Application of GRACE, Vertical GPS Station Motion and ICESat Altimeter Data for Generating Simultaneous Constrains on Ice Mass Balance and Glacial Isostatic Adjustment in the Antarctic Peninsula

Land glacier extent and volume in the northern Antarctic Peninsula (NAP) have been in a state of dramatic demise since the early 1990’s. Using JPL global mascons, GRACE gravity trend observations are combined with Global Positioning System (GPS) bedrock uplift data in order to simultaneously solve for ice loss and for viscoelastic Earth glacial isostatic adjustment (GIA). The bedrock uplift owes to Holocene and Little Ice Age (LIA) cryospheric loading-unloading sequences. The present-day ice loss rates are determined to be -41 ± 6 Gt/yr in the NAP and regions south of 67°S. These are consistent with estimates based upon thickness and flux changes using InSAR and speckle-tracking in the 5 years that preceded the GRACE observing period; 2003-2010. Bounds are recovered for elastic lithosphere thicknesses of 20 < h < 45 km and on upper mantle viscosities of 3 x 10^19 < η < 10^20 Pa s. Antarctic Peninsula ice models with a prolonged LIA, extending to AD 1930 are favored in all χ2 fits to the GPS uplift data. This result is largely decoupled from Earth structure assumptions for a range of reasonable load-unloading histories that we sample in the study. The GIA corrections are important, as they account for a large fraction of the space-determined secular gravity change. Collectively, when combined with observations of 1998-2002, the on-land ice losses correspond to mass increases of the oceans equivalent to 0.12 ± 0.025 mm/yr of sea-level rise for the last 15 years. For several target areas near the Trinity Peninsula, the GIA-corrected mass losses are directly compared with ICESat-determined ice height changes spanning 2002-2007.