
Research interests:
The broad theme of my research is studying the often complicated array of dynamic processes that affect the evolution of ice sheets and glaciers and how they interact with and respond to past, present and future climate change. Although broadly trained as a geophysicist, my primary interests are problems in fluid and elastic mechanics. I enjoy working on complex problems that involve untangling a number of interdependent processes - especially how ice sheets and glaciers interact with the ocean and atmosphere. My approach to solving problems is to attack them from a variety of viewpoints, formulating numerical and theoretical models and testing predictions against observations. Ideally models are constructed using a first principals approach, but the complexity of processes involved usually renders such a direct approach infeasible. In these cases, I like to apply tools from dimensional analysis to look for scaling laws, often developed and tested directly using observations. One of the ice sheet processes on which I have focused is the mechanics of iceberg calving from ice shelves and marine terminating glaciers, a process that accounts for up to two thirds of the mass discharged from the cryosphere to the ocean. Not only does this have important implications for century time-scale sea level rise, but because fractures can propagate very quickly, iceberg calving introduces a “fast” time-scale into the response of the ice sheets to climate change that is not accounted for in numerical models. Studying iceberg calving is challenging because calving is a richly dynamic process with a wide variety of spatio-temporal scales.
Iceberg calving and ice shelf rift propagation (previously funded by NSF, now funded by NASA): Rifts, large fractures that penetrate the entire ice thickness, are precursors to iceberg calving events. These fractures can extend up to hundreds of kilometers and propagate for decades before becoming the detachment boundary of icebergs. Little is known about the forces and mechanisms that lead to rift initiation and propagation and hence iceberg calving, because we have very few measurements against which hypotheses can be tested. A fundamental question that needs to be addressed to develop models of iceberg calving is what forces are the primary drivers of rift propagation, e.g., what role do atmospheric winds, oceanographic tides or storm induced ocean swell play in driving rift propagation rates. To address this, I’ve been working with an international team of scientists to deploy global positioning system receivers (GPS) and seismometers around the tip of a propagating rift on the Amery Ice Shelf, East Antarctica. By comparing the timing of the bursts of rift propagation, deduced from sudden rift widening measured with our GPS coincident with swarms of seismicity detected with our seismometers, with winds from automatic weather stations and tides measured by our GPS along with other proxy data I showed that the timing of the bursts of propagation did not correspond to any extreme environmental effects. Order-of-magnitude calculations, combined with satellite observations of rift propagation rates provide further confidence in this result and indicate the magnitude of most environmental stresses is small compared to that the internal glaciologic stress. We are now funded by NASA to extend this study to use satellite images (MODIS and MISR) to measure rift propagation rates for dozens of rifts on 5 different ice shelves. The goals of this study are to (i) determine what differences (if any) exist between different rifts on different ice shelves; (ii) if differences do exist, determine what variables control rift propagation rates (e.g., are differences related to atmospheric oceanic temperatures or due to the internal stress within the ice); (iii) compare measured rift propagation rates with linear elastic fracture mechanics derived propagation rates; (iv) incorporate rift propagation into an ice shelf model and predict how calving rates for different ice shelves will vary under different climate forcings. Depending on our success in predicting rift propagation rates and iceberg calving rates, our parameterization of rift propagation rates will be incorporated into the community ice sheet model (developed by our colleagues at the Los Alamos National Laboratory).
New approximations for the large-scale flow of ice sheets: Consensus is emerging that to explain the full range of ice sheet behavior, we require an approximation to the equations of ice sheet motion that includes ice-stream like behavior near the ice sheet margins and ice-sheet like behavior in the interior. One approach that is being pursued by the larger ice sheet modeling community is to solve the fully three-dimensional higher-order or full Stokes models. However, this approach is not feasible for model runs over tens to hundreds of thousands of years, especially if we wish to couple the ice sheet model to a climate model to study paleo-climate and paleo-ice sheet configurations. Unlike traditional, higher-order models that explicitly solve for all stress components (at great computational cost), this model is based on the assumption that the vertical velocity profile varies weakly in comparison to variations in basal sliding, thus reducing the governing equation to a (nonlinear) partial differential equation. The key prediction of this formulation is that rapid-flow features like ice streams are “boundary layers” embedded within the more slowly moving vertical shear dominant ice sheet domain. With this approximation, we can begin to model abrupt ice sheet changes, such as Heinrich evets. We are on the verge of submitting a paper detailing our approximation to the Journal of Glaciology.
Fingerprinting glacigenic seismicity (funded by NSF): We were recently funded by NSF in collaboration with colleagues at the USG, Scripps Institution of Oceanography and Northwestern University to re-analyze historic seismic, infrasound and hydroaccoustic signals with glacigenic sources. The goal is to see if we can (i) identify the source of the signal based on the waveforms and moment tensor inversions and (ii) determine if we can detect any change in iceberg or ice fracture related seismicity.
Meltpond formation and drainage on Greenland: I am collaborating the Dr. Doug MacAyeal (University of Chicago) and Mac Cathles (a graduate student at the University of Chicago) to develop energy balance models of the thermodynamic processes that lead to the creation and subsequent drainage of large surface lakes on the Greenland Ice Sheet. These not only contribute to the mass balance of the ice sheet, we now know that these lakes also have the potential to drain through more than one kilometer of ice where it lubricates the bed, causing an increase in the sea-ward discharge of the ice sheet.
Publications:
Bassis, J.N. and J.V. Johnson, in preparation, Particle approximations for ice sheet modeling: Mass and momentum conservation, Journal of Geophysical Research-Earth Surfaces
Bassis, J.N. and D.R. MacAyeal, in preparation, Hamilton’s Principle Applied to Ice Sheet Dynamics: New approximations for the large-scale flow of ice sheets, Journal of Glaciology
Bassis, J.N., H.A. Fricker, J.B. Minster, submitted, A Dynamic Stability Criterion for Calving Glaciers, Geophysical Research Letters
Bassis, J.N., The Physics of Ice Sheets, (2008), special International Polar Year edition of Physics Education, 43(4), 375-382.
MacAyeal, D.R., E. Okal, R. Aster, J.N. Bassis, accepted, Seismic and Hydro-Acoustic Tremor Generated by Colliding Icebergs, Journal of Geophysical Research
Bassis, J.N., H.A. Fricker. R. Coleman, Y. Bock, J. Behrens, D. Darnell, M. Okal, J.B Minster, (2008), An Investigation Into the Forces that Drive Ice Shelf Rift Propagation, Journal of Glaciology. 184(54), 17-27. Chosen to be highlighted
Bassis, J.N., H.A. Fricker, J.B, (2007), Seismicity and Deformation Associated with Ice Shelf Rift Propagation, , Journal of Glaciology, 183(53), 523-536. Chosen to be highlighted
Jansen, V., Coleman, R., J.N. Bassis, in press, GPS-derived Strain Rates on an Active Ice Shelf Rift, Survey Review
MacAyeal, D.R., E. Okal, J.N. Bassis, et al., (2006), Transoceanic wave propagation links iceberg calving margins of Antarctica with storms in Tropics and Northern Hemisphere, Geophysical Research Letters 33, doi:10.1029/2006GL027235
Fricker, H.A., N. W. Young, R. Coleman, J. N. Bassis, J.B. Minster (2005), Multi-year monitoring of rift propagation on the Amery Ice Shelf, East Antarctica, Geophysical Research Letters., 32, L02502, doi:10.1029/2004GL021036.
Bassis, J. N., R. Coleman, H. A. Fricker, J. B. Minster (2005), Episodic propagation of a rift on the Amery Ice Shelf, East Antarctica, Geophysical Research Letters, 32, L06502, doi:10.1029/2004GL022048.
Fricker H. A., J.N. Bassis, J.B. Minster, D. R. MacAyeal (2005), ICESat's new perspective on ice shelf rifts: The vertical dimension, Geophysical Reseach Letters, 32, L23S08, doi:10.1029/2005GL025070.
Martinez, M., H. Harder, T.A. Kovacs, J.B. Simpas, J.N. Bassis, et al., (2003) OH and HO2 concentrations, sources, and loss rates during the Southern Oxidants Study in Nashville, Tennessee, summer 1999, Journal of Geophysical Research, 108 (D19), 4617, doi:10.1029/2003JD003551.
