Abstract
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 6.5 ka. 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 6.5 ka with an accumulated change in elevation of about 2 m. 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.
Highlights
The elevation of the present beach-dune interface relative to MSL was estimated using two approaches: (i) the elevation of the limit between the beach and the dune using digital terrain models (e.g. LiDAR dataset), aerial photography, and ground-truthing, and (ii) the elevation of the maximum runup defined by the debris based on fieldwork surveys carried out following the impact of major storms (Fig. 2)
In order to improve our understanding of this key coastal driver, here we have explored alternative sea-level indicators extracted from the stratigraphy of coastal barriers dated by OSL in combination with aerial photographs, and developed a new sea-level curve for the last 6.5 ka
We have used the morphological features representing the contact between the dune and the beach, and the beach berm from Troia Peninsula, central Portugal
Summary
The elevation of the present beach-dune interface relative to MSL was estimated using two approaches: (i) the elevation of the limit between the beach and the dune using digital terrain models (e.g. LiDAR dataset), aerial photography, and ground-truthing, and (ii) the elevation of the maximum runup defined by the debris based on fieldwork surveys carried out following the impact of major storms (Fig. 2). The latter assumes that the dune is initiated in the lee of the beach debris or within the inland limit of the maximum penetration of the marine influence. For the first approach we mapped a total of 34 points along 2 km while for the second we mapped 6 points along 40 km in order to capture the morphological variability of selected feature
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