70 research outputs found
Volcanism and the Greenland ice cores: A new tephrochronological framework for the last glacial-interglacial transition (LGIT) based on cryptotephra deposits in three ice cores
Get PDFChemical profiles from Greenland ice cores show that the frequency of volcanism was higher during the last glacial-interglacial transition (LGIT) and early Holocene, (17–9 ka b2k) than in any other period during the last 110 kyr. This increased frequency has partly been linked to climate-driven melting of the Icelandic ice sheet during the last deglaciation, with regional isostatic changes thought to alter mantle viscosity and lead to more eruptions. Our study is the first to construct a comprehensive tephrochronological framework from Greenland ice cores over the LGIT to aid in the reconstruction of volcanic activity over this period. The framework is based on extensive high-resolution sampling of three Greenland ice cores between 17.4 and 11.6 ka b2k and comprises a total of 64 cryptotephra deposits from the NGRIP, GRIP and NEEM ice cores. We show that many of these tephras are preserved within the core without an associated chemical signature in the ice, which implies that reconstructions of volcanism based solely on glacio-chemical indicators might underestimate the number of events. Single glass shards from each deposit were geochemically characterised to trace the volcanic source and many of these deposits could be correlated between cores. We show that the 64 deposits represent tephra deposits from 42 separate volcanic events, and of these, 39 are from Iceland, two from the north Pacific region (Japan and USA) and one has an unknown source. Six deposits can be correlated to terrestrial and/or marine tephra deposits in the Northern Hemisphere and the remaining 36 are unreported in other archives. We did not locate tephra from the compositionally distinctive Laacher See eruption (∼13 ka b2k) in our records. Combining our new discoveries with the previously published tephra framework, raises the number of individual tephra horizons found in Greenland ice over this interval to 50. This significantly improves the regional tephrochronological framework, our knowledge of the eruptive history of Iceland during the LGIT and provides new tephra constraints over key LGIT climate events. Consequentially, this framework can guide sampling strategies of future tephra studies in the terrestrial and marine realms aiming to link these records to the Greenland ice cores to assess regional climate synchroneity
Managing hyponatraemia in a patient with malignant melanoma: a case report
Get PDFWe report the case of a 46-year-old male with a known diagnosis of metastatic malignant melanoma who presented with hyponatraemia. The report details the challenges we faced in identifying the cause of his hyponatraemia and in attempting to reverse his electrolyte disturbance
A Holocene cryptotephra record from the Chukchi margin: the first tephrostratigraphic study in the Arctic Ocean
Get PDFDeveloping geochronology for sediments in the Arctic Ocean and its continental margins is an important but challenging task complicated by multiple problems. In particular, the Chukchi/Beaufort margin, a critical area for reconstructing paleoceanographic conditions in the Pacific sector of the Arctic, features widespread dissolution of calcareous material, which limits posibilities for radiocarbon chronology. In order to evaluate the untapped potential of tephrochronology for constraining the age of these sediments, we investigated a sediment core from the eastern Chukchi Sea margin for cryptotephra. The core was collected in the area of sediment focusing on the upper slope (Darby et al., 2009). Samples were taken from the upper sedimentary unit composed of homogenous, fine-grained mud inferred to represent marine environmental conditions of the last 8-9 ka. Based on this age estimate, the initial set of 36 samples has an average resolution of ~250 years. Freeze-dried samples (0.5 g) were treated with HCl, wet-sieved to obtain a 80-25-μm fraction, treated with 1% NaOH to disaggregate clay clumps, and separated at specific density between 2.3 and 2.5 g/cm3. Residues in all samples featured abundant shards of colorless volcanic glass with an admixture of brown shards in the lower part of the unit. Three apparent tephra peaks were identified in the upper part of the record. The electron microprobe analysis of individual shards from these peaks showed nearly identical chemical compositions indicative of the late-Holocene tephras of the Aniakchak volcano in southwestern Alaska (e.g., Kaufman et al., 2012). The glasses analyzed exhibit a continuous composition range from 55 to 77 wt% SiO2 overlapping with two major populations of Aniakchak glasses (andesitic and dacitic) and also including some intermediate compositions. We infer that the three tephra peaks identified correspond to the three prominent tephra layers investigated in lake deposits between Aniakchak and the core site and dated to ~0.4, 3.1, and 3.7 ka (Kaufman et al., 2012). Further detailed study of tephra distribution in the Chukchi margin cores is underway. Identification of distinct tephra peaks with the composition traceable to specific known eruptions provides a powerful, independent chronological tool, much needed for Arctic paleoceanography. The consistent presence of cryptotephra in the analyzed samples suggests its wide occurrence in at least the Chukchi margin sediments; studies from other Arctic shelves and basins are needed to understand the geographic pattern of tephra distribution in seafloor sediments from this part of the world.
Darby, D.A., Ortiz, J. Polyak, L., et al., 2009. The role of currents and sea ice in both slowly deposited central Arctic and rapidly deposited Chukchi-Alaskan margin sediments. Global Planet. Change 68, 58-72.
Kaufman, D.S., Jensen, B.J.L., Reyes, A.V., et al., 2012. Late Quaternary tephrostratigraphy, Ahklun Mountains, SW Alaska. J. Quatern. Sci. 27, 344–359
Extending the limits of the Borrobol Tephra to Scandinavia and detection of new early Holocene tephras
Get PDFAbstract Analyses of two infilled lakes in Blekinge, southeast Sweden, indicate the presence of at least three tephra horizons of Termination 1 and early Holocene age. Geochemical analyses confirm the presence of the Borrobol Tephra, the Askja Tephra (10,000 14 C yr B.P.), and one previously unreported tephra of Icelandic origin. Extending the limits of the Borrobol Tephra to Scandinavia illustrates that this ash is far more widespread than previously realized and is therefore, an important marker horizon for determining the rate and timing of the initial warming at the start of Greenland Interstade 1 (GI-1) within Europe. The relatively unknown Askja Tephra and the newly discovered Hässeldalen Tephra are stratigraphically placed at the Younger Dryas/Preboreal transition. This paper demonstrates the suitability and success associated with the extraction techniques for tracing microtephra horizons in areas distal to volcanic sources
Climatic variability during the last millennium in Western Iceland from lake sediment records
Get PDFThe 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 Snæfellsnes 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.
Keywords : iceland, palaeolimnology, chironomids, little ice age, medieval climate anomaly, north atlantic oscillatio
Identification of the Askja-S Tephra in a rare turlough record from Pant-y-Llyn, south Wales
Get PDFTephrochronology and especially crypto-tephrochronology is an established chronological technique employed in a range of depositional environments in Europe and beyond. During the late Quaternary, Icelandic cryptotephra deposits are widely found in palaeorecords across northern latitudes of Europe e.g. Scotland, Ireland, Norway, Sweden and the Faroe Islands but are sporadic in southerly latitudes as distance from Iceland increases. As yet, very few Icelandic cryptotephras have been identified in Wales or southern England which may well reflect the geographical limit of Icelandic tephra distribution. Here, however, we report the discovery of an Icelandic cryptotephra deposit within a sediment sequence retrieved from the Pant-y-Llyn turlough (Carmarthenshire, south Wales), the only known turlough in Britain. Turloughs are groundwater-fed ephemeral lakes associated with limestone bedrock and can accumulate sediments that may yield records suitable for palaeoreconstructions. A discrete peak of glass shards originating from the Askja-S eruption is identified in the sediment record. This discovery extends the distribution of this early Holocene eruption giving new insight into its dispersal patterns and also indicates that sedimentary sequences from sites in these more southerly latitudes are valuable repositories for ash preservation. Furthermore, its discovery within a carbonate-rich sequence provides a minimum age constraint on the timing of sediment accumulation and provides an alternative tool for what is typically a problematic dating environment
Geochemical ice-core constraints on the timing and climatic impact of Aniakchak II (1628 BCE) and Thera (Minoan) volcanic eruptions
Get PDFThis work was supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement 820047 to M.Si.), the Malcolm H. Wiener Foundation (Interdisciplinary Chronology of Civilizations Project to C.P.) and a UKRI Future Leader Fellowship (MR/S035478/1 to P.A).Decades of research have focused on establishing the exact year and climatic impact of the Minoan eruption of Thera, Greece (c.1680–1500 BCE). Ice cores offer key evidence to resolve this controversy, but attempts have been hampered by a lack of multi-volcanic event synchronization between records. In this study, Antarctic and Greenland ice-core records are synchronized using a double bipolar sulfate marker and calendar dates are assigned to each eruption revealed within the ‘Thera period’. From this global scale sequence of volcanic sulfate loading, we derive indications towards each eruption’s latitude and potential to disrupt the climate system. Ultra-fine sampling for sulfur isotopes and tephra conclusively demonstrate a colossal eruption of Alaska’s Aniakchak II as the source of stratospheric sulfate in the now precisely dated 1628 BCE ice layer. These findings end decades of speculation that Thera was responsible for the 1628 BCE event, and place Aniakchak II (52 ± 17 Tg S) and an unknown volcano at 1654 BCE (50 ± 13 Tg S) as two of the largest Northern Hemisphere sulfur injections in the last 4000 years. This opens possibilities to explore widespread climatic impacts for contemporary societies and, in pinpointing Aniakchak II, confirms that stratospheric sulfate can be globally distributed from eruptions outside the tropics. Dating options for Thera are reduced to a series of precisely dated, constrained stratospheric sulfur injection events at 1611 BCE, 1562-1555 BCE and c.1538 BCE which are all below 14 ± 5 Tg S, indicating a climatic forcing potential for Thera well below that of Tambora (1815 CE).Publisher PDFPeer reviewe
Traces of volcanic ash from the Mediterranean, Iceland and North America in a Holocene record from south Wales, UK
Get PDFA tephra record is presented for a sediment core from Llyn Llech Owain, south Wales, spanning the early‐ to mid‐Holocene. Seven cryptotephra deposits are discovered with three thought to correlate with known eruptions and the remaining four considered to represent previously undocumented events. One deposit is suggested to correlate with the ~6.9 cal ka bp Lairg A tephra from Iceland, whereas more distant sources are proposed as the origin for two of the tephra deposits. A peak of colourless shards in early‐Holocene sediments is thought to tentatively correlate with the ~9.6 cal ka bp Fondi di Baia tephra (Campi Flegrei) and a second cryptotephra is tentatively correlated with the ~3.6 cal ka bp Aniakchak (CFE) II tephra (Alaska). The Fondi di Baia tephra has never been recorded beyond proximal sites and its discovery in south Wales significantly extends the geographical distribution of ash from this eruption. The remaining four cryptotephra deposits are yet to be correlated with known eruptions, demonstrating that our current understanding of widespread tephra deposits is incomplete. This new tephra record highlights the potential for sites at more southerly and westerly locations in northwest Europe to act as repositories for ash from several volcanic regions
Tracing marine cryptotephras in the North Atlantic during the last glacial period: Improving the North Atlantic marine tephrostratigraphic framework
Get PDFTephrochronology is increasingly being recognised as a key tool for the correlation of disparate palaeoclimatic archives, underpinning chronological models and facilitating climatically independent comparisons of climate proxies. Tephra frameworks integrating both distal and proximal tephra occurrences are essential to these investigations providing key details on their spatial distributions, geochemical signatures, eruptive sources as well as any available chronological and/or stratigraphic information. Frameworks also help to avoid mis-correlation of horizons and provide important information on volcanic history. Here we present a comprehensive chronostratigraphic framework of 14 tephra horizons from North Atlantic marine sequences spanning 60-25 cal ka BP. Horizons previously discovered as visible or coarse-grained deposits have been combined with 11 newly recognised volcanic deposits, identified through the application of cryptotephra identification and characterisation methods to a wide network of marine sequences. Their isochronous integrity has been assessed using their physical characteristics. All horizons originated from Iceland with the vast majority having a basaltic composition sourced from the Grímsvötn, Kverkfjöll, Hekla/Vatnafjöll and Katla volcanic systems. New occurrences, improved stratigraphic placements and a refinement of the geochemical signature of the NAAZ II are reported and the range of the FMAZ IV has been extended. In addition, several significant geochemical populations that further investigations could show to be isochronous are reported. This tephra framework provides the foundation for the correlation and synchronisation of these marine records to the Greenland ice-cores and European terrestrial records to investigate the phasing, rate, timing and mechanisms controlling rapid climate changes that characterised the last glacial period
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