Decadal variations of Earth's oblateness and surface mass balance in polar ice sheets from 1979 to 2012

Gravity variations associated with Earth's oblateness (J2) have been observed by satellite laser ranging (SLR) since 1976. More than three-decades long satellite observation of J2 has been useful to understand dynamical process of Earth from mantle to atmosphere. However, causes of decadal J2 variations were still uncertain while ice mass change in polar region was generally believed to be one of the driving forces. In this study, we use anomalous surface mass balance (SMB) in Antarctica and Greenland as a proxy of past anomalous ice mass variation in both ice sheets and quantify their contribution to J2. The SMB contribution in polar ice sheets depicts decadal J2 variations, which agree well with those of SLR observations from 1979 to 2012. This result also suggests an important implication that SMB variations have been important contributors to polar ice mass changes along with ice dynamics. There are still unknown J2 variations with about 10-year periods, and its cause is probably due to limitation of numerical models to depict climate variations associated with solar activity.