181 research outputs found
A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25–45 ka b2k
Get PDFThe late Quaternary tephrochronology of the Adriatic region: implications for the synchronisation of marine records
Get PDFVolcanism 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
Tephrochronology of core PRAD 1-2 from the Adriatic Sea: insights into Italian explosive volcanism for the period 200-80ka
No full textCore PRAD 1-2, located on the western flank of the Mid-Adriatic Deep, was investigated for tephra content within the part of the sequence assigned on biostratigraphic and sapropel-layer stratigraphy to MIS 5 and 6 (ca. 80–200 ka BP). A total of 11 discrete tephra layers are identified, 8 visible and 3 cryptotephra layers. 235 geochemical measurements obtained from individual glass shards using WDS-EPMA enabled 8 of the 11 tephras to be correlated to known eruption events, 5 of which are represented in the Lago Grande di Monticchio (LGdM) regional tephra archive sequence. Three of these layers are recognised ultra-distally for the first time, extending their known distributions approximately 210 km further north. The results provide an independent basis for establishing an age-depth profile for the MIS 5–6 interval in the PRAD 1-2 marine record. This approach allowed age estimates to be interpolated for the tephra layers that could not be correlated to known events. It also provides an independent test of, and support for, the broad synchroneity of sapropel-equivalent (S-E) events in the Adriatic Sea with the better-developed sapropel layers of the eastern Mediterranean, proposed by Piva et al. (2008a)
Age and geochemistry of tephra layers from Ischia, Italy: constraints from proximal- distal correlations with Lago Grande di Monticchio
Get PDFUnraveling the eruptive history of the Island of Ischia (southern Italy) is problematic due to its burial, caldera collapse, resurgent uplift and erosion. Here, we present new major and trace element glass data for 39–75 ka proximal tephra deposits, including those of the caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Correlations with the distal tephra archive preserved at Lago Grande di Monticchio (LGdM) are used to constrain the timing of as yet undated eruptive events. Out of 13 LGdM tephras analysed from the 39–104 ka time window, glass geochemical data show that all are compositionally consistent with the explosive volcanic eruptions of Ischia, whilst 5 of them can be correlated with specific proximal deposits.Pre-MEGT pyroclastic sequences comprise three compositional groups, these groups occur repeatedly in sucessive eruptions. Proximal-distal correlations indicate that the Porticello eruption occurred at 59 ± 2 ka and the Tisichiello eruption probably occurred at 76 ± 3 ka. The MEGT eruption is correlated with LGdM TM-19, which has been directly dated at 55 ± 2 ka. Post-MEGT tephras form compositional groups that overlap with the pre-MEGT but are displaced to lower FeO and TiO2 and lower incompatible element contents. Proximal-distal correlations indicate that the Schiappone and Pietre Rosse eruptions occurred at 50.6 ± 2.0 ka and 45 ± 6 ka, respectively.Tephra from the MEGT eruption span a wide compositional range, broadly overlapping the three pre-MEGT compositional groups but are displaced to higher Nd and Y and contain an additional less evolved glass population. Glass geochemistry is used to recognise and confirm distal equivalents of the MEGT at LGdM (TM-19) and in the Ionian (Y-7), Adriatic (PRAD 1870) and Tyrrhenian (C-18, MD 28) seas. Distal occurences of MEGT tephra define a dispersal axis to the south-southeast and are found as far as 540 km from Ischia, making the MEGT one of the most widely dispersed late Quaternary pyroclastic deposit erupted in the Campanian region. We estimate a volume of approximately 40 km3 for the fallout portion of the MEGT pyroclastic sequence on the basis of proximal and distal deposit thicknesse
Evidence for Lignocellulose-Decomposing Enzymes in the Genome and Transcriptome of the Aquatic Hyphomycete Clavariopsis aquatica
Get PDFFungi are ecologically outstanding decomposers of lignocellulose. Fungal lignocellulose degradation is prominent in saprotrophic Ascomycota and Basidiomycota of the subkingdom Dikarya. Despite ascomycetes dominating the Dikarya inventory of aquatic environments, genome and transcriptome data relating to enzymes involved in lignocellulose decay remain limited to terrestrial representatives of these phyla. We sequenced the genome of an exclusively aquatic ascomycete (the aquatic hyphomycete Clavariopsis aquatica), documented the presence of genes for the modification of lignocellulose and its constituents, and compared differential gene expression between C. aquatica cultivated on lignocellulosic and sugar-rich substrates. We identified potential peroxidases, laccases, and cytochrome P450 monooxygenases, several of which were differentially expressed when experimentally grown on different substrates. Additionally, we found indications for the regulation of pathways for cellulose and hemicellulose degradation. Our results suggest that C. aquatica is able to modify lignin to some extent, detoxify aromatic lignin constituents, or both. Such characteristics would be expected to facilitate the use of carbohydrate components of lignocellulose as carbon and energy sources
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 GrÃmsvötn, 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
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
Variations on the Pear Tree Experiment : different variables, new results?
Get PDFInspired by the Pear Stories Project, the Pear Tree Project has investigated how different cultures and languages describe the same film in order to apply its findings to audio description (AD). Participants from different countries were asked to "write down what they saw" in a controlled setting. This article proposes an alternative experiment, also based on the original Pear Stories Project, which aims to shed light on two issues: how different describer profiles (translation students with AD training/without AD training) and different instructions concerning the target audience profiles (blind/non-blind) could alter the final production. The results are analysed in this paper, taking into account the elements covered in the original Pear Stories Project as well as some additional elements proposed by the authors
Age and geochemistry of tephra layers from Ischia, Italy: constraints from proximal-distal correlations with Lago Grande di Monticchio
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