Absolute gravimetry in South Patagonia for geodynamic applications

Abstract

The project “Gravimetric determination of the solid earth reaction due to mass changes in south Patagonia”, funded by the German Research Foundation (DFG), focuses on the viscoelastic characteristics of the upper mantle and its ongoing response to past and present changes in stress caused by the surface loading of the changing ice masses of the Patagonian ice fields. Such in-situ data form an important pre-requisite to constrain the information on present-day ice mass balance obtained by the GRACE and GRACE-Follow On satellite missions.The GNSS observations carried out by the TU Dresden group in southern Patagonia in the recent decade have shown high uplift rates but at a relatively small spatial scale. These uplift rates are mainly due to glacial mass loss for the time period from the little ice age to present. However, the GNSS data used to determine the surface deformation cannot unambiguously separate elastic and viscoelastic processes. This project seeks to add absolute gravimetry at selected locations which are both situated close to the southern Patagonian ice field and further radiate from the maximum observed uplift. Due to the east-west asymmetry of the observed uplift rates, the measurement range has been extended by stations up to the coast of the Atlantic Ocean. It is well established but little applied in practice, that using GNSS together with absolute gravity time series allows these two processes to be separated. Combining the gravimetric and GNSS observations with seismic measurements and with modelling we hope to improve the observational evidence in this region undergoing rapid viscoelastic deformation. Thus, we aim to yield new insights into the physical properties of the Earth’s interior, especially of the rheology of the mantle, to be later combined with GIA modelling.We will present the observations covering the working area between the Atlantic coast in the east and the southern Patagonian ice field in the west. In 2020 and 2022 two observation campaigns were performed including absolute gravimetry, relative gravimetry, GNSS, precise leveling and particular water level observations. In this presentation we will focus on the absolute gravity measurements which have been performed at eight locations in southern Patagonia using a micro-g LaCoste FG5 absolute gravimeter. We will discuss the observational setup, the instrumental performance and the results obtained so far together with the uncertainties of the observations.