It seems probable that the existence of Rockall has been known for a very long time but the first recorded landing we have is of a party from H.M.S. Endymion, with Lt Basil Hall, in 1811 (Fisher 1956). Records at that time of good fishing in its vicinity are frequent but the true extent of Rockall Bank was not known until 1831 when it was surveyed by Captain Alexander Thomas Emeric Vidal on H.M.S. Pike (Wigley 1831). The tiny prominence of rock bore little relation to the enormous extent of the shallow bank from which it protruded above the waves, more often than not, because of its white cap, mistaken for a ship under sail.

From direct sampling, the deeper Rockall Trough and Faeroe-Shetland Channel are known to have a Tertiary-Quaternary sedimentary sequence up to 3000 m thick, which is in places, particularly in the north, underlain by early Tertiary basaltic volcanic rocks. The seamounts in the Rockall Trough are of basic volcanics of probable Upper Cretaceous age. The eastern shelf areas have a rifted basement of Precambrian-Devonian (-?Carboniferous) age, overlain by Permian + Mesozoic sedimentary rocks that reach 5000 m in thickness in rift basins. Tertiary sediments thicken rapidly from the shelf into deep water. The western shelf areas have extensive early Tertiary basalts from the Faeroe Islands to the southern part of Rockall Bank. A thin Tertiary—Quaternary cover exists and Precambrian basement lies beneath.

The pre-Tertiary geology of the deep water areas and the overall crustal structure have been inferred from geophysical investigations. In the Rockall Trough the crust is of oceanic thickness, about 6 km, but it is probably slightly thicker beneath the Faeroe-Shetland Channel. This fact, coupled with the size of the channel compared with other small ocean basins and the knowledge that fully developed oceanic crust exists just outside the mouth of the Rockall Trough, strongly suggests that at least parts of the deep water areas are floored by oceanic crust. However, seismic reflection and magnetic anomaly profiles do not yield observations characteristic of normal oceanic crust.

The age of any oceanic crust in the Rockall Trough and Faeroe-Shetland Channel is equivocal. Between 54° and 59° N a succession of largely sedimentary rocks up to 3000 m in thickness occurs between the Tertiary and the acoustic basement. To the north this succession is masked on seismic profiles by early Tertiary basalts but it is probably present; to the south it is interrupted by a series of acoustically opaque basement ridges. With slow sedimentation rates, this succession could extend back to the late Palaeozoic, but with rapid rates, only to the mid-Upper Cretaceous. An age of mid-Lower to mid-Upper Cretaceous for oceanic crust, equal to that of the ocean crust outside the mouth of the Rockall Trough, is accepted here. Although rapid subsidence and infill in Upper Cretaceous time is not characteristic of major shelf basins around Britain, it may be acceptable for the Rockall Trough and Faeroe-Shetland Channel if they are underlain by oceanic crust rather than continental crust.

A likely model for the formation of the Rockall Trough and Faeroe-Shetland Channel is of continental rifting and subsidence from late Palaeozoic or earliest Mesozoic to mid-Cretaceous time, then sea-floor spreading in Albian (c.105My)–Santonian (c.85 My) time, accompanied and immediately followed by rapid subsidence and deposition. The Tertiary was heralded by widespread basaltic igneous activity which briefly arrested subsidence, but was largely a period of subsidence without sedimentation keeping pace.

The geological structure and history of the Rockall Trough margin to the west of the Outer Hebrides (57°N-59°N) has been inferred from the analysis of bottom samples, seismic, sonar, magnetic, satellite altimeter and surface-ship gravity observations. Much of the continental shelf consists of a shallow platform of Precambrian Lewisian basement, covered by a thin (<300m) blanket of Cenozoic sediments. Apart from areas near the shelf break and immediately west of Lewis, the basement has not undergone the large-scale subsidence typical of many regions adjacent to the Rockall Trough. Beneath the outer shelf, the Lewisian dips steeply towards the deeper water and is covered by a westwardthickening succession (>3km) of Mesozoic and Cenozoic sediments.

The eastern margin of the Rockall Trough appears to have been well established as a site of deposition by the end of the Triassic. Further subsidence occurred during the late Jurassic and continued into the Cretaceous when the axial province of the Rockall Trough off the Hebrides was invaded by basic volcanic material. Subsequently, the region was profoundly affected by early Cenozoic igneous activity. The long-term buoyancy of the Lewisian basement under the Outer Hebridean platform and early-formed structural discontinuities within it have influenced the overall pattern of sediment accumulation and the distribution of volcanic activity along the margin. During the later stages of deposition, sedimentation was closely controlled by the presence of early Cenozoic volcanics, by bottom currents and by glacial processes.

Single channel, analogue, seismic reflection profiles using Sparker and small capacity Air gun sources were used to investigate late Tertiary and Quaternary sedimentation both around the margins and on the floor of the north Rockall Trough. The data complement, by being intermediate in penetration and resolution, previous seismic studies; particularly, they allow the upper 500 m of the sediment sequence to be examined in greater detail than hitherto.

The basic premise that foraminiferal test morphology is related to function, in this case life position and feeding strategy, and thus indirectly to habitat, is detailed in Jones & Charnock (in press). The following account is based on that work but is in the form of a summary since a detailed description will be published elsewhere. The information used in this paper is from Pearce (1980) who examined Foraminifera in semi-quantitative multiple cores collected in a series of transects running approximately perpendicular to the axis of the Rockall Trough. The Foraminifera were from the surface sections, 0-2 cm, of the cores.

The water masses, major circulation features and long-term variability of Rockall Channel waters are reviewed in relation to work in recent years. Data collected with modern instruments disclose more detail in the water mass structure than found previously, and the range of water masses present in the Channel is examined.

The use of recording current meter moorings has amplified our knowledge of the processes occurring within the Rockall Channel circulation, although net flows remain difficult to evaluate. Eddy motions suggested by current meter records and geostrophic data are confirmed by the trajectories of satellitetracked drogues.

Changes in the temperature and salinity of the upper waters of the Rockall Channel from the early years of this century to the present are clearly detectable, and a brief account is given of these.

Recent knowledge of physical-oceanographic processes is reviewed for the eastern shelf-edge boundary of the Rockall Channel.

A year-round northward current flows along the steep continental slope. Mean currents vary from 3 to 30cm/s, generally increasing northwards, but estimates of transport inshore of the 2000 m depth contour are much more consistent, averaging about 1·5 × 106m3/s. The current is thought to be forced largely by a long-shelf pressure gradient, associated with large-scale N-S density variations in the upper ocean.

Although cross-slope changes of temperature and salinity are much less than occur, for example, east of the U.S.A., cross-slope exchange velocities appear to be only around 2cm/s (1/5 of long-slope fluctuations). There is a sharp change between winter-cooled water on the shelf and adjacent slope water. Upwelling against the upper continental slope may occur following northerly long-slope winds. Tidal currents and surges depend strongly on continental shelf wave properties. At near-diurnal frequencies, and in response to winds of short scale (< 100 km), clockwise-rotating currents near the shelf break are expected, especially where the shelf is broadest. Tidal currents show this character.

Internal tides are significant; any non-linearity is most likely when stratification is present but weak. Bottom stirring has been observed, and may be important at some depth (where the bottom slope becomes as steep as the semi-diurnal internal characteristics) almost everywhere around the Rockall Channel. The energetic internal waves should contribute significant internal mixing as they approach the shelf break, intensify and dissipate.

Though our knowledge of the circulation in this complex region is still incomplete, recent direct current measurements have identified four separate elements of the circulation which appear to undergo a seasonal variation of some sort. These are: (i) a summer-autumn maximum in the deep overflow of Norwegian Sea Deep Water across the Wyville-Thomson Ridge; (ii) an autumn minimum in the upper-ocean circulation around Rockall Bank, ascribed to Taylor Column processes; (iii) an autumn-winter maximum in the strength and breadth of the slope current along the European continental margin; (iv) a winter-spring maximum in eddy kinetic energy in the open waters of the Rockall Channel, and over the full depth range, as a function of windstress and stratification. The first three of these elements are of localised occurrence along the northern, western and eastern margins of the Channel and are described only briefly. The fourth process, encountered at a range of sites in the northeast Atlantic, is described in detail using a total data set of 68 instrument-years of direct current measurements recovered from the Rockall Channel in 1977–84. In the seasonally-varying 3–27 day (d) band of periods, eddy kinetic energies (kE) are shown to be depth-dependent in amplitude, but with little evidence of any significant phase-lag with either depth or location between the individual timeseries of kE estimates. These time-series demonstrate clearly and for the first time that the winterspring peaks in eddy kinetic energy lag the winter peaks in windstress by between 1 and 3 months. This phase-lag is explained as the cumulative result of wind forcing and eddy dissipation.

Preliminary results from a winter and a summer cruise in 1984 to the area west of the U.K. continental slope are presented to discuss the structure and the spatial scales of convection. Winter convection events were found to reach a depth of 630 m with horizontal scales of the order of 50 km. The number of areas with actual convection to maximum depth was small at the particular time of the cruise, but the vertical structure in the investigated area indicated numerous convection events over a longer period. The principal vertical structure of the upper 600 m in winter was preserved until the following summer, which agreed with the age of the summer upper layer water estimated from the tritium/helium ratio. This characterises the area to be one of low advection, which can also be indirectly concluded from the fact that the northward flow of 4 Sverdrup of Atlantic Water through the Faeroe-Shetland Channel is supplied by 2 Sverdrup from the current over the continental slope west of U.K. and 2 Sverdrup of flow along the Arctic Front between Iceland and the Faeroes.

For the last twenty-five years the pace of international deep-sea benthic investigations has been gaining momentum, first as a genuine basic scientific exploration of the largest unknown area of the Earth's surface and later as a place man might exploit for the disposal of high energy radioactive wastes and to mine for manganese.

A brief historical account of the early faunal investigations is given. Modern studies concentrate on qualitative and quantitative description and interpretation of the processes taking place within the Rockall Trough. Demographic analyses are feasible on a variety of species allowing estimation of growth and production rates. The pelagic fauna impinges on the benthopelagic environments of the slope regions of the Trough. There it is predated by populations of demersal fish. Advection of fauna takes place to the north and northeast, probably primarily in the slope current.

More than 300 bottom samples taken in the Rockall Trough and neighbouring areas (Northeast Atlantic) since 1973 provide an opportunity to study the distributions of the commoner megafaunal species. These include 131 species of echinoderms, for the most abundant of which the bathymetric and regional distributions are defined. Analysis of samples by means of the coincidence-of-range method along a bathymetric transect shows peaks-in the first and last occurrences of species at the 800–1200m and 1800 m levels. Cumulative curves of the recruitment of all echinoderm species with increasing depth show step-like increases in the rate of species recruitment with depth. These maxima in rate of faunal change are related to water–mass structure, particularly the depth of the seasonal and permanent thermoclines. A considerably broader bathymetric range is shown by post-larvae and juvenile stages compared to adults.

The reproductive biology of a wide variety of deep-sea echinoderms from the northeast Atlantic has been examined. Time series samples of asteroids, ophiuroids, echinoids and holothurians are available from Station “M” and the Scottish Marine Biological Association's Permanent Station in the Rockall Trough and from opportunistic sampling in other areas of the northern Rockall Trough. Examination of these time series samples has established three main reproductive patterns in these taxa and one example of protandric hermaphroditism. The dominant reproductive pattern is the aperiodic production of relatively few large eggs usually in excess of 600μm diameter. Although the oogenic pattern is similar in most of these species, the follicle cell distribution and breakdown of relict oocytes vary considerably, particularly at family level. A second reproductive pattern is the production of numerous small eggs c. 100μm diameter, indicative of planktotrophic development. The five species exhibiting this pattern show intra- and interspecific synchrony of egg production with a proliferation of young oocytes in February to April of each year, vitellogenesis during summer and autumn and a synchronous spawnout in January–April of each year. In the apparent constant conditions of the deep sea, this synchrony of reproduction is related to the rapid descent of surface primary production. Two rarer reproductive patterns observed are the production of intermediate sized eggs (c. 300–400μm diameter) suggesting the formation of a lecithotrophic larva, and lastly a single case of protandric hermaphroditism, and the subsequent production of a large egg. In none of the species examined have we found any evidence of brooding. The variation in the reproductive pattern of individual species is discussed in relation to the constancy of the physico-chemical environment of the deep-sea.

The fish populations of the Rockall Trough were poorly known until the early seventies, when there was an interest in the possible exploitation of the demersal fish of the upper slopes. These surveys were carried out by fisheries laboratories with commercial trawls fished on paired warps. At the same time the SMBA began an investigation into the seasonal aspects of the fish of the slopes, using paired warp and single warp otter trawls and an Agassiz trawl. These studies have resulted in a wealth of information on the fish collected by several towed gears and have enabled comparison to be made between different trawls. Of particular interest has been the difference in abundance and biomass estimates between paired and single warp trawls. The small amount of information on the biology of the fish species is briefly reviewed and the populations of the Rockall Trough are considered in the broader context of the northeast Atlantic.

For the onset of the phytoplankton spring bloom in temperate waters, the irradiance, the concentration of accumulated nutrients and the stability of the water column are of great importance. The “new” production in spring is produced mainly by chain forming diatoms.

The dissipation of the spring bloom is due to nutrient depletion in the stabilised surface layer, loss of cells by sinking and grazing by herbivorous zooplankton. After the nutrient concentration is lowered, the rate of production will depend primarily on the rate of replenishment of nutrients. In open ocean environments we find “regenerated production” which is due to exudated and excreted nutrient salts e.g. ammonium. The dominating group of phytoplankters are small flagellates. It is argued that a substantial part of the phytoplankton standing stock in spring is lost from the euphotic zone due to direct sinking of cells or accelerated sinking of cell-aggregates. It is postulated that faecal pellets of micro- and mesozooplankton are retained and recycled in the mixed layer, whereas macrozooplankton faecal strings transport a considerable amount of organic matter to the benthal.

Data from the Continuous Plankton Recorder survey are used to compare the distribution and seasonal and year-to-year variations in the abundance of the plankton of the area of the Rockall Channel with both the shelf and the adjacent oceanic areas. It is argued that the distribution and size of overwintering stocks of zooplankton provide the key to understanding the dynamics of the plankton of this area.

It would appear that, due to inherent limitations to the net rate of increase of zooplankton populations, the distribution of the overwintering stocks has an influence on the distribution and abundance of most species through the rest of the year. This affects the dynamics of the seasonal cycle and also influences the form of year-to-year changes in abundance

The plankton of the area of the Rockall Channel is characterised by low overwintering stocks, coupled in spring with higher rates of population increase as compared with the adjacent shelf. There is a pronounced spring bloom of phytoplankton, which does not appear to be controlled by grazing, followed by a period of nearly five months of relative stability of stocks of both phytoplankton and zooplankton. It is suggested that during this period the zooplankton graze the daily production of phytoplankton, the growth of which is determined to a large extent by nutrients recycled from the zooplankton. The effects of this pattern of dynamics on the form of year-to-year changes in the abundance of the plankton over the last few decades is discussed.

Ship and satellite studies along the shelf edge to the south west of the British Isles have demonstrated the persistence of relatively high standing crops of phytoplankton during the summer months in a region of strong tidal currents and internal wave activity. Off southwest Ireland there is also evidence that salinity stratification has a significant influence on phytoplankton growth, at least during the spring months. Coastal Zone Color Scanner (CZCS) images for the region to the north and west of Scotland indicate that phytoplankton distributions close to the shelf edge are influenced by mesoscale eddies in the Rockall Trough impinging on the upper slope. Coccolithophore blooms are frequent, and changes in their surface distributions are good indicators of water motion.

Evidence has accumulated over the past twenty years to suggest that the deep-sea environment is not as constant as was at one time thought, but exhibits temporal variations related to the seasonally in the overlying surface waters. Recent results from deep-moored sediment traps suggest that this coupling is mediated through the sedimentation of organic material, while observations in the Porcupine Seabight indicate that in this region, at least, there is a major and rapid seasonal deposition of aggregated phytodetritus to the sea-floor at slope and abyssal depths.

This paper summarises the results of the Porcupine Seabight studies over the past five years or so, using time-lapse sea-bed photography and microscopic, microbiological and chemical analyses of samples of phytodetritus and of the underlying sediment. The data are to some extent equivocal, but they suggest that the seasonal deposition is a regular and dramatic phenomenon and that the material undergoes relatively little degradation during its passage through the water column. The mechanisms leading to the aggregation of the phytodetritus have not been identified, and it is not yet known whether the phenomenon is geographically widespread nor whether it is of significance to the deep-living mid-water and benthic communities.

An attempt was made to interpret the core to core variation in oxygen uptake observed during an in situ determination of sediment community oxygen consumption (SCOC) at a station in the Rockall Trough using the “suspended core” technique. No direct relationships between macrofaunal abundance or biomass and SCOC were observed. The results obtained suggested that the use of experimental chambers of small cross-sectional area (26.2cm2) allow for greater influence on SCOC of the activity of individual organisms which would otherwise be averaged out by larger, grab-type enclosures. The possible significance of other components of the benthos is discussed.

Following the presentation of research papers, a group of invited participants examined the opportunities for further research in the Rockall Channel area. The chairman suggested that fundamental oceanographic problems which were well displayed in the area should be the focus of attention rather than regional studies for their own sake. It is indeed fortunate that a region so close to home ports should show many features whose examination would lead to general advances in oceanography. The area has an important slope current on its east side and influx of Norwegian Sea Overflow along the west. These produce differing sedimentary signatures. The downward flux of energy and rapid flux of particles are perhaps responsible for seasonality shown in reproduction of benthos. The continental margin shows significant upwelling and high organic productivity