Theocharis A. Plomaritis

Coastal barrier stratigraphy for Holocene high-resolution sea-level reconstruction

The uncertainties surrounding present and future sea-level rise have revived the debate around sea-level changes through the deglaciation and mid- to late Holocene, from which arises a need for high-quality reconstructions of regional sea level. Here, we explore the stratigraphy of a sandy barrier to identify the best sea-level indicators and provide a new sea-level reconstruction for the central Portuguese coast over the past 6.5u2009ka. The selected indicators represent morphological features extracted from coastal barrier stratigraphy, beach berm and dune-beach contact. These features were mapped from high-resolution ground penetrating radar images of the subsurface and transformed into sea-level indicators through comparison with modern analogs and a chronology based on optically stimulated luminescence ages. Our reconstructions document a continuous but slow sea-level rise after 6.5u2009ka with an accumulated change in elevation of about 2u2009m. In the context of SW Europe, our results show good agreement with previous studies, including the Tagus isostatic model, with minor discrepancies that demand further improvement of regional models. This work reinforces the potential of barrier indicators to accurately reconstruct high-resolution mid- to late Holocene sea-level changes through simple approaches.

Beaches of Cadiz

The coast of Cadiz province (SW Spain) constitutes a complex system with a wide variety of hydrodynamic and geological-geomorphological conditions. Morphodynamic behaviour of beaches in this area shows more dissipative states in the Atlantic coast and more reflective states in the Mediterranean coast. Recent shoreline trends indicate a relatively stable behaviour along most part of Cadiz coast over the last decades, although there are numerous sectors with a clearly erosive trend, mainly in the Northern half of the province. The great spatial and temporal variability of shoreline changes observed is related to the heterogeneity of the coast, as well as to the diversity of factors contributing to erosion processes on each sector. Several coastal hazard hotspots appear along the study zone, mostly related to extreme meteorological events and short-term trends, namely coastal erosion and flooding. The frequency and severity of the risks derived from these hazards have increased over the last decades, mainly due to the increased anthropogenic pressure and urban development on the coast. The coast of Cadiz province (SW Spain) constitutes a complex system with a wide variety of hydrodynamic and geological-geomorphological conditions. Morphodynamic behaviour of beaches in this area shows more dissipative states in the Atlantic coast and more reflective states in the Mediterranean coast. Recent shoreline trends indicate a relatively stable behaviour along most part of Cadiz coast over the last decades, although there are numerous sectors with a clearly erosive trend, mainly in the Northern half of the province. The great spatial and temporal variability of shoreline changes observed is related to the heterogeneity of the coast, as well as to the diversity of factors contributing to erosion processes on each sector. Several coastal hazard hotspots appear along the study zone, mostly related to extreme meteorological events and short-term trends, namely coastal erosion and flooding. The frequency and severity of the risks derived from these hazards have increased over the last decades, mainly due to the increased anthropogenic pressure and urban development on the coast.

Tide circulation patterns in a coastal lagoon under sea-level rise

This study evaluates the patterns and effects of relative sea-level rise on the tidal circulation of the basin of the Ria Formosa coastal lagoon using a process-based model that is solved on an unstructured mesh. To predict the changes in the lagoon tidal circulation in the year 2100, the model is forced by tides and a static sea level. The bathymetry and the basin geometry are updated in response to sea-level rise for three morphological response scenarios: no bed updating, barrier island rollover, and basin infilling. Model results indicate that sea-level rise (SLR) will change the baseline current velocity patterns inside the lagoon over the ~100-year study period, due to a strong reduction in the area of the intertidal basin. The basin infilling scenario is associated with the most important adjustments of the tidal circulation (i.e., increases in the flood velocities and delays in the ebb tide), together with an increase in the cumulative discharges of the tidal inlets. Under sea-level rise and in the basin infilling scenario, the salt marshes and tidal flats experience increases in the tidal range and current asymmetry. Basin infilling changes the sediment flushing capacity of the lagoon, leading to the attenuation of the flood dominance in the main inlet and the strengthening of the flood dominance in the two secondary inlets. The predictions resulting from these scenarios provide very useful information on the long-term evolution of similar coastal lagoons that experience varying degrees of SLR. This study highlights the need for research focusing on the quantification of the physical and socio-economic impacts of SLR on lagoon systems, thus enabling the development of effective adaptation strategies.