Overall objectives in the EU GO project are to assess the promising potential of seismic imaging for physical oceanography, in view of its combination of fine resolution and coverage unmatched by conventional oceanographic measurements. D318 was to provide the means of assessment by obtaining a unique, comprehensive, oceanographic and seismic dataset at the same time and place. Specific objectives for R.R.S. Discovery cruise 318a were to deploy four ADCP moorings, three adjacent temperature-logger moorings and STABLE, in an L-shape array in 750-1000m depth east of Portimao Canyon, carrying out adjacent CTD stations, deploy two OBH moorings, carry out seismic sections using the Ifremer high-frequency air-guns and streamer, accompanied by regular XBT and less frequent XCTD casts. In addition underway data was logged including ship-borne ADCP, surface temperature and salinity, meteorology, gravity and magnetics (to test new NERC magnetometers).

Overall objectives in the EU GO project are to assess the promising potential of seismic imaging for physical oceanography, in view of its combination of fine resolution and coverage unmatched by conventional oceanographic measurements. D318 was to provide the means of assessment by obtaining a unique comprehensive oceanographic and seismic dataset at the same time and place. Specific objectives for R.R.S. Discovery cruise 318b were to (i) recover four ADCP moorings, three adjacent temperature-logger moorings and STABLE, from 750-1000m depth east of Portimao Canyon (ii) perform deep water CTD casts (iii) carry out seismic sections using the NMF supplied Bolt airgun and streamer, accompanied by regular XBT and less frequent XCTD casts, iv) work with MV Poseidon to test novel seismic data acquistion strategies. In addition underway data was logged including ship-borne ADCP, surface temperature and salinity, meteorology, gravity and magnetics (to test new NERC magnetometers).

The three key objectives of our original proposal were to test: 1. The hypothesis that mantle upwelling and melting is focused at the centres of slow spreading ridge segments and transposed by sub-horizontal flow away from there. 2. The hypothesis that plate accretion and separation mechanisms are fundamentally different in 'magma-starved' areas. 3. Mechanisms of detachment faulting and extensional strain localisation in the lower crust and upper mantle. We proposed to achieve these objectives by detailed surveying and sampling across an extensive region of magma-poor seafloor spreading around Fifteen Twenty Fracture Zone (FTFZ), coupled with microstructural, geochemical and palaeomagnetic analyses. TOBI deep-towed sidescan and magnetic data were to be obtained both to inform the choice of sampling sites and to aid in structural, lithological and geodynamic interpretations. We spent 29 days on the Mid-Atlantic Ridge (MAR) in the vicinity of 13 to 15N. We collected multibeam ship-based bathymetry, gravity and magnetic data and TOBI sidescan, magnetic and water-column data from a total area of about 8,000 km2. We recovered samples from 47 drill and dredge stations throughout the area, in support of the objectives.