Periodic Reporting for period 1 - NEMOSID (Next-generation Modeling of Sedimentary Ice-sheet Dynamics)
Période du rapport: 2020-07-01 au 2022-06-30
The ice sheets in Antarctica and Greenland contribute to the global sea level, but their contribution to future sea-level trends are highly uncertain.
The uncertainty comes from limitations in observational data coverage, lack of complete understanding of some glacial processes, and simplifications and approximations used in the computational tools we use today for projecting ice flow in the coming centuries. The NEMOSID project focused on one of the missing processes: fast ice movement occurs on deformable sediments. From the geological record, ice-driven sediment transport can dramatically change the Earth's surface on parts covered by ice during past glaciations. Some of the key objectives of the NEMOSID project were: 1) What controls the amount of transported sediment by ice flow? 2) How can we include sediment transport in ice-sheet models? 3) What are the effects of sediment transport on ice-sheet sensitivity to sea-level rise?
The uncertainty comes from limitations in observational data coverage, lack of complete understanding of some glacial processes, and simplifications and approximations used in the computational tools we use today for projecting ice flow in the coming centuries. The NEMOSID project focused on one of the missing processes: fast ice movement occurs on deformable sediments. From the geological record, ice-driven sediment transport can dramatically change the Earth's surface on parts covered by ice during past glaciations. Some of the key objectives of the NEMOSID project were: 1) What controls the amount of transported sediment by ice flow? 2) How can we include sediment transport in ice-sheet models? 3) What are the effects of sediment transport on ice-sheet sensitivity to sea-level rise?
In the NEMOSID project, I first looked at the physics community's state-of-the-art models for granular mechanics. These mechanical models were promising, as they reconcile observations with physical behavior deemed realistic for general sediment mechanics. However, the models were untested and uncalibrated for glacial sediments. The next task consisted of collecting glacial sediment in the field and performing rigorous laboratory studies where specialized geotechnical equipment deformed the sediment under conditions similar to those in glacial environments. I used the laboratory results to tweak the granular mechanics model. In the process, I discovered that changes in water pressure are, by far, the most critical factor controlling the magnitude of sediment transport. This realization implies that daily glacier melt and tidal oscillations may be the primary governers of how glacial landforms emerge. Next, I put the calibrated granular mechanics model into a popular ice-sheet model called PISM (Parallel Ice Sheet Model). Climate modelers worldwide use PISM to understand past glaciations and predict the future of the Antarctic and Greenland ice sheets in a warming climate. This task required diving deep into the source code of PISM to understand its internals and then figure out how to bolt my model into it. I found two solutions and published them in open repositories so that other ice-sheet modelers can benefit from the advance. The advance in PISM means that we can now simulate how glaciers reshape their beds and test the influence of this process on sea-level rise. I modeled various glacial settings and found that sediment transport results in glacial landforms, as seen in the geological record from past glaciations. Additionally, the formation of sedimentary landforms can conditionally stabilize ice sheets against sea level rise.
The methodological advances developed in the NEMOSID allow ice-sheet modelers worldwide to include a process that we previously thought may be important but did not know how to model realistically. The new development is easy for others to use. The socio-economic consequences of the NEMOSID project are that future sea-level rise predictions can be made more precise, benefiting all countries and people living in areas close to the present sea level.