GLOBAL SEA LEVEL FROM TOPEX/POSEIDON SATELLITE DATA: PREDICTED SIGNATURES FROM MODELS OF GLACIAL ISOSTASY

Concerns about sea-level rise resulting from global warming have motivated many studies of past and present sea-level changes. Tide gauge records provide data of modern sea-level change but these data are limited to shoreline locations and use the Earth's solid surface as a reference. In contrast the TOPEX/Poseidon satellite uses radar altimetry to measure sea level over the open ocean with a reference at the Earth's center. The data accuracy is better than 2 cm and a decade of measurements exists. Glacial isostasy influences all of these records because the solid Earth reference deforms under tide gauges and mass redistribution within and on the Earth affects the geoid observed by satellite. We have therefore developed a computer model of global Earth deformation predicting the sea-level signatures that should be observed by both tide gauges and the TOPEX/Poseidon satellite as a result of ice-sheet fluctuations during past ice ages and at present. Predictions for both the tide gauge and satellite cases indicate that the sea-level signature from modern ice-sheet melting will not be uniform. Our figure shows predicted sea-level change as would be observed by satellite resulting from uniform thinning of the Greenland ice sheet (given as a percentage of oceanwide average rate of sea-level rise). Sea level falls near the source and rises at distant regions. If global warming is causing sea level to rise, the sea-level change gradient will be large and would indicate the sources of meltwater.