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

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.

A high‐resolution sea‐level proxy dated using quartz OSL from the Holocene Skagen Odde spit system, Denmark

“…This boundary has been detected in ground-penetrating radar studies of a number of Danish beach-ridge systems and used to reconstruct relative and absolute sea-level variation (e.g. Van Heteren et al 2000;Costas et al 2016). However, due to aeolian erosion at some locations, and a lack of development of the topmost parts of the beach ridges at others, the transition between foreshore and shoreface strata cannot be used as a sea-level proxy for the Skagen Odde spit system.…”

Technical note: Optimizing the utility of combined GPR, OSL, and LiDAR (GOaL) to extract paleoenvironmental records and decipher shoreline evolution

“…Over roughly a year, three studies have utilized GOaL on prograded systems to: 1. reconstruct sea level (Coastas et al, 2016(Costas et al, 2016, 2. determine the impact of storms (Oliver et al, 2017b), and 3. decipher barrier evolution and 15 sediment supply (Oliver et al, 2017a). These studies are used here as a framework to discuss the significance of GOaL and potential pitfalls.…”

“…Where necessary, recommendations are offered in order to improve robustness of interpretations. Costas et al (2016) provides an excellent example of how GOaL can be used to reconstruct Holocene sea-level from Troia Peninsula, Portugal. Initially this complicated spit system did not appear as an ideal site to extract a sea level 20 history, but LiDAR highlights a classic prograded section targeted for GPR and OSL (Figure 6a).…”

Reconstructing Coastal Sediment Budgets From Beach‐ and Foredune‐Ridge Morphology: A Coupled Field and Modeling Approach

“…Coastal ridge and swale systems, composed predominantly of relict wave‐built beach ridges and/or aeolian foredune ridges, are found in association with progradational shorelines around the world (Tamura, ). The morphology of these elongate, shore‐parallel to subparallel features preserve paleoenvironmental signatures which have been used to infer changes in shoreline position (Mason, ), coastal sediment delivery rates and textures (Bristow & Pucillo, ; Hein et al, ), relative sea level (Billy et al, ; Hede et al, ; Long et al, ), and storm frequency (Buynevich et al, ; Costas et al, ). Subsequently, ridge proxies could be useful in predicting future changes to the coastal zone in response to autogenic forcings, climate change, and anthropogenic interventions.…”