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  • 1.
    Acton, Gary
    et al.
    University of California, Davis.
    et al., incl. Jan Backman,
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Magnetostratigraphic and Cyclostratigraphic Records from Eocene-Miocene Sediments Cored in the Paleoequatorial Pacific: Initial Results from IODP Expedition 3202009Conference paper (Other academic)
    Abstract [en]

    Sediments from the paleoequatorial Pacific record the paleomagnetic field with high-fidelity and contain cyclic variations in chemical and physical properties that can be astronomically tuned, as has been shown from past Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) cruises, e.g., Legs 85, 138, 198, and 199. In an effort to fill gaps from past coring and to construct complete stratigraphic sections spanning the Cenozoic, Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321 cored sediments along a Pacific Equatorial Age Transect (PEAT) earlier this year. A total of 23 holes at 8 Sites (Sites U1331 through U1338) were cored, recovering 6,141 m of sediment (Preliminary Reports are available at http://iodp.tamu.edu/publications/PR.html). Initial paleomagnetic results from Expedition 320 include measurements at 56,222 intervals along ~2000 split-core sections, as well as detailed progressive alternating field (AF) and thermal demagnetization of over 400 discrete samples (7 cm3 cubes). The cleaned paleomagnetic data were characterized by shallow inclinations, consistent with the sites being near the paleoequator, and by 180° alternations in declination downhole, reflecting magnetic polarity zones. The resulting magnetostratigraphies, which are used to develop initial age models for the drill sites, yield 803 dates ranging from 51.743 Ma (the base of Chron 23n.2n at Site 1331) to the present (Chron C1n; 0 to 0.783 Ma at Site U1335). In addition, 83 short polarity intervals were observed that might correspond to cryptochrons or geomagnetic excursions. We will discuss initial efforts to further resolve the PEAT magnetostratigraphies and to integrate them with bio-, chemo-, and cyclo- stratigraphies from the equatorial Pacific and elsewhere in order to improve and extend astronomical calibration of the geologic timescale.

  • 2.
    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, p. 245-259Article 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.

  • 3.
    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, p. 143-159Article 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.

  • 4.
    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, p. 63-72Article 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.

  • 5.
    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, p. 111-122Chapter 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.

  • 6. 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, p. 41-52Article 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.

  • 7.
    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, p. 3182-3192Article 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.

  • 8. 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, p. 8-28Article 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.

  • 9.
    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, p. 163-168Article 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.

  • 10.
    Bergstrand, Christoffer
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geophysical characterization of fluid flow and hydrocarbon migration features in the SW Loppa High area, Norwegian Barents Sea2015Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Download full text (pdf)
    Geophysical characterization of fluid flow and hydrocarbon migration features in the SW Loppa High area, Norwegian Barents Sea
  • 11.
    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, E-ISSN 1525-2027, Vol. 13, p. Q05005-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.

  • 12.
    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, p. 207-217Article 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.

  • 13. 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, p. 33-55Article 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.

  • 14. 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, p. 1196-1201Article 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.

  • 15. 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, p. 364-365Article in journal (Other academic)
  • 16. 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, p. 641-660Article 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.

  • 17.
    Ekman, Annica
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Engström, Anders
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Max Planck Institute for Chemistry, Mainz, Germany.
    Williams, Jonathan
    Max Planck Institute for Chemistry, Mainz, Germany.
    Andreae, Meinrat
    Max Planck Institute for Chemistry, Mainz, Germany.
    Do organics contribute to small particle formation in the Amazonian upper troposphere?2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no L17810, p. 5-Article in journal (Refereed)
    Abstract [en]

    3-D cloud-resolving model simulations including explicit aerosol physics and chemistry are compared with observations of upper tropospheric (12 km) aerosol size distributions over the Amazon Basin. The model underestimates the aerosol number concentration for all modes, especially the nucleation mode (d < 18 nm). We show that a boundary layer SO2 mixing ratio of approximately 5 ppb would be needed in order to reproduce the high nucleation mode number concentrations observed. This high SO2 mixing ratio is very unlikely for the pristine Amazon Basin at this time of the year. Hence, it is suggested that vapours other than H2SO4 participate in the formation and growth of small aerosols. Using activation nucleation theory together with a small (0.4–10%) secondary organic aerosol mass yield, we show that isoprene has the potential of substantially increasing the number of small particles formed as well as reducing the underestimate for the larger aerosol modes.

  • 18.
    Eleman, Folke
    Stockholm University.
    On some real and apparent time variations in the geomagnetic field1967Doctoral thesis, comprehensive summary (Other academic)
  • 19. 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, p. 475-482Article 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.

  • 20.
    Fransner, Oscar
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geophysical Mapping around Björkö Island in Lake Mälaren, South central Sweden2013Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    The former Viking settlement Birka is located on Björkö Island in Lake Mälaren, the third largest lake in Sweden. Birka is a well-known archeological site that onshore has been carefully examined. The lake floor of the waters surrounding the island has been less investigated but has a great potential to host not yet discovered archeological objects from this former hub for seafarers. Therefore, a geophysical survey including multibeam sonar mapping and subbottom profiling was carried out mainly along the shores of western Björkö Island. Processing and analysis of these collected data form the basis of this thesis. The main aims of this study are to produce a suite of geological maps and stratigraphic profiles that are used to geologically interpret the uppermost sediment stratigraphy and the bathymetry of the area. In addition, the processed data are investigated for archeological objects.

    The result shows that the acoustic records of the sediment stratigraphy reaches back to glacial clay formed as a consequence of the retreat of the Late Weichselian ice sheet, and that the uppermost sediment units probably are from the time after the isolation of Lake Mälaren from the Baltic Sea. The bathymetry and backscatter results have revealed that this relatively shallow study area contains several objects that potentially could be of interest from an archeological point of view. These objects include several unidentified objects in the Björkö strait and two unregistered shipwrecks where ground truthing data need to be collected to determine their respective origin.

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    Master thesis_Oscar Fransner
  • 21.
    Freire, Francis
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Acoustic characterization of submarine geomorphological features in the Polar Oceans2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Marine glacial environments contain unique seafloor features resulting from the dynamic glacial processes. Studying these submarine geomorphological features can help us understand the glacial paleo-environments so that we can predict the likely responses of present day glaciers and ice sheets to future changes in the climate. This thesis details different approaches in understanding glacial seafloor features using acoustic systems. It focuses on the novel technique of automated mapping seafloor properties using the backscatter intensity collected by acoustic multibeam echosounder systems (MBES). The aim of this thesis is to assess the potential of this unexploited data source in characterizing different glacial landforms in the polar oceans. This is done by examining the voluminous backscatter data collected by Swedish icebreaker Oden from different cruises to the polar oceans and employing an automated backscatter processing technique, the ARA algorithm, to extract surficial sediment characteristics. The results from the sediment characterization are used together with outputs from other marine acoustical systems and sediment core data to understand formational processes of the glacial submarine features. Operational issues encountered in using this technology and its viability as a tool in characterization of glacial seafloor features are discussed and suggestions are given on the improvements needed to effectively implement the method in future studies. The final part of the manuscript is a paper, published in Geo-marine Letters, where I and my co-authors show a practical application of the acoustic systems ability to characterize geomorphological features of a mass-wasting event in the deepest part of the Arctic, the Molloy Hole. 

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    fulltext
  • 22. Ghignone, Stefano
    et al.
    Prencipe, Mauro
    Manzotti, Paola
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bruno, Marco
    Boero, Federica
    Borghini, Alessia
    Costa, Emanuele
    Ciriotti, Marco
    Scaramuzzo, Emanuele
    The Raman spectrum of florencite-(REE) [REEAl3(PO4)2(OH)6]: An integrated experimental and computational approach2023In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555Article in journal (Refereed)
    Abstract [en]

    Florencite is a hydrous light rare-earth elements (LREE) aluminium phosphate [REEAl3(PO4)2(OH)6], that amongst the REE-rich minerals is quite common. The main end-members are Ce-, La- and Nd-rich terms that were found in several genetic environments. Despite the large occurrence worldwide, to the authors' knowledge, florencite has attracted very few studies, particularly concerning the characterization of its Raman spectrum. We present a detailed study of the Raman spectrum of florencite, combining experimental measurements and theoretical calculations. Experimental Raman spectra (in the 100–1300 cm−1 spectral range) are measured on four florencite samples characterized by different chemical composition, that is, different REE abundance. The results highlight a remarkable coincidence between different Raman spectra measured on each sample, despite the significantly different chemical compositions in terms of their REE content. The same similarities were also observed in the computed spectra at the ab initio level; moreover, the calculations allowed the attributions of the different Raman signals to specific vibrational modes. 

  • 23.
    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, p. 392-403Article 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.

  • 24.
    Godinho, José R. A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Oak Ridge National Laboratory, USA.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences. Macquarie University, Australia.
    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, p. 398-410Article 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.

  • 25.
    Hallengren, Anders
    Stockholm University, Faculty of Humanities, Department of Literature and History of Ideas.
    Jordbävningen i Tangshan1976In: Värld och vetande, ISSN 0346-4873, Vol. 25, no 11, p. 321-329Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Photo report on the natural disaster in the Chinese city of Tangshan, the rescue work—its political significance and aftermath—with the Chinese media emphasis on the boldness and heroism of the people, understatements regarding the destruction, and in excess of the rapid reconstruction work and optimism about the future. — This article also foreshadows the fall of the recently deceased Mao Zedong as guiding-star in Chinese politics, which explicitly occurred the year after Mao's mausoleum was opened to the public at Tiananmen Square (November 1977)—when Deng Xiaoping in his first year as the Communist Party's supreme leader in 1978 initiated socialist market reforms, thus beginning the radical change of ideology in the People's Republic of China (PRC).

  • 26.
    Hell, Benjamin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gridding heterogeneous bathymetric data sets with stacked continuous curvature splines in tension2011In: Marine Geophysical Researches, ISSN 0025-3235, E-ISSN 1573-0581, Vol. 32, no 4, p. 493-501Article in journal (Refereed)
    Abstract [en]

    Gridding heterogeneous bathymetric data sets for the compilation of Digital bathymetric models (DBMs), poses specific problems when there are extreme variations in source data density. This requires gridding routines capable of subsampling high-resolution source data while preserving as much as possible of the small details, at the same time as interpolating in areas with sparse data without generating gridding artifacts. A frequently used gridding method generalizes bicubic spline interpolation and is known as continuous curvature splines in tension. This method is further enhanced in this article in order to specifically handle heterogeneous bathymetric source data. Our method constructs the final grid through stacking several surfaces of different resolutions, each generated using the splines in tension algorithm. With this approach, the gridding resolution is locally adjusted to the density of the source data set: Areas with high-resolution data are gridded at higher resolution than areas with sparse source data. In comparison with some of the most widely used gridding methods, our approach yields superior DBMs based on heterogeneous bathymetric data sets with regard to preserving small bathymetric details in the high-resolution source data, while minimizing interpolation artifacts in the sparsely data constrained regions. Common problems such as artifacts from ship tracklines are suppressed. Even if our stacked continuous curvature splines in tension gridding algorithm has been specifically designed to construct DBMs from heterogeneous bathymetric source data, it may be used to compile regular grids from other geoscientific measurements.

  • 27. 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, p. 4157-4178Article 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.

  • 28.
    Homeister, Anne
    Stockholm University, Faculty of Humanities, Department of Archaeology and Classical Studies, Archaeological Research Laboratory.
    Reflections in the dark: Ground-penetrating radar surveys for the detection of Viking Age and early medieval harbor remains in Sigtuna, Sweden2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis a ground-penetration radar survey was carried out in four areas, Borgmästarängen, Draken, Urmakaren and Koppardosan in Sigtuna. The aim of this paper is to detect remnants of the Viking Age harbor at those chosen sites. Former research investigations have discovered findings which are related to shipbuilding like clench nails, rivets and boat nails; however, the question remains whether Sigtuna ever had a central harbor, and researchers suggested instead that every town plot had its own mooring. This paper addresses this question by deploying geophysical surveys to increase the understanding of the town’s organization. Furthermore this paper will discuss how the detected structures can be understood in comparison to earlier Viking Age and early Medieval towns, in this case Birka, Hedeby and Schleswig where central harbors have been discovered and investigated.

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    Reflections in the dark
  • 29.
    Horst, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Thornton, Brett F.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wishkerman, Asher
    Keppler, Frank
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Stable bromine isotopic composition of methyl bromide released from plant matter2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 125, p. 186-195Article in journal (Refereed)
    Abstract [en]

    Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (delta Br-81) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (epsilon) of -2.00 +/- 0.23 parts per thousand (1 sigma, n = 8) for pectin and -1.82 +/- 0.02 parts per thousand (1 sigma, n = 4) for Salicornia (the relative amount of the heavier Br-81 was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300 degrees C. For longer incubations of up to 90 h at 180 degrees C the delta Br-81 values increased from -2 parts per thousand to 0 parts per thousand for pectin and to -1 parts per thousand for Salicornia. These delta Br-81 source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget.

  • 30. Jacks, Gunnar
    et al.
    Slejkovec, Zdenka
    Mörth, Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bhattacharya, Prosun
    Redox-cycling of arsenic along the water pathways in sulfidic metasediment areas in northern Sweden2013In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 35, p. 35-43Article in journal (Refereed)
    Abstract [en]

    Arsenic has emerged as a problem element in groundwater. The most common mechanism of mobilising As from the solid phase into water is through the reductive dissolution of ferric oxyhydroxides. This investigation was made in northern Sweden where metasediments containing pyrite, pyrrhotite and arsenopyrite underlay about 4000 km(2). The overlying till contains as much as up to 100 mg kg (1) As. Speciation of the dissolved As shows that arsenite dominates largely over arsenate. The Fe oxyhydroxides formed may contain up to 0.5% As. Sandy sediments may contain 100-500 mg kg (1). Arsenic and Fe are closely correlated. The cycling of As in water, flora and fauna in wetlands has been studied. Ferric reduction occurs in wetlands and groundwater rich in Fe, and As is found to be discharging into ditches, brooks and streams. Wetland trees and plants show a moderately elevated content of As with a few species showing above 2 mg kg (1), the permissible level in fodder for domestic animals. The only plants having a high content of As are Equisetum species showing up to 26 mg kg (1). These plants make up a small fraction of the food of wild, grazing and browsing animals, for example moose and reindeer, and does not seem to constitute an environmental risk. However, the animals could be exposed to considerable amounts of As by drinking water from springs in wetlands. In the fauna, an elevated As content has so far been found in a limited number of benthic macroinvertebrate samples (1.23-42.1 mg kg (1) dry weight), in which inorganic As species (arsenate) predominate in the extractable fraction (62-82%) with lower amounts of arsenite, mono-and dimethylarsenic acid. Some samples also contained arsenobetaine, trimethylarsine oxide and tetramethylarsonium ion. To the authors' knowledge, this is the first report on As speciation in benthic macroinvertebrates. Fish species from polluted streams (pike and brown trout) had normal As levels (0.57-1.84 mg kg (1) dry weight), mainly present in a form of arsenobetaine (brown trout) or arsenobetaine and dimethylarsinic acid (pike). As both fish species also contained minor amounts of arsenite and arsenate, it is estimated that there is no serious health risk to potential consumers.

  • 31.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fornander, Rickard
    Ricfor AB, Sweden.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wagner, Anton
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    EL21-Estonia: Report of the MS Estonia shipwreck site survey with RV Electra2021Report (Other academic)
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    EL21-Estonia-main-report
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    Appendix 1 Expedition Daily notes
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    Appendix 2 Multibeam bathymetry and backscatter
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    Appendix 3 Sub-bottom profiling
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    Appendix 4 Side-scan sonar
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    Appendix 5 Mid-water sonar and ADPC
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    Appendix 6 CTD
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    Appendix 7 Sediment cores
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    Appendix 7 Sediment coring-measured parameters.xlsx
  • 32.
    Jansen, John D.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Nanson, G. C.
    Cohen, T. J.
    Fujioka, T.
    Fabel, D.
    Larsen, J. R.
    Codilean, A. T.
    Price, D. M.
    Bowman, H. H.
    May, J. -H
    Gliganic, L. A.
    Lowland river responses to intraplate tectonism and climate forcing quantified with luminescence and cosmogenic Be-102013In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 366, p. 49-58Article in journal (Refereed)
    Abstract [en]

    Intraplate tectonism has produced large-scale folding that steers regional drainage systems, such as the 1600 km-long Cooper Ck, en route to Australia's continental depocentre at Lake Eyre. We apply cosmogenic Be-10 exposure dating in bedrock, and luminescence dating in sediment, to quantify the erosional and depositional response of Cooper Ck where it incises the rising Innamincka Dome. The detachment of bedrock joint-blocks during extreme floods governs the minimum rate of incision (17.4 +/- 6.5 mm/ky) estimated using a numerical model of episodic erosion calibrated with our 10Be measurements. The last big-flood phase occurred no earlier than similar to 112-121 ka. Upstream of the Innamincka Dome long-term rates of alluvial deposition, partly reflecting synclinal-basin subsidence, are estimated from 47 luminescence dates in sediments accumulated since similar to 270 ka. Sequestration of sediment in subsiding basins such as these may account for the lack of Quaternary accumulation in Lake Eyre, and moreover suggests that notions of a single primary depocentre at base-level may poorly represent lowland, arid-zone rivers. Over the period similar to 75-55 ka Cooper Ck changed from a bedload-dominant, laterally-active meandering river to a muddy anabranching channel network up to 60 km wide. We propose that this shift in river pattern was a product of base-level rise linked with the slowly deforming syncline-anticline structure, coupled with a climate-forced reduction in discharge. The uniform valley slope along this subsiding alluvial and rising bedrock system represents an adjustment between the relative rates of deformation and the ability of greatly enhanced flows at times during the Quaternary to incise the rising anticline. Hence, tectonic and climate controls are balanced in the long term.

  • 33.
    Jönsson, Bror
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology.
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology.
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology.
    Lundberg, Peter
    Stockholm University, Faculty of Science, Department of Meteorology.
    Standing waves in the Gulf of Finland and their relationship to the basin-wide Baltic seiches2008In: Journal of Geophysical Research: Oceans, Vol. 113, p. C03004-Article in journal (Refereed)
    Abstract [en]

    A linear shallow-water model was used to study different harmonic oscillations in the Baltic Sea. The model was initialized using a linear sea-surface slope from east to west, and was hereafter run without forcing. In our results, we could identify three different local oscillatory modes: one in the Gulf of Finland, with the two distinct periods 23 and 27 hours, one in the Danish Belt Sea, with a less distinct period in the range 23-27 hours, and one in the Gulf of Riga, with the period 17 hours. The most pronounced mode is that in the Gulf of Finland. No clear indications of basin-wide seiches in the Baltic could be found from our simulations. These results were further corroborated by a frequency analysis of sea-level observations from the Baltic. This shows an amplification of the K1 and O1 tidal modes in the Gulf of Finland, but not of the M2 and S2 modes. No such amplification was seen in the rest of the Baltic Sea. On the basis of our model simulations, we propose that sea-level oscillations of the Baltic be regarded as a ensemble of weakly coupled local oscillators. Each oscillator corresponds to a ''fjord mode" or "harbour mode" in a particular bay or sub-basin. These are not proper eigenmodes since their energy gradually leaks out to the rest of the Baltic Sea, resulting in radiation damping. Nevertheless, their resonance may in fact be sharper than that of the proper basin-wide eigenmodes.

  • 34.
    Kirchner, N.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hutter, Kolumban
    Swiss Federal Institute of Technology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Capabilities and limitations of numerical ice sheet models: a discussion for Earth-scientists and modelers2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 25-26, p. 3691-3704Article in journal (Refereed)
    Abstract [en]

    The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The ‘zero order’(Shallow Ice Approximation, SIA)-,‘higher order’-, and‘full Stokes’ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheetice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model.

  • 35. Klaminder, J.
    et al.
    Grip, H.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Laudon, H.
    Carbon mineralization and pyrite oxidation in groundwater: Importance for silicate weathering in boreal forest soils and stream base-flow chemistry2011In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 26, no 3, p. 319-324Article in journal (Refereed)
    Abstract [en]

    What role does mineralized organic C and sulfide oxidation play in weathering of silicate minerals in deep groundwater aquifers? In this study, how H(2)CO(3), produced as a result of mineralization of organic matter during groundwater transport, affects silicate weathering in the saturated zone of the mineral soil along a 70 m-long boreal hillslope is demonstrated. Stream water measurements of base cations and delta(18)O are included to determine the importance of the deep groundwater system for downstream surface water. The results suggest that H2CO3 generated from organic compounds being mineralized during the lateral transport stimulates weathering at depths between 0.5 and 3 m in the soil. This finding is indicated by progressively increasing concentrations of base cations-, silica- and inorganic C (IC) in the groundwater along the hillslope that co-occur with decreasing organic C (OC) concentrations. Protons derived from sulfide oxidation appear to be an additional driver of the weathering process as indicated by a buildup of SO(4)(2-) in the groundwater during lateral transport and a delta(34)S parts per thousand value of +0.26-3.76 parts per thousand in the deep groundwater indicating S inputs from pyrite. The two identified active acids in the deep groundwater are likely to control the base-flow chemistry of streams draining larger catchments (>1 km(2)) as evident by delta(18)O signatures and base cation concentrations that overlap with that of the groundwater.

  • 36. Konter, Oliver
    et al.
    Holzkämper, Steffen
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Johannes Gutenberg University of Mainz, Germany.
    Helle, Gerhard
    Buentgen, Ulf
    Saurer, Matthias
    Esper, Jan
    Climate sensitivity and parameter coherency in annually resolved delta C-13 and delta O-18 from Pinus uncinata tree-ring data in the Spanish Pyrenees2014In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 377, p. 12-19Article in journal (Refereed)
    Abstract [en]

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

  • 37.
    Käpylä, Petri J.
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Helsinki, Finland.
    Mantere, M. J.
    Brandenburg, Axel
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Oscillatory large-scale dynamos from Cartesian convection simulations2013In: Geophysical and Astrophysical Fluid Dynamics, ISSN 0309-1929, E-ISSN 1029-0419, Vol. 107, no 1-2, p. 244-257Article in journal (Refereed)
    Abstract [en]

    We present results from compressible Cartesian convection simulations with and without imposed shear. In the former case the dynamo is expected to be of 2 type, which is generally expected to be relevant for the Sun, whereas the latter case refers to 2 dynamos that are more likely to occur in more rapidly rotating stars whose differential rotation is small. We perform a parameter study where the shear flow and the rotational influence are varied to probe the relative importance of both types of dynamos. Oscillatory solutions are preferred both in the kinematic and saturated regimes when the negative ratio of shear to rotation rates, qS/, is between 1.5 and 2, i.e. when shear and rotation are of comparable strengths. Other regions of oscillatory solutions are found with small values of q, i.e. when shear is weak in comparison to rotation, and in the regime of large negative qs, when shear is very strong in comparison to rotation. However, exceptions to these rules also appear so that for a given ratio of shear to rotation, solutions are non-oscillatory for small and large shear, but oscillatory in the intermediate range. Changing the boundary conditions from vertical field to perfect conductor ones changes the dynamo mode from oscillatory to quasi-steady. Furthermore, in many cases an oscillatory solution exists only in the kinematic regime whereas in the nonlinear stage the mean fields are stationary. However, the cases with rotation and no shear are always oscillatory in the parameter range studied here and the dynamo mode does not depend on the magnetic boundary conditions. The strengths of total and large-scale components of the magnetic field in the saturated state, however, are sensitive to the chosen boundary conditions.

  • 38. Lampert, Astrid
    et al.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ritter, Christoph
    Neuber, Roland
    Yoon, Young Jun
    Chae, Nam Yi
    Shiobara, Masataka
    Inclined Lidar Observations of Boundary Layer Aerosol Particles above the Kongsfjord, Svalbard2012In: Acta geophysica, ISSN 1895-6572, Vol. 60, no 5, p. 1287-1307Article in journal (Refereed)
    Abstract [en]

    An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Alesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data.

  • 39. Lihavainen, Heikki
    et al.
    Kerminen, Veli-Matti
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Aaltonen, Veijo
    Arola, Antti
    Hatakka, Juha
    Hyvärinen, Antti
    Viisanen, Yrjö
    Observational signature of the direct radiative effect by natural boreal forest aerosols and its relation to the corresponding first indirect effect2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114Article in journal (Other academic)
    Abstract [en]

    By using a screened set of long-term aerosol measurement data, the contribution of natural boreal forest aerosols to the direct radiative effect (DRE) was observed at a remote continental site in northern Finland. Averaged over the summer season, the magnitude of this effect at the top of the atmosphere was estimated to be in the range -(0.37-0.74) W m(-2) in our study region and possibly somewhat higher over the whole boreal forest region. Globally, the DRE owing to boreal forest aerosols is much smaller than that owing to natural sea salt or dust aerosols, as well as direct radiative forcing by anthropogenic aerosols. We also updated the earlier estimates of the first indirect radiative effect (IRE) by natural boreal forest aerosols. We found that this IRE is likely to be substantially higher, perhaps more than an order of magnitude, than the corresponding DRE

  • 40. Mamtani, Manish A.
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greiling, Reinhard O.
    Kontny, Agnes
    Hrouda, Frantisek
    Process of magnetite fabric development during granite deformation2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 308, no 1-2, p. 77-89Article in journal (Refereed)
    Abstract [en]

    This study evaluates the fabric defined by magnetite grains in a syntectonically deformed granite and deciphers the processes that led to magnetite fabric development. Anisotropy of anhysteretic remanence magnetization (AARM) analysis is performed in samples taken from different parts of the granite to establish that the magnetite grains define a fabric. Along with microstructural studies, the AARM data help conclude that this fabric is on account of shape preferred orientation (SPO) of the magnetite grains. The intensity of magnetite fabric (degree of anisotropy of the AARM ellipsoid) is higher in the southern parts as compared to the north, which is inferred to indicate a strain gradient. Electron back scattered diffraction (EBSD) analyses of magnetite grains were performed to determine if there are intracrystalline deformation features that could have influenced magnetite shape and SPO, and thus AARM data. Detailed crystallographic orientation data coupled with orientation contrast imaging did not reveal any subgrains and/or significant variations in crystallographic orientations within magnetite grains. Instead, grains exhibit fractures and are in places associated with quartz pressure fringes. Hence, neither the SPO nor the variation in the magnetite fabric intensity in the granite can be attributed to intracrysta Hine deformation of magnetite by dislocation creep. It is concluded that the magnetite grains were rheologically rigid and there was relative movement between the magnetite and the matrix minerals (quartz, feldspar and biotite). These matrix minerals actually define the fabric attractor and the magnetite grains passively rotated to align with it. Thus it is demonstrated that the magnetite fabric in the granite stems from rigid body movement rather than dislocation creep.

  • 41.
    Mattsson, Tobias
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of St. Andrews, UK; Uppsala University, Sweden.
    Benoît, Petri
    Almqvist, Bjarne
    McCarthy, William
    Burchardt, Steffi
    Palma, J. Octavio
    Hammer, Øyvind
    Galland, Olivier
    Decrypting magnetic fabrics (AMS, AARM, AIRM) through the analysis of mineral shape fabrics and distribution anisotropy2021In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 126, no 6, article id e2021JB021895Article in journal (Refereed)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X-ray micro-computed tomography to directly compare mineral shape-preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and > 50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: the magnetite and the amphibole shape fabrics and the magnetite spatial distribution. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P’ = 1.079). If shape fabrics and/or magnetite distribution are non-coaxial, the resulting AMS is weakly anisotropic (P’ = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first-order implications for the interpretation of petrofabrics using magnetic methods. 

  • 42.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kate
    University of Rhode Island.
    Deep-water methane hydrates in the Arctic Ocean: Re-assessing the significance of a shallow BSR on the Lomonosov Ridge2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, ISSN 115, B05102, 13 PP., 2010, Vol. 115Article in journal (Refereed)
    Abstract [en]

    Recently published multi-channel seismic data from the Lomonosov Ridge image a reversed polarity bottom-simulating reflector (BSR) tentatively attributed to the presence of deepwater marine hydrates and recognized throughout a survey area exceeding 100,000 km2. In addition to the importance of these findings for estimating Arctic hydrate reserves, if shown to correspond to the base of the hydrate stability zone, this seismic marker could provide a means for expanding spatial cover of heat flow data in deepwater settings of the Amerasian Basin, where little is known about the tectonic origin and nature of plate boundaries. As an initial test on the validity of this assumption, we develop a petrophysical model using sediments collected from circumpolar regions of the Lomonosov Ridge to derive an estimate of surface heat flow patterns from the BSR. The results show that the BSR inferred geothermal gradient and surface heat flow are exceedingly high when compared to published regional measurements. Although potential errors in the analysis may explain some of this discrepancy, the observation that the BSR remains at a constant sub-bottom depth despite large variations in water depths (> 2400 m) and relative sedimentation rates provides additional evidence that it cannot mark the base of the hydrate stability zone. A further understanding of its origin requires a more detailed investigation of the existing seismic data and highlights the need for renewed collection of heat flow data from the Arctic Ocean.

  • 43.
    Piazolo, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Austrheim, Hakon
    Whitehouse, Martin
    Brittle ductile microfabrics in naturally deformed zircon: deformation mechanisms and consequences for u pb dating2012In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 97, no 10, p. 1544-1563Article in journal (Refereed)
    Abstract [en]

    We present an electron backscatter diffraction, cathodoluminescence, and radiogenic U-Pb dating study of large zircon grains (0.8-1.5 mm) that show evidence of intracrystalline deformation, fracturing, grain size reduction and a large spread in U-Pb ages. The samples are from an amphibolite facies deformation zone within granulite facies anorthositic rocks (Bergen Arc, Norway). Large zircon grains show three main lattice distortion types: (I) distortions with rotations around < 001 > and an orientation change of similar to 0.3 degrees/mu m subparallel to (100); (II) highly distorted, half circular shaped zones located at grain edges with at least 0.8-1 degrees/mu m distortions; and (III) low-angle boundary networks forming deformation zones up to 100 mu m wide. Types II and III distortions exhibit significant disturbances of the otherwise homogeneous CL signature. Crystal plastic deformation with the slip system [010](100) resulted in type I distortions. Stress concentrations at grain contacts between rheologically hard grains caused localized crystal plastic deformation with minor amount of microfracturing forming type H distortions. Type Ill distortions formed by crystal plastic deformation often associated with inclusions using several slip systems. Distortions of types I and II show minor and moderate resetting of the original ca. 900 Ma zircon grains, respectively, due to enhanced pipe diffusion along dislocation walls. In type II distortions, accelerated lattice diffusion through the highly distorted crystal lattice, combined with exceptionally high boundary to volume ratio, caused significant chemical disturbance and age resetting to 410 Ma. Fine-grained aggregates contain grains with low internal deformation and an oscillatory zoned CL signature (Z-grains) or high internal deformation and a disturbed CL signature (D-grains). Z- and D-grains are interpreted to have formed by heterogeneous nucleation and growth, and fracturing along strain-hardened low-angle boundaries present within types I and II, respectively. Z-grains show a clustered chemical signature with a 437 +/- 11 Ma age interpreted to directly date the Caledonian amphibolite facies reworking.

  • 44. Plumper, Oliver
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Austrheim, Hakon
    Olivine Pseudomorphs after Serpentinized Orthopyroxene Record Transient Oceanic Lithospheric Mantle Dehydration (Leka Ophiolite Complex, Norway)2012In: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 53, no 9, p. 1943-1968Article in journal (Refereed)
    Abstract [en]

    We examine the partial survival of high-temperature mantle microstructures throughout multi-stage hydration-and dehydration-mediated pseudomorphism at differing pressure-temperature-fluid conditions. Throughout the harzburgitic mantle section of the Leka Ophiolite Complex (Norway), finite domains of parallel olivine encompassed by mesh-textured olivine resembling 'perfectly cleaved' olivine grains were identified. Crystallographic orientation mapping, combined with micro-computed tomography, reveals that the parallel olivine grains are highly misoriented (up to 90 degrees) with no crystal-preferred orientation, despite remaining parallel in three dimensions. Parallel olivine grains exhibit free dislocations with low dislocation density, whereas within mesh-textured olivine dislocations are aligned into walls. MnO is enriched (up to 1.8 wt %) and NiO depleted (0.21 +/- 0.24 wt %) within parallel olivine grains compared with mesh-textured olivine (0.29 +/- 0.14 wt % MnO; 0.38 +/- 0.19 wt % NiO). Clinopyroxene lamellae that are crystal-plastically deformed occur sandwiched in lizardite layers between every parallel olivine grain or fully enclosed within olivine. Al2O3 and Cr2O3 concentrations of clinopyroxene lamellae (2.09 +/- 0.88 wt % Al2O3; 0.79 +/- 0.27 wt % Cr2O3) overlap with those of primary clinopyroxene grains (2.43 +/- 0.69 wt % Al2O3; 0.83 +/- 0.36 wt % Cr2O3) and are distinctly different from those of secondary diopside found within the parallel olivine domains. Intragranular serpentine inclusions (X-Mg = 0.95 +/- 0.01), displaying elevated Al2O3 (3.92 +/- 4.10 wt %) and Cr2O3 (0.78 +/- 0.82 wt %) concentrations, are exclusively found within parallel olivine grains. Lizardite (X-Mg = 0.92 +/- 0.02) within the domains originates from hydration of parallel olivine and compositionally overlaps with mesh-texture lizardite. Antigorite (X-Mg = 0.95 +/- 0.01) replaces both types of olivine grains. Whole-rock compositions indicate a harzburgitic composition; however, microstructural and chemical observations and the current absence of primary orthopyroxene suggest that the precursor silicate of every parallel olivine domain was a single orthopyroxene grain that was initially serpentinized and later dehydrated to result in the present microstructure. Although desilicification is necessary during the transformation of orthopyroxene to olivine via a bastite stage, calculations based on whole-rock compositions imply that the released SiO2(aq) was mobile only over micrometer to centimeter scales, reacting with the surrounding olivine directly to form serpentine. Crosscutting relationships and serpentine compositions imply that dehydration occurred prior to the now evident lizardite-and antigorite-serpentinization. Comparison with the regional geological setting indicates that dehydration may have occurred transiently within the oceanic lithosphere prior to obduction.

  • 45.
    Polyak, Leonid
    et al.
    Bird Polar Research Center, Ohio State University.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Quaternary sedimentation in the Arctic Ocean: Recent advances and further challenges2011In: Oceanography, ISSN 1042-8275, Vol. 24, no 3, p. 52-64Article in journal (Refereed)
    Abstract [en]

    This paper reviews current knowledge of sedimentation patterns in the Arctic Ocean during the pronounced climatic cycles of the last several hundred thousand years, an especially relevant time period that provides long-term context for present climate change. The review is largely based on data collected during recent research icebreaker cruises to the Arctic Ocean, with a focus on the 2005 Healy-Oden TransArctic Expedition (HOTRAX) and 2007 Lomonosov Ridge Off Greenland (LOMROG) expedition. The sediment cores and geophysical seafloor mapping data collected enable reconstruction of past oceanic environments. Evaluation of these data suggests that the two major Arctic Ocean circulation systems, the Trans-Polar Drift and the Beaufort Gyre, persisted throughout most of the Late to Middle Quaternary, approximately the last 0.5 to 0.7 million years. Extreme conditions, nonanalogous to modern environments, also occurred in the past, especially during Pleistocene glacial intervals. Some of these intervals likely featured much thickened and/or concentrated sea ice and incursions of ice shelves and armadas of megasized icebergs from the margins to the center of the Arctic Ocean. In contrast, much warmer conditions with reduced sea ice extent existed during interglacial periods. Characterization of ice conditions during these intervals is critical for evaluating the present and projected future reduction of Arctic sea ice.

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  • 46.
    Regnéll, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Becher, Gustaf Peterson
    Ohrling, Christian
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Blomdin, Robin
    Brendryen, Jo
    Goodfellow, Bradley W.
    Mikko, Henrik
    Ransed, Gunnel
    Smith, Colby
    Ice-dammed lakes and deglaciation history of the Scandinavian Ice Sheet in central Jämtland, Sweden2023In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 314, article id 108219Article in journal (Refereed)
    Abstract [en]

    Extensive glacial lakes dammed in the Scandinavian Mountains during the retreat of the last Scandinavian Ice Sheet were first hypothesised over a century ago. Here, using high-resolution LiDAR, we report >4500 relict shorelines, deltas and palaeo-channels related to ice-dammed lakes over a -30 000 km2 area of central Jämtland, west-central Sweden. Shorelines occur as flights on the valley sides, a consequence of sequential lowering of palaeo-lake levels during ice margin retreat and lower threshold outlets becoming ice-free. Based on the extent and elevation of shorelines, we identify requisite lake-damming ice-margin positions and lake drainage outlets, and we reconstruct the coupled evolution of ice-dammed lakes and the retreating ice margin. Beginning as a series of smaller ice-dammed lakes along the Swedish-Norwegian border, draining westward across the present-day water divide and into the Atlantic Ocean, the lakes successively coalesced during eastward ice margin retreat to form water bodies covering 1000s of km2 with 10s of km-long calving margins. Ultimately, the lake system coalesced into a single lake: the Central Jämtland Ice Lake, which exceeded 3500 km2 in area and 360 km3 in volume. Eventually, the damming ice-margin split in two, resulting in a large (-200 km2) catastrophic glacial lake outburst flood (GLOF) that reversed the drainage of the entire lake system from the west to an eastern outlet draining to the Baltic basin. We present new radiocarbon ages for one lake drainage event prior to the eastward outburst flood and, together with previously published deglacial ages and local varve records, we suggest that the region was possibly deglaciated within just 350 years, sometime between 10.5 and 9.2 cal ka BP. We tentatively correlate the penultimate drainage of the Central Jämtland Ice Lake to the zero-varve of the Swedish Time Scale, a drainage varve at Döviken, eastern Jämtland, raising the tantalising prospect of using the evolution of the ice-dammed lake system to tie the varve-based Swedish Time Scale to the radiocarbon timescale with a new programme of radiocarbon dating in central Jämtland. 

  • 47. Rosenbaum, Gideon
    et al.
    Menegon, Luca
    Glodny, Johannes
    Vasconcelos, Paulo
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Massironi, Matteo
    Thiede, David
    Nasipuri, Pritam
    Dating deformation in the Gran Paradiso Massif (NW Italian Alps): Implications for the exhumation of high-pressure rocks in a collisional belt2012In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 144, p. 130-144Article in journal (Refereed)
    Abstract [en]

    The Gran Paradiso massif, situated in the internal part of the Western Italian Alps, records a complex tectono-metamorphic history involving high-pressure metamorphism and subsequent exhumation during retrograde metamorphism. The exact timing of deformation and, consequently, the geodynamic evolution of this part of the Western Alps is still debated and is addressed here by the application of Rb/Sr geochronology, Ar-40/Ar-39 step heating and Ar-40/Ar-39 total fusion dating techniques. Geochronological results are presented from shear zone samples in the core of the Gran Paradiso massif (Piantonetto Valley). and in the area closer to the contact with the overlying Piedmont ophiolitic domain (south and southwest of Pont Valsavarenche). The shear zones operated during crustal thinning and exhumation of the Gran Paradiso massif. Ar-40/Ar-39 step heating results from shear zones in the Piantonetto Valley show acceptable plateau ages that are interpreted to represent two events of mica growth. Similar ages, and an additional younger age cluster, are recognised in the Ar-40/Ar-39 total fusion analyses, indicating that specific cleavage domains operated at 39.2 +/- 0.2, 36.5 +/- 0.6 and 33.3 +/- 0.4 Ma. P-T pseudosections show a progressive decrease in metamorphic conditions during deformation, suggesting that the age of incipient exhumation and the related deformation in the Piantonetto Valley is equal to or older than 39.2 +/- 02 Ma. In the Pont area, the last increments of deformation in a top-to-W shear zone postdate 36.6 +/- 0.6 Ma (Rb/Sr mineral data), whereas the present-day top-to-W contact of the Gran Paradiso massif with the overlying Piedmont domain is dated at 41.2 +/- 1.1 Ma (Rb/Sr multi-mineral isochron age). We propose a model that considers exhumation of the Gran Paradiso nappe at 41-34 Ma. During this period, the nappe was coupled with the Zermatt-Saas zone, forming an extruding wedge. The kinematics associated with this wedge involved top-to-W shearing within the Gran Paradiso nappe (e.g. Pont area shear zones) and top-to-E shearing at the top of the extruding wedge (e.g. Orco shear zone). Subsequent deformation (after similar to 34 Ma) was characterised by coaxial strain involving orogenic-scale backfolding and backthrusting.

  • 48. Schmidt, Christoph
    et al.
    Pettke, Thomas
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rufer, Daniel
    Kasper, Haino Uwe
    Hilgers, Alexandra
    Quantification and spatial distribution of dose rate relevant elements in silex used for luminescence dating2012In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 12, p. 65-73Article in journal (Refereed)
    Abstract [en]

    Thermoluminescence (TL) is routinely used to date heated lithic artefacts which mostly consist of silex (a mixture of amorphous opal and microcrystalline chalcedony). Analytical investigations of bulk samples confirmed that these materials contain considerable concentrations of radioactive elements, generating an internal dose rate contribution. Common dosimetric models assume the latter to be homogeneous throughout the sample. If this assumption would prove invalid, this will result in systematic errors in the calculated age, especially in the course of so called 'hot spots' of alpha-emitters (and associated local changes in a-sensitivity) and the dose response characteristics of alpha-radiation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of 22 silex samples are presented here, quantifying element concentrations at several tens analytical spots per sample. Along with radioactive elements (K, Rb, U, Th), another 21 major, minor and trace elements were measured in order to allow characterization of the impurities present in most of the samples. The dataset provides a detailed picture of the spatial distribution of radionuclides and hence of the uniformity of the internal alpha- and beta-dose rate. It is shown that the silex itself mostly contains low amounts of K (<0.1 wt.%), U (<1.0 mu g g(-1)) and Th (<0.4 mu g g(-1)), and dosimetrically negligible Rb concentrations. Systematically higher concentrations are obtained by ICP-MS measurements of the bulk samples. This matches with the finding that impurities (veins, inclusions) often yield significantly elevated radionuclide concentrations, up to two orders of magnitude higher than the silex values. These veins and inclusions, for example Ca or Mg carbonates and Fe-Mn-oxy-hydroxides, lead to steep gradients mainly in the internal alpha-radiation field. Alternative approaches are required to account for the non-uniform internal dose rate and improve the reliability of TL dates of problematic samples.

  • 49. Selver, Ayca Dogrul
    et al.
    Talbot, Helen M.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Boult, Stephen
    van Dongen, Bart E.
    Soil organic matter transport along an sub-Arctic river-sea transect2012In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 51, p. 63-72Article in journal (Refereed)
    Abstract [en]

    Bacteriohopanepolyols (BHPs) and glycerol dialkyl glycerol tetraethers (GDGTs) have potential as soil-tracing biomarkers for the extensive shelves of the Arctic Ocean. In this work these biomarkers were analysed in surface sediments along a well characterised sub-Arctic transect in the northernmost Baltic Sea from the Kalix River to the central Bothnian Bay to assess their environmental behaviour and potential for tracing the contribution of soil in this type of system. There was a high BHP diversity and enhanced total BHP concentration in the estuarine sediments, whereas a much less diverse pattern could be observed in the open bay with lower total BHP concentration. In addition, both soil marker BHPs (adenosylhopanes) and branched GDGTs were substantially more abundant in the estuarine than the open bay sediments. The R'(soil) index, based on the R-soil index minus the contribution from the methylated soil marker BHPs, is suggested as a new approach for tracing soil derived organic matter (OM) in the (sub)-Arctic region. The index decreased along the transect in an off-river direction, correlating strongly with both the branched and isoprenoid tetraether (BIT) index and the stable carbon isotopic composition of the sedimentary organic carbon. These field results indicate that both the R'(soil) and the BIT indices have potential for tracing soil derived OM in sub-Arctic to Arctic waters.

  • 50. Shanahan, Timothy M.
    et al.
    Hughen, Konrad A.
    Bergqvist Ampel, Linda
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sauer, Peter E.
    Fornace, Kyrstin
    Environmental controls on the H-2/H-1 values of terrestrial leaf waxes in the eastern Canadian Arctic2013In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 119, p. 286-301Article in journal (Refereed)
    Abstract [en]

    The hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the Arctic. However, in contrast to the mid-and low-latitudes, significantly less effort has been directed towards understanding the factors controlling D/H fractionation in high latitude plant waxes and the impact of these processes on the interpretation of sedimentary leaf wax delta D records. To better understand these processes, we examined the D/H ratios of long chain fatty acids in lake surface sediments spanning a temperature and precipitation gradient on Baffin Island in the eastern Canadian Arctic. D/H ratios of plant waxes increase with increasing temperature and aridity, with values ranging from -240 parts per thousand to -160 parts per thousand over the study area. Apparent fractionation factors between n-alkanoic acids in Arctic lake sediments and precipitation(epsilon(FA-ppt)) are less negative than those of mid-latitude lakes and modern plants by 25 parts per thousand to 65 parts per thousand, consistent with n-alkane data from modern Arctic plants (Yang et al., 2011). Furthermore, epsilon(FA-ppt) values from Arctic lakes become systematically more positive with increasing evaporation, in contrast to mid-latitude sites, which show little to no change in fractionation with aridity. These data are consistent with enhanced water loss and isotope fractionation at higher latitude in the Arctic summer, when continuous sunlight supports increased daily photosynthesis. The dominant control on delta D-FA variations on Baffin Island is temperature. However, changing epsilon(FA-ppt) result in steeper delta D-FA-temperature relationships than observed for modern precipitation. The application of this delta D-FA-based paleotemperature calibration to existing delta D-FA records from Baffin Island produces much more realistic changes in late Holocene temperature and highlights the importance of these effects in influencing the interpretation of Arctic delta D-FA records. A better understanding of the controls on hydrogen isotope fractionation in high latitude leaf waxes will be essential to the proper interpretation of isotope records from sedimentary plant waxes in the Arctic.

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