Institute Of Oceanographic Sciences Research Articles

A new multiple rectangular midwater trawl (RMT 1+8M) and some modifications to the institute of oceanographic sciences' RMT 1+8

A new multiple rectangular midwater trawl (the RMT 1+8M) is described. It consists of three 1 m2 and three 8 m2 mouth area nets combined within the same frame and is based upon the Institute of Oceanographic Sciences RMT 1+8. It is acoustically operated and controlled and has been successfully used to a depth of 4500 m. The condition of the catch is excellent and use of the multiple net has resulted in considerable saving in ship's time. Some modifications to the existing RMT 1+8 are also described.

Mean sea level volume completed

The Permanent Service for Mean Sea Level, housed within the Institute of Oceanographic Sciences at Bidston on Merseyside, is charged with task of collating mean sea level data from all known tide gauge stations on a worldwide scale. This information has been published in a number of volumes, the first of which appeared in 1940. By the late 1960s several of the earlier publications were out of print, and the opportunity was taken to review the entire method of data publication.The most serious single criticism of the original system stemmed from the common practice of relating sea level to a national fundamental reference point remote from the station. The difficulties of transferring levels across great distances with high precision are well known, and in consequence the problems of geodesy become confused with those of oceanography. The recommendation therefore was to strive to achieve homogeneous data series in which the datum for sea level at a station is referred to a local Tide Gauge Bench Mark and to ensure that this relationship is maintained. In this way the movements of sea level with respect to the bench mark on the one hand and the repeated definition of the height of that bench mark within a leveling network on the other hand became the responsibility of separate disciplines. On this basis it was agreed that the total mean sea level data bank should be reviewed, revised, and republished.

Pop-up bottom seismic recorder (PUBS) of the Institute of Oceanographic Sciences, U.K.

A pop-up bottom seismic recorder designed for seismic refraction experiments was built by the Institute of Oceanographic Sciences in 1968. The device is housed within a 71 cm diameter sphere weighing 270 kg when launched. signals picked up by a hydrophone are recorded in analogue form on magnetic tape in the band 2–100 Hz. The total continuous recording period is 12 hr but the lifetime of the system can be effectively extended by cycling the tape-recorders to allow shooting to go on for up to 3 days. Ballast release is by acoustic command or by pre-set clock. The instruments have been used in water depths from 150 to 4820 m making a total of 63 deployments with a 95% recovery rate. A new version with three-component geophones is being built.

A deep sea temperature and pressure sensor for tidal measurement

With ever increasing information being collected by the offshore continental shelf tide gauges, it became inevitable that researches into ocean tides would require instrumentation to collect tidal data in the deep oceans. This paper briefly describes the temperature and pressure sensors developed, and used by the Institute of Oceanographic Sciences (Wormley), in response to this requirement. Also described are the techniques and equipment used to calibrate these sensors. The deep sea tide gauges, each of which include two pressure and one temperature sensor, have now been operationally deployed on four occasions at pressures up to 300 bars (3000 m) providing well over 100 days of tidal data. In an international exercise to evaluate the performance of existing deep sea pressure sensors, results show that the unit described in this paper compares favourably with the other sensors. For example, the amplitude of the semi-diurnal components were within 1% of the average value, determined by all the sensors. The temperature sensor has an operational range within the limits — 1° and + 40°C and exhibiting a stability of the order 8 milli°C/month.

The distribution of the coralCaryophyllia smithiiS. & B. on the Scottish continental shelf

The published records of the occurrence of the Devonshire Cup CoralCaryophyllia smithiiStokes and Broderip in Scottish waters are widely scattered throughout the literature. Rees (1962, 1966) listed several of these and suggested that the paucity of records was a reflexion of the comparatively little systematic collecting that had been done on the Scottish coasts and on the continental shelf.The purpose of the present paper is to collate and review the published records of the distribution ofC. smithiiand to present new data derived from extensive investigations carried out by the Institute of Oceanographic Sciences, Wormley, as part of a study of shelly faunas and sediments on the continental shelf west and north of Scotland. Additional records obtained from several other sources are also included.

Vertical distribution of cephalopods at 11°N, 20°W in the North Atlantic

This is one of a series of four papers dealing with vertical distribution of cephalopods in the North Eastern Atlantic at six stations near 20° W and at about 10° intervals from 60°N to 11° N (Clarke & Lu, 1974, 1975 a; Lu & Clarke, 1975). The present study is based upon a series of hauls made at discrete horizons between o and 2000 m with opening-closing nets during both daylight and darkness. The collections were made for the ecological programme of the National Institute of Oceanography, Wormley, Surrey, England (now part of the Institute of Oceanographic Sciences).

Vertical distribution of cephalopods at 40°N, 53°N and 60°N at 20°W in the North Atlantic

Little work on vertical distribution of cephalopods was possible before the development, in the 1960s, of sophisticated opening-closing devices usable on midwater trawls such as the 10 ft Isaacs Kidd trawl (IKMT; Foxton, 1963; Aron et al. 1964) and the series of rectangular midwater trawls developed by the Institute of Oceanographic Sciences (previously the National Institute of Oceanography) (Clarke, 1969 a; Baker et al. 1973). These developments have resulted in three papers on vertical distribution of cephalopods in the North Atlantic (Clarke, 1969 ft; Gibbs & Roper, 1970; Clarke & Lu, 1974) and one for the Mediterranean (Roper, 1972). The present paper describes the vertical distribution of cephalopods caught at 40° N 20° W, 53° N 20° W and 60° N 20° W in the North Atlantic based upon day and night series of horizontal hauls between the surface and 2000 m using the RMT combination net (Baker et al. 1973).

Ocean Science

In this paper the Lucasian Professor of Applied Mathematics in the University of Cambridge studies the role of ocean science in the service of mankind, and examines the interaction between the many disciplines which make up that science. The paper, which was written in May 1972 (and a version of which was published in the Bulletin of the Institute of Mathematics and its Applications for February 1973), was presented at a conference held in Greenwich on 12–14 September 1973 to celebrate the hundredth anniversary of the Royal Naval College. (Note: the National Institute of Oceanography referred to in the text is now known as the Institute of Oceanographic Sciences.)

An experimental survey of a herring fishery by long-range sonar

For 3 years, the Institute of Oceanographic Sciences has operated a long-range side-scan sonar for viewing the texture and topography of the ocean floor (project G.L.O.R.I.A., Geological Long Range Inclined Asdic). It was recommended that an experiment should be arranged to discover if such a device could detect commercial pelagic fish on the Continental Shelf at long ranges and, if so, to determine any research on commercial applications. This paper describes such a trial, carried out on a Scottish inshore herring fishery in the Sea of the Hebrides, during late September,1971. A survey was first made in the area by echosounder and short-range side-scan sonar to confirm the bathymetry, to locate false targets, and to observe the distribution and diurnal vertical movement of the herring. During the subsequent G.L.O.R.I.A. runs, up to 9kW of acoustic power was transmitted at 6.4 kHz, with the signal returns processed by a linear correlator with a time-bandwidth product of 400, so that signal/noise ratios obtained were equivalent to a short-pulse sonar with peak powers in excess of 1 mW. Due to the summer water-conditions, it was found that the propagation depended critically on the position of the source in the water column. Under the best conditions, with the source towed at 33 m in an isothermal surface layer, herring were detected to a range of 15 km in a water depth of 120 to 170 m. For a period of 3 days, a fishery area of 170 km2 was kept under surveillance by steaming up and down 13 km-long base lines at a speed of 13 km/h facing SE towards Hawes Bank and the islands of Tiree and Coll. As a result, a plan view of the area, including both fish and the geological features of the bank, was generated every 1 1/4 h. It was found possible to track certain aggregations of herring using these records for periods up to 5 h. On the final might, remotely directed catches were made on 3 aggregations by guiding a purse-seine vessel to within 1 km of each target. The internal composition of the aggregations detected by G.L.O.R.I.A. is discussed in terms of both the echosounding data and expanded A-scan excerpts from the recorded G.L.O.R.I.A. target signals. Possible research and commercial applications for the long-range detection of pelagic fish by low-frequency towed or fixed sonar systems are briefly discussed.