RRS Discovery D144
Cruise summary report
|Ship name (ship code)||RRS Discovery (74E3)|
|Cruise period||1984-01-22 — 1984-02-20|
|Port of departure||Dakar, Senegal|
|Port of return||Gibraltar, Gibraltar|
|Objectives||The main objective of the cruise was to study the sediments and sedimentary processes in an area known at Great Meteor East - part of a feasibility study into the ocean disposal of high-level radioactive waste commissioned by the Department of the Environment. Previous cruises had done much of the ground work, consequently the area was already well known but not necessarily well understood for the purposes of our investigation.
It had already been ascertained that the surface sediments consist of a series of distal turbidites which uniformly cover most of the abyssal plain area and are interbedded by much thinner pelagic units of clays and marls. Within the area there are a number of abyssal hills whose character was not so well known. In particular, the sedimentary processes involved when massive amounts of material are deposited as turbidites are not clear. One objective, therefore, of this cruise was to look more closely at the pelagic/turbidite boundary to gain an insight into the mechanisms involved. It was intended to take long piston cores and conduct a camera survey over the pelagic/turbidite boundary to the south of the area to cover the objective.
Another major sedimentary objective revolved around the so-called 'faults' which had been observed on 3.5 kHz records on previous cruises. The nature of these features had been the subject of much discussion and, in an attempt to resolve some of the uncertainties and implications, a detailed seismic survey was planned for the area of their greatest known abundance. Using near-surface air guns and 3.5 kHz together with an experimental Near-Bottom High-Resolution Profiler developed by R.Babb it was intended to run a detailed survey over a small area with the aid of three 5 kHz bottom transponders to provide accurate navigation. The objective, apart from mapping and observing the 'faults' in relation to basement, was to record the features on magnetic tape for subsequent analysis and modelling.
Another main objective on the GME area was to investigate the possibility of pore water advection occurring naturally within the sediments. To meet this objective it was planned to measure both differential pore pressure using the new Pop-Up Pore Pressure Instrument (PUPPI) and Heat Flow with the recently modified prove over a well navigated transect.
On a hill to the north, a previous cruise had photographed vast number of pebbles, the nature of which was not clear. During this cruise it was planned to run a camera survey over a hull in the west of the area to see if they exist there and, if so, to dredge for them if time permitted. In addition to this, it was planned to lay a transect of three current meter moorings on the abyssal plain, on the flank of the hill and on the top of the hill to look at bottom water current regimes around these abyssal hills.
On the passages to and from the GME area, GLORIA transects were planned to reveal the distribution and frequency of turbidite cannels and pathways on the northwest African continental rise.
|Chief scientist||Peter Schultheiss (Institute of Oceanographic Sciences Wormley Laboratory)|
|Cruise report||(0.86 MB)|
|General||North East Atlantic Ocean (limit 40W)|
|Specific||East of Great Meteor Seamount|
|Current meters||Quantity: number of deployments = 9|
Description: 3 c.m. st.with 3 c.m. on each mooring (at 10,100,1000m) left deployed for recovery on another cr.
|Geology and geophysics|
|Dredge||Quantity: number of deployments = 1|
|Core - soft bottom||Quantity: number of cores = 6|
|Single-beam echosounding||Quantity: track kilometres = 3700|
|Long/short range side scan sonar||Quantity: track kilometres = 2997|
|Single channel seismic reflection||Quantity: track kilometres = 3330|
Description: some data in analogue form on magnetic tape
|Gravity measurements||Quantity: track kilometres = 1370.48|
|Magnetic measurements||Quantity: track kilometres = 3000.24|
|Other geological/geophysical measurements||Quantity: number of measurements = 2|
Description: heat flow;raw data- mag.tape;processed- ms