Long-term monitoring of temporal geoid change is important for updating the static
geoid model. The change of the geoid with time is caused by the redistribution of
masses within the Earth. Generally it can be observed by repeated geodetic observations such as gravimetric observations, including space gravity and gradiometry, and from geodetic height observed by precise levelling and/or GNSS observations (cf. Sjöberg and Bagherbandi 2017, Chapter 8).
In order to obtain the secular trend of the geoid change a long observation period should be considered. The plot in the following uses all monthly GRACE data sets between 2002 and 2016.
The reason for the geoid change in Fennoscandia is because of the the last glacial period and the deloading of ice sheets that reduces the land masses and increases the glacial isostatic adjustment (GIA) induced deformation of the solid Earth in much of northern Europe, which areas were covered by large ice sheets during the last glacial period. The ice was as thick as 3 km in Fennoscandia during the last glacial maximum about 20,000 years ago. The deloading of an ice sheet is accompanied by an inflow of subcrustal mass, and this process (GIA) starts directly during the deloading, leading to a mass increase and thereby a geoid uplift.