Scotland and its surrounding shelf area have undergone significant changes over the last 1Ma from the impacts of global glacial to inter-glacial cycles. In particular, over the last 500,000yrs Scotland has experienced at least 6 periods of glaciation with lowering of sea-level to a maximum of c -120m below the present day level. Each of the glacial periods, however, has been separated by intervals characterised by interglacial conditions where exposed landmasses extended terrestrial habitats into large landscapes with favourable conditions for human occupation (Coles 1998). Subsequent glacial action and flooding by the sea with associated sea level rise have led to conditions conducive to the erosion of these landscapes, and their associated evidence of human occupation. This combined with the general great difficulty today facing those investigating these presently flooded areas has resulted in a great scarcity of information or finds for the period prior to the Mesolithic in Scotland. Modern research techniques and new information resulting from increased activity in the offshore areas of the coast and shelf of Scotland will lead to increased finds and the accompanying increased knowledge of these earlier periods of occupation. This situation is clearly demonstrated in Denmark where commercial dredging activity has led to a quantum increase in material found related to human occupation on the now-drowned North Sea bed.
The coastal edges, near shore and shelf areas therefore have the potential not only to add additional knowledge to a missing period of archaeology, but have the potential to add new knowledge that cannot be gained from onshore sites.
2.2.1 Submerged Archaeological Potential – Scotland and the Palaeo-landscapes of the last 10,000yrs
The relative sea level history of Scotland during the Holocene (conventionally, if arbitrarily dated to the last 10,000 years i.e. approx. 8000 calBC-2000 calAD) is complex. This is due to the distribution and thickness of the overburden of ice when the last Scottish ice sheet covered the region and the different geological terrain that makes up Scotland. Ice cover was concentrated in the western Highlands with thinner areas of cover towards the peripheries of Scotland. Thus, 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 has led to varying amounts of isostatic rebound or subsidence and therefore, the position in the landscape where we see relict shorelines today. For the Oban area, this translates to visible shorelines dated to c.10ka yrs (c.8000 calBC) up to 10 metres above present OD. However, the same Lateglacial Shoreline is well below present sea level on the islands of Coll and Tiree, Islay and along the Solway coastline. Predicted shorelines for the Outer Hebrides and the Orkney Isles suggest they are located between 20-30 metres below present OD.
The net result of relative sea level change for Scotland is thus that there are areas where the sea bed has been dry land within the last 10,000 years. As this is the period within which Scotland has a comprehensive record of settlement, it is likely that these areas were once settled. They offer the possibility that submerged archaeological sites may be preserved. Perhaps the best known area is that around the archipelago of Orkney where sea did not reach present levels until about 4000 years ago, but another area lies to the west of the Western Isles, and there are small localized areas elsewhere, e.g. around Coll, Tiree and Islay. Although there is no specific data on relative sea level rise for some of these areas, it is assumed that sea level reached roughly its present level between 5000-3000 years ago suggesting 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 currently have little evidence on land for Mesolithic settlement (with some exceptions). Mesolithic sites are few and far between in Orkney and lacking (with the exception of a few dates on anthropogenic deposits) 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 off shore area. Recent field research in Orkney suggests the possible preservation of stone structures relating to the Neolithic on the seabed (Benjamin 2010).
It is also worth remembering that large areas of the Scottish shelf have been dry land for considerable periods in the last 700,000 years – the period of human (Palaeolithic) settlement in Britain. England and Wales have a good record of early settlement sites, particularly in the south, but there are no dated Palaeolithic sites in Scotland so far. Environmental and osteological evidence suggests that this submerged landscape has, at times, been suitable for human settlement and it is possible that surviving Palaeolithic sites from the “Scottish sector” of the sea bed still survive, comparable sites on land having been destroyed or buried by the actions of the last Ice Age which blanketed mainland Scotland.
Submerged archaeology will comprise a considerable resource for Scotland, a resource that, unlike other parts of Britain, is relatively unexplored in Scotland to date. With the increased pressures on the submarine landscape as a result of renewable energy sources and supplies, archaeologists are faced with opportunities to investigate our submerged landscapes that have not previously been possible.