Glacio–isostatic Adjustment in the Po Plain and in the Northern Adriatic Region

Abstract

Vertical movements in the Po plain (northern Italy) are controlled by natural and anthropogenic effects. Since Italy is located in the far–field of the former late Pleistocene ice sheets, isostatic deformations are primarily driven by melt water loading and represent a major component of long–term natural movements across the entire Mediterranean. In addition to far–field sources, here we consider the isostatic effects of melting of the nearby Würm Alpine ice–sheet, suggesting that it is possible to put bounds on its maximum thickness, extent and chronology by Holocene relative sea level observations from the northern Adriatic. Using various plausible ice models, and adopting a viscosity profile that matches Holocene relative sea level observations in the Mediterranean, we find that melting of the Alpine ice sheet is always responsible for upward movements in the Po plain, currently at rates of ~ 0.5 mm/yr. When both far– and near–field sources are considered, the rate of sea level change in the Venetian Lagoon for the most reasonable mantle rheology and melting chronology is negative, i.e., opposite to that attributed to human activity and recent climatic variations. However, its amplitude (fractions of mm/yr) is small compared to the secular signal observed by tide gauges (~2 mm/yr), which makes glacial isostasy a second–order mechanism of sea level variation in this region.