Resumen de Antarctic ice sheet mass loss, glacio-isostatic adjustment and surface processes from ENVISAT, ICESat, CryoSat-2, GRACE and GPS
Alba Martín Español, Jonathan L. Bamber, Andrew Zammit-Mangion, Scott Luthcke, Liz Petrie, Bert Wouters, Matt King, Jonty Rougier
Constraining past ice mass changes, identifying their cause(s) and determining rigorous error estimates, is important for closing the sea level budget and as an input for and test of numerical models. For the Antarctic ice sheet, considerable uncertainty remains between different methods and groups. Estimates obtained from altimetry, gravimetry, and mass-budget methods can yield conflicting results with error estimates that do not always overlap, while the, commonly adopted, use of different forward models to isolate and remove the effects of glacio-isostatic adjustment (GIA) and surface mass balance (SMB) processes introduces another source of uncertainty which is hard to quantify.
To address both these issues, we present a statistical modelling approach to the problem. We combine the observational data, including satellite altimetry, GRACE, GPS and InSAR, and use the different degrees of spatial and temporal smoothness to constrain the underlying geophysical processes. This is achieved via a spatio-temporal Bayesian hierarchical model, employing dimensionality reduction methods to allow the solution to remain tractable in the presence of the large number (> 10ˆ7) of observations involved. The resulting trend esmates are only dependent on length and smoothness properties obtained from numerical models, but are otherwise entirely datadriven.
As a consequence, the solutions provide a valuable independent test of the forward models. Here, we present the annually- resolved spatial fields for i) dynamic ice loss, ii) SMB anomaly, iii) firn compaction and iv) (the time invariant) GIA, using a combination of GRACE, ICESat, ENVISat, CryoSat 2 and GPS vertical uplift rates, for 2003-2013. The elastic flexure of the crust is also determined simultaneously. We focus here primarily on the mass trends rather than solid earth effects which are presented elsewhere in this conference. We obtain a mean rate of -82±23 Gt/yr for the 11 year period with a sustained negative mean trend of dynamic imbalance to which West Antarctica is the largest contributor, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade following the destabilization of the Southern Antarctic Peninsula. The total mass loss is partly compensated by a significant mass gain in East Antarctica due to a positive trend of SMB anomalies.
