Postglacial Rebound Model ICE-6G_C (VM5a) Constrained by Geodetic and Geologic Observations

Abstract:

We fit the revised global model of glacial isostatic adjustment ICE-6G_C (VM5a) to all available data, consisting of several hundred GPS uplift rates, a similar number of ¹⁴C dated relative sea level histories, and 62 geologic estimates of changes in Antarctic ice thickness. The mantle viscosity profile, VM5a is a simple multi-layer fit to prior model VM2 of Peltier (1996, Science). However, the revised deglaciation history, ICE-6G (VM5a), differs significantly from previous models in the Toronto series.

(1) In North America, GPS observations of vertical uplift of Earth's surface from the Canadian Base Network require the thickness of the Laurentide ice sheet at Last Glacial Maximum to be significantly revised. At Last Glacial Maximum the new model ICE-6G_C in this region, relative to ICE-5G, roughly 50 percent thicker east of Hudson Bay (in and northern Quebec and Labrador region) and roughly 30 percent thinner west of Hudson Bay (in Manitoba, Saskatchewan, and the Northwest Territories).the net change in mass, however, is small. We find that rates of gravity change determined by GRACE when corrected for the predictions of ICE-6G_C (VM5a) are significantly smaller than residuals determined on the basis of earlier models.

(2) In Antarctica, we fit GPS uplift rates, geologic estimates of changes in ice thickness, and geologic constraints on the timing of ice loss. The resulting deglaciation history also differs significantly from prior models. The contribution of Antarctic ice loss to global sea level rise since Last Glacial Maximum in ICE-6G_C is 13.6 meters, less than in ICE-5G (17.5 m), but significantly larger than in both the W12A model of Whitehouse et al. [2012] (8 m) and the IJ05 R02 model of Ivins et al. [2013] (7.5 m). In ICE-6G_C rapid ice loss occurs in Antarctica from 11.5 to 8 thousands years ago, with a rapid onset at 11.5 ka thereby contributing significantly to Meltwater Pulse 1B. In ICE-6G_C (VM5a), viscous uplift of Antarctica is increasing gravity as observed by GRACE by an equivalent 105 Gt/yr in surface mass which is equivalent to an increase in global sea level of 0.30 mm/yr, about twice as large as the most recent estimates based on the W12A and IJ05 R02 models of Antarctic postglacial rebound but very close to the previous estimate of Peltier (2009, QSR).

(3)In Eurasia ICE-6G_C (VM5a) remains similar to ICE-5G (VM2).