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Postglacial Relative Sea-Levels from near- to intermediate-field regions. A key tool to quantify the on-going isostatic signal along global coastlines
Matteo Vacchi, Dipartimento di Scienze della Terra, Università di Pisa
Keywords: Sea-level, isostatic adjustment, Holocene, North America, Mediterranean
Reconstructions of relative sea level (RSL) since the last glacial maximum (~21 ka BP) have implications for investigation of crustal movements, calibration of earth rheology models, and the reconstruction of ice sheet extent, thickness, and deglacial chronology. In recent years, efforts have been made to create RSL databases following a standardized methodology. These regional databases provide a framework for developing our understanding of the primary mechanisms of RSL change during the last millennia (Khan et al., 2015) and a long-term baseline against which to gauge the changes in sea level observed during the 20th century and forecast for the 21st century and beyond. Here, it will be presented the results of recently compiled databases that span distinct spatial and climatic regions of the globe: the Atlantic and Pacific coast of North America, the SE Asia and the Western Mediterranean Sea.
The re-evaluation of sea-level indicators from geological and archaeological investigations have yielded more than 2500 RSL data points, comprised of sea-level index points and marine/terrestrial limiting data. The indicators are derived mainly from salt and freshwater marshes or adjacent estuarine sediment, isolation basins, beach ridges, fixed biological indicators, beachrocks and coastal archaeological structures. Some of the common difficulties and potential solutions to analyse sea-level data in such different depositional environments will be outlined. In particular, problems related to the definition of standardized indicative meaning (i.e., the relationship between the indicator and paleo mean sea level) and to the re-evaluation of old radiocarbon samples will be emphasized. The presentation will further address complex tectonic influences and the framework to compare such large variability of RSL data points.
The result is a comprehensive and quality controlled RSL database for a large portion of North American and Mediterranean coastlines that allows us to compare and contrast data from different geomorphological contexts in order to obtain basin-scale insights into the processes driving postglacial RSL changes. The data better constrains GIA spatial variability and its role in the evolution of RSL in different coastal areas.
Furthermore, an innovative empirical Bayesian spatio-temporal statistical model (Kopp et al., 2016) to this large dataset has been applied on this dataset. The application of the model to RSL index points with wide spatial and temporal coverage enables calculating rates of RSL change through time and space (averaged 1 ka time-steps). The model produces estimated rates of change regardless of data presence, but the rates are particularly robust where suites of index points are available and well distributed throughout the postglacial period. This analysis provided new and robust insights into the pattern of on-going GIA processes in these regions.
Matteo Vacchi is a coastal geomorphologist and his research is mainly focused on the Quaternary evolution of the coastal zones and on the impacts of global change on both landscape evolution and ecological assemblages of littoral areas. His current fields of interest are on palaeo-environmental
reconstructions, late Quaternary sea level changes, geoarchaeology, marine biogeomorphology as well as geologic and geomorphologic mapping of marine and coastal areas.
After his Phd, obtained in 2012 at the University of Genova, he moved to France as postdoctoral researcher (University of Aix-Marseille and Montpellier III, 2013-2017) and in the UK, where he served as Lecturer at the University of Exeter (UK) in 2017-2018.
In 2018, he was awarded with the Rita Levi Montalcini fellow, an Italian financial scheme to re-attract young scientists in Italy. For this reason, he moved to the University of Pisa in January 2019.
His on-going projects and collaborations are centred on the multiproxy reconstructions of the sea-level evolution in the last millennia in order to better assess the future sea level scenarios in the context of the climate change. On these topics, he authored and co-authored more than 40 ISI papers since 2010.
He is currently involved in several research activities along the Atlantic, Mediterranean, Pacific, Persian and Caribbean coasts. He is the team leader of the INQUA working group MOPP-Medflood (modelling palaeo processes) and in January 2019 he was elected vice president of the INQUA coastal and marine processes (CMP) commission.