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Recent measurements of reactive trace gas species in volcanic plumes have offered intriguing hints at the chemistry occurring in the hot environment at volcanic vents. This has led to the recognition that volcanic vents should be regarded not only as passive sources of volcanic gases to the atmosphere, but also as ‘reaction vessels’ that unlock otherwise inert volcanic and atmospheric gas species. The atypical conditions created by the mixing of ambient atmosphere with the hot gases emitted from magma give rise to elevated concentrations of otherwise unexpected chemical compounds. Rapid cooling of this mixture allows these species to persist into the environment, with important consequences for gas plume chemistry and impacts. This paper discusses some examples of the implications of these high-temperature interactions in terms of nitrogen, halogen and sulphur chemistry, and their consequences in terms of the global fixed nitrogen budget, volcanically induced ozone destruction and particle fluxes to the atmosphere. Volcanically initiated atmospheric chemistry was likely to have been particularly important before biological (and latterly anthropogenic) processes started to dominate many geochemical cycles, with important consequences in terms of the evolution of the nitrogen cycle and the role of particles in modulating the Earth's climate.

Particle size distributions for soluble and insoluble species in Mt. Etna's summit plumes were measured across an extended size range (10 nm < d < 100 μm) using a combination of techniques. Automated scanning electron microscopy (QEMSCAN) was used to chemically analyze many thousands of insoluble particles (collected on pumped filters) allowing the relationships between particle size, shape, and composition to be investigated. The size distribution of fine silicate particles (d < 10 μm) was found to be lognormal, consistent with formation by bursting of gas bubbles at the surface of the magma. The compositions of fine silicate particles were found to vary between magmatic and nearly pure silica; this is consistent with depletion of metal ions by reactions in the acidic environment of the gas plume and vent. Measurements of the size, shape and composition of fine silicate particles may potentially offer insights into preemission, synemission, and postemission processes. The mass flux of fine silicate particles from Mt. Etna released during noneruptive volcanic degassing in 2004 and 2005 was estimated to be ∼7000 kg d-1. Analysis of particles in the range 0.1 < d/μm < 100 by ion chromatography shows that there are persistent differences in the size distributions of sulfate aerosols between the two main summit plumes. Analysis of particles in the range 0.01 μm < d < 0.1 μm by scanning transmission electron microscopy (STEM) shows that there are significant levels of nanoparticles in the Mt. Etna plumes although their compositions remain uncertain. Copyright 2008 by the American Geophysical Union.

Filter packs have been used to collect sulphur and oxygen from air for isotope analysis from many areas of the world. Here we discuss their use to determine the sulphur isotope systematics of SO2 and the sulphur and oxygen systematics of sulphate particles from volcanic vents. Our field data suggest that fractionation of sulphur isotopes occurs during the collection of SO2 from concentrated volcanic gas plumes on alkali-impregnated filter papers. The collection of volcanogenic HCl on the same filters may play a role in this fractionation. Comparison with previous studies, which sampled areas of cleaner atmosphere, suggests that isotopic fractionation only becomes significant where elevated filter loadings occur (e.g., when sampling gas streams with SO2 concentrations greater than ∼1 μmol m-3), although this requires further investigation. Previous studies also suggest that for volcanic sulphate particle samples collected at the same time, oxygen isotopes are fractionated while sulphur isotopes are not. Minimising the filter loading reduces these effects, but there is a trade-off with the amount of SO2 or SO42 - required for isotopic measurements. Despite the convenience of the filter pack technique these fractionation effects limit the use of filter packs for determining δ34S for SO2 in volcanic gases and δ18O and δ17O for the sulphate in volcanic particles, and they will certainly not be useful for determining small variations in the source isotopic signature of the sulphur in the SO2 or the oxygen in the SO42 - being measured. This highlights the importance of collecting SO2 quantitatively for isotopic analysis. These effects may also have implications if using similar methods to collect SO2 in other environments, especially where concentrations are high. © 2008 Elsevier Ltd. All rights reserved.

Although the negative impacts of volcanism on society are well documented and accepted, many possible benefits from volcanoes are not always fully considered. This paper provides suggestions for understanding and implementing volcanoes' benefits by suggesting further application of existing risk management frameworks to volcanology: living with risk by using the sustainable livelihoods approach at the local level. This paper presents an overview bringing established paradigms into volcanic risk management where they are sometimes absent despite their advantages. The sustainable livelihoods approach is important in its application to volcanic scenarios in four ways:(i)Understanding, communicating, and managing vulnerability and risk and local perceptions of vulnerability and risk beyond immediate threats to life.(ii)Maximising the benefits to communities of their volcanic environment, especially during quiescent periods, without increasing vulnerability.(iii)Managing crises.(iv)Managing reconstruction and resettlement after a crisis. An overview of case studies is provided showing how volcanic opportunities could be used for sustainable livelihoods. The approach of living with volcanic risks and benefits could be adopted and implemented as an integral part of changing perceptions of volcanoes and of managing volcano-related crisis and non-crisis situations. However, the sustainable livelihoods approach is not a panacea, so limitations are discussed along with why living near a volcano cannot solve all livelihood concerns. In particular, livelihood diversity and livelihood transferability to other locations assists in living with volcanoes. © 2007 Elsevier B.V. All rights reserved.

International audience; Ir and Pt are siderophile elements that are considered proxies of meteoric material of cosmic origin entrapped within polar ice layers. However, volcanic and anthropogenic fallouts have the potential to perturb their characteristic extraterrestrial signature even in remote polar areas. Here we show a record of Ir and Pt concentrations in snow samples collected from a 2.7 m pit, which was dug at Summit (Central Greenland), and covered five years from winter 1991 to summer 1995. A well-defined peak of Pt, and a spike of Ir, were found at the base of the snow pit record. These maxima occur in close concurrence with large concentration peaks in Al, Ag, Cd and Hg. Dating of the snow layers together with some geochemical evidence suggests that these peaks originated from the fallout to Greenland of volcanic ash emitted by the nearby Hekla volcano (Iceland), during the eruption of January–March 1991. Interestingly, an anomalous peak of methane sulfonic acid (MSA) in Greenland snow also corresponds to the Hekla ash fallout. This might point to an early biomass production in the North Atlantic Ocean during the first half of 1991, which was possibly stimulated by the fertilizing action of the Hekla ash fallout to seawater. During the following years (1992–1995) the global atmosphere was under the influence of the large perturbation produced by the eruption of Mt. Pinatubo (Philippines) in June 1991. Relatively high Ir and Pt concentrations with super-chondritic ratios are recorded especially during summer 1993. We discuss if this can be interpreted as the possible stratospheric input of Pinatubo's aerosol or fallout of extraterrestrial origin. During the same period the snow pit record was also influenced by the advection of air masses enriched in Pt with respect to Ir. One possibility is that this additional Pt contribution originated from widespread emissions into the troposphere produced by vehicles equipped with catalytic converters. In any case, Pt concentration levels found in recent Greenland snow are about two orders of magnitude lower than previously thought, pointing to a much lower anthropogenic contamination of the Arctic regions from Pt. This challenges the concept of an important hemispheric contamination of Pt from vehicles equipped with catalytic converters.

Measuring Hg/SO2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real-time simultaneous measurement of Hg and SO2 in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO2 ratios with a far better time resolution than possible with more conventional methods. The Hg/SO2 ratio in the plume of FO fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO2 ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 × 10-6 and 2.9 × 10-6, respectively). The factor 2 difference between plume and fumarole compositions provides evidence for fast Hg chemical processing, the plume. Copyright 2007 by the American Geophysical Union.

Tree cores (Pinus nigra ssp. laricio) and leaves (Castanea sativa) from the flanks of Mount Etna, Sicily were analysed by ICP-MS to investigate whether volcanogenic cations within plant material provide an archive of a volcano's temporal and spatial depositional influence. There is significant compositional variability both within and between trees, but no systematic dendrochemical correlation with periods of effusive, explosive or increased degassing activity. Dendrochemistry does not provide a record of persistent but fluctuating volcanic activity. Foliar levels of bioaccumulated cations correspond to modelled plume transport patterns, and map short-term volcanic fumigation. Around the flanks of the volcano foliar variation is greater for volatile cations (Cs, Cd, Pb) than for lithophilic cations (Ba, Sr), consistent with trace-metal supply from volcanic aerosol during quiescent periods.

The explosions and subsequent fire at the Buncefield oil depot in December 2005 afforded a rare opportunity to study the atmospheric consequences of a major oil fire at close range, using ground-based remote-sensing instruments. Near-source measurements (less than 10 km) suggest that plume particles were approximately 50% black carbon (BC) with refractive index 1.73−0.42i, effective radius ( R eff ) 0.45–0.85 μm and mass loading approximately 2000 μg m −3 . About 50 km downwind, particles were approximately 60–75% BC with refractive index between 1.80−0.52i and 1.89−0.69i, R eff ∼1.0 μm and mass loadings 320–780 μg m −3 . Number distributions were almost all monomodal with peak at r 2 (70 ppbv), NO 2 (140 ppbv), HONO (20 ppbv), HCHO (160 ppbv) and CS 2 (40 ppbv). Our measurements are consistent with others of the Buncefield plume, and with studies of the 1991 Kuwaiti oil-fire plumes; differences from the latter reflecting in part contrasts in combustion efficiency and source composition (refined fuels versus crude oils) leading to important potential differences in atmospheric impacts. Other measurements made as the plume passed overhead approximately 50 km downwind showed a reduced solar flux reaching the surface, but little effect on the atmospheric potential gradient (electric field). The wind speed data from the day of the explosion hint at a possible explosion signature.

On 28 February 2000, a volcanic cloud from Hekla volcano, Iceland, was serendipitously sampled by a DC-8 research aircraft during the SAGE III Ozone Loss and Validation Experiment (SOLVE I). It was encountered at night at 10.4 km above sea level (in the lower stratosphere) and 33-34 hours after emission. The cloud is readily identified by abundant SO2 (≤1 ppmv), HCl (≤70 ppbv), HF (≤60 ppbv), and particles (which may have included fine silicate ash). We compare observed and modeled cloud compositions to understand its chemical evolution. Abundances of sulfur and halogen species indicate some oxidation of sulfur gases but limited scavenging and removal of halides. Chemical modeling suggests that cloud concentrations of water vapor and nitric acid promoted polar stratospheric cloud (PSC) formation at 201-203 K, yielding ice, nitric acid trihydrate (NAT), sulfuric acid tetrahydrate (SAT), and liquid ternary solution H2SO4/H2O/HNO3 (STS) particles. We show that these volcanically induced PSCs, especially the ice and NAT particles, activated volcanogenic halogens in the cloud producing >2 ppbv ClOx. This would have destroyed ozone during an earlier period of daylight, consistent with the very low levels of ozone observed. This combination of volcanogenic PSCs and chlorine destroyed ozone at much faster rates than other PSCs that Arctic winter. Elevated levels of HNO3 and NOy in the cloud can be explained by atmospheric nitrogen fixation in the eruption column due to high temperatures and/or volcanic lightning. However, observed elevated levels of HOx remain unexplained given that the cloud was sampled at night. Copyright 2006 by the American Geophysical Union.

Aircraft measurements in the Hekla, Iceland volcanic plume in February 2000 revealed large quantities of hydrogen halides within the stratosphere correlated to volcanic SO2. Investigation of the longer-term stratospheric impact of these emissions, using the 3D chemical transport model, SLIMCAT suggests that volcanic enhancements of H2O and HNO 3 increased HNO3·3H2O particle availability within the plume. These particles activated volcanic HCl and HBr, enhancing model plume concentrations of ClOx (20 ppb) and BrO x (50 ppt). Model O3 concentrations decreased to near-zero in places, and plume average O3 remained 30% lower after two weeks. Reductions in the model O3 column reduced UV shielding by 15% for 2 days. Plume incorporation into the winter polar vortex after 1 March elevated model vortex Cly and Bry by 0.15 ppb and 7 ppt respectively, and doubled vortex ClOx and BrO. Model results agree quantitatively with the observations made by the DC-8 aircraft. Copyright 2006 by the American Geophysical Union.

The number concentrations and size distributions of aerosol particles >0.3 mm diameter were measured at the summit of Mount Etna and up to 10 km downwind from the degassing vents during July and August 2004. Aerosol number concentrations reached in excess of 9 106 L1 at summit vents, compared to 4–8 104 L1 in background air. Number concentrations of intermediate size particles were higher in emissions from the Northeast crater compared to other summit crater vents, and chemical composition measurements showed that Northeast crater aerosols contained a higher mineral cation content compared to those from Voragine or Bocca Nuova, attributed to Strombolian or gas puffing activity within the vent. Downwind from the summit the airborne plume was located using zenith sky ultraviolet spectroscopy. Simultaneous measurements indicated a coincidence of elevated ground level aerosol concentrations with overhead SO2, demonstrating rapid downward mixing of the plume onto the lower flanks of the volcano under certain meteorological conditions. At downwind sites the ground level particle number concentrations were elevated in all size fractions, notably in the 2.0–7.5 mm size range. These findings are relevant for assessing human health hazard and suggest that aerosol size distribution measurements may aid volcanic risk management.

Recent measurements of BrO, NOx, and near-source sulfate in volcanic plumes suggest that volcanic vents might not simply act as point sources of emissions into the troposphere, but may also act as hightemperature reaction sites where mixtures of magmatic and ambient atmospheric gases may combine, giving new and previously unexpected reaction products. The detection of such species demands that a more complex model be developed for the interaction of volcanoes and atmospheres. We show that general thermodynamic models can be applied successfully to volcanic gas equilibria by comparing the results from HSC Chemistry with those from two volcanic gas equilibrium models (Solvgas and Gasmix). Using a thermodynamic model optimized for volcanic gas chemistry (C-O-S-H-F-Cl-Br-I-N-Ar speciation), we show that the volume ratio of atmospheric gas to magmatic gas in a high-temperature mixture is an important parameter of the volcanic plume chemistry, and our results suggest that even small amounts of air (a few % for an H2O-rich magmatic gas) in the high-temperature mixture are sufficient to yield elevated levels of reactive nitrogen, halogen (Cl, Br, and I), and sulfur species within the volcanic plume. Further modifications of the plume chemistry may also occur due to low-temperature reactions, and chemical schemes for the modification of halogen (Cl, Br, I), nitrogen, and sulfur chemistry are suggested, within the constraints imposed by recent measurements. Copyright 2006 by the American Geophysical Union.

The Central American volcanic arc supplies a significant proportion of the persistent annual global sulphur dioxide emissions from volcanoes. In November/December 2003, we completed a survey of the arc section from Mombacho to San Cristobal in Nicaragua recording individual mean fluxes of 800, 530 and 220 Mg day � 1 in the plumes from San Cristobal, Telica and Masaya, respectively. An assessment of fluxes published since 1997 along the entire Central America arc yields a mean total arc flux of SO2 of 4360 Mg day � 1 or 8-16% of the annual estimated global volcanic SO2 flux to the troposphere. New field data shows that Masaya volcano continues to show stable HCl/SO2 and HF/SO2 ratios, suggesting a sustained flux of these components of ~220 and 30 Mg day � 1 , respectively (1997 to 2004). Masaya's plume composition also appears to have been stable, between 2001 and 2003, with respect to all the particulate species measured, with significant fluxes of SO4 2� (4 Mg day � 1 ), Na + (0.9-1.3 Mg day � 1 ) and K + (0.7 Mg day � 1 ). Extrapolating the Masaya plume species ratios to the entire Central American arc gives mean HCl and HF fluxes of 1300 and 170 Mg day � 1 and a particulate sulphate flux of 40 Mg day � 1 for 1997 to 2004, although without further understanding of the degassing processes and sources at depth of these different volatiles, these arc-scale estimates should be treated with caution. Combining our arc scale mean SO2 flux with published measurements of volcanic gas compositions with respect to CO2 and H2O allows us to estimate mean CO2 fluxes of 4400-9600 Mg day � 1 and H2O fluxes of 70,000-78,000 Mg day � 1 for the arc. Preliminary comparisons of these estimates of outgassing rates with published volatile input fluxes into the Central American subduction zone, suggest that Cl is more efficiently recycled through the subduction zone than CO2. The results for H2O are inconclusive. D 2005 Elsevier B.V. All rights reserved.

Chile, reveal that both are significant and sustained emitters of SO2 (28 and 3.7 kg s � 1 , respectively), HCl (9.6 and 1.3 kg s � 1 , respectively), HF (4.5 and 0.3 kg s � 1 , respectively) and near-source sulfate aerosol (0.5 and 0.1 kg s � 1 , respectively). Aerosol plumes are characterized by particle number fluxes (0.08–4.0 mm radius) of � 10 17 s � 1 (Lascar) and � 10 16 s � 1 (Villarrica), the majority of which will act as cloud condensation nuclei at supersaturations >0.1%. Impactor studies suggest that the majority of these particles contain soluble SO4� . Most aerosol size distributions were bimodal with maxima at radii of 0.1–0.2 mm and 0.7–1.5 mm. The mean particle effective radius (Reff) ranged from 0.1 to 1.5 mm, and particle size evolution during transport appears to be controlled by particle water uptake (Villarrica) or loss (Lascar) rather than sulfate production. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 8409 Volcanology: Atmospheric effects (0370); 8494 Volcanology: Instruments and techniques; KEYWORDS: volcanoes, degassing, aerosol sulphur dioxide, sulphate, Llaima

A novel, low-cost passive sampling procedure for monitoring of volcanogenic hydrogen sulfide is reported. The technique is based on absorption of H2S onto treated sections of photographic paper, which are housed in plastic film canisters during exposure. The H2S reacts with silver halide in the photographic paper, causing a colour-change reaction from white, through brown, to black, depending on concentration of atmospheric H2S. The sampler is sensitive to << 30 ppb to approximately 1000 ppb of H2S. Here we present results from a series of optimization and quantification experiments. An active sampling procedure for rapid H2S measurement is also reported, based on absorption of H2S onto Whatman No. 41 cellulose filters treated with silver nitrate, and was shown to be quantitative using a single filter at flow rates

Gruppo Nazionale per Vulcanolgia (GNV), the EC 5th Framework project ‘‘MULTIMO’’, and NERC grant GR9/04655

Volcanic plumes generate lightning from the electrification of plume particles. Volcanic plume charging at over 1200 km from its source was observed from in situ balloon sampling of the April 2010 Eyjafjallajökull plume over Scotland. Whilst upper and lower edge charging of a horizontal plume is expected from fair weather atmospheric electricity, the plume over Scotland showed sustained positive charge well beneath the upper plume edge. At these distances from the source, the charging cannot be a remnant of the eruption itself because of charge relaxation in the finite conductivity of atmospheric air. © 2010 IOP Publishing Ltd Printed in the UK.

Repetitive and violent Vulcanian explosion sequences are common hazards at many volcanoes. Statistical analyses of such sequences form the basis of forecasting models and reveal underlying explosive processes. However, no single statistical model describes interexplosion repose intervals in Vulcanian systems. Soufrière Hills, Montserrat, is best described by a log-logistic model, while Sakurajima, Japan, shows a transition from a log-logistic to a Weibull model as activity intensifies. Anak Krakatau, Indonesia, displays two failure modes on different time scales, both described by Weibull distributions. At the Kameni Islands, Santorini, Greece, model-fitting parameters vary between eruption cycles. Rates of magma rise and pressurization may be the most important controls in determining the statistical distribution of repose intervals in Vulcanian systems. © 2007 The Geological Society of America.

Hot volcanic vents promote the thermal fixation of atmospheric N 2 into biologically available forms. The importance of this process for the global nitrogen cycle is poorly understood. At Masaya volcano, Nicaragua, NO and NO2 are intimately associated with volcanic aerosol, such that NOx levels reach as much as an order of magnitude above local background. In-plume HNO 3 concentrations are elevated above background to an even greater extent (≤50 μmol·m-3). We estimate the production efficiency of fixed nitrogen at hot vents to be ∼3 × 10-8 mol·J-1, implying present-day global production of ∼109 mol of fixed N per year. Although conversion efficiency would have been lower in a preoxygenated atmosphere, we suggest that subaerial volcanoes potentially constituted an important source of fixed nitrogen in the early Earth, producing as much as ∼1011 mol·yr-1 of fixed N during major episodes of volcanism. These fluxes are comparable to estimated nitrogen-fixation rates in the prebiotic Earth from other major sources such as bolide impacts and thunderstorm and volcanic lightning. © 2004 Geological Society of America.

[1] We report here the first measurements of volcanic SO2 fluxes obtained on foot, using a miniature ultraviolet spectrometer. Our measurements, based on differential optical absorption spectroscopy (DOAS), were performed ≈1 km from the summit of Masaya volcano (Nicaragua) in December 2001, and yielded a mean SO2 emission rate of 4 kg s−1, comparable with a set of contemporaneous measurements obtained by road vehicle traverses (average 6 kg s−1). SO2 flux estimates (average 4 kg s−1) were also obtained from a fixed position by scanning the plume. This range of fluxes confirms an apparent decrease in gas output from the volcano since 2000. The portability and ease of use of the spectrometer offer considerable scope for routine measurements of SO2 emissions from volcanoes, especially where road access or opportunities for airborne campaigns are limited. These approaches can be readily extended to monitor other sources and gases.

Extremely voluminous magmatic systems known as large igneous provinces (LIPs) punctuate Earth’s history, and the gases they release plausibly link large-scale geodynamic and magmatic processes with major climate shifts in Earth’s geological record. However, quantifying the relationships between magmatism, gas release and environmental changes remains challenging. In this Review, we explore the major insights and outstanding questions regarding the linked evolution of mantle melting, expansive magmatic systems and the redistribution of volatiles from the solid Earth to the atmosphere. The evolution of mantle melt generation during LIP episodes sets the fundamental tempo of magma emplacement throughout the crust. The progression of crustal LIP magmatism and associated hydrothermal activity help shape the chemical evolution of the continental lithosphere and surface environment. Percolation of magmatic and metamorphic volatiles can decouple the tempo of gas release — a potential key driver of environmental changes — from the tempo of extrusive volcanic activity. LIPs demonstrate how large-scale magmatic systems interact with the surrounding lithosphere to propel evolving regimes of magma and volatile transfer through the crust. New, temporally resolved constraints on the evolution of LIP plumbing systems are needed to keep pace with increasingly precise timelines of palaeoenvironmental change during LIP emplacement. Major environmental disruptions throughout Earth’s history are often linked to extensive magmatic events, termed large igneous provinces. This Review explores the coupled evolution of mantle melting, magmatism and volatile release over the life cycle of large igneous provinces.

This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present, and future). W.H., T.A.M., and D.M.P. are supported by and contribute to the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes, and Tectonics (COMET). W.H. M.J.S. were supported by a NERC studentships NE/J5000045/1 and NE/K500811/01 respectively. The Main Ethiopian Rift hosts a number of peralkaline volcanic centres, with many showing signs of recent unrest. Due, in part, to the low number of historical eruptions recorded in the region, volcanism in the Main Ethiopian Rift remains understudied relative to other volcanic settings and conditions of magma storage remain almost entirely unknown. Aluto is one of these restless caldera systems and identifying magma storage conditions is vital for evaluating the risks posed by recent periods of unrest. In this study, we ran ~ 150 fractional crystallisation models, using the Rhyolite-MELTS thermodynamic software, within the range P = 50–300 MPa, starting H2O = 0.5–3 wt% and fO2 = QFM-2 − QFM + 1. This represents a realistic range of potential magma storage conditions at Aluto. We assessed the fractionation trends produced using two different starting compositions, which represent different estimates of the parental melt feeding the system. The predicted liquid lines of descent produced by these models are compared with Aluto whole-rock data from the literature, and are presented along with new observations of the natural phase assemblage and erupted mineral compositions to provide information on the magma storage conditions. Using a new, quantitative statistical approach to compare empirical data and thermodynamic model-outputs, we find that the compositions of evolved peralkaline rhyolites from Aluto are best reproduced by isobaric fractional crystallisation from a rift-related basaltic composition, without the need for significant crustal assimilation. Around 90% protracted fractional crystallisation is required to produce these compositions. This indicates that the magmatic system is likely to exist as a highly crystalline mush. The best agreement between models and natural samples is at low pressures (150 MPa), low initial H2O concentrations (0.5 wt%) and relatively high oxygen fugacity (QFM). The depth of magma storage derived from these results (~ 5.6 ± 1 km) agrees well with the source depths modelled from measured ground deformation at Aluto in 2008. Data from other peralkaline volcanic centres in the Main Ethiopian Rift, such as Boset and Gedemsa, and at other locations globally (e.g. Pantelleria, Italy) suggest that these storage conditions are a common feature of many peralkaline volcanic centres. Our data is consistent with the formation of a Daly Gap at Aluto due to compositional stratification of the magma reservoir beneath the caldera, and the non-linear relationship between temperature and SiO2 concentration during magmatic differentiation. Postprint

The Permian-Triassic mass extinction is widely attributed to the global environmental changes caused by the eruption of the Siberian Traps. However, the precise temporal link between marine and terrestrial crises and volcanism is unclear. Here, we report anomalously high mercury (Hg) concentrations in terrestrial strata from southwestern China, synchronous with Hg anomalies in the marine Permian-Triassic type section. The terrestrial sediments also record increased abundance of fossil charcoal coincident with the onset of a negative carbon isotope excursion and the loss of tropical rainforest vegetation, both of which occurred immediately before the peak of Hg concentrations. The organic carbon isotope data show an ∼5‰–6‰ negative excursion in terrestrial organic matter (bulk organic, cuticles, and charcoal), reflecting change in atmospheric CO2 carbon-isotope composition coincident with enhanced wildfire indicated by increased charcoal. Hg spikes provide a correlative tool between terrestrial and marine records along with carbon isotope trends. These data demonstrate that ecological deterioration occurred in tropical peatlands prior to the main marine mass extinction.

Records suggest that the Permo–Triassic mass extinction (PTME) involved one of the most severe terrestrial ecosystem collapses of the Phanerozoic. However, it has proved difficult to constrain the extent of the primary productivity loss on land, hindering our understanding of the effects on global biogeochemistry. We build a new biogeochemical model that couples the global Hg and C cycles to evaluate the distinct terrestrial contribution to atmosphere–ocean biogeochemistry separated from coeval volcanic fluxes. We show that the large short-lived Hg spike, and nadirs in δ202Hg and δ13C values at the marine PTME are best explained by a sudden, massive pulse of terrestrial biomass oxidation, while volcanism remains an adequate explanation for the longer-term geochemical changes. Our modelling shows that a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant biogeochemical changes, and cascaded organic matter, nutrients, Hg and other organically-bound species into the marine system., The environmental changes at the Permian–Triassic boundary are thought to have been caused primarily by volcanic eruptions. Here the authors develop a model to show that the loss of ecosystems on land and consequent massive terrestrial biomass oxidation triggered large biogeochemical changes in the oceans at the time of the marine mass extinction.

Large perturbations in the global carbon cycle recorded as carbon-isotope (δ13C) excursions (CIEs) in both organic carbon and carbonate records have been linked to volcanism during the emplacement of Large Igneous Provinces (LIPs). This link is based primarily on the purported temporal coincidence between CIEs and LIP emplacement. Mercury (Hg) concentration in sedimentary rocks has been used as a regional to global tracer of large-scale volcanic activity, yet few studies have been undertaken on Upper Jurassic – Lower Cretaceous sediments from Boreal localities compared to those for Tethyan (northern mid-latitude) successions. This has limited our understanding of the regional-to-global spatial impact of volcanic activity during this period. This study examines the Hg record as a proxy for volcanism, and the δ13C records from organic matter (δ13Corg) of CIEs from the uppermost Jurassic to Lower Cretaceous (Callovian – Aptian) successions from Axel Heiberg and Spitsbergen in the Canadian Arctic and Svalbard archipelagos, respectively. This interval includes three regional- to global CIEs. These sections show no significant variation in the ratio of Hg to total organic carbon (TOC) across the Boreal-wide Volgian negative CIE (Volgian Isotopic Carbon Excursion, “VOICE”), which has not been associated with LIP volcanism. The examined successions spanning this interval all show some influence from changing environmental or post-burial parameters, however, which could have (partially) overprinted a volcanic signal. Despite some problems in stratigraphically constraining the Weissert Event, increased Hg/TOC ratios are observed across this interval, which may be partially driven by volcanism associated with the emplacement of the Paraná-Etendeka Traps. A spike in Hg/TOC is observed immediately prior to the negative peak of the Aptian Oceanic Anoxic Event (OAE1a) CIE, supporting recent evidence of a pulse of High Arctic Large Igneous Province (HALIP) volcanic activity preceding this oceanic anoxic event.