Ice sheet modeling
Estimating current and future ice sheet contributions to sea level rise is a very active area of research, and despite recent advances in ice sheet modeling, key controlling aspects of ice dynamics, such as basal friction or ice hardness, are still poorly understood and poorly constrained. Ice sheet models will not be reliable unless we better understand these physical processes and include them in numerical models.
Data assimilation techniques such as inverse methods, that combine ice sheet modeling and surface observations, provide the tools to tackle these questions. We have used inverse methods to investigate the patterns of basal friction under grounded ice using surface velocities derived from Satellite interferometry (Morlighem et al. 2011). More recently, we have applied these techniques at the scale of Antarctica (Morlighem et al. 2013) and we discovered that basal sliding is widespread beneath the Antarctic Ice Sheet. This suggests that coastal perturbations may be transmitted further inland than expected.
Our group has co-founded the Ice Sheet System Model in partnership between UC Irvine and the NASA Jet Propulsion Laboratory. ISSM is a large scale, high-resolution, massively parallelized finite element model dedicated to ice sheet modeling and is our primary tool to address the science questions we are interested in.
International Thwaites Glacier Collaboration
The largest Earth science funding agencies in the United Kingdom and the United States are collaborating to investigate one of the most unstable glaciers in Antarctica: Thwaites Glacier. The International Thwaites Glacier Collaboration is the largest joint UK-US project undertaken on the southern continent in 70 years.
Thwaites Glacier, in West Antarctica, has been accelerating and widening over the past three decades. How fast Thwaites will disintegrate or how quickly it will find a new stable state have become some of the most important questions of the future of the West Antarctic Ice Sheet and its contribution to sea level rise over the next century and beyond. Our group is leading the project “PROcesses, drivers, Prediction: modeling the History and Evolution of Thwaites” (PROPHET)! We will work with Hilmar Gudmundsson (Univ. Northumbria), Daniel Goldberg (Univ. Edinburgh), Brent Minchew (MIT), Indrani Das (Lamont). We will rely on three independent numerical models of ice flow, coupled to an ocean circulation model to (1) improve our understanding of the interactions between the ice and the bedrock, (2) analyze how sensitive the glacier is to external changes, such as changes in ocean-induced melt under its floating extension or calving front position, (3) assess the processes that may lead to a collapse of Thwaites, and, most importantly, (4) forecast future ice loss of Thwaites. By providing predictions based on a suite of coupled ice-ocean models, PROPHET will also assess the uncertainty in model projections.
Warmer ocean waters trigger ice-front retreats of marine-terminating glaciers, and the corresponding loss in resistive stress leads to glacier acceleration and thinning. We have implemented a level-set based method to track moving boundaries within our ice sheet model. More work is needed to find a universal calving law, the holy grail of ice sheet modelers…
Bed topography inferred from mass conservation
We have devised a new method to infer the bed topography beneath the ice sheets at high resolution (150 m) based on the conservation of mass and optimization. The traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging. While this approach provides continuous and seamless maps of ice thickness, it generates products that are not consistent with ice flow dynamics and are impractical for high-resolution ice flow simulations. Recently, we mapped the entire coast of Greenland (Morlighem et al. 2014) and showed that glaciers flow down well-defined, deep topographic channels with deep narrow depressions within mountain block landscapes, suggesting that the ice sheet will be vulnerable to more rapid retreat in the coming century than previously thought.
We released in September 2017 an updated bed topography map of Greenland: BedMachine v3