Northeast Iceland Research Articles

Hydraulically linked reservoirs simultaneously fed the 1975–1984 Krafla Fires eruptions: Insights from petrochemistry

The 1975–1984 Krafla Fires in northeast Iceland was the first plate-boundary rifting episode to be tracked using seismic and geodetic monitoring. Geophysical observations from this episode have inspired conceptual models of magma transport during plate spreading, but a lack of complementary petrologic insights has hindered a holistic understanding of the events. To address this knowledge gap, we studied the petrochemistry of all nine Krafla Fires basaltic eruptions. Our large dataset of new whole-rock, matrix glass and mineral analyses from samples collected during or shortly after each eruption reveal a clear compositional bimodality in the erupted magmas that persisted across the episode, with evolved quartz tholeiite (MgO = 5.7–6.4 wt.%) erupted inside Krafla caldera, and more primitive (usually olivine-normative) tholeiite (MgO = 6.4–8.7 wt%) erupted north of the caldera margin. Barometric calculations indicate tapping of these magmas from distinct reservoirs: a primitive lower-crustal reservoir at a most probable depth of ∼14–19 km, and a more evolved, shallower reservoir at a most probable depth of ∼7–9 km beneath the caldera. These reservoirs were tapped simultaneously in several of the nine eruptions, and in three events the two magma types mixed near the northern caldera margin. Varying levels of trace element depletion in the deep-sourced primitive melts reflect incomplete mixing of diverse mantle-derived melts at depth; the most enriched of these melts could be parental to evolved inside-caldera magma via fractional crystallization. Clinopyroxene rims on gabbroic nodules from primitive September 1984 lavas record lower crustal pressures, while diffusion models suggest that these rims grew up to within a few months before eruption. Ascent of the primitive magma from the lower crust thus occurred over timescales much shorter than eruptive repose periods, without prolonged stalling at shallow depths. These observations are inconsistent with the view that the eruptions were entirely fed by lateral magma outflow from the shallow reservoir. They instead require some decoupling of the flow paths of the two magma types: the primitive magma either bypassed the sub-caldera reservoir laterally or ascended vertically beneath the northern vents. The two reservoirs nonetheless shared a hydraulic connection and jointly responded to rifting. Comparison of the Krafla Fires with other rifting events and eruptions highlights the complexity and diversity of magma transport during plate boundary rifting events, which is not yet captured by a generalizable model. Integration of petrologic, geochemical and geophysical data is essential to provide a holistic view of future rifting events in Iceland and at other spreading centres.

To See and to Respect: On the Relations between Humans, Supernatural Beings and the Landscape in Northeast Iceland

To See and to Respect: On the Relations between Humans, Supernatural Beings and the Landscape in Northeast Iceland

Entrepreneurship at the edge? The characteristics and role of creative entrepreneurs in peripheral regions

ABSTRACT To advance the understanding of the nature and dynamics of creative entrepreneurship in specific contexts, this paper explores how creative entrepreneurship both shapes and is shaped by its peripheral context. This paper adds to the growing work that is helping us understand that when looking at the periphery through the lens of cultural and creative practice we find a much more nuanced set of relations between place and practice. We focus on geographically separate regions facing the same obstacles of geographic peripherality. Underpinning the findings are semi-structured interviews reflecting the experience of creative entrepreneurs in North East Iceland, Västernorrland in Mid Sweden and the western region of Ireland. While we recognise that problems still exist in the creative industries policy domain, we argue that policy supports would be best designed in line with the characteristics of the sector in particular places. This work also helps to develop knowledge of the multifaceted role of the creative entrepreneur in peripheral societies and economies.

The prey availability and diet of juvenile Atlantic salmon (Salmo salar L.) in low-productivity rivers in northern Europe.

The availability of resources varies across a species distributional range, and a low-productivity area can make a species more vulnerable. We investigated the invertebrate composition and prey choice of juvenile Atlantic salmon (Salmo salar L.) in low-productivity rivers in northeast Iceland, which is one of the species' most northerly distributions. By sampling benthic and drift invertebrate populations, we found that prey availability was similar within and between rivers. Gut content samples showed that the main prey choice for juvenile S. salar was the Chironomidae. The type of food items consumed varied across different weight groups of S. salar, with smaller juveniles having more diverse diet. S. salar did not have a selection preference for chironomids, which indicates that they were eating the highly available prey in their environment, rather than hunting high biomass items such as terrestrial invertebrates and large Dipterans. Estimates of dietary niche showed that S. salar in these low-productivity rivers relied on consuming what was most readily available, the chironomids, and that they must share resources with other salmonid species. This may be due to the low diversity of freshwater invertebrates (fewer prey options), whereas S. salar in nutrient-rich rivers could rely more on terrestrial invertebrates as an additional subsidy in their diet. In conclusion, with limited prey choices, juvenile S. salar in nutrient-poor rivers, especially in a biogeographically isolated region with low species diversity, may increase in vulnerability and decrease in adaptability to environmental change. Management methods that increase benthic prey abundance and diversity are recommended for conserving the S. salar population in a nutrient-poor river.

POPs in long-finned pilot whales mass stranded in Iceland as a proxy for their physiological condition

Long-finned pilot whales (Globicephala melas) are the most frequently stranded cetaceans in the world; however, the predominant drivers of these events are poorly understood. In this study the levels of persistent organic pollutants from pilot whales stranded in North-east Iceland were quantified and compared to historical data and physical parameters to investigate whether contaminant load may have influenced the physiological state of stranded individuals, how these loads fluctuate with sex and age group, and if this is consistent with the literature. Historical comparison was also carried out to discern how pollutant contamination has changed throughout the past few decades. DDE, transnonachlor and PCB-153 were the top three pollutants respectively. The accumulation of POPs was greater on average in immature individuals than adults, whilst among adults, males had higher concentration than females. Moreover, despite an indication of decreasing POP loads throughout the years, knowledge of harmful thresholds remains exceedingly limited.

Wintering and migration strategies of Slavonian Grebes Podiceps auritus breeding in Iceland

ABSTRACT Capsule Slavonian Grebes Podiceps auritus breeding in Iceland moult on freshwater, before migrating to the seas around the British Isles for the winter. Aims The aims were to describe the migration strategies and identify wintering areas of Slavonian Grebes breeding in Iceland. Methods Geolocators were fitted to 37 Slavonian Grebes breeding on two lakes in north-east Iceland from 2009 to 2012. Of these, 19 were recovered and provided useful data on wintering areas and migration timing. Results The results indicated that the grebes moulted on freshwater lakes before gradually moving to the sea and later migrating to the wintering areas. Most of the birds wintered on the sea around the British Isles. However, there was surprisingly high variation in wintering strategies and little overlap of wintering areas. Grebes tracked for consecutive years showed high wintering philopatry. Conclusion Individual Slavonian Grebes may be vulnerable to local environmental conditions, but the high variability in wintering strategies and relatively large non-breeding distribution is expected to make the population generally less sensitive to local environmental conditions in the wintering areas over the long term.

Morphometric analysis of ice scour lakes in Iceland: A proxy for ice sheet dynamics

AbstractGlacial erosion rates on the Iceland landscape throughout the Pleistocene are not well quantified. Ice scour lakes provide an opportunity to investigate glacial erosive activity and relative intensity because they commonly form in areas beneath ice sheets due to intense quarrying. This study evaluates ice scour lake morphology and density as a potential proxy for paleo‐ice flow direction and basal thermal regime for parts of the Iceland Ice Sheet. Using GIS analysis, properties of ice scour lakes are examined in regions that experienced different rates of ice flow during and following the Last Glacial Maximum (LGM), as interpreted from streamlined subglacial landforms. The primary input datasets were topographic, hydrologic and bedrock data. Lake distribution and morphology were quantified for all natural lakes of Iceland (n = 30 169), with close examination of three 400 km2 sub‐regions in Vestfirðir (n = 904), Húnaflói (n = 69) and Bakkaheiði (n = 232). Lake distribution parameters include density, packing and centroid elevation. PolyMorph‐2D was used to quantify lake morphology including orientation, area and elongation ratio. Ice scour lake density, packing and elevation were all greatest on Vestfirðir. The high density and packing of lakes across Vestfirðir suggests unique ice dynamics relative to the other two sub‐regions, and multidirectional flow of lake axes supports the presence of an independent ice cap covering Vestfirðir. Differential intensity of glacial erosion interpreted from regions of high and low lake density on Bakkaheiði supports a proposed ice divide in Northeast Iceland. The orientation of lakes align with the flow directions of proposed LGM ice streams in Northern and Northeast Iceland. Ice scour lakes were most elongate on average on Bakkaheiði, which supports fast ice flow. Improving understanding of former ice sheet basal thermal regime and paleo‐ice flow velocity serves to inform modern controls on ice sheet stability and ice sheet basal processes.

Dispersal rate of Potamophylax cingulatus and Micropterna sequax (Trichoptera) in Iceland

During the 20th and 21st century, two species of Trichoptera have colonised Iceland. One species is Potamophylax cingulatus and the other is Micropterna sequax. Potamophylax cingulatus was not found in several extensive surveys before 1942, conducted by several entomologists. During a survey in streams in 1974–1978, the species was found to be common in east and north-east Iceland, but the Trichoptera species Apatania zonella was absent, where it was common before 1942. Searching collections of unidentified Trichoptera, a single specimen was found in east Iceland on 30 July 1959. The survey was repeated in 2004–2006 and the species had colonised most streams and rivers in Iceland and A. zonella had disappeared from many of them. Potamophylax cingulatus was first recorded in two light traps in south Iceland in 1997 with two specimens. The catch has increased continuously to 267 in 2022. Micropterna sequax was found in a single light trap at Mógilsá near Reykjavik in 2008. The annual catch has since grown from two specimens to 144. The species was found at Hvanneyri, 40 km north of the original site it was recorded from in 2018 (8 specimens) and, in 2021, it was found in Kjós, 11 km from the original site (one specimen based on a photograph). The dispersal rate for P. cingulatus was about 7–9 km/year, but the dispersal rate for the more recent settler M. sequax was found to be 4 km/year.

Wood mouse (Apodemus sylvaticus L.) as intermediate host for Mesocestoides canislagopodis (Rudolphi, 1810) (Krabbe 1865) in Iceland.

Mesocestoides canislagopodis is a common parasite of the arctic fox (Vulpes lagopus) in Iceland. In the past, household dogs (Canis familiaris) and cats (Felis catus) were also reported in Iceland to be infected. Recently, scolices of a non-maturing Mesocestoides sp. were detected in the intestines of the gyrfalcon (Falco rusticolus), and tetrathyridia were isolated in the body cavity of rock ptarmigan (Lagopus muta) and subsequently described. All stages were confirmed, using both morphological and molecular methods, to belong to the same species, M. canislagopodis. In the present study, post-mortem examination of wood mice (Apodemus sylvaticus), sampled in autumn 2014 on a farm in Northeast Iceland, revealed the presence of tetrathyridia in the peritoneal cavity and in the liver. Most tetrathyridia in the peritoneal cavity were free, but some were encapsulated in a thin connective tissue stroma and loosely attached to the inner organs. They appear as whitish, heart-shaped, flattened, unsegmented bodies with a slightly pointed posterior end. In the liver, tetrathyridia were seen as pale-tanned nodules embedded in the parenchyma. Comparative molecular analysis, both at the generic level (D1 domain LSU ribosomal DNA), and at the specific level (cytochrome c oxidase subunit I (cox1) and 12S mitochondrial DNA), revealed that the tetrathyridia belonged to M. canislagopodis. A. sylvaticus represents a new second intermediate host record in Iceland, and the first description of a rodent as intermediate host for this species, thus participating in the life cycle of the parasite.

Ice‐stream shutdown during deglaciation: Evidence from crevasse‐squeeze ridges of the Iceland Ice Sheet

AbstractBoth modern and palaeo‐ice streams experience shutdown, which has critical implications for their mass balance and influence on relative sea level. Reconstructions of palaeo‐ice streams have mainly focused on their phase of active flow and thus less is understood of their shutdown and style of deglaciation. Mapping of streamlined subglacial bedforms (SSBs), including drumlins and mega‐scale glacial lineations, in northeast Iceland reveals cross‐cutting flow‐sets of palaeo‐ice streams within the Iceland Ice Sheet (IIS) during and following the last glacial maximum (LGM). Here we map geometrical ridges (linear and reticular) within the Bakkaflói and Þistilfjörður flow‐sets and combine the morphological data with sedimentological analyses to increase our understanding of the dynamics of the IIS during deglaciation in northeast Iceland. We interpret the ridges as crevasse‐squeeze ridges (CSRs), based on their interconnected network, primary orientation transverse and/or oblique to former ice flow and internal composition of homogenous subglacial till. In both areas, the CSRs are superimposed on the SSBs, indicating that they post‐date the SSBs and signify the waning stage of ice streaming associated with the readvance of the IIS during the Younger Dryas period. The preservation of the CSRs suggests ice stagnation following the readvance and ice‐stream shutdown. The morphological difference of the CSRs between the flow‐sets is taken to indicate different kinematic setting within the ice streams; the linear CSRs in Bakkaflói formed further upstream where extensional forces parallel to ice flow were dominant, whereas the reticular CSRs in Þistilfjörður are more indicative of transverse and longitudinal forces near the terminal zone. Future research reconstructing past ice‐sheet behaviour and ice‐stream dynamics would benefit from high‐resolution bathymetric data from the adjoining shelf as well as enhanced geochronological constraints.

Habitat preference of common minke whale (Balaenoptera acutorostrata) in Skjálfandi Bay, Iceland

Anthropogenic activity has contributed to increased extinction rates, creating a need to monitor and conserve vulnerable species. Understanding the distribution and habitat preference of threatened species can identify crucial habitats, for which protection can improve the population size numbers. Here, we investigate the habitat preference of the common minke whale, a rapidly declining yet understudied cetacean species. We analysed minke whale sightings over time and in relation to environmental factors (depth, sea surface temperature, sediment, chlorophyll), based on long-term monitoring data from Skjálfandi Bay in the northeast of Iceland. We found minke whales have a preference for water depth between 9-70m, and water temperature of either colder than 6°C or warmer than 9°C. Shallow depth was a strong predictor of minke whale presence, which matched sandeel distribution. Sandeels require shallow depths for spawning and overwinter burrowing, and the match between minke whale depth presence and sandeel habitat is in good agreement with sandeels being an important minke whale food source. Although the relationship between minke whale presence and sea surface temperature is weak, it also matched sandeel distribution. We also detected a decline in minke whale population size over the study period (2009-2018). The population decline observed here is consistent with the population trend estimated for the Icelandic population. We suggest that the habitat preferences identified here should be considered for conservation recommendations and minimising disturbance in the identified, crucial feeding areas.

Photo-identification rate and wide-scale movement of common minke whales (Balaenoptera acutorostrata) in the coastal waters of Faxaflói and Skjálfandi Bays, Iceland

Information on movement and site fidelity is important for conservation and management. Photo-ID of common minke whales (Balaenoptera acutorostrata) was conducted from whalewatching vessels within the coastal waters of Faxaflói (a bay on the southwest coast of Iceland) and Skjálfandi (a bay on the northeast coast) between 2007–10 and 2001–10 respectively, to examine fidelity to the sampling locations and movement between them. Images of 292 individual minke whales were obtained in Faxaflói and 61 in Skjálfandi, with an overall ‘annual re-capture proportion’ of 23.3% in the former and 16.4% in the latter. Most (about 80%) of the resighted animals in each bay were re-sighted in one year only. The total number of identified whales has increased in both Faxaflói and Skjálfandi Bays since 2007 and 2001 respectively, suggesting the existence of an open population in both bays. One match was found between the two bays, eight years apart; the distance was approximately 600km between southwest and northeast Iceland. This study shows the value of photo-ID studies from platforms of opportunity such as whalewatching vessels. More data are required from broader geographic areas before firm conclusions can be drawn about movements and site fidelity within Icelandic waters.

Slope Dynamics in Relation to the Occupation and Abandonment of a Mountain Farm in Þistilfjörður, Northeast Iceland

Extreme weather events such as storms, heavy snow accumulation, rapid snowmelt, and heavy rain have been closely related to slope instability in arctic and subarctic regions. In this paper, we investigate the historical activity of slope processes such as snow avalanches and debris flows in Þistilfjörður, northeastern Iceland, and examine their possible role in the occupation and abandonment of three archaeological sites located on slopes of Mt. Flautafell. The study combines geomorphological and stratigraphical surveys with historical records, notably Jarðabók Árna Magnússonar og Páls Vídalíns and Sýslu og sóknarlýsingar Bókmenntafélagsins Svalbarðssókn. Geomorphological surveys show numerous features that are indicative of active slope movement processes in and around the investigated sites. Our results suggest that the slopes experienced periods of instability during the occupation of these sites. The burial or destruction of some parts of the homefield at the Flautafell farm reveals slope activity, which may also be related, at least indirectly, to the abandonment of the farm at Norður Hús sometime before A.D. 1300. Nearby auxiliary farm installations of Stekkur remained untouched by slope processes even though they are situated in a vulnerable area. Further study and dating of slope processes and farm occupation could allow them to be used as proxies for deteriorating environmental conditions affecting the region.

Autumn food of rock ptarmigan Lagopus muta: the effect of age, sex, year and location

We analysed food data for rock ptarmigan Lagopus muta collected during a 10 day period at the end of September and beginning of October 2006–2014 in northeast Iceland or for nine years. The total sample was 679 birds, including 455 juveniles and 224 adults; the annual range was 48–88 birds. To describe the importance of items consumed we used percentage by dry biomass (total 1399 g) and percentage by frequency of occurrence. A total of 80+ species were identified, the most important were Betula nana (27% biomass, 62% frequency), Empetrum nigrum (14%, 63%), Dryas octopetala (11%, 64%), and Salix herbacea (10%, 41%). Important plant parts consumed were berries, woody shoots with buds, buds, catkins, seeds and leaves. Difference in diet, both with respect to species and plant parts consumed, depended on year and altitude of collection site but not on ptarmigan sex, age or sex*age interaction. The only significant age difference observed was that juveniles consumed more seeds and less woody parts than did adult birds. Betula spp. dominated the diet in five years and Salix spp. in four years. Betula and Vaccinium spp. were most important at low and medium elevations but Salix spp. showed an opposite pattern. Berries (E. nigrum and Vaccinium spp.) were the dominant plant parts in the diet for six years and woody parts of Salix and Betula spp. in three years. Berries dominated in the diet at low to medium elevations and woody parts showed an opposite pattern.

Geothermal potential of small sub-volcanic intrusions in a typical Icelandic caldera setting

Geothermal exploration targets large magmatic intrusions as heat sources because of their size, longevity, and amount of stored energy, but as shallow volcanic plumbing systems comprise numerous smaller intrusions, their geothermal potential warrants consideration. Here, we evaluate the geothermal impact of dykes and sills on caldera-infill rocks. We present geological data and geothermometry on intrusions in the eroded Breiðuvík caldera in Northeast Iceland, which serves as an analogue to the active, and geothermally exploited, Krafla volcano. These data inform 2D finite element models of dyke and sill intrusions that consider heat transfer in porous media. Our results indicate that small intrusions create considerable thermal anomalies in their immediate vicinity. These anomalies are larger-magnitude and longer-lasting for individual thick sills and dykes, but networks of smaller sills and dykes emplaced close in time and space can create more widespread thermal anomalies that may be viable economic targets for decades after their emplacement.

Drumlin formation within the Bustarfell drumlin field, northeast Iceland: integrating sedimentological and ground‐penetrating radar data

ABSTRACTDrumlins are important bedforms of former glaciated landscapes as they demonstrate past ice‐flow directions and elucidate processes that operated at the ice/bed interface. Recently mapped drumlins and other streamlined subglacial bedforms in northeast Iceland reveal the flow‐sets of cross‐cutting palaeo‐ice streams that were active within the Iceland Ice Sheet (IIS) during and following the Last Glacial Maximum. Here we study the Bustarfell drumlin field within the Vopnafjörður–Jökuldalsheiði flow‐set. The internal architecture of two drumlins was investigated using sedimentological analysis and ground‐penetrating radar (GPR, 50 and 100 MHz) to illuminate subglacial processes that contributed to drumlin formation, as well as the history and dynamics of the IIS. On the stoss side of one of the drumlins, two subglacial traction till units were identified, separated by a thick unit of deformed glaciofluvial sand and gravel. The core of glaciofluvial material suggests that the drumlin formed around well‐drained patches (sticky spots) in the subglacial bed that retarded the ice flow locally through increased basal drag and encouraged till deposition. Furthermore, our GPR data indicate a combination of erosional and depositional processes. We suggest that the glaciofluvial sediments were deposited as small ice‐marginal fans on the Bustarfell plateau, possibly during the Bølling–Allerød interstadial, and that the drumlins were formed around these fans during a subsequent readvance during the Younger Dryas.

Life cycle assessment of the Theistareykir geothermal power plant in Iceland

One of Iceland‘s key energy sources, geothermal energy, provides the country with more than 25% of its total electrical energy supply and nearly all of its heating supply. The country‘s latest installation is the 90 MW Theistareykir geothermal power station in northeast Iceland, which has been in full operation since 2018. A “cradle to grave” life cycle assessment in accordance with ISO 14040 and ISO 14044 was carried out for the power station, providing numerical results on a variety of environmental impacts throughout the life cycle, including the manufacturing of all construction materials and equipment, construction work, operation and end of life. The largest contributors to environmental impacts are direct CO2 and H2S emissions during the operation of the station during its lifetime, fuel use during construction, including the drilling of wells, and indirect emissions due to the manufacturing of all station components. The carbon footprint of electricity generation at Theistareykir is 13.9 g CO2-eq per kWh leaving the station, and 14.8 g CO2-eq per kWh when electricity transmission has been included. The carbon footprint is dominated by direct CO2 emissions from the geothermal fluid during the 40-year lifetime, amounting to 10.9 g CO2-eq per kWh or 78% (excluding transmission), while the manufacturing and construction of station buildings, infrastructure and machinery account together for 18% of the carbon footprint. Make-up wells and the renewal of machinery during the operation accounts for another 4% to the carbon footprint. The most carbon intensive units are the wells, in total constituting 8% of the carbon footprint during the entire life cycle. Direct hydrogen sulphide (H2S) emissions at Theistareykir is the main contributor to the impact category acidification, another important contributor besides climate change after applying weighting and normalisation. The LCA results identify environmental hot spots and many opportunities for improvement of future development projects and for the operational years ahead, such as measures to reduce CO2 and H2S emissions from the geothermal fluid via CCS technologies or utilization of residual geothermal sources (hot water, steam, CO2) as soon as possible, improving the station's capacity or extending its lifetime with good maintenance. Although there is uncertainty regarding the number of make-up wells needed during the station's lifetime, this LCA identifies opportunities to reduce their environmental impacts, for example via electrification of drilling and sustainable procurement practices for make-up wells.

Predicted sea-ice loss will terminate Iceland's driftwood supply by 2060 CE

Driftwood supply was a pivotal factor for the Norse expansion in medieval times and still exhibits an essential resource for Arctic settlements. The physical causes and societal consequences of long-term changes in the distribution of Arctic driftwood are, however, poorly understood. Here, we use dendrochronology to reconstruct the age and origin of 289 driftwood samples that were collected at remote shorelines in northeast Iceland. Based on 240 reference tree-ring width chronologies from the boreal forest zone, and an overall provenance success of 73%, we show that most of the driftwood is pine and larch from the Yenisei catchment in central Siberia. Our study reveals an abrupt decline in the amount of driftwood reaching Iceland since the 1980s, which is corroborated by the experience of local farmers and fishers. Despite the direct and indirect effects of changes in both, logging activity across Siberia as well as Arctic Ocean currents, the predicted amount of sea-ice loss under anthropogenic global warming is likely to terminate Iceland's driftwood supply by 2060 CE.

Atmospheric rivers and associated precipitation patterns during the ACLOUD and PASCAL campaigns near Svalbard (May–June 2017): case studies using observations, reanalyses, and a regional climate model

Abstract. Recently, a significant increase in the atmospheric moisture content has been documented over the Arctic, where both local contributions and poleward moisture transport from lower latitudes can play a role. This study focuses on the anomalous moisture transport events confined to long and narrow corridors, known as atmospheric rivers (ARs), which are expected to have a strong influence on Arctic moisture amounts, precipitation, and the energy budget. During two concerted intensive measurement campaigns – Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) and the Physical feedbacks of Arctic planetary boundary layer, Sea ice, Cloud and AerosoL (PASCAL) – that took place at and near Svalbard, three high-water-vapour-transport events were identified as ARs, based on two tracking algorithms: the 30 May event, the 6 June event, and the 9 June 2017 event. We explore the temporal and spatial evolution of the events identified as ARs and the associated precipitation patterns in detail using measurements from the French (Polar Institute Paul Emile Victor) and German (Alfred Wegener Institute for Polar and Marine Research) Arctic Research Base (AWIPEV) in Ny-Ålesund, satellite-borne measurements, several reanalysis products (the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA) Interim (ERA-Interim); the ERA5 reanalysis; the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2); the Climate Forecast System version 2 (CFSv2); and the Japanese 55-Year Reanalysis (JRA-55)), and the HIRHAM regional climate model version 5 (HIRHAM5). Results show that the tracking algorithms detected the events differently, which is partly due to differences in the spatial and temporal resolution as well as differences in the criteria used in the tracking algorithms. The first event extended from western Siberia to Svalbard, caused mixed-phase precipitation, and was associated with a retreat of the sea-ice edge. The second event, 1 week later, had a similar trajectory, and most precipitation occurred as rain, although mixed-phase precipitation or only snowfall occurred in some areas, mainly over the coast of north-eastern Greenland and the north-east of Iceland, and no differences were noted in the sea-ice edge. The third event showed a different pathway extending from the north-eastern Atlantic towards Greenland before turning south-eastward and reaching Svalbard. This last AR caused high precipitation amounts on the east coast of Greenland in the form of rain and snow and showed no precipitation in the Svalbard region. The vertical profiles of specific humidity show layers of enhanced moisture that were concurrent with dry layers during the first two events and that were not captured by all of the reanalysis datasets, whereas the HIRHAM5 model misrepresented humidity at all vertical levels. There was an increase in wind speed with height during the first and last events, whereas there were no major changes in the wind speed during the second event. The accuracy of the representation of wind speed by the reanalyses and the model depended on the event. The objective of this paper was to build knowledge from detailed AR case studies, with the purpose of performing long-term analysis. Thus, we adapted a regional AR detection algorithm to the Arctic and analysed how well it identified ARs, we used different datasets (observational, reanalyses, and model) and identified the most suitable dataset, and we analysed the evolution of the ARs and their impacts in terms of precipitation. This study shows the importance of the Atlantic and Siberian pathways of ARs during spring and beginning of summer in the Arctic; the significance of the AR-associated strong heat increase, moisture increase, and precipitation phase transition; and the requirement for high-spatio-temporal-resolution datasets when studying these intense short-duration events.

The Origin of Rhyolitic Magmas at Krafla Central Volcano (Iceland)

AbstractWe present a detailed petrologic study of rhyolites from seven eruptions spanning the full (∼190 ky) history of rhyolitic volcanism at Krafla volcano, northeast Iceland. The eruptions vary widely in size and style, but all rhyolites are crystal-poor (<6 modal%: plagioclase + augite ± pigeonite ± orthopyroxene ± titanomagnetite ± fayalite) and have similar evolved compositions (73.7–75.8 wt% normalized whole-rock SiO2) and trace element patterns. Macrocryst rim compositions from each eruption cluster within a narrow range and are appropriate for equilibrium with their carrier melt. Crystal cores and interiors display complex growth patterns and commonly host resorption surfaces, but compositional variations are slight (e.g. typically <10 mol% An for plagioclase, Mg# <10 for pyroxene), and consistent with an overall trend of cooling and differentiation by crystal fractionation. Although most crystal core and interior compositions are broadly appropriate for equilibrium with melts similar to their host whole-rock, variable growth histories, juxtaposition of grains with distinct trace element compositions, and scatter in melt inclusion compositions indicate mixing of antecrysts from compositionally similar evolved melts and/or assimilated felsic mush or intrusions before final rim growth. Evidence for mafic recharge (e.g. coupled increases in An and Fe in plagioclase) is absent in most crystals; rhyolite storage and fractionation thus occurred largely in isolation from the underlying mafic system. Comparison of observed matrix glass compositions with published experimental work on melting of altered (meta)basalts casts doubt on previous models favouring rhyolite generation by partial melting of hydrothermally altered basalts, instead supporting recent isotopic and modelling arguments for a crystallization-driven process [Hampton, R. L. et al. (2021). Journal of Volcanology and Geothermal Research 414, 107229]. MELTS fractional crystallization and assimilation-fractional crystallization (AFC) models at 1 kbar predict liquid major and trace element compositions similar to Krafla rhyolites after ∼60–70 vol% crystallization of a quartz tholeiite melt representative of the evolved crystal-poor basalts commonly erupted within Krafla caldera. We thus suggest that stalling and crystallization of these evolved basalts at shallow depth forms crystal mushes from which evolved (broadly dacitic to rhyolitic) melts are extracted. These melts ascend and mix with other compositionally similar melt bodies and/or assimilate felsic intrusive material in the uppermost crust. The Daly gap between ∼57 and 71 wt% SiO2 at Krafla is consistent with preferential extraction of evolved melts from quartz tholeiite mushes in the ∼50–70% crystallinity window. Residual solid (cumulate) compositions predicted by MELTS are exclusively mafic, hence efficient silicic melt extraction from quartz tholeiite mushes may also explain the apparent compositional bimodality in some Icelandic plutonic suites.