1Recent severe winters have opened observation windows along the Aquitaine coastline (SW France) with particularly drastic impacts along the northern Gironde shores (Castelle et al., 2015), where, exceptionally, palaeoenvironmental sedimentary records and archaeological materials sealed below modern sand dunes are exposed in the intertidal zones (e.g. Tastet & Pontee, 1998; Aubié & Tastet, 2000). Historically these sedimentological sequences have been the focus of archaeologists ever since important discoveries were made along the coastline (e.g. Buffault, 1897; Fabre, 1939; Welsch, 1917; Roussot-Larroque, 1979, 1994); however, they have been underexploited so far in terms of their potential for illustrating changes to the regional landscape in contexts of high rates of sea-level rise, such as those predicted for the next century (Church et al., 2014). Such records are invaluable evidence of environmental mitigation under changing climatic pressure as seen during the late Quaternary.

2Thanks to the recent LITAQ project, these sedimentary records have been re-assessed as part of a multi-disciplinary approach. Our team – made up of palaeoecologists, geologists, archaeologists and geographers – benefited from harsh winter storms that scoured the sand that otherwise masks the old formations. Conversely, these meteorological conditions called for urgent preservation of the archaeological sites. This was partly achieved at the Lède du Gurp (LDG) site through several field campaigns (including a one-month archaeological exploration in October 2014; Verdin et al., 2018). Most of the field campaigns in the Soulac-sur-Mer area have already resulted in important discoveries. This special issue is the outcome of two years of financial supports provided by the LITAQ project (supported by the French National Research Agency/ANR in the framework of the Investments for the Future Programme, within the Cluster of Excellence COTE – ANR-10-LABX-45 and within the Cluster of Excellence LaScArBx – ANR-10-LABX-45). The papers included summarize key achievements over this short period with a special focus on the co-evolution of landscapes, climate and human settlements over time.

3Six contributions have been compiled. They are centred on stratigraphic and palaeoenvironmental issues as presented in the work of Bosq et al. and Beauval et al. for the Pleistocene, Faye et al. for the Holocene and Stephan et al. for the late Holocene. There is also a focus on the evolution of landscapes and the associated populations, especially on human settlements, their history and dynamics in space and time in contributions from Verdin et al. and Bertrand et al.

4This compilation provides a reappraisal of observations made in the final decades of the twentieth century and published in several comprehensive works, especially those of Tastet and colleagues (e.g. Tastet, 1999; Clarke et al., 2002). Those works, supported by a European LIFE project (Coastal Change, Climate and Instability. LIFE97 ENV/UK/000510), paved the way for future research, demonstrating a close connection on millennial and sub-millennial scales between the northern hemisphere climatological context and coastal environments and societies on the western European margin. Already at that time, major observations were made by mixing approaches from the geosciences and archaeology: it is worth mentioning here the key role of Julia Roussot-Larroque, whose work highlighted the exceptional richness of Neolithic and protohistorical habitats in this area and thus secured recognition of the shore sites of Soulac-sur-Mer as being of international heritage value. Julia passed away in March 2017. She was part of the LITAQ project team.

5Research conducted for the duration of the LITAQ project has actually provided new constraints for the chrono-stratigraphical framework of the Lower Médoc coastal formations directly tied to the evolution of palaeogeography and of human activities. Among the most important results are those related to:

6- the Pleistocene stratigraphy of the Lède du Gurp, which has been enriched by new observations and dating (OSL, IR-RF, ESR) (Bosq et al., 2019). According to these new results, the “Argiles du Gurp” record a transition from an estuarine environment to a freshwater marsh during the Holsteinian (MIS 11), a biotope favourable to the occurrence of Paleoloxodon antiquus elephants, bones of which have been discovered regularly over the last 150 years (Beauval et al., 2019). The terminal peat filling of the marsh precedes the thick “Sables du Gurp” formation, re-interpreted here as an aeolian spreading, dated from a glacial stage, possibly MIS 8 or 10;

7- the depression (probably of karstic/thermokarstic origin) of the archaeological site of the “Lède du Gurp”. This further developed in a comparably low sea-level context and was the ideal candidate for a thick accumulation of peaty sedimentological facies throughout the Holocene. New lithostratigraphic results, coupling classical imagery and X-ray imaging, spectrocolorimetry, XRF elementary measurements and particle size analysis together supported by radiocarbon dating are presented here (Faye et al., 2019). The infilling of this pond by alternately peaty and more sandy-clayed formations attests to sedimentation in calm waters, probably in a marsh formed after the postglacial flooding;

8- the geomorphology of the sedimentary deposits visible further north at L’Amélie on the foreshore and the dune front (Stéphan et al., 2019). They were studied during the LITAQ project with innovative tools (DGPS, TLS surveys) and accurately dated and sampled for new palaeoenvironmental reconstructions (carbon-14, archaeological constraints, grain size, micro-fauna). A vast tidal channel, which was mainly filled during the Holocene, has been identified on the basis of this new set of data. The channel was initially open to tidal influences (ca. 5 ka BC) before evolving into an estuarine marsh protected by a line of dunes that underwent an erosion phase between 1.5 and 1 ka BC. The channel was finally covered by dune deposits at the end of Antiquity (50 BC to 400 AD, i.e. 2-1.55 ka cal. BP);

9- human occupations, which are attested from the fifth millennium onwards. These are part of a context of relatively stable sea levels (fig. 1). Archaeological surveys and excavations show that, from the Neolithic period until the end of Antiquity, societies found in these wetlands an environment that was conducive to the exploitation of food resources – especially salt – until the sandy aeolian formations modified the conditions of occupation (Verdin et al., 2019). The evolution of population dynamics and the types of activities that are witnessed opens up very current lines of thought as to how humans adapt to a changing and vulnerable environment, and as to the perception of hazard and risk by societies in the past (Bertrand et al., 2019).

10The LITAQ project was the starting point for rich interdisciplinary collaborations between the geosciences and the humanities with a joint focus on the study of a specific coastal environment. This research, which is ongoing in other projects, has also strengthened institutional partnerships with the French Ministry of Culture and with communities through the National Integrated Coastal Area Management Plan. We would like to thank everyone who has made the project and the publication of its results possible.

Fig. 1: Compilation of the chrono-stratigraphical systems and major records of climatic and environmental changes used for the Marine Isotope Stage (MIS) 1 outcrops in the LITAQ study zone.

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From left to right: cultural and climatological (derived from palynological chronozones) periods (compilation drawn after Jansen and Bjorklund, 1985; Guadelli, 1996; Eynaud et al., 2004; Straus, 2018), compared to the NGRIP 50-yr average δ¹⁸O record along the GICC05 timescale (after Rasmussen et al., 2014), the sea-level rise rate (after Stanford et al., 2011) and to seasonal SST in the Bay of Biscay (after Zumaque et al., 2017). The middle column refers to the terminology of the Formal Holocene subdivisions ratified last year (Gibbard, 2018, https://www.qpg.geog.cam.ac.uk/​news/​formalsubdivisionoftheholoceneseriesgeogr18.pdf) together with the North Atlantic climatological main trends (after Eynaud et al., 2018). The pink band identifies periods of denser human presence at the study sites centred the Bronze and Iron Age periods (beige band) corresponding to stable conditions in the proximal marine environment.