The Postglacial Rebound Signal of Fennoscandia Observed by Absolute Gravimetry, GPS, and Tide Gauges

We have compiled time derivatives of gravity and vertical motion for a dozen sites in Fennoscandia. Time series of absolute gravimetry and permanent GPS cover a time span of about a decade. Tide gauges have operated for many decades near seven of the sites. Linear relations are found to range from ？0.17 to ？0.22 for the slope between gravity and vertical uplift rates. An eustatic sea level rate of 1.2？mm/year is derived from these data. This compares well with results for North America and with theoretical predictions for viscoelastic Earth models. 1. Introduction The postglacial movements of Fennoscandia have been monitored geometrically by terrestrial as well as space geodetic observing techniques. Vertical uplift rates relative to mean sea level have been derived to map the apparent uplift (e.g., [1]). Time series of permanent GPS-stations reveal both vertical and horizontal movements [2, 3]. The geographical distribution of vertical uplift rates from these two independent sets of observations reveals an oval shaped uplift area with the major axis oriented towards northeast and maximum uplift in the northern part of the Gulf of Bothnia. The western perimeter of the uplift oval indicates a zero uplift line at or just outside the western coastline of Norway. Investigations of gravity changes related to the postglacial uplift of Fennoscandia began in 1966 with relative gravimeters. Longitudinal land uplift gravity lines between 56°N and 65°N were established under the auspices of the Nordic Geodetic Commission. Observations are being collected episodically [1, 4]. Several campaigns with absolute gravimeters were organized between 1976 and 1998. This effort became annual in 2003. We have compiled GPS uplift rates for a dozen sites in Fennoscandia for which time series of absolute gravimetry also exists, spanning about a decade. Seven of these sites are located at the coast with nearby tide gauges having produced times series for the last 50–100 years. 2. Data Gravity was first measured by absolute gravimeters in Fennoscandia in 1976 [5, 6]. The number of observing sites increased in 1993 when two FG5-instruments [7] campaigned Finland, Norway, and Sweden. Episodic follow-up observations were made in 1995 and 1998 [8]. An ongoing observing program was initiated in 2003, employing several recently acquired FG5-instruments on an annual basis at more than three dozen sites throughout the Nordic countries [9]. Currently available data produce time series of absolute gravity observations for about a dozen sites covering a time span of a decade or more. They