West Iceland Research Articles

Strike‐slip faulting, normal faulting, and lateral dike injections along a single fault: Field example of the Gljúfurá fault near a Tertiary oblique rift‐transform zone, Borgarfjörður, west Iceland

The crustal block of Borgarfjörður in western Iceland was caught between the propagating Reykjanes‐Langjökull Rift Zone (RLRZ) and the receding Snæfellsnes Rift Zone (SRZ) during a Tertiary rift jump at ∼7 Ma. This Tertiary rift jump configuration presents an analogy with the presently unstable plate boundary in south and southwest Iceland. Field examination of the Gljúfurá fault in the Tertiary lavas of Borgarfjörður reveals a complicated history of movements and magmatic activity. During its evolution since Tertiary time, this N‐S fault acted as follows: (1) The fault acted as a possible dextral strike‐slip fault, as judged from Riedel fractures in the oldest associated fault breccia. (2) Then the fault acted as a normal fault, resulting in vertical displacement, new brecciation of part of the oldest breccia, hydrothermal activity, and mineralization dominantly in N‐S mode I veins. (3) The fault acted again as a dextral strike‐slip fault, when the fault was injected laterally by dikes. Magma was injected mainly into the N‐S strike‐slip fault and secondarily into adjacent NNE normal faults. Evidence of this stage are the en échelon geometry of the northerly dikes, cooling cracks oblique to dike edges, flow lineation, elongated vesicles, and soft striations on dike edges, as well as bending and displacement of preexisting dikes. (4) After the emplacement and partial erosion of the northerly dikes, the fault acted dominantly as a strike‐slip fault, with possible reactivation as an open fissure. The Gljúfurá fault strikes obliquely to the NNE trending rifting structures active during crustal formation in this area. Its activity was initially related to a transform zone or an oblique rift connected to the SRZ. Then a shift in the plate boundary occurred around 7–6 Ma when the RLRZ became active. During this shift the Gljúfurá fault probably played a role similar to the N‐S strike‐slip faults of the presently active plate boundary within the South Iceland Seismic Zone and the oblique rift of the Reykjanes Peninsula. These faults may, similar to the Gljúfurá fault, change mode and be injected by dikes if they are sufficiently close to a magma source.

Future wind, wave and storm surge climate in the northern North Atlantic

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 23:39-49 (2002) - doi:10.3354/cr023039 Future wind, wave and storm surge climate in the northern North Atlantic Jens Debernard*, Øyvind Sætra, Lars Petter Røed Research and Development Division, Norwegian Meteorological Institute, PO Box 43, Blindern, 0313 Oslo, Norway *Email: jens.debernard@met.no ABSTRACT: In this paper we consider a possible change in future wind, wave, and storm surge climate for the regional seas northeast of the Atlantic: the northern North Atlantic. Conclusions are based on a statistical analysis of the results derived with state-of-the-art wave and storm surge models run for two 20 yr time-slice periods, one for the period 1980 to 2000 (control climate) and one for the period 2030 to 2050 (future climate). Forcing was derived by extracting atmospheric wind and sea level pressure from a state-of-the-art regional atmospheric climate model for the same two 20 yr periods. These regional atmospheric simulations constitute dynamical downscales of the Max Planck Institute¹s global scenario which includes greenhouse gases, sulphate aerosols (direct and indirect effects) and tropospheric ozone. Generally the changes we found are small. However, there are some important exceptions, such as a significant increase in all variables in the Barents Sea and a significant reduction in wind and waves north and west of Iceland. Also, there is a significant increase in wind speed in the northern North Sea and westwards in the Atlantic Ocean, and a comparable reduction southwest of the British Isles in the autumn. The same change is suggested for wave height, but this is not statistically significant. There is a significant increase in the seasonal 99 percentile of the sea level in autumn in the southwest part of the North Sea. These results are consistent with earlier studies predicting a rougher maritime climate in the northern North Sea in autumn. KEY WORDS: Dynamical downscaling · Sea state · Climate change · Wave climate · Surge climate Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 23, No. 1. Online publication date: December 20, 2002 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2002 Inter-Research.

Biological aspects of two deep-water squalid sharks: Centroscyllium fabricii (Reinhardt, 1825) and Etmopterus princeps (Collett, 1904) in Icelandic waters

This paper describes some aspects of the biology of the black dogfish ( Centroscyllium fabricii) and the greater lantern shark ( Etmopterus princeps) based on material collected during surveys of Marine Research Institute, Iceland. C. fabricii was most abundant at depths between 800 and 1200 m (range 436–1653 m). The overall sex ratio was 1.00:1.19 in favour of females. Males were more numerous in shallower waters but in depths >1000 m, the sex ratio was significantly in favour of females. E. princeps was most abundant between 800 and 1000 m (range 436–1653 m). The overall sex ratio was 1.00:1.59 in favour of females, females being significantly more numerous in depths >1000 m. For both species there was a trend for a decrease in mean length with increasing depth. Both species were sexually dimorphic with females growing to a larger size than males and being larger at first maturity. Maturity stages were observed during two seasons and indicated that neither of these two species have a defined breeding season. A study of the diets showed that larger specimens of C. fabricii fed mainly on teleosts but smaller specimens seemed to feed more opportunistically on teleosts, cephalopods and crustaceans. E. princeps fed mainly on three prey categories: teleosts, cephalopods and crustaceans. A considerable amount of these two species, and especially of C. fabricii, are likely to be discarded by the commercial fishery for Reinhardtius hippoglossoides off the West of Iceland.

Azimuthal variation of the P phase in Icelandic receiver functions

SUMMARY A curious observation has been made on radial receiver functions calculated from teleseisms recorded by 29 broad-band seismometers distributed over Iceland. The arrival time of the direct P phase of the radial receiver functions depends critically upon the azimuth of the teleseismic source. For a seismic station in West Iceland, the direct P phase of the radial receiver function arrives consistently later for easterly source azimuths than for westerly source azimuths. The reverse applies for stations in East Iceland. In the original seismograms, the delayed P phase of the receiver function appears up to 450 ms later on the radial than on the vertical component. The seismometer locations in East and West Iceland are separated by the Neovolcanic Zone, a constructive plate boundary. The delayed P phases occur for seismic rays travelling across this zone. However, it is not obvious how wave propagation across the plate boundary zone could cause the observed delays. The tentative explanation proposed here involves the regional dip of the Icelandic lava sequences towards the Neovolcanic Zone. A dipping interface at shallow depth results in a P–S converted phase arriving shortly after the P phase. These phases cannot be separated in the radial receiver functions, given the bandwidth of the observed signals. However, a calculation of receiver functions from estimates of the P, SV and SH wavefields clearly reveals a P–S converted phase at about 500 ms for easterly source azimuths in West Iceland and for westerly source azimuths in East Iceland. The amplitudes of the direct P phase and the P–S phase converted at a dipping interface would be expected to vary strongly with azimuth in accordance with the observed behaviour.

Wood and Plant-use in 17th–19th Century Iceland: Archaeobotanical Analysis of Reykholt, Western Iceland

As part of a multidisciplinary investigation of post-medieval Icelandic land and plant use practices, archaeobotanical samples were collected from Reykholt, west Iceland in 1988 and 1989. Analyses included plant macrofossils (seeds and leaves) and wood identification from excavated rooms in a 17th century farm house. In conjunction with earlier palaeoentomological studies, the functions of three different excavated rooms are inferred. Archaeobotanical results suggest that the farm was a prosperous one, with imported foodstuffs and wood implements from continental Europe.

High-resolution Seismic Evidence for Multiple Glaciation across the Southwest Iceland Shelf

Geophysical and lithological data collected from the southwest margin of Iceland provide clear evidence of multiple glaciations across the shelf, many of which reached the shelf-slope break. These paleo-ice sheets delivered much glacial sediment to the slope facing Denmark Strait. A large moraine some 20 to 100 m in height lies at the shelf break due west of Látra Bank. The moraine may mark the Late Weichselian extent of the western Iceland ice, although a single date from a 50-cm gravity core collected from the seaward side of the moraine provided an age of 35,650 ± 560 14C BP. Retreat of this ice sheet appears to have been rapid, except for a minor pause when the ice sheet terminus approached the coastline. A marine reservoir-corrected basal date of 12,705 ± 85 14C BP was obtained from a 17-m giant piston core collected in Jökuldjúp (a shelf trough) which sampled glacial marine sediments close to underlying ice-contact sediment. Because this date is very close to the age of shells near the marine limit in West Iceland, some 100 km to the east-northeast, it suggests that this margin of the Iceland Ice Sheet retreated extremely rapidly during the Bølling/Allerød interstadial (13,000 to 11,000 14C BP).

Anisakid (Nematoda) Infestations in Icelandic Grey Seals (Halichoerus grypusFabr.)

Anisakid nematode infestations in stomachs of 196 grey seals from Icleandic waters were examined during the period 1989–93, and Pseudoterranova decipiens s . l . , Contracaecum osculatum s.l., Phocascaris cystophorae and Anisakis simplex s.l. were found in seals from all areas and seasons. No difference in nematode abundance was observed between the sexes of grey seal but the number of worms increased with the weight of the seals. Abundance of P. decipiens and C. osculatum showed geographical and seasonal differences. Seals from the Breidafjord and Faxafloi areas had greatest abundance of P. decipiens with an increasing trend from spring to autumn, reaching the highest levels during period of reduced feeding in the breeding season in October to December. Abundance of C. osculatum was greatest in seals from the Breidafjord area and decreased from spring to autumn. The abundance was low in seals from the Faxafloi area and remained unchanged from spring to autumn. Most samples from the south coast were collected from August to December and showed low and declining abundance of all anisakid species during the breeding season. No indications of changes in P. decipiens abundance were observed in grey seals from West Iceland between 1979–82 and 1989–93. Proportions of adult P. decipiens and C. osculatum showed a decreasing trend when abundance of each species in the seal stomachs was increasing.

Anthurideans (Crustacea, isopoda) from the North Atlantic and the Arctic Ocean

Abstract Eight species of the suborder Anthuridea (Crustacea, Isopoda) were collected in the northernmost part of the North Atlantic and in the Arctic Ocean during the BIOICE project. Two species were new to science: Haliophasma mjoelniri sp. nov. found at depths between 340 and 508 m west ofIceland, and Quantanthura tyri sp. nov. at depths between 304 and 1212 m south-west and west ofIceland. Other species found were Ananthura sulcaticauda Barnard, 1925, Calathura brachiata (Stimpson, 1853), Leptanthura affinis (Bonnier, 1896), L. chardyi Negoescu, 1992, L. micrura Kensley, 1982, and L. victori Negoescu, 1985. All eight species were found in the North Atlantic Ocean, and only Ananthura sulcaticauda and Calathura brachiata were additionally found in the Arctic Ocean. A. sulcaticauda and L. affinis are redescribed. The male of L. affinis shows remarkable sexual dimorphism in the shape of per eo pods 4 to 6. A new character, the structure of the comb of setae on article 3 of the mandibular palp, is suggeste...

Oxygen isotope studies from Iceland to an East Greenland Fjord: behaviour of glacial meltwater plume

A detailed study of the oxygen isotope composition (δ18O) was carried out along a transect between Iceland and East Greenland, which includes the West Iceland Shelf, Denmark Strait, the Kangerdlugssuaq Trough on the East Greenland Shelf and the Kangerdlugssuaq Fjord. Vertical profiles of the oxygen isotope composition in a fjord with tidewater glaciers were studied for the first time. In this study, three distinct water masses are identified from oxygen isotope measurements: (1) North Atlantic Water of δ18O ≈ 0%. occupies the Icelandic Shelf, Denmark Strait subsurface, and deep waters of the Kangerdlugssuaq Trough and Fjord; (2) the East Greenland Current of δ18O ≈ −2%. occupies surface water at the western Denmark Strait and the Kangerdlugssuaq Trough; (3) glacial meltwater (δ18O ranges from −30 to −20%. in source) flows at the surface of the Kangerdlugssuaq Fjord. Surface δ18O data distinctively identify the East Greenland Front between North Atlantic Water and the East Greenland Current in Denmark Strait. Vertical profiles of δ18O show the steady increase from surface to deep water at the stations west of the front with well mixed water at stations east of the front. We did not find any subsurface glacial meltwater intrusion in Kangerdlugssuaq fjord, unlike the reported ‘cold tongue’ in Antarctic fjords. Instead Arctic Intermediate Water (winter cooled North Atlantic Water) penetrates to the head of the fjord and fills the bottom part of the fjord. A linear relationship between salinity and δ18O shows that there was no significant contribution from the sea ice meltwater in this study site. The dominant source of freshwater in the Kangerdlugssuaq Fjord is glacial meltwater. A simple model using δ18O was developed to illustrate glacial meltwater dynamics in the fjord, and to estimate the length of the glacial meltwater plume. Model results agree well with the data within the fjord and near the fjord mouth and a plume length is estimated to be 250 km from the glacial face. However, a diversion of the model from the data is observed at about 70 km away from the mouth of the fjord because of the influence by the East Greenland Current and the Coriolis effect.

Stress fields controlling strike-slip faulting in Iceland

Large-scale strike-slip faults, generating earthquakes that can reach M 7–7.5, are common in the Tjörnes fracture zone in North Iceland, the Borgarfjördur area in West Iceland, and the South Iceland seismic zone. Strike-slip faulting in the Tjörnes fracture zone is controlled by a typical oceanic transform-fault stress field. The two other areas are located between partly overlapping volcanic zones where shear-stress concentration controls the strike-slip faulting. The maximum cumulative strike-slip displacement on the faults is a few tens of metres. Some faults have been subject to both dextral and sinistral slip. Boundary-element results indicate that the remote applied shear stress available in the areas of strike-slip faulting in Iceland is 7–12 MPa. The shear stress that drives the largest strike-slip faults, however, is of the order of 1–3 MPa.

Variations in Atlantic surface ocean paleoceanography, 50°‐80°N: A time‐slice record of the last 30,000 years

Eight time slices of surface‐water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea‐ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep‐sea cores, 20 of which are accelerator mass spectrometry (AMS)‐14C dated and 30 of which have high (>8 cm /kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The δ18O and δ13C distributions depict three main modes of surface circulation: (1) The Holocene‐style interglacial mode which largely persisted over the last 12.8 14C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice‐free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S‐N flow across the eastern Iceland‐Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface‐water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene‐style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during δ18O event 3.1 and the Bölling. Meltwater phases markedly influenced the European continental climate by suppressing the “heat pump” of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell.An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95PA01453, Variations in Atlantic surface ocean paleoceanography, 50°‐80°N: A time‐slice record of the last 30,000 years, M. Sarnthein et al.) Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.

Long-term changes in zooplankton biomass in Icelandic waters it spring

Since the early 1960s studies on zooplankton biomass and species composition have been carried out on standard transects during late May and early June in the waters north of Iceland. In the early 1970s the studies were extended to also cover the waters south, west, and east of the island. The present article summarizes these long-term investigations in spring for 62 stations on 9 transects. Calanus finmarchicus usually constituted about 50–80% of the number of animals in the zooplankton samples. Other species/groups of considerable importance in certain areas were C. glacialis, C. hyperboreus, Metridia longa, euphausiid larvae, and cirripede larvae. The horizontal distribution of the zooplankton biomass from shallow to deep water and in different areas was usually relatively uniform (2–4 g m−2), except for the frontal area between coastal and Atlantic Water south of Iceland (ca. 10 g m−2) and in the waters off the north-east coast beyond the shelf in the Arctic East Icelandic Current (9–11 g m−2). North-east of Iceland this is explained by both differences in the state of development and in the composition of the zooplankton. The difference between the highest and lowest biomass on the different transects was 7–24-fold. Principal component analysis (PCA) for the transects in the Atlantic Water south of Iceland revealed maxima in biomass during the mid-1970s, 1980s, and an upward trend since the early 1990s. Lows were observed in the Atlantic Water during the late 1970s and late 1980s. In the transitional waters north-west and north of Iceland (mixed Atlantic/Arctic) PCA demonstrated maxima in the early 1960s, late 1970s and a clear upward trend since the early 1990s. During the minima observed in the intervening periods, slight upward shifts occurred during 1971–1973 and 1984–1986. For the Arctic waters of the north-east and east coasts the PCA showed maxima during the mid-1970s, 1980s, an upward trend since the early 1990s and minima during the late 1970s and late 1980s. Thus, for both the Atlantic and Arctic Waters PCA reveals a period of approximately 10 years between maxima in biomass, while in the transitional waters (mixed Atlantic/Arctic) this period appears to be 16 years. The abundance of 0-group cod in Icelandic waters during 1974–1992 suggests strong interactions with the zooplankton on their spawning grounds and larval drift route to the south and west of Iceland.

Longitudinal study of caries, cariogenic bacteria and diet in children just before and after starting school

Fifty 5-yr-old preschool children living in Akranes, a small community in West Iceland known to have a high caries prevalence, were investigated with respect to caries, salivary counts of mutans streptococci and lactobacilli, and consumption of cariogenic foods. Fifteen months later, after being in school for half a year, 43 of the 50 children were reexamined and investigated as before. Mean dmfs scores rose from 7.1 to 9.0, but the scores including initial caries rose from 9.7 to 15.3. Mutans streptococci were carried by 84% of children on both occasions with a mean count 2.1 and 3.6 x 10(5) cfu/ml. Lactobacillus carriage increased from 29 to 38% and the mean count from 5.1 to 13 x 10(3) cfu/ml at 6 yr. The frequency of consumption of sugar-containing foods increased from 4.2 to 5.2 intakes per day and between-meal snacks rose from 3.0 to 3.7 per day. Children classified as "misusing" sugar were 59% at 5 yr and 83% at 6 yr. The mean caries score at 6 yr for children "misusing" sugar was 10.7 but only 2.0 for those not misusing sugar. Thus the deterioration in dental health appears, in these children, to be associated with the increased consumption of sweets and other cariogenic between-meal snacks after starting school.

Proglacial glaciotectonic deformation at Melabakkar‐Ásbakkar, west Iceland

A study of proglacial deformation associated with a Late Weichselian glaciomarine sequence was carried out at Melabakkar‐Ásbakkar, west Iceland. At this site, coarse‐grained sediments have been deformed into compressive structures with no associated push moraine morphology. Two large structures were examined, Structure A which consists of large‐scale reverse (and normal) faulting and overturned bedding; and Structure B, which is more complex, with open folding, high‐angle reverse faulting, nappe structures and normal faulting. The structures were interpreted as the result of increasing compressive proglacial deformation, followed by subglacial deformation, which destroyed the surface morphology of the push moraine and incorporated some of the sediments into a subglacial diamicton. The results from this study were compared with other examples of proglacial deformation, and it is suggested that at sites where deformation was restricted to the margin, longitudinal strain was lower than at sites where deformation extended out into the foreland. It is also suggested that if deformation increases downglacier, this is indicative of an overall glacial advance, whilst if the deformation decreases downglacier, this is indicative of a glacial retreat.

The Iceland scallop, Chlamys islandica (O.F Müller), in Breidafjördur, west Iceland. III. Growth in suspended culture

During two years, from September 1989 to September 1991, a study was carried out to evaluate the potential of pearl net cultivation of Iceland scallop, Chlamys islandica (O.F Müller), in Breidafjördur, west Iceland. In September 1989 1-year-old spat (mean height 9.8 mm±2.0 s.d.) were transferred from collectors to pearl nets suspended from flotation at 6–8 m depth. Shell increment, chlorophyll- a, temperature and salinity were monitored each month at the experimental site. During the second year in the pearl net culture, growth of soft parts of the body was also measured. By September 1990 the scallops had an average shell height of 24.6 mm±6.0 s.d. and in September 1991, three years after settlement, a height of 43 mm±8.3 s.d. was reached. Growth rate was related to food availability (measured as chlorophyll- a). During both years of the investigation height-specific growth rate reached a maximum (0.7% day −1 and 0.3% day −1, respectively) in early spring and again in summer, but it gradually decreased as the scallops grew older. The growth season lasted from March to October during both years of investigation. The results showed that the growth of Iceland scallops can be increased markedly by suspending the animals in hanging culture in more favourable environmental conditions than found on the natural scallop beds. The feasibility of cultivating Chlamys islandica in Breidafjördur is discussed.

The Iceland scallop, Chlamys islandica (O.F. Müller), in Breidafjördur, West Iceland : II. Gamete development and spawning

Annual cycles of gamete development in male and female Chlamys islandica (O.F. Müller), in Breidafjördur, west Iceland, were investigated for 2 years (August 1988–August 1990) by histological and stereological techniques. Spermatogenesis proceeded rapidly after spawning in July and continued while food was available. During winter a resting phase was observed and at that time mature sperm were present in small follicles. Spermatogenesis continued in early spring when the follicles became larger and in May 80–85% of the males had fully matured. Oogenesis started immediately after spawning and continued throughout the autumn with a resting phase during the winter. The follicles in overwintering females contained no mature ova. In early spring the follicles became larger and oocytes developed further. The first fully developed ova were detected in April–May but females were not fully mature until June. During both years spawning occurred at the beginning of July. In 1989 this coincided with both maximum chlorophyll- a level and highest temperature while in 1990 the maximum temperature and chlorophyll- a were observed approximately 1 month after spawning.

Effect of local and regional stress fields on sheet emplacement in West Iceland

At the Tertiary Reykjadalur central volcano in West Iceland, there is a remarkable change in strike, dip, thickness and percentage of sheets at a distance of about 9 km from the centre of the volcano. At distances of less than 9 km, the sheets strike in several main directions, their average (arithmetic mean) dip is 45° and the average thickness 1 m. Locally, the sheets make up nearly 90% of the rock, but in 1–1.5-km-long profiles they are 5.8–7.9%. One-third of the sheets are porphyritic, containing as much as 50% of plagioclase phenocrysts. Within, and in the vicinity of, the central volcano there is thus a clear swarm of inclined (cone) sheets. At distances greater than 9 km the sheets suddenly dip much more steeply (average 81°), become thicker (average 3.15 m), strike parallel to the nearby volcanic zones, and have all the characteristics of regional dyke swarms. In 2.5–10.5-km-long profiles these dykes are only 0.83–1.84% of the rock. One-fourth of the dykes are porphyritic, but the percentage of plagioclase phenocrysts is normally less than 10%. We interpret this abrupt change from a local swarm of inclined sheets to swarms of regional dykes as reflecting changes in the stress field. We propose that a local stress field controlled the strike, dip and, partly, thickness of the sheets to a distance of 9 km from the centre of the volcano. This local stress field, which is also thought to have given rise to the collapse caldera associated with the volcano, is attributed to a crustal magma chamber at a shallow depth below the volcano. This crustal magma chamber is regarded as the source of most of the inclined sheets. The regional stress fields associated with the volcanic zones is thought to have controlled dyke emplacement at greater distances from the volcano. We suggest that many of the regional dykes were injected from a deep-seated magma reservoir, located at boundary between the crust and upper mantle.

NADW formation as a branch of the hydrological cycle

The wide interest in the nature and evolution of deep ocean circulation as a key factor to understanding climate change set the stage for a conference devoted to North Atlantic Deep Water (NADW) formation held at Lamont‐Doherty Geological Observatory (LDGO), Palisades, N.Y., from November 11 to 12, 1991. Sponsored by the LDGO Climate Center and hosted by Wally Broecker, about seventy scientists attended. Twenty‐seven invited papers were presented at the 2‐day conference.The rates and paths of NADW formation were the focus of the first day. Bob Dickson, Lowestoft, U.K., summarized the present state of the “northern end” of global thermohaline circulation. In contrast to the view one obtains from many existing numerical models, especially the simpler ones, NADW derives, in reality, from a mixture of distinctly different water masses before it spreads into the world ocean. At most, 50% of the estimated 20 Sv (1 sverdrup = 106 m3/s) of North Atlantic overturning actually comes from the Arctic via the overflows east and west of Iceland; the rest is thought of as recirculating water from the Labrador Sea. The Greenland‐Iceland ridge overflow conspicuously lacks both seasonal and interannual variability in the transport. This is an important constraint for future modeling efforts.

The Iceland scallop, Chlamys islandica (O.F. Müller) in Breidafjördur, west Iceland. I. Spat collection and growth during the first year

Spat of the Iceland scallop Chlamys islandica (O.F. Müler), was artificially collected, using onion bags of 6 mm mesh size filled with monofilament of 0.4 mm, and polyethylene bags of 4.5 mm mesh size filled with monofilament of 0.2 mm. The spat collectors were placed at 25–35 m depth in Breidafjördur on the west coast of Iceland, in the middle of July 1988. The settlement of the spat was observed in the middle of September. No significant difference was found in the settlement at different depths but it varied greatly according to the diameter of the monofilament in the bags. Heaviest settlement was observed on the thinner monofilament (0.2 mm). The instantaneous growth rate was highest from the middle of September to the middle of October (3.6%/day) but decreased during the winter. In May the growth increased again concurring with an observed increase in sea temperature and abundance of phytoplankton. In September 1989, 1 year after settlement, the spat had reached an average size of 9.8 mm. Some evidence of secondary migration was observed for Chlamys islandica 1 year after settlement.

Records ofEucopia grimaldii, Hansenomysis fyllae, Hemimysis lamornae, andMysis litoralis(Mysidacea) from Icelandic waters

Abstract The first records of Eucopia grimaldii NOUVEL, 1942, Hansenomysis fyllae (HANSEN, 1887), Hemimysis lamornae (COUCH, 1856). and Mysis litoralis (BANNER, 1948) are reported from south-west and west Iceland. E. grimaldii was caught in a pelagic trawl at c. 290 m depth on the Dohrn Bank grounds in the Denmark Strait. H. fyllae originates from the stomach of cod taken at 330 m depth on the Iceland shelf, while H. lamornae and M. litoralis were collected in shallow waters near Reykjavik. M. litoralis appears to be common in coastal waters on the south-west coast where it occurs together with M. oculata.