Seacore was awarded the £2.5M contract in 2005 by the Natural Environmental Research Council, on behalf of the European Consortium for Ocean Research Drilling, to perform a marine site investigation of the seabed at three offshore locations around the coast of the French Polynesian island of Tahiti in the South Pacific Ocean.
The detailed and challenging investigation required Seacore to sink 19 boreholes and take core samples of seabed sediments and substrata at up to 105m penetration in water depths ranging from 30-310m. The ocean floor drilling project is part of the Integrated Ocean Drilling Program (IODP), an international marine research programme involving the collaboration of international scientific research organisations aimed at exploring Earth’s history and structure, recorded in seafloor sediments and rocks, and monitoring subsea floor environments. Ocean floor drilling provides essential material for the study of climate change, bio-diversity, geophysics and geodynamics. The project was managed by ECORD Science Operator, a group of European Institutions coordinated by the British Geological Survey.
The scientific objectives of the Tahiti expedition were to reconstruct the sea-level rise following the last major glacial event 21,000 years ago, when half of North America and most of Northern Europe were covered by thick ice sheets and sea level was about 120m lower than today. In addition the expedition aimed to reconstruct associated changes in sea surface temperatures and to analyse the effects of climatic and sea level changes on reef building. The project followed on from last year’s successful expedition to the Arctic Ocean for IODP, where working in water depths of 800m-1400m, Seacore recovered cores up to 428m into the seabed from sites along the 1800 km long Lomonosov ridge, extending from Greenland towards Russia.
For the Tahiti project Seacore mounted its own heave-compensated R100 drill rig, built initially for the Lomonosov ridge project, onto the multi service construction vessel DP Hunter, to provide drilling and sampling services. Seacore also used a novel, purpose-built borehole drilling and seabed re-entry template, known as a DART. Seacore, one of Europe’s leading specialist marine geotechnical exploration drilling and large diameter offshore drilling contractors, recently and successfully used the R100 with a larger DART in the Strait of Gibraltar, contending with strong winds and withstanding complex and exceptionally strong currents throughout the 300m water depth, to drill and recover core samples up to 350m below the seabed.
The DART considerably minimised the risk of any localised damage to the Tahiti reefs during core sampling.