GNGTS 2023 - Atti del 41° Convegno Nazionale

KEYLECTURE GNGTS 2023 Understanding sea-level rise during the last centuries and millennia: regional and global interactions between the cryosphere, the oceans, and the solid Earth.  Giorgio Spada University of Bologna Field observations and physical modelling clearly indicate that the sea-level variations due to the melting of continental ice sheets are characterized by non-uniform spatial and temporal patterns. To a large extent, regional sea-level variations result from Glacial Isostatic Adjustment (GIA), the geophysical processes that manifests multiscale interactions between the cryosphere and the oceans, but that is also tightly related with the rheology-dependent solid Earth response to the waxing and waning of continental-scale ice sheets. GIA is responsible of various geophysical phenomena including but not limited to vertical and horizontal deformations, relative and absolute sea-level variations, gravity field variations and rotational fluctuations of the Earth’s pole of rotation, changes in the Earth’s landscapes through horizontal migration of the shorelines, stress accumulation within the crust etc. These phenomena can be modelled by solving the so-called “Sea level Equation” (SLE) introduced by Farrell and Clark in 1976, but they cannot be disentangled from other contributions to contemporary sea-level change. The two basic unknowns of the SLE, i.e. , the history of deglaciation and the rheological profile of the Earth’s mantle can be constrained by the observed variations of sea-level since the Last Glacial Maximum (21,000 years ago). The regional impact of GIA on currently observed geodetic variations can be described in terms of “ fingerprints ”, or spatial patterns that describe the response of the Earth to GIA. These are strongly contaminating all the geodetically observable variables, including the sea-level observations from tide gauges deployed along the coastlines and those detected from altimetry during the last two decades. In this talk, my focus will be on the role of the solid Earth in the GIA process and on the causes of the regional imprint of GIA, with examples from key-areas of the world that are currently subject to significant isostatic disequilibrium and sea-level variations. The problem of uncertainties in GIA modelling, especially those associated with the response of the solid Earth, will be also discussed.