Abstract The smallest tephra grains present special challenges in their preparation for quantitative microbeam chemical analysis by EPMA and LA-ICP-MS. High-quality polished surfaces are an essential pre-requisite for the collection of high quality quantitative chemical data, as these shards also present significant difficulties for analysis. A method for the preparation of tephra grains as small as 10–50 µm is described in detail. This method uses inexpensive, widely available materials and is easily implemented in facilities in which polished geological samples are prepared for microanalysis. Samples prepared in this way reduce or eliminate the difficulties in microbeam analysis associated with small grains, when appropriate analytical protocols are used.

Abstract Correlation of tephra deposits frequently relies on the analysis of glass shards separated from their host. Small shards from distal deposits (marine-, ice- or lake-cores, peat bogs) are difficult to analyse. Here current methods for glass shard analysis from (particularly) marine tephra deposits are reviewed. These methods apply equally to other distal deposits, where linking repositories of climatic information is central to many research programmes. Electron probe microanalysis is used widely to determine the major element compositions of volcanic glass. However, electron beam irradiation causes permanent damage to glass, especially hydrated or silica- and alkali-rich compositions. Recent developments have shown that reliable data is obtained with beam diameters >3 µm on basaltic or moderately hydrated rhyolitic glass, provided low electron beam current densities are used. For robust correlation of tephra deposits from different environments, it is recommended that analytical data are normalized to an anhydrous basis. Glass trace element analysis is commonly performed by laser ablation inductively coupled plasma mass spectrometry, which determines approx. 30 elements at <1 ppm from ablation craters 10 µm diameter, and although element fractionation occurs, it can be corrected. Recent developments in both methods should facilitate analysis of smaller, more distal material, expanding the geographical range over which reliable tephra correlations can be achieved.

Abstract Tephra deposits in the deep sea can survive undisturbed for long periods of time and, on regional scales, tend to be much better preserved than their subaerial counterparts. In this study, grain size distributions and thicknesses of tephra deposits from the Campanian Ignimbrite (CI) eruption (39 000 yr BP; magnitude c. 7.7) preserved in thirty-three deep sea cores are analysed to infer key eruption parameters. Distal deep sea tephra thickness data show an exponential decrease with distance from source. Such trends are difficult to identify in distal subaerial data owing to reworking and limited exposure. We find that tephra grain size distributions are much less affected by depositional environment than thickness, with trends that are consistent across distal subaerial, lacustrine and deep sea environments. The CI layer exhibits bimodal grain size distributions to distances of c. 1000 km, after which it becomes unimodal. Such trends can be related to different mechanisms of tephra transport in the atmosphere, whereby at proximal to medial distances the Plinian and co-ignimbrite phases produce distinct plumes. Within 150 and 900 km from source, Plinian tephra constitutes 40±5% of the deposit volume. Beyond this region where coarse particles are deposited, the plumes merge and fines derived largely from co-ignimbrite elutriation are spread in the atmosphere at velocities greater than the settling velocities of the particles.

Abstract 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 Kerlingarfjöll 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.

Abstract A basaltic tephra layer from MIS 3 has been discovered by analysis of cores from the Faroe Islands margin. The tephra layer appears up to 20 cm thick in some records. After the first main fall-out event the tephra is believed to be mainly deposited and redistributed by bottom currents. Geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed. The peak occurrences are in the lower part of GIS (Greenland Interstadial) 12 and we suggest naming this new tephra Faroe Marine Ash Zone IV (FMAZ IV), following the nomenclature adopted for previous ash zones found on the Faroe Islands margin. Geochemical analyses of the tephra show affinities with the Grímsvötn volcanic system in the Eastern Volcanic Zone in south Iceland. The average age of FMAZ IV from four independent age models is 46 800±1000 years BP. We suggest that the V5 ash zone, found on the Reykjanes Ridge is a correlative to the FMAZ IV. Supplementary material: Single-grain analyses of tephra from FMAZ IV in cores from the northern Faroe margin and the central Faroe-Shetland Channel are available at http://www.geolsoc.org.uk/SUP18714

Abstract Cooling and sinking of dense saline water in the Norwegian–Greenland Sea is essential for the formation of North Atlantic Deep Water. The convection in the Norwegian–Greenland Sea allows for a northward flow of warm surface water and southward transport of cold saline water. This circulation system is highly sensitive to climate change and has been shown to operate in different modes. In ice cores the last glacial period is characterized by millennial-scale Dansgaard–Oeschger (D–O) events of warm interstadials and cold stadials. Similar millennial-scale variability (linked to D–O events) is evident from oceanic cores, suggesting a strong coupling of the atmospheric and oceanic circulations system. Particularly long-lasting cold stadials correlate with North Atlantic Heinrich events, where icebergs released from the continents caused a spread of meltwater over the northern North Atlantic and Nordic seas. The meltwater layer is believed to have caused a stop or near-stop in the deep convection, leading to cold climate. The spreading of meltwater and changes in oceanic circulation have a large influence on the carbon exchange between atmosphere and the deep ocean and lead to profound changes in the 14 C activity of the surface ocean. Here we demonstrate marine 14 C reservoir ages ( R ) of up to c. 2000 years for Heinrich event H4. Our R estimates are based on a new method for age model construction using identified tephra layers and tie-points based on abrupt interstadial warmings.

Abstract The paper focuses on dispersal of airborne tephra that may have reached the marine environment north of Iceland during the last millennium, particularly the shelf off north Iceland. Many of these tephra horizons may extend into the Nordic Seas and the Arctic. The tephrochronology of Iceland after the settlement in the late ninth century AD relates to volcanic events that have been dated with documentary records as well as ice cores. The relevant eruptions for long-distance transport of tephra have been explosive or partly explosive, and mostly deposited from volcanic plumes. However, other methods of transport into the area north of Iceland are also considered. These include rafting of pumice from offshore eruptions elsewhere around Iceland, leading to instantaneous flotation of tephra, and river-rafted pumice from inland areas of heavy tephra fall, as well as potential contributions from volcanogenic glacial bursts. Airborne tephra in 25–30 explosive and partly explosive eruptions had the potential to reach the north Icelandic shelf and beyond during the time slice considered here. Four instances of ocean-rafted pumice off the north coast are known. Tephra from 15 of these eruptions has been identified in marine cores from the north Icelandic shelf and eastern Norwegian sea.

Abstract Ice-rafted tephra deposits, of Marine Isotope Stage 6 (MIS 6) age, from Site U 1304 on the Gardar Drift, North Atlantic were examined for their shard size distribution and major element composition. The heterogeneous composition, large shard sizes and association with ice-rafted debris (IRD) indicate that these late MIS 6 deposits were transported by iceberg-rafting from Iceland to Site U 1304. Comparison of individual shard geochemistry with the geochemistry of Holocene volcanic systems from Iceland allows the identification of different potential volcanic source regions. This detailed geochemical analysis, when combined with Icelandic Ice Sheet (IIS) flow models for the Last Glacial Maximum (LGM), suggests that the IIS had calving margins to both the north and south during the late MIS 6 and that icebergs could have been transported to the Site U 1304 by following surface ocean circulation patterns similar to those that prevailed during the LGM. We demonstrate that the descriptive concept of Icelandic glass in the characterization of tephra components within North Atlantic IRD can be significantly improved through quantitative characterization and that such data hold the potential to help constrain surface ocean circulation models, while also potentially yielding new information about the IIS during earlier glacial periods. Supplementary material: Statistical tests, major element concentrations of analysed shards, primary and secondary standards are available at http://www.geolsoc.org.uk/SUP18716

Abstract The record of Icelandic volcanic events in Holocene marine sediments off SE Greenland provides evidence for the frequency and timing of atmospheric tephra plume dispersal from Iceland towards Greenland. Geochemistry of tephra abundance peaks from two SE Greenland shelf cores: MD99-2322 and JM96-1215-2GC are compared with core MD99-2269, north Iceland shelf, to evaluate the dispersal direction of Icelandic eruptions. Glass shard counts (106–1000 µm) in MD99-2322 revealed 16 distinct cryptotephra peaks. Geochemical analyses of eight cryptotephra peaks in MD99-2322 and two in JM96-1215 indicate sources in the volcanic systems of Iceland and Alaska. A tephra layer matching in geochemistry and stratigraphy to the c. 3600 BP eruption of the Aniakchak Volcano in the Aleutian Islands was identified in JM96-1215/2GC. The Settlement Tephra (AD 871±2) and Hekla B (H-B) were identified in MD99-2322. A new marker horizon, Katla EG-6.73, was found in both SE Greenland cores. Three basaltic peaks between 9.9 and 10.4 cal kyr BP, exhibit major-element geochemistry indistinguishable from the c. 10.2 kyr Saksunarvatn tephra. These layers represent 3 out of≥seven westward and northward-dispersed Grímsvötn layers found on the SE Greenland shelf and the north Iceland shelf between 9.9 and 10.4 cal kyr BP. supplementary material: a list of all analyses performed for this study is available at http://www.geolsoc.org.uk/SUP18715

Abstract Tephrochronology allows the establishment of ‘isochrons’ between marine, lacustrine, terrestrial and ice cores, typically based on the geochemical fingerprint of the tephra. The development of cryptotephrochronology has revealed a vast inventory of isochrons which hold the potential to improve stratigraphic correlation and identify systemic leads and lags in periods of rapid climate change. Unfortunately, bioturbation acts to blur these isochrons, reducing the temporal resolution in marine and lacustrine records. In order to better resolve these event horizons, we require a better understanding of bioturbative processes, and the depth and time over which they operate. To this end, an ash fall event was simulated on the intertidal zone of the Eden Estuary, Fife, Scotland and sediment cores were collected over 10 days. A novel approach to tephra quantification was developed, using the imaging software ImageJ. Our results showed limited bioturbation (mixed depth=18 mm), most likely owing to the fine grain size, low-energy environment and the resulting faunal composition of the sediments. These results imply a strong ecological control on bioturbation, and suggest that inferences may be made about palaeoenvironments from the observed bioturbation profiles. supplementary material: The ImageJ macro used in this study, as well as raw tephra concentration data and details of the method validation are available at http://www.geolsoc.org.uk/SUP18725 .

Abstract This Special Publication includes articles presenting recent advances in marine tephrochronological studies and outlines innovative techniques in geochemical fingerprinting, stratigraphy and the understanding of depositional processes. It represents a significant resource for the palaeoceanographic community at a time when marine tephrochronology is being more widely recognized. It will also serve as a valuable reference to a much wider community of Earth scientists, climate scientists and archaeologists, particularly in highlighting the role of tephra studies in stratigraphy and regional/extra-regional correlations, as well as in tracing the long-term history of regional and global volcanism in the deep-sea archive.

Abstract The current volume brings together a selection of papers which have variously, but not exclusively, been presented in recent years at one of three international meetings on the theme of Fjords . The first of these meetings on ‘ Fjord Environments: Past, Present and Future ’ was held as a workshop following the Challenger Society Conference hosted by The Scottish Association for Marine Science, Scottish Marine Institute, Oban, UK in June 2006. The second meeting was convened as a formal session (CGC-13) entitled ‘ Fjords: Climate and Environmental Change ’ during the 33rd International Geological Congress, Oslo, Norway in August 2008. The third of these meetings, representing the 2nd international workshop on the theme ‘ Fjord Environments: Past, Present and Future ’ was held at the University of Bergen, Norway in May 2009. The aims of these meetings were to bring together physical oceanographers, biogeochemists, biologists and earth scientists who could contribute to an improved understanding of fjord systems, both in terms of modern processes and as palaeoenvironmental archives. This publication consists of 23 papers and a glossary, dealing with various aspects of fjord systems and their associated archives. Three of the papers focus on the physics of fjord hydrography and circulation; three address aspects of fjord biology; two concern modern sediment processes; six consider fjord sediments and their depositional architecture; and eight highlight fjords as depositional archives and their palaeoenvironmental significance.

Abstract Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution. In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines. Supplementary material: The Glossary is available at: http://www.geolsoc.org.uk/SUP18440 .

Abstract A rich and wide variety of fluid dynamic processes occur in fjords. Although a fjord may at one level be simply defined a glacially formed coastal inlet, this simple definition belies a huge range of geomorphological manifestations and environmental forcing conditions. It is the interplay between geomorphology and environmental forcing which defines the relative importance of differing physical fluid processes within a given fjord. In this chapter we present a non-mathematical review of the dominant physical processes which are found to occur in fjordic systems, how their relative importance may depend on geomorphology and forcing, and how, in turn, the dominant physical processes effect circulation and sediment distribution. Our aim is to provide the non-physical oceanographer with an insight into the rich and varied fluid dynamical processes presented to us by the fascinating ‘mini-ocean’ geo-type generically referred to as a fjord.

Abstract Fjords have long been recognized for their value as sites of sediment deposition, recording past climatic conditions. Recently, Arctic fjords have been recognized as the critical gateway through which oceanic waters can impact on the stability of glaciers. Arctic fjords are also used as idealized locations to study ice-influenced physical, biological and geochemical processes. In all cases a clear understanding of the physical oceanographic environment is required to interpret and predict related impacts and linkages. In this review we consider the characteristic elements of Arctic fjords and the important dynamical processes. We show how the intense seasonality of these regions is reflected in the varying stratification of the fjords. In particular, we show that sea ice has a central role in terms of the fjord salinity which ultimately influences the exchange with oceanic waters. When the fjord is ice free, wind forcing from the intense down-fjord katabatic winds gives rise to rapidly changing cross-fjord gradients, upwelling and strong surface circulations. The stratification and dimensions of Arctic fjords mean that they are often classed as ‘broad’ fjords where rotational effects are important in their circulation. We refer to the link between the physical oceanographic conditions and the related depositional records throughout.