Computer modelling of the mass balance and dynamics of the Antarctic Ice Sheet
Entry ID:
ASAC_1261
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Summary
Abstract:
Computer models have been developed to investigate the present and future balance of ice accumulation and loss for the Antarctic ice sheet. New information about the flow properties of ice has been included to improve models. Comparisons with field observations and projections for sea-level and climate change will be investigated. This metadata record is a parent metadata record for several child ... metadata records. The child records contain information on:
1) Balance ice fluxes for the Antarctic Ice sheet
2) Balance ice velocities for the Antarctic Ice sheet
For details on the model used, etc, see the child metadata records.
This work is now part of AAS (ASAC) project 2698.
Project objectives:
This multi-strand project aims to improve our understanding of the dynamical system of ice sheet and ice shelves and their place within the global climate system, with the major objectives of quantifying (a) the contribution of Antarctica to sea-level change, past, present and future, and (b) variations in the discharge of fresh-water into the Southern Ocean from ice shelf ocean interactions.
Specifically the project will
- assess the state of mass balance of individual drainage basins of East Antarctica, to improve understanding of the present contribution to global sea level rise
- improve understanding of the flow properties of ice through modelling, laboratory studies and analysis of remote sensing data, and incorporate this into dynamical models of the Antarctic ice sheet and ice shelves
- refine our quantitative understanding of the interaction between ice shelves and the underlying ocean and determine the influence of ice shelves on dynamics of the grounded ice sheet and hence on mass budgets and sea level change
- determine whether, and on what time scale, global warming might lead to irreversible change in the ice sheet-ice shelf system
- develop models of the ice sheet and ice shelves that can be linked to coupled atmosphere/ocean models (in an Earth Systems Model)
The project is constructed around the Science Strategy, season workplan, and the goals of the Antarctic Climate and Ecosystems CRC, as discussed under 3.1.2 below.
These are long term objectives, and this proposal seeks approval for a five year period culminating in the final round of ACE CRC research milestone/outputs in 2010 - and accordingly a workplan briefly indicating research for future years is included.
Taken from the 2008-2009 Progress Report:
Public summary of the season progress:
Patterns of present day ice sheet flows have been contrasted with marine geological evidence of palaeo ice stream flow in the Amundsen Sea region of West Antarctica. Models predicting Antarctic ice sheet thickness have assisted aerogeophysical field programs. Several theoretical models of ice flow have been tested using ice deformation experiments and crystal microstructure measurements. Interpretation of our measured ice velocities for Mertz Glacier tongue is revealing dynamic interactions with surrounding fast ice, with implications for mutual stability. Development of an ice sheet system model continues, aimed at improving predictions of ice sheet evolution and sea level rise.
Taken from the 2009-2010 Progress Report:
Progress against objectives:
- Antarctic Mass Balance
Roberts has improved the algorithm in his Lagrangian ice sheet balance flux computer code, vastly reducing the computational running time.
New Antarctic balance fluxes have been calculated with the Lagrangian code using the latest available Antarctic ice sheet digital elevation models, including that of Bamber, Gomez-Dans and Griggs (2009) and for ice accumulation fields from a regional atmospheric modelling study (van de Berg, W., M. van den Broeke, C. Reijmer, and E. van Meijgaard, 2006. 'Reassessment of the Antarctic surface mass balance using calibrated output of a regional atmospheric climate model.' J. Geophys. Res. 111, D11104.), as well as earlier accumulation data compilations.
New computed ice fluxes for the Amundsen Sea sector of West Antarctica advanced our collaboration with Frank Nitsche (Columbia University's Lamont-Doherty Earth Observatory) , exploring the contrasts between present day ice sheet drainage, and paleo-ice sheet ice streams deduced from exploration of submarine troughs across the continental shelf.
Work comparing the new computed balance fluxes to the observed flows in the East Antarctic Ice Sheet to explore patterns of ice sheet mass imbalance at a regional scale is nearing completion.
Warner has also continued collaboration with Jaehyung Yu (Texas A and M University), Hongxing Liu (University of Cincinnati), Kenneth Jezek (Byrd Polar Research Center) and Jiahong Wen (Shanghai Normal University) on the mass balance of the drainage basins that feed the Amery ice shelf. The detailed analyses suggests the ice sheet catchment is in overall positive budget, partially offsetting losses elsewhere in Antarctica, but they also highlight a crucial need for ice flow estimates at the southernmost grounding zone to resolve conflicts with other published estimates.
- Ice Flow Properties
Warner continued to be involved with Prof W. F. Budd in finalizing revision of a major paper connecting ice deformation studies under combined compressive and shear stresses with a simple model for enhanced ice flow proposed for use in ice sheet modeling.
The investigation of crystal fabrics in glacial and marine ice samples from Amery Ice Shelf bore-holes (led by Adam Treverrow - UTAS) was prepared for publication (joint activity with AMISOR project- AAS 1164).
- Ice shelf - ocean interaction
Warner's mass balance collaboration with Yu, Liu, Jezek and Wen (above) also arrived at new broad-scale estimates of the rates of basal melting and freezing beneath the Amery ice shelf.
Ben Galton-Fenzi (UTAS) completed his Ph D thesis on 'Modelling ice shelf ocean interaction'. Warner advised regarding calculation of the accretion of marine ice beneath the Amery ice shelf from the ocean model basal melt/freeze pattern. Galton-Fenzi's results for the Amery ice shelf basal melt/freeze show good general agreement with estimates from glaciological observations when realistic present day climate forcing is applied in the model, and this ocean model development brings capacity to make projections of how ice shelves will respond to climate change much closer. His work also indicates the importance of treating frazil ice processes in marine ice accretion.
Warner and Galton-Fenzi commenced collaboration on coupling the current ACE CRC ice shelf dynamics model with the ROMS subglacial circulation ocean model.
- Ice shelf dynamics
Research on the dynamics of the floating Mertz Glacier Tongue (MGT) led by Robert Massom continued, particularly regarding the possible stabilising influence on the MGT of a large slab of thick and consolidated landfast multi-year sea ice ("fast ice") attached to its eastern edge. To date this has mainly involved interpretation of remote sensing work (also associated with AAS 3024 Remote Sensing of Near-Coastal Antarctic Sea Ice and Its Impacts on Ice Shelves and Ecosystems), but also provides material for future ice shelf modelling work. Ironically, after our study the main, more northerly, section of the MGT calved in February 2010.
- Ice Sheet System model development
Progress continued on developing a next generation "full stress solution" model for treating the dynamics of ice sheet, ice stream and ice shelf flow. Roberts has developed a numerical method that allows for the efficient calculation of derivatives for arbitrarily distributed points. This method will be used in the ice-sheet model, allowing the selection of the discretisation grids for numerical solutions to be based on accurate implementation of boundary conditions rather than dictated by requirements for evaluating gradients. In the vertical, the grid will be of terrain following type - but with minimum grid spacing and automatic clustering in areas of high gradients.
In a separate modelling activity, Roberts has developed a novel scheme for interpolating between ice sheet thickness measurements, typically from Radio Echo Sounding (RES), drawing on ice flow trajectories, ice balance fluxes and earlier thickness inference modelling (Warner, R.C. and W.F. Budd (2000) Derivation of ice thickness and bedrock topography in data-gap regions over Antarctica. Annals of Glaciology, 31. 191-197). The skill of this interpolation scheme has been evaluated using the denser coverage from the first season of RES data gathered by the ICECAP international collaboration (see AAS 3103) over the region south of Casey station, encompassing the Aurora Subglacial Basin and Totten and Denman glacier streams. Warner and Roberts have recently applied this interpolation scheme to the generally sparse publicly available ice thickness data for the entire Antarctic continent, to produce a new view of the broad-scale subglacial landscape. We hope this scheme will be of value in the international effort (BEDMAP 2) to assemble a new ice thickness and bedrock dataset from existing and new IPY-era RES data. 
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Description:
Public information for ASAC project 1261
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Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
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N: -60.0
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S: -70.0
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E: 159.0
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W: 62.0
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Quality
Values provided in temporal and spatial coverage are approximate only.
Taken from the 2008-2009 Progress Report:
Difficulties affecting project:
The loss of a PhD student has resulted in significant delays in the major ice shelf modelling work.
Progress was made on adding basal drag to the CRC ice shelf model, and on modelling rifting in the Amery ice ... shelf, and on a study of the sensitivity of the Mertz Glacier Tongue to global warming, but some topics were not commenced.
At present the main changes envisaged are for a decrease in the depth of research carried out on some facets of the project.
Taken from the 2009-2010 Progress Report:
Variations to work plan or objectives: Were any variations made to the work plan or objectives for the project since it was last submitted for assessment? If 'Yes', please describe below what those variations are and why they have been made. If you intend making any changes to the future work plan for the project, what are the changes and why are they required? Will the changes affect the project?
The most recent revision of this year's work-plan envisaged the major focus on two modelling topics - coupled modelling of ice shelf-ocean interactions, and ice sheet system modelling. These contribute to the goals of the old ACE CRC. In the event more time was expended on what were then indicated as a range of subordinate topics.
Coupled modelling of ice shelf ocean interaction and of the response of the Amery ice shelf to global warming (Warner and Roberts with John Hunter and Ben Galton-Fenzi of ACE CRC) were not substantially advanced. This was partly due to Galton-Fenzi being occupied with other tasks - including completing his thesis, making useful subglacial ocean simulations involving the Mertz Glacier and Mertz polynya region, and his being assigned responsibility for circum-Antarctic coastal ocean modelling following the departure of Frank Kohlberg from the ACE CRC Oceans program. Warner and Roberts were also heavily committed elsewhere. There was still relevant progress. Galton-Fenzi's PhD thesis provides valuable new sensitivity studies for the Amery under warming scenarios, but the task of coupling ice shelf and ocean models was not implemented. This is expected to commence in earnest in June-July 2010. The work on the high resolution modeling of the Antarctic coastal ocean was in any case planned as contributing to the future effort to estimate response of other ice shelves to global warming.
Warner's collaboration with Yu, Liu, Jezek and Wen also provided additional perspectives on present day Amery aggregate basal melting and freezing, and some progress was also made towards addressing marine ice accretion via a derivation of new map of marine ice distribution (involving Allison, Fricker, Hyland, Warner and Young).
In ice sheet system modelling, Roberts developed the new component to enable derivative computations over arbitrary spatial discretizations, but he and Warner were more engaged than anticipated in other studies. Regarding the intentions of commencing new ice sheet simulations, the expectations of substantial new ice sheet bedrock data from ICECAP, AGAP and BEDMAP2 were in any case premature. The appointment of new ACE CRC staff in the coming year is also expected to assist in managing the workloads involved in assembling atmospheric and ocean forcing fields for climate change simulations.
On the other topics:
- Ice Flow Properties - (Warner, Budd, Treverrow):
Generation of research publications from 2008/2009 season and from Adam Treverrow's PhD project in general progressed but was not completed. This was partly due to Treverrow's participation in this season's AMISOR field program in Antarctica. Time and personnel constraints also led postponement of work on inferring ice flow relations from inverse modelling of ice shelf flow to early 2010/2011.
- Ice shelf dynamics (Warner, Roberts, Court, Massom, Legresy, Giles):
Progressing the ice shelf modelling projects associated with the ACE CRC ice shelf model and John Court's (abandoned) PhD project through to publication also had to be postponed - in part due to time constraints, and in part to delays in Court finding time to deliver definitive versions of the code and simulations. It is proposed that at least the major work on Amery ice shelf rifts will be completed in the coming year (paper by Warner, Court and others).
The team led by Massom decided to concentrate on studying the connection between the Mertz Glacier Tongue and the region of adjoining multi-year fast ice before returning to the detailed analysis of the time series of glacier tongue velocity maps - which will be completed in 2010.
- Antarctic Mass Budget Studies
The reassessment of East Antarctic drainage basins is almost completed. This is now expected to be done in 2010.
Access Constraints
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Use Constraints
This data set conforms to the PICCCBY Attribution License
(http://creativecommons.org/licenses/by/3.0/).
Please follow instructions listed in the citation reference at the provided URL when using these data.
Data Set Progress
IN WORK
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Land Processes Distributed Active Archive Center
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https://lpdaac.usgs.gov/
Dataset ID:
MOD11A1
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Distribution
Distribution Media:
HTTP
Distribution Size:
V005: 2.1 MB; V041: 2.2 MB; V004: 24 MB
Distribution Format:
HDF-EOS
Publications/References
Moderate Resolution Imaging Spectroradiometer (MODIS) publications written by the MODIS Science Team: [available online at http://modis.gsfc.nasa.gov/sci_team/pubs/] National Aeronautics and Space Administration, 2000, MODIS data products catalog (EOS AM platform): [Greenbelt, Maryland], Goddard Space Flight Center, http://modis.gsfc.nasa.gov/data/dataprod/index.php. National Aeronautics and Space Administration, revised 2004, EOS Reference Handbook, a Guide to NASA's Earth Science Enterprise and the Earth Observing System: Greenbelt, Maryland, Goddard Space Flight Center, 261 p. [available online in pdf format at http://eospso.gsfc.nasa.gov/ftp_docs/data_products_1.pdf].
Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date:
2007-01-30
Last DIF Revision Date:
2013-01-31
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