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  • 201.
    Dahlgren, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A sedimentological study of Cryogenian glacial-interglacial cycles recorded by the Port Askaig Tillite Formation on Islay, Scotland2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An interglacial mudstone sequence from the Port Askaig Tillite Formation on Islay was analysed using an Olympus XRF detector. The resulting geochemical log was compared with an XRF dataset acquired from a Quaternary sedimentary core from the Lomonosov Ridge in the Arctic Ocean. Chemical proxies representing climatic and environmental changes were analysed in an effort to specifically identify evidence of orbital forcing in the Cryogenian Period.

    The studied non-glacial rock-section from the Port Askaig Formation was interpreted as being deposited in a shallow marine setting at semitropical latitudes during an episode of global warming at some stage of the Sturtian glaciation (ca 717 – 660 Ma). The transport mechanism of glaciogenic material was by ice rafting. High hematite content was interpreted as an oxygenation event in a peritidal zone when isostatic rebound caused a sea level regression. Increasing amount of muscovite is interpreted to indicate increased weathering. Underlaying sequence of dolostone and overlaying sequence of sandstone were consistent with these interpretations. One interglacial phase is thus observed, which possibly could be attributed to Milankovitch orbital forcing.

    The interpretation of the paleoclimatic setting of the studied interglacial mudstone did not provide support for the Snowball Earth hypothesis in its “hard” version. Neither did other observations such as evidence of repeating glacial-interglacial cycles and banded iron formations (BIF) appearing also within the Sturtian glaciation.

  • 202.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sobek, Anna
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Smedberg, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Modeling total particulate organic carbon (POC) flows in the Baltic Sea catchment2016In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 128, no 1-2, p. 51-65Article in journal (Refereed)
    Abstract [en]

    The largest input source of carbon to the Baltic Sea catchment is river discharge. A tool for modeling riverine particulate organic carbon (POC) loads on a catchment scale is currently lacking. The present study describes a novel dynamic model for simulating flows of POC in all major rivers draining the Baltic Sea catchment. The processes governing POC input and transport in rivers described in the model are soil erosion, in-stream primary production and litter input. The Baltic Sea drainage basin is divided into 82 sub-basins, each comprising several land classes (e.g. forest, cultivated land, urban areas) and parameterized using GIS data on soil characteristics and topography. Driving forces are temperature, precipitation, and total phosphorous concentrations. The model evaluation shows that the model can predict annual average POC concentrations within a factor of about 2, but generally fails to capture the timing of monthly peak loads. The total annual POC load to the Baltic Sea is estimated to be 0.34 Tg POC, which constitutes circa 7-10 % of the annual total organic carbon (TOC) load. The current lack of field measurements of POC in rivers hampers more accurate predictions of seasonality in POC loads to the Baltic Sea. This study, however, identifies important knowledge gaps and provides a starting point for further explorations of large scale POC mass flows.

  • 203.
    Dahlgren Strååt, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Undeman, Emma
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea2018In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 177, p. 8-20Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or -) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the middle CO2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.

  • 204.
    Dalsätt, Johan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fossil birds: Contributions to the understanding of avian evolution2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The study of the evolution of birds began about 150 years ago with the finding of Archaeopteryx. Yet, many unsolved questions about avian evolution remain to be answered. This thesis aims at addressing some of these questions.

    The Early Cretaceous Confusiusornis is the most well-represented Mesozoic bird in the fossil record. The abundance of fossils facilitates a study of the preservation of specimens in the two geological formations in which this taxon is found. It was demonstrated that specimens in the Yixiang Formation always are represented by complete, articulated skeletons, while those in the Jiofutang Formation often lack the pectoral girdle and the wings.

    Despite the many specimens available of Confusiusornis few clues to the diet of this taxon have been found. We describe a Confusiusornis specimen with a pellet of fish remains preserved in the throat region.

    The enantiornithid birds probably constituted the most species-rich and diverse bird group during the Cretaceous. Several well-preserved specimens have been found in China, e.g. Grabauornis lingyuanensis described herein.

    The mass extinction at the end of the Cretaceous probably gave the only surviving group of birds,Neornithes,chance to radiate and evolve into new niches. One such group is the Strigiformes (owls). We describe a new species from the Eocene Green River Formation in USAthat we suggest is closely related to the contemporary European Prosybris antique and P. medius.

    Although birds are known from several Miocene localities in Europe, the discovery of vertebrate fossils in the Hambach opencast lignite mine was thus unexpected and remarkable. The most significant bird found in Hambach is a specimen of darter, genus Anhinga. It agrees in size, proportions and morphology the fossil species Anhinga pannonica to which we refer the Hambach specimen. Fossils of ducks and galliforms have also been found in deposits at Hambach dated to the Pliocene.

  • 205.
    Dalsätt, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of National History, Sweden.
    Ericson, Per G. P.
    Zhou, Zhonge
    A New Enantiornithes (Aves) from the Early Cretaceous of China2014In: Acta Geologica Sinica, ISSN 1000-9515, E-ISSN 1755-6724, Vol. 88, no 4, p. 1034-1040Article in journal (Refereed)
    Abstract [en]

    A new bird from the early Cretaceous Yixian Formation of Liaoning, China is described. This new species, Grabauornis lingyuanensis, shares several synapomorphies with the Enantiornithes. The specimen is relatively well preserved. The skeletal morphology of Grabauornis bears close resemblance to that of other Chinese members of this clade. The brachial index (the ratio between the lengths of humerus and ulna) is 0.95, which is close to the average for enantiornithine birds. It indicates that Grabauornis was a rather good flyer, and the presence of an alula in the wing further testifies to this.

  • 206.
    Dalsätt, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ericson, Per P. G.
    A new species of owl (Aves: Strigiformes) from the Eocene Wasatch Formation, WyomingArticle in journal (Other academic)
  • 207.
    Dalsätt, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ericson, Per
    Zhou, Z.
    Differential preservation of Confuciusornis specimens in the Yixian and Jiufotang formationsArticle in journal (Other academic)
  • 208. Danielsson, Åsa
    et al.
    Rahm, Lars
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raymond, Caroline
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Svensson, Ola
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Yekta, Sepehr Shakeri
    Reyier, Henrik
    Gunnarsson, Jonas S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of re-oxygenation and bioturbation by the polychaete Marenzelleria arctia on phosphorus, iron and manganese dynamics in Baltic Sea sediments2018In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 23, p. 15-28Article in journal (Refereed)
    Abstract [en]

    Sediments underlying hypoxic or anoxic water bodies constitute a net source of phosphorus to the bottom water. This source has the potential to enhance eutrophication. Benthic fluxes of dissolved phosphorus, iron and manganese were measured from hypoxic, normoxic, and normoxic bioturbated by the invasive polychaete Marenzelleria arctia sediment in a mesocosm experiment. The highest benthic phosphorus efflux was detected in mesocosms with the hypoxic treatment. Normoxic, bioturbated sediments led to weaker retention of phosphorus compared to oxic, defaunated sediments. Both iron and manganese fluxes increased under bioturbated conditions compared to defaunated sediments. This study shows that re-oxygenation of previously anoxic coastal sediments enhance phosphorus retention in the sediments. Colonisation by M. arctia induce strong mobilisation of iron and manganese due to its intense bioirrigation, which facilitates organic matter degradation and decreases the phosphorus retention by metal oxides in sediment.

  • 209.
    Darby A., Dennis
    et al.
    Old Dominion University.
    Myers, Wesley B.
    Old Dominion University.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rigor, Ignatius
    University of Washington.
    Modern dirty sea ice characteristics and sources: The role of anchor ice2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no C09008Article in journal (Refereed)
    Abstract [en]

    Extensive dirty ice patches with up to 7 kg m−2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central Arctic. The Fe grain fingerprint determination of sources for these sampled dirty ice floes indicated both Russian and Canadian sources, with the latter dominating. The presence of benthic shells and sea weeds along with thick layers (2–10 cm) of sediment covering 5–10 m2 indicates an anchor ice entrainment origin as opposed to suspension freezing for some of these floes. The anchor ice origin might explain the dominance of Canadian sources where only narrow flaw leads occur that would not favor suspension freezing as an entrainment process. Expandable clays, commonly used as an indicator of a Kara Sea origin for dirty sea ice, are present in moderately high percentages (>20%) in many circum-Arctic source areas, including the Arctic coasts of North America. Some differences between the Russian and the North American coastal areas are found in clay mineral abundance, primarily the much higher abundance of chlorite in North America and the northern Barents Sea as opposed to the rest of the Russian Arctic. However, sea ice clay mineralogy matched many source areas, making it difficult to use as a provenance tool by itself. The bulk mineralogy (clay and non-clay) does not match specific sources possibly due to reworking of the sediment in dirty floes through summer melting or the failure to characterize all possible source areas.

  • 210. Davidson, Jonathan Robert Joseph
    et al.
    Fairley, Jerry
    Nicol, Andrew
    Gravley, Darren
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Canterbury, New Zealand.
    The origin of radon anomalies along normal faults in an active rift and geothermal area2016In: Geosphere, ISSN 1553-040X, E-ISSN 1553-040X, Vol. 12, no 5, p. 1656-1669Article in journal (Refereed)
    Abstract [en]

    Radon anomalies are widely reported in the vicinity of active faults, where they are often inferred to result from upward migration of fluids along fault zones. We examine the up-fault flow hypothesis by measuring radon (Rn-220 and Rn-222) in soil gas above two active normal fault zones within the central Taupo rift, New Zealand. In agreement with previous investigations, we find that the average concentrations of both radon isotopes are generally higher near mapped faults, although in some cases we find that the difference with background populations is not significant. Soil samples recovered from 1 m depth indicate that some of the radon anomalies along faults may reflect local changes in soil types. The Rn-220 isotope emanation measured from extracted soil samples shows a linear correlation with the field concentration measurements (R-2 = 0.90, p value = 3 x 10(-6)), whereas Rn-222 emanation shows no linear correlation (R-2 = 0.17, p value = 0.17). The soil gas isotopes measured show a significant linear correlation of Rn-220 and Rn-222 concentrations (R-2 = 0.44-0.55, p value <10(-5)) near faults. This correlation suggests a constant radon isotopic ratio is emitted from the soils tested, and this finding is supported by emission data measured on extracted soil samples. The distribution of Rn-222 concentration compared to Rn-220 can be explained by small-scale diffusion for >90% of the soil gas measurements, showing that a majority of radon anomalies along faults are not necessarily caused by advection of gases along fault planes and can be explained by an increase in radon soil emanation. However, diffusion cannot account for all of the observed patterns in the data, and in some specific locations along faults, Rn-222 concentrations are most likely produced by advective flow of subsurface gases, suggesting channelized gas flow in portions of some faults.

  • 211. Davies, Frazer J.
    et al.
    Renssen, Hans
    Blaschek, Michael
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The impact of Sahara desertification on Arctic cooling during the Holocene2015In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 11, p. 571-586Article in journal (Refereed)
    Abstract [en]

    Since the start of the Holocene, temperatures in the Arctic have steadily declined. This has been accredited to the orbitally forced decrease in summer insolation reconstructed over the same period. However, here we present climate modelling results from an Earth model of intermediate complexity (EMIC) that indicate that 17–40% of the cooling in the Arctic, over the period 9–0 ka, was a direct result of the desertification that occurred in the Sahara after the termination of the African Humid Period. We have performed a suite of sensitivity experiments to analyse the impact of different combinations of forcings, including various vegetation covers in the Sahara. Our simulations suggest that over the course of the Holocene, a strong increase in surface albedo in the Sahara as a result of desertification led to a regional increase in surface pressure, a weakening of the trade winds, the westerlies and the polar easterlies, which in turn reduced the meridional heat transported by the atmosphere to the Arctic. We conclude that during interglacials, the climate of the Northern Hemisphere is sensitive to changes in Sahara vegetation type.

  • 212. Dawson, Samantha K.
    et al.
    Fisher, Adrian
    Lucas, Richard
    Hutchinson, David K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Berney, Peter
    Keith, David
    Catford, Jane A.
    Kingsford, Richard T.
    Remote Sensing Measures Restoration Successes, but Canopy Heights Lag in Restoring Floodplain Vegetation2016In: Remote Sensing, ISSN 2072-4292, E-ISSN 2072-4292, Vol. 8, no 7, article id 542Article in journal (Refereed)
    Abstract [en]

    Wetlands worldwide are becoming increasingly degraded, and this has motivated many attempts to manage and restore wetland ecosystems. Restoration actions require a large resource investment, so it is critical to measure the outcomes of these management actions. We evaluated the restoration of floodplain wetland vegetation across a chronosequence of land uses, using remote sensing analyses. We compared the Landsat-based fractional cover of restoration areas with river red gum and lignum reference communities, which functioned as a fixed target for restoration, over three time periods: (i) before agricultural land use (1987-1997); (ii) during the peak of agricultural development (2004-2007); and (iii) post-restoration of flooding (2010-2015). We also developed LiDAR-derived canopy height models (CHMs) for comparison over the second and third time periods. Inundation was crucial for restoration, with many fields showing little sign of similarity to target vegetation until after inundation, even if agricultural land uses had ceased. Fields cleared or cultivated for only one year had greater restoration success compared to areas cultivated for three or more years. Canopy height increased most in the fields that were cleared and cultivated for a short duration, in contrast to those cultivated for >12 years, which showed few signs of recovery. Restoration was most successful in fields with a short development duration after the intervention, but resulting dense monotypic stands of river cooba require future monitoring and possibly intervention to prevent sustained dominance. Fields with intensive land use histories may need to be managed as alternative, drier flood-dependent vegetation communities, such as black box (Eucalyptus largiflorens) grasslands. Remotely-sensed data provided a powerful measurement technique for tracking restoration success over a large floodplain.

  • 213.
    de Boer, Agatha M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Collier, Andrew B.
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Processes driving thunderstorms over the Agulhas Current2013In: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, ISSN 2169-897X, Vol. 118, no 5, p. 2220-2228Article in journal (Refereed)
    Abstract [en]

    Lightning occurs predominantly over land and is not common over the open ocean. We study here one oceanic region in which thunderstorms are frequently found, namely the warm Agulhas Current off the southeast coast of South Africa. The seasonal and interannual lightning variability is derived from satellite and terrestrial data sets. Favorable climatic conditions for lightning are investigated using both ERA-Interim and NCEP/NCAR reanalysis data. We find peak lightning in austral autumn over the Agulhas Current but with low seasonality (i.e., there is considerable lightning throughout the year). While the climatological wind direction varies strongly with latitude and season, the wind direction is predominantly northerly throughout the region during thunderstorms. A composite of sea level pressure during thunderstorm days indicates that thunderstorms are related to eastward-propagating synoptic-scale wave trains passing through the Agulhas Current region. The strong convective activity during thunderstorms occur in the warm sector of a cyclone and is associated with horizontal convergence and lifting of warm, moist surface air originating over the warm Agulhas Current.

  • 214.
    de Boer, Agatha M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Graham, Robert M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thomas, Matthew D.
    Kohfeld, Karen E.
    The control of the Southern Hemisphere Westerlies on the position of the Subtropical Front2013In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 118, no 10, p. 5669-5675Article in journal (Refereed)
    Abstract [en]

    In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.

  • 215.
    De Boer, Agatha M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogg, Andrew McC.
    Control of the glacial carbon budget by topographically induced mixing2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 12, p. 4277-4284Article in journal (Refereed)
    Abstract [en]

    Evidence for the oceanic uptake of atmospheric CO2 during glaciations suggests that there was less production of southern origin deep water but, paradoxically, a larger volume of southern origin water than today. Here we demonstrate, using a theoretical box model, that the inverse relationship between volume and production rate of this water mass can be explained by invoking mixing rates in the deep ocean that are proportional to topographic outcropping area scaled with ocean floor slope. Furthermore, we show that the resulting profile, of a near-linear decrease in mixing intensity away from the bottom, generates a positive feedback on CO2 uptake that can initiate a glacial cycle. The results point to the importance of using topography-dependent mixing when studying the large-scale ocean circulation, especially in the paleo-intercomparison models that have failed to produce the weaker and more voluminous bottom water of the Last Glacial Maximum.

  • 216.
    de Boer, Agatha M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pascual-Ahuir, Estanislao Gavilan
    Stevens, David P.
    Chafik, Léon
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hutchinson, David K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Sime, Louise C.
    Willmott, Andrew J.
    Interconnectivity Between Volume Transports Through Arctic Straits2018In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 123, no 12, p. 8714-8729Article in journal (Refereed)
    Abstract [en]

    Arctic heat and freshwater budgets are highly sensitive to volume transports through the Arctic-Subarctic straits. Here we study the interconnectivity of volume transports through Arctic straits in three models; two coupled global climate models, one with a third-degree horizontal ocean resolution (High Resolution Global Environmental Model version 1.1 [HiGEM1.1]) and one with a twelfth-degree horizontal ocean resolution (Hadley Centre Global Environment Model 3 [HadGEM3]), and one ocean-only model with an idealized polar basin (tenth-degree horizontal resolution). The two global climate models indicate that there is a strong anticorrelation between the Bering Strait throughflow and the transport through the Nordic Seas, a second strong anticorrelation between the transport through the Canadian Arctic Archipelago and the Nordic Seas transport, and a third strong anticorrelation is found between the Fram Strait and the Barents Sea throughflows. We find that part of the strait correlations is due to the strait transports being coincidentally driven by large-scale atmospheric forcing patterns. However, there is also a role for fast wave adjustments of some straits flows to perturbations in other straits since atmospheric forcing of individual strait flows alone cannot lead to near mass balance fortuitously every year. Idealized experiments with an ocean model (Nucleus for European Modelling of the Ocean version 3.6) that investigate such causal strait relations suggest that perturbations in the Bering Strait are compensated preferentially in the Fram Strait due to the narrowness of the western Arctic shelf and the deeper depth of the Fram Strait. Plain Language Summary The Arctic is one of the most fragile places on the Earth, facing double the rate of warming as the rest of the globe. This warming is partly due to melting of sea ice because open water reflects less sunlight than ice. One of the major controls on Arctic sea ice concentration is the heat flowing into the Arctic through its straits. However, due to the harsh conditions in the Arctic, there are limited long-term observations of the currents flowing through these straits. Here we turn to climate models to investigate these Arctic straits flows and in particular focus on how flows into and out of the Arctic balance each other. We find that in some instances specific pairs of strait flows are simultaneously affected by large-scale atmospheric. In other instances, the inflow through one strait flows out through another distant strait because of the way the ocean floor guides the currents. Traditionally, the flows through Arctic straits are studied in relation to local forces such as wind and sea level. Our work suggests value in a more holistic approach; one that also accounts for flow changes in a strait as a response to flow changes in other straits.

  • 217. De Brabandere, L.
    et al.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kononets, M.
    Viktorsson, Lena
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Stigebrandt, A.
    Thamdrup, B.
    Hall, P. O. J.
    Oxygenation of an anoxic fjord basin strongly stimulates benthic denitrification and DNRAManuscript (preprint) (Other academic)
  • 218. De Brabandere, Loreto
    et al.
    Bonaglia, Stefano
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kononets, Mikhail Y.
    Viktorsson, Lena
    Stigebrandt, Anders
    Thamdrup, Bo
    Hall, Per O. J.
    Oxygenation of an anoxic fjord basin strongly stimulates benthic denitrification and DNRA2015In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 126, no 1-2, p. 131-152Article in journal (Refereed)
    Abstract [en]

    Hypoxia hampers eutrophication reduction efforts by enabling high nutrient fluxes from sediment to bottom waters. Oxygenation of hypoxic water bodies is often proposed to reduce benthic ammonium and phosphate release. This study investigates the functional response of benthic nitrate-reducing processes to a long-term engineered oxygenation effort in a density-stratified fjord with euxinic bottom waters. Oxygenation was achieved by mixing surface water with deep, euxinic water, which increased oxygen and nitrate concentrations in the deep water column. The presence of nitrate instigated benthic nitrate reduction in the newly oxidized sediments by equally stimulating denitrification and dissimilatory nitrate reduction to ammonium (DNRA). DNRA and total nitrate reduction rates, as well as the contribution of DNRA to total nitrate reduction, decreased with increasing exposure time of the sediments to oxygen. The relative importance of DNRA as a nitrate sink was correlated to nitrate concentrations, with more nitrate being reduced to ammonium at higher bottom water nitrate concentrations. Overall, engineered oxygenation decreased the net efflux of dissolved inorganic nitrogen from the sediments by stimulating net nitrate removal through denitrification.

  • 219. de Souza, Claudio M. D.
    et al.
    Carneiro, Cristine E. A.
    Bau, Joao Paulo T.
    da Costa, Antonio C. S.
    Ivashita, Flavio F.
    Paesano, Andrea, Jr.
    di Mauro, Eduardo
    de Santana, Henrique
    Holm, Nils G.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Neubeck, Anna
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zaia, Cassia T. B. V.
    Zaia, Dimas A. M.
    Interaction of forsterite-91 with distilled water and artificial seawater: a prebiotic chemistry experiment2013In: International Journal of Astrobiology, ISSN 1473-5504, E-ISSN 1475-3006, Vol. 12, no 2, p. 135-143Article in journal (Refereed)
    Abstract [en]

    In the present work, the interactions between forsterite-91 with distilled water and forsterite-91 with artificial seawater were studied at two pHs (2.0 and 8.0) using different techniques. A large increase in pH was observed for samples incubated at an initially acidic pH (2.0) due to the dissolution of forsterite-91 in distilled water and artificial seawater. Thus, in acidic hydrothermal vents, an increase in the amount of hydrocarbons and magnetite should be expected due to the release of Fe(II). The pH(PZC) decreased and the pH(IEP) increased when forsterite-91 was treated with distilled water and artificial seawater. The ions from the artificial seawater had an effect on zeta potential. Scanning electron microscopy (SEM) images and X-ray diffractograms showed halite in the samples of forsterite-91 mixed with artificial seawater. The presence of halite or adsorption of ions on the surface of forsterite-91 could affect the synthesis of magnetite and hydrocarbons in hydrothermal vents, due to a decrease in the dissolution rates of forsterite-91. The dissolution of forsterite-91 yields low concentrations of Fe(III) and Mn(II) as detected by electron paramagnetic resonance (EPR) spectroscopy. Microanalysis of forsterite-91 showed a higher amount of Mn, with an oxidation that was likely not + II, as Mn in supernatant solutions was only detected by EPR spectroscopy after mixing with artificial seawater at pH 2.0. As Fe(III) and Mn(II) are catalyst constituents of magnetite and manganese oxide, respectively, their presence is important for synthesis in hydrothermal vents. Etch pits were observed only in the forsterite-91 sample mixed with distilled water at pH 8.0. Na, Cl, S, Ca and K were detected in the samples mixed with artificial seawater by SEM-EDS. Si, Mg, Fe and Al were detected in almost all supernatant samples due to forsterite-91 dissolution. Cr was not dissolved in the experiments, thus Cr in the mineral could serve as an effective catalyst for Fischer Tropsch Types (FTT) reactions in hydrothermal vent systems. X-ray diffractograms of the original forsterite-91 also showed peaks arising from zeolites and clinochlore. After the samples were treated with artificial seawater, X-ray diffractograms showed the dissolution of zeolite. Experiments should be performed in the natural environment to verify the potential for zeolites to act as a catalyst in hydrothermal vents.

  • 220.
    Demina, Ludmila
    et al.
    P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Holm, Nils
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Galkin, Sergey
    P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Lein, Alla
    P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Concentration function of deep-sea vent benthic organisms2010In: Cahiers de Biologie Marine, Vol. 51, p. 369-373Article in journal (Refereed)
  • 221.
    Demina, Ludmila
    et al.
    P.P Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Holm, Nils
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Galkin, Sergey
    P.P Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Lein, Alla
    P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences.
    Some features of the trace metal biogeochemistry in the deep-sea hydrothermal vent fields (Menez Gwen, Rainbow, Broken Spur at the MAR and 9°50'N at the EPR): A synthesis2013In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 126, no SI, p. 94-105Article in journal (Refereed)
    Abstract [en]

    Along with summarizing the published literature and our own data some new results on properties of the trace metal biogeochemistry in the deep-sea hydrothermal ecosystems at the Mid-Atlantic Ridge (MAR) and East Pacific Rise (EPR) are shown. Differences in mean concentrations of big group of trace metals (Fe, Mn, Zn, Cu, Ni, Cr, Co, As, Pb, Cd, Ag, Hg) between the biotope water of the low- and high-temperature hydrothermal vent fields were firstly revealed. The same trace metals were studied in different groups of organisms within different temperature zones at one and the same vent field (9°50′N EPR), as well as in fauna inhabiting geochemically different vent sites. Distribution patterns of Fe, Mn, Zn, Cu, Cd, Pb, Ag, Ni, Cr, Co, As, Se, Sb, and Hg in different taxa gave an evidence of the influence of environmental and biological parameters on their bioaccumulation in organisms. Among the animals a particular “champion” with respect to the trace metal content was found to be a polychaeta Alvinella pompejana that inhabits the hottest places of the vent sulfide chimneys of the 9°50′N field, EPR. New data on the trace metal distribution between soft tissues and carbonate shell let us estimate a role of biomineralization in the accumulation of metals in the Bathimodiolus mussels. Contrasting geochemical behavior was revealed for Cu that is enriched in soft tissues of mussels and depleted in shells, on the one hand, and Mn that is accumulated almost totally in mussel shells, on the other hand.

    Deep-sea hydrothermal biological communities demonstrate a strong concentration function, and bioconcentration factors (BCF) of trace metals estimated for Bathimodiolus mussels collected at the four hydrothermal fields vary within the limits of n102–n105 and are similar to that of the littoral mussels. Due to this and to the high values of biomasses per square meter, the hydrothermal fauna may be considered as a newly discovered biological filter of the oceans.

  • 222. Deng, J.
    et al.
    Li, C.
    Frolking, S.
    Zhang, Y.
    Bäckstrand, Kristina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 17, p. 4753-4770Article in journal (Refereed)
    Abstract [en]

    Northern peatlands in permafrost regions contain a large amount of organic carbon (C) in the soil. Climate warming and associated permafrost degradation are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is uncertain. We incorporated a permafrost model, Northern Ecosystem Soil Temperature (NEST), into a biogeochemical model, DeNitrification-DeComposition (DNDC), to model C dynamics in high-latitude peatland ecosystems. The enhanced model was applied to assess effects of permafrost thaw on C fluxes of a subarctic peatland at Stordalen, Sweden. DNDC simulated soil freeze-thaw dynamics, net ecosystem exchange of CO2 (NEE), and CH4 fluxes across three typical land cover types, which represent a gradient in the process of ongoing permafrost thaw at Stordalen. Model results were compared with multiyear field measurements, and the validation indicates that DNDC was able to simulate observed differences in seasonal soil thaw, NEE, and CH4 fluxes across the three land cover types. Consistent with the results from field studies, the modeled C fluxes across the permafrost thaw gradient demonstrate that permafrost thaw and the associated changes in soil hydrology and vegetation not only increase net uptake of C from the atmosphere but also increase the annual to decadal radiative forcing impacts on climate due to increased CH4 emissions. This study indicates the potential of utilizing biogeochemical models, such as DNDC, to predict the soil thermal regime in permafrost areas and to investigate impacts of permafrost thaw on ecosystem C fluxes after incorporating a permafrost component into the model framework.

  • 223. Deng, Jia
    et al.
    McCalley, Carmody K.
    Frolking, Steve
    Chanton, Jeff
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Varner, Ruth
    Tyson, Gene
    Rich, Virginia
    Hines, Mark
    Saleska, Scott R.
    Li, Changsheng
    Adding stable carbon isotopes improves model representation of the role of microbial communities in peatland methane cycling2017In: Journal of Advances in Modeling Earth Systems, ISSN 1942-2466, Vol. 9, no 2, p. 1412-1430Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to have significant and uncertain impacts on methane (CH4) emissions from northern peatlands. Biogeochemical models can extrapolate site-specificCH(4) measurements to larger scales and predict responses of CH4 emissions to environmental changes. However, these models include considerable uncertainties and limitations in representing CH4 production, consumption, and transport processes. To improve predictions of CH4 transformations, we incorporated acetate and stable carbon (C) isotopic dynamics associated with CH4 cycling into a biogeochemistry model, DNDC. By including these new features, DNDC explicitly simulates acetate dynamics and the relative contribution of acetotrophic and hydro-genotrophic methanogenesis (AM and HM) to CH4 production, and predicts the C isotopic signature (delta C-13) in soil C pools and emitted gases. When tested against biogeochemical and microbial community observations at two sites in a zone of thawing permafrost in a subarctic peatland in Sweden, the new formulation substantially improved agreement with CH4 production pathways and delta C-13 in emitted CH4 (delta C-13-CH4), a measure of the integrated effects of microbial production and consumption, and of physical transport. We also investigated the sensitivity of simulated delta C-13-CH4 to C isotopic composition of substrates and, to fractionation factors for CH4 production (alpha(AM) and alpha(HM)), CH4 oxidation (alpha(MO)), and plant-mediated CH4 transport (alpha(TP)). The sensitivity analysis indicated that the delta C-13-CH4 is highly sensitive to the factors associated with microbial metabolism (alpha(AM), alpha(HM), and alpha(MO)). The model framework simulating stable C isotopic dynamics provides a robust basis for better constraining and testing microbial mechanisms in predicting CH4 cycling in peatlands.

  • 224.
    Dickens, Gerald R.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Down the Rabbit Hole: toward appropriate discussion of methane release from gas hydrate systems during the Paleocene-Eocene thermal maximum and other past hyperthermal events2011In: Climate of the Past Discussions, ISSN 1814-9340, E-ISSN 1814-9359, Vol. 7, no 3, p. 831-846Article in journal (Refereed)
    Abstract [en]

    Enormous amounts of (13)C-depleted carbon rapidly entered the exogenic carbon cycle during the onset of the Paleocene-Eocene thermal maximum (PETM), as attested to by a prominent negative carbon isotope (delta(13)C) excursion and deep-sea carbonate dissolution. A widely cited explanation for this carbon input has been thermal dissociation of gas hydrate on continental slopes, followed by release of CH(4) from the seafloor and its subsequent oxidation to CO(2) in the ocean or atmosphere. Increasingly, papers have argued against this mechanism, but without fully considering existing ideas and available data. Moreover, other explanations have been presented as plausible alternatives, even though they conflict with geological observations, they raise major conceptual problems, or both. Methane release from gas hydrates remains a congruous explanation for the delta(13)C excursion across the PETM, although it requires an unconventional framework for global carbon and sulfur cycling, and it lacks proof. These issues are addressed here in the hope that they will prompt appropriate discussions regarding the extraordinary carbon injection at the start of the PETM and during other events in Earth's history.

  • 225. 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)
  • 226.
    Dickens, Gerald R.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Core alignment and composite depth scale for the lower Paleogene through uppermost Cretaceous interval at Deep Sea Drilling Project Site 5772013In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 46, no 1, p. 47-68Article in journal (Refereed)
    Abstract [en]

    Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

  • 227. Divine, D. V.
    et al.
    Sjolte, J.
    Isaksson, E.
    Meijer, H. A. J.
    van de Wal, R. S. W.
    Martma, T.
    Pohjola, V.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Godtliebsen, F.
    Modelling the regional climate and isotopic composition of Svalbard precipitation using REMOiso: a comparison with available GNIP and ice core data2011In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 25, no 24, p. 3748-3759Article in journal (Refereed)
    Abstract [en]

    Simulations of a regional (approx. 50 km resolution) circulation model REMOiso with embedded stable water isotope module covering the period 1958-2001 are compared with the two instrumental climate and four isotope series (d18O) from western Svalbard. We examine the data from ice cores drilled on Svalbard ice caps in 1997 (Lomonosovfonna, 1250 m asl) and 2005 (Holtedahlfonna, 1150 m asl) and the GNIP series from Ny-angstrom lesund and Isfjord Radio. The surface air temperature (SAT) and precipitation data from Longyearbyen and Ny-angstrom lesund are used to assess the skill of the model in reproducing the local climate. The model successfully captures the climate variations on the daily to multidecadal times scales although it tends to systematically underestimate the winter SAT. Analysis suggests that REMOiso performs better at simulating isotope compositions of precipitation in the winter than summer. The simulated and measured Holtedahlfonna d18O series agree reasonably well, whereas no significant correlation has been observed between the modelled and measured Lomonosovfonna ice core isotopic series. It is shown that sporadic nature as well as variability in the amount inherent in precipitation process potentially limits the accuracy of the past SAT reconstruction from the ice core data. This effect in the study area is, however, diminished by the role of other factors controlling d18O in precipitation, most likely sea ice extent, which is directly related with the SAT anomalies.

  • 228. Douglas, P. M. J.
    et al.
    Stolper, D. A.
    Smith, D. A.
    Anthony, K. M. Walter
    Paull, C. K.
    Dallimore, S.
    Wik, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Winterdahl, Mathias
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Eiler, J. M.
    Sessions, A. L.
    Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues2016In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 188, p. 163-188Article in journal (Refereed)
    Abstract [en]

    Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. Here we apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium Delta(18) values spanning a range of more than 5 parts per thousand.

  • 229. Dowdeswell, J. A.
    et al.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogan, K. A.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evans, J.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Noormets, R.
    O'Cofaigh, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sölvsten, M.
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3518-3531Article in journal (Refereed)
    Abstract [en]

    High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.

  • 230.
    Downs, Kenneth
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Iron and Manganese Reduction and Associated Phosphorus Release in Coastal Baltic Sea Sediment2013In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 5, article id 1007Article in journal (Refereed)
  • 231. Drake, Henrik
    et al.
    Heim, Christine
    Roberts, Nick M. W.
    Zack, Thomas
    Tillberg, Mikael
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ivarsson, Magnus
    Whitehouse, Martin J.
    Åström, Mats E.
    Isotopic evidence for microbial production and consumption of methane in the upper continental crust throughout the Phanerozoic eon2017In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 470, p. 108-118Article in journal (Refereed)
    Abstract [en]

    Microorganisms produce and consume methane in terrestrial surface environments, sea sediments and, as indicated by recent discoveries, in fractured crystalline bedrock. These processes in the crystalline bedrock remain, however, unexplored both in terms of mechanisms and spatiotemporal distribution. Here we have studied these processes via a multi-method approach including microscale analysis of the stable isotope compositions of calcite and pyrite precipitated in bedrock fractures in the upper crust (down to 1.7 km) at three sites on the Baltic Shield. Microbial processes have caused an intriguing variability of the carbon isotopes in the calcites at all sites, with delta C-13 spanning as much as -93.1 parts per thousand (related to anaerobic oxidation of methane) to +36.5 parts per thousand (related to methanogenesis). Spatiotemporal coupling between the stable isotope measurements and radiometric age determinations (micro-scale dating using new high spatial methods: LA-ICP-MS U-Pb for calcite and Rb-Sr for calcite and co-genetic adularia) enabled unprecedented direct timing constraints of the microbial processes to several periods throughout the Phanerozoic eon, dating back to Devonian times. These events have featured variable fluid salinities and temperatures as shown by fluid inclusions in the calcite; dominantly 70-85 degrees C brines in the Paleozoic and lower temperatures (<50-62 degrees C) and salinities in the Mesozoic. Preserved organic compounds, including plant signatures, within the calcite crystals mark the influence of organic matter in descending surficial fluids on the microbial processes in the fracture system, thus linking processes in the deep and surficial biosphere. These findings substantially extend the recognized temporal and spatial range for production and consumption of methane within the upper continental crust.

  • 232. Drake, Henrik
    et al.
    Mathurin, Frédéric A.
    Zack, Thomas
    Schäfer, Thorsten
    Roberts, Nick M. W.
    Whitehouse, Martin
    Karlsson, Andreas
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Åström, Mats E.
    Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer2018In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 2, p. 493-502Article in journal (Refereed)
    Abstract [en]

    Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water rock interaction in the upper crust and for retention mechanisms associated With underground, repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest, for nuclear waste repositories. Here, we report a microanalytical study: of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 degrees C), neutral (pH: 7.4-7.7), and brackish (Cl: 1700-7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.

  • 233. Drake, Henrik
    et al.
    Whitehouse, Martin J.
    Heim, Christine
    Reiners, Peter W.
    Tillberg, Mikael
    Hogmalm, K. Johan
    Dopson, Mark
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Åstrom, Mats E.
    Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks2018In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 16, no 5, p. 556-574Article in journal (Refereed)
    Abstract [en]

    In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR-related S-isotope systematics, particularly regarding formation of large fractions of S-34-rich pyrite.

  • 234. Drake, Henrik
    et al.
    Åström, Mats E.
    Heim, Christine
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Åström, Jan
    Whitehouse, Martin
    Ivarsson, Magnus
    Siljeström, Sandra
    Sjövall, Peter
    Extreme C-13 depletion of carbonates formed during oxidation of biogenic methane in fractured granite2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 7020Article in journal (Refereed)
    Abstract [en]

    Precipitation of exceptionally C-13-depleted authigenic carbonate is a result of, and thus a tracer for, sulphate-dependent anaerobic methane oxidation, particularly in marine sediments. Although these carbonates typically are less depleted in C-13 than in the source methane, because of incorporation of C also from other sources, they are far more depleted in C-13 (delta C-13 as light as - 69% V-PDB) than in carbonates formed where no methane is involved. Here we show that oxidation of biogenic methane in carbon-poor deep groundwater in fractured granitoid rocks has resulted in fracture-wall precipitation of the most extremely C-13-depleted carbonates ever reported, delta C-13 down to - 125% V-PDB. A microbial consortium of sulphate reducers and methane oxidizers has been involved, as revealed by biomarker signatures in the carbonates and S-isotope compositions of co-genetic sulphide. Methane formed at shallow depths has been oxidized at several hundred metres depth at the transition to a deep-seated sulphate-rich saline water. This process is so far an unrecognized terrestrial sink of methane.

  • 235. Dredge, Ian
    et al.
    Parnell, John
    Lindgren, Paula
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bowden, Stephen
    Elevated flux of cosmic spherules (micrometeorites) in Ordovician rocks of the Durness Group, NW Scotland2010In: Scottish Journal of Geology, ISSN 0036-9276, E-ISSN 2041-4951, Vol. 46, p. 7-16Article in journal (Refereed)
    Abstract [en]

    Limestone samples from the Cambro-Ordovician Durness Group were crushed, acid-digested and searched for evidence of micrometeorites. Eleven melted micrometeorites were extracted from the magnetic fraction of samples from the Balnakeil and Croisaphuill formations near the top of the group. Other formations in the Durness Group did not yield micrometeorites. Only melted spherules with a distinctive dendroidal crystalline structure (I-type cosmic spherules) were accepted as definite micrometeorites. They represent a flux of micrometeorites one to two orders of magnitude greater than at present. The micrometeorite-bearing formations are of Arenig age, coincident with the onset of an enhanced flux of extraterrestrial material identified by the occurrence of fossil meteorites in Sweden.

  • 236.
    Duc, Nguyen Thanh
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Abiotic and biotic methane dynamics in relation to the origin of life2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Methane (CH4) plays an important role in regulating Earth’s climate. Its atmospheric concentrations are related to both biotic and abiotic processes. The biotic one can be formed either by chemoautotrophic or heterotrophic pathways by methanogens. Abiotic CH4 formation can occur from several sequential reactions starting with H2 production by serpentinization of Fe-bearing minerals followed by Fischer-Tropsch Type reactions or thermogenic reactions from hydrocarbons. In the presence of suitable electron acceptors, microbial oxidation utilizes CH4 and contributes to regulating its emission.  From the perspectives of astrobiology and Earth climate regulation, this thesis focuses on: (1) Dynamics of CH4 formation and oxidation in lake sediments (Paper I), (2) Constructing an automatic flux chamber to facilitate its emission measurements (Paper II), (3) dynamics of both abiotic and biotic CH4 formation processes related to olivine water interaction in temperature range 30 - 70°C (Paper III and IV).

    Paper I showed that potential CH4 oxidation strongly correlated to in situ its formation rates across a wide variety of lake sediments. This means that the oxidation rates could be enhanced in environments having the high formation rates. Thereby, the oxidation would likely be able to keep up with potentially increasing the formation rates, as a result diffusive CH4 release from freshwater sediments might not necessarily increase due to global warming. Paper II presented a new automated approach to assess temporal variability of its aquatic fluxes. Paper III and IV together revealed that H2 can be formed via olivine-water interaction. Abiotic CH4 formation was formed likely by Fischer-Tropsch Type reactions at low inorganic carbon concentration but by thermogenic processes at high inorganic carbon concentration. Paper IV showed that biotic methanogenic metabolism could harvest H2 and produce CH4. The dynamics of these processes seemed strongly affected by carbonate chemistry.

  • 237.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick, M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Implications of temperature and sediment characteristics on methane formation and oxidation in lake sediments2010In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 100, no 1-3, p. 185-196Article in journal (Refereed)
    Abstract [en]

    Methane emissions from aquatic environments depend on methane formation (MF) and methane oxidation (MO) rates. One important question is to what extent increased temperatures will affect the balance between MF and MO. We measured potential MF and MO rates simultaneously at 4, 10, 20 and 30A degrees C in sediment from eight different lakes representing typical boreal and northern temperate lake types. Potential MF rates ranged between 0.002 and 3.99 mu mol CH4 g(d.w.) (-1) day(-1), potential MO rates ranged from 0.01 to 0.39 CH4 g(d.w.) (-1) day(-1). The potential MF rates were sensitive to temperature and increased 10 to 100 fold over the temperature interval studied. MF also differed between lakes and was correlated to sediment water content, percent of organic material and C:N ratio. Potential MO did not depend on temperature or sediment characteristics but was instead well explained by MF rates at the in situ temperature. It implies that elevated temperatures will enhance MF rates which may cause increased methane release from sediments until MO increases as well, as a response to higher methane levels.

  • 238.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Neubeck, Anna
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The potential for abiotic methane formation fueled by olivine dissolutionIn: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908Article in journal (Refereed)
  • 239. Duc, Nguyen Thanh
    et al.
    Silverstein, Samuel B.
    Stockholm University, Faculty of Science, Department of Physics.
    Lundmark, Lars
    Reyier, Henrik
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Automated Flux Chamber for Investigating Gas Flux at Water-Air Interfaces2013In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 47, no 2, p. 968-975Article in journal (Refereed)
    Abstract [en]

    Aquatic ecosystems are major sources of greenhouse gases (GHG). Representative measurements of GHG fluxes from aquatic ecosystems to the atmosphere are vital for quantitative understanding of relationships between biogeochemistry and climate. Fluxes occur at high temporal variability at diet or longer scales, which are not captured by traditional short-term deployments (often in the order of 30 min) of floating flux chambers. High temporal frequency measurements are necessary but also extremely labor intensive if manual flux chamber based methods are used. Therefore, we designed an inexpensive and easily mobile automated flux chamber (AFC) for extended deployments. The AFC was designed to measure in situ accumulation of gas in the chamber and also to collect gas samples in an array of sample bottles for subsequent analysis in the laboratory, providing two independent ways of CH4 concentration measurements. We here present the AFC design and function together with data from initial laboratory tests and from a field deployment.

  • 240.
    Duc, Nguyen Thanh
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Silverstein, Samuel
    Stockholm University, Faculty of Science, Department of Physics.
    Lundmark, Lars
    Reyier, Henrik
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    An automatic flux chamber for investigating gas flux at water – air interfacesManuscript (preprint) (Other academic)
    Abstract [en]

    Aquatic ecosystems are major sources of greenhouse gases (GHG).  Representative measurements of GHG fluxes from aquatic ecosystems to the atmosphere are vital for quantitative understanding of climate related biogeochemistry. Fluxes occur at high temporal variability at diel or longer scales which are not captured by traditional short term deployments (typically on the order of 30 minutes) of floating flux chambers. High temporal frequency measurements are necessary but are extremely labor intensive if manual flux chamber based methods are used. Eddy correlation methods require expensive equipment and lead to uncertain results because of the high spatial variability of fluxes from restricted areas. Therefore we designed an inexpensive and easily mobile automatic flux chamber system (AFC) for extended deployments. This device includes a flux chamber and a box with the controller/datalogger, valves, a pump, a 12 V battery and a solar cell. Sensors tested in this study recorded CH4 concentration in the chamber headspace, temperature in the water and air and barometric pressure, but other sensors for CO2 and weather variables can also be attached to the system. The unit was designed to measure in situ accumulation of gas in the chamber and also to collect gas samples in an array of sample bottles for subsequent analysis in the laboratory, providing two independent ways of CH4 concentration measurements.  We here present the AFC design and function together with data from initial laboratory tests and from a field deployment.

  • 241. 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.

  • 242. Dutton, Andrea
    et al.
    Webster, Jody M.
    Zwartz, Dan
    Lambeck, Kurt
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107, p. 182-196Article in journal (Refereed)
    Abstract [en]

    In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between similar to 129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 +/- 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require similar to 5-8 m of polar ice sheet contribution, relative to today's volume, of which only similar to 2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 +/- 1.7 m eustatic sea level position by 128.6 +/- 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

  • 243. Ebner, Marcus
    et al.
    Piazolo, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Renard, Francois
    Koehn, Daniel
    Stylolite interfaces and surrounding matrix material: Nature and role of heterogeneities in roughness and microstructural development2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 8, p. 1070-1084Article in journal (Refereed)
    Abstract [en]

    Rough pressure solution interfaces, like stylolites, are one of the most evident features of localized slow deformation in rocks of the upper crust. There is a general consensus that the development of these rough structures is a result of localized, stress enhanced, dissolution of material along a fluid filled interface, but little is known on the initiation of this roughness. The aim of this article is to reveal the role of heterogeneities initially present in the host-rock on roughness initiation. This should give insights on whether stylolite roughness is generated by a stress-induced instability or by the presence of disorder in the material (i.e. quenched noise). We use a microstructural approach based on SEM/EBSD analysis combined with orientation contrast (OC) image analysis of stylolites in limestones. We found that the stylolite roughness is induced by heterogeneities in the host rock (clay particles and detrital quartz grains in our case). In addition, close to mature stylolite interfaces matrix modifications occur, which can be attributed to the compaction along the stylolite. The grain size decreases by 15-25% and a pre-existing shape- and lattice-preferred orientation (SPO, LPO) are significantly modified in the vicinity of the stylolite. The results presented here imply that localized pressure solution along stylolites is not necessarily restricted to the actual interface but influences the adjacent matrix. The heterogeneity data might serve as a quantitative basis for elaborate numerical models of localized compaction.

  • 244.
    Edberg, Frida
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Anders F.
    Kungliga tekniska högskolan.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bacterial community composition in an artificial lake of a former open pit mine – effects of extreme chemistry and anoxic conditionsManuscript (preprint) (Other academic)
  • 245.
    Edberg, Frida
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Anders F.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bacterial community composition in the water column of a lake formed by a former uranium open pit mine2012In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 64, no 4, p. 870-880Article in journal (Refereed)
    Abstract [en]

    Mining of pyrite minerals is a major environmental issue involving both biological and geochemical processes. Here we present a study of an artificial lake of a former uranium open pit mine with the aim to connect the chemistry and bacterial community composition (454-pyrosequencing of 16S rRNA genes) in the stratified water column. A shift in the water chemistry from oxic conditions in the epilimnion to anoxic, alkaline, and metal and sulfide-rich conditions in the hypolimnion was corresponded by a strong shift in the bacterial community, with few shared operational taxonomic units (OTU) between the water layers. The epilimnetic bacterial community of the lake (similar to 20 years old) showed similarities to other temperate freshwater lakes, while the hypolimnetic bacterial community showed similarity to extreme chemical environments. The epilimnetic bacterial community had dominance of Actinobacteria and Betaproteobacteria. The hypolimnion displayed a higher bacterial diversity and was dominated by the phototrophic green sulphur bacterium of the genus Chlorobium (ca. 40 % of the total community). Deltaproteobacteria were only represented in the hypolimnion and the most abundant OTUs were affiliated with ferric iron and sulfate reducers of the genus Geobacter and Desulfobulbus, respectively. The chemistry is clearly controlling, especially the hypolimnetic, bacterial community but the community composition also indicates that the bacteria are involved in metal cycling in the lake.

  • 246.
    Edberg, Frida
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hägglund, Anna
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Wällstedt, Teresia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Borg, Hans
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geochemistry of metals in a former uranium open pit mine – size fractionation of the water columnManuscript (preprint) (Other academic)
  • 247.
    Edberg, Frida
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kalinowski, Birgitta E..
    Swedish Nuclear Fuel and Waste Mangament Co, Stockholm .
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holm, Karin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mobilization of metals from uranium mine waste: the role of pyoverdines produced by Pseudomonas fluorescens2010In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 8, no 4, p. 278-292Article in journal (Refereed)
    Abstract [en]

    Microorganisms produce chelating agents, such as siderophores and other ligands, which allow them to mobilize and scavenge essential elements from the environment when bioavailability is low. To better understand the effects of biologically mediated leaching of metals from mine waste, Pseudomonas fluorescens was cultivated in the presence of processed ore from the former uranium mine in Ranstad, southern Sweden. Light conditions, the concentration of the mineral source and oxygen availability were varied. The presence of ore in the culture flasks enhanced bacterial growth and raised the pH of the culture medium. Increasing the amount of ore or enhancing aeration of the medium further encouraged cell growth and pH rise. Bacteria mobilized Fe, Ni and Co from the ore. Fe-siderophore complexes were detected and estimated to be present at approximately 9 μm. In the presence of bacteria and light, dissolved Fe and U concentrations were higher compared to dark conditions. Increasing the amount of ore resulted in higher dissolved Ni concentrations but lower dissolved Fe, most likely due to precipitate formation. Data from this study support siderophore production by bacteria that allowed mobilization of essential nutrients from the processed ore. However, the availability of potentially toxic metals like Ni and U may also be enhanced. Microbial-promoted mobilization could contribute to leaching of toxic metals in current and historic mining areas. This process should be considered during design and implementation of remediation projects where trace metals are of environmental concern.

  • 248. Edwards, Thomas W. D.
    et al.
    Hammarlund, Dan
    Newton, Brandi W.
    Sjolte, Jesper
    Linderson, Hans
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Amour, Natalie A. St.
    Bailey, Joscelyn N. -L.
    Nilsson, Anders L.
    Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 165, p. 102-110Article in journal (Refereed)
    Abstract [en]

    Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.

  • 249. Ehrenfreund, Pascale
    et al.
    Spaans, Marco
    Holm, Nils G.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The evolution of organic matter in space2011In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 369, no 1936, p. 538-554Article in journal (Refereed)
    Abstract [en]

    Carbon, and molecules made from it, have already been observed in the early Universe. During cosmic time, many galaxies undergo intense periods of star formation, during which heavy elements like carbon, oxygen, nitrogen, silicon and iron are produced. Also, many complex molecules, from carbon monoxide to polycyclic aromatic hydrocarbons, are detected in these systems, like they are for our own Galaxy. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly high number of molecules that are used in contemporary biochemistry on the Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites and interplanetary dust particles. Large quantities of extra-terrestrial material were delivered via comets and asteroids to young planetary surfaces during the heavy bombardment phase. Monitoring the formation and evolution of organic matter in space is crucial in order to determine the prebiotic reservoirs available to the early Earth. It is equally important to reveal abiotic routes to prebiotic molecules in the Earth environments. Materials from both carbon sources (extra-terrestrial and endogenous) may have contributed to biochemical pathways on the Earth leading to life’s origin. The research avenues discussed also guide us to extend our knowledge to other habitable worlds.

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

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

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