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  • 1
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    CO2 content beneath northern Iceland and the variability of mantle carbon (2018)
    Geological Society of America
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geology 46 (2018): 55-58, doi:10.1130/G39413.1.
    Description: Primitive basalt melt inclusions from Borgarhraun, northern Iceland, display large correlated variations in CO2 and nonvolatile incompatible trace elements (ITEs) such as Nb, Th, Rb, and Ba. The average CO2/ITE ratios of the Borgarhraun melt inclusion population are precisely determined (e.g., CO2/Nb = 391 ± 16; 2σM [two standard errors of the mean], n = 161). These data, along with published data on five other populations of undegassed mid-oceanic ridge basalt (MORB) glasses and melt inclusions, demonstrate that upper mantle CO2/Ba and CO2/Rb are nearly homogeneous, while CO2/Nb and CO2/Th are broadly correlated with long-term indices of mantle heterogeneity reflected in Nd isotopes (143Nd/144Nd) in five of the six regions of the upper mantle examined thus far. Our results suggest that heterogeneous carbon contents of the upper mantle are long-lived features, and that average carbon abundances of the mantle sources of Atlantic MORB are higher by a factor of two than those of Pacific MORB. This observation is correlated with a similar distinction in water contents and trace elements characteristic of subduction fluids (Ba, Rb). We suggest that the upper mantle beneath the younger Atlantic Ocean basin contains components of hydrated and carbonated subduction-modified mantle from prior episodes of Iapetus subduction that were entrained and mixed into the upper mantle during opening of the Atlantic Ocean basin.
    Description: Maclennan is supported by Natural Environment Research Council grant NE/M000427/1. This research was supported by the Carnegie Institution of Washington.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Electronic Resource
    Electronic Resource
    Specialization of the hindgut wall for the attachment of symbiotic micro-organisms in a termite Procubitermes aburiensis (Isoptera, Termitidae, Termitinae) (1980)
    Springer
    Zoomorphology 96 (1980), S. 103-112 
    Details
    ISSN: 1432-234X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The posterior colon of worker-caste termites accommdates an abundant, heterogeneous population of procaryotic organisms which are retained by attachment to prominent cuticular spines elaborated from the gut wall. The spines extend to nearly one half the diameter of the lumen and are each supported by a specialized root cell in which bundles of parallel microtubules traverse the cytoplasm from the apical to the basal surfaces. Additional epithelial cells are present which show infoldings of the apical plasma membrane and are overlain by cuticle containing deep, vase-shaped pits opening to the gut lumen. It is proposed that the root cells are designed to resist shearing forces transmitted to the base of each spine during contractions of the gut. The cuticular pits may represent sites of permeability to the end products of microbial metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310080
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  • 3
    Electronic Resource
    Electronic Resource
    Sulfur, chlorine, and fluorine degassing and atmospheric loading by the 1783–1784 AD Laki (Skaftár Fires) eruption in Iceland (1996)
    Springer
    Bulletin of volcanology 58 (1996), S. 205-225 
    Details
    ISSN: 1432-0819
    Keywords: Key words Laki ; Effusive basaltic volcanism ; Fissure eruption ; Eruption dynamics ; Magma degassing ; Volcanic gases ; Volcanic glass chemistry ; Volcanic aerosols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The 1783–1784 Laki tholeiitic basalt fissure eruption in Iceland was one of the greatest atmospheric pollution events of the past 250 years, with widespread effects in the northern hemisphere. The degassing history and volatile budget of this event are determined by measurements of pre-eruption and residual contents of sulfur, chlorine, and fluorine in the products of all phases of the eruption. In fissure eruptions such as Laki, degassing occurs in two stages: by explosive activity or lava fountaining at the vents, and from the lava as it flows away from the vents. Using the measured sulfur concentrations in glass inclusions in phenocrysts and in groundmass glasses of quenched eruption products, we calculate that the total accumulative atmospheric mass loading of sulfur dioxide was 122 Mt over a period of 8 months. This volatile release is sufficient to have generated ∼250 Mt of H2SO4 aerosols, an amount which agrees with an independent estimate of the Laki aerosol yield based on atmospheric turbidity measurements. Most of this volatile mass (∼60 wt.%) was released during the first 1.5 months of activity. The measured chlorine and fluorine concentrations in the samples indicate that the atmospheric loading of hydrochloric acid and hydrofluoric acid was ∼7.0 and 15.0 Mt, respectively. Furthermore, ∼75% of the volatile mass dissolved by the Laki magma was released at the vents and carried by eruption columns to altitudes between 6 and 13 km. The high degree of degassing at the vents is attributed to development of a separated two-phase flow in the upper magma conduit, and implies that high-discharge basaltic eruptions such as Laki are able to loft huge quantities of gas to altitudes where the resulting aerosols can reside for months or even 1–2 years. The atmospheric volatile contribution due to subsequent degassing of the Laki lava flow is only 18 wt.% of the total dissolved in the magma, and these emissions were confined to the lowest regions of the troposphere and therefore important only over Iceland. This study indicates that determination of the amount of sulfur degassed from the Laki magma batch by measurements of sulfur in the volcanic products (the petrologic method) yields a result which is sufficient to account for the mass of aerosols estimated by other methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050136
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  • 4
    Electronic Resource
    Electronic Resource
    The 1991 eruption of Hekla, Iceland (1992)
    Springer
    Bulletin of volcanology 54 (1992), S. 238-246 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The eruption that started in the Hekla volcano in South Iceland on 17 January 1991, and came to an end on 11 March, produced mainly andesitic lava. This lava covers 23 km2 and has an estimated volume of 0.15 km3. This is the third eruption in only 20 years, whereas the average repose period since 1104 is 55 years. Earthquakes, as well as a strain pulse recorded by borehole strainmeters, occurred less than half an hour before the start of the eruption. The initial plinian phase was very short-lived, producing a total of only 0.02 km3 of tephra. The eruption cloud attained 11.5 km in height in only 10 min, but it became detached from the volcano a few hours later. Several fissures were active during the first day of the eruption, including a part of the summit fissure. By the second day, however, the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed. The average effusion rate during the first two days of the eruption was about 800 m3 s−1. After this peak, the effusion rate declined rapidly to 10–20 m3 s−1, then more slowly to 1 m3 s−1, and remained at 1–12 m3 s−1 until the end of the eruption. Site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption. A notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption, but it levelled off on the 6th day and then remained essentially constant. The volume and initial silica content of the lava and tephra, the explosivity and effusion rate during the earliest stage of the eruption, as well as the magnitude attained by the associated earthquakes, support earlier suggestions that these parameters are positively related to the length of the preceeding repose period. The chemical difference between the eruptive material of Hekla itself and the lavas erupted in its vicinity can be explained in terms of a density-stratified magma reservoir located at the bottom of the crust. We propose that the shape of this reservoir, its location at the west margin of a propagating rift, and its association with a crustal weakness, all contribute to the high eruption frequency of Hekla.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00278391
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  • 5
    Electronic Resource
    Electronic Resource
    Fluorine in basalts from Iceland (1986)
    Springer
    Contributions to mineralogy and petrology 94 (1986), S. 263-271 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The fluorine content of Icelandic tholeiitic and alkaline basalts matches values found in similar rocks from other areas. Covariation between fluorine and incompatible minor elements such as potassium or phosphorus is found in evolved tholeiites and alkali basalts. Lack of such covariation in primitive olivine tholeiites indicates that fluorine and other incompatible minor and trace elements are not controlled by minerals such as amphibole, mica or apatite in the mantle residue, and that the covariation between these elements in the evolved basalts cannot be inherited from the mantle. Model calculations on rocks from the Langjökull area show that olivine tholeiite suites are, if derived by simple fractional crystallization, enriched in incompatible elements much in excess of the increase due to crystal removal. These observations are taken to indicate that the well documented covariation between fluorine and other incompatible elements is not established until evolution of the basaltic magma has started in crustal holding chambers. The constancy of element ratios and enrichment in excess of what can be accounted for by crystal fractionation or incremental addition of new batches of primitive magmas does indicate (1) mineral control involving amphibole, mica or apatite and (2) addition of fluorine, potassium and phosphorous from an external source. It is argued that this source is the crustal envelope of the holding chamber.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371435
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  • 6
    Electronic Resource
    Electronic Resource
    Stratigraphy of fossil pigments and Cladophora and its relationship with deposition of tephra in Lake Mývatn, Iceland (1993)
    Springer
    Journal of paleolimnology 8 (1993), S. 15-26 
    Details
    ISSN: 1573-0417
    Keywords: Fossil pigments ; Cyanobacteria ; myxoxanthophyll ; palaeolimnology ; Lake Mývatn ; Iceland ; tephra ; Cladophora
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Fossil plant pigments and Cladophora fragments were analyzed in a 6.53 m long sediment profile from Lake Mývatn, Iceland, covering most of its history of about 2300 years. A decrease in myxoxanthophyll (produced by Cyanobacteria) with time and an increase in the benthic Cladophora reflects a gradual shift from planktonic to benthic primary production as water depth is reduced (to 3.15 m at the core site) because of sediment accumulation. Two periods of relatively high concentrations of myxoxanthophyll coincided with relatively frequent deposition of tephra (volcanic ash) but did neither conform with tectonic activity which might have changed the water level nor the available climatic record. Sediment depth, tephra content and percent undegraded chlorophyll (an indicator of pigment preservation) together could explain 56.7% of the variation in myxoxanthophyll. It is hypothesized that temporary increases in myxoxanthophyll resulted from periodic nutrient enrichment by fresh tephra deposited in the watershed or because tephra increased the erosion of organic soil in the water catchment area. Fluctuations in Cladophora show an inverse relationship with myxoxanthophyll in the uppermost 4 m of the core, and may result from a shading effect of planktonic Cyanobacteria on the phytobenthos or competition for nutrients released by the bottom sediments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210055
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  • 7
    Electronic Resource
    Electronic Resource
    Charged particle spectra in16O induced nuclear collisions at the CERN SPS (1988)
    Springer
    The European physical journal 38 (1988), S. 51-57 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Charged particle multiplicity distributions and pseudo-rapidity density distributions from16O induced nuclear collisions at 200 and 60A GeV are presented. The data were taken, using a minimumbias trigger, with the WA80 set-up at the CERN SPS. In this presentation we focus on how the yield of charged particles depends on the projectile energy, the mass number of the target nucleus and the energy measured in a uranium-plastic sampling calorimeter covering angles close to zero degrees. The data are compared to simulations from the event generator FRITIOF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01574514
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  • 8
    Electronic Resource
    Electronic Resource
    Bioavailability of lead from various milk diets studied in a suckling rat model (1995)
    Springer
    BioMetals 8 (1995), S. 231-236 
    Details
    ISSN: 1572-8773
    Keywords: casein ; intestinal absorption ; lead
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The bioavailability of lead from various milk diets was studied in 14 day old suckling rats. Human milk, infant formula, cow's milk, rat milk and deionized water labeled with 203Pb were given to rat pups by gastric intubation. Animals were killed after 2 or 6 h and the radioactivity in the tissues was measured. At 2 h after administration the lead bioavailability, defined as lead uptake in the body, excluding the gastrointestinal tract, was 47% from water, 42% from human milk, 40% from infant formula, 31% from cow's milk and 11% from rat milk. After 6 h the bioavailability of lead was about 50% from water and human milk, 45% from infant formula and cow's milk, and 36% from rat milk. The blood lead levels in the pups reflected the total body uptake and were also correlated to the brain lead levels. Thus, rat pups given lead in human milk had approximately twice as high lead levels in blood and brain than pups given lead in rat milk. The intestinal absorption of lead was dependent on the milk diet given to the sucklings. In duodenum, the highest uptake of lead was found in rats given water or human milk, whereas in rats given rat or cow's milk the highest uptake of lead was found in ileum. The distribution of lead in cream, whey and casein fractions of the milk diets after in vitro labeling with 203Pb was also studied. The casein fraction in cow's and rat milk contained 90–96% of the total amount of lead in the diet. In infant formula and human milk, 77 and 56% lead was found in the casein fraction, respectively. The higher lead bioavailability observed in the suckling rat fed human milk than in those fed rat and cow's milk may partly be explained by a lower proportion of lead bound to casein in human milk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00143381
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  • 9
    Electronic Resource
    Electronic Resource
    Erosion testing of a Ti--15% Mo alloy (TIMETAL 21SJL160209) under simulated gun barrel conditions (1997)
    Springer
    Journal of materials science 16 (1997), S. 147-151 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abstracts are not published in this journal
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018502329128
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  • 10
    Electronic Resource
    Electronic Resource
    Methylmercury exposure during lactation: Milk concentration and tissue uptake of mercury in the neonatal rat (1991)
    Springer
    Bulletin of environmental contamination and toxicology 46 (1991), S. 255-262 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01691946
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