Iceland Faroe Research Articles

Variability of Frontal Structure in the Southern Norwegian Sea

Abstract A hydrographic survey (CTD) was conducted in the vicinity of the Iceland–Faeroe Island oceanic front (IFF) north of the Faeroe Islands during October 1980. It consisted of CTD transects on three horizontal scales ranging from kilometers to hundreds of kilometers. Intense interleaving of different water masses is found in the IFF in the presence of horizontal current shear. Significant alongfront variability on scales of about 50 km is present, consistent with earlier findings. Estimates of cross-front heat flux of 5.16 × 104 W m−2 and salt flux of 1.58 g m−2 s−1 are greater than those found for the Antarctic Polar Front but are of the same order as eddy heat flux across the IFF found by Willebrand and Meincke. Evidence suggests that intrusive interleaving in the IFF on 50 m vertical scales is driven by double-diffusive convection.

Grain-size variations in North Atlantic non-carbonate sediments and sources of terrigenous components

Fine-silt to medium-sand grain-size spectra of the carbonate-free fractions of 115 sea bed samples from the northern North Atlantic, the Labrador Sea and Baffin Bay can be explained as mixtures of five distinct end-members. The five end-members resemble combinations of grain-size modes which are characteristic of till-matrix (Dreimanis and Vagners, 1972). Therefore the ultimate source of most of the terrigenous deep-sea sediments in the study area is probably the veneer of glacial comminution products on the surrounding continents. Three sand-rich end-members exhibit patterns of distribution that are largely compatible with the modern transport of ice-rafted debris as inferred from iceberg drift observations. The best sorted of those sandy end-members however also appears to be concentrated in regions characterized by high-energy turbidity and contour currents and so may also represent hydraulically winnowed sediment. The distribution of two lutite end-members appears in general to reflect the transport of fines by moderate to low energy thermohaline currents; although, in Baffin Bay and the northeastern North Atlantic the lutite could have accumulated primarily in turbidites. Ice-rafting by icebergs calved from Greenland glaciers, the reworking of glacigenic sediments on the Iceland—Faeroes Ridge and injection of turbid glacial meltwater into deep Baffin Bay from West Greenland fiords are suggested as the principal means of introduction of clastic particles into the sediment distribution (redistribution) budget of the deep North Atlantic.

Geological/geophysical observations and inferred bottom-current flow: South flank Iceland—Faeroe Ridge

The surface morphology of the Iceland—Faeroe Ridge and Hatton Drift, as shown by seismic reflection (3.5 kHz) and bottom photographic data, is predominantly shaped by vigorous bottom currents but also influenced, in the case of the ridge, by a generally smooth acoustic basement of probable basaltic composition. Redistribution by the currents has sculpted the sediment on the south flank of the ridge into lens and wedge-like drift deposits having remarkably smooth surfaces and uniform internal stratification. In other areas, notably over large areas of the ridge crest, acoustic basement appears to be exposed. Estimated current velocities range from a few centimeters per second on off-ridge areas up to and perhaps greater than 30 cm s −1 on the ridge itself. Three distinct current flows can be differentiated: an intense mid-flank flow representing the outflow of Norwegian Sea Deep Water from the Faeroe Channel; a moderately strong flow on the upper flank produced by water passing over the ridge crest; and a weak to moderate flow on the lower flank which is a continuation of the north-flowing Hatton Drift current. Discontinuous, channel-like features on the eastern part of the ridge flank are attributed to the erosive action of the currents as they accelerate around topographic highs. In contrast, the extreme western end of the ridge and Icelandic slope is cut by several turbidity current channels which transport basaltic debris from Iceland to the Maury Fan. Turbidite deposits account for the characteristic prolonged echo type exhibited in the 3.5-kHz profiles across the upper fan; the south flank and Hatton Drift contourites produce sharp bottom echoes with continuous, parallel subbottom reflectors, whereas sharp bottom echoes with no subbottom reflectors typify the ridge crest and outcrop areas. Sediment thicknesses on the ridge range from virtually zero on the crest to usually 0.3 s on the lower flank. Near Iceland and over the Maury Fan the sediment accumulation may exceed 1.0 s.

Crust and uppermost mantle structure of the Iceland--Faroes region from Rayleigh wave group velocity dispersion

Summary Fundamental mode Rayleigh wave group velocities over the period range 13—85 s have been measured at stations in the British Isles from earthquakes in the Iceland—Jan Meyen region. Published models for the British Isles upper mantle have been used to correct the observations for the continental portion of their propagation path, and thus isolate the group velocity dispersion curve associated with the Iceland—Faroes Ridge area alone. This has been inverted to shear-velocity depth profiles to a depth of c. 150 km using a combined Monte-Carlo/Hedgehog technique. The results show that the Iceland—Faroes Ridge has an anomalous crustal thickness, for oceanic areas, of 20—24 km, supporting the conclusion of other published geophysical studies. Upper mantle structure, which has been determined for the first time, appears less atypical of oceanic regions, with a lithospheric thickness of some 60 km and ‘lid’ velocities of 4.5—4.55 km s-1.

Evolution of the Iceland hotspot

Mantle geochemical enrichment beneath the Iceland–Faeroes hotspot has been episodic, suggesting that blobs rather than a continuous plume may be rising in the region. Recurring rift propagation southward from central Iceland causing progressive melting of the lower crust followed by the upper mantle, best explains the geochemical variations found along the south-west and south-east neovolcanic zones and their degree of thermal maturity.

Volcanics from the Sierra Leone Rise

THE Sierra Leone Rise, located in the east equatorial Atlantic, forms a discontinuous chain of seamounts as shallow as 2 km extending with a general NE–SW trend from near the Sierra Leone coast of Africa, to the St Paul fracture zone near the Mid-Atlantic Ridge (Fig. 1). The origin of this feature has remained a topic of discussion. Sheridan et al.1 have hypothesised that the Sierra Leone Rise is a volcanic structure formed at the beginning of the opening of the Atlantic in the early Cretaceous period. The twin features of the Sierra Leone and the Ceara Rises are probably of oceanic origin and were created 80 Myr ago or later in their present-day position with respect to Africa and South America2. The Atlantic ocean exhibits several similar aseismic structures which appear symmetrically oriented with respect to the mid-oceanic ridge, such as the Walvis–Rio Grande Rise and the Iceland Faeroes–Iceland Greenland Ridges. These structures are volcanic edifices having a composition similar to that found in their associated islands3–7. Deep sea drilling of the Ceara Rise8,9 penetrated a basaltic basement of the upper Cretaceous period (Maestrichtian) (Leg 39, Site 354). Similarly, a DSDP hole (Leg 41, Site 366) on the Sierra Leone Rise, penetrated sediments of the same period, without reaching basement10. We report here the discovery of alkali-rich volcanics in an area of the Sierra Leone Rise. The sediment overlying the rock fragments is aged ∼45 Myr.

Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

SummaryA lower Tertiary lateritic paleosol resting on a plateau basalt was penetrated by drilling at DSDP Site 336 on the NE flank of the Iceland—Faeroe Ridge. The sea floor at the site is about 800 m below sea level and about 400 m below the generally smooth, flat and largely sediment-free top of the ridge. The paleosol is approximately 30 m thick and can be divided into four subunits, in ascending order, basaltic rubble, red clay with altered basaltic clasts, interlayered red and pale-orange clay, and red clay. The paleosol is overlain by about 300 m of marine mudstone of medial Eocene to medial late Oligocene age that was deposited in progressively deeper water through time. About 170 m of Pliocene and Pleistocene glacio-marine sediments unconformably overlie the Paleogene deposits.In the lowest subunit of the paleosol, feldspar, pyroxene, magnetite and chlorite decrease in abundance abruptly upward and are replaced by montmorillonite and small amounts of hematite and goethite. At the contact between the second and third subunits of the paleosol, kaolinite becomes an important constituent and increases greatly in abundance upward. In the uppermost red clay subunit, kaolinite has completely replaced montmorillonite and the amount of hematite and goethite increases markedly. Within the paleosol subunits, the relative amounts of silicon, ferrous iron, magnesium, calcium, sodium, and potassium decrease upward, whereas the amounts of aluminum, ferric iron, and titanium increase upward. The red and pale-orange clay subunit contains layers characterized by veinlet-like structures alternating with more massive layers. The veinlet network is thought to have developed by segregation of ferric iron and alumina as a result of chemical weathering of basalt and possibly thin overlying airfall tuffs.The paleosol indicates a humid, warm climate and demonstrates that the Iceland-Faeroe Ridge was above sea level during the early Tertiary. The ridge formed the main part of the Thulean land bridge that permitted free migration of land mammals between North America-Greenland and Europe prior to late Eocene time. It developed during the early Tertiary break-up and rifting apart of North America-Greenland and Europe. Formerly situated over an active mantle plume or hot spot, the ridge subsequently subsided in late Eocene and Oligocene time, eventually permittingfree interchange of marine waters between the Norwegian-Greenland Sea and the North Atlantic Ocean. Basalts of the Iceland-Faeroe Ridge are simijar in age and character to other basalts of the North Atlantic early Tertiary igneous province on the Rockall and Voring Plateaus, northern Ireland, Scotland, the Faeroe Islands, East and West Greenland, and Baffin Island. Bauxite, lignite, and laterite associated with some of these basalt sequences, as well as vertebrate, plant, and microfossil remains, suggest a relatively uniform, warm, humid climate in the early Tertiary throughout the North Atlantic area and into the region of the Arctic Ocean.

Lower Tertiary laterite on the Iceland–Faeroe Ridge and the Thulean land bridge

CORES of a lower Tertiary lateritic palaeosol resting on basalt were recovered1 from Deep Sea Drilling Project Site 336 (Leg 38) on the north-east flank of the Iceland–Faeroe Ridge (Fig. 1), a major aseismic oceanic ridge that, together with Iceland, forms the Icelandic transverse ridge2. The transverse ridge extends from the West European continental margin to the East Greenland continental margin, forming the geographic boundary and a partial barrier to flow of water between the Norwegian–Greenland Sea to the north and the northern North Atlantic Ocean to the south. The palaeosol indicates that at least part of the Iceland–Faeroe Ridge was above sea level during early Tertiary time3. Palaeogeographic and palaeooceanographic reconstructions suggest that it formed the main part of the Thulean land bridge that connected South-east Greenland and the Faeroe islands during the early Tertiary4. This report summarises the subsidence history of the Iceland–Faeroe Ridge relative to early Tertiary seafloor spreading, basaltic volcanism, and the development of the proposed Thulean land bridge.

The geochemistry of sediments from the northern Reykjanes Ridge and the Iceland—Faroes Ridge

Samples from the active Reykjanes Ridge and the inactive Iceland—Faroes Ridge have been investigated sedimentologically, mineralogically, and geochemically. The sediments display polymodal grain-size distributions and are poorly sorted, indicating deposition by various mechanisms and contributions from numerous sources. The mineralogy is fairly typical for the region and strongly reflects the large input of volcanic ash and ice-rafted material. Bulk chemical analyses indicate that the Reykjanes Ridge sediments appear to be enriched in Fe, Mn, Cu, Cr, and Zn as has been reported for other active ridges while the inactive Iceland—Faroes Ridge does not display such enrichments. The enriched metals in the ridge sediments do not show a particular affinity for any one size class. Partition studies indicate that the enriched Fe and Mn are held in separate phases while the other metals are present in all phases. Adsorption is not a major concentrating mechanism for the enhanced elements. Li distributions are apparently unaffected by active ridges and Pb seems to be partially concentrated biologically. There are indications that other criteria must be used in conjunction with bulk chemical analyses, in order to establish the presence of active ridge metal contributions.

The North Atlantic Ocean as a source of atmospheric N2O

In 1969, 1970, and 1971 N 2 O measurements of sea water were carried out during 3 cruises in the open North Atlantic ocean. Water samples were taken from the sea's surface and from depths down to 3000 m at several stations. Surface water concentrations in the tropical-subtropical latitudes averaged 0.5 ?g N 2 O per liter sea water. For the range from 38.5° N to 48.5° N, an average of 0.4 ?g N 2 O per liter sea water was found. In the area of the Iceland—Faroe ridge, the surface water concentrations averaged 0.4 ?g N 2 O per liter' sea water when water temperatures were 10°C, and 0.5 ?g N 2 O per liter sea water when water temperatures were 5°C. The vertical N 2 O concentration profiles often show two maxima: a smaller one between 100 and 200 m and a large one between 400 and 1000 m with N 2 O concentrations up to 0.8 ?g per liter sea water. With the exception of a few samples, the measurements indicated that the North Atlantic sea water is supersaturated with N 2 O. Supersaturation values up to more than 100% were found in the upper layers of the sea water from the tropical-subtropical latitudes up to 48.5° N. Further north the N2O supersaturation of the sea water decreases. For the upper sea water layers down to 1000 m the following average values were obtained from vertical profiles: in tropical latitudes about 66% super-saturation, in subtropical latitudes about 47%, in the range from 38.5° N to 48.5° N about 42%, and in the area of the Iceland—Faroe ridge about 12–20% supersaturation. One may conclude that the North Atlantic ocean acts as a net source of atmospheric N 2 O. It is probable that the other oceans have the same ability. DOI: 10.1111/j.2153-3490.1974.tb01962.x

The North Atlantic Ocean as a source of atmospheric N<sub>2</sub>O

In 1969, 1970, and 1971 N 2 O measurements of sea water were carried out during 3 cruises in the open North Atlantic ocean. Water samples were taken from the sea's surface and from depths down to 3000 m at several stations. Surface water concentrations in the tropical-subtropical latitudes averaged 0.5 ?g N 2 O per liter sea water. For the range from 38.5° N to 48.5° N, an average of 0.4 ?g N 2 O per liter sea water was found. In the area of the Iceland—Faroe ridge, the surface water concentrations averaged 0.4 ?g N 2 O per liter' sea water when water temperatures were 10°C, and 0.5 ?g N 2 O per liter sea water when water temperatures were 5°C. The vertical N 2 O concentration profiles often show two maxima: a smaller one between 100 and 200 m and a large one between 400 and 1000 m with N 2 O concentrations up to 0.8 ?g per liter sea water. With the exception of a few samples, the measurements indicated that the North Atlantic sea water is supersaturated with N 2 O. Supersaturation values up to more than 100% were found in the upper layers of the sea water from the tropical-subtropical latitudes up to 48.5° N. Further north the N2O supersaturation of the sea water decreases. For the upper sea water layers down to 1000 m the following average values were obtained from vertical profiles: in tropical latitudes about 66% super-saturation, in subtropical latitudes about 47%, in the range from 38.5° N to 48.5° N about 42%, and in the area of the Iceland—Faroe ridge about 12–20% supersaturation. One may conclude that the North Atlantic ocean acts as a net source of atmospheric N 2 O. It is probable that the other oceans have the same ability. DOI: 10.1111/j.2153-3490.1974.tb01962.x

Geophysical observations on the Iceland–Faeroe ridge

Geophysical observations on the Iceland–Faeroe ridge

Bacteria in Cream

Abstract We present a revised tectonostratigraphy of the Jan Mayen microcontinent (JMMC) and its southern extent, with the focus on its relationship to the Greenland–Iceland–Faroe Ridge area and the Faroe–Iceland Fracture Zone. The microcontinent9s Cenozoic evolution consists of six main phases corresponding to regional stratigraphic unconformities. Emplacement of Early Eocene plateau basalts at pre-break-up time (56–55 Ma), preceded the continental break-up (55 Ma) and the formation of seawards-dipping reflectors (SDRs) along the eastern and SE flanks of the JMMC. Simultaneously with SDR formation, orthogonal seafloor spreading initiated along the AEgir Ridge (Norway Basin) during the Early Eocene (C24n2r, 53.36 Ma to C22n, 49.3 Ma). Changes in plate motions at C21n (47.33 Ma) led to oblique seafloor spreading offset by transform faults and uplift along the microcontinent9s southern flank. At C13n (33.2 Ma), spreading rates along the AEgir Ridge started to decrease, first south and then in the north. This was probably complemented by intra-continental extension within the JMMC, as indicated by the opening of the Jan Mayen Basin – a series of small pull-apart basins along the microcontinent9s NW flank. JMMC was completely isolated when the mid-oceanic Kolbeinsey Ridge became fully established and the AEgir Ridge was abandoned between C7 and C6b (24–21.56 Ma).