Greenland Ice Sheet “Sliding” a Small Contributor to Future Sea-Level Rise
Modeling experiments assess impacts of key melting behavior.
The Science
A warming climate is expected to melt large portions of the Greenland and Antarctic ice sheets, contributing to sea-level rise. However, since the behavior of melting ice sheets is poorly known, estimating how soon major changes will occur is difficult. To help predict these impacts, a team of researchers have used a series of modeling experiments to gain insights into a key factor in ice sheet melting.
The Impact
Important behaviors in the Greenland ice sheet include surface melting; iceberg break-off around the edges; and enhanced sliding as meltwater slips through cracks to the bedrock, lubricating ice sheet slippage into the sea. The third behavior, lubrication, was carefully estimated in a study by scientists from several institutions, including Department of Energy researchers from Los Alamos National Laboratory. These experiments predict that by 2200, increases in the ice sheet’s contribution to sea-level rise from basal lubrication will be no more than 5% of the contribution from surface mass budget forcing alone.
Summary
A wide range of observations suggests that water generated by melt at the ice sheet surface reaches the bed by both fracture and drainage through moulins (roughly circular, vertical to nearly vertical well-like shafts within a glacier through which water enters from the surface). However, these observations are insufficient to determine whether the water enhances ice flow. The research team performed a modeling analysis, varying flow formulations to find two contrasting possibilities: continuously increasing or bounded changes in lubrication and glacier speed with increased meltwater input. These contrasting scenarios were applied to four sophisticated ice sheet models in a series of experiments for a warmer future scenario, forced by likely changes in ice sheet surface mass, lubrication, and a combination of these. The team determined that additional sea-level rise resulting from lubrication is small (≤8 mm) in comparison with that from experiments forced only by changes in surface mass balance (~170 mm). Although changes in lubrication generate widespread effects on ice sheet flow and form, they do not substantially affect net mass loss.
Contact
Sarah R. Shannon
Department of Geographical Science, University of Bristol, Bristol BS8 1SS, UK
sarah.shannon@bristol.ac.uk
Funding
This research was funded by the European Commission’s Seventh Framework Programme through grant 226375 (ice2sea manuscript no. 121). Elmer/Ice simulations were performed using high-performance computing resources from Grand Équipement National de Calcul Intensif – Centre Informatique National de l’Enseignement Supérieur (grant /2011016066/) and from the Service Commun de Calcul Intensif de l’Observatoire de Grenoble. Additional supported provided by (1) the U.S. Department of Energy
(DOE) Office of Science, Advanced Scientific Computing Research and Biological and Environmental Research programs and (2) the Center for Remote Sensing of Ice Sheets at the University of Kansas through U.S. National Science Foundation grant ANT-0424589. Simulations were conducted at the National Energy Research Scientific Computing Center (supported by DOE’s Office of Science under contract DE-AC02-05CH11231) and at Oak Ridge National Laboratory (supported by DOE’s Office of Science under contract DE-AC05-00OR22725). The Community Ice Sheet Model (CISM) version 2.0 development and simulations relied on additional support by K. J. Evans, P. H. Worley, and J. A. Nichols (all of Oak Ridge National Laboratory) and by A. G. Salinger (Sandia National Laboratories).
Publications
Shannon, S. R., et al. “Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise,” Proc. Natl. Acad. Sci. USA 110 (35), 14156–161 (2013). [DOI: 10.1073/pnas.1212647110].
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