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Glacial isostatic adjustment on a rotating earth



We extend and complete previous work to compute the influence of perturbations to the rotation vector on a suite of observables associated with glacial isostatic adjustment (GIA). We emphasize observables relevant to present and future geodetic missions (for example, present-day 3-D crustal motions, relative sea-level change and geoid or absolute sea-level variations). Our calculations adopt spherically symmetric, self-gravitating, Maxwell viscoelastic earth models while incorporating realistic mass (ice plus ocean) load and rotation variations. The predicted rotation-induced signals are dominated by the influence of true polar wander (TPW). The spatial geometry of the TPW-induced relative sea level, geoid and radial velocity fields is primarily that of a degree two, order one surface spherical harmonic. The spatial variation of the horizontal velocity vectors is given by the gradient of this harmonic. The peak radial and horizontal velocities are of the order of 0.5 mm yr−1; however, we show that this value is sensitive to the adopted profile of mantle viscosity. We also demonstrate that an accurate prediction of TPW-induced sea level and 3-D crustal deformation rates requires that a realistic number of glacial cycles be incorporated into the ice load history. We conclude that geodetic observations of the GIA process should be analysed using a GIA theory valid for a rotating planet. Finally, we also consider variations in rotation driven by simple present-day polar melting scenarios and predict the influence of these variations on a suite of geophysical observables. We find that the rotational feedback associated with Greenland melting is capable of significantly perturbing both relative and absolute sea-level variations.

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