Chapter 9
Paleolandscapes of the Celtic Sea and the Channel/La Manche

R. Helen Farr,1 Garry Momber,2 Julie Satchell2 and Nicholas C. Flemming3

1Southampton Marine and Maritime Institute, Archaeology, University of Southampton, Highfield, UK

2Maritime Archaeology Trust, National Oceanography Centre, Southampton, UK

3National Oceanography Centre, Southampton, UK

Introduction

This chapter provides an overview of the work that has been undertaken in the region of the English Channel and Celtic Sea area. Whilst not exhaustive, it contains background information about the environment, geology and paleogeography of the region alongside a summary of current research, data sets and knowledge of submerged prehistoric sites. Bibliographic references of key texts and URLs are provided to sources of data.

Earth Sciences and Sources of Data

Modern coastline, best sources of high-resolution data

The Channel/La Manche and Celtic Sea area encompasses the south and south-west coast of the UK, the English Channel and the coastal waters of northern France (Fig. 9.1). The modern coastline consists of a wide range of coastal units from hard and soft rock cliffs, estuaries and barrier beaches.


Map shows areas subject to study where nautical miles are from 0 to 150 and kilometres are from 0 to 300.

Figure 9.1 Map indicating area subject to study. Julian Whitewright; Maritime Archaeology Trust. Reproduced with permission.

This region extends from Dover and Calais in the east, to St. David's Head in the north-west, and expands out across the Celtic Sea to the continental shelf edge, Brest and the Cotentin Peninsula. As such this region incorporates the Channel/La Manche, the Solent and Isle of Wight, the Cornish Peninsula, southern Wales, and the north coast of France. Water depths are generally shallower in the eastern channel (<50 m), deepening to 50 m to 200 m further west, and dropping to 1000 m towards the outer continental shelf boundary (UKMMAS 2010) (Fig. 9.2). The eastern Channel is characterized by shelving sand, shingle and pebble beaches interspersed with cliffs, whilst the western coastline is predominantly rocky. Areas of intertidal sediment and salt marsh can be found in bays and inlets, especially those in the Solent (Chichester, Langstone, and Portsmouth harbors, and Southampton Water), Poole Harbour and the Bristol Channel and Milford Haven, St. Malo, the Seine Estuary, and along the Normandy river estuaries.


Map shows bathymetric contours in La Manche and Western approaches, where Isle of Wight is at North central region, western approaches are seen in east region, Jersey is at south, et cetera.

Figure 9.2 Bathymetric contours in the Channel/La Manche and the Western Approaches. Jasmine Noble-Shelley; Maritime Archaeology Trust, after Paphitis (2000). Reproduced with permission.

Data sources

There are many multidisciplinary assessments of the modern coastline that may be useful for the investigation of coastal change in this region. This is probably one of the most intensively studied sea areas in the world with a substantial number of marine research centers.

On the French coast these include La Station de biologie marine de Concarneau, La Station biologique de Roscoff (SBR), Boulogne and IFREMER (Institut français de recherche pour l'exploitation de la mer), Brest. National coastal monitoring programs include the SOMLIT project (Service d'Observation du Milieu Littoral) which co-ordinates the monitoring activities carried out by marine stations on French coasts in order to understand the impact of global change on coastal zones. The French processing and archiving facility CERSAT (Centre ERS d'Archivage et de Traitement), the Coriolis Centre for in situ oceanographic data, and Sextant, a server for georeferenced marine data, provide access to databases of gridded and vector data produced by IFREMER and its partners. Most of these data are fully accessible to the public.

SISMER (Systèmes d'Informations Scientifiques pour la Mer) is the national oceanographic data center of France, and archives French oceanographic data from 1968 onwards including physical, chemical oceanography and geophysical data.

Across the Channel, the southern British coast is well mapped by the Ordnance Survey (OS) and the British Geological Survey (BGS) and many data sets are available as high-resolution vector and raster data. Over the last decade, English Heritage has undertaken a series of projects to characterize the nature of the English coast including Rapid Coastal Zone Assessment Surveys (RCZAS) and the Historic Seascape Characterization (HSC). These expand historic landscape characterization into the marine environment. Additional regional surveys include Charting Progress 2: the State of UK Seas (UKMMAS 2010), which assessed the coastal environment and marine ecosystem around Britain, and the Marine Aggregates Levy Sustainability Fund (ALSF) Regional Environmental Characterizations (REC) — a series of regional coastal surveys of Britain's submerged habitats and heritage. RECs of the south coast are available for 2007–2010.

The Marine Aggregate Industry Protocol (MAI) for reporting finds of archaeological interest was set up in 2005, and is run in partnership with the British Marine Aggregate Producers Association (BMAPA), The Crown Estate and Historic England, and is implemented by Wessex Archaeology. Unexpected finds by offshore industries is covered by the Offshore Renewables Protocol for Archaeological Discoveries (ORPAD), established in 2010 and run by The Crown Estate and Wessex Archaeology. Since their creation, over 2000 objects have been reported.

The Channel Coastal Observatory (CCO) is the data management center for the regional coastal monitoring programs of England. It has freely accessible data for the Channel and Celtic Sea region including aerial photography, LiDAR (Light Detection and Ranging) data, topographic data, hydrogeographic data, photogrammetric data, seabed mapping, sediment distribution data, cliff lines and wave and tidal information. This resource enables modern coastal dynamics to be searched and mapped both by region and date.

The Standing Conference on Problems Associated with the Coastline (SCOPAC) sediment transport study (Carter et al. 2004) covers the coastline of central/southern England between Lyme Regis, Dorset and Shoreham-by-Sea, West Sussex. SCOPAC includes strategic regional coastal monitoring programs, analysis of coastal processes and a bibliographic database. The sediment transport study is regionally searchable and provides an overview of the coastal sediment types involved in transport and the transport mechanism involved.

Offshore wave and tidal data is available from the United Kingdom Hydrographic Office (UKHO), the Proudman Oceanographic Laboratory (POL) (now the National Oceanography Centre (NOC) — Liverpool), and the British Oceanographic Data Centre (BODC) — a national facility for preserving and distributing marine data.

The PISCES project (Partnerships Involving Stakeholders in the Celtic Sea Eco-System) was a three-year project funded by the European Commission to unite people across different sectors and countries for the sustainable management of the marine ecosystem. It provides interactive maps of the present-day Celtic Sea marine environment. Partnership projects provide routes for managing multi-disciplinary research on regional coastal problems.

Further studies of coastal geomorphology and erosion modeling for coastal management include the European-wide EUROSION and Response projects that looked to integrate EU climate change policy (2003–06) and the UK Futurecoast project.

A number of current EU projects researching and looking to manage the effects of coastal change are located within the INTERREG IVA European Regional Development Fund (ERDF) program. These have built on early INTERREG projects such as MESSINA (2003–06), EMDI (2004–07), and IMCORE (2008–11) and include:

  • FLOODCOM — led by Essex County Council
  • 3i — Integrated Coastal Zone Management led by Delft University of Technology
  • Flood Aware, led by Provincie Zeeland
  • CC2150 — Coastal Communities 2150 and Beyond, led by the UK Environment Agency
  • PRISMA — led by Waterwegen en Zeekanaal NV
  • Arch-Manche — led by the Maritime Archaeology Trust (Hampshire and Wight Trust for Maritime Archaeology).

Further resources

Wetlands, deltas, marshes, lagoons, coastal lakes

Much of the offshore Channel and Celtic Sea area is dominated by high-energy, scour environments. However low-energy coastal formations such as wetlands, marshes and lagoons exist in specific sheltered locations and provide areas of potential preservation of archaeological material. There are extensive wetlands, lagoons, marshes and mudflats on the French coast east of St. Malo, around Mont-Saint-Michel in Normandy, around the mouth of the River Seine, the Somme Estuary and on the west-facing coasts of Pas-de-Calais. The coastline of Brittany was formed where the Armorican Massif reaches the sea. Here, hard headlands and cliff lines are interspersed with ria inlets that track the course of submerged paleovalleys. These now form sheltered inlets with marshes and lagoons (Prigent et al. 1983). Figure 9.3 shows the distribution of geomorphological features including the wetland areas across the region.


Map shows characterization of coastal geological and geomorphological features, where hard paleozoic rocks are seen in border of some regions, cliffs are seen in border of south regions, et cetera.

Figure 9.3 General characterization of coastal geological and geomorphological features. Note the areas of intertidal mud flats and estuarine marsh. Jasmine Noble-Shelley; Maritime Archaeology Trust after Paphitis (2000). Reproduced with permission.

Wetlands and mudflats in England include the Severn Estuary, Dartmouth and Kingsbridge estuaries, the Tamar, Falmouth, Fowey estuaries and the Taw-Torridge Estuary, Christchurch and Poole harbors along with the harbors and waterways around the Solent. Wetland areas have been the focus of particular prehistoric archaeological interest. This includes work by the West Coast Palaeolandscapes Survey (Fitch & Gaffney 2011) and the Severn Estuary Levels Research Committee (SELRC). SELRC formed in 1985 because of the increasing awareness of the potential of the estuary wetlands for preserving archaeology. The Mesolithic site at Goldcliff and findings at Uskmouth, both on the Severn Estuary, including preserved Mesolithic human footprints (Bell 2007) highlight the excellent preservation within this wetland environment. In the Solent, there has been a long history of research. Many local surveys have been undertaken by the Maritime Archaeology Trust (formerly the Hampshire and Wight Trust for Maritime Archaeology), Wessex Archaeology and the New Forest Council, as well as various projects by the University of Southampton, the University of Bournemouth and the Isle of Wight County Council. Collaborative projects have mapped the effects of dredging and coastal development on these environments (e.g. Hodson & West 1972), as well as monitoring change. Work on the submerged landscape at Bouldnor Cliff addressed the formation of the Solent in relation to the archaeological, sedimentological and paleoenvironmental studies of submerged Holocene deposits (Momber et al. 2011).

The RESPONSE Project, a three-year project supported by the LIFE financial instrument of the European Community, launched in December 2006 to investigate the risks from climate change on both sides of the Channel. This built on the Coastal Change, Climate and Instability EC LIFE project that concluded in 2000.

Further information on the geology of southern England and intertidal estuary environments including a comprehensive bibliography can be found online on Ian West's University of Southampton website (www.southampton.ac.uk/~imw/). In addition, a UK country-wide survey of intertidal and offshore peat deposits has been compiled by English Heritage/Historic England into one searchable database organized by region (Hazell 2008). Reports are available from the website.

Further resources

Coastal geomorpho-dynamics, erosion, accumulation

Rates and patterns of erosion vary across the region depending on the susceptibility of the coastal topography and geology to weathering. Exposure of the coastline to the large Atlantic fetch has resulted in complex coastal geomorphology. Rugged outcrops along hard rock shorelines are often interspersed with sheltered, sediment-filled bays, inlets or estuaries. Where the underlying bedrock is softer, wide bays are backed by lines of eroding cliffs.

Towards the eastern end of the Channel, dune systems have developed along low-lying alluvial coastlines. These are particularly notable around the estuary mouths of the Seine and the Somme, the west coast of the Contentin Peninsula and along the south-facing coasts from Kent to West Sussex. In the adjacent county of Hampshire a complex of natural harbors contains a rich archaeological and sediment archive (Collins & Ansell 2000; Wenban-Smith & Horsfield 2001).

The intermittent exposures of soft cliffs along the Channel from Kent and the Pas-de-Calais in the east, to Lyme Bay and the Contentin Peninsula in the west, are the source of sediments that are transported to form spits such as Chesil Beach, and sandy headlands like that at Dungeness. Sediment also accumulates at the mouth of the major rivers such as the Somme and Seine. These sedimentary features can protect archaeological deposits beneath them or in the areas they shelter. Conversely, erosion of land that produces the sediment can have a negative impact on the cultural resource. Cliff erosion often manifests itself in the form of landslides or rotational slumping that carries material into the sea. The south-east facing cliffs of the Isle of Wight form the largest coastal landslip complex in Europe.

The west Cornish Peninsula is geologically similar to the Armorican Massif. It is a rocky, eroded, high-energy coast exposed to Atlantic storms. Despite this, coastal prehistoric sites have been preserved in the sheltered bays and protected inlets etched into the rocky headlands. For a map of the Armorican sites see Prigent et al. (1983: fig. 1). The incised valleys provide effective shelters from the dominant westerly waves and storms. The area around Vannes in southern Brittany is particularly significant as it is rich in archaeological Neolithic and Mesolithic monuments that extend into the intertidal zone and underwater; the stone circles of Er Lannic in the Golfe du Morbihan being the most visible example (www.stonepages.com/france/erlannic.html). In addition, prehistoric sites and hundreds of fish traps are found in embayments and estuaries around Brittany and Normandy. These are subject to study and recording by the Centre de Recherche en Archéologie, Archéosciences, Histoire (CReAAH), a network of organizations that are actively researching threats to the coastal heritage around the coastline of northwest France. Many of these archaeological features are dateable and can be used as indicators of coastal change.

The north coasts of Cornwall, Devon and Somerset contain protective environments in sheltered inlets where they are covered by the fluvial sediments. Submerged forests and Mesolithic material have been found off Westward Ho!, Porlock and Hele Bay; however the steep valleys of the north Devon coast and the broad catchments of Exmoor above can lead to devastating flash floods causing severe coastal erosion (e.g. Lynmouth in 1952).

For further information on local geomorphology, erosion and accumulation, reference should be made to the French Geological Survey (Bureau de Recherches Géologiques et Minières — BRGM), and the British Geological Survey in addition to the RCZAs and RECs for the region of interest. In the Solent region, SCOPAC also maps erosion and sediment transport.

Further resources

Solid geology

The two dominant geologic processes acting in this region are the east–west extensional forces caused by the break-up of Europe from America, and the north–south compressional forces caused by the Alpine orogeny. The fault-bounded Western Approaches Trough forms a sedimentary basin between the Armorican Massif in Brittany and the Cornubian Massif in Cornwall (Evans 1990). The planation surface of the sea floor in this area and that of the Celtic Sea is thought to date to the Mid Tertiary. At depths of 38 m to 69 m, submerged cliffs and terrace features dating to the Miocene and Pliocene have been eroded into the southern offshore region of Cornwall and Devon (Evans 1990).

Between 1 Ma and 400 ka, Britain was joined to the mainland of Europe at all times, despite glacially controlled fluctuations of sea level (Gibbard 1988; Stringer 2006). To the east of our study area, a high chalk plateau, the Weald-Artois anticline provided a solid bedrock link between southern Kent and northern France, even at times of interglacial high sea level. Some time between 400 ka and 200 ka this chalk ridge was eroded, and at subsequent times of interglacial high sea level, Britain and Ireland were cut off from Europe. The geology of the eastern Channel, the Weald–Artois anticline (Dover Strait) and southern Bight are well presented in Hijma et al. (2011).

The French Geological Society (Société géologique de France) has a variety of collated resources including the Geology of France journals which cover both sub-surface and surface geology, and 1:50,000 maps. The BRGM offers access to its geoscientific and environmental data through its InfoTerre portal.

The BGS has undertaken research into bedrock geology and seabed sediments across the region. This work is available as a series of publications and maps (1:250,000 and 1:65,000). A searchable database (GeoIndex) is also available online, comprising both onshore and offshore geological and geophysical data. 3D geology models (50-m grid) are available for terrestrial regions. The Strategic Environment Assessment program (SEA), funded by the Department for Business, Energy and Industrial Strategy (DBEIS), provides a shelf-wide resource with summaries of the geology of eight designated regions around the United Kingdom.

Further regionally specific geological reviews are numerous. The bedrock geology of the Channel and Celtic Sea is summarized by Evans (1990) for the Western Approaches, and Hamblin et al. (1992) for the UK sector of the Channel. The geology of the Bristol Channel is outlined by Tappin et al. (1994) and that of the Solent by Dix (2001), Velegrakis (2000), and Velegrakis et al. (1999). Gibbard (1988) describes the background of tectonic processes that have formed the depressions of the English Channel and the North Sea over many millions of years and influenced the courses of the great rivers flowing onto and across the continental shelf. The shelf valley systems in the Channel have been studied by Gupta et al. (2008). A special issue of the Journal of Quaternary Science was published in 2003 devoted to the Quaternary history of the English Channel (Gibbard & Lautridou 2003). Further details of regional and local geology of the coast and the seabed are given by a number of papers in that journal (e.g. Bourillet et al. 2003; Lagarde et al. 2003; Reynaud et al. 2003).

Understanding of local geological features is necessary for assessment of potential archaeological preservation. The lee of rocky outcrops can provide protection for paleoterrestrial features and anthropogenic material. One famous archaeological example of this within this region is the Fermanville Paleolithic site (Scuvée & Verague 1988; Cliquet et al. 2011). Prehistoric artifacts have been found in 20 m of water in the protective shadow of the Cap Lévi–Biéroc granite outcrop, east of Cherbourg. The submerged occupation site is shielded from storm damage and as such has withstood climatic variations for over 60,000 years (Fig. 9.4).


Image shows granite headland which protects Paleolithic site of Cap Lévi, where flood plain is depicted at Southwest region above which area with approximate area of lithic scatter is seen.

Figure 9.4 Cap Lévi, Fermanville, showing the granite headland that is protecting the Paleolithic site at 20 m depth on the eastern side. Jasmine Noble-Shelley after Garry Momber; Maritime Archaeology Trust. Source of image Google. Reproduced with permission.

Further resources

Bathymetry

The Western Approaches are located on the north-west corner of the European continental shelf where water depths are generally less than 300 m. Around the coastlines of England and Wales, the main features of the bathymetry are nearshore water depths generally less than 50 m (see Fig. 9.2). The deepest areas (>100 m) are found offshore on the south coast to the west of Start Point, and also on the west coast off the westernmost tip of Wales. Off the west coast, the Celtic Sea is characterized by a deep (100–200 m) channel running north–south, and off the south coast the western half of the Channel is characterized by a fairly deep (100 m) central channel which runs (and shallows) in a west–east direction. West of Normandy, the continental shelf drops gently towards the Channel Islands. As such, these islands were accessible from mainland Europe for large parts of the Pleistocene. This is evidenced by sites like La Cotte de St. Brelade on the island of Jersey, indicating that prehistoric hominins exploited the landscape when sea levels were lower (Callow & Cornford 1986; Scott et al. 2014).

The bathymetry of the Channel and Celtic Sea provides further information on the potential for survival of archaeological remains. By identifying deeper areas it is possible to target those sites that are less likely to be affected by hydrodynamic processes, which can scour and disturb archaeological remains. The depth of the archaeological resource also affects the biological and chemical conditions influencing the preservation of sites. Archaeological material can survive for hundreds of thousands of years in the right taphonomic context if undisturbed or exposed by human action or changes in hydrodynamic patterns.

Maritime and hydrographic data sources

There are a range of publicly accessible data sets for this region. The most readily available and wide-ranging are the satellite-derived combined topography and bathymetry data sets (ETOPO1) from the National Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center. ETOPO1 provides a 1 arcminute global relief model of topography and bathymetry. An equally extensive database is that from General Bathymetric Chart of the Oceans (GEBCO) providing a 30 arcseconds gridded bathymetry. However, this data set was designed to target the deep oceans, and as such, data from the continental shelves is limited.

A number of higher resolution data sets generated from single-beam echo sounder (SBES), multibeam echo sounder (MBES) and bathymetric LiDAR surveys also cover parts of the region. Some of the main data sources are listed here:

  • – Maritime Coastguard Agency (MCA) Hydrographic Data. These data sets are not directly available for download, but it is possible to obtain agreements between organizations to access them for research purposes. Data for the length of southern England is available through the Channel Coastal Observatory;
  • – Service hydrographique et océanographique de la Marine (SHOM), the French hydrographic agency, provides access to bathymetric data at varying resolutions. Data is available for the whole Golfe de Gascogne (Bay of Biscay), the Manche (Channel) region and the Atlantic coast;
  • – The national Litto3D program, maps the coastal zone at higher resolution, aiming for a seamless onshore/offshore survey combining LiDAR and bathymetric data;
  • – IFREMER manages national oceanographic data including SISMER. Amongst other forms of oceanographic data, SISMER manages geophysical data;
  • – SeaZone Solutions Ltd is a commercial organization affiliated with the United Kingdom Hydrographic Office data. Bathymetric data includes MBES data, gridded SBES data and digitized Admiralty data. The data must be purchased;
  • – MEDIN (Marine Environmental Data & Information Network) contains some publicly available alternative sources of bathymetric data;
  • – REC projects were funded through the Marine ALSF from 2002–2011. RECs include large-scale bathymetric seismic and acoustic surveys. Sub-bottom data and core log material were collected in collaboration with the marine aggregates industry. Those of interest within the Channel and Celtic Sea zone include the offshore Arun River (Gupta et al. 2008; Wessex Archaeology 2008a,b), eastern English Channel and the Severn Estuary (MoLAS 2007).

The commercial sector provides an additional source of bathymetric data. Offshore surveys required for the renewable energy sectors or offshore infrastructure are making their data available through the Cowrie Data Management System.

Small localized data sets within the research region include:

  • New Forest District Council, north shore, Western Solent, 2006;
  • Hampshire and Wight Trust for Maritime Archaeology/Maritime Archaeology Trust;
  • University of Southampton;
  • EMODnet (European Marine Observation and Data Network) hydrography portal has access to digital terrain models and metadata for selected maritime basins across Europe including the Channel and Celtic Seas and Western Approaches.

For a fuller account of available geophysics data across the UK see Dix and Sturt (2013).

Further resources

Vertical earth movements

The dominant influence on vertical earth movement in this region is glacio-isostatic adjustment (GIA) (see Chapter 2, pages 20–24). The complex relationship between the rates of rebound and subsidence, and the global eustatic rise in the postglacial are key factors in determining the varying impacts of the sea on the land in different regions today. The process is long term and led to the separation of the British Isles from continental Europe around 7500 years ago (Flemming 1998; Bradley et al. 2009; 2011).

There has been much work modeling glacio-isostatic adjustment across the region. High-resolution GIAs are in constant development. The most recent GIA, 11 ka time slab for the British Isles is reproduced in Fig. 9.5.


Image shows GIA model at 11,000 BP superimposed on map of British Isles, where superimposition is seen in north central region.

Figure 9.5 GIA model at 11,000 BP, superimposed on a map of the British Isles. Courtesy of Fraser Sturt (2015). Map produced in part from GEBCO 08 (www.gebco.net) data. Reproduced with permission.

The south coast of England and northern Brittany are subsiding from postglacial readjustment. On the French Armorican coast numerous megalithic passage graves and other prehistoric remains are preserved in the intertidal zone down to the low-tide limit where the tidal range is very large (5–10 m) (Giot 1968; Prigent et al. 1983). Discussion of preserved sites can be seen below.

Pleistocene and Holocene sediment thickness on the continental shelf

The unconsolidated sediment cover in the Channel is relatively thin when compared with the North Sea, which is a net area of accumulation. There are recent sediments in shallow water including peat deposits dating to the last postglacial transgression. The sediment cover is plotted on the BGS Bottom Sediment map series (BGS, 1:250,000). The thickest sediment deposits are in the over-deepened troughs of the Hurd Deep, the Fosse de L’île Vierge and the Fosse d'Ouessant. The Hurd Deep analyzed by Evans (1990: 75–76) is a narrow graben (Antoine et al. 2003), which has been successively infilled at periods of low sea level and then partially scoured out by tidal currents during and after marine transgressions. It is located far to the south of any phase of ice scour. The incision reaches a maximum depth of 240 m with a sediment infill thickness of 80 m, while the surrounding sea bed is quite flat at a depth of 70 m to 90 m, with a sediment cover often less than 0.5 m.

The Channel river system is an erosive landscape and a relatively sediment-starved part of the Northwest European Shelf (Gupta et al. 2008); strong tidal streams have led to scouring of sediments. Large areas of the Bristol Channel, Pembrokeshire and north Devon coasts have been eroded of Quaternary sediments (Tappin et al. 1994).

Data sources

Much of the sediment thickness data can be found summarized regionally within the Marine ALSF REC projects. Offshore geological records include seismic profiles, bathymetry and backscatter data, core or borehole and grab samples. The offshore geological records are held by the BGS along with some borehole data. The BGS Offshore Regional Reports for Cardigan Bay and the Bristol Channel (Tappin et al. 1994) and the western English Channel and Western Approaches (Evans 1990) contain data for this region. Borehole data is collected during port and offshore development projects. The MAREMAP project holds seabed mapping data across the UK. Industry data from the UK offshore oil and gas companies can be searched via the UK Oil and Gas Data website. The University of Southampton holds various boomer sub-bottom data sets from within the Channel and Celtic Sea region.

On a European scale, EMODnet has collated national data sets for habitat mapping that contains bathymetry, oceanographic and geologic seabed data and the Geo-Seas project collates offshore geological data from national providers. There is some overlap with the BGS archives.

SISMER is the designated national oceanographic data center for France. It is based at IFREMER, Brest. Local bathymetric data is being collected in the region for archaeological purposes by the Association pour le développement de la recherche en archéologie maritime (ADRAMAR). Surveys by the vessel L'André Malraux (launched in 2012) by Le Département des recherches archéologiques subaquatiques et sous-marines (DRASSM) is collecting data for archaeological purposes around French coastal waters, although this is usually focused on shipwreck research.

Further resources

Post-LGM Climate, Sea Level, and Paleoshorelines

The Last Glacial cycle has been studied intensively for global eustatic sea-level change and coastal evolution (see for example Lambeck 1991; 1993a,b; Lambeck & Chappell 2001; van Andel & Davies 2003; Waller & Long 2003) and the regional ice loading and isostatic response (Lambeck 1995; Peltier et al. 2002; Shennan & Horton 2002; Shennan et al. 2002; 2006) although no definitive reconstructions exist for this region as a whole (Westley et al. 2013). Paleolandscape reconstructions have been limited to areas where 3D seismic data has been available (Gaffney et al. 2007). Within the Channel and Celtic Sea region this includes parts of the English Channel including Poole Harbour and Christchurch Bay.

General climatic conditions and changes after the LGM

Sea-level research and modeling has been a rapidly growing field of research in the last decade, and for an introduction to literature focusing on fluctuations during the Last Glacial cycle see Rohling et al. (1998; 2008), Lambeck and Chappell (2001), and Siddall et al. (2003; 2010). Van Andel and Davies (2003) have published a multi-disciplinary analysis of the climatic fluctuations during Marine Isotope Stage 3 (MIS 3), approximately 60 ka to 20 ka, and the consequent effects on the distribution of Neanderthal and anatomically modern humans (AMH), leading up to the LGM. During MIS 3 the Greenland ice core data GISP2 (Meese et al. 1997; Johnsen et al. 2001) show rapid fluctuations of temperature of the order of 5–10°C every few thousand years, the so-called Dansgaard-Oeschger oscillations (van Andel & Davies 2003: 58). The sequence of calculations and plotted maps, correlated with summaries of known major archaeological sites, provides an interesting analysis. By integrating archaeological data from the seabed, these maps and calculations can be used as a starting point to identify potential areas of interest for locating submerged habitation sites at times of low sea level. For an early example of this approach see Louwe Kooijmans (1970–71).


Maps show various reconstructions of permafrost distribution during Devensian/Weichselian, with indications like permafrost is largely absent, 74–59 ka: continuous permafrost, 27–20 ka: discontinuous permafrost, et cetera.

Figure 9.6 Map showing various reconstructions of permafrost distribution during the Devensian/Weichselian. Maps are labelled as (a) to (f) from left to right and from top to bottom as follows (a) Last Glacial Period, based on Williams (1969); (b) 74–69 ka, based on Huijzer & Vandenberghe (1998); (c) 27–20 ka, based on Huijzer & Vandenberghe (1998); (d) 20–13 ka, based on Huijzer & Vandenberghe (1998); (e) 20 ka, based on van Vliet-Lanöe (2000); (f) 12.9–11.5 ka (Younger Dryas), based on Isarin (1997). After Murton & Lautridou (2003, fig.2). Adapted by Jasmine Noble Shelley, Maritime Archaeology Trust.

Reconstructions of the last glacial ice sheet (Clark et al. 2012) show at its greatest extent that it covered Scotland, Ireland and northern England and stretched west across to the Atlantic shelf edge at the LGM. Southern England avoided glaciation, and the ice had retreated from the Celtic Sea and southwest Wales by ca. 19 ka. Murton and Lautridou (2003) cite a number of authors to indicate the probable limits of continuous permafrost at different dates (Fig. 9.6). Most models show continuous permafrost barely extended south of the English coastline. Even the coldest estimates show Cornwall and Brittany free of continuous permafrost at the peak of the LGM. Thus the western Channel and Western Approaches may have served as a refuge for Paleolithic communities, highlighting the importance of the finds that have been uncovered from submerged sites such as the Fermanville, Biéroc, Paleolithic site (Scuvée & Verague 1988; Cliquet et al. 2011), Bouldnor Cliff (Momber et al. 2011) or the artifacts recovered from paleochannels in the paleo-Arun tributary of the Channel River (www.wessexarch.co.uk/book/export/html/1200).

Evolution of sea level and coastline since the LGM

Following the LGM ca. 22,000 years ago, the climate continued to oscillate. Conditions ameliorated as deglaciation continued, reaching a peak in the Woodgrange or Windermere Interstadial at ca. 12.9 ka to 14.7 ka. This was followed by the colder harsher conditions of the Younger Dryas/GS-1 (ca. 12.9–11.5 ka) which then led into the ameliorated dry climate of the Holocene, Boreal regime. By ca. 6 ka to 7 ka there was a shift into the Atlantic regime which brought warmer and wetter conditions once more.

The process of sea-level rise that resulted from the thawing ice following the LGM has been subject to several studies (see for example Lambeck 1991; 1993a,b; 1995; Shennan & Horton 2002; Shennan et al. 2002; 2006; Waller & Long 2003; Bradley et al. 2009; 2011). Shelf-scale paleogeographic reconstructions (Fig. 9.7) have been undertaken using a combination of high-resolution bathymetry and glacio-isostatic modeling. However due to local variations in ice-sheet extent and deglaciation processes, and the need to account for differing rates of sedimentation and erosion, reconstructions of the sea-level evolution varies from region to region and there are many uncertainties (Brooks & Edwards 2006).


Map shows paleogeographic reconstructions from 11,000 BP over kilometre scale ranging from 0 to 1,000 and MSL scale ranging from -200 to 700.

Figure 9.7 Paleogeographic reconstructions from 11,000 BP. Courtesy of Fraser Sturt, (2015). Map produced in part from Ordnance Survey Digimap, SeaZone solutions and GEBCO 08 (www.gebco.net) data. ©Crown Copyright/database right 2015. An Ordnance Survey/EDINA supplied service. ©Crown Copyright/SeaZone Solutions. All rights reserved. Licence no. 052006.001 31 July 2011. Not to be used for navigation. Additional data courtesy of the Channel Coastal Observatory.

Britain became an island approximately 7500-7000 years ago, in the latter part of the Mesolithic (ca. 11000–6000 years ago). Within the Channel region, Waller and Long (2003) show rapid sea-level rise in the Early Holocene that led to marine transgression. This rapid sea-level rise began to decline ca. 6800 years ago as evidenced by a change from minerogenic to organogenic sedimentation. This was characterized by Scaife as part of the EU LIFE project, ‘Coastal Change, Climate and Instability’, and interpreted by Momber when looking at sea-level rise and formation of the Solent (Momber 2011: 132).

Notwithstanding regional earth movements and hydro-isostatic readjustment, global eustatic sea level reached within a few meters of the present level around 6 ka to 5 ka. Following this time, relative sea levels are dominated by isostatic realignment. Lambeck (1993a,b) models relative sea-level curves for different parts of the British coast indicating submergence over the last 6000 years along the Channel coast. Waller and Long (2003: 357) compare curves of sea-level indicators for the south coast, indicating a general submergence of the order of 4 m to 5 m in the last 6000 years. Carter (1988: 263) cites tide gauge data from a number of authors to illustrate a range of submergence rates from 1.7 to 5.4 mm/year along the south coast.

The appreciation of coastal geomorphology and dynamics in the consideration of paleocoastlines has a scholarly history in this region. In 1948, Steers reviewed the coastal geomorphology along the whole length of the English coast, describing historical changes, alluviation, the growth of Dungeness, erosion of parts of the coastline, the existence of drowned forests and rates of cliff retreat. These processes are reviewed in a more technical way by Carter (1988). Cracknell (2005) conducted a useful literature review when considering the impact of storm floods and coastal erosion during the last 2000 years. This theme is being developed with the EU, INTERREG IVa, Arch-Manche Project which is using artistic representations, archaeology and paleoenvironmental material to indicate change.

Climate conditions on the shelf

Review of the available literature and research associated with the human occupation of northern France and southern Britain, and associated climate changes, has highlighted how essential it is to understand the changing landscape for human occupation. This provides context for the often sparsely scattered archaeological remains that have been discovered to date.

Four typical and repeated phases of activity and occupations can be identified that are directly associated with each glacial cycle:

  1. Migration into the British Isles. After a phase of abandonment, people migrated across the shelf to re-occupy parts of Britain (see Clark et al. (2012) for discussion on the retreat of the ice sheet). Occupation may have been short-lived; however, if it were sustained, a full breeding population must have crossed the shelf, or inter-breeding must have continued with the rest of Europe;
  2. Mainland British Isles are occupied. The shelf area may have been exposed as dry land during climate amelioration, geomorphology of the Channel allowing, but, conversely, must have been abandoned if the shelf were inundated by high sea levels in the interglacial. Stringer (2006: 300) argues that Britain was a peninsula continuously during this phase. If this was the case, the shelf itself may have been occupied. The major determinant of the length of occupation period is geology and inundation; for a more recent discussion of this see Hijma et al. (2011);
  3. Climate deterioration, ice increase and population decline. The population may have retreated across the shelf, or died out in situ. In these conditions occupation of the shelf is possible, but did not necessarily occur;
  4. Cold periods, maximum shelf area exposed as periglacial tundra environment. Inuit-type occupation of the shelf would be possible, but did not necessarily occur.

Evidence for Submerged Terrestrial Landforms and Ecology

The change in relative sea level across southern England and northern France has caused submergence of important archaeological sites. These include intertidal Mesolithic footprints in clay below a peat dating from 6260±90 BP (CAR-1178) in the Severn Estuary (Bell 2007); Bronze Age walls in the shallow water between the Isles of Scilly (Crawford 1927; Thomas 1985; Garrow & Sturt 2011); numerous intertidal sites in the Solent such as the Bronze Age occupation and burial evidence from Langstone Harbour (Allen & Gardiner 2000); Neolithic trackways from Wootton Quarr (Loader et al. 1997) and submerged occupation sites associated with Bouldnor Cliff and the northwest Solent (Momber et al. 2011). In France, archaeological evidence includes the Middle Paleolithic site of La Mondrée, near Fermanville, Cherbourg (Cliquet et al. 2011); the submerged Neolithic standing stones in the Golfe du Morbihan (Cassen et al. 2011); the intertidal Neolithic monuments around the Brittany coast such as the passage grave on Kernic Beach at Plouescat; the standing stones on the archipelago of Mullein (Giot 1968; Prigent et al. 1983); and the many fish traps set at different altitudes on the beaches of Brittany and Normandy currently being investigated by CReAAH. Yet the archaeological record for northwest Europe extends much further back to around one million years (Stringer 2006), and the now-submerged continental shelf would have been part of the terrestrial landscape for most of the Pleistocene, as evidenced by recent discoveries at Happisburgh (Ashton et al. 2014). It is clear that an understanding of the submerged terrestrial landscape is required, both for the recognition of the potential location of sites, but also to provide a fuller understanding of the regional landscape and ecology. Archaeological remains are likely to have existed across the whole of the Channel and Celtic Sea area at some time in the last 700,000 years. However, the potential survival of material from the prehistoric period is dependent on taphonomy, sedimentation, erosion and ongoing coastal/marine geomorphological processes (Dix et al. 2008).

Submerged river valleys

For the Mesolithic period the association between wetlands, estuaries and human occupation is well-established. Bailey (2004) has made the case that Paleo- lithic cultures at least as far back as the Last Interglacial were capable of exploiting marine resources, and it is noteworthy that both La Mondrée off Fermanville, Boxgrove and Pakefield are situated in coastal plain environments, even if there is no direct evidence of exploiting marine species for food. Sites such as Pontnewydd (Green 1984; Aldhouse-Green et al. 2012), La Cotte de St. Brelade (Callow & Cornford 1986; Scott et al. 2014) and Paviland (Aldhouse-Green 2000; Jacobi & Higham 2008) are deposits in caves, and such deposits in a sheltered location underwater could survive, especially if consolidated in rockfalls. Many of the Paleolithic sites discovered on land are associated with river gravels. Thus the potential for pre-LGM sites in the Channel and Celtic Sea is influenced by possible association both with rivers and/or coastlines, and also with caves. The pattern of rivers at any given date, the associated shoreline, and the intermediate wetlands and marshes, are important indicators of the probability of human occupation and the survival of remains. The submerged archaeological sites of La Mondrée, Bouldnor Cliff and the finds from the paleo-Arun are all associated with paleochannels that have survived the transgression. Work to detect and preserve the prehistory of the sea floor in the Channel and Celtic Sea area depends upon our understanding of the river drainage pattern. Work by Gibbard (1988), Gibbard and Lautridou (2003), Antoine et al. (2003), Lericolais et al. (2003) and Hijma et al. (2011) has addressed this challenge in the Channel. Research focusing on the Solent River as a significant tributary of the Channel river system can be found in Dix (2001).

The rivers, tributary junctions, deltas, braids, and over-deepened channels which are seen today on the Channel floor have been influenced by multi-cycle glacial retreats and re-advances of the sea level over the fluvial and deltaic features. In the Channel, the shoreline at the eastern terminal, prior to the erosion of the Weald–Artois Ridge, reached approximately from Brighton to Le Crotoy (Bates et al. 2003: 325, fig. 4A). The ridge was over 100 km wide, providing a permanent land connection even at times of high sea level. It has been suggested that the lowering of the chalk barrier at the Dover Strait could have been a catastrophic rupture (Gupta et al. 2008). If so, the erosive forces would have been one of the greatest influences on the relict seabed as the southern North Sea drained. For a discussion of this proposition see Gibbard (1988: 588-591), Hamblin et al. (1992: 80-81), Stringer (2006: 162-163) and Hjima et al. (2011). However, the evidence for a catastrophic flood is not convincing. When the level of the glacio-lacustrine water body trapped in the southern North Sea between the ice sheet to the north and the Dover Ridge to the south overtopped the ridge, the flow out would be identical to the input into the lake. The erosion may have been rapid, combined with frost shattering, but need not have been catastrophic, and the progressive widening and lowering of the sill may have been the result of several different events. Work in the Bay of Biscay has dated distal sediments associated with discharge from the North Sea that suggest that the rapid flooding that created the Channel river system was initiated during MIS 12 (Toucanne et al. 2009). For further review of chronology and paleogeography see Dix and Sturt (2013).

The gradient of the Channel River from the Dover Strait to the shelf edge is of the order of 1:4000. This is comparable with the present-day Rhine from the border of Switzerland to the North Sea at 1:2000, which in prehistoric times meandered through massive bends and oxbow lakes. Given the southward flow of the Thames and Rhine through the Channel, and the addition of tributaries from the Somme, Seine, and southern English rivers, one would therefore expect frequent changes of channel course, with meanders and braids. The incised and submerged valleys of the various rivers on the floor of the English Channel are shown on the BGS Bottom Sediment Maps and are analyzed by Hamblin et al. (1992: 78-79). Some, but not all, of the archaeological material within the landscape deposits would have been redeposited or reworked as the watercourses migrated.

Descriptions or maps of known seabed-submerged terrestrial features

Whilst submerged forests are known in several locations, including in the Solent and Severn Estuary, known submerged terrestrial features are still relatively rare, but are likely to increase given the recent proliferation of seabed mapping, and the coverage and availability of large industry data sets. Recent winter storms (2014) exposed new features and preserved paleolandscapes (Ashton et al. 2014).

Paleoclimate and faunal indicators

Peat deposits dating between 12,650 to 7000 years ago exist in the Dover Strait area, the Solent, and within the inlets along the south coast of Devon, Cornwall, Normandy and Brittany. The La Mondrée site is also associated with peat from before the LGM. Prehistoric archaeological discoveries in the Channel and Celtic Sea are frequently associated with submerged peat and drowned forests. While there is circumstantial evidence that prehistoric settlements, especially in the Mesolithic, were often close to coasts, rivers and marshes, this association should not be exaggerated. More logically, if a settlement is in a location which is a wetland, or which subsequently becomes a wetland, with peat formation, the archaeological materials are likely to become embedded in the cohesive sediments, and thus to survive. In addition to this, peat provides preserved evidence for paleoclimate. Detailed reports are found within site reports (e.g. Bouldnor Cliff 2012) and within RECs and Historic England's peat database (Hazell 2008).

Further resources

Some records are held in online European or global databases; for example the European Pollen Database and NEOTOMA.

Taphonomy and Potential for Archaeological Site Survival

Factors favorable for the survival of archaeological strata in the original area of deposition can include:

  • – Very low beach gradient and offshore gradient so that wave action is attenuated and is constructional in the surf zone;
  • – Minimum fetch so that wave amplitude is minimal, wavelength is short, and wave action on the seabed is minimal;
  • – Original deposit embedded in peat or packed lagoonal deposits to give resistance and cohesion during marine transgression. Drowned forests and peat are good indicator environments;
  • – Deposits in a cave or rock shelter, where roof falls, accumulated debris, concretions, breccia, conglomerate formation and indurated wind-blown sand can all help to secure the archaeological strata;
  • – Local topography that contains indentations, re-entrants, bays, estuaries, beach-bars, lagoons, nearshore islands, or other localized shelter from dominant wind fetch and currents at the time of transgression of the surf zone;
  • – Frozen ground or permafrost enclosing archaeological deposit at time of inundation;
  • – Braided river pattern or deltaic islands, which can provide numerous lee environments protected locally from wave action from the west and south-west.

The factors above are those which promote survival of the original deposit in situ. However, if an archaeological deposit is buried under 5 m to 10 m of mud or sand it is unlikely to be discovered, except in very unusual circumstances. Thus, in the absence of major industrial excavation or dredging, the final requirements for survival and discovery are:

  • low-net modern sediment accumulation rate so that the artifacts are not buried too deeply;
  • no fields of sand waves or megaripples over the site;
  • a slight change in oceanographic conditions so that the site is being gently eroded to expose deposits when visited by archaeologists;
  • absence of heavy and continuous erosion which could remove the deposit completely;
  • absence of accumulation of successive layers of sediment during successive glacial cycles which would bury the archaeological material completely.

Oceanographic conditions, wind, waves, and currents

The Channel and Celtic Sea wave climate is dominated by westerly winds from the Atlantic, and the open-ocean swell waves generated by the fetch of many thousands of kilometers to the west and south-west. Within the Channel itself, winds from other directions are only blowing over a few hundred kilometers of sea and can generate only shorter period waves of limited amplitude. Wave data are summarized conveniently by Draper (1991) in atlas format, with successive maps showing the distribution of the significant wave height which is exceeded for different percentages of the time for spring, summer, autumn, winter, and the average for the whole year. More sophisticated data, and local data, can be obtained from databases and numerical models, including wave period and directional spectra, but the climatic data on wave height are usefully presented by Draper. This provides a general picture of the extent to which different parts of the seabed are exposed to wave action and possible erosion.

As would be expected, maximum wave height is found in the open Atlantic, decreasing to the east from the shelf edge. At the shelf edge the significant wave height (Hs) exceeds 5 m for 10% of the year. This decreases to 4 m around the Irish southern coast, Pembroke, Land's End, and Brittany, and drops progressively to 1.5 m to 2.0 m at Dover. There are sheltered lee areas to the east of Start Point and Torbay, and east of Portland Bill and Cherbourg, where the 10% annual exceedance Hs drops to 0.5 m to 1.0 m.

Since winter is the season when storm waves are likely to be highest, and with the longest period, so that they interact with the seabed in deeper water, it is important to consider the wave climate specifically in this season. In winter Hs exceeds 6 m at the shelf edge for 10% of the time. The 10% winter exceedance Hs then drops to 5 m on the exposed western headlands, and decreases steadily further east in the Channel, dropping to 1.5 m to 2.0 m in the Dover Strait.

Maximum bed stress is caused by a combination of waves and tidal currents. While shelter from waves in areas of limited fetch is generally a favorable condition for the survival of seabed archaeological remains, the exceptionally high current velocities and tidal amplitudes in the English Channel mean that erosion may continue in locations that are fetch-limited. Thus the Solent is more eroded and scoured than one would expect from its sheltered wave climate, and tidal current gyres generated by headlands such as Portland Bill also promote bed stress and erosion.

Hamblin et al. (1992: 87) summarize the tidal current environment in the Channel and Celtic Sea. Greater detail can be obtained from Meteorological Office models or commercial models available to support offshore operations in the area. Some of the highest tidal amplitudes in the world occur in this area, with over 11 m in the Severn Estuary and a similar amplitude in the Golfe de Saint-Malo. In the English Channel, Bristol Channel, and southern Irish Sea the amplitude is generally more than 2 m. Tidal amplitude around the Isle of Wight and the Solent is in the range of 2 m to 5 m.

Tidal current velocities are greatest around the Pembroke coast, in the Severn Estuary, around Land's End, the Channel Islands, the central Channel between the Isle of Wight and Cherbourg, and in the narrowest part of the Dover Strait. This pattern of currents and associated bottom stress results in the bed-load parting of the central Channel, and the resulting accumulation of sediments on the outer shelf, the eastern Channel and the southern North Sea. Massive tidal sand ridges accumulate on the French side of the Dover Strait. While the strong currents make archaeological work on the seabed difficult to carry out, the winnowing effect of currents is tending to reveal deposits which may contain prehistoric remains. In the extreme cases, archaeological materials will be eroded completely, and the context destroyed.

Data sources

There are a variety of data sources on modern oceanographic conditions. The UKHO holds information on tides and currents around the British Isles as does the NOC — Liverpool (formerly the POL). The CCO hold tidal stream information. Finally, historic tide gauge records for the UK are accessible via the BODC.

Further resources

Areas with the potential for discovery of archaeological material

The potential for the discovery of archaeological material within the Channel/Celtic Sea area is considered below in light of the oceanographic, climatic and geomorphological parameters outlined above. The area has been split into four zones, each with distinct geographical characteristics (Fig. 9.8).


Image shows four different zones showing their potentials for preservation of prehistoric archaeology in light of oceanographic, climate, and geomorphological parameters.

Figure 9.8 Image showing the four zones which have been divided to show their potential for preservation of prehistoric archaeology. Julian Whitewright; Maritime Archaeology Trust. Reproduced with permission.

Zone A: Celtic Sea, shelf margin, and Western Approaches up to the Start–Cotentin Ridge

Kenyon and Stride (1970), Johnson et al. (1982) and Hamblin et al. (1992: 88) describe the impact of bed-load parting on the sediment transport in the central English Channel. From an area between the Isle of Wight to Cherbourg the sediments tend to migrate in both directions on a west–east axis.

Bourillet et al. (2003: 261) describe the flow of sediments westwards through the dune fields or banks of the Celtic Sea into the valleys and canyons of the Biscay Margin. The origin of the Celtic Banks is complex and unresolved (Bourillet et al. 2003: 262). They occur between the 120-m and 200-m isobaths, and might be regarded as too deep to have been exposed during glaciations. However, the probable eustatic lowering of sea level to 130 m to 150 m, combined with the slight isostatic uplift outside the glaciated area, indicates that the coastline would have been well to the west of the present 120-m isobaths (see also the model outputs of Lambeck 1995, and Shennan et al. 2002). River valleys in this area are not deeply incised (Antoine et al. 2003: 230) and the rivers flowing from western Normandy, Cornwall, and Brittany did not flow into the Channel River or join to each other. They made separate courses to the shelf margin (Antoine et al. 2003).

Oppenheimer (2006) shows that much of the later Upper Paleolithic re-occupation of Britain may have taken place on the western margins of Europe. It has been demonstrated above that the Celtic Sea and western Channel would have formed either a refugium or an exit route whenever the climate in the British Isles deteriorated and the ice advanced during earlier glaciations. Thus, in principle, this is an area where important archaeological deposits might have occurred that would shed considerable light on the understanding of the occupation of northwest Europe and the British Isles. During the transgression, however, it was exposed to the maximum force of the Atlantic waves and is now partly covered in sand waves (Evans 1990; Bourillet et al. 2003). The western part of Zone A is therefore an area where the chances of discovery of artifacts are low, and the costs of work would be extremely high.

The archaeological potential along the coastline is more favorable for preservation. There are submerged sites within estuaries and ria systems that have now been flooded. An area that is particularly rich is the Golfe du Morbihan, which has many Late Mesolithic and Neolithic monuments. Er Lannic is now isolated in the gulf but was occupied by people before it was turned into an island by rising sea levels. It contains two large, adjoining stone circles, one of which is now totally submerged. Much of the gulf saw inundation during the early periods of settlement; therefore we would expect to find more material underwater. Indeed, recent acoustic survey has recorded submarine Neolithic standing stones on the northern edge of the gulf (Cassen et al. 2011).

Along the coastline at Quiberon, a Mesolithic site dating to around ca. 6200 cal BC was threatened by erosion (Marchand & Dupont 2014). It was a shell midden and was excavated by the Centre national de la recherche scientifique (CNRS) and CReAAH. On the north coast of Brittany, at Le Penthièvre, Côtes d'Armor, France, Pleistocene sea-level changes during the three last interglacial/glacial cycles and associated Paleolithic occupations have been studied by the University of Rennes (Daire et. al. 2012; 2013).

Zone A is potentially important because it may have acted as a route for migrations and as a refugium, but in water deeper than 100 m the potential for either survival of archaeological deposits, or the possibility of finding and studying them, is low. In areas shallower than 100 m, and especially in coastal waters shallower than 50 m around the Channel Islands (Sebire 2005), Brittany, Cornwall (Crawford 1927) and Devon, there is a higher chance of finding prehistoric archaeology, probably in association with peat deposits (Evans 1990: 11).

Further resources

Zone B: The Bristol Channel and Severn Estuary

The southern Irish Sea was analyzed in the report on the prehistoric potential of SEA6 (Flemming 2005). The northern borders of the Channel and Celtic Sea in the open-sea zone are similar, with paleoglacial features (Tappin et al. 1994). The geology of the Bristol Channel is also reviewed by Tappin et al. (1994). The Irish Sea has not so far revealed submerged prehistoric sites of any period, which is odd, given the preservation of many geomorphological features of periglacial origin on the sea floor (see Chapter 10, this volume).

There are many proven Paleolithic and Mesolithic sites in Wales, and one would expect some materials from these periods to survive in the Bristol Channel, particularly in sheltered embayments and areas that have been subject to deposition in the past. Mesolithic footprints have been found stratified within postglacial marine sediments on the intertidal foreshore at Uskmouth and Magor Pill, near Newport, Gwent (Bell et al. 2004; Bell 2007). Human interference with the coastline along the Severn Estuary is affecting the hydrodynamic regime and inducing erosion in areas where previously there was none. These areas of localized scour have the potential to uncover more archaeological evidence as the sediments continue to be removed.

Zone C: The central English Channel from the Start–Cotentin Ridge to Beachy Head

This zone is the area of bed-load divergence (Johnson et al. 1982), and hence maximum regional and local erosion. It also includes the confluence of the major submerged river channels converging on the Hurd Deep, the Seine and Somme submerged valleys, the Northern Paleovalley, the Arun River extension, and the Solent River. Many handaxes have been recovered from the river terrace deposits around the UK (Wymer 1999), a number of which have been found in trawls from coastal waters (Wessex Archaeology 2003). The braided river valleys in the English Channel are a unique feature of this part of the continental shelf. Given that so many terrestrial prehistoric deposits in Britain are found in river gravels and on abandoned river terraces it is relevant to consider whether the gravels in the area of the submerged rivers might contain similar remains. In general, where tidal currents or wave action have winnowed out the fines and left a lag gravel, the larger stone tools are likely to remain, albeit after some disturbance. If they have also been eroded or rounded beyond recognition, then no archaeological signal is likely to be detected. However, the general circumstance of the bed-load parting towards the center of the channel makes it likely that nearsurface archaeological sites will be exposed or eroded, rather than buried.

In the coastal regions of Zone C, more shelter is afforded by the land resulting in some locally sheltered and protected environments. This zone is potentially highly prospective for prehistoric archaeology especially where there are well-preserved river valleys infilled with sediments. A paleochannel that has become exposed is found at Bouldnor Cliff, off the Isle of Wight. This was a low-lying river flood plain in the western Solent, surrounded by hills, and possibly, with lakes. It was occupied during the Mesolithic around 8100 years ago when sea level was in the order of 10 m lower. As the Flandrian transgression progressed, the water rose and a layer of brackish sediments was deposited. They covered and protected the landscape including fine organic material and archaeological remains. Around 3500 years ago a new marine channel, the Solent, was formed as the sea level rose. This ran across the Holocene deposits, perpendicular to the initial waterway. Consequently, the sediments laid down during the transgression were exposed by the new current and washed away to leave thin strips of material along the edges of the waterway (Fig. 9.9). This example demonstrates potential for well-preserved paleolandscapes buried within the submerged river valleys. The distribution and concentrations of anthropogenic material within these landscapes can only be identified by visual inspection or sampling once the archaeological horizon is exposed.


Image shows side-scan of sonar, which is submerged cliff at Bouldnor, having Brackish sediment deposited between 8,000 BP and 6,000 BP at 7 m and submerged forest - dry land at 20 m.

Figure 9.9 Side-scan sonar image across the submerged cliff at Bouldnor. The underlying geology is exposed to the right. The peat-covered woodland bench is in the middle, while the sediment deposited over the landscape during the transgression is seen on the left. The area is now subject to erosion from right to left. Jasmine Noble-Shelley after Garry Momber; Maritime Archaeology Trust. Reproduced with permission.


Map shows distribution of Paleolithic and Mesolithic sites, where Gough’s cave is in North central region, La Cotte de St. Brelade is at South central region, Wootton Quarr is at west central region, et cetera.

Figure 9.10 Distribution of Paleolithic and Mesolithic sites bordering the Celtic and Channel Sea area coastline. Jasmine Noble-Shelley; Maritime Archaeology Trust. Reproduced with permission.

Just offshore from Cap Lévi, east of Cherbourg, on the south side of the Channel, the site of La Mondrée contains a sediment sequence within a river-drainage system that has remained undisturbed for tens of thousands of years. Over 2500 worked flints were recovered after the initial discovery in the 1970s (Scuvée & Verague 1988). The archaeological material is lying on the seabed and below the surface in stratified deposits that were laid in a hollow or paleochannel. Excavation in 2002 and coring in 2010 revealed over a meter of sediment remaining undisturbed beneath the surface (Cliquet et al. 2011). The sediments were interlaced with organic material that indicated human occupation in a flood plain environment during a climatic downturn ca. 70,000 years ago during MIS 5a. The layering of the archaeological material suggests there was ongoing or repeated occupation in the same area as the deposits built up across the paleochannel. The surface finds show there has been deflation of the seabed but the stratified deposit within the channel still remains intact despite fluctuating sea levels and climatic oscillations.

Zone D: The eastern Channel

This zone is dominated by the strong tidal currents through the Dover Strait, and the accumulation of marine sands. The BGS Bottom Sediment charts show active features such as megaripples and sand ribbons consisting of coarse and medium sand. In view of the active modern sediment bedforms and the strong tidal currents, this is not a prospective area for the survival and accessibility of prehistoric deposits. The tidal current regime and the active sand banks of the eastern Channel are described by Reynaud et al. (2003).

Hamblin et al. (1992) report peat beds detected in bore holes and cores, with peat at 36 m and 37 m dated at 10,530 and 9920 years old respectively (Hamblin et al. 1992: 81), and a borehole at Cap Gris Nez showing peat with ages 12,650 and 8250 years old (Hamblin et al. 1992: 81). The occurrence of peat is a positive indicator, but if it is buried under thick layers of modern marine sand it is unlikely that any investigation could be made to search for prehistoric indicators. However, as with areas A, B and C, the potential does remain to find archaeological material within the sheltered channels that have become filled with protective sediments before becoming submerged as sea level has risen.

General conclusions about possibility of site preservation

This section brings together the factors tending to favor occurrence, preservation, and accessibility of submerged prehistoric materials in the Channel and Celtic Sea. We have not tried to apply all the discriminatory factors to all areas or features in the region, but it is apparent that they do correlate well with the actual archaeological sites already found, and the assessment made of the potential in the Zones A–D (see Fig. 9.10). The unknown factor is the extent to which archaeological deposits protected from the initial stages of inundation may have survived the subsequent strong tidal currents and scour which may have occurred in the Bristol Channel, the central English Channel, the Western Approaches or the Dover Strait.

In view of the work of Pitulko et al. (2004) it is important to consider the effect of sea water rising over prehistoric archaeological deposits in permafrost, which would indicate the possibility of good preservation of artifacts. Although other factors also apply, for example river scour, frost shattering, and normal sub-aerial erosion processes, the critical period for survival of an archaeological deposit is the time when the surf zone starts to impact on the site, the ensuing few hundred years as the sea level rises over the site, and coastal shallow water waves are breaking over it, or washing into a cave mouth. The literature on these processes has been reviewed by Dix and Westley (2006). Favorable factors for survival of archaeological strata in the original area of deposition are outlined above.

This analysis demonstrates that survival or destruction of an archaeological deposit, whether originally inland or on the coast, depends acutely upon the local topography within a few hundred meters or a few kilometers of the site. Generalized coarse resolution maps tend to omit the details which show the necessary local topographic clues. The BGS 1:250,000 maps, although they are primarily designed to present sediment data, map isobaths at 10-m intervals and therefore provide a more accurate representation of topography than the Admiralty Charts. Additional high-resolution swath bathymetry and sub-bottom profiling would be valuable in detecting probable sites. It is no coincidence that the most prolific area in Europe of proven submerged Mesolithic sites is between the islands of the Danish archipelago, where many hundreds of sites have been mapped and sampled by the National Museum of Denmark's Institute of Maritime Archaeology, and the Danish Nature Agency, assisted by amateur divers (e.g. Skaarup & Grøn 2004). Further submerged Baltic sites have been discovered in sheltered waters off the coast of northern Germany (Lübke 2001; 2002). The Bouldnor Cliff and La Mondrée sites associated with protected paleochannels are textbook examples of preservation by local topography.

Potential Example Areas for Future Work

The archaeological record for the British Isles extends back almost 1,000,000 years and across at least six glacial cycles. In the course of each interglacial the environment on the British mainland ameliorated making it habitable. As the climate warmed, the ice sheets melted causing a rise in sea level. This process would have taken thousands of years during which time the Channel and Celtic Sea area would have been suitable for occupation. The research for this report has identified several sources of evidence that demonstrate why the Channel and Celtic Sea area would have been occupied on many occasions by Homo heidelbergensis, Homo sapiens neanderthalensis and Homo sapiens sapiens.

The archaeological material from Boxgrove, Clacton, Swanscombe, Purfleet, Crayford and the Cotentin Peninsula (notably at La Mondrée) was associated with deposits that were laid at times when sea level was rising or falling and was not at its maximum height. Large parts of the Channel would have been dry and habitable, potentially for long periods, before rising waters or a deteriorating climate forced people to move.

Middle Paleolithic activity during cold phases of the glacial oscillation is found in La Cotte de St. Brelade in Jersey (Callow & Cornford 1986; Scott et al. 2014), Harnham near Salisbury (Bates et al. 2014) and La Mondrée, France (ca. 250–45 ka)(Scuvée & Verague 1988; Cliquet et al. 2011). This demonstrates that Middle Paleolithic people had developed strategies that enabled them to endure a harsher climate. An ability to survive in the cold extends the window of opportunity for exploitation of Channel and Celtic Sea areas by Homo sapiens neanderthalensis.

The arrival of varying Upper Paleolithic technologies to mainland Britain may have followed a similar pattern to that which has been postulated during the Lower and Middle Paleolithic. The concept of a steady colonization by different peoples is endorsed by studies of mitochondrial DNA dispersal which identified a distinct western ‘Celtic’ population that originated from the Basque region and another from refugia to the east. The colonizers from the south migrated along the Atlantic Margin and reached Britain first. Throughout this process there may well have been populations occupying the continental shelf, which in turn acted as a springboard into the British Isles.

The final and current interglacial, the Holocene, marks the start of the Mesolithic (ca. 11–6 ka). Sea levels rose about 30 m during this transgression and large areas of the Channel and Celtic Sea were finally inundated. The Mesolithic came to a close about the same time as sea level reached comparable levels to those we see today. Coastal and riverine resources were exploited extensively during the Mesolithic. Europe's northwest peninsula was severed for the last time when the English Channel met the North Sea as the Mesolithic Age was drawing to a close. Water transport was now necessary to reach the British Isles.

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