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  • 1. Agnini, C
    et al.
    Fornaciari, E
    Rio, D
    Tateo, F
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Giusberti, L
    Responses of calcareous nannofossil assemblages, mineralogy and geochemistry to the environmental pertubartions across the Paleocene/Eocene boundary in the Venetian Pre-Alps2007In: Marine micropaleontology, Vol. 63Article in journal (Refereed)
  • 2.
    Agnini, Claudia
    et al.
    University of Padova.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    An early Eocene carbon cycle perturbation at ~52.5 Ma from the southern Alps: Chronology and biotic response2009In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 24, no PA2209, p. 1-14Article in journal (Refereed)
  • 3.
    Agnini, Claudia
    et al.
    University of Padova.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    It Paleognee inferiore in facies pelagica ne Venetor nord-orientalie2009In: Rendiconto online Soc. Geol. It, Vol. 4, p. 5-12Article in journal (Refereed)
  • 4. Agnini, Claudia
    et al.
    Fornaciari, Eliana
    Raffi, Isabella
    Catanzariti, Rita
    Paelike, Heiko
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rio, Domenico
    Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes2014In: Newsletters on stratigraphy, ISSN 0078-0421, Vol. 47, no 2, p. 131-181Article in journal (Refereed)
    Abstract [en]

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

  • 5. Agnini, Claudia
    et al.
    Fornaciari, Eliana
    Rio, Domenico
    Tateo, Fabio
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Responses of calcareous nannofossil assemblages, mineralogy, and geochemistry to the environmental perturbations across the Paleocene/Eocene boundary in the Venetian Pre-Alps2007In: Marine Micropaleontology, Vol. 63, p. 19-38Article in journal (Refereed)
  • 6.
    Ahmed, Engy
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmström, Sara J. M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Siderophores in environmental research: roles and applications2014In: Microbial Biotechnology, ISSN 1751-7907, E-ISSN 1751-7915, Vol. 7, no 3, p. 196-208Article, review/survey (Refereed)
    Abstract [en]

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

  • 7.
    Alasdair, Skelton
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Fredrik, Arghe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pitcairn, Iain
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spatial coupling between spilitization and carbonation ofbasaltic sills in SW Scottish Highlands: evidence of amineralogical control of metamorphic fluid flow2011In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 11, no 3, p. 245-259Article in journal (Refereed)
    Abstract [en]

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

  • 8.
    Alexanderson, Helena
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Brattforsheden: Vad sanden kan berätta om dess historia2007Other (Other (popular science, discussion, etc.))
  • 9.
    Alexanderson, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Håkansson, Lena
    Dating the glacial history of northeast Greenland2007In: First Conference on Arctic Palaeoclimate and its Extremes, 2007Conference paper (Other (popular science, discussion, etc.))
  • 10.
    Alexanderson, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Johnsen, Timothy
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Murray, Andrew S.
    Nordic Laboratory for Luminescence Dating, Department of Earth Sciences, Aarhus University Risø DTU, DK-4000 Roskilde, Denmark .
    Re-dating the Pilgrimstad Interstadial with OSL: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian (MIS 3)?2010In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 39, no 2, p. 367-376Article in journal (Refereed)
    Abstract [en]

    Pilgrimstad in central Sweden is an important locality for reconstructing environmental changes during the last glacial period (the Weichselian). Its central location has implications for the Scandinavian Ice Sheet as a whole. The site has been assigned an Early Weichselian age (marine isotope stage (MIS) 5 a/c; >74 ka), based on pollen stratigraphic correlations with type sections in continental Europe, but the few absolute dating attempts so far have given uncertain results. We re-excavated the site and collected 10 samples for optically stimulated luminescence (OSL) dating from mineral- and organic-rich sediments within the new Pilgrimstad section. Single aliquots of quartz were analysed using a post-IR blue single aliquot regenerative-dose (SAR) protocol. Dose recovery tests were satisfactory and OSL ages are internally consistent. All, except one from an underlying unit that is older, lie in the range 52–36 ka, which places the interstadial sediments in the Middle Weichselian (MIS 3); this is compatible with existing radiocarbon ages, including two measured with accelerator mass spectrometry (AMS). The mean of the OSL ages is 44±6 ka (n=9). The OSL ages cannot be assigned to the Early Weichselian for all reasonable adjustments to water content estimates and other parameters. The new ages suggest that climate was relatively mild and that the Scandinavian Ice Sheet was absent or restricted to the mountains for at least parts of MIS 3. These results are supported by other recent studies completed in Fennoscandia.

  • 11.
    Alexanderson, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Murray, Andrew
    Problems and potential of OSL-dating deglacial and interstadial sediments in Sweden2009Conference paper (Other academic)
    Abstract [en]

    Several recent OSL-ages from Sweden have been inconsistent with geological interpretation, commonly due to age overestimation, and have been met with some scepticism. We explore the problems and potential of OSL-dating in Sweden by analysing quartz OSL-ages from several known-age deglacial sites in southern and central Sweden and by investigating their luminescence properties. Two problems for obtaining good and reliable ages are incomplete bleaching and low-sensitivity quartz. Incomplete bleaching is partly, but not entirely, the cause of age overestimation and can be avoided by selecting suitable sediment facies. Low sensitivity leads to practical problems in measurements and larger uncertainties in dose estimates. On the other hand, potential for good OSL-dating is shown by high-sensitivity quartz from sites that contain both Dala sandstone clasts and sediments that may have had extensive reworking during the Quaternary.

    This knowledge is useful for interpreting OSL-results from unknown-age interstadial sites. Most interstadial sites in Sweden contain only fragmentary records and represent single events and OSL-ages from such sites lack a context to which the results can be related. It is for example rarely possible to get OSL-samples from a stratigraphic succession that spans a significantly longer time than the resolution of the method or find sites where dates from more than one stratigraphically overlying interglacial, interstadial or deglacial bed can be compared. As interstadial OSL-ages thus largely have to stand on their own, multiple samples and detailed data analyses are necessary to give credibility to the results given the Swedish record of OSL-difficulties. From a luminescence point of view, sites fulfilling the positive criteria identified for deglacial deposits should be selected, but the setting and nature of the most geologically interesting interstadial sites are not always obliging.

  • 12.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dansgaard-Oeschger cycles and Heinrich events in western Europe - A diatom perspective2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The last glacial period was characterised by several abrupt climatic shifts referred to as Dansgaard-Oeschger (DO) cycles and Heinrich events. These shifts were most frequent between 60,000 and 20,000 years before present coinciding with Marine Isotope Stages (MIS) 3 and 2. DO cycles and Heinrich events have been most thoroughly investigated in marine and ice core records while their impact on terrestrial environments is less well known. The high-resolution, multi-proxy investigation of a long sediment sequence, obtained from the former lake at Les Echets in France, aims at filling this gap and allows determining the impact of these climatic events on the lake and its catchment. The site and its surroundings experienced distinct shifts in lake organic productivity and catchment conditions as a consequence of DO climate variability and Heinrich events. The detailed analysis of the fossil diatom record shows distinct changes in diatom productivity, diversity and community composition, which are most likely due to variations in the length of lake ice cover, thermal stratification regimes and catchment conditions during a DO cycle. The distinct reduction in lake organic productivity and particularly low concentrations of diatom valves during intervals corresponding to Heinrich events suggest that these cold and arid phases had the most severe impact on the paleolake at Les Echets. The results of this thesis provide new insight into the impact of abrupt climate change on lacustrine ecosystems and show the potential of high-resolution and multi-proxy studies in paleoenvironmental research.

  • 13.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bigler, Christian
    Department of Ecology and Environmental Science, Umeå University.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lotter, André F.
    Institute of Environmental Biology, Laboratory of Palaeobotany and Palynology, Utrecht University.
    Veres, Daniel
    “Emil Racovita” Speleological Institute, Clinicilor 5, 400006 Cluj-Napoca, Romania.
    Modest summer temperature variability during DO cycles in western Europe2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 11-12, p. 1322-1327Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Identifying changes in Arctic Ocean sea ice conditions north of Greenland during the Holocene2012In: APEX Sixth International Conference and Workshop: Quaternary Glacial and Climate Extremes / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, Oulu: Oulun yliopisto , 2012, p. 32-32Conference paper (Other academic)
  • 15.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Steinthorsdottir, Margret
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 1, p. 94-102Article in journal (Refereed)
    Abstract [en]

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

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

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

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

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

  • 18.
    Andersson, Carin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pliocene foraminiferal biostratigraphy and paleoceanography of the Ontong Java Plateau, western equatorial Pacific Ocean1995Doctoral thesis, comprehensive summary (Other academic)
  • 19.
    Andersson, Sofia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Late Holocene humidity variability in central Sweden2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. Stable isotopes (δ18O and δ13C) on Chara spp encrustations and Pisidium spp mollusc shells and carbon content were analysed in the lake record, whereas peat stratigraphy, humification, testate amoebae assemblages, C/N ratio and stable isotopes (δ13C and δ15N) were analysed in the mire record. Stable isotopes (δ2H and δ18O) on lake water showed that Lake Blektjärnen responded to changes in the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate during which evaporation and atmospheric equilibration likely enrich lake water in 18O and 13C, respectively, and vice versa for a low E/I ratio. The relatively high Chara δ18O and δ13C values between ca 4400 and 4000 cal yr BP thus suggest relatively dry and likely warm conditions, whereas depleted values suggest wetter and probably cooler conditions between ca 4000 and 3000 cal yr BP. Again, drier and probably warmer conditions were inferred from the relatively enriched δ18O values between ca 2500 and 1000 cal yr BP, and depleted δ18O values were recorded between ca 1000 and 50 cal yr BP indicating wetter and likely cooler conditions. The results from the mire mainly indicated vegetation succession, however, the changes inferred at ca 2600 and 1000 cal yr BP could have been triggered by climate change. This study shows that the proxies responded sensitively to humidity changes in the investigated archives allowing for reconstruction of climate change in central Sweden during late Holocene.

  • 20.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bergman, Jonas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Schoning, Kristian
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Synthesis of proxy response to climate change in central Sweden during the late HoloceneArticle in journal (Other academic)
    Abstract [en]

    Biological and geochemical proxies from two lakes and two peat sites in central Sweden are used to test if the inferred climate change can be connected to previously reported temperature anomalies, inferred from stacked pollen mean annual and mean July temperatures mainly in Fennoscandia, during the late Holocene. We show that the reported temperature deviations (lower temperatures between 3800-3000, higher temperatures between 3000-500, and lower temperatures again between 500-50 cal yr BP), can be related to recorded changes in the investigated proxies. These periods correspond to changes inferred from two of the sites; in one of the lakes the reconstructed evaporation and input ratio (E/I) show a high ratio from a dry and likely warmer climate, with decreased importance of precipitation input, and vice versa for a low ratio, and, from one of the peat humification records. Beyween 600-300 cal yr BP magnetic susceptibility increased in a lacustrine sediment record and water table rose according to peat records. The proxies from central Sweden seem to support a late Holocene temperature maximum around ca 2000 cal yr BP, although this is speculative since it is represented by a few samples only.

  • 21.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Leng, Melanie J
    NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham NG12 5GG, UK.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Blaauw, Maarten
    School of Geography, Archaeology and Palaeoecology, Queen's University Belfast, BT7 1NN Belfast, UK.
    Late Holocene climate change in central Sweden inferred from lacustrine stable isotope dataIn: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417Article in journal (Other academic)
    Abstract [en]

    Stable isotopes (18O and 13C) of lacustrine carbonates (Chara spp algae and Pisidium spp molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (18O and 2H) show that Lake Blektjärnen water isotope composition is responsive to the water balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara 18O values we infer that conditions were dry and warm between 4400-4000 cal yr BP whereas more negative values indicate that conditions were wetter and probably cooler between 4000-3000 cal yr BP. A drier climate is inferred from more positive values between 2500-1000 cal yr BP. However, a successive depletion after ca 1750 cal yr BP, also detected in several other 18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased zonal flow.

  • 22.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Rosqvist, Gunhild
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Leng, Melanie
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Blaauw, Maarten
    Late Holocene humidity changes inferred from stable isotopes in Chara encrustations and Pisidium shells in a lacustrine sediment sequence from central Sweden2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 8, no 25, p. 1305-1316Article in journal (Refereed)
    Abstract [en]

    Stable isotopes (δ18O and δ13C) of lacustrine carbonates (Chara spp. algae and Pisidium spp. molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes (δ18O and δ2H) show that Lake Blektjärnen water isotope composition is responsive to the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate, decreasing the relative importance of precipitation input. Under such conditions evaporation and atmospheric equilibration probably enrich lake water in 18O and 13C, respectively, which is reflected in the isotopic composition of the carbonates in the lake. From the relatively positive Chara δ18O values we infer that conditions were dry and warm between 4400 and 4000 cal. a BP, whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal. a BP. A drier climate is inferred from more positive values between 2500 and 1000 cal. a BP. However, a successive depletion after ca. 1750 cal. a BP, also detected in several other δ18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased strength of the zonal flow.

  • 23.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Schoning, Kristian
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Surface wetness and mire development during the late Holocene in central SwedenIn: Boreas, ISSN 0300-9483, E-ISSN 1502-3885Article in journal (Refereed)
    Abstract [en]

    Late Holocene mire development and surface wetness changes have been studied in a small mixed mire located in central Sweden. Today the mire is characterised by a mainly ombrotrophic centre dominated by Sphagnum mosses whereas Carex content increase towards the more minerotrophic mire margins. Two peat sequences extracted from the central ombrotrophic part were investigated for stratigraphy, humification, testate amoebae analysis, C/N ratio and 13C and 15N stable isotopes. Three main stages of mire development are identified with a first stage between ca 4200-2600 cal yr BP, characterised by water-logged conditions suggesting a minerotrophic fen stage. The second stage between ca 2600-1000 cal yr BP is characterised by more ombrotrophic conditions and Sphagnum dominated vegetation. The onset of the prominent change at ca 2600 cal yr BP could have been initiated by by climate change coincident with a change in solar activity. The last stage, between ca 1000-50 cal yr BP, is dominated by more ombrotrophic conditions suggesting increased precipitation. This study shows that the response of hydrological proxies in a mixed mire during its development towards more ombrotrophic conditions might result in conflicting results, which has to be considered in palaeoenvironmental reconstructions from mires that changes between ombrotrophic and minerotrophic settings.

  • 24.
    Andersson, Sofia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Schoning, Kristian
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Surface wetness and mire development during the late Holocene in central Sweden2010In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 39, no 4, p. 749-760Article in journal (Refereed)
  • 25.
    Andersson, Thommy
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

  • 26. Andersson, Ulf B.
    et al.
    Rutanen, Henrikki
    Johansson, Åke
    Mansfeld, Joakim
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
    Rimsa, Andrius
    Characterization of the Paleoproterozoic mantle beneath the Fennoscandian Shield: geochemistry and isotope geology (Nd, Sr) of ≈1.8 Ga mafic plutonic rocks of the Transscandinavian Igneous Belt in southeast Sweden2007In: International Geology Review, Vol. 49, p. 587-625Article in journal (Refereed)
  • 27.
    Andrén, Elinor
    Stockholm University.
    Holocene environmental changes recorded by diatom stratigraphy in the southern Baltic Sea1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Sediment cores from the southern Baltic Sea and the Oder River estuary are analysed for their siliceous microfossil assemblages and organic carbon content. Long piston cores from the Bornholm and Gotland Basins provide data on the long-term Holocene history of the Baltic proper and serve as a natural background when evaluating the most recent environmental changes recorded in the short gravity cores. Corrected and calibrated 14C dates for the Holocene part, together with 210Pb and 137Cs dates for the sediments deposited during the last century, are used as a basis for constructing chronologies and age models. The main results are:

    • The brackish phase of the Yoldia Sea stage in the Bornholm Basin is recorded by a diatom assemblage of periphytic taxa indicating a shallower water depth than today and more marine conditions than are recorded by the planktonic assemblage found in the Gotland Basin.
    • The transition between the Yoldia Sea and the Ancylus Lake stages is distinguished in the offshore facies and recorded in the sediments in the form of a small increase in organic carbon coinciding with a peak in the diatom abundance and increased diatom diversity.
    • The onset of the Initial Litorina Sea stage, recorded about 10,100 calendar years BP (c. 8900 14C years BP) in the Bornholm Basin, indicates a complex transition with different phases of brackish-water inflow.
    • Six periods with major marine water inflow into the Baltic basin are recorded during the Holocene. Once an open connection was established with the North Sea, climatic influence seems to have been the most important factor controlling such inflow events.
    • Comparison between the organic carbon content, the absolute abundance of siliceous microfossils and a regional climate proxy, the Greenland (GRIP) ice core (18O record, shows a tentative link between primary production in the Baltic proper and climate. A high temperature on Greenland corresponds to high organic carbon content and increased diatom abundance in the Baltic proper.
    • Climate change is recorded in both the siliceous microfossil assemblages and the organic carbon content. A sediment sequence indicating high productivity c. 950-800 calendar years BP (AD 1000-1150) correlates with the Medieval warm period. An alteration in the diatom assemblage interpreted as being due to a deterioration in the climate correlates with the start of the Little Ice Age about 850-700 calendar years BP (AD 1100-1250).
    • The effects of eutrophication are recorded AD 1850-1860 in the southwestern Baltic proper, AD 1900 in the Oder estuary and AD 1950-1960 in the Gotland Basin. These effects were probably caused by increased discharge of nutrients deriving from fertilisers, as the responding diatom species partly indicate a cold climate rather than a warm one, as would have been expected if this had been only a response to the warmer climate documented during the last 100 years or so.
  • 28. Andrén, T.
    et al.
    Bitinas, A.
    Björck, S.
    Emelyanov, E
    Harff, J.
    Houmark-Nilelsen, M.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jensen, J.B.
    Jørgensen, B.B:
    Kotilainen, A.
    Knudsen, K.L.
    Lambeck, K.
    Moros, M.
    Spiess, V.
    Uscinowicz, S.
    Veski, S.
    Zelchs, Z.
    The Baltic Sea IODP project2012In: EGU General Assembly Conference Abstracts, 2012, p. 7682-7682Conference paper (Other academic)
  • 29.
    Antevik, Fredrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Undersökning av metamorfa förhållanden för skarn-, metapelit- och sulfidbergarter på nordöstra Utö, Stockholms skärgård, Sverige2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

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

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

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

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

  • 31.
    Armands, Gösta
    Stockholm University, Faculty of Science.
    Geochemical studies of uranium, molybdenum and vanadium in a Swedish alum shale1972Doctoral thesis, monograph (Other academic)
  • 32. Arndt, J.E.
    et al.
    Schenke, H.W.
    Barrios, F.
    Black, J.
    Buys, G.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nitsche, Frank
    Lamont-Doherty Earth Observatory of Columbia University.
    Rebesco, M.
    Reynoso-Peralta, W.
    Wigley, R.
    Wilson, O.
    IBCSO v1: A preview on Version 1 of the International Bathymetric Chart of the Southern Ocean2012Conference paper (Other academic)
  • 33. Austin, William E. N.
    et al.
    Abbott, Peter M.
    Davies, Siwan
    Pearce, Nicholas J. G.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Marine tephrochronology: an introduction to tracing time in the ocean2014In: Marine Tephrochronology / [ed] W. E. N. AUSTIN, P. M. ABBOTT, S. M. DAVIES, N. J. G. PEARCE, S. WASTEGÅRD, London: Geological Society of London, 2014, Vol. 398, p. 1-5Chapter in book (Refereed)
  • 34. Aze, T.
    et al.
    - Ezard, T. H. G.
    Purvis, A.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stewart, D. R. M.
    Wade, B. S.
    Pearson, P. N.
    Identifying anagenesis cladogenesis in the fossil record2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 32, p. E2946-Article in journal (Refereed)
  • 35.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, Eliana
    University of Padova, Department of Geosciences.
    Rio, Domenico
    University of Padova, Department of Geoscience.
    Biochronology and paleoceanography of late Pleistocene and Holocene calcareous nannofossils across the Arctic Basin2009In: Marine Micropaleontology, ISSN 0377-8398, E-ISSN 1872-6186, Vol. 72, p. 86-98Article in journal (Refereed)
  • 36.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kathryn
    Introduction to special section on Cenozoic Paleoceanography of the central Arctic Ocean2008In: Paleoceanography, Vol. 23Article in journal (Refereed)
  • 37.
    Backman, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Raffi, Isabella
    Ciummelli, Marina
    Baldauf, Jack
    Species-specific responses of late Miocene Discoaster spp. to enhanced biosilica productivity conditions in the equatorial Pacific and the Mediterranean2013In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 33, no 4, p. 285-298Article in journal (Refereed)
    Abstract [en]

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

  • 38. Batki, Aniko
    et al.
    Pal-Molnar, Elemer
    Dobosi, Gabor
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Petrogenetic significance of ocellar camptonite dykes in the Ditrau Alkaline Massif, Romania2014In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 200, p. 181-196Article in journal (Refereed)
    Abstract [en]

    Camptonite dykes intrude the rift-related Mesozoic igneous body of the Ditrau Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, major and trace elements, and the Nd isotopic compositions of the dykes in order to define their nature and origin. The dykes are classified as the clinopyroxene-bearing (camptonite-I) and clinopyroxene-free (camptonite-II) varieties. Camptonite-I consists of aluminian-ferroan diopside phenocrysts accompanied by kaersutite, subordinate Ti-rich annite, albite to oligoclase and abundant calcite-albite ocelli. Camptonite-II comprises K-rich hastingsite to magnesiohastingsite, Ti-rich annite, albite to andesine, abundant accessory titanite and apatite, and silicate ocelli filled mainly with plagioclase (An(4-34)). Age-corrected Nd-143/Nd-144 ratios vary from 0.51258 to 0.51269. The high epsilon(Nd) values of +4.0 to +6.1 which are consistent with intra-plate composition, together with light rare earth element (LREE), large ion lithophile element (LIE) and high field strength element (HFSE) enrichment in the camptonites is ascribed to the formation of small melt batches of a metasomatised sub-lithospheric mantle source. The presence of an asthenospheric 'high mu' ocean island basalt (HIMU-OIB)-type mantle component in the source region has also been revealed. A 1-4% degree of partial melting of an enriched garnet Iherzolite mantle source containing pargasitic amphibole followed by fractionation is inferred to have been involved in the generation of the camptonites. They are deduced to be parental melts to the Ditrau Alkaline Massif.

  • 39. Beltran, Catherine
    et al.
    Rousselle, Gabrielle
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wade, Bridget S.
    Sicre, Marie Alexandrine
    Paleoenvironmental conditions for the development of calcareous nannofossil acme during the late Miocene in the eastern equatorial Pacific2014In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 29, no 3, p. 210-222Article in journal (Refereed)
    Abstract [en]

    Repeated monospecific coccolithophore dominance intervals (acmes) of specimens belonging to the Noelaerhabdaceae familyincluding the genus Reticulofenestra and modern descendants Emiliania and Gephyrocapsaoccurred during the Neogene. Such acme was recognized during the late Miocene (similar to 8.6Ma), at a time of a major reorganization of nannofossil assemblages resulting in a worldwide temporary disappearance of larger forms of the genus Reticulofenestra (R. pseudoumbilicus) and the gradual recovery and dominance of its smaller forms (< 5 mu m). In this study we present a multiproxy investigation of late Miocene sediments from the east equatorial Pacific Integrated Ocean Drilling Program Site U1338 where small reticulofenestrid-type placoliths with a closed central areaknown as small Dictyococcites spp. (< 3 mu m)formed an acme. We report on oxygen and carbon stable isotope records of multispecies planktic calcite and alkenone-derived sea surface temperature. Our data indicate that, during this 100 kyr long acme, the east equatorial Pacific thermocline remained deep and stable. Local surface stratification state fails to explain this acme and thus contradicts the model-based hypothesis of a Southern Ocean high-latitude nutrient control of the surface waters in the east equatorial Pacific. Instead, our findings suggest that external forcing such as an extended period of low eccentricity may have created favorable conditions for the small Dictyococcites spp. growth. Key Points < list list-type=bulleted id=palo20081-list-0001> < list-item id=palo20081-li-0001> EEP thermocline deep during the late Miocene small Dictyococcites acme <list-item id=palo20081-li-0002>Low eccentricity favorable for the small Dictyococcites spp. growth

  • 40.
    Bender, Hagen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Testing Tectonic Concepts in the Seve Nappe Complex, Jämtland, Sweden2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    When continental plates collide, one of the involved continents is subducted beneath the other one. As a consequence, the lithosphere thickens along the convergent plate boundary and causes the formation of a mountain belt. High-grade metamorphic rocks, formerly parts of the subducted continent, can be exhumed back to the surface and are commonly found in the central domain of mountain belts. The leucogranite- bearing Seve Nappe Complex in the central part of the Scandinavian Caledonides is a good example of such commonly migmatic rock units, which hold the key to understanding the tectonic evolution of a mountain range. This study aims to develop a tectonic model for the Swedish Caledonides, which integrates new structural data, collected during extensive fieldwork, and new geochronological constraints. Here we present the results of the first part of this study. We show how top-to-the-foreland directed shearing affected the migmatic part of the Seve Nappe Complex from bottom to top at amphibolite-facies conditions. Subsequently, the entire Caledonian nappe stack underwent a greenschist-facies overprint, associated with pervasive, again, top- to-the-foreland directed shearing. This last tectonic event resulted in the assembly of the presently observed nappe architecture, which is characterized by the excision of large sections of the lithosphere.

  • 41. Bengtson, S.
    et al.
    Ivarsson, M.
    Astolfo, A.
    Belivanova, V.
    Broman, Curt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marone, F.
    Stampanoni, M.
    Deep-biosphere consortium of fungi and prokaryotes in Eocene subseafloor basalts2014In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 12, no 6, p. 489-496Article in journal (Refereed)
    Abstract [en]

    The deep biosphere of the subseafloor crust is believed to contain a significant part of Earth's biomass, but because of the difficulties of directly observing the living organisms, its composition and ecology are poorly known. We report here a consortium of fossilized prokaryotic and eukaryotic micro-organisms, occupying cavities in deep-drilled vesicular basalt from the Emperor Seamounts, Pacific Ocean, 67.5m below seafloor (mbsf). Fungal hyphae provide the framework on which prokaryote-like organisms are suspended like cobwebs and iron-oxidizing bacteria form microstromatolites (Frutexites). The spatial inter-relationships show that the organisms were living at the same time in an integrated fashion, suggesting symbiotic interdependence. The community is contemporaneous with secondary mineralizations of calcite partly filling the cavities. The fungal hyphae frequently extend into the calcite, indicating that they were able to bore into the substrate through mineral dissolution. A symbiotic relationship with chemoautotrophs, as inferred for the observed consortium, may be a pre-requisite for the eukaryotic colonization of crustal rocks. Fossils thus open a window to the extant as well as the ancient deep biosphere.

  • 42. Bentley, Michael J.
    et al.
    Cofaigh, Colm O.
    Anderson, John B.
    Conway, Howard
    Davies, Bethan
    Graham, Alastair G. C.
    Hillenbrand, Claus-Dieter
    Hodgson, Dominic A.
    Jamieson, Stewart S. R.
    Larter, Robert D.
    Mackintosh, Andrew
    Smith, James A.
    Verleyen, Elie
    Ackert, Robert P.
    Bart, Philip J.
    Berg, Sonja
    Brunstein, Daniel
    Canals, Miguel
    Colhoun, Eric A.
    Crosta, Xavier
    Dickens, William A.
    Domack, Eugene
    Dowdeswell, Julian A.
    Dunbar, Robert
    Ehrmann, Werner
    Evans, Jeffrey
    Favier, Vincent
    Fink, David
    Fogwill, Christopher J.
    Glasser, Neil F.
    Gohl, Karsten
    Golledge, Nicholas R.
    Goodwin, Ian
    Gore, Damian B.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hall, Brenda L.
    Hall, Kevin
    Hedding, David W.
    Hein, Andrew S.
    Hocking, Emma P.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johnson, Joanne S.
    Jomelli, Vincent
    Jones, R. Selwyn
    Klages, Johann P.
    Kristoffersen, Yngve
    Kuhn, Gerhard
    Leventer, Amy
    Licht, Kathy
    Lilly, Katherine
    Lindow, Julia
    Livingstone, Stephen J.
    Masse, Guillaume
    McGlone, Matt S.
    McKay, Robert M.
    Melles, Martin
    Miura, Hideki
    Mulvaney, Robert
    Nel, Werner
    Nitsche, Frank O.
    O'Brien, Philip E.
    Post, Alexandra L.
    Roberts, Stephen J.
    Saunders, Krystyna M.
    Selkirk, Patricia M.
    Simms, Alexander R.
    Spiegel, Cornelia
    Stolldorf, Travis D.
    Sugden, David E.
    van der Putten, Nathalie
    van Ommen, Tas
    Verfaillie, Deborah
    Vyverman, Wim
    Wagner, Bernd
    White, Duanne A.
    Witus, Alexandra E.
    Zwartz, Dan
    A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 100, p. 1-9Article in journal (Refereed)
    Abstract [en]

    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

  • 43.
    Beranek, Luke P.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    van Staal, Cees R.
    McClelland, William C.
    Israel, Steve
    Mihalynuk, Mitch G.
    Detrital zircon Hf isotopic compositions indicate a northern Caledonian connection for the Alexander terrane2013In: Lithosphere, ISSN 1941-8264, E-ISSN 1947-4253, Vol. 5, no 2, p. 163-168Article in journal (Refereed)
    Abstract [en]

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

  • 44. Berger, Alfons
    et al.
    Thomsen, Tonny B.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ovtcharova, Maria
    Kapferer, Notburga
    Mercolli, Ivan
    Dating emplacement and evolution of the orogenic magmatism in the internal Western Alps: 1. The Miagliano Pluton2012In: Swiss Journal of Geosciences, ISSN 1661-8726, E-ISSN 1661-8734, Vol. 105, no 1, p. 49-65Article in journal (Refereed)
    Abstract [en]

    The Canavese Line in the Western Alps represents the position in the Alpine chain, where alkaline and calc-alkaline magmatism occur in close spatial and temporal association. In addition to available data on the alkaline Valle del Cervo Pluton, we present petrological and geochemical data on the Miagliano tonalite. The latter is of special interest, because it is located in the south-eastern side of the Canavese Line, in contrast to most Periadriatic Plutons. The dioritic to tonalitic rocks of the Miagliano Pluton represent an intermediate stage of a calc-alkaline differentiation, demonstrated by relics of two different pyroxenes as well as the texture of allanite. Hornblende barometry indicates pressures of similar to 0.46 GPa consistent with the presence of magmatic epidote. Field relationships between the two Plutons, the volcanic and volcaniclastic rocks of the Biella Volcanic Suite and numerous dykes cross-cutting the different units, allow reconstruction of a more refined chronology of the calc-alkaline and alkaline magmatic series. High precision zircon geochronology yields an age of 33.00 +/- A 0.04 Ma for the central tonalitic part of the Miagliano Pluton and 30.39 +/- A 0.50 Ma for the granitic core of the Valle del Cervo Pluton. The difference in age combined with cooling data and intrusion depth indicates dissimilar tectonic transport east and west of the Canavese Line. The earlier emplaced Miagliano Pluton has to be exhumed from an intrusion depth of similar to 12-15 km, whereas the neighbouring and younger Valle del Cervo Pluton is exhumed from a depth of 5-7 km. This tectonic scenario is related to upper crustal rigid block rotation responsible for the burial of the lowermost Rupelian paleosurface of the Sesia-Lanzo Zone. Thus, the new ages constrain the paroxysm of the orogenic magmatism in the internal Western Alps to an extremely short lapse of time in the first half of the Rupelian.

  • 45. Bergström, Stig M.
    et al.
    Bergström, JanKumpulainen, RistoStockholm University, Faculty of Science, Department of Geology and Geochemistry.Ormö, JensSturkell, Erik
    GFF 129 No. 2, 65-1762007Collection (editor) (Other academic)
  • 46. Bergström, Stig M.
    et al.
    Bergström, Jan
    Kumpulainen, Risto
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Ormö, Jens
    Sturkell, Erik
    Maurits Lindström - A renaissance geoscientist2007In: GFF, ISSN 1103-5897, Vol. 129, no 2, p. 65-69Article in journal (Other academic)
    Abstract [en]

    This issue of the GFF is dedicated to Professor Maurits Lindström on the occasion of his 75th birthday by students, colleagues, and friends in recognition of his profound impact on the Science of Geology as researcher and teacher during more than half a century.

  • 47.
    Berntsson, Annika
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Reconstruction of centennial scale climate change in NW Sweden, using Chironomids and high resolution XRF-data2010In: ESF TOPO-EUROPE Workshop and PhD Summer School on Detecting Landscape Change / [ed] Achim A. Beylich and Katja Laute, Trondheim: Norsk Geologisk Forening (NGF) , 2010, p. 75-77Conference paper (Other academic)
  • 48.
    Berntsson, Annika
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    The sensitivity of Swedish alpine lakes to hydro-climatic changes during the Late Holocene2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis objective is to use lake sediments to investigate the relationships between chironomids, as proxy for temperature, and δ18O and minerogenic in-wash, as precipitation proxies, in northern Sweden during the Late Holocene. Three lakes along a N–S transect in the Scandes were studied using biological, geochemical and physical sediment properties, together with numerical methods. Emphasis was put on changes in hydrological and erosional regimes and the configurations of lake catchments in an attempt to avoid misinterpretation of the climate signals. Mean July air temperatures were inferred from the chironomid composition in sediment records covering the last 5000 yrs in Vindelfjällen Mountains in Mid Lapland and the last 1000 yrs in Jämtland. The temperature reconstructions underwent significance tests, suggesting reliable results for the Vindelfjällen reconstruction but not the Jämtland reconstruction. Data from XRF core scanning and grain size variations, interpreted together with catchment geomorphology, suggested periods with increased fluvial erosion. A major flood event occurred at the Vindelfjällen site c. 2800 cal. yr BP. Furthermore, this record indicates stream flow and wetland surface erosion during the last 1200 yrs. Seasonal variations in the amount of precipitation, reflecting changes in atmospheric circulation during the last 1000 yrs, were reconstructed based on δ18O in diatoms from one lake in Jämtland and one in northern Lapland. Relatively higher summer precipitation was inferred between AD 1000 and 1080, AD 1300 and 1440, and during the early 19th century as a result of a positive Arctic Oscillation mode. Changes in chironomid composition in the Jämtland lake were concurrent with shifts in δ18Odiatom suggesting indirect responses to circulation changes. Changes in precipitation are suggested to be an important factor that may cause the spatially variable results among chironomid-based July air temperature reconstructions in Scandinavia.

  • 49.
    Berntsson, Annika
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    De Vleeschouwer, François
    CNRS, EcoLab, Castanet Tolosan, France.
    Bertrand, Sebastien
    Ghent University.
    Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology, Lake Vuoksjávrátje, NW SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, we highlight the importance of combining multi-proxy analysis of lake sediments with associated catchment geomorphology to better understand the late Holocene palaeoenvironmental evolution in a high latitude Alpine lake in N Sweden. Previous studies have suggested that such lakes may be highly sensitive to variations in catchment erosion and variations in precipitation, and that this sensitivity may influence ecologically-based reconstructions of past temperature changes. Here we have analysed lake sediments covering the last 5100 years from Lake Vuoksjávrátje in NW Sweden to identify different erosional regimes in the lake catchment and to identify sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. Methods that were used include XRF core scanning, grain size analysis and geomorphological mapping, supported by previously published chironomid, total organic carbon and carbon/nitrogen data. From the integrated results we identify time intervals when increased amounts/intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event in our record occurred between 3090 and 2750 cal. a BP and is interpreted to be the result of excessive precipitation in relation to the 2.8 ka event. By combining the multi-proxy analysis of a lake sediment core with a detailed catchment characterisation it is possible to reach a better understanding of the processes active within the lake catchment, the factors governing the erosional regimes and the way these are recorded in lake sediments. For future palaeoclimatological research based on lake sediments we recommend increasing the integration of catchment geomorphology, sedimentology and palaeoecology.

  • 50.
    Berntsson, Annika
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rosqvist, Gunhild C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Velle, Gaute
    Late-Holocene temperature and precipitation changes in Vindelfjallen, mid-western Swedish Lapland, inferred from chironomid and geochemical data2014In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 24, no 1, p. 78-92Article in journal (Refereed)
    Abstract [en]

    In this article, we present results from a palaeolimnological study from Lake Vuoksjavratje in the mountain tundra region in the Vindelfjallen Mountains, northwest Sweden. We suggest that the influence of precipitation may be one of the factors causing discrepancies between chironomid-based late-Holocene July temperature (JulyT) reconstructions from Fennoscandia. We combine quantitative temperature reconstruction using chironomids for the last 5100 years with qualitative analysis of chironomid composition and geochemical analyses, such as x-ray fluorescence (XRF), total organic carbon (TOC) and C/N analysis. The studied sequence is dated by Pb-210, Cs-137 and 11 C-14 datings from terrestrial macrofossils. The aim of the study was to use chironomids to reconstruct late-Holocene summer temperature variation on a multi-centennial to centennial timescale and to use geochemical data to identify periods during which the changes in chironomid composition might have been forced by environmental variables other than temperature, such as within lake processes or precipitation. Based on ordination techniques, and a comparison between chironomid-inferred JulyTs and changes in minerogenic sedimentation with regional temperature and wetness records, it is concluded that the JulyT signal was modulated by precipitation. The proxies indicate that both JulyT and annual precipitation have influenced the chironomid communities in Lake Vuoksjavratje, and that catchment-related processes caused by enhanced precipitation have overridden the summer temperature signal between 3000 and 2200 cal. yr BP, and between 1050 and 100 cal. yr BP.

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