[1] Antarctic volume changes during the past 21 thousand years are smaller than previously thought, and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment (GIA) gravity signal. The new model, in turn, should give predictions that are constrained with recent uplift data. The impact of the GIA signal on a Gravity Recovery and Climate Experiment (GRACE) Antarctic mass balance estimate depends on the specific GRACE analysis method used. For the method described in this paper, the GIA contribution to the apparent surface mass change is re-evaluated to be +55˙13 Gt/yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the GPS observations at 18 high-quality stations. Although the GIA model spans a range of possible Earth rheological structure values, the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness. GRACE monthly solutions from the Center for Space Research Release 04 (CSR-RL04) release time series from January 2003 to the beginning of January 2012, uncorrected for GIA, yield an ice mass rate of +2.92 9 Gt/yr. The new GIA correction increases the solved-for ice mass imbalance of Antarctica to -57˙34 Gt/yr. The revised GIA correction is smaller than past GRACE estimates by about 50 to 90 Gt/yr. The new upper bound to the sea level rise from the Antarctic ice sheet, averaged over the time span 2003.0-2012.0, is about 0.160.09 mm/yr.

S U M M A R YEnhanced melt productivity as a consequence of buoyant upwelling and small-scale convection of the mantle during rifting may play an important role in determining the fundamental structure of igneous crust produced during and following continental breakup. This paper investigates the relationship between rift-related decompression melting and the influence of small-scale mantle convection and rift geometry on the subsequent production and distribution of melt-related crust. Extension of the lithosphere is modelled numerically using a 2-D planestrain finite element method for viscous-plastic creeping flows. The evolving temperature and pressure fields within the model are coupled to an algorithm that predicts the amount and timing of decompression melting of upwelling mantle. Predicted melt fractions are converted to equivalent thicknesses of igneous crust, and the predicted crustal thicknesses for a series of models are compared to the observed crustal structure of rifted margins inferred from seismic data. Models characterized by small-scale mantle convection can to first order reproduce the general architecture of most volcanic rifted margins, that is, a relatively narrow band of thick (12-13 km) igneous crust (inferred to occur along strike of the margin), juxtaposed with thinner oceanic crust farther offshore. The variability in thickness (4-7 km) predicted for the laterstage thinner igneous crust is however difficult to reconcile with global observations of oceanic crustal thickness (7 ± 1 km). Also, the peak 13 km thickness of igneous crust predicted for models with convectively enhanced upwelling fails to match the great thicknesses (≥20 km) of igneous crust observed at many volcanic margins. Composite models that include both smallscale convection and a small increase to mantle potential temperature predict large pulses in initial magmatism and generation of 17 to 21-km-thick crust, followed by unstable production of thinner igneous crust. The results indicate that models with small-scale convection and no temperature anomaly may play a role in explaining the formation of volcanic margins with only moderately thick (11-15 km) igneous crust. Further, convection coupled with small increases to mantle temperature may be important during the initial phase of very thick igneous crust generation at some volcanic margins. Predicted distributions of igneous crust are moderately sensitive to asymmetric rifting of the lithosphere. Prior to breakup, igneous crust accretion is asymmetric; subsequent to breakup, symmetry in the thermal structure of the upwelling sublithospheric mantle is the dominant control on the final distribution of igneous crust.

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Sea‐level rise and decadal variability along the northwestern coast of the North Atlantic Ocean are studied in a self‐consistent framework that takes into account the effects of solid‐earth deformation and geoid changes due to large‐scale mass redistribution processes. Observations of sea and land level changes from tide gauges and GPS are compared to the cumulative effect of GIA, present‐day mass redistribution, and ocean dynamics over a 50 year period (1965–2014). GIA explains the majority of the observed sea‐level and land motion trends, as well as almost all interstation variability. Present‐day mass redistribution resulting from ice melt and land hydrology causes both land uplift and sea‐level rise in the region. We find a strong correlation between decadal steric variability in the Subpolar Gyre and coastal sea level, which is likely caused by variability in the Labrador Sea that is propagated southward. The steric signal explains the majority of the observed decadal sea‐level variability and shows an upward trend and a significant acceleration, which are also found along the coast. The sum of all contributors explains the observed trends in both sea‐level rise and vertical land motion in the region, as well as the decadal variability. The sum of contributors also explains the observed acceleration within confidence intervals. The sea‐level acceleration coincides with an accelerating density decrease at high latitudes.