Chapter 8
Northern North Sea and Atlantic Northwest Approaches

Sue Dawson,¹ Richard Bates,² Caroline Wickham-Jones³ and Alastair Dawson³

¹Geography, School of Social Sciences, University of Dundee,Scotland, UK

²Department of Earth Sciences and Scottish Oceans Institute, University of St.Andrews, Fife,Scotland, UK

³Department of Archaeology, School of Geosciences, University of Aberdeen, St Mary's,Scotland, UK

Introduction

This section provides a general overview of existing knowledge and information relating to the submerged prehistoric landscape and archaeology of the continental shelf of the northern North Sea and Atlantic Northwest Approaches (Fig. 8.1). Research in this area (apart from in a few isolated cases) is still in its infancy and this document serves primarily to highlight potential. For this region we must be aware of the significant impact that Late Glacial and Holocene changes in relative sea level (RSL) have had, not only on the coastal landscape, but also across the continental shelf area that has undoubtedly supported human settlement throughout large parts of the period under consideration.

Figure 8.1 Northwest Scotland and its position in relation to the North Sea and adjacent countries. Image by R. Bates.

The sea area of the northern North Sea and Atlantic Northwest Approaches roughly encircles Scotland, spans the North Sea from Scotland to southern Norway, and runs west towards Rockall. For significant periods in the past this area not only formed a land bridge that allowed prehistoric populations to migrate between existing landmasses, but it also formed a hidden continent that is likely to have supported its own cultural groupings (Gaffney et al. 2009). To the south was a land that has now been well documented with its own topography, including hills, rivers, marshland and lakes, about which we are only just beginning to understand the detail (Gaffney et al. 2007). Based on simple bathymetric reconstructions this land likely extended far to the north. Recent research has dubbed the submerged North Sea terrestrial landscapes ‘Doggerland’ (Coles 1998) and this name will be used here.

Archaeological evidence from the land suggests that the archaeological potential of this seabed area should be taken seriously, and this is supported by isolated finds of artifacts as well as finds of animal bone (see ‘Known Submerged Finds’, pages 204–205).

Earth Sciences and Sources of Data

Geomorphological background

The geomorphological pattern of the Scottish coastline follows that of the UK generally, showing a strong influence of broad geological variation with generally older and more resistant rocks to the north and west, and younger weaker rocks on the east coast. Local geological variation combined with the legacy of past glacial erosion and the dominant influence of the prevailing westerly climate has resulted in a highly complex shoreline.

The north and west coast today is dominated by erosion on a highly irregular coastline that bears the strong marks of glacial erosive sequences during and subsequent to the Last Glacial Maximum (LGM). The west coast is characterized by over-deepened fjords behind narrow and shallow inlets or sills, and over the highlands and islands to the far north and west by a landscape that has been planed clean by ice scour. Within both these types of landscapes, sediment deposition is minor and usually occurs in small isolated pockets that have been protected not only from the scour of ice but also from subsequent erosion by the strong westerly climate.

Scotland shows an unusually high tidal range, with stormy conditions a frequent occurrence due to its exposure to the strong westerly winds and North Atlantic swell. The east coast experiences both the tidal movements and the influence of waves in relatively shallow waters of the North Sea to create currents and the associated movement of sediment in the nearshore\ zone. In addition, the central northern North Sea area links to the Norwegian coastal zone and a renewed area of interest for the preservation of sediments. The interplay of the Atlantic and North Sea forces is most strongly manifest along the north coast, for example in the Pentland Firth where extreme currents are channeled between the mainland and the Orkney Isles.

While erosion is a feature around most of the coastline, deposition of sediment tends to occur more widely on the east coast, where the legacy of glaciation in the form of glaciogenic sediments (such as sands and gravels) is found both in the nearshore zone and offshore. The east coast also features the terminus of most Scottish major rivers that supply the majority of modern sediment to the shelf. The heads of these estuaries are the main locations for salt marshes, although due to the strong North Sea current regime and large wave fetch, the marshes are not as extensive as their counterparts in Wales and England.

Across all coastlines the complex history of eustatic and isostatic change is manifest by particular geomorphological features. For example, onshore raised beaches are testament to high sea levels in the past (see pages 195–200 for specific descriptions) and flooded lagoons over previous marsh and coastal lakes. Offshore, submerged cliff lines and platforms are accompanied by drowned river valleys, for example in the Firth of Forth.

Data sources: BGS seabed sediments and Quaternary sheets 1:250,000

Relatively high-resolution mapping vector and raster data for the coast of Scotland is held by the Ordnance Survey (OS), the Crown Estates and the British Geological Survey (BGS). Very high-resolution mapping using LiDAR (Light Detection and Ranging) has not been accomplished in a systematic manner around the Scottish coast to the extent that it has in Wales and England, with small surveys acquired on the Outer Hebrides, Orkney and around the urban centers of Glasgow and Edinburgh. This information is held with the commissioning bodies: Scottish Natural Heritage, Historic Environment Scotland and the Scottish Parliament. High-resolution vertical and oblique aerial photographs are held by the Royal Commission on Ancient and Historic Monuments for Scotland. Data on wave and tidal conditions are held by the United Kingdom Hydrographic Office (UKHO) and also by the British Oceanographic Data Centre (BODC).

The BGS collaborated with its opposite numbers in the Netherlands and Norway during the 1980s and 90s to produce a series of seabed sediment maps for the UK continental shelf at a scale of 1:250,000. These maps, and the associated cores, are an essential tool for assessing the prehistoric archaeological potential and sensitivity of areas of the sea floor. They provide classification of surface sediments by grain size, thickness of active marine sediments, thickness of Holocene deposits, standard cross-sections, information on tidal currents, sand waves and sand ripples, carbonate percentage, and other items of information which vary from sheet to sheet. Some sheets, but not all, include copious technical notes, sections, core profiles, and analysis of sources, references, and comments on the various facies. All sheets show positions of platforms and pipelines at date of publication. Notes on some of the most relevant sheets follow (from north to south). This analysis refers only to the geological, sedimentary, and taphonomic conditions relevant to primary occupation in the area, and the preservation of sites.

There have been numerous studies (e.g. Bates et al. 2013) of coastal change within the context of archaeological potential and potential loss for the strip of land that is intertidal and just above high-water mark. Significant work has been done on a number of sectors around the Scottish coast by Scottish Coastal Archaeology and the Problem of Erosion (SCAPE) (Dawson 2007).

Background Bedrock and Quaternary Geology

Bedrock geology

The north and west of the area is situated on continental crust that is part of the Eurasian tectonic plate. The region is divided by a number of globally significant sutures that separate ancient terrains with Archaen (>2500 Ma) rocks separated by the Moine Thrust from Proterozoic rocks to the east. The oldest rocks consist mainly of quartzofeldspathic gneisses, ultrabasic to acid intrusives and metasediments of the Lewisian Complex with Proterozoic rocks consisting of psammites and pelitic schists. Closer to shore and onshore, the Lewisian is overlain by a cover sequence of predominantly fluvial sandstones, conglomerates and shallow marine sediments. There is a strong dominance of northeast–southwest trending sutures that cross the seazone inherited from events during the Caledonian orogeny (470–410 Ma). This regional weakness is exploited throughout geological history with the most recent glacial activity reinforcing the deep Faroe–Shetland Channel. Subsequent to the Caledonian orogeny, local extension and strike-slip tectonics allowed depositional centers to form extended sequences of sediment during the Mid to Late Devonian, most notably in the Orcadian basin. During the Late Paleocene to Early Eocene the region experienced uplift associated with volcanic extrusions and extensive intrusive activity with associated extension. The Miocene to Pliocene is marked by shallow shelf deposition with small regional uplift toward the Holocene lowstand.

While the North Sea also sits within the Eurasian plate, its bedrock geology is dominated by structural features associated with a complex pattern of down-faulted basins separated by uplifted platforms formed through the Mesozoic and Cenozoic. Sediment cover is thin in the northern sector apart from sediments in marginal basins and within the fault-controlled uplift area of the Inner Moray Firth basin. To the south the Forth Approaches basin represents a Carboniferous extensional setting along northeast–southwest aligned structures with sediments thickening to the depositional centers offshore. A major graben, the Viking Graben, dominates the sub-surface structure along the southeast Norwegian coast.

Interpretation of the regional geology is supported by legacy geological data for this area, which is prolific from offshore exploration activity in the North Sea over the last 40 years. Exploration for oil and gas and the formation of archives of geophysical acoustic data and cores have been carried out in all countries bordering the northern North Sea. Examples of this data exist as both 3D seismic survey blocks (Fig. 8.2) and 2D seismic lines (Fig. 8.3). In addition to these data is a program of regional seismic data in the UK acquired by the BGS in the form of single airgun, boomer and sparker profiles.

Figure 8.2 3D seismic survey blocks acquired as part of hydrocarbon exploration licenses. Image by R. Bates.

Figure 8.3 Example of 2D seismic exploration lines acquired as part of hydrocarbon exploration licenses. Holdings for metadata are with the BGS and geological surveys of Norway, Denmark and the Netherlands. Image by R. Bates.

While these data exist, they were not acquired, and have not necessarily been processed, with the near-surface Quaternary geology in mind. However, it is likely that reprocessing the data, in a similar manner to that which has yielded such successful results for the southern North Sea (Gaffney et al. 2007), would yield significant new information of prehistoric archaeological significance.

Quaternary geology

Two BGS monographs summarize the Quaternary geology, seabed sediments and bathymetry of the area. 1) The geology of the Malin-Hebrides sea area (Fyfe et al. 1994) and 2) the geology of the Hebrides and West Shetland shelves, and adjacent deepwater areas (Stoker et al. 1993). The Malin-Hebrides area has a varied offshore topography. Deep water occurs in the Inner Sound, east of Raasay, at 316 m, the deepest recorded on the UK continental shelf. The topography of the sea floor has been altered by Quaternary ice sheets which have eroded the weaker sedimentary rock rather than the igneous and metamorphic rocks, thus leading to the over-deepening of the sedimentary basins. These basins have been infilled with Quaternary sediments of considerable thicknesses. The presence of seabed sediments is related to the strength of the tidal streams which have swept and eroded much material. The geology of the Hebrides and West Shetland shelves summarizes the Quaternary sediments, seabed sediments and bathymetry to the west of the Outer Hebrides. The coastal geomorphology is of a drowned landscape due to the interaction of eustatic processes and isostatic changes in relative sea level since deglaciation. Below sea level there is a northward increase in the gradient of the coastal slope. West of the Uists (Outer Hebrides) the 20-m isobath occurs up to 10 km offshore and there is no well-defined break of slope. The shelf edge and slope comprise a marked break of slope at the Geikie Escarpment with a descent into the Rockall Trough at ca. –700 m.

Bathymetry

The continental shelf to the west and north of Scotland consists of a west to northwest dipping shelf intersected by a series of deep troughs (depths greater than 150 m) out to the shelf break of slope at 100 km to 200 km from the present coastline. Large topographic variation resulting from ice-scoured bedrock of geologically controlled erosion results in a bathymetry of upstanding reefs set with occasional pockets of fine-grained sediments. In contrast to this, the east coast consists of a gently sloping (to 50 m depth) and undulating platform extending toward the center of the North Sea where depths increase to over 100 m. This slope is broken by a series of moraine ridges and sand banks. The nearshore on all coastlines is marked by shore-parallel shelf margins that extend out from the present coast to 3 km to 12 km at depths of 10 m to 30 m.

The offshore bathymetry across the continental shelf is available in vector and raster form as DigBath250 from the BGS. This covers the region of interest and extends to include the whole of the UK continental shelf and slope and the northern North Sea across to Norway and Denmark, compiled from data gathered from the BGS, the UKHO, Flemish Hydrographic Survey, German Hydrographic Office, Netherlands Hydrographic Office, Norwegian Hydrographic Service and the Royal Danish Administration of Navigation and Hydrography.

A continuing program of shelf multibeam survey at higher resolution is ongoing by the UKHO and is supplemented by both commissioned survey for offshore development and speculative academic-related survey. Much has been made recently of SeaZone TruDepth points data sets for investigation of archaeological potential and this holds great promise for regional appraisal. Of particular note in regards to high-resolution data acquisition are the recent surveys undertaken by Marine Scotland in collaboration with various government partners and academic institutes. An example of the recent multibeam data sets is shown in Fig. 8.4 for the area to the south of Skye and east of Soay. From the high-resolution data the bedrock geology and the moraine records resulting from deglaciation are readily apparent.

Figure 8.4 Multibeam sonar bathymetry map of Loch Scavaig, south of the island of Skye on the west coast of Scotland. Color image shows depth variation from red (shallow) to blue (deep). The high-resolution bathymetry highlights moraine ridges that show ice advance limits together with bedrock signatures such as the dipping layers of the Torridonian Sandstones on the west side of the map. Image by R. Bates.

Post-Last Glacial Maximum Climate, Sea Level and Paleoshorelines

During the timescale covered by this chapter, that is the period from the Last Glacial Maximum onwards (a period of some 20,000 years), the climate and environment across northern Doggerland varied. While precise information relating to vegetation and ground conditions is still lacking, it is possible to reconstruct more detail for climate. For much of this period the surrounding landmasses were almost entirely glaciated and this increased the importance of the available land as a potential homeland for the prehistoric populations who were well established in the area. It was the impact of the isostatic adjustment of the landmasses on either side, due to the weight of glacial ice, together with the eustatic changes in oceanic waters that resulted in the emergence of a landmass of such size during the glacial maximum and for several millennia afterwards.

The submergence of this area took place at the start of the Holocene, but it was not a uniform process. To reconcile the detail of submergence it is necessary to know ice retreat and detailed sea-level changes that are not yet documented in great detail. As the ice melted and retreated across the continental shelves, land rebounded in certain areas of Scotland and Norway but global ice melt led to increases in the eustatic sea level and an overall submergence (Lambeck 1995). The submergence was greatest in the central North Sea and the area around the periphery of the last Scottish ice sheet such as Orkney, Shetland and the Outer Hebrides. Here, final submergence of coastal areas may not have taken place until ca. 4000 years ago (Bates et al. 2013). According to most authorities, the western extent of the Late Devensian ice sheet reached as far as the edge of the continental shelf (Fig. 8.5) (Hughes et al. 2011).

Figure 8.5 Ice extent at the maximum of the last Scottish ice sheet. Clark et al. (2012). Reproduced with permission from Elsevier.

During the maximum extent of glaciation, regional sea level was ca. 120 m lower than present (Fairbanks 1989). However, owing to the loading of the last British ice sheet on the underlying lithosphere (crust), the position of relative sea level during the Last Glacial Maximum around the former ice sheet was much higher. This was due to the glacio-isostatic depression of the crust beneath the ice, the amount of depression increasing towards the western Highlands where the ice was thickest. During the LGM, the sea floor beyond the maximum limit of the ice and across a belt several hundred kilometers in width was raised vertically. This was due to a compensatory radial outward movement of sub-crustal material from beneath the lithosphere underneath the ice sheet (Peltier 1998). In such areas during the glacial maximum therefore, the sea level was lowered on the one hand but on the other, the crust beneath the sea floor was raised, causing a regional shallowing and increased exposure of the continental shelf. Figure 8.6 shows a schematic paleogeography off western Scotland. Areas of glacio-marine sedimentation, possible land areas and over-deepened basins are noted. The position of the shelf break is seen to the north-west of the Outer Hebrides.

Figure 8.6 Paleoglaciological reconstruction of ice-sheet configuration at maximum extent. LGM limit ca. 27 ka (MIS 2) (Bradwell et al. 2008). HIS = Hebrides Ice Stream (this study); MIS = Minch Ice Stream (Bradwell et al. 2008); BFIS = Barra-Fan Ice Stream (Scourse et al. 2009; Dunlop et al. 2010). Black lines are ice-stream flow lines inferred from this study; gray lines are hypothesized ice-sheet flow lines for the rest of the ice-stream catchment (not proven). Dark blue shading is ice-stream onset zone (deduced from this study); light blue shadings are hypothesized (glaciologically plausible) ice-stream onset zones for the rest of the catchment. Thick blue dashed line is the probable location of ice divide at time of HIS operation. Orange arrows show ice-sheet flow direction inferred from seabed drumlins (Dunlop et al. 2010; Ó Cofaigh et al. 2012). Blue arrows show ice-sheet flow direction from other evidence within the study area; these probably relate to later flow events (or possibly earlier). Offshore gray shaded areas are trough-mouth fans; SSF = Sula Sgeir Fan; BDF = Barra Donegal Fan (after Stoker 1995). Thin gray lines are bathymetric contours with values in meters.

As the ice sheet started to melt, regional sea level started to rise as a result of the melting of ice sheets worldwide. At the same time, as the British ice sheet started to retreat and thin, the land underneath the ice sheet started to rise. The rate of vertical rise of the land surface beneath the ice varied regionally with the greatest rates of rise in areas where the ice was formerly thickest. By contrast, smaller amounts of vertical rebound took place towards the edge of the ice sheet where the ice thicknesses were much less. Beyond the ice margin, as sub-crustal material started to migrate back into areas underneath the lithosphere underlying the former ice sheet, the areas of ocean floor started to sink (Lambeck et al. 1996).

Accompanying the eastward retreat and thinning of the ice sheet was a rapid rise in regional sea level. For the most part the early stages of ice-sheet decay (deglaciation) were characterized by a rise of (glacio-eustatic) sea level. Thus, one might imagine that as the ice sheet retreated eastwards towards the present Scottish mainland the rapidly rising sea level was immediately flooding into land areas exposed by the melting ice. During the early stages of regional deglaciation there were no new land areas exposed for possible Paleolithic habitation.

This complex interplay between the global eustatic component of sea-level rise and the rebounding of the land with the removal of the ice sheets leads to a variable pattern of relative sea-level changes around the Scottish coast and in the central North Sea. For Scotland, this trend, of rising sea level outpacing the rate of rise of the land surface, continued until the end of the Younger Dryas (Loch Lomond Stadial ca. 11–10 ka) period. For archaeology, the end of the Younger Dryas is highly significant since it is at this stage that parts of the Scottish coastline close to the center of glacio-isostatic rebound in the western Highlands started to experience a rate of crustal rebound faster than the rate of rise in regional sea level (graphs for a range of sites across Scotland demonstrate this variability — Fig. 8.7). Farther west and north (i.e. towards the periphery of the UK landmass) however, throughout the Western Isles and Orkney and Shetland, the rate of crustal rebound remained insufficient to exceed the rate of rise in sea level caused by an increasing volume of sea water in the Global Ocean. Such areas, therefore, continued to experience net submergence, as did the land area in the central North Sea. The central North Sea upon deglaciation opened up an exceptional area of dry land, an area known as Doggerland (Coles 1998).

Figure 8.7 Relative sea-level change graphs for selected areas across the north and west coast of Scotland. Modified from Jordan et al. (2010).

Late Glacial shoreline isobase map

The history of relative sea level in Scotland during the Holocene (last 10,000 years) is complex. The area around Oban in the west had greater thickness of ice than areas of the Outer Hebrides, the north coast and the Northern Isles. This led to varying amounts of isostatic rebound and therefore the various positions in the landscape where we see relict shorelines today. For the Oban area, this translates to visible shorelines dated to ca. 10 ka up to 10 m Ordnance Datum (OD). However, the same Late Glacial shoreline is well below present sea level in the areas of the islands of Coll, Tiree, and Islay, and the Solway Firth coastline. Predicted shorelines for the Outer Hebrides and Orkney suggest they are located between 20 m and 30 m below present (Fig. 8.8).

Figure 8.8 Shoreline uplift isobases (m OD) for the Main Late Glacial Shoreline. Locations for key locations in text, (1) Orkney Islands; (2) Outer Hebrides; (3) Skye; (4) Mull. Image by R. Bates.

Shoreline uplift isobases (in meters OD) for the Main Late Glacial shoreline of Younger Dryas age have been extrapolated to 40-m water depth (below OD) based on various sources (Fig. 8.8). The best estimate of regional eustatic sea level for the Younger Dryas is between –40 m and –45 m OD. Thus, the shoreline isobases are plotted to –40 m but no further. The coastal areas shown inside (and above) the 0 m shoreline contour indicate those areas where any coastal settlement archaeology of early Holocene age would be preserved at or above present day sea level. Outside of the 0 m isobase contour, any existing Mesolithic coastal settlement archaeology could occur below sea level across those areas of seabed shallower than the contours indicated. Figure 8.9 shows a GIS (Geographic Information System) reconstruction of dry land areas around Scotland's west coast that would have existed at the start of the Holocene interglacial and Fig. 8.10, areas around Orkney.

Figure 8.9 GIS reconstruction of additional dry land areas around Scotland's west coast and Outer Hebrides which would have existed at the start of the Holocene. Image by R. Bates.

Figure 8.10 GIS reconstruction of dry land areas around the Orkney Islands which would have existed at the start of the Holocene. Image by R. Bates.

Holocene Relative Sea-Level Changes

Smith et al. 2006 and Fig. 8.7 show the most recent analysis of shorelines around the Scottish coast with the production of empirical models, based upon shoreline altitude data. The isobase maps show how the sequences of Holocene shorelines reflect variations in the relationship between isostatic movements and sea-surface change with increasing distance from the center of the Late Devensian ice sheet, with differences of as much as 10 m in elevation between shorelines of the same age. Thus, towards the heads of estuaries (such as the Forth, Tay and Clyde) close to the center of uplift, shorelines are uplifted and easily identified. On the peripheries of the Scottish uplift center, for example the Outer Hebrides to the west (including the Isle of Harris, Fig. 8.7), shorelines are now buried below present coastal sediments. Thus, some areas of the sea floor may have been dry land 10,000 to 12,000 years ago, flooded by rising sea level around 7000 years ago, and then exposed again a few thousand years later by the isostatic uplift of the land.

Along the east coast of Scotland shallow coastal waters range from the inland heads of the Firths where the land uplift is 8 m to 10 m out to the headlands of Wick and Fraserburgh on the zero-isobase. This means that the rate of RSL change varies radically at different points on the coast. Edinburgh has been continuously uplifted more rapidly than the rising sea for the last 15,000 years, so that the sea level has undergone relative lowering throughout that time. At Lerwick, Shetland, however, the land has been sinking continuously since the ice melted so that the RSL has been continuously rising. Cromarty and Ythan are interesting because their rate of uplift has been closely similar to the sea-level rise, with a relative fall of sea level from 14 ka to 9 ka dropping below the present coastline, rising again to a maximum above the present coastline at about 5 ka and then dropping gradually to the present level. To the east of the present coastline, exposure of land across extensive areas of the entire North Sea area allows for a greater potential occupation area than hitherto realized (Gaffney et al. 2007; 2009).

Off the east coasts of Shetland, Fair Isle and Orkney, one would expect to find submerged caves or materials trapped in gullies and cracks in the bedrock. Various combinations of floating sea ice, rocky shelters, terrestrial mammals such as reindeer, or marine mammals such as seals, walrus, otter, and cetaceans, would have been present, depending on the exact local topography and conditions. Andrews et al. (1990) indicate scattered small islands emerging from the sea-ice typically a few tens of kilometers across. Their estimate of exposed land is conservative and they note that the areas of exposed land may have been more extensive than they show on their maps. This suggests a complex terrain of sheltered sea almost totally protected from North Atlantic storms, dotted with islands, covered with floating sea ice, and bordered to the west by the grounded Scottish ice cap.

Models of Postglacial Isostatic Adjustment

Rheological models of glacio-hydro-isostatic rebound, based upon geophysical data and modeled to fit the available sea-level data, have been developed by Lambeck et al. (1996) and Peltier et al. (2002). Models of British ice-sheet behavior since the LGM have also been developed. The model ICE-4G (VM2) is the model used to constrain the RSL pattern for the British Isles, and gives the best fit to the observational data (Peltier et al. 2002). Nevertheless, there are discrepancies between model predictions and the observational data sets for some areas of Scotland, e.g. Orkney (Bates et al. 2013) and Wick (Dawson & Smith 1997), both in the north of Scotland. Models of glacio-hydro-isostatic sea-level change have also been developed for the Irish Sea basin as the original British Isles models failed to represent the changes observed along the Irish Sea margins since deglaciation (Lambeck & Purcell 2001).

Relative Sea-Level Changes

Rockall

The Rockall Plateau is an extensive shallow-water area to the west of the British Isles and separated from the Scottish mainland by the 3000-m-deep Rockall Trough. The trough is a southwest-trending basin which lies between the mainland and the Rockall Plateau. The small pinnacle of Rockall Island is the only area to appear now subaerially on the plateau. A possibly wave-cut platform around the island exists at ca. 110 m. Beyond the island a break of slope at ca. 180 m depth and dredged beach material suggest subaerial erosion during a Holocene sea-level stillstand (Roberts 1975). The continental margin north-west and west of the British Isles consists of a broad continental shelf, a narrow continental slope and a broader continental rise. Between latitudes 55°N and 60°N, an inner and an outer shelf are separated by the Outer Hebrides. A shallow basin separating the islands of Rona, Flannan and St. Kilda from the Outer Hebrides is the only area of relief on the outer shelf.

St. Kilda

The St. Kilda archipelago (57°49’N, 08°35’W) lies 64 km to the west of the Outer Hebrides towards the edge of the western Scottish continental shelf. The shelf slopes gently westward from the Outer Hebrides to a depth of 120 m to 140 m around St. Kilda over a distance of ca. 100 km. There is little sediment deposition on the shelf, and mainly erosional landforms. Near-vertical and cliff-like, the marginal slope exhibits a pronounced break of slope with the western margin fronted by a near-level surface at ca. 120 m depth (Sutherland 1984). The cliffed coastline of the islands and stacks that comprise the archipelago plunges to depths of 40 m. This shallows at –120 m to –80 m and then to –40 m around the base of the clifflines around the islands. This upper erosional surface culminates in a clear marine erosional platform at ca. –40 m. Planation of the bedrock surfaces and cliff formation must have occurred during periods of sea-level stability. It is suggested that during the peak of the Late Devensian ice sheet, sea levels around St. Kilda were around 120 m lower than present. The marine planation surfaces that occur between –70 m and –40 m are thought to have been formed during the last period of Northern Hemisphere glaciation, the Loch Lomond Stadial (Younger Dryas, 11–10 ka), when local RSL may have stood at around –40 m (Sutherland 1984).

Outer Hebrides

The sedimentary evidence for Holocene RSL fluctuations in the Outer Hebrides is somewhat limited. Radiocarbon dating of intertidal peats can be indirectly related to a sea level at least as low as the occurrence of the peat/organic deposits. Thus, a date of ca. 5700 BP was obtained for intertidal deposits in Benbecula (Ritchie 1998), which correlate to a sea level at least 5 m lower than the present. Work on the isles of Lewis and Harris by Jordan (2004) shows that the Mid–Late Holocene RSL record can be summarized as comprising two main events occurring between 5500±60 BP and 4500±100 BP, and between 3000±80 BP and 820±50 BP. Rising sea levels throughout the Holocene controlled the onshore movement of vast amounts of sediment from the extensive and fairly shallow coastal shelf to the west, which in turn has developed into the modern beach and dune systems and the machair grassland that fringes the western Atlantic seaboard of the whole island chain. The sea-level index points (SLIPs) identified by Jordan (2004) are thought to be representative of coastal barrier formation as opposed to direct shoreline development. However, as barrier formation is closely related to the relative movement of the sea, it is believed that both the Main Postglacial Transgression and the later Blairdrummond Shoreline (Smith et al. 2000) are recorded in the sediments. One site in particular, Northton on the Isle of Harris, has also recorded an Early/Mid Holocene (7370±80 BP) storm surge event that was imprinted upon the rising RSL trend for the area. Sediments from this event have a similar sedimentological signature to deposits from the storm surge that occurred in January 2005 across the southern areas of the Outer Isles.

Northwest Scotland mainland

The northwest of Scotland has been subject to extensive study of RSL change during the last twenty years (Peacock 1970; Shennan et al. 1994; 1995; 2000; 2005). Peacock (1970) defined the local marine limit around Arisaig at ca. 41 m OD from terraces and banks of shingle and sand interpreted as raised beaches at Sunisletter. The marine limit occurs between Upper Loch Dubh (sill elevation 36.48 m OD) and Cnoc Pheadir (sill elevation 42.5 m OD). Rapid RSL fall continued until at least 14,000 cal BP. The relative sea level then rose and reached no higher than ca. 10 m during the Holocene.

Northeast Scotland and the Northern Isles

South of Fraserburgh the situation changes because the Scandinavian ice sheet extended across the Norwegian Trench onto the UK shelf as far west as the Greenwich meridian, and a substantial dryland area of tundra was exposed between the Scandinavian grounded ice and the sea-lake. This dry land continued widening to the south and east over the southern North Sea basin, and was continuous with the land which is now Germany and France. The River Elbe discharged across this shelf to the north, and probably other rivers drained the landscape, as in northern Russia today. The combination of extensive land to the south, the proximity of the ice sheets, the large sea-lake, and the scattered islands projecting from the floating ice suggest a complex topography which could have supported humans exploiting sea mammals, fishing and land mammals. The tidal range is of the order of 3 m to 4 m along much of the coast, and tidal streams in the north-east area, where the tide flows through the gaps in the Orkney–Shetland ridge, have velocities of 2 m/sec to 3 m/sec. This area is co-extensive with a seabed of bare bedrock with very little sediment. In the Moray Firth the currents drop to 1.0 m/sec to 1.2 m/sec, with a further peak of 1.8 m/sec around Fraserburgh. In the southern half of the Moray Firth this is associated with 10 m to 20 m thickness of Quaternary sediments. Further offshore the currents over the whole area are of the order of 0.8 m/sec to 1.0 m/sec (Blackham et al. 1985). Where the currents have exposed the bedrock, artifacts would only survive trapped in gullies or caves. Over much of the area the currents have been strong enough to winnow out fine mud or clay, but this process would leave lithic artifacts in place.

Taphonomy and Potential for Archaeological Site Survival

In a glaciated area such as the submerged landscape of northern Doggerland, specialized conditions such as ice scour, glacial erosion, frost shattering, and normal subaerial erosion processes all have to be taken into account when considering the survival of archaeological material. In view of the work of Pitulko et al. (2004) it is also important to consider the effect of sea water rising over archaeological deposits in permafrost, which can result in the good preservation of artifacts.

An extreme event which needs to be taken into account is the Storegga Submarine Slide, which occurred off the coast of Norway at 7200 BP (about 8100 cal BP), and caused a tsunami which has been detected in coastal sediments on land on the east coast of Scotland (Dawson et al. 1988; Smith et al. 2004). At the date of the submarine landslide the sea level was still approximately 20 m to 30 m below present, and Dogger Bank was a promontory connected to north Germany, while the land bridge from the Netherlands to the Humber coast had recently been inundated. The tsunami wave locally may have penetrated several hundred meters inland, with a run-up of 1 m to 2 m in open areas, and much greater in enclosed lochs. Long and Holmes (2001) suggest that the human impact would have been small, due to the low population (op.cit. p.365), though this is disputed by Weninger et al. (2008). The impact may have been greater on the north shore of the Dogger Bank, if people were living there, and in Elbe Estuary.

Large areas of the Scottish shelf have been dry land for considerable periods in the last 700,000 years — the period of human (Paleolithic) settlement in Britain. England and Wales have a good record of early settlement sites on land, particularly in the south, but there are no absolutely-dated Paleolithic sites in Scotland so far, though artifact finds from three sites are significant. Typologically-specific lithics from Fairnington (Saville 2004), Howburn (Ballin et al. 2010a) and Kilmelfort (Saville & Ballin 2009) have been interpreted as providing evidence for human activity in the Late Glacial Period between 14,000–11,000 years ago. Environmental and osteological evidence suggests that the submerged landscape of the northern North Sea has, at times, been suitable for human settlement and it is possible that surviving Paleolithic sites from the ‘Scottish sector’ of the seabed still survive (Long et al. 1986), while comparable sites on land have been destroyed or buried by the actions of the Last Glacial ice sheet, which blanketed mainland Scotland.

The relative sea-level history of Scotland during the Holocene (last 10,000 years) is complex and the net result of this is that in some areas the present seabed has been dry land within the last 10,000 years. As this is the period within which Scotland has a comprehensive record of human activity, it is likely that these areas were once settled. They offer the possibility that submerged archaeological sites may be preserved.

Perhaps the best-known submerged landscape is that around the archipelago of Orkney, where the sea did not reach present levels until about 4000 years ago (Flemming 2003; Bates et al. 2013), but another area lies to the west of the Western Isles (Wickham-Jones & Dawson 2006), and there are small localized areas elsewhere, for example around Coll, Tiree and Islay. Although there is no specific data on RSL rise for some of these areas, it is assumed that sea level reached roughly its present level between 3000 and 5000 years ago, meaning that any submerged archaeological sites are likely to relate to Mesolithic or Early Neolithic settlement. Interestingly, both Orkney and the Western Isles stand out from the rest of Scotland in that they have little evidence on land for Mesolithic settlement. Mesolithic sites are few and far between in Orkney and lacking, with the exception of a few dates on anthropogenic deposits, e.g. at Northton (Gregory et al. 2005; Simpson et al. 2006), in the Western Isles. Given the importance of coastal resources in the Mesolithic and the apparent concentration of sites around Scotland's coastlands, this may be significant as an indication that evidence for the first 5000 years of human settlement in these areas is lying in the present offshore area. Recent field research in Orkney suggests the possible preservation of stone structures relating to the Neolithic on the seabed (Bates et al. 2013), and Benjamin (2010) has proposed a model for investigating the potential for submerged archaeology in other parts of Scotland, which gives practitioners the opportunity to test different techniques.

Large parts of the seabed sediments west of mainland Scotland towards the Outer Hebrides are not of marine origin but are submerged terrestrial deposits and deposits resulting from the erosion and re-deposition of material by glaciers and ice sheets. Sands, gravels, silts, clays and organic-rich deposits are referred to as Marine Aggregate Deposits (MAD) (Wenban-Smith 2002). The potential for preservation of archaeological remains within these sediments depends upon the depositional and post-depositional processes on the offshore landscape prior to inundation. Many areas will have been subject to repeated glaciations and marine inundation since the peak of the ice sheet at ca. 22 ka. Material will have been transported, remixed and reworked. Rising water levels may favor the preservation of associated intercalated organic deposits. Once buried by fine-grained material, these may be more resistant to the effects of aerial exposure during marine regression (Wenban-Smith 2002). Evidence offshore for estuarine clays and silts, littoral and estuarine peats and silt-rich floodplain deposits is likely to provide good preservation potential for archaeological material, (e.g. Clachan Old Harbour, Raasay, Inner Sound: Richardson & Cressey 2007; Ballin et al. 2010b).

Many sites are likely to be deeply buried. Reconstruction of the conditions which may have buried archaeological sites and facilitated their re-discovery has recently been improved by new analytical techniques. Praeg (2003) for example, has used seismic imaging to detect buried glacial tunnels under modern sediments. Fitch et al. (2005) have re-interpreted extensive sub-bottom seismic records to detect the changes in sediment characteristics indicating buried river valleys. This technique has exposed a wide meandering river system draining northwards from the north-east flank of the Dogger Bank, and it is now being tested on other parts of the UK shelf, including the northern North Sea. Detailed reconstruction of the prehistoric topography of the submerged shelf is important as it may then be ‘populated’ using modeling based on the known locations of prehistoric sites in similar landscapes (Lakes et al. 1998; Fitch 2011). This allows construction of a hypothetical settlement pattern that may be tested, e.g. through diving, coring and remote sensing as appropriate. In this way, a more accurate map of potential sites can be drawn up.

Potential discovery hotspots in northern Doggerland cannot be listed exhaustively at this stage because of the lack of research in the area, but see the following section ‘Potential Example Areas for Future Work’ for a preliminary discussion of some areas. The steps needed to create high-resolution local sensitivity maps can however be identified. In principle the key factors that increase the potential for both early human settlement, and archaeological survival, are:

• ‘fossil’ estuaries and river valleys;
• valleys, depressions, or basins with wetland or marsh deposits;
• nearshore creeks, mudflats, and peat deposits;
• ‘fossil’ archipelago topographies where sites would have been sheltered by low-lying islands as the sea level rose;
• niche environments in present coastal zones, wetlands, intertidal mudflats, lochs, and estuaries;
• caves and rock shelters in re-entrant bays;
• deposits of sediments formed within, or washed into rocky gullies and depressions.

Potential Example Areas for Future Work

The coastlands and islands contain some of the earliest recorded settlement in the area, dating back to the early ninth millennium BC and relating to the Mesolithic, or to Late Stone Age hunters who settled in Scotland after the end of the Last Glacial (Saville 2008). Several of Scotland's earliest dated archaeological sites come from the coast and islands of the north and west (Mithen & Wicks 2008; Hardy & Wickham-Jones 2009; Mithen et al. 2015). This undoubtedly reflects an element of bias in that archaeologists have long been attracted to the wealth of archaeological material surviving here, but it also reflects the importance of the area to an early population who were reliant upon water-based transport and who were attracted to the rich resources of the coastal lands and islands. Not only did the coast offer concentrations of marine and terrestrial food in terms of fish, shellfish, seabirds, mammals, nuts, roots and berries, it also had other advantages such as the shelter afforded by the many rock shelters and caves, and easy access to boat travel in inshore waters (Wickham-Jones 2014).

Initial study of these island areas suggests good prospects for the conservation of submarine prehistoric remains. They are likely to have been settled from earliest times though evidence for Paleolithic occupation on land has been affected by ice action during the Late Devensian glaciation which ended ca. 14,000 years ago. A complex history of RSL change, however, means that parts of the seabed have been exposed as dry land during and since this period. These areas were suitable for human settlement from early on and they may well preserve the record of that settlement. Some of these submerged areas remained exposed well into recent times (4 ka) and are thus likely to have been settled through the Mesolithic and into the Neolithic. Indeed the lack of Mesolithic sites in the Western Isles, Orkney and Shetland is notable and probably to be explained by this history of sea-level change. This dearth of terrestrial sites means that any archaeological sites to be found on the submerged landscape would be particularly important. Furthermore the terrestrial record can now be shown to be biased. The changing landscape means that terrestrial sites must be interpreted not so much as coastal in nature but rather in line with the topography created by lower relative sea levels.

Nevertheless not all archaeological sites will have survived submergence by the sea. In general, the lack of detailed research in an archaeological context means that hotspots cannot at present be mapped. However, as oil and gas exploration continues around Scotland and Scandinavia, data from coring and seismic survey ahead of major pipeline installation may yield valuable sources of information and this remains an area of future potential.

Known Submerged Finds

Compared to the southern North Sea where there are abundant faunal remains and occasional artifacts, the fossils from the bed of the northern North Sea are of more fragmentary distribution. The species of mammal recorded from the Scottish North Sea are (in order of abundance of fossils) reindeer (Rangifer tarandus), bison (Bison sp.), musk-ox (Ovibos moschatus), woolly mammoth (Mammuthus primigenius), red deer (Cervus elaphus), and some woolly rhinoceros (Coelodonta antiquitatis) (Flemming 2003).

With regard to Scotland, finds of artifacts are limited to a single worked flint from vibrocore number 60+01/46 obtained as part of a BGS program in the UK shelf some 150 km north-east of Lerwick, near the Viking Bank, in a water depth of 143 m (Long et al. 1986). It is possible that this find came from an area of dry land and is thus to be regarded as a submerged indication of prehistoric occupation in a beach environment.

Many intertidal peat deposits and examples of submerged woodland have been noted along the western coastal stretches of the Hebrides, though few have been accurately recorded or studied. The result is considerable evidence for submergence in the last few thousand years. Recent storm activity in the Outer Hebrides has uncovered many new exposures of intertidal peats and on-going studies include those on Coll (Dawson et al. 2001), and Raasay (Dawson 2009; Ballin et al. 2010b). These provide evidence of a slowly rising RSL with stillstands of sufficient length to permit the growth of woodland. Conditions like this would have permitted the local Mesolithic inhabitants to settle in the vicinity of the (now-submerged) coastline.

At Clachan Old Harbour on the south coast of Raasay there is a deposit of submerged peat and tree roots. Much of this has been destroyed by recent digging for fuel, though this digging has now stopped. There is anecdotal evidence for the removal of stone tools from here and when the site was visited by archaeologists in the summer of 2001, a single stone flake was recovered. Since then, further work, including excavation by CFA Archaeology Ltd, has resulted in the recovery of a small assemblage of worked stone, indicative of activity which has been dated to the Early Mesolithic (Ballin et al. 2010b). Dawson's work has shown that this site relates to a slightly lower stillstand in RSL that lasted long enough, probably 500–1000 years, to allow the growth of woodland (Dawson 2009).

In 1991, a scallop boat dredged a gold torc from the seabed near the Shiant Isles (Cowie 1994). This artifact is Bronze Age in date and assumed to relate to loss at sea, whether deliberate or accidental. During the Bronze Age the deliberate deposition of valuable objects in water was a common phenomenon. The characteristics of the Sound of Shiant mean that this artifact could have travelled here from some distance, but the find is also an indication that similar prehistoric material might occur elsewhere on the seabed.

In 1981, a group of divers recovered a gold arm ring from the seabed near to Ruadh Sgeir at the north end of the Sound of Jura (Graham-Campbell 1983). This artifact has been dated to the Viking period, probably tenth century AD, and is assumed to have resulted from a loss at sea. Again, it signifies the potential of the seabed to yield prehistoric remains that reflect to maritime trade and travel rather than direct settlement.

Areas of high potential

There is great likelihood of finds relating to the Mesolithic (10–6 ka) and Neolithic (6–4 ka) periods on the shallower parts of the Scottish shelf (down to ca. –45 m) in areas where the conditions for site preservation can be met. There is also a high possibility of finds relating to the Paleolithic period, prior to the Mesolithic, especially on lower stretches of the Scottish shelf and in the central northern North Sea across to Norway, though it is difficult to pinpoint hotspots for this.

Areas of high potential include the waters around Orkney and Shetland, as well as the Western Isles. Research around Orkney has provided local detail of past RSL change (Bates et al. forthcoming) and indicates the probability that stone-built structures relating to the Neolithic may have survived on the seabed (Bates et al. 2013).

Research around Shetland has focused on the period ca. 8.2 ka related to the Storegga tsunami event, and there is less detail of RSL change extending into more recent periods of human settlement. Nevertheless, paleogeographic models suggest the presence of a considerable submerged landscape around Shetland which may well hold the key to little-known periods of settlement here such as the Mesolithic. The potential archaeological importance of this submerged landscape is high.

Recently, work to investigate the potential for submerged archaeology has been initiated around the Western Isles (Benjamin & Hale 2012). Relative sea-level change suggests a considerable submerged landscape here. Further potential locations for the survival of archaeological material on the seabed include the shelf to the west of the Hebrides; the Hawes Bank and seabed around Coll and Tiree; and between and around Islay, Jura, Colonsay and Oronsay. More specific locations include parts of the Rum and Canna coastline, sheltered inlets and reaches to the east of the Hebrides, and sheltered inlets around Skye. Recent research at the University of Ulster, Coleraine, has highlighted the previous existence of a low-energy strait with various islands between the north Irish coast and the south Hebrides in the Early Holocene (Cooper et al. 2002) thus confirming the importance of this area as another potential archaeological hotspot.

Conclusion and Outlook

Submerged prehistoric archaeology comprises a considerable resource for Scotland, a resource that, unlike other parts of Britain, is relatively unexplored to date.

The development of increasingly sophisticated detection methods, mapping, and underwater excavation means that the recovery of archaeological information from the northern North Sea is increasingly likely. While research has started, it is still patchy and underfunded. Some networks have already been set up by those working elsewhere, (e.g. the Submerged Landscapes Archaeological Network – submergedlandscapes.wordpress.com) and there is considerable scope for Scotland to benefit from the experience of those already working in the field.

A systematic approach is needed in order to catalogue areas that need investigation. These areas should be subject to targeted investigations following a wide area assessment for paleolandscape reconstruction. Specific features of pilot projects should include:

• increased data on relative sea-level change, especially for island groups;
• detailed mapping of Scotland showing the coast at various dates and based on evidence, not modeling;
• predictive modeling for submerged site survival, including 3D modeling derived from energy and aggregate industry (third party) sources;
• survey for submerged sites in locations with high potential;
• a database of submerged paleoenvironmental information.

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