Time filter

Source Type

Reykjavík, Iceland

Marteinsson V.,Environment and Genetics | Marteinsson V.,Agricultural University of Iceland | Klonowski A.,Environment and Genetics | Reynisson E.,Environment and Genetics | And 3 more authors.
Biogeosciences | Year: 2015

Colonization of life on Surtsey has been observed systematically since the formation of the island 50 years ago. Although the first colonisers were prokaryotes, such as bacteria and blue-green algae, most studies have been focused on the settlement of plants and animals but less on microbial succession. To explore microbial colonization in diverse soils and the influence of associated vegetation and birds on numbers of environmental bacteria, we collected 45 samples from different soil types on the surface of the island. Total viable bacterial counts were performed with the plate count method at 22, 30 and 37 °C for all soil samples, and the amount of organic matter and nitrogen (N) was measured. Selected samples were also tested for coliforms, faecal coliforms and aerobic and anaerobic bacteria. The subsurface biosphere was investigated by collecting liquid subsurface samples from a 181 m borehole with a special sampler. Diversity analysis of uncultivated biota in samples was performed by 16S rRNA gene sequences analysis and cultivation. Correlation was observed between nutrient deficits and the number of microorganisms in surface soil samples. The lowest number of bacteria (1 × 104 1 × 105 cells gg-1) was detected in almost pure pumice but the count was significantly higher (1 × 1061 × 109 cells gg-1) in vegetated soil or pumice with bird droppings. The number of faecal bacteria correlated also to the total number of bacteria and type of soil. Bacteria belonging to Enterobacteriaceae were only detected in vegetated samples and samples containing bird droppings. The human pathogens Salmonella, Campylobacter and Listeria were not in any sample. Both thermophilic bacteria and archaea 16S rDNA sequences were found in the subsurface samples collected at 145 and 172 m depth at 80 and 54 °C, respectively, but no growth was observed in enrichments. The microbiota sequences generally showed low affiliation to any known 16S rRNA gene sequences. © 2015 Author(s). Source

Marks N.,University of California at Davis | Schiffman P.,University of California at Davis | Zierenberg R.A.,University of California at Davis | Franzson H.,ISOR | Fridleifsson G.O.,Hitaveita Sudurnesja Ltd. Brekkustigur 36
Journal of Volcanology and Geothermal Research | Year: 2010

The Reykjanes geothermal system is a seawater-recharged hydrothermal system that appears to be analogous to seafloor hydrothermal systems in terms of host rock type and low water/rock alteration. The similarities make the Reykjanes system a useful proxy for seafloor vents. At some time during the Pleistocene, the system was dominated by meteoric water recharge, and fluid composition at Reykjanes has evolved through time as a result of changing proportions of meteoric water influx as well as differing pressure and temperature conditions. The purpose of this study is to characterize secondary mineralization, degree of metasomatic alteration, and bulk composition of cuttings from well RN-17 from the Reykjanes geothermal system. The basaltic host rock includes hyaloclastite, breccia, tuff, extrusive basalt, diabase, as well as a marine sedimentary sequence. The progressive hydrothermal alteration sequence observed with increasing depth results from reaction of geothermal fluids with the basaltic host rock. An assemblage of greenschist facies alteration minerals, including actinolite, prehnite, epidote and garnet, occurs at depths as shallow as 350 m; these minerals are commonly found in Icelandic geothermal systems at temperatures above 250 °C (Bird and Spieler, 2004). This requires hydrostatic pressures that exceed the present-day depth to boiling point curve, and therefore must record alteration at higher fluid pressures, perhaps as a result of Pleistocene glaciation. Major, minor, and trace element profiles of the cuttings indicate transitional MORB to OIB composition with limited metasomatic shifts in easily mobilized elements. Changes in MgO, K2O and loss on ignition indicate that metasomatism is strongly correlated with protolith properties. The textures of alteration minerals reveal alteration style to be strongly dependent on protolith as well. Hyaloclastites are intensely altered with calc-silicate alteration assemblages comprising calcic hydrothermal plagioclase, grandite garnet, prehnite, epidote, hydrothermal clinopyroxene, and titanite. In contrast, crystalline basalts and intrusive rocks display a range in alteration intensity from essentially unaltered to pervasive and nearly complete albitization of igneous feldspar and uralitization of clinopyroxene. Hydrothermal anorthite (An92-An98) occurs in veins in the most altered basalt cuttings and is significantly more calcic than igneous feldspar (An48-An79). Amphibole compositions change from actinolite to hornblende at depth. Hydrothermal clinopyroxene, which occurs in veins, has greater variation in Fe content and is systematically more calcic than igneous pyroxene and also lacks uralitic textures. Solid solutions of prehnite, epidote, and garnet indicate evolving equilibria with respect to aluminum and ferric iron. © 2009 Elsevier B.V. All rights reserved. Source

Schiffman P.,University of California at Davis | Zierenberg R.A.,University of California at Davis | Mortensen A.K.,ISOR | Frioleifsson G.T.,HS Orka hf | Elders W.A.,University of California at Riverside
Geothermics | Year: 2014

A rhyolite magma body within the Krafla geothermal system that was encountered at a depth of 2.1km during drilling of the IDDP-1 borehole is producing high temperature metamorphism within a conductive boundary layer (CBL) in adjacent host rocks. Cuttings recovered during drilling within a few meters of the intrusive contact in IDDP-1 are mainly comprised of granoblastic hornfelses, the rock type which confirms the presence of the CBL at the base of the IDDP-1 bore hole. The two pyroxenes in these hornfelses record temperatures that are in the range of 800-950°C. The minimum heat flow across the CBL is 23Wm-2. Country rocks at distances beyond 30m of the intrusive contact are essentially unaltered, implying that they have been emplaced very recently and/or as yet unaffected by hydrothermal fluid flow. © 2012 Elsevier Ltd. Source

Palsson B.,Landsvirkjun | Holmgeirsson S.,Landsvirkjun | Guomundsson T.,Landsvirkjun | Boasson H.,Mannvit | And 3 more authors.
Geothermics | Year: 2014

The first well of three proposed by the Iceland Deep Drilling Project (IDDP) was drilled in the Krafla Geothermal Field in 2008-2009 by Landsvirkjun, the National Power Company of Iceland. The well was designed to reach supercritical conditions at 4500. m, temperatures above 374. °C and pressures above 22. MPa. Drilling progress was as planned down to around 2000. m when drilling became quite challenging, including becoming stuck at 2094 and 2095. m depth, followed by twist offs and subsequent side tracking. Finally, drilling came to an end at 2096. m depth in the third leg when cuttings of fresh glass indicated the presence of a magma body at the bottom. As the well had such a rigorous well design, the steering committee of the IDDP decided to complete and flow test the well, rather than abandoning it. The well was very powerful and the project has proved to be a valuable experience for drilling supercritical wells in the future and what happens when magma is encountered. Most importantly, it has been proven that it is possible to drill and complete a well in a very hot zone and produce fluid from an environment near a magma body. If sustained long term production proves possible, the drilling of well IDDP-1 will mark a new era in power production in Krafla. © 2013. Source

Hannington M.,Leibniz Institute of Marine Science | Hannington M.,University of Ottawa | Hardardottir V.,ISOR | Garbe-Schonberg D.,University of Kiel | Brown K.L.,GEOKEM
Nature Geoscience | Year: 2016

The origins of high-grade hydrothermal ore deposits are debated, but active geothermal systems provide important clues to their formation. The highest concentrations of gold are found in geothermal systems with direct links to island arc magmatism. Yet, similar concentrations have also been found in the absence of any input from arc magmas, for example, in the Reykjanes geothermal field, Iceland. Here we analyse brine samples taken from deep wells at Reykjanes and find that gold concentrations in the reservoir zone have increased over the past seven years from an average of 3 ppb to 14 ppb. The metal concentrations greatly exceed the maximum solubility of gold in the reservoir under saturated conditions and are now nearly two orders of magnitude higher than in mid-ocean ridge black smoker fluids - the direct analogues of Reykjanes deep liquids. We suggest that ongoing extraction of brine, the resulting pressure drop, and increased boiling have caused gold to drop out of solution and become trapped in the reservoir as a colloidal suspension. This process may explain how the stock of metal in the reservoirs of fossil geothermal systems could have increased over time and thus become available for the formation of gold-rich ore deposits. © 2016 Macmillan Publishers Limited. All rights reserved. Source

Discover hidden collaborations