ITRF2008 contribution to glacial isostatic adjustment and recent ice melting assessment

Abstract

We investigate what information station vertical velocities of the ITRF2008 provide on global geodetic parameters and by extension on glacial isostatic adjustment (GIA) and recent ice melting (RIM) processes. We infer degree‐2 spherical harmonic coefficients (SHC) of the Earth figure change and theJ2 gravity rate (J˙2), which we compare with five GIA models. We find J˙2 to be (0.0 ± 2.4) × 10−11 yr−1, which is consistent with recent studies that propose a J˙2 change in the 1990s, due to RIM whose contribution to the J˙2 would be today around (3.5–4.0 ± 2.4) × 10−11 yr−1. Such results favor Peltier (2004) VM2 or Paulson et al. (2007) GIA models. The ITRF2008 SHC that are directly impacted by the GIA rotational feedback, confirm with a good precision recent results from GRACE mission that initiated a debate on GIA rotational feedback and about Peltier GIA model quality. We find a coefficient consistent with Paulson's (and other) model and more than 7 times smaller than coefficients in Peltier's models. Two explanations are possible: (1) if the model of Peltier (2004) VM2 were to be correct, then the strong rotational feedback in the model must be counteracted by a strong rotational feedback in the opposite direction generated by current ice loss, (2) if the model of Paulson et al. (2007) were to be correct, therefore GIA and RIM separately induce negligible rotational feedbacks. Both answers are quite extreme and call for more investigation on GIA modeling and rotational feedback.