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  • 51.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Davies, Siwan M.
    Tephrochronology of North Europe during the last 1000 years – a contribution to the MILLENNIUM project2007In: XVII INQUA Congress, July 28-August 3 2007, Cairns, Australia. Programs with Abstracts, 2007Conference paper (Other academic)
    Abstract [en]

    The Millennium project is a multidisciplinary consortium of more than 39 European universities and research institutes, with the aim of answering a single question: Does the magnitude and rate of 20th Century climate change exceed the natural variability of European climate over the last millennium? One aspect of this project includes high-resolution investigation of different palaeoclimatic archives such as lake, peat, marine and ice-core records covering the last 1000 years. A key objective of Millennium is to examine the lead and lag responses between these different archives, which requires synchronisation of these proxy records on common timescales. Here we report on the use of tephrochronology for achieving this goal. The detection of tephras in more distal areas now provides the opportunity for improving and validating chronological models and for producing precise tie-points between sparsely located records. For the purposes of the Millennium project and also for other similar studies that focus on the last 1000 years, we demonstrate the applicability of employing tephra horizons from Icelandic volcanic eruptions for the precise correlation of palaeoclimatic archives in northern Europe. For instance, tephra associated with the Hekla-1 (AD 1104), Öræfajökull (AD 1362), Veidivötn (AD 1477) and Askja (AD 1875) eruptions have been widely dispersed in northern Europe. These isochrones are used to date and synchronise the different Millennium archives.

  • 52.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Davies, Siwan M.
    Tine L., Rasmussen
    Tephrochronology of the North Atlantic Region: linking marine, terrestrial and ice-core records from OIS 5-22007In: First Conference on Arctic Palaeoclimate and its Extremes (APEX), March 28-29 2007, 2007Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Major achievements have been made recently regarding the tephrochronology of the North Atlantic area. For the first time a tephra-based correlation between marine cores from the North Atlantic and a terrestrial site on the Faroe Islands of Eemian age (OIS 5e) have been achieved (Wastegård et al., 2005). This is the first time that tephrochronology has been used in order to correlate between marine and terrestrial archives older than OIS 4 in the North Atlantic region. Several new tephras from OIS 5-2 have been identified in North Atlantic sediments and the geochemical composition and distribution of the well-known North Atlantic Ash Zone II (ca 54 ka cal BP) has been refined (Wastegård et al., 2006). The known geographical distribution of other significant tephra strata have been outlined and, as a result, have established important tie-points between diverse palaeoarchives during the last glacial cycle. One important step forward was the identification of the Fugloyarbanki tephra in the NGRIP ice core, where it is dated to 26,740 ± 390 b2k according to the new Greenland Ice Core Chronology (GICC05). This widespread marker horizon has previously been reported in marine cores from the northern North Atlantic Sea and the Labrador Sea (Wastegård et al., 2006). Detection of this tephra for the first time within the NGRIP ice-core provides a pivotal link between marine and ice-core records during the transition between OIS 3/2, enabling an unprecedented insight into the spatial complexity of rapid climatic changes during this time (Davies et al., submitted). Recently another link between marine and ice-core records was established. The FMAZ III ash zone has been described in cores from the Faroe Islands area (c. 33,000 14C years BP), slightly above Heinrich layer 4, and close to the onset of GIS8. An equivalent tephra was recently identified in NGRIP where it is situated right at the peak of GIS8.

    References

    Davies, S.M., Wastegård, S., Rasmussen, T.L., Johnsen, S.J., Steffensen, J.P., Andersen, K.K. and Svensson, A., submitted: Identification of the Fugloyarbanki tephra in the NGRIP ice-core: a key tie-point for marine and ice-core sequences during the last glacial period

    Wastegård, S., Björck, S., Greve, C., and Rasmussen, T.L., 2005: A tephra-based correlation between the Faroe Islands and the Norwegian Sea raises questions about chronological relationships during the last interglacial. Terra Nova 17, 7-12.

    Wastegård, S., Rasmussen, T.L, Kuijpers, A., Nielsen, T., and van Weering, T.C.E., 2006: Composition and origin of ash zones from Marine Isotope Stages 3 and 2 in the North Atlantic. Quaternary Science Reviews 25, 2409-2419.

  • 53.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gudmundsdóttir, Esther R.
    Lind, Ewa M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Timms, Rhys G. O.
    Björck, Svante
    Hannon, Gina E.
    Olsen, Jesper
    Rundgren, Mats
    Towards a Holocene tephrochronology for the Faroe Islands, North Atlantic2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 195, p. 195-214Article in journal (Refereed)
    Abstract [en]

    The Faroe Islands hold a key position in the North Atlantic region for tephra studies due to their relative proximity to Iceland. Several tephras have been described over the last 50 years in peat and lake sediment sequences, including the type sites for the Saksunarvatn and Mjauvotn tephras. Here we present a comprehensive overview of Holocene tephras found on the Faroe Island. In total 23 tephra layers are described including visible macrotephras such as the Saksunarvatn and Hekla 4 tephras and several cryptotephras. The importance of tephras originally described from the Faroe Islands is highlighted and previously unpublished results are included. In addition, full datasets for several sites are published here for the first time. The Saksunarvatn Ash, now considered to be the result of several eruptions rather than one major eruption, can be separated into two phases on the Faroe Islands; one early phase with two precursor eruptions with lower MgO concentrations (4.5-5.0 wt%) than the main eruption and a later phase with higher MgO concentrations (5.5-6.0 wt%), including the visible Saksunarvatn Ash. The Tjornuvik Tephra, previously considered to be a primary deposit, is now interpreted as a reworked tephra with material from at least two middle Holocene eruptions of Hekla. Several of the tephras identified on the Faroe Islands provide useful isochrons for climate events during the Holocene.

  • 54.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Johansson, Hans
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Pacheco, José M.
    New major element analyses of proximal tephras from the Azores and suggested correlations with cryptotephras in North-West Europe2020In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 35, no 1-2, p. 114-121Article in journal (Refereed)
    Abstract [en]

    The Azores Archipelago is one of the most active volcanic areas in the North Atlantic region. Approximately 30 eruptions have been reported over the last 600 years with some major VEI 5 (Volcanic Explosivity Index) eruptions further back in time. The geochemical composition of associated tephra-derived glass, however, is not well characterized. An Azorean origin of cryptotephras found in distal areas such as North Africa, the British Isles and Greenland has been suggested, but proximal data from the Azores are scarce and the correlations have only been tentative. These tephras have a traychtic composition, which excludes an Icelandic origin. In a previous study, we presented major element analyses of proximal tephra-derived glass from five Holocene eruptions on the Azores Islands. There is a striking geochemical similarity between tephras from volcanoes on Sao Miguel and Irish cryptotephras, and especially with eruptives from the Furnas volcano. Here we present new analyses of proximal tephras that confirm and strengthen a link between Furnas and cryptotephras found in south-west Ireland. We also suggest a correlation between a previously unsourced tephra found in a Swedish bog with an eruption of the Sete Cidades volcano c. 3880 a cal BP.

  • 55.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Rasmussen, Tine L.
    Faroe Marine Ash Zone IV: a new MIS 3 ash zone on the Faroe Islands margin2014In: Gas Generation and Migration in Deep Geological Radioactive Waste Repositories, London: The Geological Society Publishing House, 2014, Vol. 398, p. 81-93Chapter in book (Refereed)
    Abstract [en]

    A basaltic tephra layer from MIS 3 has been discovered by analysis of cores from the Faroe Islands margin. The tephra layer appears up to 20 cm thick in some records. After the first main fall-out event the tephra is believed to be mainly deposited and redistributed by bottom currents. Geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed. The peak occurrences are in the lower part of GIS (Greenland Interstadial) 12 and we suggest naming this new tephra Faroe Marine Ash Zone IV (FMAZ IV), following the nomenclature adopted for previous ash zones found on the Faroe Islands margin. Geochemical analyses of the tephra show affinities with the Grimsvotn volcanic system in the Eastern Volcanic Zone in south Iceland. The average age of FMAZ IV from four independent age models is 46 800 +/- 1000 years BP. We suggest that the V5 ash zone, found on the Reykjanes Ridge is a correlative to the FMAZ IV.

  • 56.
    Wastegård, Stefan
    et al.
    Stockholm University.
    Rundgren, Mats
    Schoning, Kristian
    Stockholm University.
    Andersson, Sofia
    Stockholm University.
    Björck, Svante
    Borgmark, Anders
    Possnert, Göran
    Age, geochemistry and distribution of the mid-Holocene Hekla-S/Kebister tephra2008In: the Holocene, ISSN 0959-6836, Vol. 18, no 4, p. 539-549Article in journal (Refereed)
    Abstract [en]

    The middle Holocene Hekla-S/Kebister tephra originates in the Hekla volcanic system on SW Iceland. The distal distribution of the tephra includes the Faroe Islands, Shetland and Central Sweden, indicating a main dispersal towards the east. The chemical composition of the tephra follows the pattern of other major eruptions of Hekla, and ratios between selected oxides may in some cases allow separation from other major Holocene tephras from Hekla. Tephra from the Plinian phase dominates in eastern sites, while tephra also from later phases is found in the Faroe sites. Wiggle-matching of radiocarbon dates around the tephra in a Swedish peat-bog suggests an age around 3720 cal yr BP (3750-3700 cal yr BP), which is in accordance with previous attempts to date this tephra. This is within a period with significant climate changes in NW Europe and opens possibilities for exact comparisons of peat and lake sediment records from different geographical areas.

  • 57.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Siwan M., Davies
    Tine L., Rasmussen
    Tephrochronology of the North Atlantic region: linking marine and ice-core records spanning the last glacial cycle2007In: XVII INQUA Congress, July 28-August 3 2007, Cairns, Australia. Programs with Abstracts, 2007Conference paper (Other academic)
    Abstract [en]

    Tephrochronology has recently become a key technique for the precise correlation of Late Quaternary records in the North Atlantic region. Recent developments have extended the geographical distribution of significant tephra strata and, as a result, have established important tie-points between diverse palaeoarchives during the last glacial cycle. We will report on the work being undertaken to identify, date and geochemically characterise tephra horizons in marine cores from the Faroe Islands region and the Greenland ice-cores. Four ash zones including the widespread North Atlantic Ash Zone II (NAAZ II; 52-53 ka BP) and three mainly basaltic ash zones here referred to as the Faroe Marine Ash Zones (FMAZ) I (ca 15.4 14C ka BP), II/Fugloyarbanki Tephra (ca 23-24 14C ka BP) and III (ca 33 14C ka BP) occur in several cores from the Faroe Islands margin. Detailed investigations of NAAZ II in high-resolution cores show that two separate layers can be distinguished; a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra, separated by as much as 1500 years. FMAZ III is a thick and relatively scattered basaltic ash zone found in three cores from the Faroe area. It has not been directly dated, but extrapolation of AMS radiocarbon dates from all cores suggest an age of c. 33,000 14C years BP, slightly above Heinrich layer 4, and close to the onset of GIS8. An equivalent tephra was recently identified in NGRIP where it is situated right at the peak of GIS8. The FMAZ II/Fugloyarbanki tephra occurs in all analysed marine cores in the Faroe Islands region and in NGRIP. It is dated to 26,740 ± 390 b2k according to the Greenland Ice Core Chronology (GICC05). This tephra falls right after the warmest peak of GIS3 in both the NGRIP and marine records and provides another important tie-point. Other tephras identified within the ice-core material have revealed the presence of previously unreported tephra horizons of Icelandic origin, thus, adding considerably to our knowledge of Icelandic volcanism during the last glacial cycle.

  • 58.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Veres, Daniel
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Lucian Blaga University of Sibiu .
    Kliem, P.
    Hahn, A.
    Ohlendorf, C.
    Zolitschka, B.
    Towards a late Quaternary tephrochronological framework for the southernmost part of South America - the Laguna Potrok Aike tephra record2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 81-90Article in journal (Refereed)
    Abstract [en]

    A total of 18 tephra samples have been analysed from the composite sediment sequence from Site 2 of the Laguna Potrok Aike ICDP expedition 5022 from southern Patagonia, Argentina, which extends back to ca 51 ka cal BP. Analyses of the volcanic glass show that all layers but one are rhyolitic in composition, with SiO2 contents ranging between ca 74.5 and 78 wt% and suggest an origin in the Austral Andean Volcanic Zone (AVZ; 49-55 degrees S). Nonetheless, two main data clusters occur, one group with K2O contents between ca 1.5 and 2.0 wt%, indicating an origin in the Mt. Burney volcanic area, and one group with K2O contents between ca 2.7 and 3.9 wt%, tentatively correlated with Viedma/Lautaro and the Aguilera volcanoes in the northern part of the AVZ. The early Holocene Tephra, MB1 and the late Pleistocene Reclus R-1 tephra occur in the upper part of the sequence. Periods with significant tephra deposition occurred between ca 51-44 ka cal BP, and ca 31-25 ka cal BP, with a decrease in tephra layer frequency between these two periods.

  • 59.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Veres, Daniel
    PASADO Science Team, -
    First analyses of tephra from the 2008 PASADO cores from Laguna Potrok Aike2010In: Potrok Aike Maar Lake Sediment Archive Drilling Project, Berlin: GeoUnion Alfred-Wegener-Stiftung , 2010, p. 63-64Conference paper (Other academic)
    Abstract [en]

    A total of 15 samples were analysed at the Tephrochronology Analytical Unit at the University of Edinburgh in November 2009, of which 14 are from the reference core and one is from the catchment area. Geochemical analyses were performed on a five-spectrometer Cameca SX-100 electron microprobe for concentrations of ten major oxides (Si, Al, Fe, Ti, Mn, Mg, Ca, Na, K & P). Most samples consisted of a mixture of pure glass (sometimes contaminated by phenocrysts) and minerals. Analyses of the glass show that all layers except T-35 are rhyolitic with SiO2 contents between ca 74.5 and 78% (Fig. 1). Two main groups occur, one group with K2O contents between ca 1.5 and 2.0%, indicating an origin in the Mt. Burney volcano and one group with K2O% contents between ca 2.5 and 3.2%, which suggests that these layers are products of eruptions of the Reclús volcano. The dacitic T-35 layer (SiO2 ca 70.5%) is geochemically similar to the t5-8 layer, described by Haberzettl et al. (2009) in a previous core from Laguna Potrok Aike, with an estimated age of ca 34 ka. Efforts will be undertaken in order to compare the geochemical data with previous tephrochronological studies on Laguna Potrok Aike and other sites in southernmost Patagonia. Three tephra samples have been submitted for Ar-Ar dating which will improve the chronological control of the lower part of the sediment record.

     

     

  • 60.
    Wastegård, Stefan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Veres, Daniel
    the PASADO Science Team, -
    First results of tephra analyses from the Potrok AIke Maar Lake Sediment Archive Drilling Project2010In: International Field Conference and Workshop on Tephrochronology, Volcanism and Human Activity: Active tephra in Kyushu, 2010, 2010, p. 94-Conference paper (Other academic)
  • 61. Watson, E. J.
    et al.
    Swindles, G. T.
    Lawson, I. T.
    Savov, I. P.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The presence of Holocene cryptotephra in Wales and southern England2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 4, p. 493-500Article in journal (Refereed)
    Abstract [en]

    There have been few detailed studies into the tephrostratigraphy of southern Britain. We report the tephrostratigraphy of two sites, one in southern England (Rough Tor, Cornwall) and one in Wales (Cors Fochno, west Wales). Our study extends the known southernmost reach of Icelandic cryptotephra in northern Europe. Given the large distance between sites in southern England and eruptive sources (e.g. Iceland 1500-1700km distant), most of the cryptotephra layers consist of sparse numbers of shards, even by the standards of distal tephrostratigraphy (as low as 3 shards cm(-1)), each layer spanning only 1 or 2cm in depth. We identify multiple cryptotephra layers in both sites, extending the known distribution of several tephra layers including the MOR-T4 tephra (approximate to AD 1000) most probably of Icelandic origin, and the AD 860 B tephra correlated to an eruption of Mount Churchill, Alaska. The two sites record contrasting tephrostratigraphies, illustrating the need for the inclusion of multiple sites in the construction of a regional tephrostratigraphic framework. The tephra layers we describe may provide important isochrons for the dating and correlation of palaeoenvironmental sequences in the south of Britain.

  • 62.
    Wohlfarth, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Blaauw, Maarten
    Davies, Siwan
    Andersson, Mamite
    Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Department of Physical Geography and Quaternary Geology.
    Hormes, Anne
    Possnert, Göran
    Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods2006In: Journal of Quaternary Science, Vol. 21, no 4, p. 321-334Article in journal (Refereed)
  • 63.
    Wohlfarth, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Helmens, Karin
    Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Department of Physical Geography and Quaternary Geology.
    Bohncke, Sjoerd
    Renssen, Hans
    Sanchez-Goñi, Maria Fernanda
    d'Errico, Francesco
    Rasmussen, Tine L.
    Johnsen, Sigfus
    Spötl, Christoph
    RESOLuTION – Rapid climatic and environmental shifts during Oxygen Isotope Stages 2 and 3 – linking high-resolution terrestrial, ice core and marine archives2007In: PAGES News, Vol. 15, p. 7-8Article, review/survey (Other (popular science, discussion, etc.))
  • 64. Zolitschka, B.
    et al.
    Anselmetti, F.
    Ariztegui, D.
    Corbella, H.
    Francus, P.
    Luecke, A.
    Maidana, N. I.
    Ohlendorf, C.
    Schaebitz, F.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Environment and climate of the last 51,000 years - new insights from the Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO)2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 1-12Article in journal (Refereed)
    Abstract [en]

    In this introductory paper we summarize the history and achievements of the Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO), an interdisciplinary project embedded in the International Continental Scientific Drilling Program (ICDP). The stringent multiproxy approach adopted in this research combined with radiocarbon and luminescence dating provided the opportunity to synthesize a large body of hydrologically relevant data from Laguna Potrok Aike (southern Patagonia, Argentina). At this site, lake level was high from 51 ka until the early Holocene when the Southern Hemisphere Westerlies (SHW) were located further to the north. At 9.3 ka cal. BP the SHW moved southward and over the latitude of the study area (52 degrees S) causing a pronounced negative water balance with a lake level decrease of more than 50 m. Two millennia later, the SHW diminished in intensity and lake level rose to a subsequent maximum during the Little Ice Age. Since the 20th century, a strengthening of the SHW increased the evaporative stress resulting in a more negative water balance. A comparison of our data with other hydrological fluctuations at a regional scale in south-eastern Patagonia, provides new insights and also calls for better chronologies and high-resolution records of climate variability.

12 51 - 64 of 64
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