TY  - JOUR
AB  - On April 23rd, 2019, the Aguas Zarcas meteorite fall occurred in Costa Rica. Because the meteorite was quickly recovered, it contains valuable extraterrestrial materials that have not been contaminated by terrestrial processes. Our X-ray computed tomography (XCT) and scanning electron microscopy (SEM) results on various pre-rain fragments from earlier work (Kerraouch et al., 2020; 2021) revealed several distinct lithologies: Two distinct metal-rich lithologies (Met-1 and Met-2), a CM1/2 lithology, a C1 lithology, and a brecciated CM2 lithology consisting of different petrologic types. Here, we further examined these lithologies in the brecciated Aguas Zarcas meteorite and report new detailed mineralogical, chemical, isotopic, and organic matter characteristics. In addition to petrographic differences, the lithologies also display different chemical and isotopic compositions. The variations in their bulk oxygen isotopic compositions indicate that the various lithologies formed in different environments and/or under diverse conditions (e.g., water/rock ratios). Each lithology experienced a different hydration period during its evolution. Together, this suggests that multiple precursor parent bodies may have been involved in these processes of impact brecciation, mixing, and re-assembly. The Cr and Ti isotopic data for both the CM1/2 and Met-1 lithology are consistent with those of other CM chondrites, even though Met-1 displays a significantly lower ε50Ti isotopic composition that may be attributable to sample heterogeneities on the bulk meteorite scale and may reflect variable abundances of refractory phases in the different lithologies of Aguas Zarcas. Finally, examination of the organic matter of the various lithologies also suggests no strong evidence of thermal events, but a short-term heating cannot completely be excluded. Raman parameters indicate that the peak temperature has been lower than that for Yamato-793321 (CM2, ∼400 °C). Considering the new information presented in this study, we now better understand the origin and formation history of the Aguas Zarcas daughter body.
AU  - Kerraouch, I.*
AU  - Kebukawa, Y.*
AU  - Bischoff, A.*
AU  - Zolensky, M.E.*
AU  - Wölfer, E.*
AU  - Hellmann, J.L.*
AU  - Ito, M.*
AU  - King, A.*
AU  - Trieloff, M.*
AU  - Barrat, J.A.*
AU  - Schmitt-Kopplin, P.
AU  - Pack, A.*
AU  - Patzek, M.*
AU  - Hanna, R.D.*
AU  - Fockenberg, T.*
AU  - Marrocchi, Y.*
AU  - Fries, M.*
AU  - Mathurin, J.*
AU  - Dartois, E.*
AU  - Duprat, J.*
AU  - Engrand, C.*
AU  - Deniset, A.*
AU  - Dazzi, A.*
AU  - Kiryu, K.*
AU  - Igisu, M.*
AU  - Shibuya, T.*
AU  - Wakabayashi, D.*
AU  - Yamashita, S.*
AU  - Takeichi, Y.*
AU  - Takahashi, Y.*
AU  - Ohigashi, T.*
AU  - Kodama, Y.*
AU  - Kondo, M.*
C1  - 65942
C2  - 52992
SP  - 155-186
TI  - Heterogeneous nature of the carbonaceous chondrite breccia Aguas Zarcas – Cosmochemical characterization and origin of new carbonaceous chondrite lithologies.
JO  - Geochim. Cosmochim. Acta
VL  - 334
PY  - 2022
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - On September 12, 2019 at 12:49:48 (UT) a 
      bolide was observed by hundreds of eye-witnesses from the Netherlands, 
      Germany, Belgium, Denmark and the UK. One day later a small meteorite 
      stone was found by accident in Flensburg. The presence of short-lived 
      cosmogenic radionuclides with half-lives as short as 16 days proves the 
      recent exposure of the found object to cosmic rays in space linking it 
      clearly to the bolide event. An exceptionally short exposure time of 
      ∼5000 years was determined. The 24.5 g stone has a fresh black fusion 
      crust, a low density of <2 g/cm3, and a magnetic susceptibility of logχ = 4.35 (χ in 10−9 m3/kg).
       The rock consists of relict chondrules and clusters of sulfide and 
      magnetite grains set in a fine-grained matrix. The most abundant phases 
      are phyllosilicates. Carbonates (∼3.9 vol.%) occur as calcites, 
      dolomites, and a Na-rich phase. The relict chondrules (often surrounded 
      by sulfide laths) are free of anhydrous silicates and contain abundant 
      serpentine. Lithic clasts are also surrounded by similar sulfide laths 
      partly intergrown with carbonates. 53Mn-53Cr ages 
      of carbonates in Flensburg indicate that brecciation and contemporaneous
       formation of the pyrrhotite-carbonate intergrowths by hydrothermal 
      activities occurred no later than 4564.6 ± 1.0 Ma (using the angrite 
      D'Orbigny as the Mn-Cr age anchor). This corresponds to 2.6 ± 1.0 or 
      3.4 ± 1.0 Ma after formation of CAIs, depending on the exact absolute 
      age of CAIs. This is the oldest dated evidence for brecciation and 
      carbonate formation, which likely occurred during parent body growth and
       incipient heating due to decay of 26Al.In the three oxygen isotope diagram, Flensburg plots at the 16O-rich
       end of the CM chondrite field and in the transition field to CV-CK-CR 
      chondrites. The mass-dependent Te isotopic composition of Flensburg is 
      slightly different from mean CM chondrites and is most similar to those 
      of the ungrouped C2 chondrite Tagish Lake. On the other hand, 50Ti and 54Cr isotope anomalies indicate that Flensburg is similar to CM chondrites, as do the ∼10 wt.% H2O
       of the bulk material. Yet, the bulk Zn, Cu, and Pb concentrations are 
      about 30% lower than those of mean CM chondrites. The He, Ne, and Ar 
      isotopes of Flensburg show no solar wind contribution; its trapped noble
       gas signature is similar to that of CMs with a slightly lower 
      concentration of 20Netr.Based 
      on the bulk H, C, and N elemental abundances and isotopic compositions, 
      Flensburg is unique among chondrites, because it has the lightest bulk H
       and N isotopic compositions of any type 1 or 2 chondrite investigated 
      so far. Moreover, the number of soluble organic compounds in Flensburg 
      is even lower than that of the brecciated CI chondrite Orgueil.The
       extraordinary significance of Flensburg is evident from the observation
       that it represents the oldest chondrite sample in which the 
      contemporaneous episodes of aqueous alteration and brecciation have been
       preserved. The characterization of a large variety of carbonaceous 
      chondrites with different alteration histories is important for 
      interpreting returned samples from the OSIRIS-REx and Hayabusa 2 
      missions.
AU  - Bischoff, A.*
AU  - Alexander, C.M.O.D.*
AU  - Barrat, J.A.*
AU  - Burkhardt, C.*
AU  - Busemann, H.*
AU  - Degering, D.*
AU  - Di Rocco, T.*
AU  - Fischer, M.*
AU  - Fockenberg, T.*
AU  - Foustoukos, D.I.*
AU  - Gattacceca, J.*
AU  - Godinho, J.R.A.*
AU  - Harries, D.*
AU  - Heinlein, D.*
AU  - Hellmann, J.L.*
AU  - Hertkorn, N.
AU  - Holm, A.*
AU  - Jull, A.J.T.*
AU  - Kerraouch, I.*
AU  - King, A.J.*
AU  - Kleine, T.*
AU  - Koll, D.*
AU  - Lachner, J.*
AU  - Ludwig, T.*
AU  - Merchel, S.*
AU  - Mertens, C.A.K.*
AU  - Morino, P.*
AU  - Neumann, W.*
AU  - Pack, A.*
AU  - Patzek, M.*
AU  - Pavetich, S.*
AU  - Reitze, M.P.*
AU  - Rüfenacht, M.*
AU  - Rugel, G.*
AU  - Schmidt, C.*
AU  - Schmitt-Kopplin, P.*
AU  - Schönbächler, M.*
AU  - Trieloff, M.*
AU  - Wallner, A.*
AU  - Wimmer, K.*
AU  - Wölfer, E.*
C1  - 60546
C2  - 49366
CY  - The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1gb, England
SP  - 142-186
TI  - The old, unique C1 chondrite Flensburg – Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies.
JO  - Geochim. Cosmochim. Acta
VL  - 293
PB  - Pergamon-elsevier Science Ltd
PY  - 2021
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Chondrites are exhumed from their parent bodies by impacts, which at the same time can result in heating and mechanical modification (compaction, deformation, fracturing, etc.). However, whether impacts are responsible for the occurrence of heated C2s remains controversial since radiogenic and solar heating have also been invoked to explain them. Here we report a Raman and infrared study of the composition and structure of Insoluble Organic Matter (IOM) in a series of 39 CM and C2-ungrouped chondrites. These parameters are tracers of the extent and nature of thermal metamorphism a meteorite has experienced and reflect the degree to which the thermally driven and irreversible carbonization of IOM has proceeded. We propose a carbon-based classification of heated C2 chondrites that reveals a high occurrence frequency of thermally processed C2 chondrites (>36%). This classification is in agreement with the mineralogical classification scheme of Nakamura (2005). Strongly heated C2 chondrites (PCA 02012, PCA 91008, Y 96720) display an IOM structural evolution that is dissimilar to that of type 3 chondrites that experienced long duration radiogenic thermal metamorphism. These differences almost certainly reflect kinetic constraints on IOM modification during short duration heating events. QUE 93005 is a weakly heated chondrite that experienced a retrograde aqueous alteration. Its very aliphatic-rich IOM points to a parent body hydrogenation through interactions with water. The closed-system conditions required by this mechanism could be satisfied by a kinetic confinement during a very short duration impact. MET 01072, a heavily compacted and uni-axially deformed chondrite, did not experience post-accretional heating. In this case, the deformation features probably reflect a low-velocity impact. In contrast, the weakly metamorphosed chondrite EET 96029 experienced one or several low pressure impacts that triggered mild heating and partial dehydration without deformation features. The study of a series of lithologies from the Tagish Lake C2-ungrouped chondrite confirms the coexistence of various degrees of post-accretional alteration, the most altered lithologies having experienced a moderate degree of heating. Overall, the high prevalence of heating in C2 chondrites, the evidence of short-duration heating in the most heated C2s and the ability of low velocity collisions to trigger heating favor impacts (against solar heating), as the dominant heating mechanism. Finally, our set of data does not support the action of a low temperature oxidation process that would control the aliphatic abundance in unheated primitive C2s.
AU  - Quirico, E.*
AU  - Bonal, L.*
AU  - Beck, P.*
AU  - Alexander, C.M.O.D.*
AU  - Yabuta, H.*
AU  - Nakamura, T.*
AU  - Nakato, A.*
AU  - Flandinet, L.*
AU  - Montagnac, G.*
AU  - Schmitt-Kopplin, P.
AU  - Herd, C.D.K.*
C1  - 54322
C2  - 45501
CY  - The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1gb, England
SP  - 17-37
TI  - Prevalence and nature of heating processes in CM and C2-ungrouped chondrites as revealed by insoluble organic matter.
JO  - Geochim. Cosmochim. Acta
VL  - 241
PB  - Pergamon-elsevier Science Ltd
PY  - 2018
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Microcosm experiments with the well-studied denitrifier Thaurera aromatica show a link between a higher maximum membrane concentration (MMC) of the toxic organic solvents 1-octanol and 4-chlorophenol and a higher degree of saturation (DoS) of the fatty acids in the cell membrane. This coincides with less pronounced stable isotope fractionation during denitrification. We suggest that the change in cell membrane fluidity and the cell's stress response leads to a decrease in nitrate transport across the cell membrane and/or an increase in the relative ratio of respiratory nitrate reduction rate versus efflux of unreacted nitrate. Both models show that the apparent kinetic isotope effect (AKIE) approach unity and thus reduce the extent of the resulting stable isotope enrichment factor epsilon N-15-NO3 in dissolved nitrate during denitrification, as experimentally and mathematically shown in this study. This may lead to an underestimation of nitrate reduction determined by nitrate stable isotope analysis in aquatic habitats where various types of stresses may affect the physiology of the driving microorganisms. (C) 2018 Elsevier Ltd. All rights reserved.
AU  - Wunderlich, A.*
AU  - Heipieper, H.J.*
AU  - Elsner, M.
AU  - Einsiedl, F.*
C1  - 54179
C2  - 45372
CY  - The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1gb, England
SP  - 275-283
TI  - Solvent stress-induced changes in membrane fatty acid composition of denitrifying bacteria reduce the extent of nitrogen stable isotope fractionation during denitrification.
JO  - Geochim. Cosmochim. Acta
VL  - 239
PB  - Pergamon-elsevier Science Ltd
PY  - 2018
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Dissimilatory sulphate reduction (DSR) has been proven to be one of the most relevant redox reactions in the biodegradation of contaminants in groundwater. However, the possible role of sulphur species of intermediate oxidation state, as well as the role of potential re-oxidative sulphur cycling in biodegradation particularly at the groundwater table are still poorly understood. Here we used a combination of stable isotope measurements of SO42−, H2S, and S0 as well as geochemical profiling of sulphur intermediates with special emphasis on SO32−, S2O32−, and S0 to unravel possible sulphur cycling in the biodegradation of aromatics in a hydrocarbon-contaminated porous aquifer. By linking these results to the quantification of total bacterial rRNA genes and respiratory genes of sulphate reducers, as well as pyrotag sequencing of bacterial communities over depth, light is shed on possible key-organisms involved. Our results substantiate the role of DSR in biodegradation of hydrocarbons (mainly toluene) in the highly active plume fringes above and beneath the plume core. In both zones the concentration of sulphur intermediates (S0, SO32− and S2O32−) was almost twice that of other sampling-depths, indicating intense sulphur redox cycling. The dual isotopic fingerprint of oxygen and sulphur in dissolved sulphate suggested a re-oxidation of reduced sulphur compounds to sulphate especially at the upper fringe zone. An isotopic shift in δ34S of S0 of nearly +4‰ compared to the δ34S values of H2S from the same depth linked to a high abundance (∼10%) of sequence reads related to Sulphuricurvum spp. (Epsilonproteobacteria) in the same depth were indicative of intensive oxidation of S0 to sulphate in this zone. At the lower plume fringe S0 constituted the main inorganic sulphur species, possibly formed by abiotic re-oxidation of H2S with Fe(III)oxides subsequent to sulphate reduction. These results provide first insights into intense sulphur redox cycling in a hydrocarbon contaminant plume, which widens the perspective of redox processes and microbial interactions ongoing in contaminated aquifers.
AU  - Einsiedl, F.*
AU  - Pilloni, G.
AU  - Ruth-Anneser, B.
AU  - Lueders, T.
AU  - Griebler, C.
C1  - 44049
C2  - 36727
CY  - Oxford
SP  - 207-221
TI  - Spatial distributions of sulphur species and sulphate-reducing bacteria provide insights into sulphur redox cycling and biodegradation hot-spots in a hydrocarbon-contaminated aquifer.
JO  - Geochim. Cosmochim. Acta
VL  - 156
PB  - Pergamon-elsevier Science Ltd
PY  - 2015
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Microbial reduction of ferric iron is partly dependent on Fe hydroxide particle size: nanosized Fe hydroxides greatly exceed the bioavailability of their counterparts larger than 1 μm. Citrate as a low molecular weight organic acid can likewise stabilize colloidal suspensions against aggregation by electrostatic repulsion but also increase Fe bioavailability by enhancing Fe hydroxide solubility. The aim of this study was to see whether adsorption of citrate onto surfaces of large ferrihydrite aggregates results in the formation of a stable colloidal suspension by electrostatic repulsion and how this effect influences microbial Fe reduction. Furthermore, we wanted to discriminate between citrate-mediated colloid stabilization out of larger aggregates and ferrihydrite dissolution and their influence on microbial Fe hydroxide reduction. Dissolution kinetics of ferrihydrite aggregates induced by different concentrations of citrate and humic acids were compared to microbial reduction kinetics with Geobacter sulfurreducens. Dynamic light scattering results showed the formation of a stable colloidal suspension and colloids with hydrodynamic diameters of 69 (±37) to 165 (± 65) nm for molar citrate:Fe ratios of 0.1 to 0.5 and partial dissolution of ferrihydrite at citrate:Fe ratios ⩾ 0.1. No dissolution or colloid stabilization was detected in the presence of humic acids. Adsorption of citrate, necessary for dissolution, reversed the surface charge and led to electrostatic repulsion between sub-aggregates of ferrihydrite and colloid stabilization when the citrate:Fe ratio was above a critical value (⩽ 0.1). Lower ratios resulted in stronger ferrihydrite aggregation instead of formation of a stable colloidal suspension, owing to neutralization of the positive surface charge. At the same time, microbial ferrihydrite reduction increased from 0.029 to 0.184 mM h−1 indicating that colloids stabilized by citrate addition enhanced microbial Fe reduction. Modelling of abiotic dissolution kinetics revealed that colloid stabilization was most pronounced at citrate:Fe ratios of 0.1 – 0.5, whereas higher ratios led to enhanced dissolution of both colloidal and larger aggregated fractions. Mathematical simulation of the microbial reduction kinetics under consideration of partial dissolution and colloid stabilization showed that the bioaccessibility increases in the order large aggregates < stable colloids < Fe-citrate. These findings indicate that much of the organic acid driven mobilization of Fe oxy(hydr)oxides is most likely due to colloid formation and stabilization rather than solubilisation.
AU  - Braunschweig, J.
AU  - Klier, C.
AU  - Schröder, C.*
AU  - Händel, M.*
AU  - Bosch, J.
AU  - Totsche, K.U.*
AU  - Meckenstock, R.U.
C1  - 31589
C2  - 34573
CY  - Oxford
SP  - 434-446
TI  - Citrate influences microbial Fe hydroxide reduction via a dissolution-disaggregation mechanism.
JO  - Geochim. Cosmochim. Acta
VL  - 139
PB  - Pergamon-elsevier Science Ltd
PY  - 2014
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000-6000years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50°N to 70°S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising δ14C values from -229‰ to -495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to ~100ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment ("island of stability"). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17±0.13), and O/C (average of 0.52±0.10) and molecular masses (360±28 and 497±51Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3±3.3μM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, representing average surface water DOM ages of 4920±180a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index IDEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate.
AU  - Lechtenfeld, O.J.*
AU  - Kattner, G.*
AU  - Flerus, R.*
AU  - McCallister, S.L.*
AU  - Schmitt-Kopplin, P.
AU  - Koch, B.P.*
C1  - 29215
C2  - 33181
SP  - 321-337
TI  - Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean.
JO  - Geochim. Cosmochim. Acta
VL  - 126
IS  - 1
PB  - Pergamon-Elsevier
PY  - 2014
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The stable isotopes N-15/N-14 and O-18/O-16 of nitrate are frequently used to determine sources of nitrate and to assess denitrification processes in the environment. Nitrate isotope ratios are thought to be conservative unless involved in (bio-) chemical conversion processes. Thus, stable isotopes are considered to be a reliable tool to determine sources of nitrate in aquatic habitats even after transport and dilution has occurred. Denitrification is known to shift both isotope ratios towards higher delta-values. A fixed ratio of 0.5 for Delta delta O-18/Delta delta(15) N has been proposed and has been widely used to detect denitrification in terrestrial environments, predominantly in aquifers. However, it is observed in environmental and laboratory studies that this ratio actually varies between less than 0.5 and 1 for uncertain reasons with laboratory studies usually describing a ratio close to 1. Here we report results of anoxic incubation experiments with natural populations of nitrate-reducing microorganisms using sediments from three different environments. In our experiments we used water with a delta O-18 in excess of 500 parts per thousand and found a microbially mediated influence of the oxygen isotopic composition of ambient water on the isotopic composition of the residual dissolved nitrate. We found up to 5.7 +/- 2.3% of the oxygen-atoms in the residual dissolved nitrate was exchanged by oxygen-atoms from ambient water within the limited timeframe of the experiments. The fastest incorporation of oxygen-atoms from water into dissolved nitrate correlated with the highest intermittent nitrite concentrations observed in our experiments. In a second series of batch experiments we also found that pure cultures of the nitrite-oxidizing bacterium Nitrobacter vulgaris promoted the incorporation of oxygen atoms from ambient water into dissolved nitrate under anoxic conditions. Presumably this happens via a reoxidation of intermediary formed nitrite by the enzyme "nitrite oxidoreductase" (NXR) in concurrence with respiratory nitrate reduction. In this context, our hypothesis is a reversibility of the reactions at the NXR enzyme even in the absence of external electron acceptors for nitrite oxidation. We suggest that the presence of nitrite-oxidizing microorganisms in aquatic environments may catalyse such an incorporation of oxygen-atoms stemming from ambient water into nitrate. This process may thus mask the original delta O-18 value of nitrate sources during denitrification and also distort the observed enrichment of O-18 that is ascribed to denitrification. Our results are highly likely an explanation of the deviation of the described variable Delta delta O-18/Delta delta N-15 ratios for denitrification in terrestrial field studies from the values observed in the laboratory on pure cultures.
AU  - Wunderlich, A.
AU  - Meckenstock, R.U.
AU  - Einsiedl, F.*
C1  - 28042
C2  - 32919
SP  - 31-45
TI  - A mixture of nitrite-oxidizing and denitrifying microorganisms affects the δ18O of dissolved nitrate during anaerobic microbial denitrification depending on the δ18O of ambient water.
JO  - Geochim. Cosmochim. Acta
VL  - 119
PB  - Pergamon-Elsevier Science
PY  - 2013
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Recent studies on the microbial reduction of synthetic iron oxide colloids showed their superior electron accepting property in comparison to bulk iron oxides. However, natural colloidal iron oxides differ in composition from their synthetic counterparts. Besides a potential effect of colloid size, microbial iron reduction may be accelerated by electron-shuttling dissolved organic matter (DOM) as well as slowed down by inhibitors such as arsenic. We examined the microbial reduction of OM- and arsenic-containing ferrihydrite colloids. Four effluent fractions were collected from a soil column experiment run under water-saturated conditions. Ferrihydrite colloids precipitated from the soil effluent and exhibited stable hydrodynamic diameters ranging from 281 (±146) nm in the effluent fraction that was collected first and 100 (±43) nm in a subsequently obtained effluent fraction. Aliquots of these oxic effluent fractions were added to anoxic low salt medium containing diluted suspensions of Geobacter sulfurreducens. Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe2+ formation ranged between 1.9 and 3.3 fmol h−1 cell−1, and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3 fmol h−1 cell−1), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07 fmol h−1 cell−1). The inhibition of microbial Fe(III) reduction by arsenic is unlikely or overridden by the concurrent enhancement induced by soil effluent DOM. These organic species may have increased the already high intrinsic reducibility of colloidal ferrihydrite owing to quinone-mediated electron shuttling. Additionally, OM, which is structurally associated with the soil effluent ferrihydrite colloids, may also contribute to the higher reactivity due to increasing solubility and specific surface area of ferrihydrite. In conclusion, ferrihydrite colloids from soil effluents can be considered as highly reactive electron acceptors in anoxic environments.
AU  - Fritzsche, A.*
AU  - Bosch, J.
AU  - Rennert, T.*
AU  - Heister, K.*
AU  - Braunschweig, J.
AU  - Meckenstock, R.U.
AU  - Totsche, K.U.*
C1  - 6273
C2  - 29055
SP  - 444-456
TI  - Fast microbial reduction of ferrihydrite colloids from a soil effluent.
JO  - Geochim. Cosmochim. Acta
VL  - 77
PB  - Elsevier
PY  - 2012
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The coupled reverse osmosis-electrodialysis (RO/ED) method was used to isolate dissolved organic matter (DOM) from 16 seawater samples. The average yield of organic carbon was 75 +/- 12%, which is consistently greater than the yields of organic carbon that have been commonly achieved using XAD resins, C-18 adsorbents, and cross-flow ultrafiltration. UV-visible absorbance spectra and molar C/N ratios of isolated samples were consistent with the corresponding properties of DOM in the original seawater samples, indicating that DOM samples can be isolated using the coupled RO/ED method without any bias for/against these two properties. Five of the samples were desalted sufficiently that reliable measurements of their C-13 and H-1 NMR spectra and their Fourier transform ion cyclotron resonance (FTICR) mass spectra could be obtained. The C-13 and H-1 NMR spectra of RO/ED samples differed distinctly from those of samples that have been isolated in much lower yields by other methods. In particular, RO/ED samples contained a relatively lower proportion of carbohydrate carbon and a relatively greater proportion of alkyl carbon than samples that have been isolated using cross-flow ultrafiltration. From the FTICR mass spectra of RO/ED samples, samples from the open ocean contained a much lower proportion of unsaturated compounds and a much higher proportion of fatty acids than coastal samples.
AU  - Koprivnjak, J.-F.*
AU  - Pfromm, P.H.*
AU  - Ingall, E.*
AU  - Vetter, T.A.*
AU  - Schmitt-Kopplin, P.
AU  - Hertkorn, N.
AU  - Frommberger, M.
AU  - Knicker, H.*
AU  - Perdue, E.M.*
C1  - 1514
C2  - 26288
SP  - 4215-4231
TI  - Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis-electrodialysis.
JO  - Geochim. Cosmochim. Acta
VL  - 73
IS  - 14
PB  - Pergamon-Elsevier Science Ltd
PY  - 2009
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The stable isotopes of sulfate are often used as a tool to assess bacterial sulfate reduction on the macro scale. However, the mechanisms of stable isotope fractionation of sulfur and oxygen at the enzymatic level are not yet fully understood. In batch experiments with water enriched in 18O we investigated the effect of different nitrite concentrations on sulfur isotope fractionation by Desulfovibrio desulfuricans.
AU  - Mangalo, M.
AU  - Einsiedl, F.
AU  - Meckenstock, R.U.
AU  - Stichler, W.
C1  - 3539
C2  - 25141
SP  - 1513-1520
TI  - Influence of the enzyme dissimilatory sulfite reductase on stable isotope fractionation during sulfate reduction.
JO  - Geochim. Cosmochim. Acta
VL  - 72
IS  - 6
PB  - Elsevier
PY  - 2008
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The study of molecular transformation processes of dissolved organic carbon (DOC) in the environment significantly contributes to a better understanding of the global biogeochemical organic matter cycle. In an oxic karst groundwater system, in which the most powerful abiotic DOC degradative reactions, photodegradation and metal-mediated redox chemistry, are at best marginal contributors, a near complete turnover of fulvic acids (FAs) has been observed within decades (not, vert, similar60 years). Depletion of oxygen for a very extensive range of aliphatic and aromatic carbon chemical environments has been confirmed as well as the formation of novel classes of compounds, suggesting a major contribution from biotic processes. From these results we infer that FAs must be perceived as a rather active participant in the global carbon cycle. Molecular-level alterations of such magnitude and rapidity on such short-time scales ought to be considered as widespread in the processing of “refractory” DOC in the environment.
AU  - Einsiedl, F.
AU  - Hertkorn, N.
AU  - Wolf, M.
AU  - Frommberger, M.
AU  - Schmitt-Kopplin, P.
AU  - Koch, B.P.*
C1  - 2928
C2  - 24895
SP  - 5474-5482
TI  - Rapid biotic molecular transformation of fulvic acids in a karst aquifer.
JO  - Geochim. Cosmochim. Acta
VL  - 71
IS  - 22
PB  - Elsevier
PY  - 2007
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Bacterial sulfate reduction is one of the most important respiration processes in anoxic habitats and is often assessed by analyzing the results of stable isotope fractionation. However, stable isotope fractionation is supposed to be influenced by the reduction rate and other parameters, such as temperature. We studied here the mechanistic basics of observed differences in stable isotope fractionation during bacterial sulfate reduction. Batch experiments with four sulfate-reducing strains (Desulfovibrio desulfuricans, Desulfobacca acetoxidans, Desulfonatronovibrio hydrogenovorans, and strain TRM1) were performed. These microorganisms metabolize different carbon sources (lactate, acetate, formate, and toluene) and showed broad variations in their sulfur isotope enrichment factors. We performed a series of experiments on isotope exchange of 18O between residual sulfate and ambient water. Batch experiments were conducted with 18O-enriched (delta18Owater = +700‰) and depleted water (delta18Owater = -40‰), respectively, and the stable 18O isotope shift in the residual sulfate was followed. For Desulfovibrio desulfuricans and Desulfonatronovibrio hydrogenovorans, which are both characterized by low sulfur isotope fractionation (S > -13.2‰), delta18O values in the remaining sulfate increased by only 50‰ during growth when 18O-enriched water was used for the growth medium. In contrast, with Desulfobacca acetoxidans and strain TRM1 (S < -22.7‰) the residual sulfate showed an increase of the sulfate delta18O close to the values of the enriched water of +700‰. In the experiments with ?18O-depleted water, the oxygen isotope values in the residual sulfate stayed fairly constant for strains Desulfovibrio desulfuricans, Desulfobacca acetoxidans and Desulfonatronovibrio hydrogenovorans. However, strain TRM1, which exhibits the lowest sulfur isotope fractionation factor (S < -38.7‰) showed slightly decreasing delta18O values.Our results give strong evidence that the oxygen atoms of sulfate exchange with water during sulfate reduction. However, this neither takes place in the sulfate itself nor during formation of APS (adenosine-5'-phosphosulfate), but rather in intermediates of the sulfate reduction pathway. These may in turn be partially reoxidized to form sulfate. This reoxidation leads to an incorporation of oxygen from water into the “recycled” sulfate changing the overall 18O isotopic composition of the remaining sulfate fraction. Our study shows that such incorporation of 18O is correlated with the stable isotope enrichment factor for sulfur measured during sulfate reduction. The reoxidation of intermediates of the sulfate reduction pathway does also strongly influence the sulfur stable isotope enrichment factor. This aforesaid reoxidation is probably dependent on the metabolic conversion of the substrate and therefore also influences the stable isotope fractionation factor indirectly in a rate dependent manner. However, this effect is only indirect. The sulfur isotope enrichment factors for the kinetic reactions themselves are probably not rate dependent.
AU  - Mangalo, M.
AU  - Meckenstock, R.U.
AU  - Stichler, W.
AU  - Einsiedl, F.
C1  - 5880
C2  - 24541
SP  - 4161-4171
TI  - Stable isotope fractionation during bacterial sulfate reduction is controlled by reoxidation of intermediates.
JO  - Geochim. Cosmochim. Acta
VL  - 71
IS  - 17
PB  - Elsevier
PY  - 2007
SN  - 0016-7037
ER  - 

TY  - JOUR
AU  - Hertkorn, N.
AU  - Benner, R.*
AU  - Frommberger, M.
AU  - Schmitt-Kopplin, P.
AU  - Witt, C.*
AU  - Kaiser, K.*
AU  - Kettrup, A.
AU  - Hedges, J.I.*
C1  - 4637
C2  - 23712
SP  - 2990-3010
TI  - Characterization of a major refractory component of marine dissolved organic matter.
JO  - Geochim. Cosmochim. Acta
VL  - 70
PY  - 2006
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Stem cellulose of bean plants (Vicia faba) grown under controlled conditions exhibits inverse linear carbon-isotope reactions to changes in both relative humidity (RH) and temperature (T), readily mappable as a planar delta(13)C response surface in RH-T space. The analogous response surface for annual late-wood cellulose delta(13)C from a field calibration using fir trees (Abies alba) in the Black Forest, southern Germany, also supports resolution of independent delta-RH and delta-T effects. The response of cellulose delta(13)C to RH and T derived from this new calibration differs markedly from estimates based on univariate linear regression analysis: The sensitivity of delta(13)C to RH is stronger than that inferred previously (c. -0.17 parts per thousand/% vs. -0.12 parts per thousand/%, respectively), whereas the delta-T coefficient is weaker and reversed in sign (c. -0.15 parts per thousand/K vs. +0.36 parts per thousand/K). This new perspective on the coupled influence of moisture and temperature changes on tree-ring cellulose delta(13)C helps to unify divergent observations about carbon-isotope signals in trees, especially the broad range of apparent delta-T relations obtained in calibration studies, which are often used as paleoclimate transfer functions. Although this highlights the large potential uncertainties surrounding paleoclimate reconstruction based solely on delta(13)C data, coupling of the carbon-isotope response-surface approach with equivalent response surfaces for hydrogen or oxygen isotopes may afford new opportunities for investigating the nature of past climate variability and change from tree-ring sequences.
AU  - Edwards, T.W.D.
AU  - Graf, W.
AU  - Trimborn, P.
AU  - Stichler, W.
AU  - Lipp, J.
AU  - Payer, H.-D.
C1  - 23417
C2  - 31115
SP  - 161-167
TI  - δ13C response surface resolves humidity and temperature signals in trees.
JO  - Geochim. Cosmochim. Acta
VL  - 64
IS  - 2
PB  - Elsevier
PY  - 2000
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Ultramafic rocks in northern Oman host unusual, hyperalkaline groundwaters (pH > 11.5) which precipitate inorganic travertine by diffusive uptake of atmospheric CO2 after discharge. Stable isotope fractionation during CO2 uptake results in strong depletions of the carbonate phase (δ13C values as low as -27.5‰ and δ18O values of -16.9‰ PDB). Experiments under closed and open system conditions show that a kinetic depletion in the order of 15.5‰ for 13C occurs during hydroxylation of aqueous CO2 (CO2(aq) + OH- reaction), attributed to a lower activation energy for 12C-O vs 13C-O. The observed 18O depletion can be accounted for by CO2 reaction with OH- (ε{lunate}18OOH--H2O ≅ -40‰) without subsequent exchange and with no evidence of significant additional kinetic effects. Calculated reaction rates show hydroxylation to be the rate limiting step and that CO2(g)-CO2(aq) exchange at the gas/solution interface achieves isotopic equilibrium.
AU  - Clark, I.D.*
AU  - Fontes., J.C.*
AU  - Fritz, P.J.
C1  - 40579
C2  - 38770
SP  - 2041-2050
TI  - Stable isotope disequilibria in travertine from high pH waters: Laboratory investigations and field observations from Oman.
JO  - Geochim. Cosmochim. Acta
VL  - 56
IS  - 5
PY  - 1992
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Both field and laboratory data indicate that there is no significant isotope fractionation of sulfate during sorption in upland forest Podzols. The dominant sulfate sorption process in these soils is adsorption onto mineral surfaces. In the Plastic Lake watershed, Dorset, Ontario, Canada, fractions of sulfate from Podzol B-horizons have the following mean isotope (%.) compositions: water soluble sulfate, δ34S = +6.4; δ18O = -5.3; bicarbonate-exchanged sulfate by two methods,δ34S = + 4.5 and + 3.4; δ18O =-6.2 and -5.6; dissolved sulfate in B-horizon soilwater seepage,δ34S = + 4.8; δ18O = -5.4. These data indicate that soil sorption enriches dissolved sulfate in 34S by approximately 1 ± 1%. and in 18O by 0 +- 1 %. relative to sorbed sulfate. Similar results were obtained by laboratory sorption of sulfate by prepared goethite, which is a mineral representative of soil sorption sites in acidic Podzols like the one at Plastic Lake. The mean fractionation between sorbed and dissolved sulfate was found to be - 0.3%. for34S and 0.1 %. for 18O. Earlier literature has confused the term adsorption; in many cases the more general term sorption, or retention, should be used. Pronounced fractionation of S and O isotopes in sulfate by lake and ocean sediments has been attributed to "adsorption" or "retention" but is more likely the result of sulfate reduction. Apparently, at Earth-surface conditions the only substantial isotope shifts in sulfate occur during microbial processes.
AU  - Van Stempvoort, D.R.*
AU  - Reardon, E.J.*
AU  - Fritz, P.J.
C1  - 42139
C2  - 40262
SP  - 2817-2826
TI  - Fractionation of sulfur and oxygen isotopes in sulfate by soil sorption.
JO  - Geochim. Cosmochim. Acta
VL  - 54
IS  - 10
PY  - 1990
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The in situ production of 3H, 14C, 36Cl, 129I, 37Ar, 39Ar, 81Kr and 85Kr by neutron-induced reactions and spontaneous nuclear decay processes has been estimated within the Stripa granite, its associated fracture minerals and surrounding leptite. Experimental measurements of the neutron flux within the Stripa granite are within 15% of theoretical values and have been used to calculate neutron-induced production rates. Activities of radionuclides that may enter groundwaters from the rock matrix are discussed in relation to their initial distribution in the host rock and their subsequent release into solution. The measured radioactivities in groundwaters from the high radioélément-content granites at Stripa are compared with estimates of their in situ production within the granite and of their solution by fracture-borne fluids. The activities of 3H and 14C which enter fracture fluids from the rock matrix are close to present detection limits. For 3H, the most significant production is within the rock matrix whilst for 14C it is within the circulating fracture fluids. Chlorine-36 production by neutron-capture within the granite is much more significant than inputs from cosmogenic and nuclear fallout sources. The 36Cl Cl ratio may be used to evaluate Cl- sources in saline groundwaters. In situ production of 129I by spontaneous fission of 238U is an important source of 129I in the high radioactivity Stripa granite. Argon-37,39Ar and 85Kr are produced by in situ reactions within the rock matrix, fracture mineralisation and at the sites of U-mineralisation, respectively. The use of some cosmogenic radionuclides for the estimation of groundwater residence times may be limited because of in situ production.
AU  - Andrews, J.N.*
AU  - Davis, S.N.*
AU  - Fabryka-Martin, J.T.*
AU  - Fontes., J.C.*
AU  - Lehmann, B.E.*
AU  - Loosli, H.H.*
AU  - Michelot, J.L.*
AU  - Moser, H.
AU  - Smith, B.A.*
AU  - Wolf, M.
C1  - 42625
C2  - 36450
SP  - 1803-1815
TI  - The in situ production of radioisotopes in rock matrices with particular reference to the Stripa granite.
JO  - Geochim. Cosmochim. Acta
VL  - 53
IS  - 8
PY  - 1989
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - The carbon isotopic composition of the total dissolved inorganic carbon in groundwater associated with a granitic pluton at Stripa (Sweden) reflects both inorganic and organic carbon sources. Following the uptake of soil carbon-dioxide, calcite dissolution dominates the geochemical evolution of shallow groundwater. Calcite saturation is reached at a depth of about 100 m. In deeper waters geochemical release of Ca and increasing pH cause calcite precipitation. Radiocarbon contents suggest carbon (and water ?) ages in excess of 20 000 years for waters at 300–400 m depth.
      
      	In deep groundwaters with enhanced salinities organic carbon is added to the dissolved inorganic carbon either through bacterial activity (e.g, sulphate reducing bacteria) or the oxidation of organic compounds such as methane. The lowest radiocarbon contents were measured at the 300–400 meter levels and not in the deepest fluids.
      
      	The distribution of 13C in the deep groundwaters suggests the existence of well-defined flowsystems with limited active hydraulic interaction. Isotope analyses on fracture calcites substantiate the complex geochemical history of the pluton.
AU  - Fritz, P.
AU  - Fontes, J.-C.
AU  - Frape, S.K.
AU  - Louvat, D.
AU  - Michelot, L.
AU  - Balderer, W.
C1  - 17329
C2  - 9935
SP  - 1765-1775
TI  - The Isotope Geochemistry of Carbon in Groundwater at Stripa.
JO  - Geochim. Cosmochim. Acta
VL  - 53
IS  - 8
PY  - 1989
SN  - 0016-7037
ER  - 

TY  - JOUR
AB  - Deuterium, oxygen-18 and tritium determinations show that groundwaters in the fractures of the Stripa granite are of meteoric origin, not affected by secondary isotope effects (evaporation or isotope exchange). Deep ground-waters have lower 18O and 2H contents than recent, shallow groundwaters. The differences are most likely due to recharge during cooler climatic conditions. However, no age information can be derived because recharge could have occurred before the last major climatic improvement following the last deglaciation, during minor climatic variations during the more recent past, or could be the result of regional groundwater flow. Low 18O contents are paralleled by increasing salinities with highest salinities limited to a narrow fracture zone at a depth of about 800 m below ground surface. Most saline waters sampled appear to represent mixtures of a saline component with an isotopically depleted water and local fresh water. The presence of young groundwaters is indicated by bomb produced 3H. All surface boreholes contain tritium, indicating residence times <35 years. However, tritium is also found in some boreholes drilled at the 300 m mine levels and its presence may be due to flows induced in response to heater tests. Low but detectable 3H contents (about 0.1 to 1 TU) in V2 at about 850 m below groundsurface are discussed either as subsurface production and/or as a result of admixtures of small amounts of recent water to old groundwater.
AU  - Moser, H.
AU  - Wolf, M.
AU  - Fritz, P.
AU  - Fontes, J.-Ch.
AU  - Florkowski, T.
AU  - Payne, B.R.
C1  - 17330
C2  - 9934
SP  - 1757-1763
TI  - Deuterium, Oxygen-18 and Tritium in Stripa Groundwater.
JO  - Geochim. Cosmochim. Acta
VL  - 53
IS  - 8
PY  - 1989
SN  - 0016-7037
ER  -