Constraining models of postglacial rebound using space geodesy: a detailed assessment of model ICE-5G (VM2) and its relatives

Using global positioning system, very long baseline interferometry, satellite laser ranging and Doppler Orbitography and Radiopositioning Integrated by Satellite observations, including the Canadian Base Network and Fennoscandian BIFROST array, we constrain, in models of postglacial rebound, the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth. We test model ICE-5G VM2 T90 Rot, which well fits many hundred Holocene relative sea level histories in North America, Europe and worldwide. ICE-5G is the deglaciation history having more ice in western Canada than ICE-4G; VM2 is the mantle viscosity profile having a mean upper mantle viscosity of 0.5 × 1021 Pa s and a mean uppermost-lower mantle viscosity of 1.6 × 1021 Pa s; T90 is an elastic lithosphere thickness of 90 km; and Rot designates that the model includes (rotational feedback) Earth's response to the wander of the North Pole of Earth's spin axis towards Canada at a speed of ≈1° Myr−1. The vertical observations in North America show that, relative to ICE-5G, the Laurentide ice sheet at last glacial maximum (LGM) at ≈26 ka was (1) much thinner in southern Manitoba, (2) thinner near Yellowknife (Northwest Territories), (3) thicker in eastern and southern Quebec and (4) thicker along the northern British Columbia–Alberta border, or that ice was unloaded from these areas later (thicker) or earlier (thinner) than in ICE-5G. The data indicate that the western Laurentide ice sheet was intermediate in mass between ICE-5G and ICE-4G. The vertical observations and GRACE gravity data together suggest that the western Laurentide ice sheet was nearly as massive as that in ICE-5G but distributed more broadly across northwestern Canada. VM2 poorly fits the horizontal observations in North America, predicting places along the margins of the Laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr−1 in ICE-4G and 3 mm yr−1 in ICE-5G, in disagreement with the observation that the interior of the North American Plate is deforming more slowly than 1 mm yr−1. Substituting VM5a T60 for VM2 T90, that is, introducing into the lithosphere at its base a layer with a high viscosity of 10 × 1021 Pa s, greatly improves the fit of the horizontal observations in North America. ICE-4G VM5a T60 Rot predicts most of the North American Plate to be moving horizontally more slowly than ≈1 mm yr−1, in agreement with the data. ICE-5G VM5a T60 Rot well fits both the vertical and horizontal observations in Europe. The space geodetic data cannot distinguish between models with and without rotational feedback, in the vertical because the velocity of Earth' centre is uncertain, and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors.

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