ITRF2014 vertical velocities: the impact of climate changes

We investigate the GNSS station vertical velocities provided by the new solution of the International Terrestrial Reference Frame, the ITRF2014. Constructed, inter alia, from a network of approximately 1000 GNSS stations, this new solution provides two times more station velocities than the ITRF2008, and shows a global pattern of vertical velocities very homogeneous regionally. As in the ITRF2008 solution, large vertical velocities can be seen over North America, Northern Europe, or Antarctica, probably induced predominantly by the Glacial Isostatic Adjustment still occurring today since the last deglaciation. But the ITRF2014 solution shows also large vertical velocities over regions such as Greenland and Alaska clearly larger than in the ITRF2008, probably related to last decadal ice melting and its possible acceleration. We focus here on this specific difference between the ITRF2008 and ITRF2014 solutions by investigating the global Earth figure variations through the estimation of low degree spherical harmonics of the global vertical velocity field.