Northern hemisphere ice sheet modelling and glaciological sensitivity


Contact
phuybrechts [ at ] awi-bremerhaven.de

Abstract

Despite recent advances there is still debate regarding the volume and areal extent of ice sheets in the Northern Hemisphere since the Last Glacial Maximum. Ice sheet models are uniquely placed to offer insight into the advance and retreat of ice sheets in the Northern Hemisphere. However there are some unknowns in ice sheet models whose sensitivity must be determined before their results can be accepted with confidence.To simulate the retreat of the Northern Hemisphere ice sheets over the last glacial cycle, we use the Huybrechts thermo-mechanically coupled ice sheet model with time dependent forcing. The time dependent forcing consists of modeled temperature and precipitation from the UKMO Paleo-GCM model. Modeled surface temperature and precipitation changes between present day and LGM are used as input forcings to the ice sheet model. The GRIP ice core *18O record is rescaled to 0 at present day, and 1 at LGM to represent a time dependent 'glacial index'. The UKMO fields are then rescaled by this glacial index to generate time dependent changes in ice volume over an entire glacial cycle.For a certain combination of model parameters the ice sheet model generates a reasonable reproduction of the ice sheet extent suggested by geomorphological data and ice volume change suggested by eustatic sea level data, and we adopt this model as a useful 'reference model' with which to compare results generated by changing ice sheet model parameters. Specific parameters examined are those related to atmospheric forcing, glacial rheology, basal processes and marine calving. As marine calving processes are poorly understood, we take an empirical approach by relating the time-dependent bathymetric depth of the grounding line of geomorphologically-observed paleoicesheets to the concurrent eustatic sea level. The variation of grounding line depth with eustatic sea level is then used as a sea-level dependent calving criteria. We use this criteria to model large scale ice withdrawal from marine areas such as Hudson Bay in North America and the Barents Sea in Northern Europe in a chronologically accurate manner.Analysis of the model sensitivity expressed in terms of quantitative changes in LGM ice sheet volume suggest that it is the parameters relating to climate forcing which dominate in the ice sheet model. In particular the parameter which most sensitively controls LGM ice sheet volume is the sea level temperature difference between LGM and present day over the northern hemisphere. To first order, the ice sheet model can thus be used to estimate the temperature difference between LGM and present day using the constraints of realistic LGM ice sheet volume and extent in the model.



Item Type
Conference (Poster)
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Not peer-reviewed
Publication Status
Published
Event Details
21. Internationalen Polartagung der Deutschen Gesellschaft für Polarforschung, Kiel (D)March 2003..
Eprint ID
6939
Cite as
Zweck, C. and Huybrechts, P. (2003): Northern hemisphere ice sheet modelling and glaciological sensitivity , 21. Internationalen Polartagung der Deutschen Gesellschaft für Polarforschung, Kiel (D)March 2003. .


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