Recent Earth oblateness variations: Unraveling climate and postglacial rebound effects

Earth's dynamic oblateness (J(2)) has been decreasing due to postglacial rebound (PGR). However, J(2) began to increase in 1997, indicating a pronounced global-scale mass redistribution within Earth's system. We have determined that the observed increases in J(2) are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the Southern, Pacific, and Indian oceans. When these effects are removed, the residual trend in J(2) (-2.9 x 10(-11) year(-1)) becomes consistent with previous estimates of PGR from satellite and eclipse data. The climatic significance of these rapid shifts in glacial and oceanic mass, however, remains to be investigated.