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  • 1.
    Ahmed, Engy
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Holmström, Sara J. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Microbe-mineral interactions: The impact of surface attachment on mineral weathering and element selectivity by microorganisms2015Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 403, s. 13-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the major gaps within the field of biogeochemistry is the lack of a detailed and deep understanding of the mechanismbehind the microbial inducement of mineral dissolution. The association of microorganisms with the mineral surfaces is an important issue for understanding processes like mineral weathering, biomineralization, bioremediation and biofouling. The present study aims to investigate the performance of attached and unattached soil fungal and bacterial species in biotite weathering and in the selectivity of elements from biotite. Sterilized microplate devices were filled with biotite (>2 mm) followed by an iron limited liquid growth medium and were inoculated separately with six different microbial species isolated from podzol soil: Erwinia amylovora, Pseudomonas stutzeri, Pseudomonas mendocina, Streptomyces pilosus, Neurospora crassa and Penicillium melinii. The experiment was designed in two set-ups: 1) attached form, in which the microorganisms were inoculated directly to the biotite surface, and 2) unattached form, in which 0.4 mu m PET track etched devices were used to separate the microbial cells from the biotite surface. Our findings indicate that the surface attached microorganisms led to a greater dissolution of elements from biotite than the unattached microorganisms that was evidenced by 1) higher dissolution of Fe, Al and Si, 2) greater decrease in pH of the liquid growth medium, and 3) relatively higher production of siderophores. Furthermore, there was no significant difference in the capability of element selectivity between the attached and unattached microbial forms. The biotite dissolution was promoted initially by complexation processes and later by acidification processes for most of the attached and unattached microorganisms. Thus, we conclude that despite the mineral dissolution induced by microbial attachment on the mineral surface, the element composition of the biotite and nutritional need of the microorganisms were the main factors affecting the element selectivity.

  • 2. Fehr, Manuela A.
    et al.
    Andersson, Per S.
    Halenius, Ulf
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Iron enrichments and Fe isotopic compositions of surface sediments from the Gotland Deep, Baltic Sea2010Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 277, nr 3-4, s. 310-322Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent sediments from the Gotland Deep display enrichments in reactive Fe, associated with elevated Fe/Al ratios and light Fe isotopic signatures of the bulk sediments that are indicative of euxinic (anoxic and sulfidic) conditions. These enrichments can be explained by the Fe shuttle model where benthic Fe is transported from the shelf to the euxinic basin and transferred to the sediments by pyrite precipitation in the sulfidic water. The data provide evidence that the Fe shuttle at present results in accumulations of Fe that are larger compared to Fe enrichments during the Litorina Sea stage in the Gotland Deep probably caused by an increase of the benthic Fe flux from the shelf to the basin. The derived Fe enrichments are also larger compared to those in recent Black Sea sediments, which likely reflects the larger shelf to basin ratio of the Gotland Deep compare to the Black Sea. The Fe isotope data show no correlation with the organic C content of the samples indicating that the negative Fe isotope signatures are not associated with organic materials, as was suggested as an alternative explanation for the origin of the isotopically light Fe in sediments from the Litorina Sea stage. Conversely, pyrites carry the negative Fe isotopic signature of the sediments, which supports the Fe shuttle model. Variations in the abundance and Fe isotopic signature of reactive Fe and pyrite with depth suggest that syngenetically formed pyrite in the sulfidic water column has a less negative Fe isotopic composition compared to diagenetically produced pyrite.

  • 3.
    Gleisner, Magdalena
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Herbert, Jr, Roger B.
    Frogner Kockum, P.C.
    Pyrite oxidation by Acidithiobacillus ferrooxidans at various concentrations of dissolved oxygen.2006Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 225, nr 1-2, s. 16-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pyrite oxidation rates were examined at various concentrations of dissolved oxygen (DO) in the presence of the sulfur and iron oxidizer Acidithiobacillus ferrooxidans. Five different batch experiments were performed at room temperature for 75 days under various DO levels (273, 129, 64.8, 13.2, and ≤ 0.006 μM), containing pyrite grains (particle size 63–250 μm) and a modified 9K nutrient medium at pH 3. The reactors were inoculated with A. ferrooxidans. In all experiments, pH decreased with time and sulfur and iron were released to the solution, indicating pyrite oxidation at all DO levels. Pyrite oxidation rates (ca. 5 × 10− 10 mol m− 2 s− 1 at 273 μM DO) from all experiments showed positive correlation with DO, Fe(III), and bacterial concentration. These rates were significantly slower than rates presented in other published studies, but this is probably due to the significantly greater Fe(III) concentration at lower pH in these previous studies. The results obtained in this study suggest that ferric iron reduction at the pyrite surface is the primarily mechanism for microbial pyrite oxidation in the presence of DO. The results from our study support the indirect mechanism of sulfide oxidation, where A. ferrooxidans oxidizes ferrous iron in the presence of DO, which then oxidizes pyrite.

  • 4.
    Kaislahti Tillman, Päivi
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Holzkämper, Steffen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Kuhry, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Sannel, A. Britta K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Loader, Neil J.
    Robertson, Iain
    Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada: implications for palaeoclimate studies2010Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 270, nr 1-4, s. 216-226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stable carbon and oxygen isotope ratios in single plant components in Sphagnum peat have a good potential to reveal environmental changes in peat archives. Two peat profiles, covering the past ~6000 years, and a Sphagnum hummock from a discontinuous permafrost area in west central Canada were studied in order to evaluate the effect of decomposition rate on isotope records and to assess which plant components are most suitable for climate reconstructions. The stable isotope values from the most recently forming Sphagnum tissues were compared with observational climate data to study the impact of variations in temperature and precipitation on the peat isotopes. Our results show that there is high correlation between δ13C values in α-cellulose isolated from Sphagnum fuscum stems and summer temperatures, whereas δ18O in the plant tissues is controlled by several factors, such as summer precipitation, summer temperature and evaporation. According to our results, decomposition as derived from C/N values and colorimetry does not seem to affect the oxygen and carbon isotope values of α-cellulose from Sphagnum fuscum peat significantly. There is, however, a (quasi-) constant offset between the isotope values of branches and stems and between whole plant material and  α-cellulose, which makes it crucial to select single moss-fractions when past climate and environmental changes are to be derived from the isotope record.

  • 5.
    Kielman, Ross
    et al.
    Swedish Museum of Natural History, Sweden.
    Whitehouse, Martin
    Nemchin, Alexander
    Kemp, Anthony
    A tonalitic analogue to ancient detrital zircon2018Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 499, s. 43-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A zircon population from an Archean tonalite sample from southern West Greenland has been used as a source analogue in order to test common methods and approaches applied to ancient detrital zircon populations. Measurements of U-Th-Pb, oxygen and Lu-Hf isotopes as well as rare earth element and Ti concentrations were made in these zircon crystals and, where possible, in multiple areas within a single grain. The population is dominated by oscillatory zoned cores aged 3.82 Ga with an isotopically and compositionally distinct rim that formed at 3.59 Ga. We demonstrate that multiple age components may be erroneously inferred from within these oscillatory zoned zircon cores, both from the total population and within individual grains. This has bearing on other zircon-hosted geochemical systems, as temporal correlations may be incorrectly assigned. Oxygen and Lu-Hf isotope compositions are relatively consistent through the population with only a small number of outliers. Ranges in rare earth element and Ti abundances are evident from the total population, from which apparent inverse cooling trends may be inferred. Additionally, we show that even with enhanced filtering of Ti concentrations using light rare earth element abundances, crystallisation temperatures derived from zircon grains of a single, hand sample sized rock can yield both wide and bimodal results. Since even simple, single “source rock” zircon populations may, without careful scrutiny, portray artificially complex results, particular care must be taken in the interpretation of complex ancient detrital zircon populations.

  • 6.
    Konn, Cécile
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Charlou, Jean-Luc
    Donval, Jean-Pierre
    Holm, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Dehairs, Frank
    Bouillon, Steven
    Hydrocarbons and oxidized organic compounds in hydrothermal fluids from Rainbow and Lost City ultramafic-hosted vents2009Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 258, s. 299-314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first building blocks of life could be produced in ultramafic-hosted hydrothermal systems considering the large amounts of hydrogen and methane generated by serpentinisation and Fischer-Tropsch-Type synthesis, respectively, in those systems. The purpose of this study was to detect and characterise organic molecules in hydrothermal fluids from ultramafic-hosted hydrothermal systems in the Mid-Atlantic Ridge (MAR) region. During the EXOMAR cruise 2005, fluids from the Rainbow (36°14’N) and the Lost City (30°N) hydrothermal fields were collected and treated by Stir Bar Sorptive Extraction (SBSE) and Solid Phase Extraction (SPE). The extracts were analysed by Thermal Desorption - Gas Chromatography - Mass Spectrometry (TD-GC-MS) and GC-MS, respectively. Compared to nearby deep seawater, hydrothermal fluids were clearly enriched in organic compounds, with a more diverse spectrum of molecules. We observed a very similar range of organic compounds in fluids from both sites, with a dominance of aliphatic hydrocarbons (C9-C14), aromatic compounds (C6-C16) and carboxylic acids (C8-C18). The occurrence of these compounds is supported by other field studies on serpentinites and sulfide deposits. Literature on thermodynamic data and experimental work has suggested the possible abiogenic origin of hydrocarbons and organic acids. In addition, it has been shown elsewhere that catalytic reactions producing hydrocarbons likely occur at both Lost City and Rainbow hydrothermal fields as suggested by the evolution of δ13C with increasing C number for methane, ethane, propane and butane. In order to investigate the origin of the organic molecules in the fluids, compound-specific carbon isotope ratio measurements were performed on n-alkanes and carboxylic acids, for which the δ13C values were in the range of -46 to -20‰ (vs. V-PDB). These preliminary data did not allow conclusive support or rejection of an abiogenic origin of the compounds. Indeed, predicting δ13C signatures in hydrothermal systems is likely to be complicated, due to differences in source δ13C signatures (i.e., of the C building blocks), and a variety of, mostly unknown, fractionation steps which may occur along the synthesis pathways. In addition, even though a fraction of the compounds detected in the fluids is likely abiotically produced, a dominance of biogenic sources and/or processes might hide their characteristic signature.

  • 7. Konter, Oliver
    et al.
    Holzkämper, Steffen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Johannes Gutenberg University of Mainz, Germany.
    Helle, Gerhard
    Buentgen, Ulf
    Saurer, Matthias
    Esper, Jan
    Climate sensitivity and parameter coherency in annually resolved delta C-13 and delta O-18 from Pinus uncinata tree-ring data in the Spanish Pyrenees2014Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 377, s. 12-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We explore the 20th century climate sensitivity of annually resolved carbon and oxygen isotope ratios in five Pinus uncinata individuals from the upper treeline in similar to 2400 m asl of the Spanish Pyrenees. Time series of delta C-13 and delta O-18 are calibrated against temperature, precipitation, and drought indices over the period 1901-2009. Negative correlations of delta C-13 with summer precipitation and drought indices, as well as positive correlations with summer temperatures, confirm previous evidence from similar habitats in the Pyrenees. In contrast to this summer climate signal in the carbon isotopes, the delta O-18 record reveals mainly negative correlations with spring precipitation and drought. We explore the coherence between delta C-13 and delta O-18 time series derived from individual trees and assess the influence of widely applied delta C-13 correction procedures on the climate signal strength. Spatial correlation patterns and decomposition of the time series into high-and low-frequency components are used to develop a calibration setup for carbon and oxygen isotope ratios, which will improve long-term climate reconstructions in a region, where classical tree-ring width and density data are limited.

  • 8. Loader, N. J.
    et al.
    McCarroll, D.
    Barker, S.
    Jalkanen, R.
    Grudd, Håkan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Inter-annual carbon isotope analysis of tree-rings by laser ablation2017Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, s. 323-326Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stable carbon isotopic analysis of tree-rings for environmental, plant physiological and archaeological applications using conventional methods is occasionally limited by physical constraints (narrow rings) or administrative concerns (requirement for non-destructive sampling) that prevent researcher access to scientifically valuable wood samples. Analysis of such archives by laser-ablation can potentially address these issues and facilitate access to restricted archives. Smaller quantities of wood are required for analysis by laser ablation, hence the approach may be considered less-invasive and is virtually non-destructive compared to standard preparation methods. High levels of intra-annual isotopic variability reported elsewhere mean that a single measurement may not faithfully represent the inter-annual isotopic signal, so before such an approach can be used with confidence it is necessary to compare the stable carbon isotopic data produced using these two methods. This paper presents stable carbon isotope (delta C-13) data from the resin-extracted wood of dated Scots Pine (Pinus sylvestris L.) tree-rings analysed using a modified Schulze-type laser-ablation system with results obtained using conventional manual sampling and analysis of alpha-cellulose prepared from the same tree-ring groups. The laser sampling system is found to perform very well against established more invasive methods. High correlations are observed between the methods for both raw and Suess corrected data (r > 0.90 n = 50). These results highlight the potential for using laser-sampling to support the development of long isotope chronologies, for sampling narrow rings or for pre-screening cores prior to analysis using more detailed or labour intensive methods.

  • 9.
    Raymond, Peter A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. Yale School of Forestry and Environmental Studies, United States.
    Temperature versus hydrologic controls of chemical weathering fluxes from United States forests2017Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 458, s. 1-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chemical weathering is a dominant control on modem inland water chemistry and global element budgets over geologic time scales. Due to its central role in the earth's biogeochemistry it remains an intense area of interest. Understanding the controls on chemical weathering is difficult because it has many drivers with overlapping temporal and spatial signals. Of particular interest is the relationship between chemical weathering fluxes and global temperatures due to a negative feedback loop where warmer temperatures leads to more chemical weathering and its associated atmospheric CO2 consumption (Berner et al.,1983). Recently it has been proposed that this negative feedback loop is indirect where the acceleration of the hydrologic cycle by increased global temperatures leads to higher chemical weathering and atmospheric CO2 consumption (Maher and Chamberlain, 2014). Here, fluxes of all major cations and anions are calculated for 150 forested watersheds smaller than 500 km(2) in order to explore controls on chemical weathering from United States forests. Relationships between watershed hydrology, ion ratios and pH are reported that explain a large amount of across site variation in bicarbonate fluxes. Furthermore, across all watersheds similar to 32% of the cation flux is not balanced by bicarbonate but by sulfate. Paired alkalinity, temperature and discharge data are used to determine a temperature sensitivity of chemical weathering across 51 forested watersheds with a minimum of 70 measurements. The temperature sensitivity of bicarbonate fluxes is absent at low flow conditions because long residence times leads to chemical equilibrium and transport limitation. As discharge increases and residence time decreases, the temperature sensitivity of chemical weathering is released from transport limitation. The temperature sensitivity then increases with discharge until it levels off at high discharges as the system becomes reaction limited. Records of daily discharge, watershed discharge to flux relationships, and the temperature sensitivity are then used to estimate how chemical fluxes would change with a 20% increase in discharge, and 10 increase in temperature global change scenario. Not surprisingly it is found that increased discharge leads to higher weathering fluxes. Interestingly, wetter years have a higher temperature sensitivity due to a release of the temperature sensitivity from transport limitation. This coupled with a strong direct temperature effect leads to an approximately equal response from temperature and increased discharge using this scenario of global change. Thus periods of time and regions that are subject to both warm and wet conditions may have a particularly strong control on weathering fluxes.

  • 10. Routh, Joyanto
    et al.
    Hugelius, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Kuhry, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Filley, Timothy
    Tillman, Päivi Kaislahti
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Umea University.
    Becher, Marina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Multi-proxy study of soil organic matter dynamics in permafrost peat deposits reveal vulnerability to climate change in the European Russian Arctic2014Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 368, s. 104-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Soil organic carbon (SOC) in permafrost terrain is vulnerable to climate change. Perennially frozen peat deposits store large amounts of SOC, but we know little about its chemical composition and lability. We used plant macrofossil and biomarker analyses to reconstruct the Holocene paleovegetation and paleoenvironmental changes in two peat plateau profiles from the European Russian Arctic. Peat plateaus are the main stores of permafrost soil C in the region, but during most of the Holocene peats developed as permafrost-free rich fens with woody vegetation, sedges and mosses. Around 2200 cal BP, permafrost aggraded at the site resulting in frost heave and a drastic reduction in peat accumulation under the drier uplifted surface conditions. The permafrost dynamics (aggradation, frost-heave and thaw) ushered changes in plant assemblages and carbon accumulation, and consequently in the biomarker trends too. Detailed biomarker analyses indicate abundant neutral lipids, which follow the general pattern: n-alkanols > sterols >= n-alkanes >= triterpenols. The lignin monomers are not as abundant as the lipids and increase with depth. The selected aliphatic and phenolic compounds are source specific, and they have different degrees of lability, which is useful for tracing the impact of permafrost dynamics (peat accumulation and/or decay associated with thawing). However, common interpretation of biomarker patterns, and perceived hydrological and climate changes, must be applied carefully in permafrost regions. The increased proportion (selective preservation) of n-alkanes and lignin is a robust indicator of cumulative decomposition trajectories, which is mirrored by functional compounds (e. g. n-alkanol, triterpenol, and sterol concentrations) showing opposite trends. The distribution of these compounds follows first order decay kinetics, and concurs with the down core diagenetic changes. In particular, some of the biomarker ratios (e. g. stanol/sterol and higher plant alkane index) seem promising for tracing SOC decomposition despite changes in botanical imprint, and sites spanning across different soil types and locations. Carbon accumulation rate calculated at these sites varies from 18.1 to 31.1 gC m(-2) yr(-1), and it's evident selective preservation, molecular complexity of organic compounds, and freezing conditions enhance the long-term stability of SOC. Further, our results suggest that permafrost dynamics strongly impact the more undecomposed SOC that could be rapidly remobilized through ongoing thermokarst expansion.

  • 11. Slama, Jiri
    et al.
    Kosler, Jan
    Condon, Daniel J.
    Crowley, James L.
    Gerdes, Axel
    Hanchar, John M.
    Horstwood, Matthew S. A.
    Morris, George A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Nasdala, Lutz
    Norberg, Nicholas
    Schaltegger, Urs
    Schoene, Blair
    Tubrett, Michael N.
    Whitehouse, Martin J.
    Plesovice zircon: A new natural reference material for U-Pb and Hf isotopic microanalysis2008Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 249, nr 02-jan, s. 1-35Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Matrix-matched calibration by natural zircon standards and analysis of natural materials as a reference are the principle methods for achieving accurate results in inicrobeam U-Pb dating and Hf isotopic analysis. We describe a new potential zircon reference material for laser ablation ICP-MS that was extracted from a potassic granulite facies rock collected in the southern part of the Bohemian Massif (Plesovice, Czech Republic). Data from different techniques (ID-TIMS, SIMS and LA ICP-MS) and several laboratories suggest that this zircon has a concordant U-Pb age with a weighted mean Pb-206/U-238 date of 337.13 +/- 0.37 Ma (ID-TIMS, 95% confidence limits, including tracer calibration uncertainty) and U-Pb age homogeneity on the scale used in LA ICP-MS dating. Inhomogeneities in trace element composition due to primary growth zoning prevent its use as a calibration standard for trace element analysis. The content of U varies from 465 ppm in pristine parts of the grains to similar to 3000 ppm in actinide-rich sectors that correspond to pyramidal faces with a high degree of metamictization (present in ca. 30% of the grains). These domains are easily recognized from high intensities on BSE images and should be avoided during the analysis. Hf isotopic composition of the Plesovice zircon (>0.9 wt.% Hf) is homogenous within and between the grains with a mean Hf-176/Hf-177 value of 0.282492 +/- 0.000013 (2SD). The age and Hf isotopic homogeneity of the Plesovice zircon together with its relatively high U and Pb contents make it an ideal calibration and reference material for laser ablation ICP-MS measurements, especially when using low laser energies and/or small diameters of laser beam required for improved spatial resolution.

  • 12. Snape, Joshua F.
    et al.
    Davids, Bart
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Nemchin, Alexander A.
    Whitehouse, Martin J.
    Bellucci, Jeremy J.
    Constraining the timing and sources of volcanism at the Apollo 12 landing site using new Pb isotopic compositions and crystallisation ages2018Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 482, s. 101-112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The basaltic suites collected at the Apollo 12 landing site have been interpreted as representing a stratigraphic sequence of volcanic flows emplaced in the Oceanus Procellarum region between approximately 3100-3300 Ma. This study presents Secondary Ion Mass Spectrometry (SIMS) Pb isotopic analyses of samples from each of the basaltic suites, which have been used to constrain precise crystallisation ages and initial Pb isotopic compositions. The new crystallisation ages are consistent with the three main basaltic suites (olivine, pigeonite and ilmenite) being emplaced over a period of approximately 60 million years, and the improved precision of these ages has made it possible to reinterpret the stratigraphic sequence of basalt flows underlying the Apollo 12 landing site. Contrary to previous studies, the three ilmenite basalts are determined as having the oldest ages (with a weighted average of 3187 +/- 6 Ma; 2 sigma) and are, therefore, interpreted as representing the lowest unit in the sequence, underlying the olivine and pigeonite basalts (with an age range constrained by the oldest and youngest pigeonite basalts; 3176 +/- 6 Ma and 3129 +/- 10 Ma; 2s). The initial Pb isotopic compositions have been compared with recalculated initial Sr and Nd isotopic compositions, and are consistent with the three main basaltic suites originating from magmatic sources that incorporated different proportions of a common primitive mafic cumulate and the residual trapped liquid fraction remaining after a majority of the lunar magma ocean had crystallised. Our data also demonstrate that the feldspathic basalt (12038) is unique, both in terms of its crystallisation age (3242 +/- 13 Ma) and its derivation from a distinct mantle reservoir.

  • 13.
    Sun, Xiaole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Gustafsson, Bo
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Temporal and spatial variations of rock weathering and CO2 consumption in the Baltic Sea catchment2017Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, s. 57-69Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study provides the first estimate of silicate and carbonate weathering rates and derived CO2 consumption rates for the Baltic Sea catchment using river chemistry data of 78 rivers draining into the Baltic Sea. The silicate weathering rates (denoted as total dissolved solids) of individual river basin range from 0.014 Tg/year to 4.55 Tg/year and the carbonate weathering rates range from 0.079 Tg/year to 6.49 Tg/year. The total CO2 consumption across the Baltic catchment is approximately 3.9 Tg C/year and is almost equally shared by silicates and carbonates. Uncertainty associated with the weathering estimate is around 32%, which is mainly caused by incomplete pollution correction for a few major rivers in the south. The calculations for the boreal river basins have higher certainties because of less human impacts. The CO2 consumption rate of individual river basin vary between 0.53 and 5.66 g C/m(2)/year with an average of 2.97 g C/m(2)/year, in which carbonates consume CO2, 1.4 g C/m(2)/year and silicates take 1.5 g C/m(2)/year. This is in the same range as has been reported for the Mackenzie River and Siberian river basins, but at the lower range of tropical rivers, suggesting the Baltic Sea catchment holds solid weathering signals for high-latitude systems, especially in the pristine boreal silicatedominated areas. The amount of CO2 consumed by weathering in the Baltic Sea catchment accounts for approximately 3-30% of the net ecosystem carbon exchange (10-100 g C/m(2)/year), implying that weathering contributes as a significant sink of atmospheric CO2. Although many studies have shown the positive relation between temperature and weathering rates in various river catchments, multiple regression analysis using the 40-year continuous records of river chemistry in the boreal area of the Baltic Sea catchment reveals a strong correlation between weathering flux and precipitation, but no statistically significant correlation between weathering and temperature. This suggests not only that temperature is not necessarily to be primary controlling factor for weathering rates, but also besides precipitation, other factors, like increased soil organic matter contents and water path changes may have high impact on weathering rates. The 40-year data analysis also shows generally increasing weathering fluxes by 10-20% in the pristine boreal area over the past decades. This indicates that increased CO2 consumption by weathering and the resulting elevated dissolved inorganic carbon delivery to the ocean act as a negative feedback for ocean acidification, such as the Arctic Ocean that has become more acidic due to high terrestrial organic carbon delivery together with increased river water input.

  • 14.
    Tollefsen, Elin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stockmann, Gabrielle
    Skelton, Alasdair
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Lundqvist, Lena
    Sturkell, Erik
    Secondary alteration of the Gronnedal-Ika igneous complex and the genesis of ikaite, CaCO3 center dot 6H(2)O, SW Greenland2019Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 510, s. 18-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mineral ikaite (CaCO3 center dot 6H(2)O) precipitates from a mixture of spring water and seawater as tufa columns which grow at a rate of up to 50 cm per year reaching heights of up to 18 m in Ikka Fjord, SW Greenland. In the fjord, column formation occurs only at the base of a nepheline syenite-carbonatite complex that flanks the fjord and an association has therefore been proposed. The spring water that seeps up at the bottom of the fjord is oversaturated in Na+ and HCO3-. In this study, we show that these ions were acquired by alteration reactions in the syenite-carbonatite complex: Na+ is released during replacement of nepheline by illite and analcime in nepheline-syenite rocks and HCO3- is released by oxidation of siderite to goethite in carbonatite rocks. The chemically charged groundwater mixes with seawater and gives rise to the formation of the tufa columns. We performed a mass balance to show that the mass of the carbonatite in the complex is more than sufficient to provide the CO2 needed to produce the observed mass of tufa columns. We estimated a time frame of similar to 600 years to produce the necessary CO2 to form the 700 ikaite columns in the fjord.

  • 15. Wehrmann, Laura M.
    et al.
    Riedinger, Natascha
    Brunner, Benjamin
    Kamyshny, Alexey
    Hubert, Casey R. J.
    Herbert, Lisa C.
    Brüchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Max Planck Institute for Marine Microbiology, Germany.
    Jorgensen, Bo Barker
    Ferdelman, Timothy G.
    Formolo, Michael J.
    Iron-controlled oxidative sulfur cycling recorded in the distribution and isotopic composition of sulfur species in glacially influenced fjord sediments of west Svalbard2017Inngår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, s. 678-695Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigates how glacially delivered reactive iron (oxyhydr) oxide and manganese oxide phases influence the biogeochemical cycling of sulfur in sediments of three Arctic fjords and how the biogeochemical signatures of these processes are preserved. Results reveal differences in the concentrations of dissolved iron and manganese in pore-waters and the concentration of solid-phase sulfur species within individual fjords and amongst the three fjords, likely controlled by the varying input of reactive iron (oxyhydr) oxides to the sediment. Broadly, the stations can be divided into three categories based on their biogeochemical signals. Stations in the first category, located in Smeerenburgfjorden, are characterized by relatively low concentrations of (easily) reducible particulate iron phases, increasing concentrations of iron monosulfides, pyrite, and elemental sulfur with depth, and low pore-water dissolved iron and manganese concentrations. Biogeochemical processes at these stations are primarily driven by organoclastic sulfate reduction, sulfur disproportionation and the subsequent reaction and sequestration of sulfide in the sediment as iron monosulfide and pyrite. Sulfur and oxygen isotope values of sulfate display progressive enrichment in heavy isotopes with depth at these stations. In contrast, concentrations of (easily) reducible particulate iron phases and pore-water dissolved iron (up to 850 mu M) and manganese (up to 650 mu M) are very high at stations of the second and third category, located in Kongsfjorden and Van Mijenfjorden, while iron monosulfide and pyrite contents are extremely low. The amount of pyrite and its isotope values in conjunction with organic sulfur compounds provide evidence for a detrital origin of a fraction of these sulfur compounds. At the Kongsfjorden and Van Mijenfjorden stations, oxidative pathways of the sedimentary sulfur cycle, controlled by the high availability of reducible particulate iron phases, play an important role, leading to the effective recycling of sulfide to sulfate through sulfur intermediates and concomitant resupply of the sulfate reservoir with S-32. In both fjords, elemental sulfur was only detected at the outer fjord stations grouped into the third category. Our study provides a framework for interpreting the Fe-S-C geochemistry of similar continental shelf areas in modern settings and ultimately for identifying these environments in the rock record.

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