The petrology and chemistry of the Setberg volcanic region and of the intermediate and acid rocks of Iceland

The tertiary to Mid-Quaternary Setberg volcano in western Iceland consists of two centres. The northern, Centre 1 is tholeiitic and defined by cone sheets, a caldera and a gabbro intrusion. The southern, Centre 2 is chemically transitional between a tholeiitic and an alkalic basalt series, and contains a cone sheet swarm, gabbroic ring features and a major granophyric cone sheet. Each centre can be related to a minor magmachamber at a depth of 2-3 km. General hydrothermal alteration around both centres has resulted in aureoles of epidotization and the development of greenstones, containing garnet in the central areas. Late-Quaternary volcanism in the Setberg area has produced an alkalic basalt succession, ranging from alkalic olivine baalts to benmoreites. This activity is related to the E-W Snaefellsnes volcanic zone and its causes are explained in terms of Icelandic plate tectonics. The tholeiitic seies of centre 1, form a differentiated sequence from olivine tholeiites to rhyolites, contaning a Ca-poor pyroxene and augite in the basic and intermediate rocks, and a large compositional interval devoid of olivine. Plagioclase is the sole feldspar phase. The transistional series of Centre 2 is olivine-bearing throughout, with augite and rare phenocrysts of orthopyroxene in the basalts. Two lineages of differentiated rocks of this series are typified either by iron-enrichment (to icelandites) or by alkali enrichment (to rhyodacites and alkalic-rhyolites). The latter contains anorthoclase and potassic oligoclase or sanidine, as well as sodic pyroxene. Rocks of the alkalic series are olivine and pyroxene-bearing, with anorthoclase appearing in the benmoreites, while phlogopite and hornblende have been found in some of the lavas. Apatite occurs as a phenocryst in members of both the transitional and alkalic series. The origin of the transitional basalt magma is discussed according to two hypotheses. Its formation is accounted for by solidification from above in a magma reservoir of great vertical dimensions, leading, to confinement of the magma to depths where orthopyroxene replaces olivine on the liquidus, resulting in a trend towards undersaturation. The chemistry of the Late-Quaternary alkalic basalts of Setberg and Snaefeilsnes is related to magma generation at greater depths than in the case of the tholeiitic basalts of the Icelandic central volcanic zone. The volume, bimodal distribution and diversity of acid and intermediate magmas in Iceland are discussed. The high proportion of acid to basic volcanic rocks in eastern Iceland is contrasted with 3-4% in the rest of the country. Two types of acid centres are identified: centres of Thingmuli type, where tholeiitic basalts are associated with low-alkalic rhyolites; and alkalic centres, containing comendites, quartz- trachytes, alkalic-rhyolites and associated alkalic basalts or transitional basalts. Peralkaline acid rocks are identified and described from Iceland for the first time. Their genesis is discussed and related to fractionation from alkalic-rhyolites and trachytes by the "plagioclase effect". No evidence has been unearthed in this study which contravenes the hypothesis that the Icelandic acid rocks are a product of fractionation from basic magma

Sulfur mass loading of the atmosphere from volcanic eruptions: Calibration of the ice core record on basis of sulfate aerosol deposition in polar regions from the 1982 El Chichon eruption

Major volcanic eruptions disperse large quantities of sulfur compound throughout the Earth's atmosphere. The sulfuric acid aerosols resulting from such eruptions are scavenged by snow within the polar regions and appear in polar ice cores as elevated acidity layers. Glacio-chemical studies of ice cores can, thus, provide a record of past volcanism, as well as the means for understanding the fate of volcanic sulfur in the atmosphere. The primary objectives of this project are to study the chemistry and physical properties of volcanic fallout in a Greenland Ice Core in order to evaluate the impact of the volcanic gases on the atmospheric chemistry and the total atmospheric mass of volcanic aerosols emitted by major volcanic eruptions. We propose to compare the ice core record to other atmospheric records performed during the last 10 years to investigate transport and deposition of volcanic materials

Some Landmarks in Icelandic Cartography down to the End of the Sixteenth Century

The author presents a survey of the early accounts of voyages to Iceland and describes the maps by navigators from many nations

Exploring Submarine Arc Volcanoes

Three quarters of Earth’s volcanic activity occurs beneath the sea, predominantly along the extensive mid-ocean ridge system that winds its way through the major ocean basins. The style of eruptive activity along mid-ocean ridges has been extensively studied and well characterized. Submarine eruptions at mid-ocean ridges are dominated by effusive production of pillow and sheet-flow lavas at water depths of several thousands meters. The other major style of submarine eruptions occurs along island arcs where subduction of oceanic crust triggers melting of mantle rocks by the release of volatile components, such as water and carbon dioxide. Submarine volcanism constitutes an important component of active island arc systems, although a significant part of arc volcanism can also occur subaerially

Reduction Resistant and Rigid Nitroxide Spin-Labels for DNA and RNA

Post-print (lokagerð höfundar)Electron paramagnetic resonance (EPR) spectroscopy, coupled with site-directed spin labeling (SDSL), is a useful method for studying conformational changes of biomolecules in cells. To employ in-cell EPR using nitroxide-based spin labels, the structure of the nitroxides must confer reduction resistance to withstand the reductive environment within cells. Here, we report the synthesis of two new spin labels, EÇ and EÇm, both of which possess the rigidity and the reduction resistance needed for extracting detailed structural information by EPR spectroscopy. EÇ and EÇm were incorporated into DNA and RNA, respectively, by oligonucleotide synthesis. Both labels were shown to be nonperturbing of the duplex structure. The partial reduction of EÇm during RNA synthesis was circumvented by the protection of the nitroxide as a benzoylated hydroxylamine.The authors acknowledge financial support from the Icelandic Research Fund (173727-051). The authors thank Dr. S. Jonsdottir for assistance with collecting analytical data for structural characterization of new compounds and members of the Sigurdsson research group for helpful discussions.Peer reviewe

Nitroxide‐Derived N‐Oxide Phenazines for Noncovalent Spin‐Labeling of DNA

Post-print (lokagerð höfundar)Two o‐benzoquinone derivatives of isoindoline were synthesized for use as building blocks to incorporate isoindoline nitroxides into different compounds and materials. These o‐quinones were condensed with a number of o‐phenylenediamines to form isoindoline‐phenazines in high yields. Subsequent oxidation gave phenazine‐di‐N‐oxide isoindoline nitroxides that were evaluated for noncovalent and site‐directed spin‐labeling of duplex DNA and RNA that contained abasic sites. Although only minor binding was observed for RNA, the unsubstituted phenazine‐N,N‐dioxide tetramethyl isoindoline nitroxide showed high binding affinity and selectivity towards abasic sites in duplex DNA that contained cytosine as the orphan base.The authors acknowledge financial support from the Icelandic Research Fund (173727-051). The authors thank Dr S. Jonsdottir for assistance with collecting analytical data for structural characterization of new compounds, Dr. Thomas Halbritter for critically reading this manuscript, and the members of the Sigurdsson research group for helpful discussions.Peer reviewe

Benzoyl-Protected Hydroxylamines for Improved Chemical Synthesis of Oligonucleotides Containing Nitroxide Spin Labels

Post-print (lokagerð höfundar)Oligonucleotides containing nitroxide spin labels, used in biophysical studies of nucleic acids, are frequently prepared by chemical synthesis. However, during the synthesis of spin‐labeled oligonucleotides, the nitroxides are partially reduced to the corresponding amines. Here we report that a benzoylated hydroxylamine can be used as a protected form of the nitroxide to avoid this reduction. The benzoyl group is stable through the oligonucleotide synthesis and is readily removed under standard oligonucleotide deprotection conditions, yielding a hydroxylamine that is oxidized in situ to the nitroxide. This method was used to incorporate the rigid spin labels Ç and Çm into DNA and RNA oligonucleotides, respectively, including a doubly labeled 36‐nucleotide long DNAzyme. Enzymatic digestion of the spin‐labeled oligonucleotides and subsequent HPLC analysis showed that the nitroxides were intact. This protecting group strategy facilitates the high‐yielding synthesis of spin‐labeled DNA and RNA oligonucleotides using the phosphoramidite method.The authors acknowledge financial support by the Icelandic Research Fund (141062-051). The authors thank Dr S. Jonsdottir for assistance with collecting analytical data for structural characterization of new compounds and members of the Sigurdsson research group for helpful discussions.Peer reviewe

Nordic treatment practices survey and consensus for treatment of eyelid sebaceous carcinoma

Background The purpose was to describe the Nordic treatment practices and to reach a Nordic consensus for the treatment of sebaceous eyelid carcinoma. Methods The treatment practices data was collected by a questionnaire with 37 questions to the Nordic oculoplastic surgeons and analyzed. A PubMed MEDLINE database search was done to gather data on the published treatment practices and recommendations. A working group that consisted of in minimum one senior consultant from each leading Nordic University Eye Hospital was assigned. A structured interactive method was used to establish the consensus. Results Twenty-four doctors responded to the questionnaire. 23/24 (96%) of the respondents took a biopsy before surgery. Regional lymph node scanning was routinely done by 14/23 (61%) and a systemic screening of a metastatic disease by 13/23 (57%). 6/22 (27%) never took conjunctival mapping biopsies and 12/23 (52%) never screened for Muir- Torre. Respondents used Mohs surgery, frozen section or multi-stage excision with delayed closure, and 5-6 mm was the mostly preferred margin. Sentinel lymph node biopsy was a possible option for 9/22 (41%) and cryotherapy and Mitomycin C for 6/22 (27%) respondents. 50% of respondents considered radiation as a treatment option. 15/16 (94%) respondents always followed-up their patients, most for 5 years. Two thirds scanned regional lymph nodes during the follow-up. Consensus was reached for 18 statements representing three domains: preoperative work-up, treatment and follow-up. Conclusion Treatment practices differ in between the five Nordic countries which have similar public health care systems. In the article the authors present a Nordic consensus for the treatment of eyelid sebaceous carcinoma.Peer reviewe

Marine Investigations of Greece\u27s Santorini Volcanic Field

The most recent major explosive eruption of the Santorini volcano in Greece—around 3600 years before present (B.P.), often referred to as the Minoan eruption—is one of the largest volcanic events known in historical time and has been the subject of intense volcanological and archeological studies [Druitt et al., 1999]. The submarine volcano Kolumbo, located seven kilometers northeast of Santorini and associated with Santorini\u27s tectonic system, erupted explosively in 1650 A.D., resulting in fatalities on the island of Thera [Fouqué, 1879]. A large fraction of the erupted products from the Minoan eruption has been deposited in the sea but, up to now, only has been studied in distal marine sediments. As part of a collaborative project between the University of Rhode Island (Narragansett), the Hellenic Centre of Marine Research (Athens, Greece), and the Institute of Geology and Mineral Exploration (Athens), a marine geological survey was conducted around Santorini from April to June 2006. he new work now shows that the volume of the Minoan eruption may be comparable to that of the largest known historical eruption, the 1815 eruption of Tambora in Indonesia [Sigurdsson and Carey, 1989]; provides insights into the depositional processes and size of the Minoan eruption; and led to the discovery of important submarine hydrothermal vents with active mineralization