pmip3:design:21k:icesheet:index
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pmip3:design:21k:icesheet:index [2009/09/23 12:50] jypeter Major update of the "Ice volume" section |
pmip3:design:21k:icesheet:index [2009/10/07 21:09] jypeter Major update of the GLAC-1 section |
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| ==== Lev-MOCA ==== | ==== Lev-MOCA ==== | ||
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| === Northern Hemisphere (GLAC-1) === | === Northern Hemisphere (GLAC-1) === | ||
| - | The Greenland reconstruction is the GrB model described in Tarasov and Peltier( GJI 2002 and JGR 2003). It's a hand tuning of a 3D thermo-mechanically coupled glaciological shallow ice-sheet model and visco-elastic bedrock response model (using the same VM2 rheology used for ICE-5G) to fit the Relative Sea-Level (RSL) observations, the GRIP borehole temperature and age profiles, and approximate basal temperatures at CampCentury and Dye3 along with secondary constraints described in the references. | + | The Greenland model is from Tarasov and Peltier (2002 and 2003), a glaciological model with hand-tuned climate adjustments to enforce fit to Relative Sea-Level (RSL) records and the GRIP borehole temperature record. It was also validated against observed rated of present day uplift for 3 sites and against GPS measurements for horizontal ice surface velocity. A variant of it is the Greenland component of ICE-5G and ICE-6G. |
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| + | The North American and Eurasian reconstructions are objective Bayesian calibrations of the MUN/UofT glacial systems model. The latter incorporates a 3D thermo-mechanically coupled (shallow) ice-sheet model, with permafrost resolving bed-thermal model, asynchronously coupled down-slope surface drainage/lake depth solver, and various other components such as a thermodynamic lake ice, sub-glacial till-deformation, bouyancy and temperature dependant calving law, ice-shelf represention, ..., some of which are described in Tarasov and Peltier, QSR 2004, and Nature 2005, and a more complete description is currently being written up). The visco-elastic bedrock response uses either the VM2 (as used in ICE-5G) or VM5a (used in ICE-6G) earth rheologies. Relative Sea Level is computed using a gravitationally self-consistent formalism similar to that of Peltier, except for an eustatic approximation for dealing with changing ocean masks and the lack of accounting for rotational effects (which are mostly significant for far-field RSL records, ie records that do not locally constrain ice load history). | ||
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| + | Climate forcing involves an interpolation between present day observed climatologies and the set of highest resolution LGM fields from PMIP I and II data sets. The interpolation is weighted according to a glaciological inversion of the GRIP record for regional temperatures over the last glacial cycle. | ||
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| + | The calibration involves approximately 30 (currently 36 for North Am, 29 for Eurasia) ensemble parameters to capture uncertainties in deglacial climate and ice dynamics. The majority of these parameters are used for the climate forcing, including weighting the inter-model (ie between PMIP models) EOFs for LGM monthly precip and temperature, regional desert elevation effects, and LGM atmospheric lapse rate. Other ensemble parameters adjust calving response, effective viscosity of subglacial till, strength of margin forcing, and flow parameters for ice-shelves. Model runs are forced to stay within uncertainties of the independently derived ice margin chronologies (Dyke, 2004 for North Am, Gyllencreutz et al, in preparation for Eurasia). | ||
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| + | Model runs cover a full glacial cycle. North America and Eurasia are calibrated separately. Calibration targets include a large set of RSL observations, geologically-inferred deglacial ice-margin chronologies, and geodetic constraints. For the case of North America, the calibrated ensemble is further scored with respect to strand-lines (paleo lake level indicators) and Marine Limit (maximum level of marine inundation) observations. A key point is that model runs are penalized in proportion to the amount of margin forcing required. So the calibration is directed towards a climate forcing that is consistent with the margin chronology. | ||
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| + | The model was calibrated using the ICE4G ice load reconstruction for Antarctica and the VM2 earth rheology because the ICE6G Antarctic chronology and VM5a earth model along with a much expanded geodetic dataset were provided by Dick Peltier only in early September, which left too little time to recalibrate the models. There is the added issue that the ICE6G Antarctic chronology lacks error bars. The expanded geodetic data-set for North America included significant revisions to the previous geodetic constraints. This along with the significant reduction in LGM ice volume in ICE6G Antarctic as compared to ICE4 and 5G rendered a significant misfit with the far-field Barbados RSL record. With the limited time, a somewhat blind and largely random 2000 member ensemble was generated along with a rerun of the best 300 previously calibrated parameter sets and some 200 attempts at hand-tuning. nn450 is the weighted distribution of 7 model runs that passed certain hard threshold constraints. nn9021 is the best (though "best" depends to a certain extent on the weighting between various constraints) single run from the previous calibration and nn445 is the weighted ensemble mean for that previous calibration. | ||
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| + | The Eurasian calibration did converge, and aside from issues with the Norwegian fjords (the latter are also a problem for ICE6G), the calibration was generally successful. nn8234 is one of the best runs with the largest 26ka RSL contribution to the Barbados record. A single run was chosen to ensure consistency between drainage fields and the surface topography. The mean distribution for the calibration can be made available upon request. | ||
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| + | In summary, the GLAC-1 submission provides a set of glaciological models that are derived from a plausible climate forcing based on PMIP1 and PMIP2 results for LGM and that fit independently derived ice margin chronologies. This provides strong constraints throughout deglaciation. For Eurasia, the smaller set of constraints (among other more speculative reasons) resulted in a successful calibration that reasonably well covered the available constraint set. North America has a much larger and much more diverse set of constraints (and I suspect a much more complicated ice/climate interaction history), so the calibration has never been able to fully satisfy the whole set of constraints (strandlines are for instance a challenge to fit given their high sensitivity to drainage choke point elevations). | ||
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| + | Unfortunately, these glaciological models in combination with the ICE-6G chronology for Antarctica (and Patagonia) and Dick Peltier's VM5a earth rheology have at best a weak fit to the the LGM segment of the Barbados record. There is a significant tradeoff between Barbados fit and fit to other constraints. What is unclear at this stage is the extent to which this is due to deficiencies in the glaciological models, to problems with the ICE-6G Antarctic ice chronology, or possibly with inferred uncertainties in the Barbados record and with the VM5a earth rheology. | ||
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| + | One possibility for resolving Barbados, is to take the 1.5 sigma upper limit of the previously calibrated ensemble for North America which almost reaches the inferred Barbados record for 26 to 21 ka. Dick Peltier and Rosemarie Drummond will cross-check this dataser. The problem with using ensemble bounds is that this is no longer a glaciologically self-consistent model and RSL fits have also deteriorated. | ||
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| + | == References == | ||
| + | |||
| + | * [[http://www.atmosp.physics.utoronto.ca/people/lev/g6jgrpub.pdf|g6jgrpub.pdf]] | ||
| + | * [[http://www.atmosp.physics.utoronto.ca/people/lev/g5jpub.pdf|g5jpub.pdf]] | ||
| + | |||
| + | == Data == | ||
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| + | <note warning>Note that the North Am model is calibrated with a stub Greenland by Ellesmere. When a final model is chosen, the North American and Greenland models can be easily melded.\\ \\ Also, please note, that none of the above have yet been published, so these files are provided for discussion and consideration. Any fields and data not selected as a PMIP boundary condition are not to be used for research without prior consent.</note> | ||
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| + | * NetCDF of 21 to 10ka surface elevation, thickness, basal velocities for the nn9021 North Am model and nn8234 Eurasian model: [[http://pmip3.lsce.ipsl.fr/share/design/glac1/NAnn9021.nc|NAnn9021.nc]], [[http://pmip3.lsce.ipsl.fr/share/design/glac1/EAnn8234.nc|EAnn8234.nc]] | ||
| + | |||
| + | * NetCDF of 21 to 10ka for nn445 ensemble means and 1.5 sigma range: [[http://pmip3.lsce.ipsl.fr/share/design/glac1/NAnn445.nc|NAnn445.nc]] | ||
| + | |||
| + | * Other data available upon request from [[lev@mun.ca|Lev Tarasov]] | ||
| - | The North American and Eurasian reconstructions are objective Bayesian calibrations of the MUN/UofT glacial systems model (above 3D model plus asynchronously coupled down-slope surface drainage/lake depth solver, and various other components such as a thermodynamic lake ice, sub-glacial till-deformation, ice-shelf represention,..., some of which are described in Tarasov and Peltier, QSR 2004, and Nature 2005, and a more complete description is currently being written up). The calibration involves approximately 30 ensemble parameters to capture uncertainties in deglacial climate and ice dynamics. Model runs cover a full glacial cycle. The climate forcing for the calibration is based on interpolation between a LGM (based on a combination of PMIPI for North America and PMIP II for Eurasia) model output temperature and precipitation climatologies (along with further regional precipitation controls) and a present-day climatology. The interpolation between glacial and present-day states is weighted to the regional temperature chronology from the tuned Greenland reconstruction. Calibration targets include a large set of RSL observations, geologically-inferred deglacial ice-margin chronologies, and geodetic constraints. For the case of North America, the calibrated ensemble is further scored with respect to strand-lines (paleo lake level indicators) and Marine Limit (maximum level of marine inundation) observations. | + | == Plots == |
| - | The data sets for North America and Eurasia will include surface elevation, ice mask, lake depth, surface drainage routing pointer fields and ice flux components of the surface drainage. | + | * RSL plots for North Am and Eurasia |
| + | * North Am: (with nn8234 Eurasia)\\ [[http://pmip3.lsce.ipsl.fr/share/design/glac1/rslGLAC1RSLcompAc.pdf|rslGLAC1RSLcompAc.pdf]] nn9021 (as calibrated, ICE4G Antarctica, VM2),nn9021 with ICE6G Antarctica/VM5a, nn7280, nn445\\ \\ [[http://pmip3.lsce.ipsl.fr/share/design/glac1/rslGLAC1RSLcompBc.pdf|rslGLAC1RSLcompBc.pdf]] nn9021, nn445, nn445+1sigma, nn445-1sigma\\ | ||
| + | * Eurasia:\\ [[http://pmip3.lsce.ipsl.fr/share/design/glac1/rslGLAC1RSLcompEc.pdf|rslGLAC1RSLcompEc.pdf]] nn8234 (with nn9021), nn8234(with nn7280), nn8191(with nn9021)\\ | ||
| + | * Barbados: [[http://pmip3.lsce.ipsl.fr/share/design/glac1/GLAC1RSLcompBbarb.pdf|GLAC1RSLcompBbarb.pdf]] (note will slightly over predict barbados RSL drop around LGM due to lack of rotational effects on RSL calculation) | ||
| + | * Surface elevation and basal ice velocity area maps for 21 ka\\ Note: lakes and drainage results are not included in these plots\\ [[http://pmip3.lsce.ipsl.fr/share/design/glac1/21kaHuvnn8234.pdf|21kaHuvnn8234.pdf]], [[http://pmip3.lsce.ipsl.fr/share/design/glac1/18kaHuvnn8234.pdf|18kaHuvnn8234.pdf]], [[http://pmip3.lsce.ipsl.fr/share/design/glac1/14kaHuvnn8234.pdf|14kaHuvnn8234.pdf]] | ||
| === Southern hemisphere === | === Southern hemisphere === | ||
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| area = 360768576 km<sup>2</sup>//). | area = 360768576 km<sup>2</sup>//). | ||
| - | ^ ^ ICE-4G\\ //final// ^^ ICE-5G\\ //v1.2// ^^ ICE-6G\\ //v1.0// ^^ | + | ^ ^ ICE-4G\\ //final// (1) ^^ ICE-5G\\ //v1.2// (2) ^^ ICE-6G\\ //v1.0// ^^ |
| ^ ^ 21k ^ 26k ^ 21k ^ 26k ^ 21k ^ 26k ^ | ^ ^ 21k ^ 26k ^ 21k ^ 26k ^ 21k ^ 26k ^ | ||
| ^ North America\\ (incl Innuit area) | 64.24 | 54.92 | 81.47 | 83.71 | 79.82 | 88.14 | | ^ North America\\ (incl Innuit area) | 64.24 | 54.92 | 81.47 | 83.71 | 79.82 | 88.14 | | ||
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| ^ West Antarctica | 9.74 | 8.33 | 9.68 | 9.68 | 11.79 | 11.79 | | ^ West Antarctica | 9.74 | 8.33 | 9.68 | 9.68 | 11.79 | 11.79 | | ||
| ^ East Antarctica | 8.35 | 7.12 | 8.36 | 8.36 | 1.45 | 1.44 | | ^ East Antarctica | 8.35 | 7.12 | 8.36 | 8.36 | 1.45 | 1.44 | | ||
| - | ^ ice-shelves (1) | | | | | 2.80 | 3.00 | | + | ^ Total | **114.12** | **97.79** | **123.63** | **127.48** | **114.31** | **126.81** | |
| - | ^ Total | **114.12** | **97.79** | **123.63** | **127.48** | **117.11** | **129.81** | | + | ^ ice-shelves (3) | | | | | 2.80 | 3.00 | |
| - | * (1) The calculation only cares about grounded ice, so where it detects that the ice-model has ice that is below the predicted sea-level, it deems the ice to be melted and added to the ocean. The ice may be melted or be part of an ice-shelf eg the Ronne, Ross ice-shelves. This is a feature of the most recent version of the solver. | + | * (1) The version of the ICE-4G (VM2) model for which data are provided is not exactly the version that was employed in the original PMIP project but rather one from which a significant amount of Antarctic ice was simply eliminated (version employed for illustrative purposes in Peltier's paper for the Mt Hood volume of QSR). |
| + | |||
| + | * (2) The version of ICE-5G used for PMIP2/MOTIF was **v1.1** | ||
| + | |||
| + | * (3) The calculation only cares about grounded ice, so where it detects that the ice-model has ice that is below the predicted sea-level, it deems the ice to be melted and added to the ocean. The ice may be melted or be part of an ice-shelf eg the Ronne, Ross ice-shelves. This is a feature of the most recent version of the solver. | ||
| * The large change between ICE-4G (VM2) and ICE-5G (VM2) is due to the introduction of Art Dyke's margin chronology which had the ice being eliminated from North America earlier than in the original chronology obtained from John Andrews. This meant that more ice had to be removed in order to have the same impact on RSL during the ice-free Holocene interval. | * The large change between ICE-4G (VM2) and ICE-5G (VM2) is due to the introduction of Art Dyke's margin chronology which had the ice being eliminated from North America earlier than in the original chronology obtained from John Andrews. This meant that more ice had to be removed in order to have the same impact on RSL during the ice-free Holocene interval. | ||
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| * the analysis from Valerie Masson demonstrating that the elevation of East Antarctic ice was not significantly different than modern | * the analysis from Valerie Masson demonstrating that the elevation of East Antarctic ice was not significantly different than modern | ||
| * the results of the analyses based upon the application of the space geodetic constraints described in the Argus and Peltier paper. | * the results of the analyses based upon the application of the space geodetic constraints described in the Argus and Peltier paper. | ||
| - | |||
| - | * The version of the ICE-4G (VM2) model for which data are provided is not exactly the version that was employed in the original PMIP project but rather one from which a significant amount of Antarctic ice was simply eliminated (version employed for illustrative purposes in Peltier's paper for the Mt Hood volume of QSR). | ||
pmip3/design/21k/icesheet/index.txt · Last modified: 2009/12/23 13:25 by jypeter
