Present-day vertical crustal deformations in West Greenland from repeated GPS observations

A GPS network, consisting of 10 sites, was established in the ice-free area of West Greenland and was observed for the first time in 1995. In 2002 a complete re-observation was carried out. These repeated GPS observations served as a basis for the determination of vertical crustal deformations. The data analysis was performed using the Bernese Software version 5.0. For the central site Kangerlussuaq a negative uplift rate (subsidence) of (-3.1 +/- 1.1) mm yr(-1)was obtained, related to the reference frame IGb00. The regional pattern is characterized by an east-west gradient of up to 4 mm yr(-1) between the outer coast and the subsiding area along the present ice margin, which can be explained to a great extent as a result of the late Holocene re-advance of the Greenland ice sheet. Relative sea-level changes could be calculated taking the present eustatic sea-level rise into account. The present-day sea level rises at the outer coast between Maniitsoq and Paamiut, and in the large fjords with increasing rates of more than 4 mm yr(-1) in their innermost parts. These findings are in agreement with the general picture obtained from geomorphological and archaeological research. For Sisimiut and the Disko Bay area the present sea-level change is almost zero, whereas the crustal uplift rate for Ilulissat was observed to be 1.6 mm yr(-1). We conclude that this present vertical uplift rate in Ilulissat is affected by the retreat of the ice margin during the last 150 yr and the present negative mass balance of the Jakobshavn Isbrae and its drainage basin.