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  • 251. Elsabe, Julies M.
    et al.
    Bruchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fuchs, Bernhard M.
    Vertical shifts in the microbial community structure of organic rich Namibian shelf sediments2012In: African Journal of Microbiology Research, ISSN 1996-0808, E-ISSN 1996-0808, Vol. 6, no 17, p. 3887-3897Article in journal (Refereed)
    Abstract [en]

    This study investigates the diversity and abundance of bacteria in organic-rich Namibian shelf sediments from two sampling stations, using the 16S rRNA library approach and Catalyzed Reporter Deposition Fluorescent in situ Hybridization (CARD-FISH). Six clone libraries were constructed. Clone libraries were dominated by Delta-proteobacteria (up to 48%) and Gamma-proteobacteria (up to 98%). Bacteroidetes were dominant in the clone library of the top 6 cm (up to 17%), while actinobacteria dominated at a depth of 10 to 12 cm (up to 34%). Sequences that were related to bacteria with hydrolytic and fermenting abilities include members from the Gamma-proteobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria. Cloned sequences within the Delta-proteobacteria affiliates to sulfate reducing bacteria, including Desulfarculaceae, Desulfobacteraceae, Desulfobulbaceae, and Desulfuromonadales and were detected throughout the sediment. The two sampling stations differed in microbial diversity with a higher diversity prevailing at the station with higher metabolic rates for organic matter decomposition. At both sampling stations a shift in microbial community composition with depth was observed and is explained by gradients in organic substrate availability within the sediment, which affects the life strategies adopted by bacteria, resulting in niche diversification and ultimately affects bacterial community composition and structure throughout the sediment depth.

  • 252. Ely, Jeremy C.
    et al.
    Clark, Chris D.
    Spagnolo, Matteo
    Stokes, Chris R.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hughes, Anna L. C.
    Dunlop, Paul
    Hess, Dale
    Do subglacial bedforms comprise a size and shape continuum?2016In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 257, p. 108-119Article in journal (Refereed)
    Abstract [en]

    Understanding the evolution of the ice-bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created. However, the formation of the suite of landforms generated at this boundary - subglacial bedforms - is a contentious issue that is yet to be fully resolved. Bedforms formed in aeolian, fluvial, and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes. For subglacial bedforms, a size and shape continuum has been hypothesised, yet it has not been fully tested. Here we analyse the largest data set of subglacial bedform size and shape measurements ever collated (96,900 bedforms). Our results show that flutes form a distinct population of narrow bedforms. However, no clear distinction was found between drumlins and megascale glacial lineations (MSGLs), which form a continuum of subglacial lineations. A continuum of subglacial ribs also exists, with no clear size or shape distinctions indicating separate populations. Furthermore, an underreported class of bedform with no clear orientation to ice flow (quasi-circular bedforms) overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two, potentially merging these three bedform types into a larger continuum.

  • 253. Emerson, Joanne B.
    et al.
    Roux, Simon
    Brum, Jennifer R.
    Bolduc, Benjamin
    Woodcroft, Ben J.
    Jang, Ho Bin
    Singleton, Caitlin M.
    Soden, Lindsey M.
    Naas, Adrian E.
    Boyd, Joel A.
    Hodgkins, Suzanne B.
    Wilson, Rachel M.
    Trubl, Gareth
    Li, Changsheng
    Frokings, Steve
    Pope, Phillip B.
    Wrighton, Kelly C.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chanton, Jeffrey P.
    Saleska, Scott R.
    Tyson, Gene W.
    Rich, Virginia
    Sullivan, Matthew B.
    Host-linked soil viral ecology along a permafrost thaw gradient2018In: Nature Microbiology, E-ISSN 2058-5276, Vol. 3, no 8, p. 870-880Article in journal (Refereed)
    Abstract [en]

    Climate change threatens to release abundant carbon that is sequestered at high latitudes, but the constraints on microbial metabolisms that mediate the release of methane and carbon dioxide are poorly understood(1-7). The role of viruses, which are known to affect microbial dynamics, metabolism and biogeochemistry in the oceans(8-10), remains largely unexplored in soil. Here, we aimed to investigate how viruses influence microbial ecology and carbon metabolism in peatland soils along a permafrost thaw gradient in Sweden. We recovered 1,907 viral populations (genomes and large genome fragments) from 197 bulk soil and size-fractionated metagenomes, 58% of which were detected in metatranscriptomes and presumed to be active. In silico predictions linked 35% of the viruses to microbial host populations, highlighting likely viral predators of key carbon-cycling microorganisms, including methanogens and methanotrophs. Lineage-specific virus/host ratios varied, suggesting that viral infection dynamics may differentially impact microbial responses to a changing climate. Virus-encoded glycoside hydrolases, including an endomannanase with confirmed functional activity, indicated that viruses influence complex carbon degradation and that viral abundances were significant predictors of methane dynamics. These findings suggest that viruses may impact ecosystem function in climate-critical, terrestrial habitats and identify multiple potential viral contributions to soil carbon cycling.

  • 254. Emmanouilidis, Alexandros
    et al.
    Katrantsiotis, Christos
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sheik, Taariq Ali
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Iliopoulos, George
    Avramidis, Pavlos
    Middle to late Holocene palaeoenvironmental study of Gialova Lagoon, SW Peloponnese, Greece2018In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 476, p. 46-62Article in journal (Refereed)
    Abstract [en]

    The coastal areas of Eastern Mediterranean have long been the subject of research, due to their rapid geomorphological changes, but also because of their archaeological interest. Our study is focused on a shallow coastal lagoon of Peloponnese, Gialova Lagoon, which for several years has attracted the scientific interest of archaeologists, geomorphologists as well as sedimentologists. Gialova lagoon is located near the ancient city of Pylos, the kingdom of king Nestor during the Mycenaean period (1600-1100 BC). The objectives of this study are: (a) to reconstruct the middle to late Holocene depositional environments of the lagoon and (b) to correlate our data to already existing publications, in order to shed new light on the Holocene evolution of the lagoon and the associated coastal palaeoenvironmental changes. An 8m deep vibracore was drilled and a multi proxy analysis was carried out on the sediment sequence, including sedimentological (grain size analysis and moment measures, total organic carbon - TOC, total nitrogen e TN and total phosphorus - TP), high resolution geochemical (XRF-scanning) and palaeontological (micro-and macro faunal) analysis. The chronological framework is based on five C-14 datings forming the basis for an age depth model, calculated using the OxCal software. The radiocarbon dates from previous studies (6 cores, similar to 20 dates) were also taken into account. The data synthesis and interpretation provided robust and coherent indications regarding the palaeoenvironment, shoreline changes and the rate of geomorphological changes of the coastal area of Gialova Lagoon, as well as useful information about the palaeonvironmental and palaeoclimatic conditions that prevailed during the Mycenaean period. The interpretation, reveal a transition from a shallow marine environment (65005800 yr B.P.) to a brackish/lagoonal (5800-3300 yr B.P.), followed by a shift towards a freshwater/marsh environment (3300 yr B.P. to present).

  • 255.
    Engström, Adam
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Investigation of the metamorphic environment conditions of Persholmen, NE Utö, with SEM generated data.2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This geothermobarometric investigation of St Persholmen, Utö, in the south central part of Sweden presents an attempt at determining the metamorphic conditions of this important part of the Svecofennian province. Belonging to the geology of the Bergslagen area, Utö historically represent part of Sweden’s vast ore resources with concentrations of iron, copper and sulfides. Rock types from this area are around 1.91-1.89 Ga old (Stephens et al. 2009) and as such Paleoproterozoic in age. The rocks on Utö are considered representative of Bergslagen and record the closing of an ocean starting with subduction followed by volcanic episodes and orogeny (Talbot 2008). The bedrock we observe at Persholmen is thought to represent the remains of the aforementioned orogeny where greywackes from the oceanic stage have been preserved at the base of the mountain range (Stålhös 1982).

    The two rock types of interest at Persholmen which have been evaluated in this study are 1) normal greywackes and 2) greywackes which have been migmatised either because of the influence of fluids, reworking in an accretionary prism or melted at the base of a mountain range. In this project the area of study has been mapped and samples have been retrieved in order to distinguish the mineralogy and metamorphic history of the bedrock. After petrographic analysis I have determined mineral chemistry by the use of a SEM (Scanning Electron Microscope). These chemical data have then been entered into the computer programs AX and THERMOCALC for determination of temperature and pressure. For the normal/migmatised greywackes a temperature of 538

    ±36/756±133°C and a pressure of 3.1±1.3/3.8±3.2 kbars respectively have been estimated. Two generations of muscovite provide evidence of fluid-rock interactions and at the north coast of Persholmen the occurrence of sillimanite indicates a high grade of metamorphism.

  • 256.
    Engström, Adam
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Metal mobility during metamorphism and formation of orogenic gold deposits: Insights from the Dalradian of Scotland2013Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    Orogenic gold deposits occur within metamorphic belts throughout the world and have through time represented the source for over 25% of the world’s gold production. Although orogenic gold deposits are of great economic importance, controversies exist on the subject of fluid and metal sources and there have been few studies of gold´s distribution and mobility outside of large economic deposits. Research made by Pitcairn et al. (2006), on the Mesozoic Otago and Alpine schists of New Zealand, observed systematic depletion of Au and a suite of 6 associated elements with increasing metamorphic grade. This depletion was identical to the suite of elements enriched in the Otago gold deposits and provided strong evidence that orogenic gold deposits form due to metamorphic processes. The mobilization of metals was attributed to the recrystallization of sulfide minerals during prograde metamorphism causing dehydration and release of metal-rich metamorphic fluids. 

    This thesis is part of a larger project aimed at testing the “Otago model” in a classic metamorphic terrain: The Dalradian metamorphic belt of Scotland. Rocks in the study are from the southern higlands group and the Appin and Argyll group which range in metamorphic grade from chlorite zone greenschist facies to sillimanite zone amphibolite facies. Three main aspects, which supplement earlier research, are addressed in this study: 1) Investigation of the sulfide paragenesis at Loch Lomond and Stonehaven was carried out to map the evolution of sulfides with metamorphic grade and the possible relations to the distribution of gold. Using SEM scanning to quantify the abundance of different sulfide minerals together with previous data on the Glen Esk region, a complex sulfide evolution pattern for the Dalradian Supergroup is identified. The sulfide evolution describes the same changes in texture and chemistry as observed in the Otago Schists but is made complex by the difference in geological evolution for the different regions. 2) Reinvestigation of the higher grade zones of Glen Esk (staurolite to sillimanite) was carried out as samples from the previous study were very weathered. Results from ultralow detection limit methods (HG-AFS and a gold detection method developed by Pitcairn et al. 2006) showed significant systematic depletion of Au and As with metamorphic grade. From chlorite to sillimanite zone average values of Au and As were showed to decrease by 65% and 88% respectively. Furthermore, a suite of 10 major and 12 trace elements were analyzed using ICP methods showing no trends of systematic depletion with increased metamorphic grade.  3) Investigation of Pb-Ag Veining and vein samples from each of the metamorphic index mineral zones in the Glen Esk area was carried out to identify fluid composition and ore mineralogy. Using microthermometry and Raman laser spectroscopy two distinct fluids were identified. The first type is a H2O-CO2-N2-salt fluid of low salinity (0-15 weight percent NaCl equivalent) and medium temperature (150 to 250 °C) locally containing minor amounts of CH4. It is found in the veins from the mineral index zones of Glen Esk and was formed in the ductile regime most likely related to late stage metamorphic devolatilization released during Caledonian uplift of the Dalradian. Pb-Ag veins from the locality of Hardhill host the second fluid type which was formed in the brittle regime  accompanied by brecciation as a high salinity (15 to 20 weight percent NaCl equivalent) low temperature (70-140°C) H2O-salt fluid with calcic composition was precipitated. This fluid bears much resemblance to Carboniferous calcic brines responsible for economic base-metal precipitation with widespread occurrence in southwest Scotland and Northern Ireland.

    Results of this thesis show many similarities with the Otago study, with a connection between metal mobility and metamorphic grade, providing support for the dehydration model as a viable mechanism for the generation of orogenic gold deposits.

  • 257. Erbs-Hansen, Dorthe Reng
    et al.
    Knudsen, Karen Luise
    Gary, Anthony Cavedo
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jansen, Eystein
    Holocene climatic development in Skagerrak, eastern North Atlantic: Foraminiferal and stable isotopic evidence2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 3, p. 301-312Article in journal (Refereed)
    Abstract [en]

    A high-resolution multiproxy study of core MD99-2286 reveals a highly variable hydrographic environment in the Skagerrak from 9300 cal. yr BP to the present. The study includes foraminiferal faunas, stable isotopes and sedimentary parameters, as well as temperature and salinity reconstructions of a c. 29 m long radiocarbon-dated core record. The multivariate technique fuzzy c-means was applied to the foraminiferal counts, and it was extremely valuable in defining subtle heterogeneities in the foraminiferal faunal data corresponding to hydrographic changes. The major early-/mid-Holocene (Littorina) transgression led to flooding of large former land areas in the North Sea, the opening of the English Channel and Danish straits, and initiation of the modern circulation system. This is reflected by fluctuating C/N values and an explosive bloom of Hyalinea balthica. A slight indication of ameliorated conditions between 8000 and 5750 cal. yr BP is related to the Holocene Thermal Maximum. A subsequent increase in freshwater/Baltic water influence between 5750 and 4350 cal. yr BP is reflected by dominance of Bulimina marginata and depleted delta O-18 values. The Neoglacial cooling (after 4350 cal. yr BP) is seen in the Skagerrak as enhanced turbidity, increasing TOC values and short-term changes in an overall Cassidulina laevigata-dominated fauna suggesting a prevailing influence of Atlantic waters. This is in agreement with increased strength of westerly winds, as recorded for this period. The last 2000 years were also dominated by Atlantic Water conditions with generally abundant nutrient supply. However, during warm periods, particularly the 'Medieval Warm Period'and the modern warming, the area was subject to a restriction in the supply of nutrients and/or the nutrient supply had a more refractory character.

  • 258. Erbs-Hansen, Dorthe Reng
    et al.
    Knudsen, Karen Luise
    Gary, Anthony Cavedo
    Jansen, Eystein
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Scao, Vincent
    Lambeck, Kurt
    Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak, eastern North Atlantic: a multiproxy study2011In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 40, no 4, p. 660-680Article in journal (Refereed)
    Abstract [en]

    A high-resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multiproxy analyses of core MD99-2286 combined with palaeowater depth modelling for the area. The late Younger Dryas was characterized by a cold ice-distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis-dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom-water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south-central Sweden, which led to a strong stratification of the water column at MD99-2286, as also indicated by C. neoteretis. A short-term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice-dammed lake in southern Norway, the Glomma event. After the last drainage route across south-central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with a stable inflow of waters from the North Atlantic through the Norwegian Trench and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short-term cooling around 8300-8200 cal. a BP, representing the 8.2 ka event.

  • 259.
    Eriksson Hägg, Hanna
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Wällstedt, Teresia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Claremar, Björn
    Humborg, Christoph
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Future nutrient load scenarios for the Baltic Sea due to climate and lifestyle changes2014In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 43, no 3, p. 337--351Article in journal (Refereed)
    Abstract [en]

    Dynamic model simulations of the future climate and projections of future lifestyles within the Baltic Sea Drainage Basin (BSDB) were considered in this study to estimate potential trends in future nutrient loads to the Baltic Sea. Total nitrogen and total phosphorus loads were estimated using a simple proxy based only on human population (to account for nutrient sources) and stream discharges (to account for nutrient transport). This population-discharge proxy provided a good estimate for nutrient loads across the seven sub-basins of the BSDB considered. All climate scenarios considered here produced increased nutrient loads to the Baltic Sea over the next 100 years. There was variation between the climate scenarios such that sub-basin and regional differences were seen in future nutrient runoff depending on the climate model and scenario considered. Regardless, the results of this study indicate that changes in lifestyle brought about through shifts in consumption and population potentially overshadow the climate effects on future nutrient runoff for the entire BSDB. Regionally, however, lifestyle changes appear relatively more important in the southern regions of the BSDB while climatic changes appear more important in the northern regions with regards to future increases in nutrient loads. From a whole-ecosystem management perspective of the BSDB, this implies that implementation of improved and targeted management practices can still bring about improved conditions in the Baltic Sea in the face of a warmer and wetter future climate

  • 260. Eriksson, Jerker
    et al.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Holmgren, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, Per
    Schöberg, Hans
    Wallner, Karin
    Persson, Per-Olov
    Weichselian ice dammed lakes: New geochemical evidence for a rapidly deposited event-layer in the Eurasian Arctic Basin2012In: : 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, p. 48-48Conference paper (Other academic)
  • 261. Esposito, Alfonso
    et al.
    Ahmed, Engy
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ciccazzo, Sonia
    Sikorski, Johannes
    Overmann, Jörg
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brusetti, Lorenzo
    Comparison of Rock Varnish Bacterial Communities with Surrounding Non-Varnished Rock Surfaces: Taxon-Specific Analysis and Morphological Description2015In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 70, no 3, p. 741-750Article in journal (Refereed)
    Abstract [en]

    Rock varnish is a thin layer of Fe and Mn oxyhydroxides with embedded clay minerals that contain an increased Mn/Fe ratio compared to that of the Earth's crust. Even if the study of rock varnish has important implications in several fields, the composition of epilithic bacterial communities and the distribution of taxa on varnish surfaces are still not wholly described. The aim of this study was (i) to identify the bacterial taxa which show the greatest variation between varnish and non-varnish environments, collected from the same rock, and (ii) to describe the morphology of epilithic communities through scanning electron microscopy (SEM). Triplicate samples of rock surfaces with varnish and triplicate samples without varnish were collected from five sites in Matsch Valley (South Tyrol, Italy). The V4 region of 16S rRNA gene was analyzed by Illumina sequencing. Fifty-five ubiquitous taxa have been examined to assess variation between varnish and non-varnish. Cyanobacteria, Chloroflexi, Proteobacteria along with minor taxa such as Solirubrobacterales, Conexibaxter, and Rhodopila showed significant variations of abundance, diversity, or both responding to the ecology (presence/absence of varnish). Other taxa, such as the genus Edaphobacter, showed a more marked spatial variation responding to the sampling site. SEM images showed a multitude of bacterial morphologies and structures involved in the process of attachment and creation of a suitable environment for growth. The features emerging from this analysis suggest that the highly oxidative Fe and Mn-rich varnish environment favors anoxigenic autotrophy and establishment of highly specialized bacteria.

  • 262. Fairchild, Ian J.
    et al.
    Spencer, Anthony M.
    Ali, Dilshad O.
    Anderson, Ross P.
    Anderton, Roger
    Boomer, Ian
    Dove, Dayton
    Evans, Jonathan D.
    Hambrey, Michael J.
    Howe, John
    Sawaki, Yusuke
    Shields, Graham A.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tucker, Maurice E.
    Wang, Zhengrong
    Zhou, Ying
    Tonian-Cryogenian boundary sections of Argyll, Scotland2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 319, p. 37-64Article in journal (Refereed)
    Abstract [en]

    The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact. The Appin Group forms a regionally extensive, > 4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in delta C-13(VPDB) from +5 to + 2 parts per thousand upwards. In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re -described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with delta C-13 of -4 to -7 parts per thousand (a feature named the Garvellach anomaly, replacing the term Islay anomaly) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1 parts per thousand) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of the PAF is rich in carbonate clasts similar to slightly deeper water parts of the underlying succession. D1 is typically several metres thick with interstratified sandstone and conglomerate, but dies out laterally. Scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft -sediment deformation is interbedded with carbonate below and above D1. Dolomite beds with derived intraclasts and gypsum pseudomorphs are found above D1 (or equivalent position, where Dl is absent). Published and new Sr isotope studies, including successive leach data, demonstrate primary Tonian Sr-87/Sr-86 values of 0.7066-0.7069 on Islay, decreasing to 0.7064-0.7066 in the younger GEF limestones on the Garvellachs, with 1700-2700 ppm Sr. Other typically Tonian characteristics of the carbonates are the Sr-rich nature of limestones, molar tooth structure, and dolomitized peritidal facies with evidence of aridity. Seabed surveys suggesting uniformly-dipping strata and shallow borehole core material illustrate the potential for extending the Tonian record offshore of the Garvellachs. A candidate Tonian-Cryogenian GSSP is proposed on Garbh Eileach within the smooth delta C-13 profile at the cross-over to positive delta C-13 signatures, 4 m below the first occurrence of ice-rafted sediment and 9 m below the first diamictite. Although lacking radiometric constraints or stratigraphically significant biotas or biomarkers, the Scottish succession has a thick and relatively complete sedimentary record of glaciation, coherent carbon and strontium chemostratigraphy, lateral continuity of outcrops and 100% exposure at the proposed boundary interval.

  • 263. Faleide, Jan Inge
    et al.
    Pease, Victoria
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Curtis, Mike
    Klitzke, Peter
    Minakov, Alesander
    Scheck-Wenderoth, Madgalena
    Kostyuchenko, Sergei
    Zayonchek, Andrei
    Tectonic implications of the lithospheric structure across the Barents and Kara shelves2018In: Geological Society Special Publication, ISSN 0305-8719, E-ISSN 2041-4927, Vol. 460, p. 285-314Article in journal (Refereed)
    Abstract [en]

    This paper considers the lithospheric structure and evolution of the wider Barents–Kara Sea region based on the compilation and integration of geophysical and geological data. Regional transects are constructed at both crustal and lithospheric scales based on the available data and a regional three-dimensional model. The transects, which extend onshore and into the deep oceanic basins, are used to link deep and shallow structures and processes, as well as to link offshore and onshore areas. The study area has been affected by numerous orogenic events in the Precambrian–Cambrian (Timanian), Silurian–Devonian (Caledonian), latest Devonian–earliest Carboniferous (Ellesmerian–Svalbardian), Carboniferous–Permian (Uralian), Late Triassic (Taimyr, Pai Khoi and Novaya Zemlya) and Palaeogene (Spitsbergen–Eurekan). It has also been affected by at least three episodes of regional-scale magmatism, the so-called large igneous provinces: the Siberian Traps (Permian–Triassic transition), the High Arctic Large Igneous Province (Early Cretaceous) and the North Atlantic (Paleocene–Eocene transition). Additional magmatic events occurred in parts of the study area in Devonian and Late Cretaceous times. Within this geological framework, we integrate basin development with regional tectonic events and summarize the stages in basin evolution. We further discuss the timing, causes and implications of basin evolution. Fault activity is related to regional stress regimes and the reactivation of pre-existing basement structures. Regional uplift/subsidence events are discussed in a source-to-sink context and are related to their regional tectonic and palaeogeographical settings.

  • 264. Fehr, Manuela A.
    et al.
    Andersson, Per S.
    Halenius, Ulf
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Iron isotope variations in Holocene sediments of the Gotland Deep, Baltic Sea2008In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 72, no 3, p. 807-826Article, review/survey (Refereed)
    Abstract [en]

    Holocene sediments from the Gotland Deep basin in the Baltic Sea were investigated for their Fe isotopic composition in order to assess the impact of changes in redox conditions and a transition from freshwater to brackish water on the isotope signature of iron. The sediments display variations in delta Fe-56 (differences in the Fe-56/Fe-54 ratio relative to the IRMM-14 standard) from -0.27 +/- 0.09 parts per thousand to +0.21 +/- 0.08 parts per thousand. Samples deposited in a mainly limnic environment with oxygenated bottom water have a mean delta Fe-56 of +0.08 +/- 0.13 parts per thousand, which is identical to the mean Fe isotopic composition of igneous rocks and oxic marine sediments. In contrast, sediments that formed in brackish water under periodically euxinic conditions display significantly lighter Fe isotope signatures with a mean delta Fe-56 of -0.14 +/- 0.19 parts per thousand. Negative correlations of the delta Fe-56 values with the Fe/Al ratio and S content of the samples suggest that the isotopically light Fe in the periodically euxinic samples is associated with reactive Fe enrichments and sulfides. This is supported by analyses of pyrite separates from this unit that have a mean Fe isotopic composition of -1.06 +/- 0.20 parts per thousand for delta Fe-56. The supply of additional Fe with a light Fe isotopic signature can be explained with the shelf to basin Fe shuttle model. According to the Fe shuttle model, oxides and benthic ferrous Fe that is derived from dissimilatory iron reduction from shelves is transported and accumulated in euxinic basins. The data furthermore suggest that the euxinic water has a negative dissolved delta Fe-56 value of about -1.4 parts per thousand to -0.9 parts per thousand. If negative Fe isotopic signatures are characteristic for euxinic sediment formation, widespread euxinia in the past might have shifted the Fe isotopic composition of dissolved Fe in the ocean towards more positive delta Fe-56 values.

  • 265. Fenty, Ian
    et al.
    Willis, Josh K.
    Khazendar, Ala
    Dinardo, Steven
    Forsberg, Rene
    Fukumori, Ichiro
    Holland, David
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Moller, Delwyn
    Morison, James
    Munchow, Andreas
    Rignot, Eric
    Schodlok, Michael
    Thompson, Andrew F.
    Tinto, Kirsteen
    Rutherford, Matthew
    Trenholm, Nicole
    Oceans Melting Greenland: Early Results from NASA’s Ocean-Ice Mission in Greenland2016In: Oceanography, ISSN 1042-8275, Vol. 29, no 4, p. 72-83Article in journal (Refereed)
    Abstract [en]

    Melting of the Greenland Ice Sheet represents a major uncertainty in projecting future rates of global sea level rise. Much of this uncertainty is related to a lack of knowledge about subsurface ocean hydrographic properties, particularly heat content, how these properties are modified across the continental shelf, and about the extent to which the ocean interacts with glaciers. Early results from NASA's five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate.

  • 266. Fernandez, Marilen
    et al.
    Björck, Svante
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Maidana, Nora I.
    Unkel, Ingmar
    Van der Putten, Nathalie
    Diatom assemblage changes in lacustrine sediments from Isla de los Estados, southernmost South America, in response to shifts in the southwesterly wind belt during the last deglaciation2013In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 50, no 4, p. 433-446Article in journal (Refereed)
    Abstract [en]

    Isla de los Estados (54A degrees 45'S, 63A degrees 10'aEuro64A degrees 46'W) lies east of the main island of Tierra del Fuego and is the southeastern-most point in Argentina. Because of its geographic position near the latitudes of the Southern Hemisphere Westerlies and the strong influence of the Antarctic Circumpolar Current (ACC), the area is suitable for paleoecological and paleoclimate research. The island is not far north of the Subantarctic Front, which limits the northern boundary of the ACC. Paleoenvironmental study in this geographic location can shed light on past changes in atmospheric and marine circulation patterns. Diatom analysis of the lower part of a sediment sequence from Laguna Cascada (54A degrees 45' 51.3''S, 64A degrees 20' 20.07''W) enabled inference of changing lake conditions between 16 and 11.1 cal ka BP. Between 16 and 14.4 cal ka BP fragilarioid diatom species, often a pioneer group, dominated the record. Their presence shows seasonally open-water conditions from the onset of sedimentation. In zone II (14.4-12.8 cal ka BP), the dominance of planktonic/tychoplanktonic Aulacoseira spp. might represent longer ice-free periods and windier conditions, which would have kept this heavy species suspended in the water column. This period corresponds to the Antarctic Cold Reversal, when the Southern Hemisphere Westerlies were possibly centered on the latitudes of Tierra del Fuego, resulting in windy and wet conditions. Zone III (12.8-11.1 cal ka BP) is dominated by benthic diatom taxa that are mainly associated with peat and wetland vegetation. This suggests that climate conditions had become milder and less windy, favoring aquatic productivity and terrestrial vegetation development. This change in environmental conditions may have been a consequence of the southward movement of the Southern Hemisphere Westerlies at the start of the Antarctic Holocene thermal optimum.

  • 267. Ferreira, David
    et al.
    Cessi, Paola
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dijkstra, Henk A.
    Drijfhout, Sybren S.
    Eldevik, Tor
    Harnik, Nili
    McManus, Jerry F.
    Marshall, David P.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Schneider, Tapio
    Wills, Robert C.
    Atlantic-Pacific Asymmetry in Deep Water Formation2018In: Annual Review of Earth and Planetary Science, ISSN 0084-6597, E-ISSN 1545-4495, Vol. 46, p. 327-352Article, review/survey (Refereed)
    Abstract [en]

    While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2-3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states.

  • 268.
    Finné, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Boyd, Meighan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sundqvist, Hanna S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Löwemark, Ludvig
    Can XRF scanning of speleothems be used as a non-destructive method to identify paleoflood events in caves?2015In: International Journal of Speleology, ISSN 0392-6672, E-ISSN 1827-806X, Vol. 44, no 1, p. 17-23Article in journal (Refereed)
    Abstract [en]

    We have developed a novel, quick and non-destructive method for tracing flood events in caves through the analysis of a stalagmite thick section with an XRF core scanner. The analyzed stalagmite has multiple horizons of fine sediments from past flood events intercalated with areas of cleaner calcite. Flood events detected from the elemental XRF core scanning data show good agreement with the position of flood horizons identified in petrographic thin sections. The geochemical composition of the individual flood layers shows that in certain cases the clay horizons had a distinct geochemical fingerprint suggesting that it may be possible to distinguish individual flood layers based on their geochemistry. This presents the possibility for using flood events as marker horizons to chronologically tie different speleothems in a cave to each other.

  • 269.
    Fischer, Benjamin M. C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Frentress, Jay
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Greger, Maria
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography. The Nature Conservancy, United States.
    Mojito, Anyone? An Exploration of Low-Tech Plant Water Extraction Methods for Isotopic Analysis Using Locally-Sourced Materials2019In: Frontiers in Earth Science, ISSN 2296-6463, Vol. 7, article id 150Article in journal (Refereed)
    Abstract [en]

    The stable isotope composition of water (delta O-18 and delta H-2) is an increasingly utilized tool to distinguish between different pools of water along the soil-plant-atmosphere continuum (SPAC) and thus provides information on how plants use water. Clear bottlenecks for the ubiquitous application of isotopic analysis across the SPAC are the relatively high-energy and specialized materials required to extract water from plant materials. Could simple and cost-effective do-it-yourself MacGyver methods be sufficient for extracting plant water for isotopic analysis? This study develops a suite of novel techniques for plant water extraction and compares them to a standard research-grade water extraction method. Our results show that low-tech methods using locally-sourced materials can indeed extract plant water consistently and comparably to what is done with other state-of-the-art methods. Further, our findings show that other factors play a larger role than water extraction methods in achieving the desired accuracy and precision of stable isotope composition: (1) appropriate transport, (2) fast sample processing and (3) efficient workflows. These results are methodologically promising for the rapid expansion of isotopic investigations, especially for citizen science and/or school projects or in remote areas, where improved SPAC understanding could help manage water resources to fulfill agricultural and other competing water needs.

  • 270. Fisher, Rebecca E.
    et al.
    France, James L.
    Lowry, David
    Lanoisellé, Mathias
    Brownlow, Rebecca
    Pyle, John A.
    Cain, Michelle
    Warwick, Nicola
    Skiba, Ute M.
    Drewer, Julia
    Dinsmore, Kerry J.
    Leeson, Sarah R.
    Bauguitte, Stéphane J. -B.
    Wellpott, Axel
    O'Shea, Sebastian J.
    Allen, Grant
    Gallagher, Martin W.
    Pitt, Joseph
    Percival, Carl J.
    Bower, Keith
    George, Charles
    Hayman, Garry D.
    Aalto, Tuula
    Lohila, Annalea
    Aurela, Mika
    Laurila, Tuomas
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    McCalley, Carmody K.
    Nisbet, Euan G.
    Measurement of the C-13 isotopic signature of methane emissions from northern European wetlands2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 31, no 3, p. 605-623Article in journal (Refereed)
    Abstract [en]

    Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. In this study, isotopic signatures of emissions in the Fennoscandian Arctic have been determined in chambers over wetland, in the air 0.3 to 3m above the wetland surface and by aircraft sampling from 100m above wetlands up to the stratosphere. Overall, the methane flux to atmosphere has a coherent delta C-13 isotopic signature of -71 +/- 1%, measured in situ on the ground in wetlands. This is in close agreement with delta C-13 isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast, results from wetlands in Canadian boreal forest farther south gave isotopic signatures of -67 +/- 1%. Wetland emissions dominate the local methane source measured over the European Arctic in summer. Chamber measurements demonstrate a highly variable methane flux and isotopic signature, but the results from air sampling within wetland areas show that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures. The study suggests that for boreal wetlands (>60 degrees N) global and regional modeling can use an isotopic signature of -71 parts per thousand to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.

  • 271.
    Fitch, Peter
    et al.
    University of Leicester.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Heterogeneity and Cyclicity in the Physical Property Measurements of Cenozoic Sediments (IODP Expedition 320/321)2009In:  Eos Trans. AGU, 90(52), Fall Meet. Suppl., 2009Conference paper (Other academic)
    Abstract [en]

    The Cenozoic sediments of the Equatorial Pacific provide an ideal and unique record of oceanographic conditions and climate change over the last 50 million years of Earth’s history. Previous studies utilizing data and samples from ODP Leg 199 have provided great insight into astronomically calibrated time-scales which control depositional sequences and lithologies of the deep Pacific waters. IODP Expeditions 320 and 321 aimed to further our understanding of the time-scales, processes and geological signatures in this environment by recovering a more detailed and higher resolution record of data and samples through this important geological record.

    This study uses physical properties and wireline logging data together with detailed sedimentological descriptions from IODP Expedition 320 to investigate heterogeneity and cyclicity in the physical properties across a time-transect of six sites. The application of statistical techniques for the numerical quantification of heterogeneity to these data shows that the various discrete time periods (age units) studied along the transect (lower Eocene through upper Miocene) return consistent values allowing these age units to be traced laterally based on contrasts in heterogeneity values. Heterogeneities in bulk density, magnetic susceptibility, and natural gamma ray data are seen to vary with unit thickness and can be related to lithology, and the presence / abundance of bioturbated intervals and carbonate turbidite beds. Numerical heterogeneities are also shown to be consistent across three scale of investigation; wireline (meter scales), track (cm scales) and discrete (mm-cm scale) datasets. These results could significantly impact future sampling strategies for similar sites by guiding the minimum sampling density required to ensure resolving high-resolution heterogeneities and cyclicity.

    Analysis of cyclicity within the physical properties data using the Fourier transform and semi-variogram analysis, with depth-scale converted to a time-series based on shipboard paleontological analysis, shows a number of large wavelength cycles have been captured, ranging from 100ka to 6Ma. Further analysis of the location and intensity of bioturbation and the occurrence of carbonate turbidites  at two key sites reveals that cyclicity of similar wavelengths can still be resolved, suggesting that it may be possible to identify  and remove the bioturbated layers and/or turbidite beds prior to a more detailed study of Milankovitch cyclicity.

  • 272. Flink, Anne E.
    et al.
    Noormets, Riko
    Fransner, Oscar
    Hogan, Kelly A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Past ice flow in Wahlenbergfjorden and its implications for late Quaternary ice sheet dynamics in northeastern Svalbard2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 163, p. 162-179Article in journal (Refereed)
    Abstract [en]

    Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 +/- 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.

  • 273.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seismic refraction soundings in the area around Gotland, central Baltic.1975Book (Other academic)
  • 274.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Volume in honour of professor Ivar Hessland.1982Collection (editor) (Other academic)
  • 275.
    Fransner, Filippa
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Tedesco, Letizia
    Vichi, Marcello
    Hordoir, Robinson
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Spilling, Kristian
    Kuznetsov, Ivan
    Eilola, Kari
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. University of Helsinki, Finland.
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Non-Redfieldian Dynamics Explain Seasonal pCO2 Drawdown in the Gulf of Bothnia2018In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, Vol. 123, no 1, p. 166-188Article in journal (Refereed)
    Abstract [en]

    High inputs of nutrients and organic matter make coastal seas places of intense air‐sea CO2 exchange. Due to their complexity, the role of coastal seas in the global air‐sea CO2 exchange is, however, still uncertain. Here, we investigate the role of phytoplankton stoichiometric flexibility and extracellular DOC production for the seasonal nutrient and CO2 partial pressure (pCO2) dynamics in the Gulf of Bothnia, Northern Baltic Sea. A 3‐D ocean biogeochemical‐physical model with variable phytoplankton stoichiometry is for the first time implemented in the area and validated against observations. By simulating non‐Redfieldian internal phytoplankton stoichiometry, and a relatively large production of extracellular dissolved organic carbon (DOC), the model adequately reproduces observed seasonal cycles in macronutrients and pCO2. The uptake of atmospheric CO2 is underestimated by 50% if instead using the Redfield ratio to determine the carbon assimilation, as in other Baltic Sea models currently in use. The model further suggests, based on the observed drawdown of pCO2, that observational estimates of organic carbon production in the Gulf of Bothnia, derived with the method, may be heavily underestimated. We conclude that stoichiometric variability and uncoupling of carbon and nutrient assimilation have to be considered in order to better understand the carbon cycle in coastal seas.

  • 276.
    Fransner, Filippa
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Meier, H. E. Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Hordoir, Robinson
    Gustafsson, Erik
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Deutsch, Barbara
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tracing terrestrial DOC in the Baltic Sea - a 3-D model study2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 2, p. 134-148Article in journal (Refereed)
    Abstract [en]

    The fate of terrestrial organic matter brought to the coastal seas by rivers, and its role in the global carbon cycle, are still not very well known. Here the degradation rate of terrestrial dissolved organic carbon (DOCter) is studied in the Baltic Sea, a subarctic semi-enclosed sea, by releasing it as a tracer in a 3-D circulation model and applying linear decay constants. A good agreement with available observational data is obtained by parameterizing the degradation in two rather different ways; one by applying a decay time on the order of 10 years to the whole pool of DOCter, and one by dividing the DOCter into one refractory pool and one pool subject to a decay time on the order of 1 year. The choice of parameterization has a significant effect on where in the Baltic Sea the removal takes place, which can be of importance when modeling the full carbon cycle and the CO2 exchange with the atmosphere. In both cases the biogeochemical decay operates on time scales less than the water residence time. Therefore only a minor fraction of the DOCter reaches the North Sea, whereas approximately 80% is removed by internal sinks within the Baltic Sea. This further implies that DOCter mineralization is an important link in land-sea-atmosphere cycling of carbon in coastal- and shelf seas that are heavily influenced by riverine DOC.

  • 277. Fransner, O.
    et al.
    Noormets, R.
    Flink, A. E.
    Hogan, K. A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden, northern Nordaustlandet, Svalbard2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 3, p. 437-455Article in journal (Refereed)
    Abstract [en]

    Observations of subglacial landforms yielding the configuration and dynamics of former ice-flows have for the first time been made in Rijpfjorden and Duvefjorden, Nordaustlandet, Svalbard, using sub-bottom acoustic, swath-bathymetric data and sediment cores. Five acoustic-stratigraphic units were distinguished suggesting the presence of a complete glacial-postglacial succession in the central fjord basins. C-14 ages from the sediments indicate that the inner Rijpfjorden and central Duvefjorden were deglaciated before ca. 10.6 cal ka BP and 11.0 cal ka BP, respectively. Maximum sediment thickness in Rijpfjorden and Duvefjorden is 26 m, resulting in sediment accumulation rates of ca. 66 cm ka(-1). The landform record suggests that the ice streaming in both fjords was topographically controlled. The considerably deeper basin and higher elongation ratios of the crag-and-tails in Duvefjorden are linked to the faulted bedrock and possibly to somewhat larger ice stream and/or more focused ice-flow compared to that in Rijpfjorden. De Geer moraines suggest slower retreat of a grounded ice margin from shallow areas of Rijpfjorden. In deeper areas of the fjords, the glaciers were probably floating, resulting in the lack of ice-marginal transverse landforms. The ice margin retreat from these areas was probably relatively rapid and dominated by calving.

  • 278.
    Fransner, Oscar
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geophysical Mapping around Björkö Island in Lake Mälaren, South central Sweden2013Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

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

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

  • 279.
    Fransner, Oscar
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sediment variations in the Kuchi Lake, southern Taiwan:: Climate signal or tectonics?2011Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Climate archives are of greatest significance when it comes to paleoclimate studies, since these types of archives in a natural way have registered and preserved the conditions of the past. There are several types of climate archives, one of the most commonly used are lake sediments, because lakes can reveal different types of information, for example weathering, vegetation and precipitation. Another reason why lakes are important in climate research is because they are widely spread over the world, and therefore they can be chosen depending on where the focus of the study will be. In this study, -the Lake Kuchi in the southern part of Taiwan, situated at the boundary between the Asian Mainland and the Western Pacific, was used. What makes this densely populated region of the world particularly interesting for climate research is because it is affected not only by monsoons, but also by typhoons and earthquakes.

    In this paleoclimate study, a total 16 core sections from three different coring points in the Kuchi Lake were analyzed. The main goal was to clarify if the lake could be used as a reliable climate archive, and also interpret the depositional environment of the sediment layers in the cores. All core sections were described and analyzed with the ITRAX XRF-scanner, which lead to the conclusion that the cores consist of a sedimentary sequence of alternating gray clay and dark gray gyttja clay layers, capped by peat, gyttja or clayey gyttja at topmost part.

     By sieving samples from all different layers, it was observed that some dark gyttja clay layers contained terrestrial organic matter, and hard, angular clay clasts that suggest intense rain falls and flash floods as transportation mechanism. The uppermost part of the cores, from 310 cm to the top layers, consist of homogenous clay and in situ organic matter which indicate calmer depositional environments compared to the alternation between dark gyttja clay and homogenous gray clay. LOI-950 data indicate that the carbonate content of the Kuchi Lake is low, since the weight loss during this temperature is insignificant compared to LOI-550, which stood for the majority of the weight loss.

    Thus, the sediment sequence in the Kuchi Lake consist of alternation of clays deposited in a calm and relatively deep lake, mixed with layers apparently flushed in from land, possibly due to typhoons. This alternation is capped by organic rich layers, including peat, which indicating filling up of the basin, and shallower conditions.

  • 280. Franz, Daniela
    et al.
    Acosta, Manuel
    Altimir, Núria
    Arriga, Nicola
    Arrouays, Dominique
    Aubinet, Marc
    Aurela, Mika
    Ayres, Edward
    López-Ballesteros, Ana
    Barbaste, Mireille
    Berveiller, Daniel
    Biraud, Sébastien
    Boukir, Hakima
    Brown, Timothy
    Brümmer, Christian
    Buchmann, Nina
    Burba, George
    Carrara, Arnaud
    Cescatti, Allessandro
    Ceschia, Eric
    Clement, Robert
    Cremonese, Edoardo
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Darenova, Eva
    Dengel, Sigrid
    D'Odorico, Petra
    Filippa, Gianluca
    Fleck, Stefan
    Fratini, Gerardo
    Fuss, Roland
    Gielen, Bert
    Gogo, Sébastien
    Grace, John
    Graf, Alexander
    Grelle, Achim
    Gross, Patrick
    Grünwald, Thomas
    Haapanala, Sami
    Hehn, Markus
    Heinesch, Bernard
    Heiskanen, Jouni
    Herbst, Mathias
    Herschlein, Christine
    Hörtnagl, Lukas
    Hufkens, Koen
    Ibrom, Andreas
    Jolivet, Claudy
    Joly, Lilian
    Jones, Michael
    Kiese, Ralf
    Klemedtsson, Leif
    Kljun, Natascha
    Klumpp, Katja
    Kolari, Pasi
    Kolle, Olaf
    Kowalski, Andrew
    Kutsch, Werner
    Laurila, Tuomas
    de Ligne, Anne
    Linder, Sune
    Lindroth, Anders
    Lohila, Annalea
    Longdoz, Bernhard
    Mammarella, Ivan
    Manise, Tanguy
    Maraňón Jiménez, Sara
    Matteucci, Giorgio
    Mauder, Matthias
    Meier, Philip
    Merbold, Lutz
    Mereu, Simone
    Metzger, Stefan
    Migliavacca, Mirco
    Mölder, Meelis
    Montagnani, Leonardo
    Moureaux, Christine
    Nelson, David
    Nemitz, Eiko
    Nicolini, Giacomo
    Nilsson, Mats B.
    Op de Beeck, Maarten
    Osborne, Bruce
    Ottosson Löfvenius, Mikaell
    Pavelka, Marian
    Peichl, Matthias
    Peltola, Olli
    Pihlatie, Mari
    Pitacco, Andrea
    Pokorny, Radek
    Pumpanen, Jukka
    Ratié, Céline
    Rebmann, Corinna
    Roland, Marilyn
    Sabbatini, Simone
    Saby, Nicolas P. A.
    Saunders, Matthew
    Schmid, Hans Peter
    Schrumpf, Marion
    Sedlák, Pavel
    Serrano Ortiz, Penelope
    Siebicke, Lukas
    Šigut, Ladislav
    Silvennoinen, Hanna
    Simioni, Guillaume
    Skiba, Ute
    Sonnentag, Oliver
    Soudani, Kamel
    Soule, Patricé
    Steinbrecher, Rainer
    Tallec, Tiphaine
    Thimonier, Anne
    Tuittila, Eeva-Stiina
    Tuovinen, Juha-Pekka
    Vestin, Patrik
    Vincent, Gaëlle
    Vincke, Caroline
    Vitale, Domenico
    Waldner, Peter
    Weslien, Per
    Wingate, Lisa
    Wohlfahrt, Georg
    Zahniser, Mark
    Vesala, Timo
    Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe's terrestrial ecosystems: a review2018In: International Agrophysics, ISSN 0236-8722, Vol. 32, no 4, p. 439-+Article, review/survey (Refereed)
    Abstract [en]

    Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.

  • 281.
    Freire, Francis
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Acoustic characterization of submarine geomorphological features in the Polar Oceans2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

  • 282.
    Freire, Francis Fletcher
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High Arctic submarine glaciogenic landscapes: their formation and significance2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on studies of glacial and slope morphology in the high Arctic of western Greenland shelf and the Molloy Hole seafloor spreading area, based on high-resolution acoustic methods and other geophysical data. The main purpose is to improve our understanding of glacial dynamics and associated processes in the marginal region of a large marine-terminating ice sheet. Newly acquired data, together with existing datasets have been compiled to create bathymetric models, which were used to study the seafloor landscape and its preserved record of glacial and sedimentary processes. The new bathymetric models were used with novel processing tools combined with seismic profiles, sub-bottom profiles and overlays of geological- and gravimetric maps to describe the observed landforms and interpret causal relationships. The main conclusions are:

    1)   The underlying geology is an important control on the cross-shelf trough (CST) dimensions in western Greenland. This is likely due to the influence of underlying geology to the frictional resistance of the ice flow over the basement rock. Our observations show that ice streaming in areas with basaltic bed-types cause minimal over-deepening of the main trunk of the trough, which also has weaker lateral boundaries allowing the ice stream to shift flow direction more easily. CSTs on the Cenozoic-Mesozoic sedimentary basins indicate a stronger eroding and more focused paleo-ice streams.

    2)   Bedrock lithology has an important part in controlling the location of the head-to-trough transition in CSTs of western Greenland. The areas where the head’s network of channels converges to form the main trunk of the trough are mostly located on the boundary from crystalline to sedimentary bedrock. These areas are also marked by distinct over-deepenings.

    3)   Preglacial conditions such as faults/fractures and lithological properties of the basement rocks in western Greenland served as an important control on the erosional potential of the glacial processes, particularly on a local scale. Faults and fractures have led to the topographic steering of the ice flow that causes further excavation and erosion of the bed, while uneven erosion patterns, based on differences in glacial morphological features, is observed between areas of adjacent bedrocks with different lithology.

    4)   The occurrence of trough mouth fans is suggested to be controlled mainly by the shelf width, which governs the glacial flow length along available sediment sources. It is also controlled by the continental slope steepness, which may be too steep for sediment fans to accumulate, or may cause slope failure which eventually transports the sediments to the deep basin.

    5)   The maximum ice extent in west Greenland extended towards the shelf edge. Geomorphological evidence of ice margin standstills and slow retreat (grounding zone wedges and transverse moraines) in some areas reveal a multi-stage deglaciation process.

    6)   The view of a highly dynamic paleo-Greenland ice sheet is supported by the presence of a large number of CSTs which hosted ice streams, and evidence of ice stream flow-switching throughout one or several glaciations.

    7)   The influence of glacial sedimentary processes extends into the deepest areas of the Arctic Ocean. A submarine landslide, here termed the Molloy Slide, has been described in the Molloy Hole in the Davis Strait between Greenland and Svalbard. This slide was likely caused by massive glacial sediment deposition along the west Svalbard margin.

  • 283.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Egilsson, Arnar
    Thorsteinsson, Tomas
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain, Melville Bay, northwestern Greenland2015In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 250, p. 29-40Article in journal (Refereed)
    Abstract [en]

    Geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate. Melville Bay, in northwestern Greenland, contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere, where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings. We present here the results of high-resolution, geomorphological mapping of the offshore and onshore landscapes in Melville Bay using multibeam sonar and satellite data, at 5- and 10-m resolutions respectively. The results show a similar areally-scoured bedrock-dominated landscape with a glacially modified cnoc-and-lochan morphology on the inner shelf (150-500 m depth) and on the nearby exposed coast. This is manifested by the presence of U-shaped troughs, moutonee-type elongated landforms, stoss-and-lee forms, and streamlined features. The submarine landscape shows features that are characteristic of bedrock in folded, faulted, and weathered metamorphic terrain, and, to a lesser extent, glacially molded bedforms; while coastal landforms exhibit higher relief, irregular-shaped basins, and more subdued fracture valleys. Although generally similar, the onshore and offshore landscapes contain examples of distinctly different landform patterns, which are interpreted to reflect a longer exposure to long-term deep weathering as well as to more recent periglacial weathering processes on land. The spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock. The lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the West Greenland Current flowing northward over the area in combination with limited sediment supply from long sea ice-cover seasons. The distribution and orientation of the landforms in the offshore part indicate ice movement toward the NW, and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day Melville Bay Trough.

  • 284.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jafri, Rooh Ullah
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Acoustic evidence of a submarine slide in the deepest part of the Arctic, the Molloy Hole2014In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 34, no 4, p. 315-325Article in journal (Refereed)
    Abstract [en]

    The western Svalbard continental margin contains thick sediment sequences with areas known to contain gas hydrates. Together with a dynamic tectonic environment, this makes the region prone to submarine slides. This paper presents results from geophysical mapping of the deepest part of the high Arctic environment, the Molloy Hole. The mapping includes multibeam bathymetry, acoustic backscatter and sub-bottom profiling. The geophysical data reveal seabed features indicative of sediment transport and larger-scale mass wasting. The large slide scar is here referred to as the Molloy Slide. It is located adjacent to the prominent Molloy Hole and Ridge system. The slide is estimated to have transported >65 km(3) of sediments over the deep axial valley of the Molloy Ridge, and further into the Molloy Hole. A unique feature of this slide is that, although its run-out distance is relatively short (<5 km), it extends over an enormous vertical depth (>2,000 m) as a result of its position in a complex bathymetric setting. The slide was most likely triggered by seismic activity caused by seafloor spreading processes along the adjacent Molloy Ridge. However, gas-hydrate destabilization may also have played a role in the ensuing slide event.

  • 285.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Initial Results from Seafloor Characterization of Arctic and Antarctic Margins using Multibeam Backscatter2012In: Arctic Palaeoclimate and its Extremes: APEX VI / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, Oulu: University of Oulu , 2012, p. 51-51Conference paper (Other academic)
    Abstract [en]

    The seafloor of high-latitude Polar margins is characterized by various submarine glacigenic landforms whose shape and texture were created, and subsequently modified, by ice. These glaciogenic landforms together with deposited seafloor sediments serve as a record of the past glacial history. The Multibeam Echo Sounder (MBES) technology provides a tool to map and study submarine glaciogenic landforms and seafloor texture. MBES bathymetric images have afforded scientists a way to understand many glacial processes such as iceberg movements, advance and retreat patterns of ice sheets, and polar underwater currents, among others. Aside from measuring the bathymetry, MBES systems also record the returned intensity, or backscatter, of the acoustic pulse. Recent developments have shown that the backscatter information can be used to distinguish/classify differences in the surface sediment types. Here we present the preliminary results of an analysis of backscatter data aimed to characterize sediment types at locations of the Arctic and Antarctic margins mapped with Swedish icebreaker Oden and the installed Kongsberg EM122, 12 kHz, deep water MBES. We apply the Angular Range Analysis (ARA) method that is included in the Geocoder Backscatter processing algorithm [Fonseca and Mayer, 2007]. The results are correlated with other geophysical data and core samples to ground-truth the resulting seafloor maps.

  • 286.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zingerlersen, Karl
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Paleo-ice stream behavior inferred from cross-shelf troughs and submarine glaciogenic debris flows along the west Greenland continental marginManuscript (preprint) (Other academic)
  • 287.
    Freud, Eyal
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Leaitch, Richard
    Nguyen, Quynh T.
    Massling, Andreas
    Skov, Henrik
    Barrie, Leonard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pan-Arctic aerosol number size distributions: seasonality and transport patterns2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 13, p. 8101-8128Article in journal (Refereed)
    Abstract [en]

    The Arctic environment has an amplified response to global climatic change. It is sensitive to human activities that mostly take place elsewhere. For this study, a multi-year set of observed aerosol number size distributions in the diameter range of 10 to 500 nm from five sites around the Arctic Ocean (Alert, Villum Research Station - Station Nord, Zeppelin, Tiksi and Barrow) was assembled and analysed. A cluster analysis of the aerosol number size distributions revealed four distinct distributions. Together with Lagrangian air parcel back-trajectories, they were used to link the observed aerosol number size distributions with a variety of transport regimes. This analysis yields insight into aerosol dynamics, transport and removal processes, on both an intra- and an inter-monthly scale. For instance, the relative occurrence of aerosol number size distributions that indicate new particle formation (NPF) event is near zero during the dark months, increases gradually to similar to 40% from spring to summer, and then collapses in autumn. Also, the likelihood of Arctic haze aerosols is minimal in summer and peaks in April at all sites. The residence time of accumulation-mode particles in the Arctic troposphere is typically long enough to allow tracking them back to their source regions. Air flow that passes at low altitude over central Siberia and western Russia is associated with relatively high concentrations of accumulation-mode particles (N-acc) at all five sites - often above 150 cm(-3). There are also indications of air descending into the Arctic boundary layer after transport from lower latitudes. The analysis of the back-trajectories together with the meteorological fields along them indicates that the main driver of the Arctic annual cycle of N-acc, on the larger scale, is when atmospheric transport covers the source regions for these particles in the 10-day period preceding the observations in the Arctic. The scavenging of these particles by precipitation is shown to be important on a regional scale and it is most active in summer. Cloud processing is an additional factor that enhances the N-acc annual cycle. There are some consistent differences between the sites that are beyond the year-to-year variability. They are the result of differences in the proximity to the aerosol source regions and to the Arctic Ocean sea-ice edge, as well as in the exposure to free-tropospheric air and in precipitation patterns - to mention a few. Hence, for most purposes, aerosol observations from a single Arctic site cannot represent the entire Arctic region. Therefore, the results presented here are a powerful observational benchmark for evaluation of detailed climate and air chemistry modelling studies of aerosols throughout the vast Arctic region.

  • 288. Fripiat, F.
    et al.
    Declercq, M.
    Sapart, C. J.
    Anderson, L. G.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deman, F.
    Fonseca-Batista, D.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Roukaerts, A.
    Semiletov, I. P.
    Dehairs, F.
    Influence of the bordering shelves on nutrient distribution in the Arctic halocline inferred from water column nitrate isotopes2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 5, p. 2154-2170Article in journal (Refereed)
    Abstract [en]

    The East Siberian Sea and contiguous western Arctic Ocean basin are characterized by a subsurface nutrient maximum in the halocline, generally attributed to both Pacific inflow and intensive remineralization in shelf bottom waters that are advected into the central basin. We report nitrogen and oxygen isotopic measurement of nitrate from the East Siberian Sea and western Eurasian Basin, in order to gain insight into how nitrate is processed by the microbial community and redistributed in the Arctic Ocean. A large decoupling between nitrate delta N-15 and delta O-18 is reported, increasing and decreasing upward from the Atlantic temperature maximum layer toward the surface, respectively. A correlation between water and nitrate delta O-18 indicates that most of the nitrate (> 60%) at the halocline has been regenerated within the Arctic Ocean. The increase in nitrate delta N-15 correlates with the fixed N deficit, indicating a causal link between the loss of fixed N and the delta N-15 enrichment. This suggests that a significant share of benthic denitrification is driven by nitrate supplied by remineralization and partial nitrification, allowing residual delta N-15-enriched ammonium to diffuse out of the sediments. By increasing nutrient concentrations and fixed N deficit in shelf bottom waters, this imprint is attenuated offshore following advection into the halocline by nitrate regeneration and mixing. Estimation of the sedimentary isotope effect related to benthic denitrification yields values in the range of 2.4-3.8 parts per thousand, with its magnitude driven by both the degree of coupling between remineralization and nitrification, and fixed N concentrations in shelf bottom waters.

  • 289.
    Fritzon, Ruben
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Goodfellow, Bradley
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stroeven, Arjen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Estholm, Madelene
    Caffee, Marc
    Evaluating geochemical evidence of earthquake periodicity, Sparta Fault, Southern GreeceManuscript (preprint) (Other academic)
    Abstract [en]

    Determining prehistoric earthquake periodicity and magnitudes is important for risk assessments in seismically active areas. We evaluate a geochemical method, which has previously been used to identify prehistoric slips on normal fault scarps through an analysis of variations in the concentration of rare earth elements and Y (REE-Y) along vertical transects. Our study object is the Sparta Fault, a normal fault in southern Greece, developed in limestone and previously documented, and dated using 36Cl, to have been last active 464 BC. From geochemical analyses of 39 fault rock samples, we conclude that REE-Y concentrations correlate strongly with the abundance of quartz and possibly other heterogeneities in the fault scarp. Because the sampled fault rock is a protocataclasite, formed at depth, variations in the abundance of quartz are not associated with prehistoric movements along the fault. We therefore conclude that geochemical evidence does not provide a reliable paleoseismic proxy for fault movement. We also present data indicating a co-variation between quartz and 36Cl concentrations, which we suggest requires a re-examination of this widely used application of the cosmogenic nuclide surface exposure dating method.

  • 290. Fu, Pingqing
    et al.
    Kawamura, Kimitaka
    Chen, Jing
    Qin, Mingyue
    Ren, Lujie
    Sun, Yele
    Wang, Zifa
    Barrie, Leonard A.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tachibana, Eri
    Ding, Aijun
    Yamashita, Youhei
    Fluorescent water-soluble organic aerosols in the High Arctic atmosphere2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 9845Article in journal (Refereed)
    Abstract [en]

    Organic aerosols are ubiquitous in the earth's atmosphere. They have been extensively studied in urban, rural and marine environments. However, little is known about the fluorescence properties of water-soluble organic carbon (WSOC) or their transport to and distribution in the polar regions. Here, we present evidence that fluorescent WSOC is a substantial component of High Arctic aerosols. The ratios of fluorescence intensity of protein-like peak to humic-like peak generally increased from dark winter to early summer, indicating an enhanced contribution of protein-like organics from the ocean to Arctic aerosols after the polar sunrise. Such a seasonal pattern is in agreement with an increase of stable carbon isotope ratios of total carbon (delta C-13(TC)) from -26.8 parts per thousand to -22.5 parts per thousand. Our results suggest that Arctic aerosols are derived from a combination of the long-range transport of terrestrial organics and local sea-to-air emission of marine organics, with an estimated contribution from the latter of 8.7-77% (mean 45%).

  • 291.
    Fuentes Guerrero, César
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Grain size analysis of a short sediment core from the Lomonosov Ridge, central Arctic Ocean2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Trigger core 07, is a 53 cm long sediment core that was collected during the Danish-Swedish expedition “Lomonosov Ridge off Greenland 2012” on the slope of the Lomonosov Ridge in the Arctic Ocean at a depth of 2522 m. This part of the world has experienced critical environmental changes during the Quaternary. Ice-sheets have advanced and retreated, and deposited sediments through all the Arctic Ocean. Glacial sediments contain coarser material and are gray, whereas interglacial sediments are brown, because of high amounts of manganese, and consist of fine-grained material.  The aim of this project is to make grain size analysis on TC 07 with the purpose to make an interpretation of the grain size data in relation to glaciation history and paleo-oceanography. For that, a correlation with piston core 07 has been made, and also a correlation between piston core 07 and the Arctic Coring Expedition, ACEX. The results showed that fine-grained material is more abundant in the top brown unit down to 32 cm, suggesting an interglacial period. This is followed by a gray-beige unit that goes down to 49 cm, and consist of coarser material, indicating glacial deposits. This unit can be linked to the Marine Isotope Stage 2, MIS 2, which began approximately 29000 years ago and ended about 14000 years ago 

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

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

  • 293. Galeczka, Iwona
    et al.
    Eiriksdottir, Eydis Salome
    Hardardottir, Jorunn
    Oelkers, Eric H.
    Torssander, Peter
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gislason, Sigurdur R.
    The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skafta river, Iceland2015In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 301, p. 253-276Article in journal (Refereed)
    Abstract [en]

    This study describes the chemical composition of dissolved, degased and suspended fluxes of the 2002 Skafta glacial flood, which emerged from one of the Skafta subglacial lake due to geothermal activity beneath the Icelandic Vatnajokull glacier. The dissolved and suspended fluxes during the flood are compared with those normally observed in the Skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters. Concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the Skafta river. In addition, dissolved concentrations of nutrients such as SiO2, Fe, and V, increased more than an order of magnitude during the flood. These will affect biological processes on a local scale. The delta S-34 composition in the flood water suggests that the dissolved SO4 was derived from the oxidation of H2S and the geothermal fluid. The total suspended particulate load measured in the Skafta river during the 8-day 2002 flood was approximately half of the non-flood total annual Skafta suspended load. As particles carry the bulk of limiting nutrients to the oceans, this demonstrates the importance of glacial floods for primary production of coastal waters. The composition of the flood water and the Skafta subglacial lake, together with reaction path modelling suggest that substantial degasing of CO2 and H2S occurred at the glacial outlet during the flood. This degasing may have released as much as 262,000 and 7,980 tonnes of CO2 and H2S, respectively, to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event.

  • 294. Galfalk, Magnus
    et al.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bastviken, David
    Making methane visible2016In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 4, p. 426-430Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) is one of the most important greenhouse gases, and an important energy carrier in biogas and natural gas. Its large-scale emission patterns have been unpredictable and the source and sink distributions are poorly constrained. Remote assessment of CH4 with high sensitivity at a m(2) spatial resolution would allow detailed mapping of the near-ground distribution and anthropogenic sources in landscapes but has hitherto not been possible. Here we show that CH4 gradients can be imaged on the <m(2) scale at ambient levels (similar to 1.8 ppm) and filmed using optimized infrared (IR) hyperspectral imaging. Our approach allows both spectroscopic confirmation and quantification for all pixels in an imaged scene simultaneously. It also has the ability to map fluxes for dynamic scenes. This approach to mapping boundary layer CH4 offers a unique potential way to improve knowledge about greenhouse gases in landscapes and a step towards resolving source-sink attribution and scaling issues.

  • 295. Gallagher, K
    et al.
    Bodin, T
    Sambridge, M
    Weiss, D
    Kylander, Malin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Large, David
    Inference of abrupt changes in noisy geochemical records using transdimensional changepoint models2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 311, no 1-2, p. 182-194Article in journal (Refereed)
    Abstract [en]

    We present a method to quantify abrupt changes (or changepoints) in data series, represented as a function of depth or time. These changes are often the result of climatic or environmental variations and can be manifested in multiple datasets as different responses, but all datasets can have the same changepoint locations/timings. The method we present uses transdimensional Markov chain Monte Carlo to infer probability distributions on the number and locations (in depth or time) of changepoints, the mean values between changepoints and, if required, the noise variance associated with each dataset being considered. This latter point is important as we generally will have limited information on the noise, such as estimates only of measurement uncertainty, and in most cases it is not practical to make repeat sampling/measurement to assess other contributions to the variation in the data. We describe the main features of the approach (and describe the mathematical formulation in supplementary material), and demonstrate its validity using synthetic datasets, with known changepoint structure (number and locations of changepoints) and distribution of noise variance for each dataset. We show that when using multiple data, we expect to achieve better resolution of the changepoint structure than when we use each dataset individually. This is conditional on the validity of the assumption of common changepoints between different datasets. We then apply the method to two sets of real geochemical data, both from peat cores, taken from NE Australia and eastern Tibet. Under the assumption that changes occur at the same time for all datasets, we recover solutions consistent with those previously inferred qualitatively from independent data and interpretations. However, our approach provides a quantitative estimate of the relative probability of the inferred changepoints, allowing an objective assessment of the significance of each change.

  • 296. Garcia, Marga
    et al.
    Dowdeswell, Julian A.
    Ercilla, Gemma
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Recent glacially influenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 49, p. 64-81Article, review/survey (Refereed)
    Abstract [en]

    This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of landform development points to a predominantly glacial origin of the sediment supplied to the continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led to the development of scarps and channels on the slope and debris flows on the continental rise. The more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin.

  • 297.
    Garcia, Rina
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Terrestrial organic mater deposition on the Lomonosov Ridge, central Arctic Ocean2011In: APEX Fith International Conference and Workshop: Quaternary Glacial and Climate Extremes, The University Centre in Svalbard (UNIS) , 2011, p. 47-48Conference paper (Other academic)
  • 298.
    Gdaniec, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    231Pa and Th isotopes as tracers of deep water ventilation and scavenging in the Mediterranean Sea2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The naturally occurring isotopes 231Pa and 230Th are used as tracers of marine biogeochemical processes. They are both produced from the radioactive decay of their uniformly distributed uranium parents (235U and 234U) in seawater. After production, 231Pa and 230Th are removed by adsorption onto settling particles (scavenging) and subsequently buried in marine sediments. 230Th is more particle reactive compared to 231Pa. Consequently, 230Th will be removed from the open ocean by adsorption onto settling particles, while 231Pa tend to be laterally transported by currents and removed by scavenging in areas of high particle flux (e.g. ocean margins). The primordial 232Th indicates lithogenic supply via rivers and resuspension of sediments, which provides additional information about processes involved in the cycling of particle reactive elements in the ocean. The preferential deposition of particle reactive elements at ocean margins (boundary scavenging) has important implications for our understanding of the distribution and dispersion of micronutrients (e.g. iron) and pollutants in the ocean. It is therefore valuable to understand the nature of boundary scavenging processes in order to evaluate the relative contribution of circulation and scavenging behaviors.The major characteristics of thermohaline circulation in the Mediterranean are well known and have been studied for decades. This sea is an almost land-locked area, where limited water-exchange with the Atlantic Ocean only occurs through the Strait of Gibraltar. Therefore, this marginal sea is often referred to as a “miniature ocean” suitable as a “laboratory” for marine environmental research. In this licentiate thesis, distributions of 231Pa, 230Th and 232Th in seawater and marine particles collected during the GEOTRACES MedSeA-GA04-S cruise in 2013 are presented. Observed nuclide distributions indicate the impact of deep water formation processes, where observed differences can be linked to the type of deep water formation process that occurs in respective basin. Essentially all in-situ produced 230Th is buried in Mediterranean Sea sediments. Despite lower affinity of 231Pa for marine particles, most 231Pa is also scavenged and deposited in Mediterranean Sea sediments. The efficient scavenging of 231Pa produces a relatively low fractionation between 231Pa and 230Th in terms of the fractionation factor FTh/Pa. This licentiate thesis presents a summary of the methods used for the analysis of 231Pa and Th-isotopes with details on the exchange chromatography method and the treatment of mass spectrometric data. The study of 231Pa, 230Th and 232Th in the Mediterranean Sea has important implications for our understanding of processes that control their water column distributions and how their behavior can be utilized to trace chemical flux in modern and past ocean environments.

  • 299.
    Gdaniec, Sandra
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    231Pa and Th isotopes as tracers of deep water ventilation and scavenging in the Mediterranean Sea2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The naturally occurring isotopes 231Pa and 230Th are used as tracers of marine biogeochemical processes. They are both produced from the radioactive decay of their uniformly distributed uranium parents (235U and 234U) in seawater. After production, 231Pa and 230Th are removed by adsorption onto settling particles (scavenging) and subsequently buried in marine sediments. 230Th is more particle reactive compared to 231Pa. Consequently, 230Th will be removed from the open ocean by adsorption onto settling particles, while 231Pa tend to be laterally transported by currents and removed by scavenging in areas of high particle flux (e.g. ocean margins). The primordial 232Th indicates lithogenic supply via rivers and resuspension of sediments, which provides additional information about processes involved in the cycling of particle reactive elements in the ocean. The preferential deposition of particle reactive elements at ocean margins (boundary scavenging) has important implications for our understanding of the distribution and dispersion of micronutrients (e.g. iron) and pollutants in the ocean. It is therefore valuable to understand the nature of boundary scavenging processes in order to evaluate the relative contribution of circulation and scavenging behaviors.The major characteristics of thermohaline circulation in the Mediterranean are well known and have been studied for decades. This sea is an almost land-locked area, where limited water-exchange with the Atlantic Ocean only occurs through the Strait of Gibraltar. Therefore, this marginal sea is often referred to as a “miniature ocean” suitable as a “laboratory” for marine environmental research. In this licentiate thesis, distributions of 231Pa, 230Th and 232Th in seawater and marine particles collected during the GEOTRACES MedSeA-GA04-S cruise in 2013 are presented. Observed nuclide distributions indicate the impact of deep water formation processes, where observed differences can be linked to the type of deep water formation process that occurs in respective basin. Essentially all in-situ produced 230Th is buried in Mediterranean Sea sediments. Despite lower affinity of 231Pa for marine particles, most 231Pa is also scavenged and deposited in Mediterranean Sea sediments. The efficient scavenging of 231Pa produces a relatively low fractionation between 231Pa and 230Th in terms of the fractionation factor FTh/Pa. This licentiate thesis presents a summary of the methods used for the analysis of 231Pa and Th-isotopes with details on the exchange chromatography method and the treatment of mass spectrometric data. The study of 231Pa, 230Th and 232Th in the Mediterranean Sea has important implications for our understanding of processes that control their water column distributions and how their behavior can be utilized to trace chemical flux in modern and past ocean environments.

  • 300.
    Gdaniec, Sandra
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden; Université Paris-Saclay, France.
    Roy-Barman, Matthieu
    Foliot, Lorna
    Thil, Francois
    Dapoigny, Arnaud
    Burckel, Pierre
    Garcia-Orellana, Jordi
    Masqué, Pere
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, Per S.
    Thorium and protactinium isotopes as tracers of marine particle fluxes and deep water circulation in the Mediterranean Sea2018In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 199, p. 12-23Article in journal (Refereed)
    Abstract [en]

    Pa-231, Th-230 and Th-232 were analyzed in unfiltered seawater samples (n = 66) and suspended particles (n = 19) collected in the Mediterranean Sea during the MedSeA-GA04-S cruise along the GEOTRACES section GA04S and used to investigate mechanisms controlling the distribution and fractionation of Pa and Th in an ocean margin environment. Pa-231 and Th-230 are particle reactive radionuclides and are often used as tracers of processes such as boundary scavenging, particle transport and ocean circulation. The depth profiles of total Pa-231 and Th-230 concentrations in the Mediterranean Sea displayed non-linear shapes. Higher total Th-232 concentrations were observed at the straits and in deep waters pointing at lithogenic sources. Fractionation factors F-Th/Pa ranged from 1.4 to 9. Application of a box-model illustrated that 94% of the Pa-231 and almost all of the Th-230 (99.9%) produced in the Mediterranean Sea is removed to the sediment by scavenging. The negligible export of Th-230 to the Atlantic Ocean, leads to a reevaluation of the mean settling speed of the filtered particles, which is now estimated to 500-1000 m/y. The low F-Th/Pa fractionation factors are attributed to the efficient scavenging and lack of transport of Pa-231 to the Atlantic Ocean.

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