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• 1. Abbott, P. M.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region: The cryptotephra record2014In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 409, p. 153-168Article in journal (Refereed)

Previous studies of marine sequences from the Faroe Islands region have identified a series of coarse-grained tephra horizons deposited during Marine Isotope Stage (MIS) 5. Here we reassess the MIS 5 tephrostratigraphy of the Faroe Islands region and focus on the cryptotephra deposits preserved within the fine-grained fraction of marine core LINK 16. We also extend the record to encompass the late MIS 6 and early MIS 4 periods. A density separation technique, commonly used for tephra investigations in lacustrine settings but rarely applied to marine sediments, is utilised to explore the fine-grained material and EPMA and LA-ICP-MS are employed to determine the major and trace element composition of individual tephra shards. In total, 3 basaltic and 3 rhyolitic Icelandic cryptotephra deposits with homogeneous geochemical compositions are identified - all of which have the potential to act as isochronous tie-lines. Geochemical results highlight that the Grimsvotn volcanic system of Iceland is the predominant source of the basaltic horizons and the Oraefajokull or Torfajokull systems are the likely sources of the rhyolitic deposits. Three of the horizons have been previously recognised in Faroe Islands region marine sequences, with two of these deposits traceable into a Norwegian Sea sequence. An early MIS 4 rhyolitic horizon is the most widespread deposit as it can be traced into the Norwegian Sea and to the south into a record from the Rockall Trough. Basaltic and rhyolitic horizons deposited during late MIS 6 have not been recognised in other sequences and represent new additions to the regional tephrostratigraphy.

• 2. Abbott, Peter M.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36, p. 59-77Article in journal (Refereed)

Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval: the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grimsvotn, Grimsvotn-Kverkfjoll and either Reykjanes or Veidivotn-Bardarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICCO5 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.

• 3.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. 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)

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.

• 4.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham NG12 5GG, UK. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. 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)

Stable isotopes ($\delta$18O and $\delta$13C) of lacustrine carbonates (Chara spp algae and Pisidium spp molluscs) from a lake sedimentary sequence in central Sweden were analysed to infer changes in lake hydrology and climate during the late Holocene. Results from analysis of lake water isotopes ($\delta$18O and $\delta$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 $\delta$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 $\delta$18O records (carbonate and diatom), suggest increasingly wetter conditions in Scandinavia after that time, which is probably related to increased zonal flow.

• 5.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK). Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
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)

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.

• 6. Austin, William E. N.
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)
• 7.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Regional and local patterns of peat humification in three raised bogs in Värmland, south-central Sweden2008In: GFF, Vol. 130, no 161-176Article in journal (Refereed)

Peat humification in five cores from three ombrotrophic bogs in Värmland, south-central Sweden, was analysed in an attempt to investigate local and regional responses to climate changes during the Holocene. The chronology of the five peat sequences was constrained by means of AMS radiocarbon dates and tephrochronology. Four tephras were geochemically correlated with the Askja AD 1875, Hekla-3, Kebister and Hekla-4 tephras. A further tephra, the Stömyren tephra, dated by interpolation to 2200–2100 cal yr BP was found in one bog. A composite record of peat humification changes show several periods of wetter bog conditions. These occur during the later part of the Holocene, corresponding to known climate changes in the North Atlantic region, especially around 4500–4000, 3700–3200, 3000–2700 and 1700–700 cal yr BP. Wet shifts are inferred from individual peat cores and the composite record at c. 5500, 4200, 3700, 3500, 2900, 1700, 850, 650, 500 and 250 cal yr BP. Development of composite records could be a powerful tool to smooth the palaeohydrological records in order to reduce the influence of local fluctuations in the proxy data and to extract the regional climatic signal.

Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Luminescence dating of the PASADO core 5022-1D from Laguna Potrok Aike (Argentina) using IRSL signals from feldspar2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 70-80Article in journal (Refereed)

We have measured and tested a luminescence chronology for the PASADO core 5022-1D from the maar lake of Laguna Potrok Aike. Because of unsuitable quartz OSL characteristics, sand-sized K-feldspar extracts were chosen as a dosimeter and the dose was measured using a post-IR IRSL (pIRIR(290)) measurement protocol. Using this approach we were able to access a stable signal and thus avoid the ubiquitous problem of feldspar signal instability. Extensive laboratory tests show that the chosen pIRIR(290) protocol is applicable to these samples. We also developed a new criterion based on known relative bleaching rates of the conventional IRSL signal (IR50) and the pIRIR(290) signal and the relationship between resulting equivalent doses; this is used to identify and reject poorly bleached samples. Eighteen samples out of 47 were rejected based on this criterion, without reference to absolute doses or stratigraphy; the resulting age-depth profile is self-consistent, increases smoothly with depth and is in agreement with independent age control based on volcanic ash layers (Reclus, Mt Burney and Hudson tephras) at the top and middle of the core. Our new luminescence chronology suggests that the 5022-1D core reaches back to similar to 65 ka at similar to 96 m below lake floor.

• 9. Cage, Alix G.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Identification of the Icelandic Landnam tephra (AD 871 +/- 2) in Scottish fjordic sediment2011In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 246, p. 168-176Article in journal (Refereed)

Certain marginal marine environments, such as the Scottish fjord systems, contain high-resolution records of palaeoclimatic change in which decadal to centennial climatic events can be resolved. This paper explores the possibilities of using tephrochronology to stratigraphically constrain the timing of such events in the Loch Sunart record (MD04-2831) on the NW coast of Scotland (UK). One tephra horizon (containing both silicic and basaltic shards) is identified within Late Holocene sediment with geochemical analyses of the basaltic shards suggesting an origin in the Veidiviitn-Baroarbunga volcanic system. Radiocarbon age estimates and stratigraphic information suggests that the AD 871 Landnam tephra is the most likely candidate. The shards identified within this horizon appear hydrated and indicate the operation of post-depositional weathering processes possibly influenced by the saline conditions of the fjord environment.

• 10. Clymans, W.
Stockholm University, Faculty of Science, Department of Physical Geography.
The contribution of tephra constituents during biogenic silica determination: implications for soil and palaeoecological studies2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 12, p. 3789-3804Article in journal (Refereed)

Biogenic silica (BSi) is used as a proxy by soil scientists to identify biological effects on the Si cycle and by palaeoecologists to study environmental changes. Alkaline extractions are typically used to measure BSi in both terrestrial and aquatic environments. The dissolution properties of volcanic glass in tephra deposits and their nanocrystalline weathering products are hypothesized to overlap those of BSi; however, data to support this behaviour are lacking. The potential that Si-bearing fractions dissolve in alkaline media (Si-Alk) that do not necessarily correspond to BSi brings the applicability of BSi as a proxy into question. Here, analysis of 15 samples reported as tephra-containing allows us to reject the hypothesis that tephra constituents produce an identical dissolution signal to that of BSi during alkaline extraction. We found that dissolution of volcanic glass shards is incomplete during alkaline dissolution. Simultaneous measurement of Al and Si used here during alkaline dissolution provides an important parameter to enable us to separate glass shard dissolution from dissolution of BSi and other Si-bearing fractions. The contribution from volcanic glass shards (between 0.2 and 4 wt % SiO2), the main constituent of distal tephra, during alkaline dissolution can be substantial depending on the total Si-Alk. Hence, soils and lake sediments with low BSi concentrations are highly sensitive to the additional dissolution from tephra constituents and its weathering products. We advise evaluation of the potential for volcanic or other non-biogenic contributions for all types of studies using BSi as an environmental proxy.

• 11. Cunningham, Laura
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Preliminary Sampling Report from Stuor Guossásjavri, Northern Sweden2008In: European Climate of the Last Millennium, Millennium Milestone meeting 2, Cala Millor, Mallorca, 13th-15th March 2008, 2008, p. 80-81Conference paper (Other academic)
• 12. Davies, Siwan D.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Widespread dispersal of Icelandic tephra: how does the Eyjafjöll eruption of 2010 compare to past Icelandic events?2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 5, p. 605-611Article in journal (Refereed)
• 13. Davies, Siwan M.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Integrating the INTIMATE records using tephrochronology: rising to the challenge2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36, p. 11-27Article in journal (Refereed)

Little has challenged our understanding of climate change more so than the abruptness with which large-scale shifts in temperature occurred during the Late Quaternary. The causal mechanisms driving these rapid changes are poorly understood, largely due to the inherent difficulties of integrating palaeoclimate records which represents the key focus of the INTIMATEI project. Tephrochronology has become central to the synchronisation goals of INTIMATE, the overall aim of which is to test the degree of climatic synchroneity in relation to these rapid climatic events. Here we present a European framework of 12 volcanic events that hold considerable promise for achieving the INTIMATE goals and effecting precise correlation of widespread palaeoarchives. These tephras are widespread and fall stratigraphically in close association to rapid climatic changes. We believe that these represent the most valuable tephras for the European INTIMATE project, but also highlight those that require urgent investigation to refine their geochemical signatures, eruptive context and chronological and stratigraphical uncertainties. For instance, new data are presented for the Saksunarvatn Ash that question the sole reliance on major-element analysis for tephra characterisation and highlights some of the challenges that remain for tephra studies. Accordingly, we outline a number of key recommendations relating to geochemical characterisation, data comparison, assessing the depositional integrity of tephra horizons as well as methods for improving age estimates - all of which will optimise the application of tephrochronology to meet the INTIMATE goals.

• 14. Davies, Siwan M
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Distal tephrochronology of North Europe during the last 1000 years2008In: European Climate of the Last Millennium, Millennium Milestone meeting 2, Cala Millor, Mallorca, 13th-15th March 2008, 2008, p. 120-121Conference paper (Other academic)
• 15. Davies, Siwan M.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Tracing volcanic events in the NGRIP ice-core and synchronising North Atlantic marine records during the last glacial period2010In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 294, p. 69-79Article in journal (Refereed)

Abstract

Five basaltic tephra horizons have been identified in the NGRIP ice-core during the last glacial period. Geochemical analyses indicate that these tephras are of Icelandic origin with one horizon identified as the Faroe Marine Ash Zone III (FMAZ III) — an important marker horizon in several marine records within the Faroe Islands margin. The FMAZ III is a few millimetres thick and is constrained to 38,122 ± 723 yr b2k (before year AD 2000) according to the Greenland Ice Core Chronology (GICC05). This event falls directly at the thermal peak of Greenland Interstadial 8 (GI-8) and a marine-ice correlation, based on the position of this tephra, suggests a close coupling of the marine and atmospheric systems at this time. The remaining tephras originate from the Eastern Volcanic Zone with the Katla volcanic system pinpointed as the dominant source. These are thought to represent previously unknown volcanic events which add considerably to our knowledge of Icelandic volcanism during this period. Independent ages are assigned to these events and together with major element characterisation, form the backbone of the tephrochronology framework presented here. Despite the identification of these tephras, this study also demonstrates that the sulphate record may not always act as a suitable proxy for the identification of tephra horizons in ice-core records.

• 16. Davies, Siwan M
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Identification of the Fugloyarbanki tephra in the NGRIP ice-core: a key tie-point for marine and ice-core sequences during the last glacial period2008In: Journal of Quaternary Science, Vol. 23, no 409-414Article in journal (Refereed)
• 17. Gebhardt, Andrea Catalina
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Seismic evidence of up to 200 m lake-level change in Southern Patagonia since Marine Isotope Stage 42012In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 59, no 3, p. 1087-1100Article in journal (Refereed)

Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south-eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo-shorelines indicating a stepwise water-level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake-level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present-day lake level point towards a long period of lake-level highstand between roughly 53.5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp. Dryer conditions during the Mid-Holocene are evidenced by a dropping lake level, resulting in a basin-wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5.8 to 5.4 ka cal. bp and ca 4.7 to 4 ka cal. bp with palaeo-shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.

• 18. Heyng, Alexander M.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (delta N-15, delta C-13) of Lake Pupuke2012In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 48, no 2, p. 351-366Article in journal (Refereed)

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165 cal. year BP. The origin of organic matter was established using total-organic-carbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (delta C-13(OM)) and nitrogen (delta N-15) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. > 7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165 years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600 cal. year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the delta N-15 and delta C-13 values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600 cal. year BP.

• 19. Hibbert, F. D.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Identification of a MIS 6 age (c. 180 ka) Icelandic tephra within NE Atlantic sediments: a new potential chronostratigraphic marker2014In: Gas Generation and Migration in Deep Geological Radioactive Waste Repositories / [ed] R. P. Shaw, London: The Geological Society Publishing House, 2014, Vol. 398, p. 65-80Chapter in book (Refereed)

The incidence of volcanic ash (tephra) within marine sediments serves as a useful stratigraphic marker and tool for correlation. In addition, where an independent age estimate exists, tephra layers can provide a means of dating the sediments themselves. Here we present a geochemically characterized, size sorted tephra layer within Marine Isotope Stage (MIS) 6, most likely resulting from primary air-fall from an Icelandic volcanic source. This tephra layer is tentatively correlated to the Kerlingarfjoll volcanic system using major element geochemistry. The ash layer has an interpolated age of 181 +/- 6 ka based on the age model for MD04-2822. We briefly review the occurrence of silicic tephra in the North Atlantic region from MIS 7 to MIS 5e inclusive and find potential correlatives to the MD04-2822 MIS 6 ash layer in the Norway Basin and Irminger Sea.

• 20. Holmes, Naomi
Stockholm University, Faculty of Science, Department of Physical Geography.
Climatic variability during the last millennium in Western Iceland from lake sediment records2016In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 26, no 5, p. 756-771Article in journal (Refereed)

The aim of this research was to create a decadal-scale terrestrial quantitative palaeoclimate record for NW Iceland from lake sediments for the last millennium. Geochemical, stable isotope and chironomid reconstructions were obtained from a lake sequence constrained by tephra deposits on the Snaefellsnes peninsula, western Iceland. Obtaining a quantitative record proved problematic, but the qualitative chironomid record showed clear trends associated with past summer temperatures, and the sedimentological records provided evidence for past changes in precipitation, mediated through catchment soil in-wash. When the full range of chronological uncertainty is considered, four clear phases of climatic conditions were identified: (1) a relatively warm phase between AD 1020 and 1310; (2) a relatively stable period between AD 1310 and 1510, cooler than the preceding period but still notably warmer than the second half of the millennium; (3) a consistent reduction of temperatures between AD 1560 and 1810, with the coolest period between AD 1680 and 1810; and (4) AD 1840-2000 has temperatures mainly warmer than in the preceding two centuries, with a rising trend and increased variability from c. AD 1900 onwards. The reconstructions show clearly that the first half of the millennium experienced warmer climatic conditions than the second half, with a return to the warmer climate only occurring in the last c. 100 years. Much of the variability of the chironomid record can be linked to changes in the North Atlantic Oscillation (NAO). The reconstructions presented can track low-frequency and long-term trends effectively and consistently but high-resolution and calibrated quantitative records remain more of a challenge - not just in finding optimal sedimentary deposits but also in finding the most reliable proxy. It is this that presents the real challenge for Holocene climate reconstruction from this key area of the North Atlantic.

• 21.
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Physical Geography.
Compositions of glass in proximal tephras from eruptions in the Azores archipelago and their links with distal sites in Ireland2017In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 40, p. 120-128Article in journal (Refereed)

The Azores archipelago is one of the most active volcanic areas in the North Atlantic region, with approximately 30 eruptions during the last 600 years. The geochemical composition of associated tephra-derived glass is, however, not well characterized. This study presents major element compositions of glass shards from five major eruptives on the Azores: a trachybasaltic eruptive on the island of Faial (Capelinhos AD, 1957) and four explosive trachytic eruptives on the island of Sao Miguel (Fogo A c. 5600 cal yrs. BP, Sete Cidades c. AD 1440, Fogo AD 1563 and Furnas AD 1630). The major element compositions suggest that tephras from three active stratovolcanoes on Sao Miguel, Sete Cidades, Fogo and Furnas, can be distinguished from one another using bi-plots of FeOtot vs. TiO2 and FeOtot vs. CaO. Late Holocene tephras found on Ireland have previously been attributed to eruptions occurring on Jan Mayen but possess a strong geochemical similarity to proximal tephras from the Azores, especially those from the Furnas volcano. The similarity of the proximal tephras on Sao Miguel, especially Furnas AD 1563 and Furnas AD 1630 and distal tephras in Ireland is demonstrated by strong similarity coefficients (>0.95) and the closeness of major element composition. The dominant wind direction over the Azores is favourable for tephra dispersal to western Europe and we suggest that at least three tephras found in Ireland were erupted from the Furnas volcano, and that trachytic tephras erupted from explosive eruptions on Sao Miguel have a potential to contribute to the construction of a European-wide tephrostratigraphic framework.

• 22. Kalliokoski, Maarit
Stockholm University, Faculty of Science, Department of Physical Geography.
Rhyolitic and dacitic component of the Askja 1875 tephra in southern and central Finland: first step towards a Finnish tephrochronology2019In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 34, no 1, p. 29-39Article in journal (Refereed)

Tephra from Icelandic volcanic eruptions is frequently dispersed to northern Europe, but so far tephra has not been detected in Finnish sedimentary records. We report the first finding of a cryptotephra layer in southern and central Finland. Sediment samples from five lakes and 10 peatlands, most of them located in the tephra fallout zone of the Hekla 1947 eruption, were investigated for the presence of cryptotephra to assess the potential for tephrochronology in Finland. Tephra shards were extracted from their host matrix and electron probe microanalysis was conducted on single shards for geochemical characterization. Our results confirm the presence of Askja 1875 tephra in Finland, thus extending the known dispersal area of the Askja 1875 tephra eastwards. Most of the shards are rhyolitic, but a minor concentration of tephra with dacitic composition forms a narrow dispersal zone extending from Sweden to southern Finland. This zone possibly represents the main dispersal axis of the tephra in the distal area. Our results suggest that Finnish environmental research could benefit greatly from adding tephrochronology to the array of dating methods commonly used. Additionally, the absence of Hekla 1947 tephra in the previously inferred fall-out zone is an important result indicating the complexity of tephra deposition and preservation.

• 23. Kastner, Stephanie
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Reconstructing 2000 years of hydrological variation derived from laminated proglacial sediments of Lago del Desierto at the eastern margin of the South Patagonian Ice Field, Argentina2010In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 72, p. 201-214Article in journal (Refereed)
• 24.
Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory (NEO), Greece.
Stockholm University, Faculty of Science, Department of Geological Sciences. Navarino Environmental Observatory (NEO), Greece. Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory (NEO), Greece. Stockholm University, Faculty of Science, Department of Physical Geography.
Climate changes in the Eastern Mediterranean over the last 5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons2019In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 175, p. 36-51Article in journal (Refereed)

This research aims to improve the knowledge of the mid to late Holocene climate changes and the underlying drivers in the eastern Mediterranean. We focus on the Peloponnese peninsula, SW Greece, characterized by a W-E rainfall/temperature gradient and a strong climate-sensitivity to shifts in the large-scale atmospheric patterns. A radiocarbon-dated sediment core, taken from the ancient Lake Lerna, a former lake in NE Peloponnese, was analyzed for distribution and hydrogen isotope (δD) composition of n-alkanes and bulk organic geochemistry (δ13C, TOC). The predominantly macrophyte (submerged/floating)-derived δD23 profile exhibits the largest long-term fluctuation in the record and co-varies with δD of long-chain n-alkanes providing evidence for precipitation and temperature changes over the last 5000 years. The Lerna δD23 signal is sometimes in agreement with other n-alkane δD records from SW Peloponnese indicating wetter conditions in the peninsula at ca 5000–4600, ca 4500–4100, ca 3000–2600 (more unstable in SW) and after ca 700 cal BP with drier periods at ca 4100–3900 and ca 1000–700 cal BP. Conversely, a NE-SW climate see-saw is revealed at ca 4600–4500, ca 3200, ca 2600–1800, and ca 1200–1000 cal BP when the δD23 Lerna exhibits more positive trends (drier in NE) with a reversal at ca 3900–3300, ca 3200–3000 and ca 1800–1300 cal BP. These opposing and sometimes similar signals between NE and SW Peloponnese can be explained by the relative dominance of high-latitude atmospheric patterns over the peninsula. A similar signal would be expected when the North Atlantic Oscillation (NAO) exerts the main control with NAO (+) creating conditions of reduced moisture. The dipole pattern is likely driven by shifts in North Sea–Caspian Atmospheric pattern (NCP), which account for the present-day regional climate variability with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The Asian monsoonal system likely has an additional impact on the δD variabilities through influencing the summer temperatures. There is a consistency between the Peloponnesian δD signals and monsoonal records after ca 4000 cal BP confirming the actualistic models. Strong monsoonal periods coincide with cooler summers (lower δD values) in Lerna, due to the northerly winds, the Etesians. On the contrary, SW Peloponnese is dominated by warmer conditions during the same periods as the area is located on the lee side of the mountain and highly influenced by the adiabatic warming associated with the subsidence over the Eastern Mediterranean.

• 25. Kliem, P.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Magnitude, geomorphologic response and climate links of lake level oscillations at Laguna Potrok Aike, Patagonian steppe (Argentina)2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 131-146Article in journal (Refereed)

Laguna Potrok Aike is a large maar lake located in the semiarid steppe of southern Patagonia known for its Lateglacial and Holocene lake level fluctuations. Based on sedimentary, seismic and geomorphological evidences, the lake level curve is updated and extended into the Last Glacial period and the geomorphological development of the lake basin and its catchment area is interpreted. Abrasion and lake level oscillations since at least similar to 50 ka caused concentric erosion of the surrounding soft rocks of the Miocene Santa Cruz Formation and expanded the basin diameter by approximately 1 km. A high lake level and overflow conditions of the lake were dated by luminescence methods and tephra correlation to the early Lateglacial as well as to similar to 45 ka. The lowest lake level of record occurred during the mid-Holocene. A further lake level drop was probably prevented by groundwater supply. This low lake level eroded a distinct terrace into lacustrine sediments. Collapse of these terraces probably caused mass movement deposits in the profundal zone of the lake. After the mid-Holocene lake level low stand a general and successive transgression occurred until the Little Ice Age maximum; i.e. ca 40 m above the local groundwater table. Frequent lake level oscillations caused deflation of emerged terraces only along the eastern shoreline due to prevailing westerly winds. Preservation of eolian deposits might be linked to relatively moist climate conditions during the past 2.5 ka. Precisely dated lake level reconstructions in the rain-shadow of the Andes document high Last Glacial and low Holocene lake levels that could suggest increased precipitation during the Last Glacial period. As permafrost in semiarid Patagonia is documented and dated to the Last Glacial period we argue that the frozen ground might have increased surficial runoff from the catchment and thus influenced the water balance of the lake. This is important for investigating the glacial to Holocene latitudinal shift and/or strengthening of the Southern Hemispheric Westerlies by using lake level reconstructions as a means to assess the regional water balance. Our interpretation explains the contradiction with investigations based on pollen data indicating drier climatic conditions for the Last Glacial period.

• 26. Kliem, Pierre
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Lithology, radiocarbon chronology and sedimentological interpretation of the lacustrine record from Laguna Potrok Aike, southern Patagonia2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, p. 54-69Article in journal (Refereed)

The 106 m long composite profile from site 2 of ICDP expedition 5022 (PASADO) at Laguna Potrok Aike documents a distinct change in sedimentation patterns from pelagic sediments at the top to dominating mass movement deposits at its base. The main lithological units correspond to the Holocene, to the Lateglacial and to the last glacial period and can be interpreted as the result of distinct environmental variations. Overflow conditions might have been achieved during the last glacial period, while signs of desiccation are absent in the studied sediment record. Altogether, 58 radiocarbon dates were used to establish a consistent age-depth model by applying the mixed-effect regression procedure which results in a basal age of 51.2 cal. ka BP. Radiocarbon dates show a considerable increase in scatter with depth which is related to the high amount of reworking. Validation of the obtained chronology was achieved with geomagnetic relative paleointensity data and tephra correlation.

• 27. Kokfelt, U.
Stockholm University, Faculty of Science, Department of Physical Geography.
Diatom blooms and associated vegetation shifts in a subarctic peatland: responses to distant volcanic eruptions?2016In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 31, no 7, p. 723-730Article in journal (Refereed)

We test the hypothesis that rich occurrences of diatoms observed at transitions between major peat units representing different vegetation communities in a peat sequence from subarctic northern Sweden reflect responses to acid deposition from the Samalas AD 1257 and Laki AD 1783/1784 eruptions. We observe sudden changes in the mire ecosystem and thereby in the trophic status and biogeochemical cycling of the peatland. Both the eruptions are known to have been associated with significant acid deposition events and climatic anomalies, as recorded in polar ice cores. To test the hypothesis, new chronological analyses and age modelling were applied to existing biogeochemical and biological records from the peat sequence. This approach yielded modelled age ranges of AD 1239-1284 (1s)/AD 1210-1303 (2s) (median: AD 1260) and AD 1674-1795 (1s)/AD 1665-1875 (2s) (median AD 1743), respectively, for the stratigraphic transitions. Hence, the modelled age ranges bracket the ages of the eruptions in question and the hypothesis could therefore not be rejected. Impacts of acid deposition from the eruptions are assumed to have caused instant acidification, vegetation damage, increased nutrient cycling and blooms of opportunistic epiphytic diatoms. In addition, cooling may have contributed to vegetation changes through permafrost inception, frost heave and thereby altered hydrological conditions.

• 28.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Geological Sciences.
Recommendations for using XRF core scanning as a tool in tephrochronology2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 3, p. 371-375Article in journal (Refereed)

X-ray fluorescence (XRF) core scanning is a relatively new arrangement of a classic analytical technique which allows for non-destructive, in situ XRF analysis of sediment cores from submillimetre resolution upwards. In this contribution we explore the use of XRF core scanning for tephrochronology based on the analysis of three gyttja-rich sediment cores from the Faroe Islands. Using a combination of optical and radiographic images, analytical parameters and elemental profiles (Si, K, Ca, Ti, Mn, Fe, Sr and Zr), higher concentration basaltic tephra layers (>1000 shards/cm3) were positively identified. The XRF core scanning did not capture the lower concentration (<850 shards/cm3) rhyolitic layers found in the core. The elemental data generated for the detected tephra layers using XRF core scanning was not comparable to individual shard analysis by electron microprobe. We recommend using XRF core scanning for tephra screening in order to localize depths for high-resolution subsampling and to avoid depths where sediment mixing has caused tailing/mixing of the tephra signal. At the studied site the basaltic Saksunarvatn ash as well as a tephra belonging to the Askja-S/10 ka eruption were identified.

• 29. Langdon, P. G.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 16502011In: Quaternary Research, ISSN 0033-5894, E-ISSN 1096-0287, Vol. 75, no 3, p. 451-460Article in journal (Refereed)

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkisholmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683-1710. AD 1765-1780 and AD 1890-1917, with relative drops in summer temperatures in the order of 1.5-2 degrees C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5-2 degrees C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjokull). (C) 2010 University of Washington.

• 30.
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
The Laacher See Tephra discovered in southernmost Sweden2018In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 33, no 5, p. 477-481Article in journal (Refereed)

We present the first geochemically confirmed finding of the Laacher See Tephra (LST) on the Swedish mainland, now the northernmost extension of the LST. Sediments were sampled at the Korslattamossen fen, southernmost Sweden, and a high-concentration cryptotephra occurrence (>65000shardscm(-3)) of the LST was found in a sequence of calcareous gyttja. Tephra identification was confirmed by geochemical analysis using field-emission electron probe microanalysis and through comparison of the results with published LST data from proximal sites and distal sites north-east of Laacher See. The LST has previously been divided into eruption phases suggested to have spread in several dispersal fans, but it was not possible to confidently determine the phase of the tephra here closer than to the MLST or ULST. The finding of the LST presented here further strengthens the potential of tephrochronological studies in the south Scandinavian region.

• 31.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
A Lateglacial-early Holocene tephrochronology for SW Sweden2013In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 42, no 3, p. 544-554Article in journal (Refereed)

Four cores from southwestern Sweden are presented together with their tephra geochemistry. Two cryptotephra horizons were confirmed geochemically in the cores, the Vedde Ash and the Hässeldalen Tephra. The Lateglacial Hässeldalen Tephra (11 360–11 300 cal. a BP) offers great potential as a regional isochrone to add a new degree of certainty to the deglaciation chronology of southern Sweden, including the extent of glacial Lake Bolmen. In addition, the geographical distribution of the Hässeldalen Tephra has recently been extended outside of Sweden, making it an important time-marker horizon in northern Europe. There are potential difficulties, however. Proper identification of the actual isochrone is complicated by the vertical pattern of shard distribution, which could be the result of several eruptive events, as well as by the fact that shards from the 10-ka Askja horizon (10 500–10 350 cal. a BP) were found in close stratigraphical proximity. The geochemical data presented are the result of improved EPMA methodology, which significantly reduces sodium mobilization. The results therefore have slightly altered values, which has consequences for classifying new finds when they are compared with previous data for geochemically similar tephras. Finally, potential indications of the Borrobol/Penifiler horizon are presented, although the existence of the horizon could not be confirmed geochemically. This highlights the need to retrieve cores from different locations within a basin based on an analysis of basin morphology if horizons are to be located.

• 32.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK). Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Late Glacial tephra horizons in Southern Sweden2010In: International Field Conference and Workshop on Tephrochronology, Volcanism and Human Activity: Active Tephra in Kyushu, 2010, 2010, p. 54-Conference paper (Other academic)
• 33.
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Physical Geography.
Revisiting the Borrobol Tephra2016In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 45, no 4, p. 629-643Article in journal (Refereed)

The Borrobol Tephra has been identified as one of the key tephra horizons for the Lateglacial time period but it also exemplifies many of the promises and problems of tephrochronology. Additional horizons with similar major element composition and approximately the same age have been identified around the North Atlantic region. Here, we revisit the Borrobol Tephra identified at two Swedish sites, Hasseldala port and Skallahult, and also the Borrobol type-site in Scotland. We present the first set of minor element data (trace and rare earth analyses) along with new analyses of major elements from these three sites. The analysed minor and the trace elements have a similar signature; however, the glass from the Scottish type-site seems to imply two populations. To answer if this truly represents two populations, or if it reflects magmatic differentiation additional and larger data sets of minor elements are needed. The new major elements are compared to other Borrobol-type tephras identified in the North Atlantic region. Our results are in line with earlier investigations, which showed no differences in major elements. Further, comparison of minor elements from glass analyses from our sites with those for eruptions associated with Icelandic central volcanoes implies an Icelandic origin for the Borrobol-type tephras.

• 34.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Univ Copenhagen, Dept Geosci & Nat Resource Management.
A Late Younger Dryas-Early Holocene tephrostratigraphy for Fosen, Central Norway2013In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 28, no 8, p. 803-811Article in journal (Refereed)

A number of rapid climate oscillations occur during the Lateglacial-Early Holocene, 15-8 ka BP period and a well-developed tephrostratigraphy in association with these oscillations increases the possibilities to correlate climate archives around the North Atlantic. This paper presents a tephrostratigraphy for Fosen peninsula, Central Norway. Both the Vedde Ash ca.12.1 ka BP and the Saksunarvatn Ash approximate to 10.3 ka BP are important isochrones for correlations of Late Quaternary palaeoenvironmental records in the North Atlantic region and have been assigned ages in GICC05. Beside these tephras we have also identified a new tephra, the Fosen Tephra, with a Borrobol-type geochemistry that occurs above both the Vedde Ash and the Saksunarvatn Ash with an age approximate to 10.2 ka BP. Several tephras with Borrobol-type geochemistry have been identified around the North Atlantic. One group is the Borrobol/Penifiler tephras dated to Greenland Interstadial-1 and another group is dated to the Early Holocene. We suggest that some of the Early Holocene Borrobol-type tephras and the Fosen Tephra may actually be the same layer. If so, the Fosen Tephra is spread over a large area of the North Atlantic and has the potential to become an important marker for short-term climate variability in Scandinavia and in the northern hemisphere.

• 35.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Tephra horizons contemporary with short early Holocene climate fluctuations: New results from the Faroe Islands2011In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 246, p. 157-167Article in journal (Refereed)

The climate of the North Atlantic region was relatively unstable after the last Termination.At least three cold events superimposed upon a general warming took place during the earliest part of the Holocene: the Preboreal oscillation (11,300-11,100 cal. yr BP), the Erdalen event (10,300-10,200 cal. yr BP) and the 9.3 ka BP event. New results from the Faroe Islands could give the opportunity to test hypothesis regarding synchronous or non-synchronous response to climate forcing in the North Atlantic area. Seven tephra layers have been identified in a palaeo-lake core from the island of Sandoy on the Faroe Islands, dated to 11,700-9750 cal. yr BP. Three tephras were found below the visible Saksunarvatn Ash (ca. 10,300 cal. yr BP) and three above it. The rhyolitic Hässeldalen Tephra dated to ca. 11,350 cal. yr BP and previously only found in Sweden, a double-peaked basaltic tephra from the Veidivötn-Bárdarbunga volcanic system at the same depth and another rhyolitic tephra from the Askja volcanic system dated to ca. 10,400 cal. yr BP, tentatively correlated with the Askja-S/10 ka Tephra. Askja-S has earlier been found in large parts of the terrestrial North Atlantic region but not on the Faroe Islands. The three tephra layers above the Saksunarvatn Ash are all unreported tephras. A rhyolitic tephra with an age of ca. 10,200 cal. yr BP, that is still unidentified, one silicic layer from the Katla volcano (SILK) and a tephra correlated with the Torfajökull volcanic system, both with an estimated age of ca. 9700 cal. yr BP. These tephra horizons provide a unique potential to link not only the terrestrial records from NW Europe but alsotocorrelate them to ice-cores from Greenland. The findings of the Hässeldalen Tephra, the Askja-S Tephra and the new tephra correlating toTorfajökullvolcanic systemcould become important time-markers for correlating the Preboreal Oscillation and the Erdalen event around the North Atlantic region.

• 36. Macleod, A.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Lateglacial cryptotephra detected within clay varves in Ostergotland, south-east Sweden2014In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 29, no 7, p. 605-609Article in journal (Refereed)

Here we present a 710-year-long floating varve record from south-east Sweden. Tephra analyses confirm the presence of the rhyolitic Vedde Ash preserved within two consecutive varve years, confirming the Younger Dryas age of the varve series. This permits, for the first time, direct correlation of Swedish varved clay with other records of equivalent resolution which also preserve the Vedde Ash and demonstrates that the potential exists to independently date the Swedish Timescale. This discovery will allow direct comparison of rates, timing and duration of key climatic events across Europe and the North Atlantic region in records of equivalent resolution.

• 37.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Risberg, JanStockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.Wastegård, StefanStockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Quaternary stratigraphy, vegetation dynamics and human impact - current research projects and new results. Studies in honour of Ann-Marie Robertsson2007Conference proceedings (editor) (Refereed)
• 38.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Quaternary stratigraphy, vegetation dynamics and human impact - current research projects and new results. Studies in honour of Ann-Marie Robertsson2007In: GFF, Vol. 129, no 4, p. 273-276Article in journal (Other academic)
• 39. Monteath, A. J.
Stockholm University, Faculty of Science, Department of Physical Geography.
Evidence for distal transport of reworked Andean tephra: Extending the cryptotephra framework from the Austral volcanic zone2019In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 51, p. 64-71Article in journal (Refereed)

Cryptotephra deposits (non-visible volcanic ash beds) may extend thousands of kilometres and provide valuable chronological isochrons. Here, we present a Lateglacial-early Holocene (c. 16,500 cal yr BP-6000 cal yr BP) tephrostratigraphy from Hooker's Point, East Falkland, South Atlantic. This period spans the last glacial termination across the southern mid-latitudes, a time period during which the palaeoenvironmental record is poorly resolved in southern South America and the South Atlantic. The development of a regional tephrostratigraphy will provide chronological constraint for palaeoenvironmental records from this period. Two cryptotephra deposits from Hooker's Point are linked with Mt. Burney, including the early-Holocene MB1 tephra, while a third is likely to be derived from the R-1 eruption of Reclus volcano. The high shard abundance of these cryptotephra deposits suggests they extend further into the Southern Ocean, and may act as regional stratigraphic markers during the Lateglacial. Further peaks in shard abundance are composed of detrital glass (tephra not derived from primary air fall events), with mixed shard morphologies and geochemically heterogeneous glass populations. This detrital glass is likely to have been repeatedly reworked by wind action in the Patagonian Steppe before final deposition in the Falkland Islands. The high abundance of detrital glass in the Hooker's Point sequence suggests long distance transport of reworked tephra is common in this region, and highlights the need to carefully analyse cryptotephra deposits in order to avoid incorrectly describing reworked tephra as new isochrons. A temporal pattern of shard abundance is apparent in the Hooker's Point sequence with a reduction/absence of shards between 14,300-10,500 cal yr BP.

• 40. Monteath, Alistair J.
Stockholm University, Faculty of Science, Department of Physical Geography.
Effects of the peat acid digestion protocol on geochemically and morphologically diverse tephra deposits2019In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 34, no 4-5, p. 269-274Article in journal (Refereed)

Tephra shards for electron probe microanalysis are most efficiently extracted from peat using acid digestion, which removes organic material that hinders density separation methods. However, strong acids are known to alter glass chemical compositions, and several studies have examined how acid digestion affects rhyolitic volcanic glass. The focus on rhyolitic tephra in these studies leaves considerable uncertainty, as the dissolution rates of natural glasses (including tephra) are determined by the chemical composition and surface area/volume ratio, both of which vary in tephra deposits. Here, we use duplicate samples of basaltic, trachydacitic and rhyolitic tephra to examine physical and geochemical alteration following acid digestion. Scanning electron microscope imagery reveals no discernible degradation of glass surfaces, and electron probe microanalysis results from duplicate samples are statistically indistinguishable. These findings suggest the acid digestion protocol for organic peats does not significantly alter glass geochemistry regardless of shard morphologies or geochemical compositions.

• 41.
Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Geological Sciences. Columbia University, USA; Bjerknes Centre for Climate Research, Norway. Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Geological Sciences.
The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 4, p. 303-316Article in journal (Refereed)

The caldera-forming eruption of the Aniakchak volcano in the Aleutian Range on the Alaskan Peninsula at 3.6 cal kyr BP was one of the largest Holocene eruptions worldwide. The resulting ash is found as a visible sediment layer in several Alaskan sites and as a cryptotephra on Newfoundland and Greenland. This large geographic distribution, combined with the fact that the eruption is relatively well constrained in time using radiocarbon dating of lake sediments and annual layer counts in ice cores, makes it an excellent stratigraphic marker for dating and correlating mid-late Holocene sediment and paleoclimate records. This study presents the outcome of a targeted search for the Aniakchak tephra in a marine sediment core from the Arctic Ocean, namely Core SWERUS-L2-2-PC1 (2PC), raised from 57m water depth in Herald Canyon, western Chukchi Sea. High concentrations of tephra shards, with a geochemical signature matching that of Aniakchak ash, were observed across a more than 1.5m long sediment sequence. Since the primary input of volcanic ash is through atmospheric transport, and assuming that bioturbation can account for mixing up to ca. 10 cm of the marine sediment deposited at the coring site, the broad signal is interpreted as sustained reworking at the sediment source input. The isochron is therefore placed at the base of the sudden increase in tephra concentrations rather than at the maximum concentration. This interpretation of major reworking is strengthened by analysis of grain size distribution which points to ice rafting as an important secondary transport mechanism of volcanic ash. Combined with radiocarbon dates on mollusks in the same sediment core, the volcanic marker is used to calculate a marine radiocarbon reservoir age offset Delta R = 477 +/- 60 years. This relatively high value may be explained by the major influence of typically carbon-old Pacific waters, and it agrees well with recent estimates of Delta R along the northwest Alaskan coast, possibly indicating stable oceanographic conditions during the second half of the Holocene. Our use of a volcanic absolute age marker to obtain the marine reservoir age offset is the first of its kind in the Arctic Ocean and provides an important framework for improving chronologies and correlating marine sediment archives in this region. Core 2PC has a high sediment accumulation rate averaging 200 cm kyr(-1) throughout the last 4000 years, and the chronology presented here provides a solid base for high-resolution reconstructions of late Holocene climate and ocean variability in the Chukchi Sea.

• 42. Rasmussen, Tine L.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Atlantic surface water inflow to the Nordic seas during the Pleistocene-Holocene transition (mid-late Younger Dryas and Pre-Boreal periods, 12 450-10 000 a BP)2011In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 26, no 7, p. 723-733Article in journal (Refereed)

The inflow of Atlantic Water to the Nordic seas from mid-late Younger Dryas to earliest Holocene (12 450-10 000 a BP) is reconstructed on the basis of a high-resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice-rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid-late Younger Dryas and Pre-Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east-west temperature gradient across the Faroe-Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near-continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level.

• 43.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Shifts in precipitation during the last millennium in northern Scandinavia from lacustrine isotope records2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, p. 22-34Article in journal (Refereed)

Here we present delta P-18(diatom) data from two high-latitude lakes; one has short residence time and a water isotopic composition (delta O-18(lake)) that fluctuate due to seasonal variations in precipitation and temperature, and the other has delta O-18(lake) that is influenced by longer lake water residence times and evaporation. The delta O-18(diatom) records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from delta O-18(diatom) between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation.

• 44. Smith, Rebecca E.
Stockholm University, Faculty of Science, Department of Physical Geography.
Refining the Late Quaternary tephrochronology for southern South America using the Laguna Potrok Aike sedimentary record2019In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 218, p. 137-156Article in journal (Refereed)

This paper presents a detailed record of volcanism extending back to similar to 80 kyr BP for southern South America using the sediments of Laguna Potrok Aike (ICDP expedition 5022; Potrok Aike Maar Lake Sediment Archive Drilling Project - PASADO). Our analysis of tephra includes the morphology of glass, the mineral componentry, the abundance of glass-shards, lithics and minerals, and the composition of glass-shards in relation to the stratigraphy. Firstly, a reference database of glass compositions of known eruptions in the region was created to enable robust tephra correlations. This includes data published elsewhere, in addition to new glass-shard analyses of proximal tephra deposits from Hudson (eruption units H-1 and H-2), Aguilera (A(1)), Reclus (R-1, R2-3), Mt Burney (MB1, MB2, MBx, MB1910) and historical Lautaro/Viedma deposits. The analysis of the ninety-four tephra layers observed in the Laguna Potrok Aike sedimentary sequence reveals that twenty-five tephra deposits in the record are the result of primary fallout and are sourced from at least three different volcanoes in the Austral Andean Volcanic Zone (Mt Burney, Reclus, Lautaro/Viedma) and one in the southernmost Southern Volcanic Zone (Hudson). One new correlation to the widespread H-1 eruption from Hudson volcano at 8.7 (8.6-9.0) cal ka BP during the Quaternary is identified. The identification of sixty-five discrete deposits that were predominantly volcanic ashes (glass and minerals) with subtle characteristics of reworking (in addition to three likely reworked tephra, and one unknown layer) indicates that care must be taken in the analysis of both visible and invisible tephra layers to decipher their emplacement mechanisms.

• 45. Stanton, Tania
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Validating a Swedish varve chronology using radiocarbon, palaeomagnetic secular variation, lead pollution history and statistical correlation2010In: Quaternary Geochronology, ISSN 1871-1014, Vol. 5, p. 611-624Article in journal (Refereed)

We use statistical correlation of palaeomagnetic secular variation (PSV) curves from a varved Holocene lake sediment sequence in west central Sweden (Lake Kälksjön) against those of a Fennoscandian master stack (FENNOSTACK) to correct for an apparent error in the varve chronology. Additional correlation between a lead pollution-derived chronology for the last 2000 years corroborates the PSV results. Use of the FENNOSTACK palaeomagnetic master curve reveals no significant difference in duration between large-scale features from 2500 to 8000 cal. yrs BP. Statistical correlation, however, implies that 270 years are missing from the younger part (<1000 cal. yrs BP) of the varve chronology, and that there is an overestimation by approximately 230 years in the number of varves counted in the early Holocene (>8000 cal. yrs BP). A similar comparison between the PSV-determined ages and calibrated bulk radiocarbon ages suggests that the sediments of mid-Holocene age contain substantial amounts of old carbon, probably of soil origin, which causes bulk sediment-calibrated mean 14C ages to be up to 850 years older than the corrected varve chronology, which extends to 9193 ± 186 cal. yrs BP. This study highlights both the use of statistical correlation as a technique for detecting errors between chronologies, and the importance of validating incremental chronologies with more than one independent method.

• 46. Stivrins, Normunds
Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Department of Physical Geography.
Detection of the Askja AD 1875 cryptotephra in Latvia, Eastern Europe2016In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 31, no 5, p. 437-441Article in journal (Refereed)

We report the first geochemically confirmed findings of the Askja volcano (Iceland) AD 1875 eruption cryptotephra in Eastern Europe. The cryptotephra finding in Latvia is the easternmost finding of the Askja AD 1875 so far, providing an important time marker in the sediments. Although low concentrations of Askja AD 1875 rhyolitic glass shards were recorded, our findings suggest the possibility of also tracing other historical cryptotephras in lacustrine and peat sediments in Eastern Europe. We use the Askja AD 1875 tephra isochrone to synchronize pollen data of human activities, i.e. rye (Secale cereale) cultivation. Our comparison of Secale pollen from two sites reveals that there were minor dissimilarities in the timing of highest rye cultivation, and that a synchronous decrease of rye cultivation occurred at both sites few years after the Askja eruption at AD 1875.

• 47.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Department of Geology and Geochemistry. Department of Geology and Geochemistry.
Age, origin and significance of a new middle MIS 3 tephra horizon identified within a long-core sequence from Les Echets, France2008In: Boreas, Vol. 37, no 434-443Article in journal (Refereed)

A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c. 2 000-45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel; however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard-Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords.

• 48.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Late Quaternary tephrochronology of Sweden - state of the art2010In: International Field Conference and Workshop on Tephrochronology, Volcanism and Human Activity: Active tephra in Kyushu, 2010, 2010, p. 95-Conference paper (Other academic)
• 49.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
A new mid-Holocene tephra in central Sweden2009In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 131, no 4, p. 293-297Article in journal (Refereed)

A mid Holocene tephra, LBA-2 has been found in a peat bog in central Sweden. Geochemical analyses suggest an origin in an evolved volcanic centre, most likely the Snæfellsnes volcanic centre in western Iceland. The geochemistry of the LBA-2 tephra is similar to the youngest of three silicic tephra layers from Snæfellsjökull, Sn-1 dated to 1780 cal yr BP. However, wiggle-match dating indicates an age of 3550-3650 cal yr BP, close in age to the Hekla-S/Kebister tephra (3720 cal yr BP), previously found in several sites in Scandinavia. Detailed geochemical analyses and dating is lacking for the mid Holocene Sn-2 tephra in Iceland but it is likely that the geochemical composition is similar as the Sn-1 tephra. The LBA-2 tephra is tentatively correlated with the Sn-2 tephra and we also suggest that the ‘x’ tephra layer (ca 3500 BP) found in the Dyngjufjöll area, central Iceland (Sigvaldason et al. 1992) can be correlated with the Sn-2 tephra.

• 50.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Manchester Metropolitan Univ, Sch Sci & Environm, Manchester, England.
Distal tephrochronology of NW Europe - the view from Sweden2012In: Jökull: Journal of The Glaciological and Geological Societies of Iceland, ISSN 0449-0576, Vol. 62, p. 73-80Article in journal (Refereed)

Sigurdur Thorarinsson has inspired generations of tephrochronologists. In his thesis in 1944 he outlined the prospect of finding ash from some of the major Icelandic eruptions in peat bogs in Scandinavia. Since Christer Persson's pioneering work in the 1960s, more than 15 tephra horizons have been identified in distal peat and sediment sequences in Sweden. The most widespread tephra from the Last Glacial-Interglacial transition (LGIT, ca. 15-9 ka BP) is the rhyolitic phase of the Vedde Ash (ca. 12.1 ka BP) which has been found in several sites with lacustrine sediments and uplifted marine clays south of the Younger Dryas moraines. Two significant new additions to the LGIT tephrochronological frameworks of NW Europe are the Hasseldalen (ca. 11.3 ka BP) and Askja-S tephras (ca. 10.4 ka BP). The most significant mid to late Holocene isochrones in Sweden are Hekla-4 (ca. 4260 BP), Hekla-S/Kebister (ca. 3720 BP), Hekla-3 (ca. 3000 BP) and Askja-1875. Other layers have been identified in single sites and are so far less valuable as marker horizons, but are potentially important for the future.

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