HR: 11:50h
AN: C32A-06    [Abstracts]
TI: Constraints on recent mass changes in the Antarctic and Greenland ice sheets from an analysis of the global water cycle
AU: * Plag, H
EM: hpplag@unr.edu
AF: Nevada Bureau of Mines and Geology, and Seismological Laboratory, University of Nevada, Reno, Mailstop 178, Reno, NV 89557 United States
AB: Secular mass changes in the large ice sheets introduce a particular fingerprint in relative sea level, which can be identified in local trends in relative sea level determined from tide gauge observations [Plag and J\"uttner, 2001]. However, on decadal to century time scales, coastal relative sea level is affected by other factors, including steric changes in the volume of the sea water, mass exchange with the continental cryosphere and hydrosphere, post-glacial rebound, local vertical movement of the crust, and variations in the atmospheric circulation. In order to derive firm constraints on mass changes of the large ice sheets from sea level observations, all these factors need to be taken into account in a global analysis focusing on the ocean as the major reservoir in the water cycle. The different forcing factors for sea level are associate with distinct spatial "finger-prints". In a first step, these "finger-prints" are obtained from model predictions (general circulation models for steric effects, geophysical model for post-glacial rebound), theoretical finger-print functions (for mass exchange with the cryosphere, where the static sea-level equation is used to compute the finger-print functions for the sea-level signal due to linear trends in the Antarctic and Greenland ice sheets), and observational data (steric effect, atmospheric circulation, local vertical land motion). Then, in a second step based on the large and global databaseof monthly mean sea level values collected at the Permanent Service for Mean Sea Level, the "finger-prints" are scaled to fit the observed monthly sea levels, thus allowing maximum use of the available observations. For that, a complex regression model is used which approximates each tide gauge record through a function of the forcing factors. For each forcing factor, a parameterised contribution is included in the regression, with the parameters being both local (e.g. for the air pressure and wind effects) and global (e.g. for the ice sheet mass changes). These parameters are determined for a number of models and/or assumptions and the dependency of the parameters on models and assumptions is discussed. The results indicate a global sea level change of the order of +2.5 mm/year over the last 50 years with significant contributions from both the Antarctic and Greenland ice sheets.
DE: 4556 Sea level variations
DE: 1655 Water cycles (1836)
DE: 1223 Ocean/Earth/atmosphere interactions (3339)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting