Extending the limits of the Borrobol Tephra to Scandinavia and detection of new early Holocene tephras

Abstract 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

Hekla 1947, 1845, 1510 and 1158 tephra in Finland: challenges of tracing tephra from moderate eruptions

Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of 3 have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall-out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall-out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter-regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway

The presence of Holocene cryptotephra in Wales and southern England

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

Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region: The cryptotephra record

PMA, SMD, WENA and NJGP are supported by NERC through the SMART project (NE/F020600/1, NE/F02116X/1, NE/F021445/1). The research leading to the results for the MIS 4 and 5a tephra horizons has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° [259253]. PMA, SMD and NJGP acknowledge the support of the Climate Change Consortium of Wales (C3W). JB is funded by the Research Council of Norway through the INTERACT project (project no. 221999).Abstract 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 Grímsvötn volcanic system of Iceland is the predominant source of the basaltic horizons and the Öraefajökull or Torfajökull 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.Publisher PDFPeer reviewe

Towards a Holocene tephrochronology for the Faroe Islands, North Atlantic

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

Last Glacial Period Cryptotephra Deposits in an Eastern North Atlantic Marine Sequence: Exploring Linkages to the Greenland Ice-Cores

The establishment of a tephra framework for the Greenland ice-cores spanning the last glacial period, particularly between 25 and 45 ka b2k, provides strong potential for precisely correlating other palaeoclimatic records to these key archives. Tephra-based synchronisation allows the relative timing of past climatic changes recorded within different depositional environments and potential causal mechanisms to be assessed. Recent studies of North Atlantic marine records have demonstrated the potential of tracing cryptotephra horizons in these sequences and the development of protocols now allows a careful assessment of the isochronous nature of such horizons. Here we report on tephrochronological investigations of a marine sequence retrieved from the Goban Spur, Eastern North Atlantic, covering ?25–60 ka b2k. Density and magnetic separation techniques and an assessment of potential transport and depositional mechanisms have identified three previously unknown isochronous tephra horizons along with deposits of the widespread North Atlantic Ash Zone II and Faroe Marine Ash Zone III. Correlations between the new horizons and the Greenland ice-core tephra framework are explored and despite no tie-lines being identified the key roles that high-resolution climatostratigraphy and shard-specific trace element analysis can play within the assessment of correlations is demonstrated. The previously unknown horizons are new additions to the overall North Atlantic tephra framework for the last glacial period and could be key horizons for future correlations

First discovery of Holocene Alaskan and Icelandic tephra in Polish peatlands

Despite the discovery of cryptotephra layers in over 100 peatlands across northern Europe, Holocene cryptotephra layers have not previously been reported from Polish peatlands. Here we present the first Holocene tephra findings from two peatlands in northern Poland. At Bagno Kusowo peatland we identify the most easterly occurrence of the AD 860 B tephra, recently correlated to the White River Ash (WRAe) derived from Mount Churchill, Alaska. A shorter core from Linje peatland contains tephra from the Askja 1875 eruption, extending the spatial distribution and regional importance of this Icelandic tephra in Eastern Europe. Our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on Polish peatlands and contributes towards the development of a regional Holocene tephrostratigraphy for Poland