Recent postglacial rebound, gravity change and mantle flow in Fennoscandia

Abstract

The recent postglacial rebound of Fennoscandia is investigated using sea-level data, levelling data and gravity data. In particular, an analysis is made of the repeated data obtained hitherto on the Fennoscandian land-uplift gravity line along latitude 63". Methods for this analysis include an iterative procedure for computing the relation between gravity change and absolute land uplift, the mass-flow parameter and the geoid rise; the remaining land uplift is also estimated.The mass-flow parameter c is used to characterize the relation between additional mass and additional volume due to rebound; it is a number between 0 and 1, 1 corresponding to full inflow of mantle below the rising crust, and 0 to no inflow but some kind of decompression. The main result is that c is significantly different from 0 at the 99 per cent level: we find c % 0.8. This means that models proposed of the present uplift based on pure decompression must be ruled out, and that a viscous inflow of mantle is a necessary part of the ongoing uplift process. On the other hand, this process might be more complicated than a pure viscous flow.

Glacial isostatic adjustment in Fennoscandia from GRACE data and comparison with geodynamical models

“…We have chosen a twodimensional cosine-surface with the maximum gravity change in the centre and decreasing gravity change values towards the edges, which characterises an elastic deformation quite well. The pattern matching algorithm is applied to the GRACE results, the expected uplift signal as presented by Ekman and Mäkinen (1996) from gravity and tide gauge analyses, as well as to the geodynamical modelling results (e. g. Lambeck et al, 1998;Steffen and Kaufmann, 2005). Figure 5a shows again the trends derived from the GFZ GRACE fields, which …”

“…The spatial extension of the Fennoscandian uplift area is about 2000 km in diameter from SW to NE, and about 1400 km in diameter from NW to SE, with its centre located in the Bothnian Bay between Sweden and Finland (see e. g. Ekman, 1996;Ekman and Mäkinen, 1996;Lidberg et al, 2007;Gitlein et al, 2008). The maximum uplift rates reach about 1 cm/yr in the centre of the area (Lidberg et al, 2007), which is associated with a corresponding gravity change at the Earth's surface of about -2 µGal/yr (Ekman and Mäkinen, 1996;Gitlein et al, 2008).…”

“…The maximum uplift rates reach about 1 cm/yr in the centre of the area (Lidberg et al, 2007), which is associated with a corresponding gravity change at the Earth's surface of about -2 µGal/yr (Ekman and Mäkinen, 1996;Gitlein et al, 2008). However, regarding a reference point fixed in space, gravity is increasing with about +1 µGal/yr due to the GIA-related mass inflow.…”

“…Figure 1 shows the maximum uplift signal over the Bothnian Bay area as well as a subsidence zone from the southern North Sea over Northern Germany to Northern Poland due to the collapse of the peripheral forebulge. Commonly, GPS and other geometrical observations such as spirit levelling and tide gauges are used for uplift investigations (e. g. Ekman and Mäkinen, 1996;Milne et al, 2001;Johansson et al, 2002;Scherneck et al, 2003;Kuo et al, 2004;Lidberg et al, 2007). In addition to these observations, the gravitational uplift signal can be detected by absolute and relative gravimetry (e. g. Ekman and Mäkinen, M a n u s c r i p t 1996; Mäkinen et al, 2005;Müller et al, 2005;Wilmes et al, 2005;Timmen et al, 2006) or by the GRACE satellite mission (e. g. Wahr and Velicogna, 2003;Peltier, 2004;Müller et al, 2006a,b).…”

Modelling of the GIA-induced surface gravity change over Fennoscandia

“…Based on these relative gravity observations, precise levelling, tide gauge data and their respective observational accuracies, [10] found the ratio between the rate of change of gravityġ and the land uplift rateu to be −0.204 ± 0.058 µGal mm −1 . Recently [23] examined absolute gravity and GPS time series in North America and found aġ/u ratio of −0.17 ± 0.01 µGal mm −1 .…”