Particle transport from the West African shelves of Liberia and Sierra Leone to the deep sea: A chemical approach

The chemical and mineralogical composition of suspended particle suites has been used to assess off-shelf transport on the West African shelves of Liberia and Sierra Leone. Using the ratios of Si/Al, Fe/Al, Mg/Al and Mn/Al as tracers, it was possible to detect shelf-derived materials in slope waters. In the majority of cases, these inputs could not have been detected using particle mass or light scattering measurements and could only be measured by using the chemical signatures of the particulate matter. At the time of sampling, the suspensate which had been moved seaward over the slope was detected adjacent to submarine canyons and highly turbid areas on the outer shelf. The chemical and mineralogical composition of the suspensates, and sediments in the adjacent eastern Atlantic basin are similar to those found in the water column seaward of the West African continental shelves and yet distinct from the Sahelian dust which is considered the major source of sedimentary material for the tropical and semi-tropical areas of the deep eastern basin. These findings suggest that materials from this shelf area could be a more important input to the deep sea than was previously realised.     

Bathymetry of three deep-sea channels in the northeast and central Tufts Abyssal Plain

The drainage pattern in the northeast and central Tufts Abyssal Plain is described in detail. Satellite navigation on the systematic survey has allowed precise location of the major channel systems of the northeast Pacific Ocean. Two hundred channel profiles were collected from the echograms showing the Moresby-Scott, Mukluk, and Horizon Channel Systems trending in either a southwestward or westward direction across this section of the Tufts Plain. The channel profiles illustrate the prominence of the higher and wider right-hand levee (facing downstream). The Moresby-Scott Channel System disperses in the form of several distributaries throughout the area studied, and is probably responsible for much of the sediment deposits. Unlike the Moresby-Scott, the Mukluk extends throughout the survey area as a solitary channel with one minor branch. The Horizon Channel crosses the Sedna Fracture Zone east of the Sedna Seamount and terminates in distributary fashion in the central portion of the Tufts Plain. The Moresby-Scott, Mukluk, and Horizon Channels form one major system which encompasses the entire northeast and central Tufts Abyssal Plain.     

Studies on the determination of inorganic iodine in seawater

Existing methods for the determination of the various forms of iodine present in seawater are laborious or unwieldy in use. This paper describes modified forms of the iodate and total iodine methods described by Barkley and Thompson (1960), a spectrophotometric procedure for iodate determination derived from Johannesson's (1958) work, and an automatic method for total iodine determination. Procedures for iodate and total-iodine determination which are suitable for use aboard ship, are recommended. Both procedures for iodate determination returned a standard deviation close to 0.5 μg/l when several replicate samples of a seawater containing approximately 30 μg/l of iodate-iodine were analysed. The automatic method for total iodine determination yielded a standard deviation of 0.8 μg/l by the repeated analysis of a seawater containing a total of approximately 50 μg/l of iodine. Suitable methods for the filtration and storage of seawater are also described.     

Plate boundaries and evolution of the Solomon Sea region

The Solomon Sea Plate was widely developed during late Oligocene, separating the proto-West Melanesian Arc from the proto-Trobriand Arc. Spreading in the Bismarck Sea and in the Woodlark Basin resulted from interaction between the Pacific and Australian Plates, specifically from the collision of the proto-West Melanesian Arc with north New Guinea, which occurred after arc reversal. This model explains the extensive Miocene, Pliocene, and Quaternary volcanism of the Papua New Guinea mainland as it related to southward subduction of the Trobriand Trough. Our interpreted plate motions are concordant with the geological evidence onshore and also with complex tectonic features in the Solomon Sea Basin Region.     

A locking-compass for in situ sample orientation

A mechanically-actuated locking-compass was designed for mounting on corers to record equipment orientation during the sampling process, thereby providing magnetic orientation data on the recovered deep-sea core. Locking occurs upon impact by the corer with the sea-floor; after retrieval, the device is easily unlocked and reset for another station. Compass construction makes use of commercially available parts, requires no welding and little machining, and thus allows inexpensive and easy assembly at sea.