submerged landscape archaeology

Ireland has experienced a complex pattern of sea-level change stemming from its glaciation during the last Ice Age. In areas situated on the margins of the ice sheet (including the JIBS study area) the removal of ice during deglaciation caused the underlying crust to rebound, resulting in the emergence of large areas of continental shelf. Crustal rebound eventually slowed and the exposed shelves were flooded by the rise in global sea-level induced by vast quantities of meltwater released from the decaying ice sheets. Importantly, the emergence, and subsequent flooding of the continental shelf coincided with earliest periods of Irish prehistory. During the earliest known Mesolithic (dated to c. 10,000 BP by the Mount Sandel site in Co. Derry) sea-levels along the north coast of Ireland were lowered by 5-30m depending on the local patterns of glaciation and crustal rebound (Brooks et al, 2008; Kelley et al 2006). These emergent shelves provided an extension of the terrestrial environment and its resources and, crucially, were bounded by the past coastline. They provided access to important marine resources, coastal lithic raw materials and migration/transportation corridors along the coast and into the interior via estuaries. Through the early Holocene sea-level remained low, to the extent that Neolithic and early Bronze age landscapes could also be submerged in the JIBS area.

Multibeam echo-sounder data of the north coast of Ireland illustrating a palaeo-cliff shoreline off White Park Bay and the Giants Causeway

Given that a water crossing from Britain was the most likely migration mechanism, the Irish coast and immediate environs were the first landscapes encountered by the earliest Mesolithic settlers and would have shaped their social and subsistence strategies as well as influencing their decision to settle in Ireland rather than return to Britain. These landscapes remained important throughout subsequent periods of Irish prehistory, where there is clear evidence of settlement locations close to waterways and coasts, attesting to the importance of coastal and near-coastal resources and transport corridors. Moreover, these landscapes changed over time as a result of regional climate changes and sea-level rise, and almost certainly impacted on the settlement patterns and lifeways of their inhabitants. Therefore, if the Irish prehistoric record is to be placed in an accurate palaeo-environmental and palaeo-geographic context, it is essential to reconstruct these submerged cultural landscapes and their evolution over time.

Palaeogeographic reconstruction of the study area at a -60m lowstand

During the Ice Age, Ireland was covered by ice and experienced dramatic sea-level changes. Beyond ice sheet margins, lowering of sea level caused extensive continental shelf areas to emerge from the Atlantic Ocean. Subsequently, as ice sheets melted and sea level rose, emergent areas were slowly flooded. Inside ice sheet margins, a complex interplay of changing ocean and land levels resulted in rising and falling sea levels at different times and places (Bell et al., 2006a,b). Over the past 20 years, studies of the raised seabed in Ireland have provided insights into past marine conditions (ecology, geology and oceanography), but submerged cultural landscapes have received much less attention. Although this has been partly due to technological challenges and resources, there has also been general scepticism in the archaeological community about the value of underwater surveys and the role that coastal environments played in human development.

Palaeogeographic reconstruction of The Skerries circa 11,000 years ago when relative sea level was 30m lower than today.

Palaeogeographic reconstruction of Rathlin Island circa 11,000 years ago when relative sea level was 30m lower than today.

However, this view has slowly been reversed as underwater surveys in Scandinavia confirmed the ability to discover submerged sites (e.g. Fischer, 1995; 1997). Recently, the potential for the survival of submerged archaeological landscapes in Ireland (O' Sullivan, 2001; McErlean et al., 2002; Kelley et al., 2006; Lafferty et al., 2006) and Newfoundland (Bell and Renouf, 2001, 2003; Bell et al., 2006a,b) has also been identified. In Ireland, over the past 5-10 years, government agencies (e.g. MI, GSI, EHS) and universities (e.g. UU) have initiated marine mapping programmes with the aim of mapping the cultural component of the seafloor in the context of the geological and environmental evolution of the continental shelves (Quinn et al., 2000). In tandem, technological developments in data processing and interpretation, allied with geodynamic modelling (e.g. Shaw et al., 2002; Brooks et al., 2006), now offer realistic opportunities to predict, locate and precisely map the locations of these ancient coastlines and record the geophysical signatures of former habitation- and exploitation-sites embedded within these natural landscapes. The provision of the JIBS data offer a unique opportunity to map these features off the north coast of Ireland, at a resolution previously unattainable.  

Palaeo-lagoon off the north east coast of Rathlin Island formed at a lower sea-level