Aeolization on the Atlantic coast of Galicia (NW Spain) from the end of the last glacial period to the present day: Chronology, origin and evolution of coastal dunes linked to sea‐level oscillations

Abstract

The Atlantic coast of Galicia (NW Spain) is a high‐energy environment where shingle beaches are currently developing. These coarser sediments alternate with sandy deposits which are also considered as beaches typical of a low‐energy environment. The physical association of both types of sediment with contrasted sedimentary significance raises problems of interpretation. The study of four outcrops of fossil aeolianites on this coast has allowed us to reconstruct their evolution from the end of the Upper Pleistocene to the present day. Their chronology, estimated by optically stimulated luminescence between 35 and 14 ky at the end of the last glaciation (MIS2), coincides with a local sea level 120 m below the present one. This implies a coastline shifted several kilometres from its current location and the subaerial exposure of a wide strip of the continental shelf covered by sands. The wind blew sand to form dunes towards the continent, covering the coastal areas, which then emerged with no other limitation than the active river channels. Sea‐level rise during the Holocene transgression has progressively swamped these aeolian deposits, leaving only flooded dunes, relict coastal dunes and climbing dunes on cliffs up to 180 m high. The aeolian process continued as long as there was a sandy source area to erode, although accretion finished when the sea reached its current level (Late Holocene). Since then, the wind turned from accretion to erosion of the dunes and sand beaches. This erosion exposes the older shingle beaches (probably of Eemian age) buried under the aeolian sands, as well as old, submerged forest remains and megalithic monuments. The destruction of sand beaches and dunes currently observed along the Galician coast is linked, according to most researchers, to anthropogenic global warming. However, their management should consider these evolutive issues.

Contemporary research in coastal dunes and aeolian processes

“…Sand transport was also measured using pot traps in Nguyen et al (2022) which illustrates that not all equipment needs to rely on new(er), highly technical or costly technologies to be effective. The morphology, size, and dates of sand grains were measured using scanning electron microscopy, laser granulometers, and optically stimulated luminescence (Arce Chamorro et al, 2022; Patton et al, 2022; Saha & Sinha, 2023). Satellite images and aerial photos are still the standard for estimating land cover (Fisher et al, 2023; Garzon et al, 2022; Hesp et al, 2022; Konlechner & Hilton, 2022; Robin et al, 2022).…”

“…Many manuscripts within the special issue that investigated the coastal dynamics of naturally forming dunes also explicitly situated the research in the context of contemporary sea-level rise and climate change (Arce Chamorro et al, 2022;Fisher et al, 2023;Garzon et al, 2022;Hesp et al, 2022;Robin et al, 2022) or hazard mitigation (He et al, 2022). In many cases, dune evolution will depend on human action and management interventions driven by different, sometimes conflicting, values or needs, for example, natural (diversity; complexity; unconstrained; and dynamic) and cultural (stability; accessibility; predictability; and static) optimums (Nordstrom et al, 2000).…”

“…Coastal dunes go through various evolutionary phases over thousands of years. Along the high-energy Atlantic coast of Galicia (Spain), coastal dunes dated between 35 000 and 14 000 years were formed at the end of the last glaciation when local sea levels were 120 m lower relative to the present day (Arce Chamorro et al, 2022). Strong winds blew sediment exposed on the continental shelf landwards.…”

“…Examples of human interventions in coastal dunes in this special issue include the removal of invasive vegetation (Bauer et al, 2022; Hilgendorf et al, 2022; Konlechner & Hilton, 2022), engineered foredune notches (Nguyen et al, 2022), and intensely managed or constructed foredunes (Dickey et al, 2023; He et al, 2022; Sanromualdo‐Collado et al, 2022; Walker et al, 2023). Many manuscripts within the special issue that investigated the coastal dynamics of naturally forming dunes also explicitly situated the research in the context of contemporary sea‐level rise and climate change (Arce Chamorro et al, 2022; Fisher et al, 2023; Garzon et al, 2022; Hesp et al, 2022; Robin et al, 2022) or hazard mitigation (He et al, 2022). In many cases, dune evolution will depend on human action and management interventions driven by different, sometimes conflicting, values or needs, for example, natural (diversity; complexity; unconstrained; and dynamic) and cultural (stability; accessibility; predictability; and static) optimums (Nordstrom et al, 2000).…”

“…Large‐scale studies in this special issue are an excellent reminder that coastal dunes are part of wider coastal systems, both spatially and temporally. The erosion of coastal dunes at various sites in Galicia (Spain) exposed older shingle beaches, submerged forest remains, and even megalithic monuments (Arce Chamorro et al, 2022), all expressions of coastline changes over thousands of years. On barrier islands, coastal dunes are a key control on sediment distribution and may be indicative of changes to the entire island at medium timescales (Fisher et al, 2023).…”