A test of recent inferences of net polar ice mass balance based on long-wavelength gravity

Abstract

A 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 2100 6 92 Gt yr21 over the period 1992-2000 and22986 58Gt yr21 over the period 2000-11, representing an increase of21986 109Gt yr21 between the two epochs. The authors demonstrate that the time rate of change of the degreefour zonal harmonic of Earth's gravitational potential J_4 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 J_4 signal implied by the ice sheet mass flux cited above is (3.8 6 0.6) 3 10211 yr21, whereas the change in the J_4 harmonic across the two epochs is (2.3 6 1.1) 3 10211 yr21. In comparison, using satellite laser ranging (SLR) data, the authors estimate a GIA-corrected J_4 value of (3.8 6 0.6) 3 10211 yr21 for the epoch 2000-11 and a change across the two epochs of (5.3 6 1.6) 3 10211 yr21. 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 J_4 during the earlier epoch is underestimated. © 2013 American Meteorological Society.