Sea Level Variations from Decades to Millennia: A few Case Studies

The main goals of this Ph.D. study are to investigate the regional and global geophysical components related to present polar ice melting and to provide independent cross validation checks of GIA models using both geophysical data detected by satellite mission, and geological observations from far field sites, in order to determine a lower and upper bound of uncertainty of GIA effect. The subject of this Thesis is the sea level change from decades to millennia scale. Within ice2sea collaboration, we developed a Fortran numerical code to analyze the local short-term sea level change and vertical deformation resulting from the loss of ice mass. This method is used to investigate polar regions: Greenland and Antarctica. We have used mass balance based on ICESat data for Greenland ice sheet and a plausible mass balance for Antarctic ice sheet. We have determined the regional and global fingerprint of sea level variations, vertical deformations of the solid surface of the Earth and variations of shape of the geoid for each ice source mentioned above. The coastal areas are affected by the long wavelength component of GIA process. Hence understanding the response of the Earth to loading is crucial in various contexts. Based on the hypothesis that Earth mantle materials obey to a linear rheology, and that the physical parameters of this rheology can be only characterized by their depth dependence, we investigate the Glacial Isostatic Effect upon the far field sites of Mediterranean area using an improved SELEN program. We presented new and revised observations for archaeological fish tanks located along the Tyrrhenian and Adriatic coast of Italy and new RSL for the SE Tunisia. Spatial and temporal variations of the Holocene sea levels studied in central Italy and Tunisia, provided important constraints on the melting history of the major ice sheets.

Global and regional sea level variations in the recent past and future: insight from observations and modeling

This work is focused on the analysis of sea–level change (last century), based mainly on instrumental observations. During this period, individual components of sea–level change are investigated, both at global and regional scales. Some of the geophysical processes responsible for current sea-level change such as glacial isostatic adjustments and current melting terrestrial ice sources, have been modeled and compared with observations. A new value of global mean sea level change based of tide gauges observations has been independently assessed in 1.5 mm/year, using corrections for glacial isostatic adjustment obtained with different models as a criterion for the tide gauge selection. The long wavelength spatial variability of the main components of sea–level change has been investigated by means of traditional and new spectral methods. Complex non–linear trends and abrupt sea–level variations shown by tide gauges records have been addressed applying different approaches to regional case studies. The Ensemble Empirical Mode Decomposition technique has been used to analyse tide gauges records from the Adriatic Sea to ascertain the existence of cyclic sea-level variations. An Early Warning approach have been adopted to detect tipping points in sea–level records of North East Pacific and their relationship with oceanic modes. Global sea–level projections to year 2100 have been obtained by a semi-empirical approach based on the artificial neural network method. In addition, a model-based approach has been applied to the case of the Mediterranean Sea, obtaining sea-level projection to year 2050.

Assessment of sea-level variability for the Emilia-Romagna coastal area in the framework of the Mediterranean Sea

Sea–level change is one of the ocean characteristics closely connected to climate change. Understanding its variation is essential since a large portion of the world’s population is located in low–lying locations. Two main techniques are employed to measure sea level: satellite altimetry and tide gauges. Satellite altimetry monitors sea–level relative to a geocentric reference, is unaffected by crustal processes and covers nearly the entire surface of the oceans since 1993. Conversely, tide gauges measure sea level at specific coastal locations and relative to a local ground benchmark, therefore are impacted by vertical land movements. In this study, the linear and non–linear geocentric and relative sea–level trends along the Emilia–Romagna coast (Northern Italy) have been analyzed over different periods. In order to assess the local sea–level variability, data from satellite altimetry and tide gauges have been compared over a common time interval (1993–2019), hence disentangling the contribute of vertical land movements. Non–linearity has been also evaluated at the broader scale of the Mediterranean Sea, in order to depict the main variability in geocentric sea–level trends from regional to sub–basin scale. Furthermore, the anthropogenic and natural influence at the river basin scale has been addressed, in order to shed light on the factors inducing the drastic reduction of riverine sediment supply to the Emilia–Romagna coast over the period 1920–2020. The findings of this analysis indicate that the sediment delivery reduction to the coast by rivers has been driven by several anthropogenic processes, acting on various spatiotemporal scales. Moreover, the local absolute sea–level trend is far from linear and appear "contaminated" by the presence of natural oscillations that act at the multi–decadal, quasi–decadal and inter–annual scale, mainly driven by both large–scale climatic modes and variations in local oceanography.