Glacial isostatic adjustment observed using very long baseline interferometry and satellite laser ranging geodesy

In global space geodetic solutions, radial site motions are usually estimat ed relative to the geocenter (the center of figure of the solid Earth). Mos t geodesists estimate the motion of the geocenter assuming both that sites do not move radially and that sites move laterally as predicted by plate mo tion model NUVEL-1A [DeMets et at, 1990, 1994]. Here we estimate the motion of the geocenter assuming that the plate interiors deform radially and lat erally as predicted by the postglacial rebound model of Peltier [1994] or t hat of Peltier [1996] without assuming a priori knowledge about relative pl ate motion. Radial site motions estimated relative to this rebound-adjusted geocenter are in the same reference frame as the rebound model predictions , whereas site motions estimated without adjusting for rebound are not. We further constrain the motion of the rebound-adjusted geocenter using satell ite laser ranging's sensitivity to the center of mass (of the solid Earth, the oceans, and the atmosphere) by assuming that the mean velocity between the rebound-adjusted geocenter and the center of mass is negligible over th e: time period of geodetic measurement. Twenty years of observation with sa tellite laser ranging and very long baseline interferometry record the isos tatic response of the solid Earth to the unloading of the late Pleistocene ice sheets. The misfits of the postglacial rebound model of Peltier [1994] and that of Peltier [1996] are 34% and 16% less, respectively, than the mis fit of the rigid plate model. Sites at Onsala (Sweden) and Algonquin Park ( Ontario) are observed to be rising at 3 mm/yr and 2 mm/yr, respectively, re flecting unloading of the Fennoscandian and Laurentide ice sheets. Sites al ong the east coast of the United States are subsiding at < 2 mm/yr, indicat ing that the forebulge produced by the Laurentide ice sheet is currently co llapsing very slowly. Sites beneath the margins of the ice sheets during th e last glacial maximum are currently moving laterally away from the ice she et centers at < 1.5 mm/yr, in disagreement with the moderately fast outward motion predicted by the model of Peltier [1996].