Showing papers by "University of Iceland published in 1994"

High-resolution climate records from the North Atlantic during the last interglacial

Abstract: THE two deep ice cores recovered by the GRIP1 and GISP22 projects at Summit, Greenland, agree in detail over the past 100,000 years3 and demonstrate dramatic climate variability in the North Atlantic region during the last glacial, before the current period of Holocene stability. This glacial climate instability has subsequently been documented in the marine sedimentary record of surface-ocean conditions in the North Atlantic4. Before 100 kyr ago the two ice core records are discrepant, however, casting doubt on whether the oxygen isotope fluctuations during the last interglacial (Eemian) seen in the GRIP core1,5 represent a true climate signal. Here we present high-resolution records of foraminiferal assemblages and ice-rafted detritus from two North Atlantic cores for the interval 65 kyr to 135 kyr ago, extending the surface-ocean record back to the Eemian. The correlation between our records and the Greenland ice-core records is good throughout the period in which the two ice cores agree, suggesting a regionally coherent climate response. During the Eemian, our marine records show a more stable climate than that implied by the GRIP ice core, suggesting that localized phenomena may be responsible for the variability in the latter record during the Eemian.

Climate variations in Europe over the past 140 kyr deduced from rock magnetism

Abstract: RAPID shifts in climate during the last glacial are now well documented, particularly from the oxygen isotope records of the two Greenland ice cores GRIP1,2 and GISP23. In the GRIP record1,2 these climate events are also seen during the preceding (Eemian) interglacial which may be an analogue for the future climate, warmed by the greenhouse effect. But these shifts are not found in the Eemian section of the GISP2 core3, casting doubt on whether the rapid shifts in the GRIP oxygen isotope record really do represent a climate signal. Here we present magnetic susceptibility, pollen and organic carbon records from maar lake deposits in the Massif Central, France. These data provide an independent record of past climate and we find that they correlate well with the ice-core records during the last glacial. During the Eemian, two rapid cooling events seen in our record also correlate with those seen in the GRIP ice core, supporting the idea that rapid climate change did occur in the Eemian interglacial and demonstrating that it extended to continental Europe.

Trophic specialization in Arctic charr Salvelinus alpinus (Pisces; Salmonidae): morphological divergence and ontogenetic niche shifts

Abstract: Lake Thingvallavatn supports four trophic morphs of Arctic charr, Salvelinus alpinus (L.); two of the morphs are benthic (small and large benthivorous charr) one exploits pelagic waters (planktivorous charr) and the fourth is found in both habitats (piscivorous charr). The morphological variation among these morphs was analysed by use of principal component analysis and canonical discriminant analysis. The benthic morphs have a short lower jaw and long pectoral fins. The benthic fish also have fewer gillrakers than the other morphs. Small and large benthivorous charrs attain sexual maturity from 2 and 6 years of age, and at fork lengths from 7 and 22 cm, respectively. Small benthivorous charr retain their juvenile parr marks as adults, have beige ventral colours, and are frequently melanized under the lower jaw. Planktivorous and piscivorous charr attain sexual maturity from 4 and 6 years of age, from fork lengths of 15 and 23 cm, respectively. This phenotypic polymorphism is associated with habitat utilization and diet of the fish, and has probably arisen within the lake system through diversification and niche specialization. The pelagic morphs apparently stem from a single population, and are possibly diversified through conditional niche shifts which affect ontogeny. Juveniles reaching a body length of 23 cm may change from zooplankton to fish feeding. Asymptotic length increases thereby from 20.5 cm in planktivorous charr to 30.2 cm in piscivorous charr. The benthic morphs appear to represent separate populations, although both feed chiefly on the gastropod Lymnaea peregra . Their co-existence seems to be facilitated by size dependent constraints on habitat use. The small morph (asymptotic length 13.3 cm) exploit the interstitial crevices in the lava block substratum, whereas the large morph (asymptotic length 55.4 cm) live epibenthically.

The role of the deep ocean in North Atlantic climate change between 70 and 130 kyr ago

Abstract: THE suggestion1 that changes in North Atlantic Deep Water (NADW) production are linked through surface heat flux to the atmospheric temperature over Greenland is supported by earlier indications2,3 that NADW production decreased during glacial times, and by the subsequent finding4–6 that it declined during the Younger Dryas cool period at the end of the last glaciation. Changes in North Atlantic surface temperatures have been found7 to mirror high-frequency temperature changes recorded in Greenland ice cores over the past 80 kyr, but the connection to abyssal circulation has yet to be established, except for one or two isolated oscillations8,9. Here we present carbon and oxygen isotope analyses of benthic foraminifera in a high-resolution North Atlantic deep-sea sediment core for the period 70–130 kyr ago. These data allow us to reconstruct the history of NADW production, which shows a close correlation with Greenland climate variability for much of this time interval, suggesting that the climate influence of NADW variability was widespread. We see no evidence, however, for changes in NADW production during substage 5e (the Eemian interglacial period), in contrast with recent ice-core data10 which suggest severe climate instability in Greenland during this time period. Our results may support suggestions, based on data from a second ice core, that this apparent instability is an artefact caused by ice flow11. Alternatively, the Eemian climate instability may have had a different origin from the subsequent climate events.

The benzodiazepine withdrawal syndrome

Abstract: Physiological dependence on benzodiazepines is accompanied by a withdrawal syndrome which is typically characterized by sleep disturbance, irritability, increased tension and anxiety, panic attacks, hand tremor, sweating, difficulty in concentration, dry wretching and nausea, some weight loss, palpitations, headache, muscular pain and stiffness and a host of perceptual changes. Instances are also reported within the high-dosage category of more serious developments such as seizures and psychotic reactions. Withdrawal from normal dosage benzodiazepine treatment can result in a number of symptomatic patterns. The most common is a short-lived "rebound" anxiety and insomnia, coming on within 1-4 days of discontinuation, depending on the half-life of the particular drug. The second pattern is the full-blown withdrawal syndrome, usually lasting 10-14 days; finally, a third pattern may represent the return of anxiety symptoms which then persist until some form of treatment is instituted. Physiological dependence on benzodiazepines can occur following prolonged treatment with therapeutic doses, but it is not clear what proportion of patients are likely to experience a withdrawal syndrome. It is also unknown to what extent the risk of physiological dependence is dependent upon a minimum duration of exposure or dosage of these drugs. Withdrawal phenomena appear to be more severe following withdrawal from high doses or short-acting benzodiazepines. Dependence on alcohol or other sedatives may increase the risk of benzodiazepine dependence, but it has proved difficult to demonstrate unequivocally differences in the relative abuse potential of individual benzodiazepines.

Rhyolite volcanism in the Krafla central volcano, north-east Iceland

Abstract: At the Krafla central volcano in north-east Iceland, two main phases of rhyolite volcanism are identified. The earlier phase (last interglacial) is related to the formation of a caldera, whereas the second phase (last glacial) is related to the emplacement of a ring dike. Subsequently, only minor amounts of rhyolite have been erupted. The volcanic products of Krafla are volumetrically bimodal. Geochemically, there is a series of basaltic to basalto-andesitic rocks and a cluster of rhyolitic rocks. Rocks of intermediate to silicic composition (icelandites and dacites) show clear signs of mixing. The rhyolites are Fe-rich (tholeiitic), and aphyric to slightly porphyritic (plagioclase, augite, pigeonite, fayalitic olivine and magnetite). They are minimum melts on the quartz-plagioclase cotectic plane in the granite system (Qz-Or-Ab-An). The rhyolites at Krafla were produced by near-solidus, rather than nearliquidus fractionation. They are interpreted as silicic minimum melts of hydrothermally altered crust, mainly of basaltic composition. They were primarily generated on the peripheries of an active basaltic magma chamber or intrusive domain, where sufficient volumes of crust were subjected to temperatures favorable for rhyolite genesis (850–950° C). The silicic melts were extracted crystal-free from their source in response to crustal deformation.

Asymptotics of heavy atoms in high magnetic fields: II. Semiclassical regions

Abstract: The ground state energy of an atom of nuclear chargeZe in a magnetic fieldB is exactly evaluated to leading order asZ→∞ in the following three regions:B≪Z4/3,B≈Z4/3 andZ4/3≪B≪Z3. In each case this is accomplished by a modified Thomas-Fermi (TF) type theory. We also analyze these TF theories in detail, one of their consequences being the nonintuitive fact that atoms are spherical (to leading order) despite the leading order change in energy due to theB field. This paper complements and completes our earlier analysis [1], which was primarily devoted to the regionsB≈Z3 andB≫Z3 in which a semiclassical TF analysis is numerically and conceptually wrong. There are two main mathematical results in this paper, needed for the proof of the exactitude of the TF theories. One is a generalization of the Lieb-Thirring inequality for sums of eigenvalues to include magnetic fields. The second is a semiclassical asymptotic formula for sums of eigenvalues that isuniform in the fieldB.

There are no causality problems for Fermi's two-atom system.

Abstract: A repeatedly discussed gedanken experiment, proposed by Fermi to check Einstein causality, is reconsidered. It is shown that, contrary to a recent statement made by Hegerfeldt, there appears no causality paradox in a proper theoretical description of the experiment.

Asymptotics of heavy atoms in high magnetic fields: I. Lowest landau band regions

Abstract: The ground state energy of an atom of nuclear charge Ze in a magnetic field B is evaluated exactly to leading order as Z ∞. In this and a companion work (see [28]) we show that there are five regions as Z ∞: B Z3. Regions 1, 2, 3, and 4 (and conceivably 5) are relevant for neutron stars. Different regions have different physics and different asymptotic theories. Regions 1, 2, and 3 are described by a simple density functional theory of the semiclassical Thomas-Fermi form. Here we concentrate mainly on regions 4 and 5 which cannot be so described, although 3, 4, and 5 have the common feature (as shown here) that essentially all electrons are in the lowest Landau band. Region 5 does have, however, a simple non-classical density functional theory (which can be solved exactly). Region 4 does not, but, surprisingly, it can be described by a novel density matrix functional theory. © 1994 John Wiley & Sons, Inc.

The crustal magma chamber of the Katla volcano in south Iceland revealed by 2-D seismic undershooting

Abstract: SUMMARY Results of a 2-D, seismic undershooting experiment on the Katla central volcano in south Iceland are reported. Large localized traveltime anomalies (0.4 s) are observed on an array within the Katla caldera. The traveltimes are forward modelled using a wavefront tracker developed in Appendix A. Thus, non-linear effects encountered in traveltime tomography are avoided as well as common problems with ray tracing in the presence of strong lateral heterogeneity. An extreme variation in compressional velocity is required to extend over a significant volume in order to model the data. The resulting model is not unique, but constraints on the allowable range of velocities (2.5-6.0 km s-') render the basic features well constrained. A clear S-wave shadow is closely associated with delays in traveltime due to a shallow slow anomaly. Low-amplitude P waves go hand in hand with early arrivals due to thin structural features flanking the slow anomaly. The model is interpreted in terms of a magma chamber containing extensively molten rock. The magma chamber is shallow, with a bottom at a depth of about 1.5 km below sea-level (3.0 km below surface), and measures about 5 km across. The depth of the chamber is roughly at the level of buoyant equilibrium for basaltic melt in the crust. Owing to poor vertical resolution at shallow depths in the undershooting geometry the top of this shallow magma chamber is not well resolved. On the other hand, the bottom of the chamber is well resolved. The chamber is underlain by rocks of average or high velocity for that depth. The magma chamber is a persistent feature, big enough (10 km3) to supply magma for large eruptions and to supply heat to permit remelting of hydrated basaltic crust to produce silicic magmas at shallow levels. The chamber is fed by magma fracturing from below. The model agrees with phenomenological models of magma chambers in Iceland based on geological observations and provides a quantification of those models in terms of depth and size. On the other hand, it is fundamentally different from recent models of magma chambers at mid-ocean ridges which may be more akin to the pervasive region of partial melt at depth beneath Iceland. This underlines the important effect of the Icelandic hotspot on tectonics and volcanism in Iceland and implies a substantially different crustal and thermal structure in Iceland from that of 'normal' mid-ocean ridges.

The postantibiotic effect of antifungal agents against common pathogenic yeasts

Abstract: A total of ten strains of Candida spp. and Cryptococcus neoformans were examined for the presence of the postantibiotic effect (PAE) after 0.5-2 h exposure to amphotericin B, 5-fluorocytosine, miconazole and ketoconazole. Significant PAEs were observed for amphotericin B and 5-fluorocytosine, but none for the imidazoles. The duration of the PAEs of amphotericin B ranged from 0.5-10.4 h for the Candida spp. and 2.8-10.6 h for the cryptococcos, while 5-fluorocytosine induced PAEs from 0.8-7.4 h and 2.4-5.4 h, respectively. Even though no PAEs were demonstrated for the imidazoles, the growth rate was persistently reduced by continuous exposure to concentrations as low as 1/1000 of the MIC of these agents. These findings may have implications for dosing antifungal agents in systemic yeast infections.

Cloning and Sequencing of a Rhodothermus marinus Gene, bglA, Coding for a Thermostable β-Glucanase and its Expression in Escherichia coli

Abstract: A gene library of the thermophilic eubacterium, Rhodothermus marinus, strain 21, was prepared in pUC18 and used to transform Escherichia coli. Of 5400 transformants, two produced halos on lichenan plates after Congo-red staining. Restriction mapping showed that the two clones shared an overlapping 1200-bp DNA fragment, which was used for DNA sequencing. Five potential methionine (Met) translational-initiation codons were identified. A putative signal peptide of 30 amino acids was identified with a hydrophobic core of nine hydrophobic amino acids. The molecular mass of the mature enzyme was estimated to be 29.7 kDa. A comparison of the primary protein sequence of β-glucanase of Rhodothermus marinus with other glycosyl hydrolases showed 38.5% identity to the C-terminal part of the β-1,3-glucanase of Bacillus circulars and limited identity to bacterial endo-β-1,3–1,4-glucanases. The amino acid sequence showed high similarity to regions surrounding the catalytic Glu residue of bacterial β-glucanases. A gene fragment of 889 bp containing the catalytic domain was overexpressed in E. coli using the pET23, T7-phage RNA polymerase system. The enzyme showed activity on lichenan, β-glucan and laminarin but not on CMC cellulose or xylan. The expressed enzyme was purified by heat treatment of the host. The enzyme had a temperature and pH optima of 85°C and pH 7.0, respectively, and was shown to retain full activity after incubation for 16 h at 80°C and have a half life of 3 h at 85°C.

The interaction of monetary policy and wages

Abstract: This paper focuses on the interaction of monetary policy and wage formation in economies with strong labor unions. Government and unions are viewed as endogenous utility maximizers and the macroeconomic consequences of their strategic interaction are explored with the aid of some elements of simple game theory. Specifically, it is shown (a) how labor unions adjust wages to prices so as to maximize their utility following changes in monetary policy; (b) how the effectiveness of monetary policy is circumscribed without necessarily being nullified by the utility-maximizing reactions of unions; and (c) how the interplay of government and unions can create a persistent tendency towards inflation and unemployment simultaneously.

Paranoia, self-consciousness, and social cognition in schizophrenics

Abstract: The validity of the Paranoia Scale of Fenigstein and Vanable (1992) was investigated in a schizophrenic population. The scale was found to be correlated with clinical ratings of paranoia and marginally with a situational test of paranoia. Further, Fenigstein and Vanable's study of the relation between paranoia and self-consciousness was extended from a normal population to schizophrenic patients. Contrary to Fenigstein and Vanable, paranoia was found to be related to private, but not to public self-consciousness. This finding is discussed in the light of possible differences in self-processes between normals and schizophrenics. Finally, Fenigstein and Vanable's arguments concerning paranoid personalism in social cognition were investigated. It was expected that paranoia and public self-consciousness would be related to extreme evaluations of people. This was partly confirmed for paranoia, but not for public self-consciousness. The implications are discussed.

Effects of social support on self-assessed health in adolescence

Abstract: Based on a national survey of Icelandic adolescents, this study evaluates the effects of social support on self-assessed health. The study compares four support sources, and distinguishes between direct effects and indirect effects through (1) health-related behaviors and (2) different aspects of mental health. The study indicates that parental support has the largest total effect on self-assessed health, followed by friend support, and other adult support. (Sibling support is unrelated.) The total effect of parents is due to their pervasive indirect impact, i.e., supportive parents encourage positive health behaviors and enhance mental health, which results in favorable assessment of own health. In contrast, friends and other adults affect self-assessed health in a more specific, and sometimes negative manner. Also, friends are the only support source having direct effect on self-assessed health. The implication of these results are discussed.

Manifest Predictors of Past Suicide Attempts in a Population of Icelandic Adolescents

Abstract: Past suicide attempts have been found to be a major risk factor for both repeated attempts and completed suicide. The utility of this is, however, limited by the fact that the majority of all suicide attempts never come to professional attention. This paper explores the possibility of using manifest indicators to predict which individuals in a population of adolescents have attempted suicide. Using logistic regression, manifest predictors in the categories of school, leisure, peer and parent relations, consumption, and contact with suicidal behavior could identify either a quarter of the population containing three quarters of all suicide attempters or 2% of the population where two thirds of those predicted actually had attempted suicide. It is thus concluded that manifest predictors can complement psychiatric screening methods by efficiently reducing the number to be screened.

A review of the environmental history of Iceland, 13 000‐9000 yr BP

Abstract: A synthesis of the main environmental changes that are interpreted to have occurred in Iceland during the period 13-9 ka BP is presented. Most of the evidence available relates to variations in the position of ice margins, although some limited information on vegetation history and soil stability is also referred to. Only qualitative and limited climatic inferences can be made for this period because of the lack of detailed evidence. A summary curve of the relative extent of ice cover is presented.

Single dose azithromycin treatment of gonorrhea and infections caused by C. trachomatis and U. urealyticum in men.

Abstract: Background and objectives Single dose regimens have advantages in the treatment of STD. Azithromycin has unique pharmacokinetics that may make single dose regimens feasible. Treatment with a single 1 g dose of azithromycin was compared to 100 mg doxycycline twice daily for seven days. Study design This was a randomized third-party blinded study on 183 male patients, 176 of whom could be evaluated for efficacy. Results Chlamydia trachomatis was cultured from 148 patients, 79 receiving azithromycin and 69 receiving doxycycline. Six patients receiving azithromycin had positive cultures on follow-up, four were known to have had sexual intercourse with infected partners. Fifty-one patients had gonorrhea; 28 were treated with azithromycin and 23 with doxycycline. Neisseria gonorrhoeae was eradicated from all patients except one receiving azithromycin. He denied sexual exposure during follow-up. Sixty patients were infected with Ureaplasma urealyticum, 35 were treated with azithromycin and 25 with doxycycline. Five patients in each group had positive cultures on follow up. Three patients receiving azithromycin and two receiving doxycycline were known to have had sexual exposure during follow-up. Conclusion A single dose of azithromycin showed similar effectiveness as a 7-day regimen of doxycycline.

Inactivation of enveloped viruses in human bodily fluids by purified lipids.

Abstract: Antimicrobial lipids are found in mucosal secretions and are one of a number of nonimmunologic and nonspecific protective factors found at mucosal surfaces. Lipids can inactivate enveloped viruses, bacteria, fungi, and protozoa. Lipid-dependent antimicrobial activity at mucosal surfaces is due to certain monoglycerides and fatty acids that are released from triglycerides by lipolytic activity. Medium chain length antiviral lipids can be added to human blood products that contain HIV-1 and HIV-2 and reduce the cell-free virus concentration by as much as 11 log10 TCID50/ml. The presence of lipids does not interfere with most clinical assays performed on human blood samples. Antimicrobial lipids can disrupt cell membranes and therefore lyse leukocytes which potentially carry virus. Genital mucosal epithelial cells should be protected from damage by the mucous layer. Preliminary studies indicate that lipids decrease sperm motility and viability suggesting that lipids may potentially be used as combination spermicidal and virucidal agents.

A note on essential duality

Abstract: By considering some simple models, it is shown that the essential duality condition for local nets of von Neumann algebras associated with Wightman fields need not be fulfilled if Lorentz covariance is dropped. These models illustrate a point made by Borchers in the proof of his two-dimensional CPT theorem for local nets: The Lorentz covariant net constructed from the wedge algebras of a given two-dimensional net may not be unique. It is also shown that in higher dimensions, the Lorentz boosts constructed by means of the modular groups of wedge algebras may act nonlocally in the directions parallel to the edge of the wedge.