North Coast Of Iceland Research Articles

Some Dynamical Constraints on Upstream Pathways of the Denmark Strait Overflow

Abstract The East Greenland Current (EGC) had long been considered the main pathway for the Denmark Strait overflow (DSO). Recent observations, however, indicate that the north Icelandic jet (NIJ), which flows westward along the north coast of Iceland, is a major separate pathway for the DSO. In this study a two-layer numerical model and complementary integral constraints are used to examine various pathways that lead to the DSO and to explore plausible mechanisms for the NIJ’s existence. In these simulations, a westward and NIJ-like current emerges as a robust feature and a main pathway for the Denmark Strait overflow. Its existence can be explained through circulation integrals around advantageous contours. One such constraint spells out the consequences of overflow water as a source of low potential vorticity. A stronger constraint can be added when the outflow occurs through two outlets: it takes the form of a circulation integral around the Iceland–Faroe Ridge. In either case, the direction of overall circulation about the contour can be deduced from the required frictional torques. Some effects of wind stress forcing are also examined. The overall positive curl of the wind forces cyclonic gyres in both layers, enhancing the East Greenland Current. The wind stress forcing weakens but does not eliminate the NIJ. It also modifies the sign of the deep circulation in various subbasins and alters the path by which overflow water is brought to the Faroe Bank Channel, all in ways that bring the idealized model more in line with observations. The sequence of numerical experiments separates the effects of wind and buoyancy forcing and shows how each is important.

Spatial and temporal microsatellite variation in spawning Atlantic cod,Gadus morhua, around Iceland

The present study suggests that the observed genetic difference between Atlantic cod, Gadus morhua, off the south and the north coast of Iceland may be caused by natural selection affecting genetic variation at a microsatellite loci (Gmo34). When disregarding this locus from the analysis, no genetic difference was observed between northern and southern Iceland. The methods applied here were very sensitive, and differences as small as FST= 0.0005 are unlikely to go unnoticed. The difference between cod off the south and the north coast of Iceland is thus likely to be smaller than that. Such a small difference is negligible and is not likely to have any biological meaning. Genetic drift was detected by allele frequency comparison among different cohorts (FST= 0.0007, P = 0.0209). A small but significant difference was observed among allele frequency for cod grouped by depth at the south coast of Iceland (FST= 0.0017, P = 0.0002). This difference is very subtle and needs to be interpreted with caution.

Mineralogy and geochemistry of clay samples from active hydrothermal vents off the north coast of Iceland

Active hydrothermal vent sites were sampled during 1997 in a series of submersible dives at the active Grimsey (GHF) and Kolbeinsey (KHF) hydrothermal fields off the north coast of Iceland. This study focuses on secondary clay minerals which were formed in two different settings. The GHF is characterized by the presence of clay minerals precipitated within active chimneys. By contrast, the KHF is characterized by the presence of secondary clay minerals, which are the products of hydrothermal alteration of lava fragments. Based on XRD, electron microprobe and ICP-MS analyses, the dominant clay mineral in both hydrothermal fields is saponite (Mg-rich smectite). Chlorite and chlorite–smectite mixed-layer minerals also occur at the KHF. The Mg-rich nature of saponite from the GHF chimneys suggests intense Mg metasomatism in the mixing zone where hydrothermal fluids interact with seawater at temperatures of 250 °C. Saponite formation resulted in the additional uptake of Cu, Zn, and Pb. Enrichment in Ba is evident in the almost pure saponite from the KHF. Based on oxygen isotope data, the saponite formation at the KHF occurred at 148 °C, which is close to the maximum measured fluid temperature of 131 °C in this field.

First observations of high-temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of Iceland

High-temperature (250°C) hydrothermal vents and massive anhydrite deposits have been found in a shallow water, sediment-filled graben near 66°36′N in the Tjornes Fracture Zone north of Iceland. The site is located about 30km offshore, near the small island of Grimsey. The main vent field occurs at a depth of 400m and consists of about 20 large-diameter (up to 10m) mounds and 1–3m chimneys and spires of anhydrite and talc. A north–south alignment of the mounds over a 1-km strike length of the valley floor suggests that their distribution is controlled by a buried fault. Widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1-km2 area occupied by the vents is thermally active. A 2-man research submersible JAGO was used to map the area and to sample vent waters, gases, and chimneys. Actively boiling hydrothermal vents occur on most of the mounds, and extensive two-phase venting indicates that the field is underlain by a large boiling zone (200×300m). The presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring. The highest-temperature pore fluids were encountered in talc- and anhydrite-rich sedimentary layers that occur up to 7m below the mounds. Baked muds underlie the talc and anhydrite layers, and pyrite is common in stockwork-like fractures and veins in the hydrothermally altered sediments. However, massive sulfides (pyrite–marcasite crusts) were found in only one relict mound. Subseafloor boiling has likely affected the metal-carrying capacity of the hydrothermal fluids, and deposition of sulfides may be occurring at greater depth. Although the mounds and chimneys at Grimsey resemble other deposits at sedimented ridges (e.g. Middle Valley, Escanaba Trough, Guaymas Basin), the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system.

The Occurrence of Vagrant Seals in Iceland, in 1989–94

New findings are presented about the occurrence of hooded seals (Cystophora cristata), harp seals (Phoca groenlandica), bearded seals (Erignathus barbatus) and ringed seals (Phoca hispida) in Icelandic waters for 1989–94. These animals had been entangled in gill nets for lumpsuckers (Cyclopterus lumpus) and cod (Gadus morhua), shot by local hunters, or found dead on the shore. The majority of the animals were from the north coast of Iceland, during the spring and summer. The majority of the hooded seals, were pups and one-year-olds, although older animals occurred frequently. Males were significantly more abundant in the catch than females. Young seals, pups and one-year-olds, dominated in the catch of harp seals. Males were not significantly more abundant than females. During the period 1989–94, there seemed to have been an increase in the frequency of visits of hooded and harp seals to Icelandic waters, and they seemed to be more numerous off the north coast than about a decade ago. However, they are probably not as numerous now as in earlier times, especially in years of heavy land-ice and polar-ice in the 18th and 19th century. Ringed seals were mainly caught during the spring and early summer, while most of the bearded seals were caught in winter. The majority of the bearded seals visiting the Icelandic coast were young immature animals, while the ringed seals were sub-adults and adults.

Dikes, minor faults and mineral veins associated with a transform fault in North Iceland

The Tjörnes fracture zone is a transform fault connecting the axial rift zone in North Iceland with that of the Kolbeinsey ridge off the north coast of Iceland. On the north coast of the Flatcyjarskagi peninsula there is a 3–5 km wide zone of intense deformation, which we interpret as the main on-land part of this transform fault. This transform zone strikes N64°W and is characterized by unusually steeply dipping lavas (25–44°WNW), extensive secondary mineralization, numerous slickensided surfaces, normal faults (1–20 m throw), dikes that strike parallel to the zone, and occasional 3–20 m wide subzones of crushed rocks striking parallel to the transform fault. In a 17 km long continuous coastal profile south of the transform zone there is a 30° clockwise change (from south to north) in the lava strike. The dike strike also changes clockwise north along this profile, but only by 4°. This indicates that the clockwise change in the lava strike is original and not due to subsequent tectonic rotation. When the axial rift zones of North Iceland and the Kolbeinsey ridge are modelled as single offset mode I cracks, finiteelement results show that the Tjörnes fracture zone developed between these mode I cracks in a region of maximum shear stress. The underlap between these axial rift zones has, apparently, decreased during the past several million years. The model predicts that as this underlap decreased, the angle between the Husavik-Flatey fault and that of the associated axial rift zones increased and the activity of the Husavik-Flatey fault decreased. Both these predictions are borne out by the available data.

Structural analysis of a transform fault-rift zone junction in North Iceland

On the north coast of Iceland, the rift zone in North Iceland is shifted about 120 km to the west where it meets with, and joins, the mid-ocean Kolbeinsey ridge. This shift occurs along the Tjörnes fracture zone, an 80-km-wide zone of high seismicity, which is an oblique (non-perpendicular) transform fault. There are two main seismic lineaments within the Tjörnes fracture zone, one of which continues on land as a 25-km-long WNW-trending strike-slip fault. This fault, referred to as the Husavik fault, meets with, and joins, north-trending normal faults of the Theistareykir fissure swarm in the axial rift zone. The most clear-cut of these junctions occurs in a basaltic pahoehoe lava flow, of Holocene age, where the Husavik fault joins a large normal fault called Gudfinnugja. At this junction, the Husavik fault strikes N55°W, whereas Gudfinnugja strikes N5°E, so that they meet at an angle of 60°. The direction of the spreading vector in North Iceland is about N73°W, which is neither parallel with the strike of the Husavik fault nor perpendicular to the strike of the Gudfinnugja fault. During rifting episodes there is thus a slight opening on the Husavik fault as well as a considerable dextral strike-slip movement along the Gudfinnugja fault. Consequently, in the Holocene lava flow, there are tension fractures, collapse structures and pressure ridges along the Husavik fault, and pressure ridges and dextral pull-apart structures subparallel with the Gudfinnugja fault. The 60° angle between the Husavik strike-slip fault and the Gudfinnugja normal fault is the same as the angle between the Tjörnes fracture zone transform fault and the adjacent axial rift zones of North Iceland and the Kolbeinsey ridge. The junction between the faults of Husavik and Gudfinnugja may thus be viewed as a smaller-scale analogy to the junction between this transform fault and the nearby ridge segments. Using the results of photoelastic and finite-element studies, a model is provided for the tectonic development of these junctions. The model is based on an analogy between two offset cuts (mode I fractures) loaded in tension and segments of the axial rift zones (or parts thereof in the case of the Husavik fault). The results indicate that the Tjörnes fracture zone in general and the Husavik fault in particular, developed along zones of maximum shear stress. Furthermore, the model suggests that, as the ridge-segments propagate towards a zero-underlapping configuration, the angle between them and the associated major strike-slip faults gradually increases. This conclusion is supported by the trends of the main seismic lineaments of the Tjörnes fracture zone.

A record of Pliocene and Pleistocene glaciations and climatic changes in the North Atlantic based on variations in volcanic and sedimentary facies in Iceland

The location of Iceland directly below the Arctic Circle and on the North Atlantic plate boundary gives the island a characteristic record of interbedded lavas, glacial deposits and other sediments, opening a window on the geological and climatic history of the North Atlantic. Frequently extruded lava flows tend to shield underlying sediments from subsequent erosion. Explosive volcanism keeps the sedimentation rate high and produces extensive time markers. Continuing studies of diamictites interbedded within basaltic lava suites of Cainozoic age in Iceland deal specifically with the problem of differentiating between glacial and non-glacial sediments that have very similar attributes. A multifaceted approach has been taken in order to differentiate these deposits. This includes both lateral and vertical lithofacies description and clast fabric studies based on extensive field work, a comparison with modern analogues, and detailed laboratory work (textural studies on thin sections and palaeomagnetic studies). The results suggest that both the nature and extent of late Pliocene and early Pleistocene glaciations can be inferred from the preserved record. The rock sequence offers excellent opportunities for pinning down the age of each event through palaeomagnetic correlation and radiometric dating of the lava flows. The oldest tillite along the north coast of Iceland has been bracketed down to approximately 2.1 Ma, and in inland mid-western Iceland to approximately 2.6 Ma. It is anticipated that continuing work elsewhere in Iceland can further define the trends of Pliocene glaciation in the North Atlantic. The significance of the frequency of identified glacial deposits in the Icelandic sections may be tested through comparison with the latest deep-sea record of glacial-interglacial cycles.

Littoral Oligochaeta (Annelida) from Eyjafjörôur, North Coast of Iceland

AbstractErséus, C. (Department of Zoology, University of Göteborg, S‐400 33 Göteborg, Sweden). Littoral Oligochaeta (Annelida) from Eyjafjörôur, north coast of Iceland. Zool. Scr. 5 (1):5–11, 1976.—A total of 15 species of marine, littoral, oligochaetes are reported from northern Iceland, two of which are new to science (Tubifex litoralis sp.n. (Tubificidae), and Lumbricillus macrothecatus sp.n. (Enchytraeidae)), while Paranais litoralis (Naididae), T. costatus, Peloscolex benedeni (both Tubificidae), and L. pumillio (Enchytraeidae) are new to the Icelandic fauna. Taxo‐nomic and biological notes are given for some of the species.

Volcanic History and Tectonics of the North Langjökull Region, Central Iceland

The geology of the area around the northern part of the Langjökull ice sheet in central Iceland is outlined. This area includes the termination of the western neovolcanic zone, two silicic centers, and basaltic interglacial, intraglacial, and postglacial volcanoes. The lava succession becomes older to the northwest of the area where the zone of young volcanoes gives away to a pile of lavas of pre-Bruhnes epoch age which dip at low angles towards the active zone.This active zone undergoes a change in strike from NE–SW to north–south near latitude 64 °55′N and the volcanoes north of this are smaller in volume than those on the southern extension of the zone. The area of Bruhnes epoch activity dies out above latitude 65 °10′N but much of the area between here and the north coast of Iceland was a line of volcanic activity during the preceding Matuyama epoch.The northern part of the western active zone in Iceland became inactive in late Pleistocene times, and the southern part of the zone is an area of continuing crustal growth. The zone of active volcanism does not terminate against a transform fault and crustal growth is accommodated by deformation of the crustal plate. Lines of crustal growth which subsequently die out can be invoked to explain the anticline and syncline structures in the lava pile and the currently-active Snaefellsnes zone in western Iceland.

Grimsey, North Iceland

G RIMSEY is a small rocky island, lying some 30 miles from the north coast of Iceland, in latitude 66? 33' N. and longitude I8? o' W. Most Icelanders know of it merely as an island where enormous numbers of sea birds breed, and it is these which have attracted nearly all its visitors. In I820 Freidrich Faber, a German ornithologist, visited the island,' and he was followed the year after by F. L. A. Thienemann.2 In I826 a British fishing vessel was wrecked off the east coast of Greenland, and the crew reached Grimsey in the ship's boats, and continued to Akureyri on the north coast of Iceland, after a stay of a few days on the island. James Cumming, the ship's doctor, has left a short account of the houses of Grimsey in his 'Narrative of the Shipwreck of the Jean of Peterhead.' In 1884 Professor Th. Thoroddsen, the Icelander, visited Grimsey, and though he was only there for six hours his paper forms the most complete description of the island yet published.3 Since then it has been visited by at least five ornithological expeditions, the most recent of which was the Cambridge expedition to East Greenland, which spent four days on the island in July 1933.4 The main object of the present expedition, which consisted of four members, was to study the fauna and flora of the island, and to compare them with those of the mainland of Iceland. A map of the island on a scale of i : 20,000 was also constructed. There were two previous maps. One, published with Thoroddsen's paper, was taken from a Board of Survey sheet with additions put in by eye. The other is that published by the Danish Geodetic Institute in 1933, on a scale of i : oo00,000, and is thus too small to show the detail here required. The Iceland Steamship Company's boats, which leave Hull every fortnight, call at Siglufj6rbur, a small town on the north coast of Iceland, after a stop of four days at Reykjavik en route. We arrived at Siglufj6rbur on June 2I, having travelled from England in the S.S. Godafoss. Here we were delayed for a day by the weather, as it is not possible to land on Grimsey when the wind is between south and west. The next day we chartered a small fishing boat which took us the 40 miles out to the island in just under seven hours. We took with us sufficient food for our stay on the island, as we had been advised not to rely on the islanders for our supplies. We wish to express our very sincere thanks to Professor Debenham for his invaluable advice and assistance; also to Brian Roberts, who visited the island last year, and greatly assisted in the organization of the present expedition. Our gratitude is also due to Matthias Eggertsson, the pastor of Grimsey, for the trouble he took to help us in every way during our stay on the island. To the Committee of the Gino Watkins' Memorial Fund we are also grateful for the grant awarded to us, and to Caius College, Cambridge, for further financial assistance.