Recent Earth Oblateness Variations: Unraveling Climate and Postglacial Rebound Effects
Abstract
Earth's dynamic oblateness (J 2) has been decreasing due to postglacial rebound (PGR). However, J 2 began to increase in 1997, indicating a pronounced global-scale mass redistribution within Earth's system. We have determined that the observed increases in J 2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the Southern, Pacific, and Indian oceans. When these effects are removed, the residual trend in J 2 (–2.9 x 10−11 year−1) becomes consistent with previous estimates of PGR from satellite and eclipse data. The climatic significance of these rapid shifts in glacial and oceanic mass, however, remains to be investigated.
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REFERENCES AND NOTES
1
J. O. Dickey et al., Satellite Gravity and the Geosphere (National Research Council, Washington, DC, 1997).
2
The definition and method of calculation for J2 are given in the SOM Text.
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T/P and XBT data were assimilated into the model run starting in 1993. Further details regarding the ECCO assimilation system are available at www.ecco-group.org. A brief summary is given in the SOM Text.
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Annual volume changes in subpolar and mountain glaciers were obtained from the NSIDC Web site www-nsidc.colorado.edu/sotc/glacier_balance.html, courtesy of M. Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder.
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Glacial contributions to sea level change are not included in the ocean model, which is constrained to have constant volume (Boussinesq approximation). Before computing the oceanic J2 contribution, the model bottom pressures are adjusted uniformly such that the global ocean mass is time-invariant.
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The IB assumption accounts for oceanic compensation of atmospheric loading by substituting a spatially averaged uniform surface pressure field over the global ocean.
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The model bottom pressure is directly proportional to the mass-per-unit area above a given point.
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The authors gratefully acknowledge discussions (both oral and via e-mail) with J.-P. Boy, D. Bromwich, B. F. Chao, Y. Chao, C. M. Cox, M. B. Dyurgerov, L.-L. Fu, M. Ghil, E. Ivins, K. Mo, and Y.Yung, and the constructive comments of the reviewers. The work of J.O.D., S.L.M., and I.F. presents the results of one phase of research carried out at the Jet Propulsion Laboratory, under contract with the National Aeronautics and Space Administration. O.D.V. is a postdoctoral researcher of the National Fund for Scientific Research, Belgium. This work was accomplished during O.D.V.'s visit to JPL during Summer 2002. This is a contribution of the ECCO consortium funded by the National Oceanographic Partnership Program.
Materials and Methods
SOM Text
Figs. S1 and S2
Table S1
References and Notes
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Published In
Science
Volume 298 | Issue 5600
6 December 2002
6 December 2002
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Received: 27 August 2002
Published in print: 6 December 2002
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