A Test of Recent Inferences of Net Polar Ice Mass Balance based on Long-Wavelength Gravity

Abstract

comprehensive analysis of satellite datasets has estimated that the ice sheets of Greenland, West Antarctica, the Antarctic Peninsula, and East Antarctica experienced a net mass loss of ?100 ± 92 Gt yr?1 over the period 1992?2000 and ?298 ± 58 Gt yr?1 over the period 2000?11, representing an increase of ?198 ± 109 Gt yr?1 between the two epochs. The authors demonstrate that the time rate of change of the degree-four zonal harmonic of Earth's gravitational potential provides an independent check on these mass balances that is less sensitive to uncertainties that have contaminated previous analyses of the degree-2 zonal harmonic [e.g., due to ongoing glacial isostatic adjustment (GIA), solid Earth body tides, and core?mantle coupling]. For the period 2000?11, the signal implied by the ice sheet mass flux cited above is (3.8 ± 0.6) ? 10?11 yr?1, whereas the change in the harmonic across the two epochs is (2.3 ± 1.1) ? 10?11 yr?1. In comparison, using satellite laser ranging (SLR) data, the authors estimate a GIA-corrected value of (3.8 ± 0.6) ? 10?11 yr?1 for the epoch 2000?11 and a change across the two epochs of (5.3 ± 1.6) ? 10?11 yr?1. The authors conclude that the former supports recent estimates of melting over the last decade, whereas the latter suggests either that estimated melt rates for the earlier epoch were too high or that the uncertainty associated with the SLR-based inference of during the earlier epoch is underestimated.