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  • 1. Abdelkader, M.
    et al.
    Metzger, S.
    Mamouri, R. E.
    Astitha, M.
    Barrie, Leonard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Levin, Z.
    Lelieveld, J.
    Dust-air pollution dynamics over the eastern Mediterranean2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 16, 9173-9189 p.Article in journal (Refereed)
    Abstract [en]

    Interactions of desert dust and air pollution over the eastern Mediterranean (EM) have been studied, focusing on two distinct dust transport events on 22 and 28 September 2011. The atmospheric chemistry-climate model EMAC has been used at about 50 km grid spacing, applying an on-line dust emission scheme and calcium as a proxy for dust reactivity. EMAC includes a detailed tropospheric chemistry mechanism, aerosol microphysics and thermodynamics schemes to describe dust aging. The model is evaluated using ground-based observations for aerosol concentrations and aerosol optical depth (AOD) as well as satellite observations. Simulation results and back trajectory analysis show that the development of synoptic disturbances over the EM can enhance dust transport from the Sahara and Arabian deserts in frontal systems that also carry air pollution to the EM. The frontal systems are associated with precipitation that controls the dust removal. Our results show the importance of chemical aging of dust, which increases particle size, dust deposition and scavenging efficiency during transport, overall reducing the lifetime relative to non-aged dust particles. The relatively long travel periods of Saharan dust result in more sustained aging compared to Arabian dust. Sensitivity simulations indicate 3 times more dust deposition of aged relative to pristine dust, which significantly decreases the dust lifetime and loading.

  • 2. Abdelkader, Mohamed
    et al.
    Metzger, Swen
    Steil, Benedikt
    Klingmüller, Klaus
    Tost, Holger
    Pozzer, Andrea
    Stenchikov, Georgiy
    Barrie, Leonard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lelieveld, Jos
    Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 6, 3799-3821 p.Article in journal (Refereed)
    Abstract [en]

    We present a sensitivity study on transatlantic dust transport, a process which has many implications for the atmosphere, the ocean and the climate. We investigate the impact of key processes that control the dust outflow, i.e., the emission flux, convection schemes and the chemical aging of mineral dust, by using the EMAC model following Abdelkader et al. (2015). To characterize the dust outflow over the Atlantic Ocean, we distinguish two geographic zones: (i) dust interactions within the Intertropical Convergence Zone (ITCZ), or the dust-ITCZ interaction zone (DIZ), and (ii) the adjacent dust transport over the Atlantic Ocean (DTA) zone. In the latter zone, the dust loading shows a steep and linear gradient westward over the Atlantic Ocean since particle sedimentation is the dominant removal process, whereas in the DIZ zone aerosol-cloud interactions, wet deposition and scavenging processes determine the extent of the dust outflow. Generally, the EMAC simulated dust compares well with CALIPSO observations; however, our reference model configuration tends to overestimate the dust extinction at a lower elevation and underestimates it at a higher elevation. The aerosol optical depth (AOD) over the Caribbean responds to the dust emission flux only when the emitted dust mass is significantly increased over the source region in Africa by a factor of 10. These findings point to the dominant role of dust removal (especially wet deposition) in transatlantic dust transport. Experiments with different convection schemes have indeed revealed that the transatlantic dust transport is more sensitive to the convection scheme than to the dust emission flux parameterization. To study the impact of dust chemical aging, we focus on a major dust outflow in July 2009. We use the calcium cation as a proxy for the overall chemical reactive dust fraction and consider the uptake of major inorganic acids (i.e., H2SO4, HNO3 and HCl) and their anions, i.e., sulfate (SO42-), bisulfate (HSO4-), nitrate (NO 3) and chloride (Cl), on the surface of mineral particles. The subsequent neutralization reactions with the calcium cation form various salt compounds that cause the uptake of water vapor from the atmosphere, i.e., through the chemical aging of dust particles leading to an increase of 0.15 in the AOD under subsaturated conditions (July 2009 monthly mean). As a result of the radiative feedback on surface winds, dust emissions increased regionally. On the other hand, the aged dust particles, compared to the non-aged particles, are more efficiently removed by both wet and dry deposition due to the increased hygroscopicity and particle size (mainly due to water uptake). The enhanced removal of aged particles decreases the dust burden and lifetime, which indirectly reduces the dust AOD by 0.05 (monthly mean). Both processes can be significant (major dust outflow, July 2009), but the net effect depends on the region and level of dust chemical aging.

  • 3.
    Afrifa, Yamoah Kweku Kyei
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Reconstruction of the Southeast Asian hydro-climate using biomarkers and their hydrogen isotopic composition2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Southeast Asia is characterized by a monsoonal climate, with distinct wet and dry seasons. This has great impact on societies, agriculture and infrastructures. Despite the critical importance to understand the mechanisms that influence the variability of the Asian Monsoon, there is scarcity of both historical and paleoclimate proxy data from Southeast Asia. For this reason, two lakes from Thailand, Lake Pa Kho (LPK) and Lake Nong Thale Pron (NTP), which are located in the northeastern and southern part of Thailand, respectively, were cored. The region also offers the opportunity to study the potential influence of climate on the Angkor civilization. Overall, this project seeks to improve our understanding of the mechanisms that contribute to Asian monsoon variability and how the variability influenced Angkor Civilization. Here I present results on a 2000-years sediment record from LPK. The most important part of the work presented here consists of compound-specific hydrogen isotope ratios (δD), which are used to infer past changes in the hydrological cycle of Southeast Asia. This approach is based on the premise that δD of lipid biomarkers from plants, algae and microorganisms deposited in sediments reflects the δD of their source water, which in turn is influenced by local hydrology. A rapid increase in precipitation is inferred from ca. 700 to ca. 850 AD, after a long dry phase. The inferred shift to wet conditions likely contributed to the rise of the Angkor Civilization, by boosting agriculture. However, gradual drying occurred at around 900 AD until the 19th century. This long-term decline in precipitation, favoring ever more frequent occurrences of severe droughts, likely also contributed to the demise and fall of the Angkor, around 1400 AD. Comparison with other hydroclimate proxy records revealed that wet conditions in tropical SE Asia corresponded to a dry Western Pacific, wet conditions in the East Pacific, and vice versa - a pattern that can be explained by opposing centers of convection and subsidence. Moreover, our tropical record also appears to be anti-correlated with the subtropical East Asian Monsoon, possibly caused by rainout effects along moisture trajectories. These long-term rainfall shifts closely match patterns observed during periods of strong El Niño, and suggests a central role for Pacific Walker circulation as a driver of centennial-scale hydroclimatic change. Besides these results from LPK oriented towards reconstructing hydroclimate, I also present some initial results concerning the evolution of the plant community of LPK, based on compound specific 13C analysis, as well as first biomarker results from NTP.

  • 4. Agnini, Claudia
    et al.
    Fornaciari, Eliana
    Raffi, Isabella
    Catanzariti, Rita
    Paelike, Heiko
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rio, Domenico
    Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes2014In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 47, no 2, 131-181 p.Article in journal (Refereed)
    Abstract [en]

    Calcareous nannofossils have provided a powerful biostratigraphic tool since the 1950's and 1960's, when several milestone papers began to highlight their potential use in dating Cenozoic sediments and rocks. Here, we present a new calcareous nannofossil biozonation for the Paleogene Period, which is based on biostratigraphic data collected during the past 30 years. Semi-quantitative counting methods applied on DSDP/ODP drill sites and marine on-land sections have been used to demonstrate the details of the abundance patterns of each biostratigraphically useful calcareous nannofossil taxon. This new biozonation still partly relies on older biozonations and thus represents an integration between those classical biohorizons that proved reliable and new biohorizons proposed as substitutes for bioevents considered problematic. Thirty-eight new Paleogene biozones are proposed using a new code system: 11 Paleocene biozones (CNP1-CNP11), 21 Eocene biozones (CNE1-CNE21) and 6 Oligocene biozones (CNO1-CNO6). The new scheme uses a limited number of biohorizons, one for each biozone boundary, which guarantees more stability although with a coarser resolution. A series of additional biohorizons are included in almost every biozone. This new Paleogene biozonation has an average duration of 1.1 Myr per biozone, ranging from 0.9 Myr in the Paleocene, to 1.0 Myr in the Eocene, and 1.8 Myr in the Oligocene. Age estimates provided for calcareous nannofossil biohorizons are calculated using both magnetostratigraphic and astronomically tuned cyclostratigraphic data.

  • 5. Agnini, Claudia
    et al.
    Spofforth, David J. A.
    Dickens, Gerald R.
    Rio, Domenico
    Pälike, Heiko
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Muttoni, Giovanni
    Dallanave, Edoardo
    Stable isotope and calcareous nannofossil assemblage record of the late Paleocene and early Eocene (Cicogna section)2016In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 12, no 4, 883-909 p.Article in journal (Refereed)
    Abstract [en]

    We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81 m thick section of upper Paleocene lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate delta C-13 profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in delta C-13 and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated delta C-13 records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the delta C-13 record at Cicogna, an interpretation supported by variations in bulk carbonate 8180, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster,, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Tow eius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in the relative and absolute abundances, even some minor changes, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although the linkages between variations in calcareous nannoplankton, changes in delta C-13 records and oceanography will need additional work.

  • 6.
    Ahmed, Engy
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Microbe-mineral interactions in soil: Investigation of biogenic chelators, microenvironments and weathering processes2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The interplay between geology and biology has shaped the Earth during billions of years. Microbe-mineral interactions are prime examples of this interplay and underscore the importance of microorganisms in making Earth a suitable environment for all forms of life. The present thesis takes an interdisciplinary approach to obtain an integrated understanding of microbe-mineral interactions. More specifically it addresses how the composition and distribution of biogenic weathering agents (siderophores) differ with regard to soil horizon and mineral type in situ, what siderophore type soil microorganisms produces under laboratory conditions, what role microbial surface attachment plays in mineral weathering reactions and what central roles and applications siderophores have in the environment.

    Podzol, the third most abundant soil in Europe, and most abundant in Scandinavia, was chosen for a field experiment, where three minerals (apatite, biotite and oligoclase) were inserted in the organic, eluvial and upper illuvial soil horizons. The study started with an investigation of the siderophore composition in the bulk soil profile and on the mineral surfaces (paper I), which was followed by a study of the siderophore producing capabilities of microorganisms isolated from the soil profile under laboratory conditions (paper II). Subsequently, a study was done on the impact of microbial surface attachment on biotite dissolution (paper III). Finally, the roles of siderophores in nature and their potential applications were reviewed (paper IV).

    The major findings were that the concentration of hydroxamate siderophores in the soil attached to the mineral surfaces was greater than those in the surrounding bulk soil, indicating that the minerals stimulate the microbial communities attached to their surfaces to produce more siderophores than the microorganisms in the bulk soil. Each mineral had a unique assemblage of hydroxamate siderophores, that makes the mineral type one of the main factors affecting siderophore composition in the natural environment. Siderophore production varied between the microbial species originating from different soil horizons, suggesting that the metabolic properties of microbes in deep soil horizons function differently from those at upper soil horizons. Microbial surface attachment enhanced the biotite dissolution, showing that attached microbes has a greater influence on weathering reactions in soil than planktonic populations. In conclusion, our findings reflected that the complicated relationship between microorganisms and mineral surfaces reinforces the central theme of biogeochemistry that the mineral controls the biological activity in the natural environments. However, the importance of these relationships to the biogeochemical systems requires further investigation.

  • 7.
    Ahmed, Engy
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The interaction between microbes, siderophores and minerals in podzol soil2013Licentiate thesis, comprehensive summary (Other academic)
  • 8.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Abdulla, Hesham M.
    Mohamed, Amy H.
    El-Bassuony, Ahmed D.
    Remediation and recycling of chromium from tannery wastewater using combined chemical-biological treatment system2016In: Process Safety and Environmental Protection, ISSN 0957-5820, E-ISSN 1744-3598, Vol. 104, 1-10 p.Article in journal (Refereed)
    Abstract [en]

    Tannery wastewater containing chromium (Cr) is one of the most serious problems in leather industry. In order to develop an effective and eco-friendly treatment technology, a combined chemical-biological treatment system was performed for Cr remediation and recycling. The aim of the present study is to design a laboratory scale system using chemical precipitation of Cr(III) combined with biological removal of Cr(VI) from tannery wastewater, and to investigate the possibility of recycling the recovered Cr(III) in the tanning industry. Chemical precipitation of Cr(III) was carried out using lime and cement dust. The actinomycete strain Kitasatosporia sp. was used in microcosm studies for Cr(VI) bioremoval. Moreover, parameters such as type of porous medium, inoculum size, flow rate and culture conditions were investigated. The precipitated Cr(III) that was recovered from the chemical precipitation stage was recycled in the leather tanning industry. Our findings indicate that the maximum Cr(III) precipitation (98%) was achieved using 2 g/100 mL of lime and 2 h of settling rate. On the other hand, microcosm columns using sand that was inoculated with induced culture (OD600 = 2.43) and flow rate (2 mL/min) gave the maximum recovery (99%) of Cr(VI). The experimental Cr(III) was successfully recycled in the tanning process and the experimental leathers showed comparable properties as same as the leathers tanned with commercial Cr(III). Thus, we concluded that using combined chemical-biological treatment system for Cr remediation from tanning wastewater together with recycling process for the recovered Cr(III) is a promising strategy for economic and environmental friendly tanning industry.

  • 9.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Soil Microorganisms and Mineral Weathering: Mechanics of Biotite Dissolution2012Conference paper (Other academic)
    Abstract [en]

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

  • 10.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    THE MICROBE-MINERAL INTERACTIONS IN THE ACIDIC PODZOL SOIL2013In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 5, 564- p.Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

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

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

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

  • 11.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The Roles and Applications of Siderophores in Natural Environments2013Conference paper (Other academic)
    Abstract [en]

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

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

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

  • 12.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holm, Nils G.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The Role of Microorganisms in the diversity and distribution of siderophores in Podzolic Forest Soil2013In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 77, no 2, 161--208(48) p.Article in journal (Other academic)
    Abstract [en]

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

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

  • 13.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Microbe-mineral interactions: The impact of surface attachment on mineral weathering and element selectivity by microorganisms2015In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 403, 13-23 p.Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Siderophore Production by Microorganisms Isolated From a Podzol Soil Profile2015In: Geomicrobiology Journal, ISSN 0149-0451, E-ISSN 1521-0529, Vol. 32, no 5, 397-411 p.Article in journal (Refereed)
    Abstract [en]

    Siderophore-producing bacteria/actinobacteria and fungi were isolated from O- (organic), E- (eluvial), B- (upper illuvial), and C- (parent material) horizons of podzol soil. Siderophores were isolated and hydroxamate type siderophores were detected and quantitated by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry. The molecular identification of siderophore-producing isolates showed that there was a high diversity of fungal and bacterial/actinobacterial species throughout the soil profile. The isolated bacteria/actinobacteria showed different abilities in the production of ferrioxamines (E, B, G and D). Moreover, the isolated fungal species showed great variety in the production of ferrichromes, coprogens and fusarinines.

  • 15.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Siderophores in environmental research: roles and applications2014In: Microbial Biotechnology, ISSN 1751-7907, E-ISSN 1751-7915, Vol. 7, no 3, 196-208 p.Article, review/survey (Refereed)
    Abstract [en]

    Siderophores are organic compounds with low molecular masses that are produced by microorganisms and plants growing under low iron conditions. The primary function of these compounds is to chelate the ferric iron [Fe(III)] from different terrestrial and aquatic habitats and thereby make it available for microbial and plant cells. Siderophores have received much attention in recent years because of their potential roles and applications in various areas of environmental research. Their significance in these applications is because siderophores have the ability to bind a variety of metals in addition to iron, and they have a wide range of chemical structures and specific properties. For instance, siderophores function as biocontrols, biosensors, and bioremediation and chelation agents, in addition to their important role in weathering soil minerals and enhancing plant growth. The aim of this literature review is to outline and discuss the important roles and functions of siderophores in different environmental habitats and emphasize the significant roles that these small organic molecules could play in applied environmental processes.

  • 16.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The effect of soil horizon and mineral type on the distribution of siderophores in soil2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 131, 184-195 p.Article in journal (Refereed)
    Abstract [en]

    Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies like production of siderophores. Siderophores are operationally defined as low-molecular-mass biogenic Fe(III)-binding compounds, that can increase the bioavailability of iron by promoting the dissolution of iron-bearing minerals. In the present study, we investigated the composition of dissolved and adsorbed siderophores of the hydroxamate family in the soil horizons of podzol and the effect of specific mineral types on siderophores. Three polished mineral specimens of 3 cm x 4 cm x 3 mm (apatite, biotite and oligioclase) were inserted in the soil horizons (O (organic), E (eluvial) and B (upper illuvial)). After two years, soil samples were collected from both the bulk soil of the whole profile and from the soil attached to the mineral surfaces. The concentration of ten different fungal tri-hydroxamates within ferrichromes, fusigen and coprogens families, and five bacterial hydroxamates within the ferrioxamine family were detected. All hydroxamate types were determined in both soil water (dissolved) and soil methanol (adsorbed) extracts along the whole soil profile by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS); hence, the study is the most extensive of its kind. We found that coprogens and fusigen were present in much higher concentrations in bulk soil than were ferrioxamines and ferrichromes. On the other hand, the presence of the polished mineral completely altered the distribution of siderophores. In addition, each mineral had a unique interaction with the dissolved and adsorbed hydroxamates in the different soil horizons. Thus siderophore composition in the soil environment is controlled by the chemical, physical and biological characteristics of each soil horizon and also by the available mineral types.

  • 17.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hugerth, Luisa W.
    Logue, Jurg B.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, Anders F.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mineral Type Structures Soil Microbial Communities2017In: Geomicrobiology Journal, ISSN 0149-0451, E-ISSN 1521-0529, Vol. 34, no 6, 538-545 p.Article in journal (Refereed)
    Abstract [en]

    Soil microorganisms living in close contact with minerals play key roles in the biogeochemical cycling of elements, soil formation, and plant nutrition. Yet, the composition of microbial communities inhabiting the mineralosphere (i.e., the soil surrounding minerals) is poorly understood. Here, we explored the composition of soil microbial communities associated with different types of minerals in various soil horizons. To this effect, a field experiment was set up in which mineral specimens of apatite, biotite, and oligoclase were buried in the organic, eluvial, and upper illuvial horizons of a podzol soil. After an incubation period of two years, the soil attached to the mineral surfaces was collected, and microbial communities were analyzed by means of Illumina MiSeq sequencing of the 16S (prokaryotic) and 18S (eukaryotic) ribosomal RNA genes. We found that both composition and diversity of bacterial, archaeal, and fungal communities varied across the different mineral surfaces, and that mineral type had a greater influence on structuring microbial assemblages than soil horizon. Thus, our findings emphasize the importance of mineral surfaces as ecological niches in soils.

  • 18.
    Alasdair, Skelton
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fredrik, Arghe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pitcairn, Iain
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spatial coupling between spilitization and carbonation ofbasaltic sills in SW Scottish Highlands: evidence of amineralogical control of metamorphic fluid flow2011In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 11, no 3, 245-259 p.Article in journal (Refereed)
    Abstract [en]

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

  • 19. Alexanderson, Helena
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Funder, Svend
    Ingólfsson, Ólafur
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Landvik, Jon Y.
    Löwemark, Ludvig
    Mangerud, Jan
    März, Christian
    Möller, Per
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, 9-31 p.Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.

  • 20.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rahm, Lars
    Polehne, Falk
    Tracing terrestrial organic matter by delta34S and delta13C signatures in a subarctic estuary2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, 2594-2602 p.Article in journal (Refereed)
    Abstract [en]

    A key issue to understanding the transformations of terrestrial organic carbon in the ocean is to disentangle the latter from marine-produced organic matter. We applied a multiple stable isotope approach using 34S and 13C isotope signatures from estuarine dissolved organic matter (DOM), enabling us to constrain the contribution of terrestrial-derived DOM in an estuarine gradient of the northern Baltic Sea. The stable isotope signatures for dissolved organic sulfur (34SDOS) have twice the range between terrestrial and marine end members compared to the stable isotope signatures for dissolved organic carbon (13CDOC); hence, the share of terrestrial DOM in the total estuarine DOM can be calculated more precisely. DOM samples from the water column were collected using ultrafiltration on board the German RV Maria S Merian during a winter cruise, in the Bothnian Bay, Bothnian Sea, and Baltic proper. We calculated the terrestrial fraction of the estuarine DOC (DOCter) from both 13CDOC and 34SDOS signatures and applying fixed C: S ratios for riverine and marine end members to convert S isotope signatures into DOC concentrations. The 34SDOS signature of the riverine end member was +7.02‰, and the mean signatures from Bothnian Bay, Bothnian Sea, and Baltic proper were +10.27, +12.51, and +13.67‰, respectively, showing an increasing marine signal southwards (34SDOS marine end member 5 18.1‰). These signatures indicate that 87‰, 75‰, and 67‰, respectively, of the water column DOC is of terrestrial origin (DOCter) in these basins. Comparing the fractions of DOCter in each basin—that are still based on few winter values only—with the annual river input of DOC, it appears that the turnover time for DOCter in the Gulf of Bothnia is much shorter than the hydraulic turnover time, suggesting that high-latitude estuaries might be efficient sinks for DOCter.

  • 21.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Porcelli, D.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Anderson, L. G.
    Sanchez-Garcia, L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, P. S.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
    Degradation of terrestrial organic carbon, primary production and out-gassing of CO2 in the Laptev and East Siberian Seas as inferred from delta C-13 values of DIC2012In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 95, 143-159 p.Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Alling, Vanja
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sanchez-Garcia, Laura
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Porcelli, Don
    Pugach, Sveta
    Vonk, Jorien E.
    van Dongen, Bart
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Stockholm Resilience Centre.
    Anderson, Leif G.
    Sokolov, Alexander
    Stockholm University, Stockholm Resilience Centre.
    Andersson, Per
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Stockholm Resilience Centre.
    Semiletov, Igor
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Non-conservative behavior of dissolved organic carbon across the Laptev and East Siberian Seas2010In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 24, GB4033- p.Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to have a strong effect on the Eastern Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to 10%–20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%–50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr−1. These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming.

  • 23.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bigler, Christian
    Department of Ecology and Environmental Science, Umeå University.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lotter, André F.
    Institute of Environmental Biology, Laboratory of Palaeobotany and Palynology, Utrecht University.
    Veres, Daniel
    “Emil Racovita” Speleological Institute, Clinicilor 5, 400006 Cluj-Napoca, Romania.
    Modest summer temperature variability during DO cycles in western Europe2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 11-12, 1322-1327 p.Article in journal (Refereed)
    Abstract [en]

    Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.

  • 24.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Identifying changes in Arctic Ocean sea ice conditions north of Greenland during the Holocene2012In: APEX Sixth International Conference and Workshop: Quaternary Glacial and Climate Extremes / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, Oulu: Oulun yliopisto , 2012, 32-32 p.Conference paper (Other academic)
  • 25.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 1, 94-102 p.Article in journal (Refereed)
    Abstract [en]

    The fossil diatom record from the Hasseldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13900 and 11200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open-water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom-based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13900 to 12500 cal. a BP. From 12500 cal. a BP, coincident with the start of climate cooling, to 11300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build-up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.

  • 26.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Veres, Daniel
    Paleolimnological response to millennial and centennial scale climate variability during MIS 3 and 2 as suggested by the diatom record in Les Echets, France2008In: Quaternary Science Reviews, ISSN 0277-3791, Vol. 27, no 15-16, 1493-1504 p.Article in journal (Refereed)
    Abstract [en]

    A 27 m long sediment sequence retrieved from the central part of the Les Echets basin in France has been analysed in sub-centennial resolution for biogenic silica and fossil diatom remains. The sequence corresponds to the later part of Marine Isotope Stage (MIS) 3 and to most of MIS 2. Distinct changes in diatom productivity, diversity and taxonomic composition between 36.2 and 31.7 kyr BP appear to relate to Dansgaard–Oeschger (DO) climate variability. Intervals characterized by low diversity, productivity and small-sized benthic diatom taxa are most likely a response to colder conditions in relation to DO stadials. In contrast, higher diversity, productivity and a high abundance of planktonic taxa indicate a response to warmer temperatures during DO interstadials. The time interval between 30.3 and 15.7 kyr BP is characterized by continuous low diatom productivity and a benthic dominated community with intermediate species richness, suggesting a transition to more stable conditions. Three time intervals with extremely low concentrations of diatom valves (46.1–36.2, 31.7–30.3 and 26.3–23.6 kyr BP) overlap with ages reported for Heinrich (H) events 4, 3, and 2. We speculate that the lake at Les Echets suffered from severe ecological stress as a response to H events. This is the first detailed study exemplifying the response of a lake, based on diatoms, to climate variability during late part of MIS 3 and most of MIS 2 in Europe.

  • 27.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Veres, Daniel
    Leng, Melanie
    Kaislahti Tillman, Päivi
    Diatom assemblage dynamics during abrupt climate change: The response oflacustrine diatoms to Dansgaard-Oeschger cycles during the last glacialperiod2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 2, 397-404 p.Article in journal (Refereed)
    Abstract [en]

    The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response to several abrupt climate shifts during the last glacial period referred to as Dansgaard-Oeschger (DO) cycles. The high-resolution diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria-Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since the mid-nineteenth century.

  • 28. Anderson, John B.
    et al.
    Conway, Howard
    Bart, Philip J.
    Witus, Alexandra E.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McKay, Robert M.
    Hall, Brenda L.
    Ackert, Robert P.
    Licht, Kathy
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stone, John O.
    Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, 31-54 p.Article in journal (Refereed)
    Abstract [en]

    Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by similar to 13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by similar to 11 ka BP, just north of Ross Island by similar to 7.8 ka BP, and near Hatherton Glacier by similar to 6.8 ka BP. Farther south, Be-10 exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after similar to 13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.

  • 29.
    Anderson, John B.
    et al.
    Rice University.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nitsche, Frank Oliver
    Lamont-Doherty Earth Observatory, Columbia University.
    Geomorphic expression of collapsing ice streams revealed by latest generation swath bathymetry images2011Conference paper (Other academic)
    Abstract [en]

    There is now a substantial swath bathymetry data set from Antarctica that reveals subglacial bedforms, in particular mega-scale glacial lineations, which were formed by ice streams that occupied glacial troughs during the LGM. However, with the exception of grounding zone wedges, few studies have yielded high-resolution sea floor images that show geomorphic features formed by retreating ice streams. For example, deep-tow side-scan sonar records from Ross Sea show a range of recessional features, mostly 1-3 meters high, that overprint mega-scale glacial lineations. These features were not imaged in swath bathymetry records. During the 2010 austral summer, the Swedish ice breaker Oden was used to conduct an extensive survey in the sparsely studied central trough in Pine Island Bay using the latest generation multibeam technology. The bedforms imaged in Pine Island Bay are similar to small-scale recessional features previously imaged in Ross Sea using deep-tow side-scan sonar. These include fishbone moraines and corrugated iceberg furrows, which we argue were produced daily through tidally-influenced motion of a disintegrating ice shelf. During this event a 65 km long stretch of the trough was cleared of floating ice in about 1.5 years. The break-up occurred ~12,000 cal ka BP and was likely a response to rapid sea-level rise at that time. Acquisition of more high-resolution swath bathymetry data should greatly increase our understanding of ice stream interaction with the seafloor and those factors that have influenced ice stream behavior during retreat. Future work should focus on the rugged inner shelf, were subglacial meltwater is believed to have contributed to ice stream instability.

  • 30.
    Anderson, John
    et al.
    Rice University.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oden Southern Ocean 0910: Cruise Report2010Report (Other academic)
  • 31. Anderson, Leif G.
    et al.
    Björk, Göran
    Holby, Ola
    Jutterström, Sara
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Semiletov, Igor
    Stranne, Christian
    Stöven, Tim
    Tanhua, Toste
    Ulfsbo, Adam
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Shelf-Basin interaction along the East Siberian Sea2017In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 13, no 2, 349-363 p.Article in journal (Refereed)
    Abstract [en]

    Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 degrees E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 degrees E, while it appears in the Makarov Basin at 150 degrees E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to similar to 34.5, i.e. in the water classically named lower halocline. East of 170 degrees E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of similar to 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity similar to 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.

  • 32.
    Andersson, Rina A.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip A.
    Effect of climate change on delivery and degradation of lipid biomarkers in a Holocene peat sequence in the Eastern European Russian Arctic2012In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 53, 63-72 p.Article in journal (Refereed)
    Abstract [en]

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

  • 33.
    Andersson, Rina Argelia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lipid biomarkers and other geochemical indicators in paleoenvironmental studies of two Arctic systems: a Russian permafrost peatland and marine sediments from the Lomonosov Ridge2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The reconstruction of past environmental conditions is a fascinating research area that attracts the interest of many individuals in various geological disciplines. Paleoenvironmental reconstruction studies can shed light on the understanding of past climates and are a key to the prediction of future climate changes and their consequences. These studies take on special significance when focused on areas sensitive to climate change. The Arctic region, which is experiencing dramatic changes today in its peatlands and in its ocean, is prime example. The entire region plays a major role in global climate changes and has recently received considerable interest because of the potential feedbacks to climate change and its importance in the global carbon cycle.

    For a better understanding of the role of Arctic peatlands and the Arctic Ocean to global climate changes, more records of past conditions and changes in the region are needed. This work applies different geochemical proxies, with special emphasis on lipid biomarkers, to the study of a permafrost peat deposit collected from the Eastern European Russian Arctic and a marine core retrieved from the Lomonosov Ridge in the central Arctic Ocean. The results reported of this study show that molecular stratigraphy obtained from the analysis of lipid biomarkers in both peat and marine profiles, combined with other environmental proxies, can contribute significantly to the study of Arctic ecosystems of the past.

  • 34.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Organic matter delivery to Quaternary sediments of Amundsen Basin, central Arctic OceanManuscript (preprint) (Other academic)
    Abstract [en]

    Quaternary marine sediments retrieved from the central Arctic Ocean in a 30 cm long core, were analyzed for paleoenvironmental reconstruction. n-Alkane biomarkers combined with elemental analyses that include X-ray fluorescence (XRF) core scanning provide complementary information that suggest important influxes of terrigenous derived organic matter (OM) with depth. Changes in the variability of n-alkane-derived and elemental ratios with depth reflect the complexity of the organic carbon cycle in this region. The distributions and abundances of the long-chain n-alkanes reveal a high content of terrigenous derived components and suggest together with mathematical estimations high deliveries of the terrigenous OM in the past. XRF trace metal analyses suggest less-oxygenated bottom waters that may have allowed for better preservation conditions of OM deeper in the core.

  • 35.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Zebür, Yngve
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Impacts of paleohydrological changes on n-alkane biomarker compositions of a Holocene peat sequence in the eastern European Russian Arctic2011In: Organic Geochemistry, ISSN 0146-6380, E-ISSN 1873-5290, Vol. 42, no 9, 1065-1075 p.Article in journal (Refereed)
    Abstract [en]

    Coupled analyses of n-alkane biomarkers and plant macrofossils from a peat plateau deposit in the northeast European Russian Arctic were carried out to assess the effects of past hydrology on the molecular contributions of plants to the peat. The n-alkane biomarkers accumulated over 9.6 kyr of local paleohydrological changes in this complex peat profile in which a succession of vegetation changes occurred during a transition from a wet fen to a relatively dry peat plateau bog. This study shows that the contribution of the n-C31 alkane from rootlets to peat layers rich in fine and dark roots is important. The results further indicate that the n-alkanePaqandn-C23/n-C29 biomarker proxies that have been useful to reconstruct past water table levels in many peat deposits can be misleading when the contributions of Betulaand Sphagnum fuscum to the peat are large. Under these conditions, the C23/(C27+ C31) n-alkane ratio seems to correct for the presence of BetulaandS. fuscum and provides a better description for the relative amounts of moisture. The average chain length (ACL) n-alkane proxy also appears to be a good paleohydrology proxy in having larger values during dry and cold conditions in this Arctic bog setting.

  • 36.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip
    Hornibrook, Edward
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Morth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic2012In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 27, no 6, 545-552 p.Article in journal (Refereed)
    Abstract [en]

    A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (similar to 2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss-dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. delta 15N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in delta 13C values appear to reflect mainly changes in plant assemblages. Positive shifts in both delta 15N and delta 13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N-enrichment.

  • 37.
    Andersson, Rina Argelia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Meyers, Philip
    Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, Michigan, U.S.A..
    Hornibrook, Edward
    Bristol Biogeochemistry Research Centre & Cabot Institute, School of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, United Kingdom.
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mörth, Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Elemental and isotopic carbon and itrogen records of organic matter accumulation in a Holocene permafrots peat sequence in the East European Russian ArcticManuscript (preprint) (Other academic)
    Abstract [en]

    A peat deposit from the East European Russian Arctic, spanning nearly 10,000 years, was investigated to reconstruct past environmental conditions and to study soil organic matter (SOM) degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (~2,500 cal a BP). Total organic carbon (TOC) and total nitrogen (N) concentrations are different in the bog peat compared to the fen peat, with lower values in the moss-dominated bog peat layers.  Lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues.  The atomic ratios of bulk elemental parameters indicate better preservation of organic matter in peat deposits dominated by bryophytes relative to vascular plants.  The presence of permafrost in the peat plateau stage and water-saturated conditions at the bottom of the fen stage appear to be associated with better preservation of organic plant material.  δ15N values suggest N isotopic fractionation was driven primarily by microbial decomposition while differences in δ13C values appear to be associated mainly with changes in plant assemblages rather than diagenesis.  Positive shifts in both δ15N and δ13C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface.  This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed 15N-enrichment.

  • 38.
    Andersson, Thommy
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.

  • 39.
    Andersson, Tommy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hermelin, Otto
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bottom characterization of Lagoa das Furnas on Sao Miguel, Azores archipelago2016In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 321, 196-207 p.Article in journal (Refereed)
    Abstract [en]

    Lagoa das Furnas is a crater lake located in an area exposed to geohazards from earthquakes and volcanic activity on the island of sao Miguel in the Azores Archipelago. Geophysical mapping of Lagoa das Furnas reveals a previously undiscovered volcanic dome. This dome is comprised largely of subaquatic pyroclastic debris of trachytic composition. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the dome link it to the historically documented Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the dome suggests that it is comprised of more evolved magma than that of the main Furnas 1630 dome located 1400 m away. This suggests that the dome was formed during a final phase of the 1630 eruption in the Lagoa das Furnas area.

  • 40.
    Andrén, Margareta
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stockmann, Gabrielle
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sturkell, Erik
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Guðrúnardóttir, Helga Rakel
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Keller, Nicole Simone
    Odling, Nic
    Dahrén, Börje
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Balic-Zunic, Tonci
    Hjartarson, Hreinn
    Siegmund, Heike
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Freund, Friedemann
    Kockum, Ingrid
    Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland2016In: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 121, no 4, 2315-2337 p.Article in journal (Refereed)
    Abstract [en]

    Chemical analysis of groundwater samples collected from a borehole at Hafralaekur, northern Iceland, from October 2008 to June 2015 revealed (1) a long-term decrease in concentration of Si and Na and (2) an abrupt increase in concentration of Na before each of two consecutive M 5 earthquakes which occurred in 2012 and 2013, both 76km from Hafralaekur. Based on a geochemical (major elements and stable isotopes), petrological, and mineralogical study of drill cuttings taken from an adjacent borehole, we are able to show that (1) the long-term decrease in concentration of Si and Na was caused by constant volume replacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fractures and (2) the abrupt increase of Na concentration before the first earthquake records a switchover to nonstoichiometric dissolution of analcime with preferential release of Na into groundwater. We attribute decay of the Na peaks, which followed and coincided with each earthquake to uptake of Na along fractured or porous boundaries between labradorite and analcime crystals. Possible causes of these Na peaks are an increase of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixing between groundwater components. Both could have been triggered by preseismic dilation, which was also inferred in a previous study by Skelton et al. (2014). The mechanism behind preseismic dilation so far from the focus of an earthquake remains unknown.

  • 41. Andrén, T.
    et al.
    Bitinas, A.
    Björck, S.
    Emelyanov, E
    Harff, J.
    Houmark-Nilelsen, M.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jensen, J.B.
    Jørgensen, B.B:
    Kotilainen, A.
    Knudsen, K.L.
    Lambeck, K.
    Moros, M.
    Spiess, V.
    Uscinowicz, S.
    Veski, S.
    Zelchs, Z.
    The Baltic Sea IODP project2012In: EGU General Assembly Conference Abstracts, 2012, 7682-7682 p.Conference paper (Other academic)
  • 42.
    Antevik, Fredrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Undersökning av metamorfa förhållanden för skarn-, metapelit- och sulfidbergarter på nordöstra Utö, Stockholms skärgård, Sverige2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Detta kandidatarbete i geologi undersöker berggrunden på Utös nordöstra udde i Stockholms skärgård, med målet att fastställa metamorfa tryck-, temperatur- och fluid-XCO2-förhållanden. Utös berggrund metamorfoserades ca 1,87-1,78 Ga när en öbåge kolliderade med den arkeiska kratonen. Tidigare deponerade karbonater, vulkaniter och gråvackor blev metamorfoserade i samband med kollision och senare exstensionell kollaps. I studieområdet hittas karbonater omvandlade till marmor och skarnbergarter, som i vissa fall, troligtvis är hydrotermalt omvandlade till sulfidbergarter i samband med intrusioner i orogenesens senare skede. Gråvackor hittas omvandlade till metapeliter bärandes indexmineral.

    Kalcit-dolomit-termometri på tremolit-, talk- och flogopitbärande skarnbergarter gav temperaturer på 379°C respektive 412°C som kunde härledas till fluid-XCO2-koncentrationer på 0,0039 och 0,012. Geotermobarometri för metapeliter i området resulterade i osäkra tryck- och temperaturvärden p.g.a. en begränsad och retrograd mineralsammansättning, men antyder att metamorf grad tidigare varit högre. Skarn och relaterade sulfidbergarter kunde med vissa undantag klassificeras som Zn-Pb-skarn utifrån mineralogisk sammansättning av zinkblände, blyglans och pyrit. Retrograda förhållanden inom greenschist facies uppskattades utifrån framräknade temperaturer samt förekomst av reaktionstexturer.

  • 43.
    Antevik, Fredrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Utvärdering av efterinjektering med polyuretan utifrån geologiska och hydrogeologiska grundförutsättningar2016Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    The aim of this master thesis is to evaluate the results of selective post-excavation grouting with polyurethane resin in the subway of Stockholm.Dripping and leakage of water into hard rock tunnels is a costly and commonly occurring problem. Water leakage does not only lead to damage to tunnel installation but may also affect the area above the tunnel due to lowering of the ground water table. To solve this problem there are several methods to prevent water entering the tunnel or to divert it. One of the preventing methods are to grout using polyurethane based resins.This thesis evaluates a drip sealing project where eight point leakages where grouted during November 2015. Drip mapping was carried out before and after the grouting to evaluate the change in leakage amount to determine whether the grouting methodology is suitable for future projects. The drip mapping was carried out during a year before the sealing attempt to investigate the leakages natural variation and with greater certainty being able to evaluate the leakage change after the grouting had been carried out.The evaluation of the grouting showed that none of the point leakages were sealed to 100 %. Only three of the leakages decreased, four increased and one showed no change. The natural variations during the evaluation period, during and after the grouting attempt indicates a natural rise in leakage amount induced by an increase in precipitation and rising seasonal trend.The change in leakage amount for every leakage point was compared to geological and hydrogeological parameters to be able to explain the cause of the results and to determine which conditions the methodology depends on. The correlation with original leakage amount, grouting volume and hydraulic aperture where the strongest and could best be explained by second degree polynomials. By using the equations for the polynomials an interval could be determined where the grouting methodology theoretically would lead to the greatest decrease in leakage amount. There are some uncertainty in the interpretation whether a natural signal in the grouting results led to a correlation due to an internal coupling between the parameters.

  • 44. Arndt, Jan Erik
    et al.
    Schenke, Hans Werner
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nitsche, Frank O.
    Buys, Gwen
    Goleby, Bruce
    Rebesco, Michele
    Bohoyo, Fernando
    Hong, Jongkuk
    Black, Jenny
    Greku, Rudolf
    Udintsev, Gleb
    Barrios, Felipe
    Reynoso-Peralta, Walter
    Taisei, Morishita
    Wigley, Rochelle
    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0-A new bathymetric compilation covering circum-Antarctic waters2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 12, 3111-3117 p.Article in journal (Refereed)
    Abstract [en]

    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60 degrees S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 x 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at .

  • 45. Arndt, J.E.
    et al.
    Schenke, H.W.
    Barrios, F.
    Black, J.
    Buys, G.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nitsche, Frank
    Lamont-Doherty Earth Observatory of Columbia University.
    Rebesco, M.
    Reynoso-Peralta, W.
    Wigley, R.
    Wilson, O.
    IBCSO v1: A preview on Version 1 of the International Bathymetric Chart of the Southern Ocean2012Conference paper (Other academic)
  • 46. Aze, T.
    et al.
    - Ezard, T. H. G.
    Purvis, A.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stewart, D. R. M.
    Wade, B. S.
    Pearson, P. N.
    Identifying anagenesis cladogenesis in the fossil record2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 32, E2946- p.Article in journal (Refereed)
  • 47.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Miocene-Pliocene nannofossils and sedimentation rates in the Hatton-Rockall Basin, NE Atlantic Ocean1980Doctoral thesis, monograph (Other academic)
  • 48.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raffi, Isabella
    Ciummelli, Marina
    Baldauf, Jack
    Species-specific responses of late Miocene Discoaster spp. to enhanced biosilica productivity conditions in the equatorial Pacific and the Mediterranean2013In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 33, no 4, 285-298 p.Article in journal (Refereed)
    Abstract [en]

    Census data of a major Cenozoic calcareous nannofossil genus (Discoaster) have been acquired from Site U1338, located near the Equator in the eastern Pacific Ocean and drilled in 2009 during Integrated Ocean Drilling Program (IODP) Expedition 321. The investigated 147.53 m thick upper Miocene sediment sequence is primarily composed of biogenic carbonate and biogenic silica. Diatom biostratigraphic data were used to develop a revised biomagnetostratigraphic age model, resulting in more variable late Miocene sedimentation rates. Carbonate content variations mainly reflect dilution by biogenic silica production, although intense carbonate dissolution affects a few shorter intervals. Abundance variations of discoasters show no distinct correlation with either carbonate or biosilica contents. The two dominant Discoaster taxa are D. brouweri and D. variabilis, except for a 12 m thick interval where D. bellus outnumbers the sum of all other discoasters by a factor of 4.6. Data presented indicate that first D. hamatus and then D. berggrenii both evolved from D. bellus. Three unusual morphotypes, here referred to as Discoaster A, B and C, increase in relative abundance during episodes of enhanced biosilica production in the upper half of the investigated sequence (Messinian). Strikingly similar morphotypes have been observed previously in Messinian age sediments from the Mediterranean, characterized by alternating deposition of biogenic carbonate and biosilica. This suggests a species-specific response among some of the late Miocene discoasters to broader oceanographic and climatic forcing that promoted episodes of enhanced deposition of biogenic silica.

  • 49.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raffi, Isabella
    Università Chieti-Pescara.
    Rio, Domenico
    Università di Padova.
    Fornaciari, Eliana
    Università di Padova.
    Pälike, Heiko
    Universität Bremen.
    Biozonation and biochronology of Miocene through Pleistocene calcareous nannofossils from low and middle latitudes2012In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 45, no 3, 221-244 p.Article in journal (Refereed)
    Abstract [en]

    Calcareous nannofossils are widely used in Cenozoic marine biostratigraphy. At present, the two most widely used calcareous nannofossil biozonations were established approximately 40 years ago. These were derived from marine land sections and Deep Sea Drilling Project rotary cored sediments. Over nearly three decades, we have generated Miocene through Pleistocene calcareous nannofossil data from deep sea sediments in low and middle latitude regions. The sediments used here have been mostly recovered using the advanced piston coring technique, generating less core disturbance and complete recovery via multiple penetration of the sediment column at single sites. A consistent trait in our work on calcareous nannofossil biostratigraphy has been to use semi-quantiative methods in combination with short sample distances, close enough to capture the details of the abundance behaviour of individual calcareous nannofossil taxa. Such data represent the foundation of the new biozonation presented here, which still partly relies on the pioneering work presented by Er lend Martini and David Bukry about 40 years ago. A key aim here has been to employ a limited set of selected biohorizons for the purpose of establishing a relatively coarsely resolved and stable biozonation. We present 31 biozones using a new code system: CNM1-CNM20; Calcareous Nannofossil Miocene biozones 1 through 20. CNPL1-CNPL11; Calcareous Nannofossil Plio-Pleistocene biozones 1 through 11. As the new biozonation encompasses 23 million years, the average biozone resolution becomes 0.74 million years, ranging from 0.15 to 2.20 million years. A single biohorizon is used for the definition of each biozone boundary. Auxiliary markers are avoided, as well as subzones, in order to maintain stability to the new biozonation. Virtually every biozone holds one or several additional biohorizons. These, together with all biozone boundary markers, are assigned age estimates derived chiefly from astronomically tuned cyclostratigraphies.

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

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

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