TY - THES A1 - Abdelfadil, Khaled Mohamed T1 - Geochemistry of Variscan lamprophyre magmatism in the Saxo-Thuringian Zone N2 - Lamprophyres are mantle-derived magmatic rocks, commonly occurring as dikes. They are readily identified from their field setting, petrography, chemical and mineralogical composition. These rocks not only provide important information on melting processes in the mantle, but also on geodynamic processes modifying the mantle. There are numerous occurrences of lamprophyres in the Saxo-Thuringian Zone of Variscan Central Europe, which are useful to track the variable effects of the Variscan orogeny on local mantle evolution. This work presents and evaluates the mineralogical, geochemical, and Sr-Nd-Pb isotopic data of late-Variscan calc-alkaline lamprophyres, post-Variscan ultramafic lamprophyres, of alkaline basalt from Lusatia, and, for comparison, of pre-Variscan gabbros. In addition, lithium isotopic signatures combined with Sr-Nd-Pb isotopic data of late-Variscan calc-alkaline lamprophyres from three different Variscan Domains (i.e., Erzgebirge, Lusatia, and Sudetes) are used to assess compositional changes of the mantle during Variscan orogeny. N2 - Lamprophyre sind porphyrische, aus Mantelschmelzen gebildete Gesteine, die meist in Form von Gängen auftreten. Sie zeichnen sich durch auffällige und charakteristische texturelle, chemische und mineralogische Eigenschaften aus. Als ehemalige Mantelschmelzen liefern sie Information sowohl über Bedingungen der Schmelzbildung im Mantel als auch über geodynamische Prozesse, die zu metasomatischer Veränderung des Mantels geführt haben. Im Saxothuringikum Mitteleuropas, am Nordrand des Böhmischen Massivs, gibt es zahlreiche Lamprophyrvorkommen, die hier zur Charakterisierung der Mantelentwicklung während der variszischen Orogenese dienen. Die vorliegende Arbeit befaßt sich mit den mineralogischen, geochemischen und isotopischen (Sr-Nd-Pb) Signaturen von spätvariszischen kalkalkalischen Lamprophyren, von postvariszischen ultramafischen Lamprophyren, von Alkalibasalten der Lausitz und, zum Vergleich, von prävariszischen Gabbros. Darüberhinaus nutzt die Arbeit Lithium-Isotopensignaturen kombiniert mit Sr-Nd-Pb–Isotopendaten spätvariszischer kalkalkalischer Lamprophyre aus drei variszischen Domänen (Erzgebirge, Lausitz, Sudeten) zur Erkundung der lokalen Mantelüberprägungen während der variszischen Orogenese. T2 - Geochemie der variszischen Lamprophyre in der saxothüringischen Zone KW - lamprophyre KW - Lusatia KW - Erzgebirge KW - Saxo-Thuringia Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-68854 ER - TY - JOUR A1 - Abdrakhmatov, Kanatbek E. A1 - Walker, R. T. A1 - Campbell, G. E. A1 - Carr, A. S. A1 - Elliott, A. A1 - Hillemann, Christian A1 - Hollingsworth, J. A1 - Landgraf, Angela A1 - Mackenzie, D. A1 - Mukambayev, A. A1 - Rizza, M. A1 - Sloan, R. A. T1 - Multisegment rupture in the 11 July 1889 Chilik earthquake (M-w 8.0-8.3), Kazakh Tien Shan, interpreted from remote sensing, field survey, and paleoseismic trenching JF - Journal of geophysical research : Solid earth N2 - The 11 July 1889 Chilik earthquake (M-w 8.0-8.3) forms part of a remarkable sequence of large earthquakes in the late nineteenth and early twentieth centuries in the northern Tien Shan. Despite its importance, the source of the 1889 earthquake remains unknown, though the macroseismic epicenter is sited in the Chilik valley, similar to 100 km southeast of Almaty, Kazakhstan (similar to 2 million population). Several short fault segments that have been inferred to have ruptured in 1889 are too short on their own to account for the estimated magnitude. In this paper we perform detailed surveying and trenching of the similar to 30 km long Saty fault, one of the previously inferred sources, and find that it was formed in a single earthquake within the last 700 years, involving surface slip of up to 10 m. The scarp-forming event, likely to be the 1889 earthquake, was the only surface-rupturing event for at least 5000 years and potentially for much longer. From satellite imagery we extend the mapped length of fresh scarps within the 1889 epicentral zone to a total of similar to 175 km, which we also suggest as candidate ruptures from the 1889 earthquake. The 175 km of rupture involves conjugate oblique left-lateral and right-lateral slip on three separate faults, with step overs of several kilometers between them. All three faults were essentially invisible in the Holocene geomorphology prior to the last slip. The recurrence interval between large earthquakes on any of these faults, and presumably on other faults of the Tien Shan, may be longer than the timescale over which the landscape is reset, providing a challenge for delineating sources of future hazard. Y1 - 2016 U6 - https://doi.org/10.1002/2015JB012763 SN - 2169-9313 SN - 2169-9356 VL - 121 SP - 4615 EP - 4640 PB - American Geophysical Union CY - Washington ER - TY - THES A1 - Abon, Catherine Cristobal T1 - Radar-based rainfall retrieval for flood forecasting in a meso-scale catchment BT - the Philippines Y1 - 2015 ER - TY - JOUR A1 - Abon, Catherine Cristobal A1 - Kneis, David A1 - Crisologo, Irene A1 - Bronstert, Axel A1 - David, Carlos Primo Constantino A1 - Heistermann, Maik T1 - Evaluating the potential of radar-based rainfall estimates for streamflow and flood simulations in the Philippines JF - GEOMATICS NATURAL HAZARDS & RISK N2 - This case study evaluates the suitability of radar-based quantitative precipitation estimates (QPEs) for the simulation of streamflow in the Marikina River Basin (MRB), the Philippines. Hourly radar-based QPEs were produced from reflectivity that had been observed by an S-band radar located about 90 km from the MRB. Radar data processing and precipitation estimation were carried out using the open source library wradlib. To assess the added value of the radar-based QPE, we used spatially interpolated rain gauge observations (gauge-only (GO) product) as a benchmark. Rain gauge observations were also used to quantify rainfall estimation errors at the point scale. At the point scale, the radar-based QPE outperformed the GO product in 2012, while for 2013, the performance was similar. For both periods, estimation errors substantially increased from daily to the hourly accumulation intervals. Despite this fact, both rainfall estimation methods allowed for a good representation of observed streamflow when used to force a hydrological simulation model of the MRB. Furthermore, the results of the hydrological simulation were consistent with rainfall verification at the point scale: the radar-based QPE performed better than the GO product in 2012, and equivalently in 2013. Altogether, we could demonstrate that, in terms of streamflow simulation, the radar-based QPE can perform as good as or even better than the GO product - even for a basin such as the MRB which has a comparatively dense rain gauge network. This suggests good prospects for using radar-based QPE to simulate and forecast streamflow in other parts of the Philippines where rain gauge networks are not as dense. Y1 - 2016 U6 - https://doi.org/10.1080/19475705.2015.1058862 SN - 1947-5705 SN - 1947-5713 VL - 7 SP - 1390 EP - 1405 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Abouserie, Ahed A1 - Zehbe, Kerstin A1 - Metzner, Philipp A1 - Kelling, Alexandra A1 - Günter, Christina A1 - Schilde, Uwe A1 - Strauch, Peter A1 - Körzdörfer, Thomas A1 - Taubert, Andreas T1 - Alkylpyridinium Tetrahalidometallate Ionic Liquids and Ionic Liquid Crystals: Insights into the Origin of Their Phase Behavior JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry. KW - Ionic liquids KW - Alkylpyridinium salts KW - Structure elucidation KW - Phase transitions Y1 - 2017 U6 - https://doi.org/10.1002/ejic.201700826 SN - 1434-1948 SN - 1099-0682 SP - 5640 EP - 5649 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Abouserie, Ahed A1 - Zehbe, Kerstin A1 - Metzner, Philipp A1 - Kelling, Alexandra A1 - Günter, Christina A1 - Schilde, Uwe A1 - Strauch, Peter A1 - Körzdörfer, Thomas A1 - Taubert, Andreas T1 - Alkylpyridinium Tetrahalidometallate Ionic Liquids and Ionic Liquid Crystals: Insights into the Origin of Their Phase Behavior JF - European journal of inorganic chemistry : a journal of ChemPubSoc Europe N2 - Six N-alkylpyridinium salts [CnPy](2)[MCl4] (n = 4 or 12 and M = Co, Cu, Zn) were synthesized, and their structure and thermal properties were studied. The [C4Py](2)[MCl4] compounds are monoclinic and crystallize in the space group P2(1)/n. The crystals of the longer chain analogues [C12Py](2)[MCl4] are triclinic and crystallize in the space group P (1) over bar. Above the melting temperature, all compounds are ionic liquids (ILs). The derivatives with the longer C12 chain exhibit liquid crystallinity and the shorter chain compounds only show a melting transition. Consistent with single-crystal analysis, electron paramagnetic resonance spectroscopy suggests that the [CuCl4](2-) ions in the Cu-based ILs have a distorted tetrahedral geometry. KW - Ionic liquids KW - Alkylpyridinium salts KW - Structure elucidation KW - Phase transitions Y1 - 2017 U6 - https://doi.org/10.1002/ejic.201700826 SN - 1434-1948 SN - 1099-0682 SP - 5640 EP - 5649 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Acosta, Veronica Torres A1 - Schildgen, Taylor F. A1 - Clarke, Brian A. A1 - Scherler, Dirk A1 - Bookhagen, Bodo A1 - Wittmann, Hella A1 - von Blanckenburg, Friedhelm A1 - Strecker, Manfred T1 - Effect of vegetation cover on millennial-scale landscape denudation rates in East Africa JF - Lithosphere N2 - The mechanisms by which climate and vegetation affect erosion rates over various time scales lie at the heart of understanding landscape response to climate change. Plot-scale field experiments show that increased vegetation cover slows erosion, implying that faster erosion should occur under low to moderate vegetation cover. However, demonstrating this concept over long time scales and across landscapes has proven to be difficult, especially in settings complicated by tectonic forcing and variable slopes. We investigate this problem by measuring cosmogenic Be-10-derived catchment-mean denudation rates across a range of climate zones and hillslope gradients in the Kenya Rift, and by comparing our results with those published from the Rwenzori Mountains of Uganda. We find that denudation rates from sparsely vegetated parts of the Kenya Rift are up to 0.13 mm/yr, while those from humid and more densely vegetated parts of the Kenya Rift flanks and the Rwenzori Mountains reach a maximum of 0.08 mm/yr, despite higher median hillslope gradients. While differences in lithology and recent land-use changes likely affect the denudation rates and vegetation cover values in some of our studied catchments, hillslope gradient and vegetation cover appear to explain most of the variation in denudation rates across the study area. Our results support the idea that changing vegetation cover can contribute to complex erosional responses to climate or land-use change and that vegetation cover can play an important role in determining the steady-state slopes of mountain belts through its stabilizing effects on the land surface. Y1 - 2015 U6 - https://doi.org/10.1130/L402.1 SN - 1941-8264 SN - 1947-4253 VL - 7 IS - 4 SP - 408 EP - 420 PB - American Institute of Physics CY - Boulder ER - TY - THES A1 - Adhikari, Rishi Ram T1 - Quantification of total microbial biomass and metabolic activity in subsurface sediments T1 - Quantification of total microbial biomass and metabolic activity in subsurface sediments N2 - Metabolically active microbial communities are present in a wide range of subsurface environments. Techniques like enumeration of microbial cells, activity measurements with radiotracer assays and the analysis of porewater constituents are currently being used to explore the subsurface biosphere, alongside with molecular biological analyses. However, many of these techniques reach their detection limits due to low microbial activity and abundance. Direct measurements of microbial turnover not just face issues of insufficient sensitivity, they only provide information about a single specific process but in sediments many different process can occur simultaneously. Therefore, the development of a new technique to measure total microbial activity would be a major improvement. A new tritium-based hydrogenase-enzyme assay appeared to be a promising tool to quantify total living biomass, even in low activity subsurface environments. In this PhD project total microbial biomass and microbial activity was quantified in different subsurface sediments using established techniques (cell enumeration and pore water geochemistry) as well as a new tritium-based hydrogenase enzyme assay. By using a large database of our own cell enumeration data from equatorial Pacific and north Pacific sediments and published data it was shown that the global geographic distribution of subseafloor sedimentary microbes varies between sites by 5 to 6 orders of magnitude and correlates with the sedimentation rate and distance from land. Based on these correlations, global subseafloor biomass was estimated to be 4.1 petagram-C and ~0.6 % of Earth's total living biomass, which is significantly lower than previous estimates. Despite the massive reduction in biomass the subseafloor biosphere is still an important player in global biogeochemical cycles. To understand the relationship between microbial activity, abundance and organic matter flux into the sediment an expedition to the equatorial Pacific upwelling area and the north Pacific Gyre was carried out. Oxygen respiration rates in subseafloor sediments from the north Pacific Gyre, which are deposited at sedimentation rates of 1 mm per 1000 years, showed that microbial communities could survive for millions of years without fresh supply of organic carbon. Contrary to the north Pacific Gyre oxygen was completely depleted within the upper few millimeters to centimeters in sediments of the equatorial upwelling region due to a higher supply of organic matter and higher metabolic activity. So occurrence and variability of electron acceptors over depth and sites make the subsurface a complex environment for the quantification of total microbial activity. Recent studies showed that electron acceptor processes, which were previously thought to thermodynamically exclude each other can occur simultaneously. So in many cases a simple measure of the total microbial activity would be a better and more robust solution than assays for several specific processes, for example sulfate reduction rates or methanogenesis. Enzyme or molecular assays provide a more general approach as they target key metabolic compounds. Since hydrogenase enzymes are ubiquitous in microbes, the recently developed tritium-based hydrogenase radiotracer assay is applied to quantify hydrogenase enzyme activity as a parameter of total living cell activity. Hydrogenase enzyme activity was measured in sediments from different locations (Lake Van, Barents Sea, Equatorial Pacific and Gulf of Mexico). In sediment samples that contained nitrate, we found the lowest cell specific enzyme activity around 10^(-5) nmol H_(2) cell^(-1) d^(-1). With decreasing energy yield of the electron acceptor used, cell-specific hydrogenase activity increased and maximum values of up to 1 nmol H_(2) cell^(-1) d^(-1) were found in samples with methane concentrations of >10 ppm. Although hydrogenase activity cannot be converted directly into a turnover rate of a specific process, cell-specific activity factors can be used to identify specific metabolism and to quantify the metabolically active microbial population. In another study on sediments from the Nankai Trough microbial abundance and hydrogenase activity data show that both the habitat and the activity of subseafloor sedimentary microbial communities have been impacted by seismic activities. An increase in hydrogenase activity near the fault zone revealed that the microbial community was supplied with hydrogen as an energy source and that the microbes were specialized to hydrogen metabolism. N2 - Mikrobielle Gesellschaften und ihre aktiven Stoffwechselprozesse treten in einer Vielzahl von Sedimenten unterschiedlichster Herkunft auf. In der Erforschung dieser tiefen Biosphäre werden derzeit Techniken wie Zellzählungen, Aktivitätsmessungen mit Radiotracer-Versuchen und Analysen der Porenwasserzusammensetzung angewendet, darüber hinaus auch molekularbiologische Analysen. Viele dieser Methoden stoßen an ihre Nachweisgrenze, wenn Sedimente mit geringer Zelldichte und mikrobieller Aktivität untersucht werden. Bei der Untersuchung von Stoffwechselprozessen mit herkömmlichen Techniken kommt dazu, dass von mehreren Prozessen, die zeitgleich ablaufen können, jeweils nur einer erfasst wird. Deswegen wäre die Entwicklung einer neuartigen Messtechnik für die gesamte mikrobielle Aktivität ein wesentlicher Fortschritt für die Erforschung der tiefen Biosphäre. Ein vielversprechender Ansatz, um die gesamte lebende Biomasse auch in Proben mit geringer Aktivität zu bestimmen, ist eine Hydrogenase-Enzym-Versuchsanordnung mit Tritium als quantifizierbarer Messgröße. In dieser Doktorarbeit wurde die gesamte mikrobielle Biomasse und Aktivität von unterschiedlichen Sedimentproben einerseits mit herkömmlichen Methoden (Zellzählungen, Analyse der Porenwasserzusammensetzung) als auch mit einer neu entwickelten Hydrogenase-Enzym-Versuchsanordnung quantifiziert. Mit einer großen Anzahl eigener Zellzählungsdaten von Sedimenten aus dem Äquatorialpazifik und dem Nordpazifik und ergänzenden publizierten Daten konnte gezeigt werden, dass Zellzahlen sich in ihrer globalen geographischen Verteilung je nach Bohrlokation um 5 bis 6 Größenordnungen unterscheiden. Dabei bestehen Korrelationen zur Sedimentationsrate und zur Entfernung zum Land, mit deren Hilfe sich die Gesamtbiomasse in Tiefseesedimenten zu 4,1 Petagramm-C abschätzen lässt. Das entspricht ~0,6 % der Gesamtbiomasse der Erde und ist damit erheblich weniger als in früheren Schätzungen angegeben. Trotz der Korrektur auf diesen Wert spielt die Biomasse der tiefen Biosphäre weiterhin eine erhebliche Rolle in biogeochemischen Kreisläufen. Um die Zusammenhänge zwischen Aktivität der Mikroben, der Häufigkeit ihres Auftretens und Zustrom von organischem Material zu verstehen, wurde eine Expedition ins Auftriebsgebiet des Äquatorialpazifiks und zum nordpazifischen Wirbel durchgeführt. Daten der Sauerstoffaufnahme in Sedimenten des nordpazifischen Wirbels, die mit Sedimentationsraten von 1 mm pro 1000 Jahren abgelagert werden, zeigen, dass mikrobielle Gesellschaften über Millionen von Jahren ohne Zufuhr von frischem organischen Kohlenstoff überleben konnten. Im Gegensatz zum nordpazifischen Wirbel wird in Sedimenten des äquatorialpazifischen Auftriebsgebiets Sauerstoff bei höherer mikrobieller Aktivität und Verfügbarkeit organischer Verbindungen oberflächennah in den ersten Milli- bis Zentimetern komplett umgesetzt. Auftreten und Variabilität von Elektronenakzeptoren nach Tiefe und Bohrlokation machen die tiefe Biosphäre zu einer komplexen Umgebung für die Quantifizierung der gesamten mikrobiellen Aktivität. Aktuelle Studien zeigen das verschiedene Elektronenakzeptorprozesse gleichzeitig ablaufen können, obwohl man bisher davon ausgegangen war, dass diese sich thermodynamisch ausschließen. In vielen Fällen wäre also eine einfache Methode zur Messung der gesamten mikrobiellen Aktivität eine bessere und verlässlichere Lösung aktueller Analyseaufgaben als Messungen mehrerer Einzelprozesse wie beispielsweise Sulfatreduktion und Methanogenese. Enzym-oder Molekular-Versuchsanordnungen sind ein prozessumfassender Ansatz, weil hier Schlüsselkomponenten der Stoffwechselprozesse untersucht werden. Das Hydrogenase-Enzym ist eine solche Schlüsselkomponente und in Mikroben allgegenwärtig. Deshalb kann die Quantifizierung seiner Aktivität mit der neu entwickelten Hydrogenase-Enzym-Versuchsanordnung als Parameter für die gesamte mikrobielle Aktivität der lebenden Zellen verwendet werden. Hydrogenase-Aktivitäten wurden in Sedimenten unterschiedlicher Lokationen (Vansee, Barentssee, Äquatorialpazifik, und Golf von Mexico) gemessen. In Sedimentproben, die Nitrat enthielten, haben wir mit ca. 10^(-5) nmol H_(2) cell^(-1) d^(-1) die geringste zellspezifische Hydrogenase-Aktivität gefunden. Mit geringerem Energiegewinn des genutzten Elektronenakzeptors steigt die zellspezifische Hydrogenase-Aktivität. Maximalwerte von bis zu 1 nmol H_(2) cell^(-1) d^(-1) wurden in Sedimentproben mit >10 ppm Methankonzentration gefunden. Auch wenn die Hydrogenase-Aktivität nicht direkt in die Umsatzrate eines spezifischen Prozesses konvertierbar ist, können zellspezifische Aktivitätsfaktoren verwendet werden, um die metabolisch aktive Mikrobenpopulation zu quantifizieren. In einer weiteren Studie mit Sedimenten des Nankai-Grabens zeigen Daten der Zelldichte und der Hydrogenase-Aktivität einen Einfluss von seismischen Ereignissen auf Lebensraum und Aktivität der mikrobiellen Gesellschaften. Ein Anstieg der Hydrogenase-Aktivität nahe der Verwerfungszone machte deutlich, dass die mikrobiellen Gesellschaften mit Wasserstoff als Energiequelle versorgt wurden und dass die Mikroben auf einen Wasserstoff-Stoffwechsel spezialisiert waren. KW - Hydrogenase KW - Tritium Versuchsanordnung KW - Untergrunduntersuchung der Biosphäre KW - Hydrogenase KW - Tritium Assay KW - Subsurface Biosphere Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-67773 ER - TY - GEN A1 - Adhikari, Rishi Ram A1 - Glombitza, Clemens A1 - Nickel, Julia C. A1 - Anderson, Chloe H. A1 - Dunlea, Ann G. A1 - Spivack, Arthur J. A1 - Murray, Richard W. A1 - D’Hondt, Steven A1 - Kallmeyer, Jens T1 - Hydrogen utilization potential in subsurface sediments T2 - Frontiers in microbiology N2 - Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H(2)ases to successively higher concentrations of H-2 in successively deeper zones. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 447 KW - hydrogenase KW - tritium assay KW - deep biosphere KW - microbial activity KW - Lake Van KW - Barents Sea KW - Equatorial Pacific KW - Gulf of Mexico Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407678 ER - TY - JOUR A1 - Adhikari, Rishi Ram A1 - Glombitza, Clemens A1 - Nickel, Julia C. A1 - Anderson, Chloe H. A1 - Dunlea, Ann G. A1 - Spivack, Arthur J. A1 - Murray, Richard W. A1 - Kallmeyer, Jens T1 - Hydrogen Utilization Potential in Subsurface Sediments JF - Frontiers in microbiology N2 - Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H(2)ases to successively higher concentrations of H-2 in successively deeper zones. KW - hydrogenase KW - tritium assay KW - deep biosphere KW - microbial activity KW - Lake Van KW - Barents Sea KW - Equatorial Pacific KW - Gulf of Mexico Y1 - 2016 U6 - https://doi.org/10.3389/fmicb.2016.00008 SN - 1664-302X VL - 7 PB - Frontiers Research Foundation CY - Lausanne ER -