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Geophysical equipment types used included: Airgun/Sleeve Gun, Echo Sounder, Gravimeter, Magnetometer, Pinger and Sparker. The survey was undertaken by British Geological Survey. AIRGUN SYSTEM - Source: An array of 5 x 40 cu.in. Bolt 600B airguns with waveshape kits and time break solenoids. Routinely, up to four guns were fired simultaneously, keeping the fifth gun as a ready spare. The number of guns used was varied with water depth, with a minimum of two being used in the shallower areas. The firing rate varied from 6 – 8 seconds depending on water depth. Gun synchronisation was achieved by monitoring the time break solenoids and manually adjusting as required. This introduced a short time delay into the system of approximately 50 msec and thus the sea-bed return time was not an absolute measurement of depth. Hydrophone: Two channel Geomechanique summed to give a single channel 30m active length. The summing amplifier used was a newly developed BGS unit, which also incorporated low pass and anti-alias filters. Recording: CODA DA200 four channel digital recording and processing system. The data was recorded on Exabyte tape in CODA format with a sampling interval of 0.2 msec, record length of 4 seconds and bandpass filter of 20-800Hz. The start of recording was delayed in deep water to permit a minimum of 2 seconds (TWTT) of data below the sea bed. The CODA system also received a navigation data string from the navigation processor, and logged position on each shot. On-line processing: CODA system.Processes applied were time varied gain (TVG), time varied filtering (TVF) and trace mixing. Both TVG and TVF were applied from the sea bed, which was tracked automatically. SPARKER SYSTEM - Source: EG&G, nine candle, multi-tip array with 135 tips. High Voltage Power Supply: 2 x Applied Acoustic Engineering CSP3000 capacitor charging units, switchable output up to a maximum of 2.2 KJ. Hydrophone: Teledyne, 10 m, 7 channels with all summed to give a single output. Recording: The same CODA DA200 four channel digital recording and processing system as for the airgun. The data were recorded with a sampling interval of 0.1 msec, record length of 1.5 seconds and a bandpass filter of 103-1730 Hz. SUB- BOTTOM PROFILER - IOS 3.5kHz system: a high resolution, deep water (up to 6000m) swept or ‘chirp’ frequency profiling system transceiver: Raytheon PTR 105B producing 6 kWatts of acoustic power. Recorder: Waverley 3710 Linescan recorder and was selected for a 480 msec sweep. The towfish contained four TR109F Massa transducers wired in a parallel series combination. GRAVITYMETER - LaCoste and Romberg AIR-SEA system. MAGNETOMETER - Direct Reading Barringer M123 marine proton precession magnetometer with 1 gamma sensitivity. VECTOR MAGNETOMETER: A three-component vector magnetometer, supplied by the BGS Geomagnetism Programme. ECHO SOUNDER - Simrad EA500 hydrographic echo sounder with a 9 element tow fish operating at 10 kHz. NAVIGATION - Primary: Trimble GPS 4000DL. Secondary: Ashtech GG-24 (combined GPS + GLONASS). The differential corrections for both of these files are fed from a Sea Star (3000L DGPS set to Eik EMS). it must be assumed that prior to 0000 Day 236, positioning was GPS without differential corrections. The ship’s Ashtec ADU-2 (ships attitude) multihead GPS was logged for the duration of the cruise All position data are referred to the WGS 84 datum. For more detailed information on the acquisition equipment and data collection techniques, operational standards, data processing methods and quality control procedures used on this survey see the Report of Survey/Cruise Report and associated documentation where available. The information available may vary depending on the age of the survey. Data are checked and loaded to the BGS Coastal and Marine data management system following BGS marine data management procedures.

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