Gravimetric determination of the solid-earth response to ice-mass changes in southern Patagonia

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The proposal aims at the realization and interpretation of gravimetric observations in the region of the Southern Patagonian Icefield (southernmost South America). In the course of previous investigations conducted by the applicants an exceptionally intensive crustal uplift was inferred in this region. This deformation is caused by the response of the solid Earth to past and present ice-mass changes of the Patagonian icefields. Whereas the presently ongoing response to past changes is assigned by glacial-isostatic adjustment (GIA), present-day ice-mass changes cause an immediate elastic response. Geodetic observations of the respective effects are crucial to improve regional GIA models by providing unique insights into both the rheology of the solid Earth and the climatically driven ice-mass evolution. Repeated absolute gravimetry was proven to be a geodetic observation technique suitable for a successful determination of GIA in many other regions. However, in the region of the Patagonian icefields absolute gravity measurements have not been initiated yet. The project proposes to carry out a repeated observation of a regional network of eight sites using a FG5 absolute gravity meter during three field campaigns. Surface gravity changes over time will be derived from these observations. These will serve as an independent observable of GIA and elastic effects, closing a gap between satellite gravimetry data (GRACE and GRACE-FO missions) and the uplift rates derived by geodetic GNSS observations. The observed surface gravity changes will form the basis for a joint interpretation incorporating both the deformation rates already determined by the applicants and GRACE-FO satellite gravimetry. The interpretation will shed light on the mass distributions that accompany the deformation of the solid Earth. The separation between mass signals originating from the interior of the Earth and from the rapidly retreating ice will result in a substantial improvement of regional visco-elastic Earth models, in a better understanding of the rheological structure and of the present-day ice-mass change pattern with a spatial resolution superior to satellite gravimetry. Understanding the causes for the exceptional intensity of GIA in the region of the Southern Patagonian Icefield will help to also explain even faster uplift processes observed in the Amundsen Sea Embayment (West Antarctica). The project will benefit from the synergy with the current presence of BKG's FG5-227 gravity meter at the Argentine-German Geodetic Observatory (AGGO).