Changes in Ice-Mass Balances Inferred From Time Variations of the Geopotential Observed Through SLR and DORIS Tracking

Abstract

Analyses of Satellite Laser Ranging (SLR) tracking data have yielded estimates of rates for the low-degree zonal harmonics of the geopotential up through (J) over dot(6). Combined with observed changes in the Earth's rotation pole and global sea level rise, these observations provide a powerful constraint on aggregate mass transport within the Earth's systems. Inverse solutions, where these observed geodetic rates are used to constrain geophysical models, can yield estimates of the mantle viscosity contrast affecting postglacial rebound and ice sheet mass balance rates. In order to obtain the most accurate estimates, such analysis requires accounting for as many geophysical and environmental signals as possible that are contained in these observed trends. Analysis to date indicates that both the Antarctica and Greenland ice sheets are nearly in mass balance when the forward models are used without any accommodation for correction terms. These results are only somewhat dependent on the zonal rate solution used, despite the differences between these solutions. The ice mass balance results benefit from improved rate solutions; in particular, the Antarctic ice mass accumulation rate estimate will benefit from better separation of (J) over dot(3) and (J) overdot(5). The secular zonal rate solution can be improved using additional data. SLR and DORIS tracking of TOPEX/POSEIDON have been combined with the SLR tracking of LAGEOS, LAGEOS-2, Starlette, Stella, and Ajisai previously used to estimate the geopotential rates. Estimates of scale corrections to the forward models are also used to gain insight into the relative performance of these models and improve the estimate of the ice balances.