Faroe Shelf Research Articles

Crustal structure east of the Faroe Islands; mapping sub-basalt sediments using wide-angle seismic data

We use normal-incidence and wide-angle seismic data recorded on the Faroe Islands to study the crustal structure along two profiles extending east from the islands, across the Faroe shelf and into the Faroe-Shetland Basin. We show that massive basaltic lava flows extend eastward away from the Faroe Islands, having flowed across an older Mesozoic and early Paleocene sedimentary basin, and feathering out near the centre of the Faroe-Shetland Basin. Sediments beneath the basalts reach a thickness of several kilometres in the basin, but do not extend with a resolvable thickness beneath the Faroe Islands. The crustal thickness decreases toward the centre of the Faroe-Shetland Basin, showing that the basement beneath the centre of the basin has been stretched and thinned by a factor of at least two. The Faroe Islands themselves lie on a continental fragment, which had a total thickness of about 10-15 km of igneous rock added as extrusive lavas at the top, and as high-velocity intrusives near the base of the crust at the time of continental break-up in the Paleocene.

Food and parasitic nematodes of saithe,Pollachius virens(L.), from the Faroe Islands

Food items and metazoan parasites were identified from the stomachs of 80 yearlings and 150 two-year-old saithe (Pollachius virens (L.)), sampled from the coastal waters of the Faroe Islands. Of a total of 65 food items found, 47 were identified to species or genus. Yearlings fed mainly on Parathemisto spp., euphausiids, Pandalus sp. and Aphrodita aculeata, while the two-year-old saithe exploited mainly euphausiids (especially Meganyctiphanes norvegica), sandeels (Ammodytes spp.) and gastropods (especially Littorina spp.) Parasites found included the nematodes Anisakis simplex, Contracaecum sp., Hysterothylacium aduncum and Cucullanus cirratus; the copepod crustaceans Caligus sp. and Clavella sp.; the acanthocephalan Echinorhynchus gadi; a single digenean trematode; and a single cestode plerocercoid. Adult saithe from the Faroe Shelf preyed mainly on fish (Trisopterus esmarki, Microesistius poutassou and Melanogrammus aglefinus), and saithe from Faroe Bank on M. norvegica. A discussion on a possible transmission route of A. simplex larvae is given.

Phytoplankton variability on the Faroe Shelf

Mixing by the strong tidal currents on the Faroe Shelf causes the shallower part of the shelf water to be vertically and horizontally almost homogeneous. This water mass is separated from the surrounding, seasonally stratified, waters by a tidal front. The system is maintained by a persistent anticyclonic circulation system of currents driven by tidal rectification. Since 1990, nutrient concentrations and phytoplankton biomass and species composition in the shelf water have been studied in a systematic monitoring programme. The observations demonstrate large variations. In some years, nitrate becomes almost totally depleted in summer and the diatoms that dominate during the spring bloom are replaced by flagellates (e.g. Phaeocystis pouchetii). In other years, nitrate concentrations remain fairly high and diatoms continue to dominate the phytoplankton through summer. The inter-annual differences are more likely caused by variations in primary production rather than by variations in nutrient inflow. Furthermore, variations in primary production are more likely caused by grazing, due to the large differences in zooplankton abundance, rather than by variations in light conditions or stratification as affected by winds and tidal currents.

Life cycle, abundance and transport ofCalanus finmarchicusin Faroese waters

Abstract Calanus finmarchicus is the dominant copepod in the open ocean around the Faroe Islands. Measurements from 1990-93 showed that C. finmarchicus in the Atlantic Water outside the Faroe Shelf has two annual generations.The overwintering individuals migrate towards the surface in March-April and their spawning usually peaks in May.The majority of the individuals of this generation reaches stage CV in mid-summer.Some of the overwintering individuals remain in the upper layer and a small number of them spawn again in late summer.To the north of the Iceland-Faroes Front, C. finmarchicus has only one generation the overwintering individuals of which migrate towards the surface later than in the Atlantic Water and have their peak spawning in June.The individuals of this generation reach stages CIV and CV in August-September, when they migrate downwards.The phytoplankton biomasses in spring were higher north of the Iceland-Faroes Front than south of it.Therefore the delay of maturation and spawning north o...

Phytoplankton community structure on the Faroe Shelf

The phytoplankton distribution, biomass and species composition were investigated in relation to the hydrographical and chemical environment for the algae on the Faroe Shelf during 1995. The water on the Faroe Shelf is relatively well isolated from the surrounding waters by a tidal front, which surrounds the islands at about 100-130 m bottom depth. It has its own planktonecosystem, which is separated and is quite different from that in the surrounding oceanic environment. The phytoplankton spring bloom developed in late Aprilearly May in the shelf water which was about one month earlier than outside the tidal front. The spring bloom started in the central and the northern part of the shelf. The limited water mass on the shelf - and, hence, also the limited amount of nutrients - affected the potential new primary production and around mid July 1995, allthe nitrate on the central and northern shelf had been assimilated. From mid July and throughout the rest of the summer, the potential new production was low and was dependent on advection of nutrients from outside the tidal front.

The fauna associated with the bank-forming deepwater coralLophelia pertusa(Scleractinaria) on the Faroe shelf

Abstract Twenty five blocks of Lophelia pertusa weighing a total of 18.5 kg were studied. Associated with this substrate were 4626 individuals belonging to 256 species. An additional 42 species were identified from loose coral rubble. Of the 298 species found, 97 are recorded for the first time from the area around the Faroes. Most individuals were found in dead coral blocks from the inner parts of the bank or colony, but a few species were found close to the terminal branches of live coral blocks. The associated fauna of this branching deep-water coral was as rich and diverse as that of hermatypic branching species of coral. Some physical features of the coral as a substrate were measured. Large blocks of live coral harbour a more diverse fauna than do smaller ones. In contrast, on dead coral blocks the number of species and individuals had no simple correlation to block size, indicating the importance of other factors such as random colonization and length of time the substrate has been inhabited. Of th...

Eddies and meanders in the Iceland-Faroe Ridge area

Available hydrographic data are used to demonstrate the existence of eddies and meanders related to the polar front in the Iceland-Faroe Ridge area. The data are not sufficient to investigate the kinematics and the dynamics of the eddies, which are important for the overflow of arctic water and for the temperature conditions over the Faroe shelf. The first results of an attempt to overcome the lack of proper data sets are discussed.

Knappligar broytingar í sjóvarhitanum við Føroyar

When considering variations of the surface temperature of the sea it is common practise to concentrate on the mean values over a certain period. It is argued that for some purposes the extreme values may be as relevant. The hydrographic conditions in Faroese waters are dominated by the presence of the Polar front (fig 1—2). A unique series of daily surface temperature observations exist from Mykines. The long-term variations have been given by Smed (Smed Ann. Biol., fig 3) based on mean monthly values.
 In this paper we have looked for deviations from the mean on a shorter time scale i. e. by days. A visual inspection of the data (fig. 4) indicates that the deviations are not symmetrical but rather more negative. An analysis confirms this hypothesis. The data were high pass filtered and the number of deviations of various temperature intervals were counted. A distinction was made between positive and negative deviations. Table 1 and fig. 6 demonstrate the result. The temperature variations atMykines, thus are interpreted as composed of three parts: 1 A yearly variation, 2 »Noise« symmetrical with respect to the running mean, 3 Negative anomalies. It is the latter which has been studied in more detail. Figs. 7 and 8 demonstrate the distribution of anomalies ( > V Í ° C) through the years (1920—1940) and in various months. The anomalies are significantly more frequent during wintertime.
 As for the origin af the anomalies, it is argued that these are probably of an advective character indicating the presence of cold »blobs« or »eddies« in the waters of the Faroe shelf. Further evidence for this is presented in fig. 10 and evidence that temperature variations in these waters include advective processes as a dominant part is found also from a series of temperature ■— current observations from SuSuroyarfjørður (figs. 11, 12, 13, 14). The temperature variations observed were plotted against the Lagrangian coordinate x(t) of a fictitious water particle
 tx(t)=2v(i)-/\tKv(i) being the observed current along the main axis at the time i and A t , the sampling interval. The fact that in these plots the curves are very often retraced when the current turns — as exemplified by fig. 15 ■— indicates the importance of advective processes. As to the origin of the eddies, we assume their creation to be related to the Polar front which indeed does produce such entities (B. Hansen & J. Meincke, to be published). In conclusion we note the importance of such processes both from ahydrographical and biological point of view.