The Theistareykir Geothermal Field, NE Iceland. Isotopic Characteristics and Origin of Circulating Fluids

AbstractThe Theistareykir high temperature field in NE Iceland seems to be complex in terms of both inflow and structure, as reflected in the division of the area into several subfields. Oxygen and hydrogen isotopes in water and steam condensate from wells are reported. Some differences can be seen between the Theistareykir well fields, but the recharge is in all cases non-local in origin. The isotopic composition of some of the thermal waters is anomalously depleted in 2H, by about 35‰, compared to precipitation anywhere in Iceland today. The isotopes therefore suggest that the thermal water contains a component of past precipitation under a colder climate. The oxygen shift due to water-rock interaction is up to 6.5 ‰. The isotopic signature of the Theistareykir thermal water is compared to that from nearby low temperature fields within the westernmost part of the Northern Neovolcanic Zone

Mat á alvarleika persónuleikavandamála : athugun á spurningalistanum Severity Indices of Personality Problems (SIPP) í úrtaki íslenskra háskólanema

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenSpurningalistinn Severity Indices of Personality Problems eða SIPP er nýr spurningalisti sem metur alvarleika vandamála sem oft tengjast persónuleikaröskunum. Listinn er til í tveimur útgáfum og inniheldur önnur 118 atriði (SIPP- 118) sem skiptast á alls 16 undirþætti sem tilheyra fimm yfirþáttum. Hin útgáfan er styttri og inniheldur 60 atriði (SIPP-60) sem notuð eru til að reikna út skor þátttakenda á yfirþáttunum fimm. Tilgangur þessarar rannsóknar var að kanna próffræðilega eiginleika íslenskrar þýðingar á SIPP listunum í úrtaki 634 háskólanema. Niðurstöður sýndu að áreiðanleiki 13 af 16 undirþáttum SIPP-118 var ásættanlegur eða góður ( 0,70). Í leitandi þátttagreiningu voru þrír af fimm þáttum sambærilegir við niðurstöður erlendrar rannsóknar á SIPP-118. Skor á yfirþáttum SIPP-60 höfðu miðlungs til sterka fylgni við skor á spurningalista um lífsánægju þannig að meiri alvarleiki persónuleikavanamála tengdist minni lífsánægju. Marktækur munur var á meðaltölum á öllum yfirþáttum SIPP-60 milli hópa sem höfðu lág, miðlungs eða há skor á skimunarlista fyrir persónuleikaraskanir. Fyrstu niðurstöður á íslenskri þýðingu SIPP spurningalistans benda til að próffræðilegir eiginleikar listans séu góðir en kanna þarf betur þátttabyggingu listans. Áframhaldandi rannsóknir ættu einnig að beinast að notagildi listans við greiningu og mat á árangri meðferðar við persónuleikaröskunum

Simple Space-Time Symmetries: Generalizing Conformal Field Theory

We study simple space-time symmetry groups G which act on a space-time manifold M=G/H which admits a G-invariant global causal structure. We classify pairs (G,M) which share the following additional properties of conformal field theory: 1) The stability subgroup H of a point in M is the identity component of a parabolic subgroup of G, implying factorization H=MAN, where M generalizes Lorentz transformations, A dilatations, and N special conformal transformations. 2) special conformal transformations in N act trivially on tangent vectors to the space-time manifold M. The allowed simple Lie groups G are the universal coverings of SU(m,m), SO(2,D), Sp(l,R), SO*(4n) and E_7(-25) and H are particular maximal parabolic subgroups. They coincide with the groups of fractional linear transformations of Euklidean Jordan algebras whose use as generalizations of Minkowski space time was advocated by Gunaydin. All these groups G admit positive energy representations. It will also be shown that the classical conformal groups SO(2,D) are the only allowed groups which possess a time reflection automorphism; in all other cases space-time has an intrinsic chiral structure.Comment: 37 pages, 4 Table

Life cycles of Eukiefferiella claripennis (Lundbeck 1898) and Eukiefferiella minor (Edwards 1929) (Diptera: Chironomidae) in spring-fed streams of different temperatures with reference to climate change

The effect of temperature on the life cycles of two chironomid species, Eukiefferiella claripennis and Eukiefferiella minor, was studied by comparing populations from seven spring-fed streams, ranging in annual average temperatures between 5.4°C and 21.3°C. Dependent on stream, both species showed differences in their life cycles: E. claripennis was regarded univoltine in the two coldest streams, IS7 (annual average 5.4°C) and IS11 (5.3°C), and bivoltine or multivoltine in the warmer streams (ranging from 9.7°C to 21.3°C). E. claripennis developed and grew slower in the colder streams compared to the warmer ones. The winter generation in the warmer streams took longer time to complete compared to the summer generation. E. minor was bivoltine in all the streams, with no emergence during the winter in the colder streams, but in one of the warmer streams (IS6, 13.3°C) emergence was continuous throughout the year. In four streams (IS7, cold; IS6, IS5 and IS1, warm) E. minor may even have been multivoltine. There was no trend between the number of generations completed in one year and stream temperature for E. minor. The summer generation of E. minor in the cold stream IS7 produced smaller larvae compared to the winter generation. Following global warming the life cycle of E. claripennis is expected to change from univoltine to bivoltine, and could show changes in emergence pattern. E. minor on the other hand, will likely show less change in its life cycle. Changes in emergence pattern of E. minor could though be possible. doi: 10.5324/fn.v31i0.1367. Published online: 17 October 2012

Interpolation Theorems for Self-adjoint Operators

We prove a complex and a real interpolation theorems on Besov spaces and Triebel-Lizorkin spaces associated with a selfadjoint operator $L$, without assuming the gradient estimate for its spectral kernel. The result applies to the cases where $L$ is a uniformly elliptic operator or a Schr\"odinger operator with electro-magnetic potential.Comment: 8 pages. Submitte

Chironomidae fauna of springs in Iceland: Assessing the ecological relevance behind Tuxen’s spring classification

In 1937, S.L. Tuxen studied the animal community of hot springs in Iceland, and classified springs according to their relative temperature into cold, tepid, and hot. Eighty years after Tuxen’s study, we revisited some of the hot springs in Skagafjörður, Northern Iceland. Our aim was to compare the invertebrate community of 1937 and today, and to assess the stability of hot spring habitats over the years. To test Tuxen’s spring classification on an ecological basis, we furthermore collected chironomid larvae from 24 springs of a broad range of temperature, with samples taken both at the surface area of the spring and at the groundwater level. The chironomid species composition of hot springs differed from that of cold and tepid springs. Whereas Cricotopus sylvestris, Arctopelopia sp., and Procladius sp. characterised the chironomid community in Icelandic hot springs, cold and tepid springs were dominated by Eukiefferiella minor, Orthocladius frigidus and Diamesa spp. Community composition analyses and the exclusive occurrence of taxa in one of the temperature classes validated the ecological relevance of Tuxen’s spring classification for the chironomid species community. Both environmental parameters and invertebrate community of Icelandic hot springs seem to be the same as 80 years ago. Although springs have the potential to provide stable habitats, they are currently under high anthropogenic pressure, and should be increasingly considered in nature conservation.

Toeplitz operators on the domain {Z∈M2×2(C)∣ZZ∗<I}\{Z\in M_{2\times2}(\mathbb{C}) \mid Z Z^* < I\} with U(2)×T2\mathrm{U}(2)\times\mathbb{T}^2-invariant symbols

Let $D$ be the irreducible bounded symmetric domain of $2\times2$ complex matrices that satisfy $ZZ^* < I_2$. The biholomorphism group of $D$ is realized by $\mathrm{U}(2,2)$ with isotropy at the origin given by $\mathrm{U}(2)\times\mathrm{U}(2)$. Denote by $\mathbb{T}^2$ the subgroup of diagonal matrices in $\mathrm{U}(2)$. We prove that the set of $\mathrm{U}(2)\times\mathbb{T}^2$-invariant essentially bounded symbols yield Toeplitz operators that generate commutative $C^*$-algebras on all weighted Bergman spaces over $D$. Using tools from representation theory, we also provide an integral formula for the spectra of these Toeplitz operators

Effects of geothermal effluents on macrobenthic communities in a pristine sub-arctic lake

We studied the effects of warm effluents from the Nesjavellir geothermal power plant on benthic invertebrate communities along a depth gradient of 4 m in lake &THORN;ingvallavatn, Iceland. Four study sites were selected: 2 heataffected sites and 2 cold reference sites. Thermal pollution was detected down to 0.4 m at both heat-affected sites, which were 7-12 &deg;C higher than at the same depth at the reference sites. Sustained temperatures &ge;27 &deg;C, which is 10-17 &deg;C above ambient water temperatures, seems to be detrimental to the gastropod Radix peregra and several of the littoral chironomid species. Such effects were, however, confined to a small area inside a sheltered rift pool at one of the heat-affected sites. Moderate warming up to ~10 &deg;C above ambient lake temperature in summer, seems to benefit R. peregra, potentially through both a higher survival rate and a shorter life cycle. At the heat-affected sites, sustained high temperatures transformed a relatively diverse chironomid community to a species-poor community, dominated by Paratanytarsus sp. and Cricotopus sylvestris. In contrast, the chironomid Eukiefferiella minor was much more prominent at one of the reference sites. To separate thermal from biological effects, more studies are needed on speciesspecific attributes, including time-series data on growth, survival, and reproduction of the main littoral zoobenthic species. Although our research examined short-term responses of aquatic invertebrates to local thermal stress, our results may also be relevant to long-term responses of freshwater ecosystems at high latitudes to climate change and warming

Temperature effects on fish production across a natural thermal gradient

Global warming is widely predicted to reduce the biomass production of top predators, or even result in species loss. Several exceptions to this expectation have been identified, however, and it is vital that we understand the underlying mechanisms if we are to improve our ability to predict future trends. Here, we used a natural warming experiment in Iceland and quantitative theoretical predictions to investigate the success of brown trout as top predators across a stream temperature gradient (4–25 °C). Brown trout are at the northern limit of their geographic distribution in this system, with ambient stream temperatures below their optimum for maximal growth, and above it in the warmest streams. A five‐month mark‐recapture study revealed that population abundance, biomass, growth rate, and production of trout all increased with stream temperature. We identified two mechanisms that contributed to these responses: (1) trout became more selective in their diet as stream temperature increased, feeding higher in the food web and increasing in trophic position; and (2) trophic transfer through the food web was more efficient in the warmer streams. We found little evidence to support a third potential mechanism: that external subsidies would play a more important role in the diet of trout with increasing stream temperature. Resource availability was also amplified through the trophic levels with warming, as predicted by metabolic theory in nutrient‐replete systems. These results highlight circumstances in which top predators can thrive in warmer environments and contribute to our knowledge of warming impacts on natural communities and ecosystem functioning

Stream hydraulics and temperature determine the metabolism of geothermal Icelandic streams

Stream ecosystem metabolism plays a critical role in planetary biogeochemical cycling. Stream benthic habitat complexity and the available surface area for microbes relative to the free-flowing water volume are thought to be important determinants of ecosystem metabolism. Unfortunately, the engineered deepening and straightening of streams for drainage purposes could compromise stream natural services. Stream channel complexity may be quantitatively expressed with hydraulic parameters such as water transient storage, storage residence time, and water spiralling length. The temperature dependence of whole stream ecosystem respiration (ER), gross primary productivity (GPP) and net ecosystem production (NEP = GPP−ER) has recently been evaluated with a “natural experiment” in Icelandic geothermal streams along a 5−25 ◦C temperature gradient. There remained, however, a substantial amount of unexplained variability in the statistical models, which may be explained by hydraulic parameters found to be unrelated to temperature. We also specifically tested the additional and predicted synergistic effects of water transient storage and temperature on ER, using novel, more accurate, methods. Both ER and GPP were highly related to water transient storage (or water spiralling length) but not to the storage residence time. While there was an additional effect of water transient storage and temperature on ER (r2 = 0.57; P = 0.015), GPP was more related to water transient storage than temperature. The predicted synergistic effect could not be confirmed, most likely due to data limitation. Our interpretation, based on causal statistical modelling, is that the metabolic balance of streams (NEP) was primarily determined by the temperature dependence of respiration. Further field and experimental work is required to test the predicted synergistic effect on ER. Meanwhile, since higher metabolic activities allow for higher pollutant degradation or uptake, river restoration and management should promote habitat diversity and complexity (hyporheic zone, macrophyte patches, substrate heterogeneity), especially for microbial activity.Le métabolisme des écosystèmes aquatiques fluviaux joue un rôle critique dans les cycles biogéochimiques planétaires. La complexité des habitats benthiques et l’aire disponible pour les microbes par rapport au volume d’eau qui s’écoule sont considérées comme des facteurs importants pour le métabolisme de l’écosystème. Malheureusement, le creusement et l’alignement des cours d’eau pour le drainage des terres pourraient compromettre les services naturels fournis par les cours d’eau. Cette complexité peut être exprimée quantitativement avec des paramètres hydrauliques tels que le stokage transitoire de l’eau dans le lit de la rivière, la durée de résidence du stockage transitoire, et la longueur du flux en hélice (ou spirale) de l’eau (distance moyenne parcourue par une molécule d’eau dans la zone d’eau courante libre avant d’entrer dans la zone calme). L’effet de la température sur la respiration globale des ruisseaux (ER), productivité primaire brute (GPP) et production nette de l’écosystème (NEP) a récemment été évalué au travers d’une « expérience naturelle » dans des ruisseaux géothermiques islandais le long d’un gradient de température de 5−25 ◦C. Il resta, cependant, une quantité substantielle de variabilité non expliquée par les modèles statistiques, qui pourrait être expliquée par les paramètres hydrauliques non reliés à la température. Nous avons aussi tout particulièrement testé les effets additionnels et en synergie du stokage transitoire de l’eau et de la température sur la respiration, en utilisant de nouvelles méthodes. ER and GPP furent hautement corrélées au stockage transitoire de l’eau (ou flux en hélice de l’eau), mais pas à la durée de résidence du stockage. Le stokage transitoire de l’eau et de la température eurent un effect additionnel sur ER (r2 = 0,57 ; P = 0,015), en revanche GPP était plus liée au stockage transitoire de l’eau qu’à la température. L’effet en synergie ne put être confirmé, probablement dû aux limitations des données. Notre interpretation, basée sur un modèle statistique causal, est que l’équilibre métabolique des cours d’eau (NEP) était principalement contrainte par la réponse de la respiration à la température. D’autres travaux de terrain et expérimentaux sont nécessaires pour tester notre nouvelle hypothèse d’un effet en synergie sur ER. Dans l’attente, puisqu’une plus haute activité métabolique permet une rétention ou dégradation plus importante des polluants, la restoration et la gestion des cours d’eau devraient promouvoir la diversité et la complexité des habitats (hyporhéos, touffes de macrophytes, hété- rogénéité du substrat) particulièrement pour l’activité microbienne.This study was funded by the Scottish Government Rural and Environment Research and Analysis Directorate (RERAD), now Rural and Environment Science and Analytical Services (RESAS). J.R.M. acknowledges the support of the Richard Stockton College of New Jersey. We would like to thank Tryggvi Thordarson, director of the Research Station at Hveragerdi for lodging and his warm hospitality, Marc Stutter and two anonymous referees for their insightful comments on the manuscript.Peer ReviewedRitrýnt tímari