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Ice-sheet model

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In climate modelling, Ice-sheet models use numerical methods to simulate the evolution, dynamics and thermodynamics of ice sheets, such as the Greenland ice sheet, the Antarctic ice sheet or the large ice sheets on the northern hemisphere during the last glacial period. They are used for a variety of purposes, from studies of the glaciation of Earth over glacial–interglacial cycles in the past to projections of ice-sheet decay under future global warming conditions.

History

Beginning in the mid-18th Century, investigation into ice sheet behavior began.[1] Since the Journal of Glaciology's founding, physicists have been publishing glacial mechanics.[1]

Barnes Ice Cap

The first 3-D model was applied to the Barnes Ice Cap.[1] In 1988, the first thermodynamically coupled model incorporating ice-shelves, sheet/shelf transition, membrane stress gradients, isotatic bed adjustment and basal sliding using more advanced numerical techniques was developed and applied to the Antarctic ice sheet.[1] This model had a resolution of 40 km and 10 vertical layers.[1]

When the first IPCC assessment report came out in 1990, ice sheets were not an active part of the climate system model, their evolution was based on a correlation between global temperature and surface mass balance.[2] When the second IPCC assessment report came out in 1996, the beginning of both 2D and 3D modelling was shown with ice sheets.[2] The 1990s heralded several more computational models, bringing with it the European Ice Sheet Modelling Initiative (EISMINT).[1][3] The EISMINT produced several workshops throughout the 1990s of an international collaboration, comparing most models of Greenland, Antarctic, ice-shelf, thermomechanical and grounding-line.[3]

The 2000s included integrating first-order approximation of full Stokes Dynamics into an ice-sheet model.[1] The fourth IPCC assessment report showed ice-sheet models with projections of rapid dynamical responses in the ice, which led to evidence of significant ice loss.[2]

In 2016, part of the Coupled Model Intercomparison Project Phase 6 (CMIP Phase 6) was the Ice Sheet Model Intercomparison Project, which defined a protocol for all variables related to ice sheet modelling.[4] The project allowed for both improvement in numerical and physical approaches to ice sheets.[5]

Modelling

Ice-Flow

Shallow Ice Approximation

Shallow Ice Approximation (SIA) is a simple method to model ice flow without having to solve full-Stokes equations.[6] The approximation is best applied to ice sheet with a small depth-to-width ratio, without many sliding dynamics and a simple bed topography.[7] SIA does not include many forces on an ice sheet, and can be considered a 'zero-order' model.[7] The model assumes that ice sheets are mostly split up by basal sheer stress, and it is not necessary to consider the other forces.[8] It also assumes that the basal shear stress and the gravitational driving stress of the grounded ice balance one another out.[7] The method is computationally inexpensive.[8]

Shallow Shelf Approximation

Shallow Shelf Approximation is another method to model ice flow, in particular a membrane-type flow of floating ice, or of sliding grounded ice over a base.[9] Also known as a membrane model, they are similar to free-film models in fluid dynamics.[10] As opposed to Shallow Ice Approximation, Shallow Shelf Approximation models ice flow when longitudinal forces are strong; sliding and vertical forces.[7] SSA can also be considered a 'zero-order' model.[7]

See also

Ice-sheet models on the web

  • CISM – Community Ice Sheet Model, under development as a land-ice component of the Community Earth System Model (CESM).
  • Elmer/Ice, a multi-physics finite element code with special modules for full-stress ice dynamics analysis
  • ISSM – Ice Sheet System Model, a multi-purpose massively parallelized finite element framework dedicated to ice sheet systems modeling (thermomechanical coupling, data assimilation, sensitivity analysis,...)
  • PISM – Parallel Ice Sheet Model, which includes ice shelves and ice streams.
  • SICOPOLIS – SImulation COde for POLythermal Ice Sheets, a 3D ice-sheet model which accounts for polythermal conditions (coexistence of ice at and below the melting point in different parts of an ice sheet).

References

  1. ^ a b c d e f g Blatter, Heinz; Greve, Ralf; Abe-Ouchi, Ayako (2010). "A short history of the thermomechanical theory and modeling of glaciers and ice sheets". Journal of Glaciology. 56 (200): 1087–1094. doi:10.3189/002214311796406059. ISSN 0022-1430.
  2. ^ a b c Shepherd, Andrew; Nowicki, Sophie (2017-10). "Improvements in ice-sheet sea-level projections". Nature Climate Change. 7 (10): 672–674. doi:10.1038/nclimate3400. ISSN 1758-678X. {{cite journal}}: Check date values in: |date= (help)
  3. ^ a b Philippe, Huybrechts (1997). Report of the Third EISMINT Workshop on Model Intercomparison (PDF).
  4. ^ Nowicki, Sophie M. J.; Payne, Anthony; Larour, Eric; Seroussi, Helene; Goelzer, Heiko; Lipscomb, William; Gregory, Jonathan; Abe-Ouchi, Ayako; Shepherd, Andrew (21 December 2016). "Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6". Geoscientific Model Development. 9 (12): 4521–4545. doi:10.5194/gmd-9-4521-2016. ISSN 1991-9603. PMC 5911933. PMID 29697697.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  5. ^ Pattyn, Frank (2018-12). "The paradigm shift in Antarctic ice sheet modelling". Nature Communications. 9 (1): 2728. doi:10.1038/s41467-018-05003-z. ISSN 2041-1723. PMC 6048022. PMID 30013142. {{cite journal}}: Check date values in: |date= (help)
  6. ^ Oerlemans, J. (1982-12). "Glacial cycles and ice-sheet modelling". Climatic Change. 4 (4): 353–374. doi:10.1007/BF02423468. ISSN 0165-0009. {{cite journal}}: Check date values in: |date= (help)
  7. ^ a b c d e Davies, Bethan. "A hierarchy of ice-sheet models". AntarcticGlaciers.org. Retrieved 18 October 2021.
  8. ^ a b Van Den Berg, J.; Van De Wal, R.S.W.; Oerlemans, J. (2006). "Effects of spatial discretization in ice-sheet modelling using the shallow-ice approximation". Journal of Glaciology. 52 (176): 89–98. doi:10.3189/172756506781828935. ISSN 0022-1430.
  9. ^ "Two stress balance models: SIA and SSA – PISM, a Parallel Ice Sheet Model 1.2.1 documentation". pism-docs.org. Retrieved 19 October 2021.
  10. ^ Schoof, Christian; Hewitt, Ian (3 January 2013). "Ice-Sheet Dynamics". Annual Review of Fluid Mechanics. 45 (1): 217–239. doi:10.1146/annurev-fluid-011212-140632. ISSN 0066-4189.
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