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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B6, 2311, doi:10.1029/2002JB002290, 2003

Inversion of Earth's changing shape to weigh sea level in static equilibrium with surface mass redistribution

Geoffrey Blewitt

Nevada Bureau of Mines and Geology and Seismological Laboratory, University of Nevada, Reno, Nevada, USA


Peter Clarke

School of Civil Engineering and Geosciences, University of Newcastle, Newcastle upon Tyne, UK


Abstract

We develop a spectral inversion method for mass redistribution on the Earth's surface given geodetic measurements of the solid Earth's geometrical shape, using the elastic load Love numbers. First, spectral coefficients are geodetically estimated to some degree. Spatial inversion then finds the continental surface mass distribution that would force geographic variations in relative sea level such that it is self-consistent with an equipotential top surface and the deformed ocean bottom surface and such that the total (ocean plus continental mass) load has the same estimated spectral coefficients. Applying this theory, we calculate the contribution of seasonal interhemispheric (degree 1) mass transfer to variation in global mean sea level and nonsteric static ocean topography, using published GPS results for seasonal degree-1 surface loading from the global IGS network. Our inversion yields ocean-continent mass exchange with annual amplitude (2.92 ± 0.14) × 1015 kg and maximum ocean mass on 25 August ±3 days. After correction for the annual variation in global mean vertical deformation of the ocean floor (0.4 mm amplitude), we find geocentric sea level has an amplitude of 7.6 ± 0.4 mm, consistent with TOPEX-Poseidon results (minus steric effects). The seasonal variation in sea level at a point strongly depends on location ranging from 3 to 19 mm, the largest being around Antarctica in mid-August. Seasonal gradients in static topography have amplitudes of up to 10 mm over 5000 km, which may be misinterpreted as dynamic topography. Peak continental loads occur at high latitudes in late winter at the water-equivalent level of 100–200 mm.

Received 4 November 2002; accepted 5 March 2003; published 21 June 2003.

Index Terms: 1214 Geodesy and Gravity: Geopotential theory and determination; 1223 Geodesy and Gravity: Ocean/Earth/atmosphere interactions (3339); 1655 Global Change: Water cycles (1836); 4203 Oceanography: General: Analytical modeling; 4227 Oceanography: General: Diurnal, seasonal, and annual cycles.

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Citation: Blewitt, G., and P. Clarke (2003), Inversion of Earth's changing shape to weigh sea level in static equilibrium with surface mass redistribution, J. Geophys. Res., 108(B6), 2311, doi:10.1029/2002JB002290.