Ocean tidal loading affecting precise geodetic observations on Greenland: Error account of surface deformations by tidal gravity measurements

Air-borne and satellite based altimetry are used to monitor the Greenland i ce-cap. Since these measurements are related to fiducial sites at the coast , the robustness of the height differences depends on the stability of thes e reference points. To benefit from the accuracy of these methods on the ce ntimeter level, station corrections regarding the Earth tides and the ocean tidal loading have to be applied. Models for global corrections esp. for t he body tides are available and sufficient, but local corrections regarding the effect of the adjacent shelf area still have to be inferred from addit ional observations. Near the coast ocean tidal loading causes additional ve rtical deformations in the order of 1 to 10 cm Therefore, tidal gravity mea surements were carried out at four fiducial sites around Greenland in order to provide corrections for the kinematic part of the coordinates of these sites. Starting in 1993 four stations were occupied on Greenland for a one year record each. The results show the expected strong tidal anomalies due to ocean tidal loa ding. The loading computations confirmed these observations, but it turned out that with global models only about 50 % of the observed effect can be e xplained. This means that at these stations st vertical deformation of up t o +/-3.5 cm is not corrected applying these global models. (C) 2000 Elsevie r Science Ltd. All rights reserved.