NSFGEO-NERC:Collaborative Research: A New Mechanistic Framework for Modeling Rift Processes in Antarctic Ice Shelves Validated through Improved Strain-rate and Seismic Observations

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Calving of tabular icebergs accounts for a significant fraction of ice mass loss from the Antarctic Ice Sheet. In addition to this direct mass loss, calving may further accelerate the seaward flow of grounded ice by reducing resistive stresses provided by ice shelves, the floating extensions of the ice sheet. Tabular icebergs are much longer and wider than they are thick and form when full-thickness fractures known as rifts intersect the edges of an ice shelf. The processes and drivers of ice-shelf rifting are neither well understood nor accurately represented in ice-flow models. As a result, it is not currently possible to predict when tabular icebergs may form, how large they will be, and how calving may evolve as the climate changes. This lack of predictive capability has two important consequences. First, it is not possible to confidently project rates of mass loss due to calving from floating shelves. Second, it is not possible to confidently project how tabular iceberg calving will influence the mass loss from the grounded ice sheet. This second consequence is a major source of uncertainty in projections of sea-level rise over human timescales.In this project, the team aims to improve understanding of tabular iceberg calving using a combination of detailed observations and a suite of increasingly sophisticated models to study the processes and drivers of rifting in ice shelves. The work will focus on a natural laboratory: the ice-shelf system formed by the Brunt Ice Shelf and Stancomb-Wills Glacier Tongue, East Antarctica, which has one of the longest and most detailed observational records in Antarctica. As of early 2020, two active rift systems are propagating across the Brunt Ice Shelf, one of which should soon form a large tabular iceberg. Thus, there is a rare opportunity to observe multiple active rifts. The project will take advantage of this situation by employing remote-sensing observations collected from a variety of spaceborne instruments to make detailed time-dependent measurements of velocity and strain-rate fields across the ice shelf and, notably, in the vicinity of the active rift tips. At these tips, stresses are expected to intensify due to the presence of the rift. The observations will inform a suite of ice-flow-and-fracture models that will be developed and used to better understand how rifts propagate and how best to represent rift propagation in large scale ice-flow models. The modeling objective follows a development path that aims to yield a community ice-flow model capable of simulating rift propagation, and that has been tested against observations. Seismic data already collected in the vicinity of an active rift will provide detailed knowledge of rifting processes and will complement the remote sensing observations and inform the modeling efforts. This combination of multi-faceted observations and models aims to illuminate the fundamental processes of ice-shelf rifting, thereby contributing to the knowledge necessary to make reliable projections of ice-sheet evolution and sea-level rise.This project is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) through the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own ivestigators and component of the work.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.