Detection of a large-scale mass redistribution in the terrestrial system since 1998.

Earth's dynamic oblateness (J2) had been undergoing a decrease, according to space geodetic observations over the past 25 years, until around 1998, when it switched quite suddenly to an increasing trend that has continued to the present. The secular decrease in J2 resulted primarily from the postglacial rebound in the mantle. The present increase, whose geophysical cause(s) are uncertain, thus signifies a large change in global mass distribution with a J2 effect that considerably overshadows that of mantle rebound.