Maritime deposits dating back more than 1.5 million years among discoveries from EirGrid subsea project

Archaeological and geological investigations carried out as part of EirGrid’s Celtic Interconnector Project have revealed new insights into Ireland’s ancient past.  

The discoveries from east Cork’s land and maritime heritage were showcased at a webinar hosted by EirGrid, the national electricity grid operator as part of National Heritage Week.  

The webinar, ‘Hidden Heritage: Discoveries from the Celtic Interconnector Project’, featured onshore archaeology expert Dan Noonan of Dan Noonan Archaeological Consultancy and underwater archaeology expert Dr Michael Walsh of Coracle Archaeology Limited, who outlined the extensive programme of assessments and monitoring undertaken throughout the development. 

The Celtic Interconnector is a subsea cable linking the electricity grids of Ireland and France, allowing the exchange of 700MW of power, equal to powering 450,000 homes.  

The project has made considerable progress since it began construction in 2023, with all onshore cables for the project in Ireland successfully installed on the 44km route. Offshore, burial and protection of 84km of high voltage direct current cable (HVDC), was completed in Irish waters this summer. Significantly for fishing communities, the route has now re-opened for fishing. 

The webinar attendees learned that one of the most significant discoveries made during the investigations was the identification of ancient sediment deposits, some of which were estimated to be more than 1.5 million years old. 

Speaking following the completion of the investigations, maritime archaeologist, Michael Walsh, outlined the significant deposits found. 

"Samples recovered offshore from Claycastle Beach, Youghal, were found to predate radiocarbon dating techniques (>50,000 years), so further samples were recovered for optically-stimulated luminescence (OSL) dating, but the samples were found also to predate this technique (>1.5 million years)," Walsh noted.  

"These findings offer a rare opportunity to better understand environmental conditions from a period far earlier than can typically be studied through conventional archaeological dating techniques." 

“EirGrid’s extensive programme of investigations, licensed by the National Monuments Service, supported broader archaeological and geological research enhancing our understanding. This work has contributed valuable information that extends beyond the needs of the project itself," Walsh added. 

Analysis of the deposits ultimately led researchers to conclude that the material was too old to have been associated with human occupation in the area, providing important clarity on the site's prehistoric context. 

Dan Noonan outlined archaeological works undertaken on land along the cable route, with the highest concentration of possible features found outside Killeagh.  

Finds included fragments of 9th to 10th century clay tuyere from the Killeagh pavement scheme. A tuyere is a tube or nozzle injected into a furnace or hearth during smelting or forging. 

“From excavated features, a large number of fragments related to metal working were identified at Ballyedekin,” Noonan told the webinar, adding that the fragments may be post-medieval, dating from the 16th century onwards.  

The webinar was informed that soil samples are now being analysed, along with selected charcoal samples for radiocarbon dating. 

“The radiocarbon dates, combined with information from the artefacts uncovered during excavation, will provide valuable insights into the function of these features and how the sites were used over time,” explained Noonan.