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  • 1.
    Achimo, Mussa
    Stockholm University.
    Sedimentology and geochemistry of the recent sediments in Maputo Bay, Mozambique2002Doctoral thesis, comprehensive summary (Other academic)
  • 2.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Soil Microorganisms and Mineral Weathering: Mechanics of Biotite Dissolution2012Conference paper (Other academic)
    Abstract [en]

    Soil microorganisms play an important role in the environment by contributing to leach and release of essential elements from soil minerals that are required not only for their own nutrition but also for plants growth. This study aims to compare between the mechanisms of different fungal and bacterial species isolated from podzol soil in biotite dissolution. Microplate devices with 6 wells were used for the biological weathering experiments. All of the sterilized microplate wells were filled with 4g/l of biotite followed by 12 ml of an iron free diluted mineral liquid medium. In these conditions, biotite particles are the only source of the essential elements for the microorganisms. To characterize the mechanisms of biotite dissolution, we monitored siderophores production, microbial biomass, pH, exchangeable cations concentration and SEM analysis for mineral surface. There was a significant difference between the behavior of the fungal and bacterial species in dissolution of biotite. This difference may be due to the variation of these microorganisms in their mechanics of interaction with mineral surface. It was observed also that these microorganisms directly and indirectly induce biotite dissolution. Defining soil as a system driven by biological mechanisms rather than chemical processes has major implications for our understanding of how the system functions and how it will respond to changing conditions.

  • 3.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    THE MICROBE-MINERAL INTERACTIONS IN THE ACIDIC PODZOL SOIL2013In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 5, 564- p.Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies, like siderophores, which are operationally defined as low-molecular-mass biogenic Fe(III)-binding compounds, that can increase iron’s bioavailability by promoting the dissolution of iron-bearing minerals. In the present study, we aimed to investigate the composition of hydroxamate siderophores in the soil horizons of the acidic podzol, and study how they are affected by the presence of specific mineral types and microbial communities.

     Three different minerals (apatite, biotite and oligioclase) were inserted in the soil horizons (O (organic), E (eluvial), B (upper illuvial), and C (mineral)). After two years, soil samples were collected from both the bulk soil (next to the minerals) and from the soil attached to the mineral surfaces. The concentration of ten different fungal tri-hydroxamates and five bacterial ones were determined by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS). In addition, total microbial composition and diversity were studied.

    Our field experiment succeeded in describing the relationship between the presence of siderophores, soil horizon and mineral type, in addition to understanding the interaction between mineral type and soil microbial composition. A wide range of fungal and bacterial hydroxamates were detected throughout the soil profile. On the other hand, the presence of the minerals completely altered the diversity of siderophores. In addition, each mineral had a unique interaction with hydroxamates in the different soil horizons. There were also a good relationship between the microbial diversity and the siderophore distribution. 

  • 4.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The Roles and Applications of Siderophores in Natural Environments2013Conference paper (Other academic)
    Abstract [en]

    Siderophores are organic compounds with low molecular mass that are produced by microorganisms growing under conditions of low iron. The primary function of these compounds is to chelate ferric iron from different terrestrial and aquatic habitats and thereby make it available for microbial cells.

    Siderophores have received much attention in recent years because of their potential roles and applications in various areas of environmental research. For instance, the production of siderophores can provide a quick identification of microbes to the species level that called “siderotyping”. On the other hand, siderophores could also function as biocontrol, biosensor, and bioremediation agents, in addition to their important role in mineral weathering and enhancing plant growth. In the present study, we aimed to investigate the composition of trihydroxamate siderophores in soil samples from different horizons (O (organic), E (eluvial), B (upper illuvial), and C (parent material)) of a podzol soil in Sweden, and study how they are affected by the presence of specific mineral types (apatite, biotite and oligioclase) that were inserted in the soil for two years in a field experiment.

    Our field experiment succeeded in describing the relationship between the presence of siderophores, soil horizons and mineral types. A wide range of fungal and bacterial hydroxamates were detected throughout the soil profile. On the other hand, the presence of the minerals completely altered the diversity of siderophores. In addition, each mineral had a unique interaction with hydroxamates in the different soil horizons. Our next step is to gain greater insight into the siderotyping to illustrate the relationship between the siderophore types that was found throughout the soil profile and on the different mineral surfaces and the microbial diversity by using metagenomic applications.

  • 5.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holm, Nils G.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The Role of Microorganisms in the diversity and distribution of siderophores in Podzolic Forest Soil2013In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 2, 161--208(48) p.Article in journal (Other academic)
    Abstract [en]

    Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies. The most important one is the production of siderophores, which are operationally defined as low-molecular-mass biogenic Fe (III)-binding compounds which may greatly increase bioavailability of Fe [1]. One of the primary biogeochemical functions of siderophores is therefore to increase Fe bioavailability by promoting the dissolution of iron-bearing minerals [2]. This study aims to understand the role of microorganisms in the chemical diversity and distribution of siderophores in podzol soil and how this diversity can contribute to the bioavailability of Fe in forest soil.Soil samples were collected from an experimental site in the area of Bispgården in central Sweden (63°07′N, 16°70′E) from the O (organic), E (eluvial), B1 (upper illuvial), and C (mineral) horizons. Concentration and chemical composition of dissolved and adsorbed siderophores in the soil samples were determined using colorimetric assays and high-performance liquid chromatography.The highest siderophore concentrations were found in the O layer and thereafter decreased by depth. Concentrations of dissolved hydroxamate, catecholate and carboxylate siderophores were up to 84, 17 and 0.2 nmol/ g soil, respectively. In contrast, concentrations of adsorbed hydroxamates, catecholates and carboxylates were only up to 1.8, 3 and 0.2 nmol/ g soil, respectively.Siderophore-producing microorganisms were isolated from the same soil samples. Viable fungi, bacteria and actinomycete counts ranged from 7 to 300, from 300 to 1800, and from 0 to 5 cfu/gm, respectively. The highest counts were found in the O and E layers. Only the E layer contained the three types of siderophore-producing microorganisms investigated in this study. Siderophores were extracted from culture filtrates of the isolated microorganisms when grown under iron-limited conditions. These extracts varied considerably in siderophore composition. Fungal isolates produced up to 183 μM of hydroxamates, especially those isolated from the O layer, whereas bacteria and actinomycete isolated from the O and E layers of the soil produced high amounts of carboxylate, catecholate and hydroxamate siderophores. Actinomycete produced up to 93 μM of hydroxamates and 47 μM of catecholates, while bacteria produced up to 34 μM of carboxylates and up to 14 μM of catecholates.The depth variability in concentration and chemical composition and the good correlation between abundance of siderophore-producing microorganisms and siderophore soil concentrations strongly suggest that these siderophore-producing microorganisms play an important role in the mobilization of iron in the podzol soil that may be important in iron availability to plants in forest environment.

    [1] Clay et al. (1981) Biochemistry 20, 2432-2436. [2] Duckworth et al. (2009) ChemGeol 260, 149-158.

  • 6.
    Alasdair, Skelton
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fredrik, Arghe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pitcairn, Iain
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spatial coupling between spilitization and carbonation ofbasaltic sills in SW Scottish Highlands: evidence of amineralogical control of metamorphic fluid flow2011In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 11, no 3, 245-259 p.Article in journal (Refereed)
    Abstract [en]

    In a geochemical and petrological analysis of overprinting episodes of fluid–rock interaction in a well-studied metabasaltic sill in the SW Scottish Highlands, we show that syn-deformational access of metamorphic fluids and consequent fluid–rock interaction is at least in part controlled by preexisting mineralogical variations. Lithological and structural channelling of metamorphic fluids along the axis of the Ardrishaig Anticline, SW Scottish Highlands, caused carbonation of metabasaltic sills hosted by metasedimentary rocks of the Argyll Group in the Dalradian Supergroup. Analysis of chemical and mineralogical variability across a metabasaltic sill at Port Cill Maluaig shows that carbonation at greenschist to epidote–amphibolites facies conditions caused by infiltration of H2O-CO2 fluids was controlled by mineralogical variations, which were present before carbonation occurred. This variability probably reflects chemical and mineralogical changes imparted on the sill during premetamorphic spilitization. Calculation of precarbonation mineral modes reveals heterogeneous spatial distributions of epidote, amphibole, chlorite and epidote. This reflects both premetamorphic spilitization and prograde greenschist facies metamorphism prior to fluid flow. Spilitization caused albitization of primary plagioclase and spatially heterogeneous growth of epidote ± calcic amphibole ± chlorite ± quartz ± calcite. Greenschist facies metamorphism caused breakdown of primary pyroxene and continued, but spatially more homogeneous, growth of amphibole + chlorite ± quartz. These processes formed diffuse epidote-rich patches or semi-continuous layers. These might represent precursors of epidote segregations, which are better developed elsewhere in the SW Scottish Highlands. Chemical and field analyses of epidote reveal the evidence of local volume fluctuations associated with these concentrations of epidote. Transient permeability enhancement associated with these changes may have permitted higher fluid fluxes and therefore more extensive carbonation. This deflected metamorphic fluid such that its flow direction became more layer parallel, limiting propagation of the reaction front into the sill interior.

  • 7.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Porcelli, D.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Anderson, L. G.
    Sanchez-Garcia, L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, P. S.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Degradation of terrestrial organic carbon, primary production and out-gassing of CO2 in the Laptev and East Siberian Seas as inferred from delta C-13 values of DIC2012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 95, 143-159 p.Article in journal (Refereed)
    Abstract [en]

    The cycling of carbon on the Arctic shelves, including outgassing of CO2 to the atmosphere, is not clearly understood. Degradation of terrestrial organic carbon (OCter) has recently been shown to be pronounced over the East Siberian Arctic Shelf (ESAS), i.e. the Laptev and East Siberian Seas, producing dissolved inorganic carbon (DIC). To further explore the processes affecting DIC, an extensive suite of shelf water samples were collected during the summer of 2008, and assessed for the stable carbon isotopic composition of DIC (delta C-13(DIC)). The delta C-13(DIC) values varied between -7.2 parts per thousand to +1.6 parts per thousand and strongly deviated from the compositions expected from only mixing between river water and seawater. Model calculations suggest that the major processes causing these deviations from conservative mixing were addition of (DIC) by degradation of OCter, removal of DIC during primary production, and outgassing of CO2. All waters below the halocline in the ESAS had delta C-13(DIC) values that appear to reflect mixing of river water and seawater combined with additions of on average 70 +/- 20 mu M of DIC, originating from degradation of OCter in the coastal water column. This is of the same magnitude as the recently reported deficits of DOCter and POCter for the same waters. The surface waters in the East Siberian Sea had higher delta C-13(DIC) values and lower DIC concentrations than expected from conservative mixing, consistent with additions of DIC from degradation of OCter and outgassing of CO2. The outgassing of CO2 was equal to loss of 123 +/- 50 mu M DIC. Depleted delta C-13(POC) values of -29 parts per thousand to -32 parts per thousand in the mid to outer shelf regions are consistent with POC from phytoplankton production. The low delta C-13(POC) values are likely due to low delta C-13(DIC) of precursor DIC, which is due to degradation of OCter, rather than reflecting terrestrial input compositions. Overall, the delta C-13(DIC) values confirm recent suggestions of substantial degradation of OCter over the ESAS, and further show that a large part of the CO2 produced from degradation has been outgassed to the atmosphere.

  • 8.
    Alm, Elisabet
    Stockholm University.
    Sveconorwegian metallogenesis in Sweden2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Two main ore types are found in the Sveconorwegian Orogen in southwestern Sweden (Southwest Scandinavian Domain). One of them comprises stratabound Cu mineralizations in the Dal group, located west of lake Vänern. The other comprises quartz veins with varying precious and base metal contents, distributed over 250 km between lake Mjøsa (southeastern Norway) and lake Vänern. In this thesis, both ore types are discussed, although the main emphasis is on Au-bearing quartz veins, particularly those in the Harnäs area near lake Vänern.

    The Dal group is a 2000 m thick sequence of clastic sediments and intercalated mafic volcanic rocks, metamorphosed under greenschist facies conditions. It records deposition mainly in a shallow marine basin, formed during a rift stage preceding the Sveconorwegian orogeny (c. 1.15-0.9 Ga). The volcanic rocks have been subject to various degrees of sodic and/or potassic alteration. Geochemical and Sm-Nd isotopic evidence indicate a continental setting of volcanism. Cu mineralizations (chalcopyrite and bornite) occur at two stratigraphic levels. An ore-genetic model involving synsedimentary (or syndiagenetic) deposition of sulphides from metal-bearing fluids is favoured.

    Among Au-bearing quartz veins in the Mjøsa-Vänern ore district, four paragenetic types have been distinguished: Cu-dominated veins with chalcopyrite and/or bornite; Pb-Cu-bearing veins with pyrite, galena and chalcopyrite; Zn-Pb-dominated veins with sphalerite, galena, pyrite and chalcopyrite; Mn-bearing vein(s) with galena, chalcopyrite and hausmannite. In addition, e.g. native gold, argyrodite, hessite, tellurobismuthite and altaite are recognized. The ore lead isotopic composition is complex and metals appear to be derived from a variety of source rocks.

    The orthogneisses, which constitute the host rocks to the Harnäs veins and the Brustad Au quartz veins (Eidsvoll, near lake Mjøsa), have been investigated with respect to geochemistry, U-Pb zircon age and feldspar lead isotopic composition. The obtained intrusion age of the Brustad augen gneiss is 1674 ± 10 Ma and this rock is considered to belong to the Transscandinavian Igneous Belt. The Harnäs gneiss yielded a protolith age of 1595 +24/-17 Ma and is considered to be a member of the Åmål granitoid suite. Both orthogneisses have undergone ductile deformation during the Sveconorwegian orogeny. A complete isotopic resetting of the feldspar lead through dynamic recrystallization in conjunction with this deformation, at c. 1.0 Ga, has been demonstrated.

    The steeply dipping Harnäs veins are hosted in a local left-lateral shear zone, which transects the fabric in the surrounding orthogneisses. The moderate wall rock alteration was mainly sericitic. Fluid inclusions show that the ore-bearing vein system at Harnäs developed essentially in three stages: a quartz stage, a pyrite-gold stage and finally a galena stage. The early ore fluid was CO2-bearing, of low salinity and with a temperature of c. 200 oC, while in the galena stage it was purely aqueous, with a slightly higher salinity and a slightly lower temperature. Oxygen and sulphur isotope results imply a predominantly metamorphic origin for the ore fluid and suggest that the fluid constituents were derived from the regional orthogneisses. Ore lead isotopic compositions indicate metal derivation from these orthogneisses shortly after the Sveconorwegian deformation and resetting of feldspar lead. Subordinate Au-anomalous quartz veins in the Harnäs area as well as the Brustad Au quartz veins show characteristics similar to the Harnäs veins. Despite recognized variations, e.g. in mineralogy, a common origin is envisaged for most veins in the Mjøsa-Vänern ore district. They are characterized as late Proterozoic orogenic type Au deposits, with modern analogues e.g. in the western Alps.

  • 9.
    Andersson, Rina A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip A.
    Effect of climate change on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic2012In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 53, 63-72 p.Article in journal (Refereed)
    Abstract [en]

    Lipid biomarkers from a peat plateau profile from the Northeast European Russian Arctic were analyzed. The peat originated as a wet fen ca. 9 ka BP and developed into a peat bog after the onset of permafrost ca. 2.5 ka BP. The distributions and abundances of n-alkanols, n-alkanoic acids, n-alkanes, n-alkan-2-ones and sterols were determined to study the effect of degradation on their paleoclimate proxy information. Plant macrofossil analysis was also used in combination with the lipid distributions. The n-alkanol and n-alkanoic acid distributions in the upper part of the sequence generally correspond to compositions expected from plant macrofossil assemblages. Their carbon preference index (CPI) values increase with depth and age, whereas those of the n-alkanes decrease. The different CPI patterns suggest that n-alkanoic acids and n-alkanols deeper in the sequence may be produced during humification through alteration of other lipids. Excursions in the n-alkanoic acid content also suggest an important contribution of invasive roots to the lipid biomarker composition. The CPIs associated with these compounds show that under permafrost conditions organic material from Sphagnum is better preserved than material from vascular plants. Increasing stanol/stenol ratio values and decreasing n-alkane CPI values indicate progressive degradation of organicmatter (OM) with depth. The n-alkan-2-one/n-alkane and n-alkan-2-one/n-alkanoic acid ratioswere shown to be useful proxies that can reflect the degree of OM preservation and suggest that both microbial oxidation of n-alkanes and decarboxylation of n-alkanoic acids produce n-alkan-2-ones in this peat sequence.

  • 10.
    Applegate, Patrick
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Alley, Richard B.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Challenges in the Use of Cosmogenic Exposure Dating of Moraine Boulders to Trace the Geographic Extents of Abrupt Climate Changes: The Younger Dryas Example2011In: Abrupt Climate Change: Mechanisms, Patterns, and Impacts / [ed] Rashid, H; Polyak, L; MosleyThompson, E, Washington DC: American Geophysical Union (AGU), 2011, 111-122 p.Chapter in book (Refereed)
    Abstract [en]

    Cosmogenic exposure dating has sometimes been used to identify moraines associated with short-lived climatic events, such as the Younger Dryas (12.9-11.7 ka). Here we point out two remaining challenges in using exposure dating to identify moraines produced by abrupt climate changes. Specifically, (1) a commonly applied sampling criterion likely yields incorrect exposure dates at some sites, and (2) geomorphic processes may introduce bias into presently accepted nuclide production rate estimates. We tit a geomorphic process model that treats both moraine degradation and boulder erosion to collections of exposure dates from two moraines that were deposited within a few thousand years of the Younger Dryas. Subsampling of the modeled distributions shows that choosing boulders for exposure dating based on surface freshness yields exposure dates that underestimate the true age of the moraine by up to several thousand years. This conclusion applies only where boulders do not erode while buried but do erode after exhumation. Moreover, one of our fitted data sets is part of the global nuclide production rate database. Our fit of the moraine degradation model to this data set suggests that nuclide production rates at that site are several percent higher than previously thought. Potential errors associated with sampling strategies and production rate estimates are large enough to interfere with exposure dating of moraines, especially when the moraines are associated with abrupt climate changes. We suggest sampling strategies that may help minimize these problems, including a guide for determining the minimum number of samples that must be collected to answer particular paleoclimate questions.

  • 11. Balic-Zunic, Tonci
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Katerinopoulou, Anna
    Schmith, Johan Haagen
    Full analysis of feldspar texture and crystal structure by combining X-ray and electron techniques2013In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 98, no 1, 41-52 p.Article in journal (Refereed)
    Abstract [en]

    Feldspar crystals typically show a range of exsolution and polysynthetic twinning textures that can present problems for their full characterization, but at the same time give important information about their genesis. We present an integrated procedure for the micro-texture analysis, twin law identification plus crystal structure refinement of all components in a feldspar intergrowth. This procedure was applied to perthitic intergrowths in feldspars from two different pegmatites in the Larvik plutonic complex in the southern part of the Oslo region, Norway. It revealed that the two starting high-temperature (HT) feldspars had similar global chemical compositions but underwent significantly different cooling histories, with cooling times probably differing by over an order of magnitude. Powder X-ray diffraction with Rietveld refinement was used for a preliminary identification of the mineral components and concluding quantitative phase analysis. Electron microprobe analysis was used to bracket the chemical compositions of the constituents. Electron backscatter diffraction was used to reveal the texture of the samples, twin laws and spatial distribution and crystallographic orientation of the crystal domains. Single-grain X-ray diffraction recorded by an area detector was applied for a simultaneous integration of reflection intensities for all crystallographic domains with different orientations and severe diffraction overlaps. The crystal structures were refined using the program JANA2006 that allows a simultaneous calculation for structurally different components. Combined results of various methods helped improve accuracy and resolve ambiguities that arise from the application of a single technique. The approach is widely applicable to the study of mineral intergrowths and bridges an existing gap in the routinely accessible data on the structural characteristics of rock constituents.

  • 12. Baresel, Christian
    et al.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Uncertainty-Accounting Environmental Policy and Management of Water Systems2007In: Environmental Science & Technology, Vol. 41, no 10, 3653–3659- p.Article in journal (Refereed)
    Abstract [en]

    Environmental policies for water quality and ecosystem

    management do not commonly require explicit stochastic

    accounts of uncertainty and risk associated with the

    quantification and prediction of waterborne pollutant loads

    and abatement effects. In this study, we formulate and

    investigate a possible environmental policy that does require

    an explicit stochastic uncertainty account. We compare

    both the environmental and economic resource allocation

    performance of such an uncertainty-accounting environmental

    policy with that of deterministic, risk-prone and riskaverse

    environmental policies under a range of different

    hypothetical, yet still possible, scenarios. The comparison

    indicates that a stochastic uncertainty-accounting

    policy may perform better than deterministic policies over

    a range of different scenarios. Even in the absence of

    reliable site-specific data, reported literature values appear

    to be useful for such a stochastic account of uncertainty.

  • 13.
    Bastviken, David
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geokemi.
    Thomsen, Frida
    Karlsson, Susanne
    Svensson, Teresia
    Sanden, Per
    Shaw, George
    Matucha, Miroslav
    Öberg, Gunilla
    Chloride retention in forest soil by microbial uptake and by natural chlorination of organic matter2007In: Geochimica Cosmochimica Acta, ISSN 0016-7037, Vol. 71, no 13, 3182-3192 p.Article in journal (Refereed)
    Abstract [en]

    Inorganic chlorine (i.e. chloride; Cl-in) is generally considered inert in soil and is often used as a tracer of soil and ground water movements. However, recent studies indicate that substantial retention or release of Cl-in can occur in soil, but the rates and processes responsible under different environmental conditions are largely unknown. We performed Cl-36 tracer experiments which indicated that short-term microbial uptake and release of Cl-in, in combination with more long-term natural formation of chlorinated organic matter (Cl-org), caused Cl-in imbalances in coniferous forest soil. Extensive microbial uptake and release of Cl-in occurred over short time scales, and were probably associated with changes in environmental conditions. Up to 24% of the initially available Clin within pore water was retained by microbial uptake within a week in our experiments, but most of this Cl-in, was released to the pore water again within a month, probably associated with decreasing microbial populations. The natural formation of Clorg resulted in a net immobilization of 4% of the initial pore water Clin over four months. If this rate is representative for the area where soil was collected, Clorg formation would correspond to a conversion of 25% of the yearly wet deposition of Cl-in. The study illustrates the potential of two Clin retaining processes in addition to those previously addressed elsewhere (e.g. uptake of chloride by vegetation). Hence, several processes operating at different time scales and with different regulation mechanisms can cause Clin imbalances in soil. Altogether, the results of the present study (1) provide evidence that Cl-in cannot be assumed to be inert in soil, (2) show that microbial exchange can regulate pore water Cl-in, concentrations and (3) confirm the controversial idea of substantial natural chlorination of soil organic matter.

  • 14. Bauer, Friederike U.
    et al.
    Glasmacher, Ulrich A.
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Karl, Markus
    Schumann, Andreas
    Nagudi, Betty
    Tracing the exhumation history of the Rwenzori Mountains, Albertine Rift, Uganda, using low-temperature thermochronology2013In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 599, 8-28 p.Article in journal (Refereed)
    Abstract [en]

    The Rwenzori Mtns form a striking feature within the Albertine Rift of the East African Rift System. They are made up of a dissected Precambrian metamorphic basement block reaching heights of more than 5 km. Applying low-temperature therrnochronology a complex exhumation history becomes evident, where rock and surface uplift can be traced from Palaeozoic to Neogene times. Fission-track and (U-Th-Sm)/He cooling ages and derived cooling histories allow distinguishing different blocks in the Rwenzori Mtns. In the central part a northern and a southern block are separated by a putative NW-SE trending fault; with the northern block showing distinctly younger apatite fission-track ages (similar to 130 Ma) than the southern block (similar to 300 Ma). Cooling ages in both blocks do not vary significantly with elevation, despite considerable differences in elevation. Thermal history modelling reflects protracted cooling histories. Modelled t-T paths show decoupled blocks that were relocated separately along distinct fault planes, which reactivated pre-existing structures, inherited from Palaeozoic folding and thrusting. Initial cooling affected the Rwenzori area in Silurian to Devonian times, followed by Mesozoic and Cainozoic cooling events. Pre-Neogene evolution seems to be triggered by tectonic processes like the opening of the Indian Ocean and the south Atlantic. From thermochronological data the formation of a Mesozoic Albertine high is conceivable. In Cainozoic times the area was affected by rifting, resulting in differentiated surface uplift. Along the western flank of the Rwenzori Mtns, surface uplift was more pronounced. This is also reflected in their recent topography, formed by accelerated rock uplift in the near past (Pliocene to Pleistocene). Erosion could not compensate for this most recent uplift, resulting in apatite He ages of Oligocene to Miocene age or even older.

  • 15.
    Beranek, Luke P.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    van Staal, Cees R.
    McClelland, William C.
    Israel, Steve
    Mihalynuk, Mitch G.
    Detrital zircon Hf isotopic compositions indicate a northern Caledonian connection for the Alexander terrane2013In: Lithosphere, ISSN 1941-8264, E-ISSN 1947-4253, Vol. 5, no 2, 163-168 p.Article in journal (Refereed)
    Abstract [en]

    Various plate reconstructions predict that the Alexander terrane, a Neoproterozoic-Jurassic crustal fragment now located in the North American Cordillera, evolved in proximity to the northern Appalachian-Caledonian convergent margin during assembly of supercontinent Laurussia. To test stratigraphic connections with Laurussia that are implied by these plate reconstructions, we measured the Hf isotopic compositions of 176 detrital zircons from two relevant sedimentary sequences of the Alexander terrane. An older, Upper Silurian-Lower Devonian terrestrial to shallow-marine molasse sequence yields 405-490 Ma detrital zircons with negative epsilon(Hf(t)) values and Mesoproterozoic to Paleoproterozoic Hf model ages. In combination with paleomagnetic and biogeographic constraints, these Hf data argue for the molasse strata to be now-displaced equivalents of the Old Red Sandstone and primarily sourced from crustally contaminated granitoids in the Greenland, Svalbard, or British Caledonides. Late Silurian-Early Devonian orogenesis in the Alexander terrane is therefore likely related to the Scandian-Salinic phase of Appalachian-Caledonian mountain building. Younger, Middle Devonian sequences of the Alexander terrane are endowed in 390-490 Ma detrital zircons with positive epsilon(Hf(t)) values and Neoproterozoic Hf model ages. These isotopic signatures are consistent with the erosion of local basement rocks during the opening of the Slide Mountain-Angayucham backarc rift and tectonic separation of the Alexander terrane from northern Laurussia.

  • 16. Birkholz, Axel
    et al.
    Smittenberg, Rienk H.
    Geological Institute, ETH Zürich, Schweiz.
    Bernasconi, Stefano
    Hajdas, Irka
    Wacker, Lukas
    Isolation and compound specific radiocarbon dating of terrigenous branched glycerol dialkyl glycerol tetraethers (brGDGTs)2013In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 60, 9-19 p.Article in journal (Refereed)
  • 17.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Benthic metabolism and sediment nitrogen cycling in Baltic sea coastal areas: the role of eutrophication, hypoxia and bioturbation2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Eutrophication is one of the greatest threats for the Baltic Sea, and one of its more critical consequences is bottom water hypoxia. Nutrient enrichment and oxygen-depletion affect both the deep central basins and a number of coastal areas, even though strategies for nutrient reduction have lately been implemented. In order to better understand why those threats are expanding and formulate more effective remediation strategies two main achievements are needed: (1) new data on benthic nutrient dynamics should be available in order to develop updated budgets for sensitive Baltic areas; (2) the main transformation processes and their regulation mechanisms (i.e. oxygen availability, presence of macrofauna, different organic loading scenarios) should be better constrained.

    Paper I was able to demonstrate that re-oxygenation of previously anoxic sediment has a positive effect on the ecosystem because of better retention of nutrients and efficient conversion of fixed nitrogen to nitrogen gas. Sediment colonization by the invasive genus Marenzelleria counteracts some of the positive aspects provided by benthic oxygenation (in particular, nutrient retention, N2 loss). A possible explanation for this reversal can be that Marenzelleria does stimulate anaerobic more that aerobic metabolism.

    Results from Paper II suggest that at the outermost stations of Himmerfjärden denitrification follows a pronounced seasonal pattern, primarily regulated by bottom water temperatures. At the innermost and impacted site oxygen level in the bottom water varies considerably during the year and causes denitrification/DNRA predominance to be the main nitrate reduction pathway. On an annual scale, the net amount of lost N2 is comparable at the four sampling sites and accounts for 96% of the total DIN discharged from the sewage treatment plant, suggesting that denitrification in the estuarine sediment acts as a major nitrogen sink for external N inputs.

  • 18.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Control factors of the marine nitrogen cycle: The role of meiofauna, macrofauna, oxygen and aggregates2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The ocean is the most extended biome present on our planet. Recent decades have seen a dramatic increase in the number and gravity of threats impacting the ocean, including discharge of pollutants, cultural eutrophication and spread of alien species. It is essential therefore to understand how different impacts may affect the marine realm, its life forms and biogeochemical cycles. The marine nitrogen cycle is of particular importance because nitrogen is the limiting factor in the ocean and a better understanding of its reaction mechanisms and regulation is indispensable. Furthermore, new nitrogen pathways have continuously been described. The scope of this project was to better constrain cause-effect mechanisms of microbially mediated nitrogen pathways, and how these can be affected by biotic and abiotic factors.

    This thesis demonstrates that meiofauna, the most abundant animal group inhabiting the world’s seafloors, considerably alters nitrogen cycling by enhancing nitrogen loss from the system. In contrast, larger fauna such as the polychaete Marenzelleria spp. enhance nitrogen retention, when they invade eutrophic Baltic Sea sediments. Sediment anoxia, caused by nutrient excess, has negative consequences for ecosystem processes such as nitrogen removal because it stops nitrification, which in turn limits both denitrification and anammox. This was the case of Himmerfjärden and Byfjord, two estuarine systems affected by anthropogenic activities, such as treated sewage discharges. When Byfjord was artificially oxygenated, nitrate reduction mechanisms started just one month after pumping. However, the balance between denitrification and nitrate ammonification did not favor either nitrogen removal or its retention.

    Anoxia is also present in aggregates of the filamentous cyanobacteria Nodularia spumigena. This thesis shows that even in fully oxic waters, millimetric aggregates can host anaerobic nitrogen processes, with clear implications for the pelagic compartment. While the thesis contributed to our knowledge on marine nitrogen cycling, more data need to be collected and experiments performed in order to understand key processes and regulation mechanisms of element cycles in the ocean. In this way, stakeholders may follow and take decisions in order to limit the continuous flow of human metabolites and impacts on the marine environment.

  • 19.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Callac, Nolwenn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Vicenzi, Alessandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chi Fru, Ernest
    Stockholm University, Faculty of Science, Department of Geological Sciences. Cardiff University, UK.
    Nascimento, Francisco J. A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Methane fluxes from coastal sediments are enhanced by macrofauna2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 1, 13145Article in journal (Refereed)
    Abstract [en]

    Methane and nitrous oxide are potent greenhouse gases (GHGs) that contribute to climate change. Coastal sediments are important GHG producers, but the contribution of macrofauna (benthic invertebrates larger than 1 mm) inhabiting them is currently unknown. Through a combination of trace gas, isotope, and molecular analyses, we studied the direct and indirect contribution of two macrofaunal groups, polychaetes and bivalves, to methane and nitrous oxide fluxes from coastal sediments. Our results indicate that macrofauna increases benthic methane efflux by a factor of up to eight, potentially accounting for an estimated 9.5% of total emissions from the Baltic Sea. Polychaetes indirectly enhance methane efflux through bioturbation, while bivalves have a direct effect on methane release. Bivalves host archaeal methanogenic symbionts carrying out preferentially hydrogenotrophic methanogenesis, as suggested by analysis of methane isotopes. Low temperatures (8 °C) also stimulate production of nitrous oxide, which is consumed by benthic denitrifying bacteria before it reaches the water column. We show that macrofauna contributes to GHG production and that the extent is dependent on lineage. Thus, macrofauna may play an important, but overlooked role in regulating GHG production and exchange in coastal sediment ecosystems.

  • 20.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deutsch, Barbara
    Bartoli, Marco
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seasonal benthic nutrient cycling in a Baltic sea estuary2012In: / [ed] The Oceanography Society, American Society of Limnology and Oceanography, American Geophysical Union, 2012Conference paper (Other academic)
    Abstract [en]

    Decades of urban, industrial, and agricultural discharge of nitrogen and phosphorus to the Baltic Sea have contributed to the spreading of water column hypoxia and annual widespread cyanobacteria blooms. Central to mitigating Baltic Sea eutrophication is to resolve how much reduction strategies of external N and P loading are offset by internal loading of the Baltic through nutrient recycling from the sediment. We investigated the seasonal variation of benthic nitrogen and phosphorus cycling in an estuary of the Baltic impacted by decades of sewage discharge. Sediment nutrient fluxes, denitrification, Anammox, DNRA, potential nitrification, and total and diffusive oxygen uptake (TOU/DOU) were quantified with 15N-tracer methods and microsensor profiling. Data indicate benthic net efflux of ammonium and phosphorus during the summer months, decreasing N2 loss with increasing organic matter content, and benthic N/P regeneration with a ratio of 3 to 7 compared to the sewage discharge N/P of ≈ 25, and a significant contribution (6 to 25%) of Anammox to N2 loss. On average benthic denitrification and Anammox may reduce the N load to the estuary by up to 54%.

  • 21.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hylén, Astrid
    Rattray, Jayne E.
    Kononets, Mikhail Y.
    Ekeroth, Nils
    Roos, Per
    Thamdrup, Bo
    Brüchert, Volker
    Hall, Per O. J.
    The fate of fixed nitrogen in marine sediments with low organic loading: an in situ study2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 2, 285-300 p.Article in journal (Refereed)
    Abstract [en]

    Over the last decades, the impact of human activities on the global nitrogen (N) cycle has drastically increased. Consequently, benthic N cycling has mainly been studied in anthropogenically impacted estuaries and coasts, while in oligotrophic systems its understanding is still scarce. Here we report on benthic solute fluxes and on rates of denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) studied by in situ incubations with benthic chamber landers during two cruises to the Gulf of Bothnia (GOB), a cold, oligotrophic basin located in the northern part of the Baltic Sea. Rates of N burial were also inferred to investigate the fate of fixed N in these sediments. Most of the total dissolved fixed nitrogen (TDN) diffusing to the water column was composed of organic N. Average rates of dinitrogen (N-2) production by denitrification and anammox (range: 53-360 mu mol Nm(-2) day(-1)) were comparable to those from Arctic and subarctic sediments worldwide (range: 34-344 mu mol Nm(-2) day(-1)). Anammox accounted for 18-26% of the total N2 production. Absence of free hydrogen sulfide and low concentrations of dissolved iron in sediment pore water suggested that denitrification and DNRA were driven by organic matter oxidation rather than chemolithotrophy. DNRA was as important as denitrification at a shallow, coastal station situated in the northern Bothnian Bay. At this pristine and fully oxygenated site, ammonium regeneration through DNRA contributed more than one-third to the TDN efflux and accounted, on average, for 45% of total nitrate reduction. At the offshore stations, the proportion of DNRA in relation to denitrification was lower (0-16% of total nitrate reduction). Median value and range of benthic DNRA rates from the GOB were comparable to those from the southern and central eutrophic Baltic Sea and other temperate estuaries and coasts in Europe. Therefore, our results contrast with the view that DNRA is negligible in cold and well-oxygenated sediments with low organic carbon loading. However, the mechanisms behind the variability in DNRA rates between our sites were not resolved. The GOB sediments were a major source (237 kt yr(-1), which corresponds to 184% of the external N load) of fixed N to the water column through recycling mechanisms. To our knowledge, our study is the first to document the simultaneous contribution of denitrification, DNRA, anammox, and TDN recycling combined with in situ measurements.

  • 22.
    Borthwick, Verity E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schmidt, S.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gundlach, C.
    Quantification of mineral behavior in four dimensions: grain boundary and substructure dynamics in salt2012In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 13, Q05005- p.Article in journal (Refereed)
    Abstract [en]

    Here we present the first four dimensional (time and three dimensional space resolved) experiment on a strongly deformed geological material. Results show that even complicated microstructures with large continuous and discontinuous changes in crystallographic orientation can be resolved quantitatively. The details that can be resolved are unprecedented and therefore the presented technique promises to become influential in a wide range of geoscientific investigations. Grain and subgrain scale processes are fundamental to mineral deformation and associated Earth Dynamics, and time resolved observation of these processes is vital for establishing an in-depth understanding of the latter. However, until recently, in situ experiments were restricted to observations of two dimensional surfaces. We compared experimental results from two dynamic, in situ annealing experiments on a single halite crystal; a 2D experiment conducted inside the scanning electron microscope and a 3D X-ray diffraction experiment. This allowed us to evaluate the possible effects of the free surface on grain and subgrain processes. The extent to which surface effects cause experimental artifacts in 2D studies has long been questioned. Our study shows that, although the nature of recovery processes are the same, the area swept by subgrain boundaries is up to 5 times larger in the volume than observed on the surface. We suggest this discrepancy is due to enhanced drag force on subgrain boundaries by thermal surface grooving. Our results show that while it is problematic to derive absolute mobilities from 2D experiments, derived relative mobilities between boundaries with different misorientation angles can be used.

  • 23.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Raedler, K-H
    Yoshizawa's cross-helicity effect and its quenching2013In: Geophysical and Astrophysical Fluid Dynamics, ISSN 0309-1929, E-ISSN 1029-0419, Vol. 107, no 1-2, 207-217 p.Article in journal (Refereed)
    Abstract [en]

    A central quantity in mean-field magnetohydrodynamics is the mean electromotive force , which in general depends on the mean magnetic field. It may however also have a part independent of the mean magnetic field. Here we study an example of a rotating conducting body of turbulent fluid with non-zero cross-helicity, in which a contribution to proportional to the angular velocity occurs (Yoshizawa, A., Self-consistent turbulent dynamo modeling of reversed field pinches and planetary magnetic fields. Phys. Fluids B 1990, 2, 15891600). If the forcing is helical, it also leads to an effect, and large-scale magnetic fields can be generated. For not too rapid rotation, the field configuration is such that Yoshizawa's contribution to is considerably reduced compared to the case without effect. In that case, large-scale flows are also found to be generated.

  • 24.
    Brüchert, Volker
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raymond, Caroline
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sediment med nyckelroll i näringsväven2014In: HavsUtsikt, ISSN 1104-0513, Vol. 1, 20-21 p.Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    I sedimenten sker processer som kan vara helt avgörande för näringsbalansen i havsvattnet. Omvandlingen av fosfor till olika former är relativt väl känd, medan detaljerna i kvävets kretslopp är betydligt mindre kända. Mer än hälften av den årliga tillförseln av kväve till Östersjön beräknas omsättas till kvävgas i sedimentet, vilket sedan går förlorat för de flesta marina organismer.

  • 25. Cathalot, C.
    et al.
    Rabouille, C.
    Tisnerat-Laborde, N.
    Toussaint, F.
    Kerherve, P.
    Buscail, R.
    Loftis, K.
    Sun, M. -Y
    Tronczynski, J.
    Azoury, S.
    Lansard, B.
    Treignier, C.
    Pastor, L.
    Tesi, Tommaso
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The fate of river organic carbon in coastal areas: A study in the Rhone River delta using multiple isotopic (delta C-13, Delta C-14) and organic tracers2013In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 118, 33-55 p.Article in journal (Refereed)
    Abstract [en]

    A significant fraction of the global carbon flux to the ocean occurs in River-dominated Ocean Margins (RiOMar) although large uncertainties remain in the cycle of organic matter (OM) in these systems. In particular, the OM sources and residence time have not been well clarified. Surface (0-1 cm) and sub-surface (3-4 cm) sediments and water column particles (bottom and intermediate depth) from the Rhone River delta system were collected in June 2005 and in April 2007 for a multi-proxy study. Lignin phenols, black carbon (BC), proto-kerogen/BC mixture, polycyclic aromatic hydrocarbons (PAHs), carbon stable isotope (delta C-13(OC)), and radiocarbon measurements (delta C-14(OC)) were carried out to characterize the source of sedimentary organic material and to address degradation and transport processes. The bulk OM in the prodelta sediment appears to have a predominantly modern terrigenous origin with a significant contribution of modern vascular C-3 plant detritus (Delta C-14(OC) = 27.9 parts per thousand, delta C-13(OC) = -27.4 parts per thousand). In contrast, the adjacent continental shelf, below the river plume, seems to be dominated by aged OM (Delta C-14(OC) = -400 parts per thousand, delta C-13(OC) = -24.2 parts per thousand), and shows no evidence of dilution and/or replacement by freshly produced marine carbon. Our data suggest an important contribution of black carbon (50% of OC) in the continental shelf sediments. Selective degradation processes occur along the main dispersal sediment system, promoting the loss of a modern terrestrial OM but also proto-kerogen-like OM. In addition, we hypothesize that during the transport across the shelf, a long term resuspension/deposition loop induces efficient long term degradation processes able to rework such refractory-like material until the OC is protected by the mineral matrix of particles.

  • 26. Cory, N.
    et al.
    Andrén, Cecilia M
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bishop, K.
    Modelling inorganic Aluminium with WHAM in environmental monitoring2007In: APPLIED GEOCHEMISTRY, ISSN 0883-2927, Vol. 22, 1196-1201 p.Article in journal (Refereed)
    Abstract [en]

    Due to the varying toxicity of different Al species, information about Al concentration and speciation is important when assessing water quality. Modelling Al speciation can support operational monitoring programmes where Al speciation is not measured directly. Modelling also makes it possible to retroactively speciate older samples where laboratory fractionation was not undertaken. Organic-rich waters are a particular challenge for both laboratory analysis and models. This paper presents the modelling of Al speciation in Swedish surface waters using the Windermere Humic Acid Model (WHAM). The model was calibrated with data from operational monitoring, the Swedish national survey of lakes and rivers, and covers a broad spectrum of physical and chemical conditions. Calibration was undertaken by varying the amount of DOC active in binding Al. A sensitivity analysis identified the minimum parameters required as model input variables primarily to be total Al, organic C, pH, F-, and secondly Fe, Ca and Mg. The observed and modelled Ali had no significant differences (Spearman rank, p < 0.01), however, lake samples modelled better than rivers. Samples were placed in the correct toxicological category in 89-95% of the cases. The importance of the size of the calibration data set was assessed, and reducing the calibration data set resulted in poorer correlations, but had little impact on the toxicological placement. Overall, the modelling gave satisfactory results from samples covering a broad spectrum of physical and chemical conditions. This indicates the potential value of WHAM as a tool in operational monitoring of surface waters.

  • 27. Dahl, Tais W.
    et al.
    Hammarlund, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Do large predatory fish track ocean oxygenation?2011In: Communicative & Integrative Biology, ISSN 1942-0889, E-ISSN 1942-0889, Vol. 4, no 1, 92-94 p.Article in journal (Refereed)
    Abstract [en]

    The Devonian appearance of 1-10 meter long armored fish (placoderms) coincides with geochemical evidence recording a transition into fully oxygenated oceans.1 A comparison of extant fish shows that the large individuals are less tolerant to hypoxia than their smaller cousins. This leads us to hypothesize that Early Paleozoic O2 saturation levels were too low to support >1 meter size marine, predatory fish. According to a simple model, both oxygen uptake and oxygen demand scale positively with size, but the demand exceeds supply for the largest fish with an active, predatory life style. Therefore, the largest individuals may lead us to a lower limit on oceanic O2 concentrations. Our presented model suggests 2-10 meter long predators require >30-50% PAL while smaller fish would survive at <25% PAL. This is consistent with the hypothesis that low atmospheric oxygen pressure acted as an evolutionary barrier for fish to grow much above ~1 meter before the Devonian oxygenation.

  • 28. Dahl, Tais W.
    et al.
    Hammarlund, Emma U.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anbar, Ariel D.
    Bond, David P. G.
    Gill, Benjamin C.
    Gordon, Gwyneth W.
    Knoll, Andrew H.
    Canfield, Donald E.
    Reply to Butterfield: The Devonian radiation of large predatory fish coincided with elevated athospheric oxygen levels2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 9, E29- p.Article in journal (Refereed)
    Abstract [en]

    We welcome this opportunity to clarify the conclusions and implications of our recent publication in PNAS. Butterfield (1) raises four issues regarding the oxygenation of the Paleozoic Earth's surface and its correlation to animal evolution. Our geochemical and paleontological data supported ocean oxygenation in the Silurian-Early Devonian (2), a critical transition in Earth history that influenced biogeochemical cycles and biological systems.

    First, Butterfield suggests that evidence of charcoal in late Silurian rocks is incompatible with our claim that the earlier Paleozoic atmosphere had oxygen levels below 50% PAL (present-day atmospheric level). This counterargument rests on the assumption that the “fire window” of 62–166% PAL oxygen is well defined, but this is not the case (3).

  • 29. Dahl, Tais W.
    et al.
    Hammarlund, Emma U.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anbar, Ariel D.
    Bond, David P. G.
    Gill, Benjamin C.
    Gordon, Gwyneth W.
    Knoll, Andrew H.
    Nielsen, Arne T.
    Schovsbo, Niels H.
    Canfield, Donald E.
    Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 42, 17911-17915 p.Article in journal (Refereed)
    Abstract [en]

    The evolution of Earth's biota is intimately linked to the oxygenation of the oceans and atmosphere. We use the isotopic composition and concentration of molybdenum (Mo) in sedimentary rocks to explore this relationship. Our results indicate two episodes of global ocean oxygenation. The first coincides with the emergence of the Ediacaran fauna, including large, motile bilaterian animals, ca. 550-560 million year ago (Ma), reinforcing previous geochemical indications that Earth surface oxygenation facilitated this radiation. The second, perhaps larger, oxygenation took place around 400 Ma, well after the initial rise of animals and, therefore, suggesting that early metazoans evolved in a relatively low oxygen environment. This later oxygenation correlates with the diversification of vascular plants, which likely contributed to increased oxygenation through the enhanced burial of organic carbon in sediments. It also correlates with a pronounced radiation of large predatory fish, animals with high oxygen demand. We thereby couple the redox history of the atmosphere and oceans to major events in animal evolution.

  • 30. De Brabandere, L.
    et al.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kononets, M.
    Viktorsson, Lena
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Stigebrandt, A.
    Thamdrup, B.
    Hall, P. O. J.
    Oxygenation of an anoxic fjord basin strongly stimulates benthic denitrification and DNRAManuscript (preprint) (Other academic)
  • 31. Dickens, Gerald R.
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A comment on "Pliocene climate change of the Southwest Pacific and the impact of ocean gateways" by C. Karas, D. Nurnberg, R. Tiedemann, D. Garbe Schonberg, EPSL 301, 117-124 (2011)2012In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 331, 364-365 p.Article in journal (Other academic)
  • 32. Duffy, Brendan
    et al.
    Quigley, Mark
    Harris, Ron
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Canterbury.
    Arc-parallel extrusion of the Timor sector of the Banda arc-continent collision2013In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 32, no 3, 641-660 p.Article in journal (Refereed)
    Abstract [en]

    Structural studies of synorogenic basins in Timor using field and remote sensing techniques provide new structural and geomorphic evidence for syn-collisional extension in the converging plate boundary zone between the Australian Plate and Banda Arc. Fault mapping and kinematic analysis at scales ranging from outcrop (<1m(2)) to the dimensions of the active orogen in East Timor (similar to 100km(2)) identify a predominance of NW-SE oriented dextral-normal faults and NE-SW oriented sinistral-normal faults that collectively bound large (5-20km(2)) bedrock massifs throughout the island. These fault systems intersect at non-Andersonian conjugate angles of approximately 120 degrees and accommodate an estimated 20km of NE-directed extension across the Timor orogen based on reconstructions of fault-dismembered massifs. Major orogen-parallel ENE-oriented faults on the northern and southern sides of Timor exhibit normal-sinistral and normal-dextral kinematics, respectively. The overall pattern of deformation is one of lateral crustal extrusion sub-parallel to the Banda Arc. Stratigraphic relationships suggest that extrusion began prior to 5.5Ma, before pronounced rapid uplift of the orogen. We link this to progressive coupling of the fore-arc to an underthrust plateau on the Australian Plate and subduction of its ocean crust. Our results enable us to track the structural evolution of the upper crust during dramatic plate-boundary reorganizations accompanying the transition from subduction to collision. The deformation structures that we document suggest that both upper and lower plate deformation during incipient island arc-continent collision was largely controlled by the geometry and topography of the lower plate.

  • 33. El Albani, Abderrazak
    et al.
    Bengtson, Stefan
    Canfield, Donald E.
    Bekker, Andrey
    Macchiarelli, Roberto
    Mazurier, Arnaud
    Hammarlund, Emma U.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Boulvais, Philippe
    Dupuy, Jean-Jacques
    Fontaine, Claude
    Fuersich, Franz T.
    Gauthier-Lafaye, Francois
    Janvier, Philippe
    Javaux, Emmanuelle
    Ossa, Frantz Ossa
    Pierson-Wickmann, Anne-Catherine
    Riboulleau, Armelle
    Sardini, Paul
    Vachard, Daniel
    Whitehouse, Martin
    Meunier, Alain
    Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago2010In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 466, no 7302, 100-104 p.Article in journal (Refereed)
    Abstract [en]

    The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial(1-5). Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis(6,7), which may have been eukaryotic, evidence for morphological and taxonomic bio-diversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr)(8). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.

  • 34. Forsberg, Lovisa
    et al.
    Kleja, Dan
    Greger, Maria
    Stockholm University, Faculty of Science, Department of Botany.
    Ledin, Stig
    Effects of sewage sludge on solution chemistry and plant uptake of Cu in sulphide mine tailings at different weathering stages2009In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 24, no 3, 475-482 p.Article in journal (Refereed)
    Abstract [en]

    This climate chamber experiment examines the effects of sewage sludge (SS) on sulphide mine tailings from the Aitik Cu mine in northern Sweden. The effects of SS were determined from Cu in solution and Cu uptake and growth of plants on tailings showing 3 different degrees of weathering. Possible relationships between Cu content in plants and Cu in solution measured in tailings (total dissolved Cu and free Cu) were also evaluated. Red fescue (Festuca rubra) was grown for 6 weeks in pots of the different tailings treated with SS or NPK fertiliser. Soil solution was sampled with Rhizon tension lysimeters and analysed for pH, dissolved organic C (DOC), free Cu, total dissolved Cu and SO42-. The effects of SS on Cu in solution and plants depended on the degree of weathering. In tailings with a low degree of sulphide oxidation, SS application resulted in increased solubility and shoot accumulation of Cu compared with NPK-treated tailings, probably due to DOC forming soluble complexes with Cu. Sewage sludge also seemed to promote translocation of Cu to shoots in those tailings. In highly weathered tailings, lower contents of total dissolved Cu and free Cu in solution and lower Cu levels in shoots were found in SS-treated samples than in NPK-treated. In the moderately weathered tailings, Cu concentrations in solutions were generally similar between treatments, but lower contents of Cu were found in shoots and roots of the fescue grown in the SS-treatment. Irrespective of degree of weathering and treatment, both free Cu and total dissolved Cu concentration in tailings correlated strongly with Cu levels found in fescue shoots.

  • 35. Gaines, Robert R.
    et al.
    Droser, Mary L.
    Orr, Patrick J.
    Garson, Daniel
    Hammarlund, Emma
    Naturhistoriska riksmuseet, Enheten för paleozoologi.
    Qi, Changshi
    Canfield, Donald E.
    Burgess Shale-type biotas were not entirely burrowed away2012In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 40, no 3, 283-286 p.Article in journal (Refereed)
    Abstract [en]

    Burgess Shale–type biotas occur globally in the Cambrian record and offer unparalleled insight into the Cambrian explosion, the initial Phanerozoic radiation of the Metazoa. Deposits bearing exceptionally preserved soft-bodied fossils are unusually common in Cambrian strata; more than 40 are now known. The well-documented decline of soft-bodied preservation following the Middle Cambrian represents the closure of a taphonomic window that was only intermittently open in marine environments thereafter. The prevailing hypothesis for this secular shift in taphonomic conditions of outer shelf environments is that soft-bodied biotas were literally burrowed away from the fossil record by increasing infaunal activity in muddy substrate environments; this would have affected geochemical gradients and increased the efficiency of organic matter recycling in sediments. New and recently published data, however, suggest a more complex scenario. Ichnologic and microstratigraphic data from Burgess Shale–type deposits indicate that (1) bioturbation exerts a limiting effect on soft-bodied preservation; (2) the observed increase in the depth and extent of bioturbation following the Middle Cambrian would have restricted preservation of Burgess Shale?type biotas in a number of settings; but (3) increasing depth and extent of bioturbation would not have affected preservation in many other settings, including the most richly fossiliferous portions of the Chengjiang (China) deposit and the Greater Phyllopod Bed of the Burgess Shale (Canada). Therefore, increasing bioturbation cannot account for the apparent loss of this pathway from the fossil record, and requires that other circumstances, including, but not limited to, widespread benthic anoxia, facilitated widespread exceptional preservation in the Cambrian.

  • 36. Gaines, Robert R.
    et al.
    Hammarlund, Emma U.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hou, Xianguang
    Qie, Chi
    Gabbott, Sarah E.
    Zhao, Yuanlong
    Peng, Jin
    Canfield, Donald E.
    Mechanism for Burgess Shale-type preservation2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 14, 5180-5184 p.Article in journal (Refereed)
    Abstract [en]

    Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft-bodied fossil assemblages has remained enigmatic since Walcott’s initial discovery in 1909. Here, we demonstrate the mechanism of Burgess Shale-type preservation using sedimentologic and geochemical data from the Chengjiang, Burgess Shale, and five other principal Burgess Shale-type deposits. Sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation. Low sulfate concentrations in the global ocean and low-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier, provided by bed-capping cements that were emplaced at the seafloor, is a feature that is shared among Burgess Shale-type deposits, and resulted from the unusually high alkalinity of Cambrian oceans. Thus, Burgess Shale-type preservation of soft-bodied fossil assemblages worldwide was promoted by unique aspects of early Paleozoic seawater chemistry that strongly impacted sediment diagenesis, providing a fundamentally unique record of the immediate aftermath of the “Cambrian explosion.”

  • 37.
    Godinho, Jose
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Direct observations of the structures developed on fluorite surfaces with different orientations during dissolutionArticle in journal (Other academic)
  • 38.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evins, L. Z.
    Effect of surface orientation on dissolution rates and topography of caf22012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 86, 392-403 p.Article in journal (Refereed)
    Abstract [en]

    This paper reports how during dissolution differences in surface chemistry affect the evolution of topography of CaF2 pellets with a microstructure similar to UO2 spent nuclear fuel. 3D confocal profilometry and atomic force microscopy were used to quantify retreat rates and analyze topography changes on surfaces with different orientations as dissolution proceeds up to 468 h. A NaClO4 (0.05 M) solution with pH 3.6 which was far from equilibrium relative to CaF2 was used. Measured dissolution rates depend directly on the orientation of the exposed planes. The {111} is the most stable plane with a dissolution rate of (1.2 +/- 0.8) x 10(-9) mol m(-2) s(-1), and {112} the least stable plane with a dissolution rate 33 times faster that {111}. Surfaces that expose both Ca and F atoms in the same plane dissolve faster. Dissolution rates were found to be correlated to surface orientation which is characterized by a specific surface chemistry and therefore related to surface energy. It is proposed that every surface is characterized by the relative proportions of the three reference planes {111}, {100} and {110}, and by the high energy sites at their interceptions. Based on the different dissolution rates observed we propose a dissolution model to explain changes of topography during dissolution. Surfaces with slower dissolution rate, and inferred lower surface energy, tend to form while dissolution proceeds leading to an increase of roughness and surface area. This adjustment of the surface suggests that dissolution rates during early stages of dissolution are different from the later stages. The time-dependency of this dynamic system needs to be taken into consideration when predicting long-term dissolution rates.

  • 39.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Oak Ridge National Laboratory United States Department of Energy (DOE) .
    Piazolo, S.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Macquarie University .
    Balic-Zunic, T.
    Importance of surface structure on dissolution of fluorite: Implications for surface dynamics and dissolution rates2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 126, 398-410 p.Article in journal (Refereed)
    Abstract [en]

    Dissolution rates are usually calculated as a function of surface area, which is assumed to remain constant ignoring the changes occurring on the surface during dissolution. Here we present a study of how topography of natural fluorite surfaces with different orientation changes during up to 3200 h of dissolution. Results are analyzed in terms of changes in surface area, surface reactivity and dissolution rates. All surfaces studied present fast changes in topography during the initial 200 h of dissolution. The controlling factors that cause the development of topography are the stability of the step edges forming the initial surface and its inclination to the closest stable planes, which are specific for each surface orientation. During an initial dissolution regime dissolution rates decrease significantly, even though the total surface area increases. During a second dissolution regime, some surfaces continue to present significant changes in topography, while for others the topography tends to remain approximately constant. The observed variation of dissolution rates are attributed to a decrease of the density of step edges on the surface and the continuous increase in exposure of more stable surfaces. Calculations of dissolution rates, which assume that dissolution rates are directly proportional to surface area, are not valid for the type of surfaces studied. Instead, to develop accurate kinetic dissolution models and more realistic stochastic dissolution simulations the surface reactivity, determined by the relative stability of the planes and type of edges that constitute a surface needs to be considered. Significant differences between dissolution rates calculated based on surface area alone, and based on surface reactivity are expected for materials with the fluorite structure.

  • 40.
    Godinho, José Ricardo Assunção
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A surface approach to understanding the dissolution of fluorite type materials: Implications for mineral dissolution kinetic models2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Traditional dissolution models are based in the analyses of bulk solution compositions and ignore the fact that different sites of a surface dissolve at different rates. Consequently, the variation of surface area and surface reactivity during dissolution are not considered for the calculation of the overall dissolution rate, which is expected to remain constant with time. The results presented here show the limitations of this approach suggesting that dissolution rates should be calculated as a function of an overall surface reactivity term that accounts for the reactivity of each of the sites that constitute the surface. In contrast to previous studies, here the focus is put on studying the surface at different dissolution times. Significant changes in surface topography of CaF2 were observed during the initial seconds and up to 3200 hours of dissolution. The observed changes include the increase of surface area and progressive exposure of the most stable planes, with consequent decrease in overall reactivity of the surface. The novelty of a proposed dissolution model for fluorite surfaces, when compared with traditional dissolution models, is that it differentiates the reactivity of each characteristic site on a surface, e.g. plane or step edge, and considers the time dynamics. The time dependency of dissolution rates is a major factor of uncertainty when calculating long term dissolution rates using equations derived from dissolution experiments running for short periods of time and using materials with different surface properties. An additional factor of uncertainty is that the initial dissolution times are the most dynamic periods of dissolution, when significant variations of surface area and reactivity occur. The results are expected to have impact in the field of nuclear waste management and to the larger geological and material science community.

  • 41.
    Graham, Robert M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    De Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kohfeld, Karen E.
    Schlosser, Christian
    Identifying sources and transport pathways of iron in the Southern OceanIn: Deep Sea Research Part I: Oceanographic Research Papers, ISSN 0967-0637, E-ISSN 1879-0119Article in journal (Refereed)
    Abstract [en]

    Over large regions of the global ocean primary productivity is limited by the availability of dissolved iron. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. One of the largest sources of dissolved iron to the ocean is thought to be from shelf sediments, and this source is often parameterized in biogeochemical models as a depth dependent iron flux through the seafloor. Using the knowledge that Southern Ocean surface waters are iron limited, we infer source regions of iron to the Southern Ocean by identifying where the most intense chlorophyll blooms develop. We further derive surface current patterns from satellite sea surface height fields to assess the role of the ocean circulation in transporting iron away from these source regions. We find a tight relationship between satellite chlorophyll concentrations and sea surface height. Large chlorophyll blooms develop on the shelf and where the western boundary currents detach from the continental shelves and turn eastward into the Southern Ocean. This is likely due to shelf supplied iron becoming entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. The most intense chlorophyll blooms are located along coastal margins of islands and continents. Blooms do not develop over submerged seamounts or plateaus in the open ocean. This suggests that shelf sediments in coastal regions act as large bioavailable iron sources to the Southern Ocean. We recommend that a more accurate method of parameterizing the shelf sediment iron flux could be to prescribe this flux only through grid cells neighboring coastlines. Finally, we hypothesize how changes in sea level during glacial-interglacial cycles may have altered the distribution of shelf sediment iron sources in the Southern Ocean and helped to drive export production anomalies in the Sub-Antarctic Zone.

  • 42. Hall, Per O. J.
    et al.
    Almroth Rosell, Elin
    Bonaglia, Stefano
    Lund University, Sweden.
    Dale, Andrew W.
    Hylén, Astrid
    Kononets, Mikhail
    Nilsson, Madeleine
    Sommer, Stefan
    Van de Velde, Sebastiaan
    Viktorsson, Lena
    Influence of Natural Oxygenation of Baltic Proper Deep Water on Benthic Recycling and Removal of Phosphorus, Nitrogen, Silicon and Carbon2017In: Frontiers in Marine Science, ISSN 2296-2565, E-ISSN 1664-1078, Vol. 4, 27Article in journal (Refereed)
  • 43.
    Hammarlund, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Canfield, Don E.
    Bengtson, Stefan
    Mygind Leth, Peter
    Schillinger, Burkhard
    Calzada, Elbio
    The influence of sulfate concentration on soft-tissue decay and preservation2011In: Palaeontographica Canadiana No. 31: International Conference on the Cambrian Explosion - Proceedings / [ed] Paul A. Johnston & Kimberley J. Johnston, 2011, Vol. 31, 141-156 p.Conference paper (Refereed)
  • 44.
    Hammarlund, Emma U.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ocean chemistry and the evolution of multicellularity2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Oxygen has been assumed to be a vital trigger for the evolution of multicellular life forms on Earth, partly based on its power to promote substantial energy flux in cell respiration and partly as biosynthesis of compounds like collagen require oxygen. However, the co-evolution of large life and the Earth’s chemical environment is not well understood at present, and there is particular disagreement in the field about whether the Cambrian explosion of animal life forms was a chemical or biological event. Here, I discuss the evolution of multicellularity, divided in simple or complex forms, in light of the evolution of ocean water column chemistry in both the Proterozoic and the early Paleozoic. Even if the appearance of animals is confined to the Ediacaran, other fossil evidence of complex multicellularity can be argued to occur in the Paleo-, Meso- and Neoproterozic. These finds are, if anything, reason enough to keep searching for early experiments in complex multicellularity. In this search, we may have to expand our toolbox by looking at e.g. trace element aggregations and the isotopic composition of key elements. 

    Research over the last couple of years have accentuated that much of the interval between the Ediacaran and the Devonian was dramatic with transitional ocean chemistry at the same time that large forms of animal life experienced dynamic radiation and ecological expansion. Results presented here describe some aspects of this time, including geochemistry from Chengjiang and a mechanism for preserving non-mineralized Cambrian animals that was partly dependent on specific ocean chemistry. Also, geochemical proxies using iron and molybdenum are used to infer a Paleozoic atmosphere with less than 50% of present levels of oxygen. The possibility that the subsequent rise is due to terrestrial plants and linked to the appearance of large predatory fish is discussed. Finally, the first mass extinction in the end-Ordovician is linked to low oxygen concentrations in the water column. It appears that more than oxygen was critical to allow the radiation of large life forms on Earth, but that chemistry and tectonic activity were intimately intertwined to biology, in a dance of permitting and being determined by certain aspects of ecology.

  • 45.
    Hammarlund, Emma U.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dahl, Tais W.
    Harper, David A. T.
    Bond, David P. G.
    Nielsen, Arne T.
    Bjerrum, Christian J.
    Schovsbo, Niels H.
    Schönlaub, Hans P.
    Zalasiewicz, Jan A.
    Canfield, Donald E.
    A sulfidic driver for the end-Ordovician mass extinction2012In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 331, 128-139 p.Article in journal (Refereed)
    Abstract [en]

    The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in 34S in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats.

  • 46.
    Hemmingsson, Christoffer
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Estimating soluble arsenic and phosphorus concentrations under Precambrian oceanic conditions2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Original estimates of phosphorus (P) concentrations in the Precambrian oceans before 1.9 Ga gave a budget of ~10-25% of modern day levels. This budget was challenged by accounting for high silica (Si) concentrations that were believed to have outcompeted P for binding sites on precipitating iron oxide-hydroxide particles during the chemical oxidation and burial of iron (Fe). Such iron oxide-hydroxide particles are considered as proxies of ancient iron-rich sedimentary rocks, such as banded iron formations, which are often used to infer the dissolved chemistry of trace elements in the ancient oceans. This study raises the question of wether arsenic (As) had an effect of the binding of P to precipitating iron minerals, during the co-precipitation of Iron oxide- hydroxide in elevated Fe and Si concentrations characteristic of the early oceans. This hypothesis is based on the chemical similarities seen between P and As. Results show a more pH dependent competition between P and AsIII, whereby P outcompetes AsIII at a pH <7. The effect decreases as the pH rises until pH ~8 at which the effect cancels out and AsIII becomes somewhat predominant over P. AsV on the other hand, an analogue to P, is outcompeted by P throughout pH 5-10. Distribution coefficients (Kd) of P on iron oxide-hydroxide particles were not affected by the concentration of Si in solution. Average Kd and standard error between concentrations of Si, across the sample pH of 5-10 revealed an average Kd of 0.072 (±0.01) μM-1. This is strikingly similar to another experimental Kd at 0.075 (±0.003) μM-1, when the effects of Si are excluded. The average Kd in this study is also consistent with the average Kd of 0.06 μM-1 from a range of As-rich hydrothermal systems reported in a previous study, supporting the original idea of Precambrian P levels being low. The average Kd between concentrations of Fe revealed a Kd of 0.12 (±0.03) μM-1 although this was not statistically significant from the average Kd between groups of Si. In addition to low levels of P, the Precambrian oceans likely also contained high levels of As, due to the high hydrothermal activity. This scavenging of P from oceanic waters would have become increasingly important as surface oceans became more oxygenated and the presence of AsV would have been greater. Because the availability of Si does not show any great effect on the uptake of P by precipitating iron oxide-hydroxides, Si concentration is likely not a proxy for oceanic P concentrations. It is proposed that low dissolved P levels are consistent with early oceans that w!ere a lot more hydrothermally influenced than the oceans of today. 

  • 47.
    Hemmingsson, Christoffer
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Synthesis and characterisation of natural hydrothermal zeolites and their catalysis in N-fixation: An experimental approach2013Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The abiotic chemistry to form the components necessary for the origin of life are thought to have emerged during the hadean eon. It is thought to be characterised by a CO2/N2 atmosphere, a shallow acidic ocean with alkaline waters in hydrothermal systems, and a basaltic ocean crust. One of the necessary components for life is bioavailable N-sources such as NH4. In this study the synthesis of three common natural zeolites was attempted. These were characterised using optical microscopy, ESEM, PXRD, FT-IR and BET. The products synthesised were two zeolites, phillipsite and analcime as well as the feldspar sanidine. These were then also synthesised with an in situ Fe2+ & Fe3+ source in alkaline conditions and the products were exposed to a post-synthesis treatment of de-aluminising and were subjected to iron substitution. Incorporating iron into the crystal structure by replacing Al. Characterisation show that analcime, phillipsite, sanidine and merlinoite were produced. All products, including those with post-synthesis treatments show the presence of Brønstedt acid sites. The surface area for iron in situ synthesised products show a trend of increasing surface area and pore area/volume when iron is incorporated into the crystal structure. Phillipsite and analcime with their iron in situ products were then used in catalysis of N-reduction using a continuous flow system and an autoclave system. The catalysis was run at pH 10 & 100°C to imitate mild hydrothermal conditions. It was seen that analcime had the highest production rate of NH4+; nevertheless, both products were able to produce NH4+ from NO3-, as well as N2. This gives a new insight into hadean hydrothermal systems and their role in production of bioavailable N-sources for the origin of life. 

  • 48. Hjorth, Tomas
    Metal speciation and historical trends in lake sediments2003Doctoral thesis, comprehensive summary (Other academic)
  • 49. Hoffmann, J. Elis
    et al.
    Muenker, Carsten
    Naeraa, Tomas
    Rosing, Minik T.
    Herwartz, Daniel
    Garbe-Schoenberg, Dieter
    Svahnberg, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mechanisms of Archean crust formation inferred from high-precision HFSE systematics in TTGs2011In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, no 15, 4157-4178 p.Article in journal (Refereed)
    Abstract [en]

    It has been proposed that Archean tonalitic-trondhjemitic-granodioritic magmas (TTGs) formed by melting of mafic crust at high pressures. The residual mineralogy of the TTGs (either (garnet)-amphibolite or rutile-bearing eclogite) is believed to control the trace element budget of TTGs. In particular, ratios of high-field-strength elements (HFSE) can help to discriminate between the different residual lithologies. In order to place constraints on the source mineralogy of TTGs, we performed high-precision HFSE measurements by isotope dilution (Nb, Ta, Zr, Hf) together with Lu-Hf and Sm-Nd measurements on representative, ca. 3.85-2.8 Ga TTGs and related rock types from southern West Greenland, W-India and from the Superior Province. These measurements are complemented by major and trace element data for the TTGs. Texturally homogeneous early Archean (3.85-3.60 Ga old) and Mesoarchean (ca. 3.1-2.8 Ga old) TTGs have both low Ni (<11 ppm) and Cr contents (<20 ppm), indicating that there was little or no interaction with mantle peridotite during ascent. Ratios of Nb/Ta in juvenile Eoarchean TTGs range from ca. 7 to ca. 24, and in juvenile Mesoarchean TTGs from ca. 14 to ca. 27. Even higher Nb/Ta (14-42) were obtained for mig-matitic TTGs and intra-crustal differentiates, most likely mirroring further fractionation of Nb from Ta as a consequence of partial melting, fluid infiltration and migmatisation. In the juvenile TTGs, positive correlations between Nb/Ta and Gd/Yb, La/Yb, Sr/Y, Zr/Sm and Zr/Nb are observed. These compositional arrays are best explained by melting of typical Isua tholeiites in both, the rutile-bearing eclogite stability field (>15 kbar, high Nb/Ta) and the garnet-amphibolite stability field (10-15 kbar, low Nb/Ta). With respect to the low end of Nb/Ta found for TTGs, there is currently some uncertainty between the available experimental datasets for amphibole. Independent of these uncertainties, the TTG compositions found here still require the presence of both endmember residues. A successful geological model for the TTGs therefore has to account for the co-occurrence of both low-and high-Nb/Ta TTGs within the same geologic terrane. An additional feature observed in the Eoarchean samples from Greenland is a systematic co-variation between Nb/Ta and initial epsilon Hf(t), which is best explained by a model where TTG-melting occured at progressively increasing pressures in a pile of tectonically thickened mafic crust. The elevated Nb/Ta in mig-matitic TTGs and intra-crustal differentiates can shed further light on the role of intra-crustal differentiation processes in the global Nb/Ta cycle. Lower crustal melting processes at granulite facies conditions may generate high-Nb/Ta domains in the middle crust, whereas mid-crustal melting at amphibolite facies conditions may account for the low Nb/Ta generally observed in upper crustal rocks.

  • 50.
    Holm, Nils
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Baltscheffsky, Herrick
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Links between hydrothermal environments, pyrophosphate, Na+, and early evolution2011In: Origins of life and evolution of the biosphere, ISSN 0169-6149, E-ISSN 1573-0875, Vol. 41, no 5, 483-493 p.Article in journal (Refereed)
    Abstract [en]

    The discovery that photosynthetic bacterial membrane-bound inorganic pyrophosphatase (PPase) catalyzed light-induced phosphorylation of orthophosphate (Pi) to pyrophosphate (PPi) and the capability of PPi to drive energy requiring dark reactions supported PPi as a possible early alternative to ATP. Like the proton-pumping ATPase, the corresponding membrane-bound PPase also is a H+-pump, and like the Na+-pumping ATPase, it can be a Na+-pump, both in archaeal and bacterial membranes. We suggest that PPi and Na+ transport preceded ATP and H+ transport in association with geochemistry of the Earth at the time of the origin and early evolution of life. Life may have started in connection with early plate tectonic processes coupled to alkaline hydrothermal activity. A hydrothermal environment in which Na+ is abundant exists in sediment-starved subduction zones, like the Mariana forearc in the W Pacific Ocean. It is considered to mimic the Archean Earth. The forearc pore fluids have a pH up to 12.6, a Na+-concentration of 0.7 mol/kg seawater. PPi could have been formed during early subduction of oceanic lithosphere by dehydration of protonated orthophosphates. A key to PPi formation in these geological environments is a low local activity of water.

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