Sulfur Budget Research Articles

Infrared satellite observations of hydrogen sulfide in the volcanic plume of the August 2008 Kasatochi eruption

[1] Hydrogen sulphide (H2S) is one of the main trace gases released from volcanoes with yearly global emissions estimated between 1 and 37 Tg. With sulfur dioxide (SO2, 15–21 Tg/year), it dominates the volcanic sulfur budget, and the emission ratio H2S:SO2 is an important geochemical probe for studying source conditions, sulfur chemistry and magma-water interactions. Contrary to SO2, measurements of H2S are sparse and difficult. Here we report the first measurements of a large H2S plume from space. Observations were made with the infrared sounder IASI of the volcanic plume released after the 7–8 August 2008 eruption of Kasatochi volcano. The eruption was characterized by 5 consecutive explosive events. The first events were phreatomagmatic producing a plume rich in water vapor and poor in ash and SO2. We show that the observed H2S plume, calculated at 29 ± 10 kT with integrated columns exceeding 140 ± 25 Dobson Units (DU), is likely associated with these first explosions. H2S:SO2 ratios with maximum values of 12 ± 2 are found, representative of redox conditions in the hydrothermal envelop. With a detection threshold of 25 DU, future space observations of H2S plumes are certain. These will be important for improving the atmospheric sulfur budget and characterizing the H2S:SO2 fingerprint of different eruptions.

Pacific Atmospheric Sulfur Experiment (PASE): dynamics and chemistry of the south Pacific tropical trade wind regime

The Pacific Atmospheric Sulfur Experiment (PASE) was a comprehensive airborne study of the chemistry and dynamics of the tropical trade wind regime (TWR) east of the island of Kiritibati (Christmas Island, 157o, 20′ W, 2o 52′ N). Christmas Island is located due south of Hawaii. Geographically it is in the northern hemisphere yet it is 6–12o south of the intertropical convergence zone (ITCZ) which places it in the southern hemisphere meteorologically. Christmas Island trade winds in August and September are from east south east at 3–15 ms−1. Clouds, if present, are fair weather cumulus located in the middle layer of the TWR which is frequently labeled the buffer layer (BuL). PASE provided clear support for the idea that small particles (80 nm) were subsiding into the tropical trade wind regime (TWR) where sulfur chemistry transformed them to larger particles. Sulfur chemistry promoted the growth of some of these particles until they were large enough to activate to cloud drops. This process, promoted by sulfur chemistry, can produce a cooling effect due to the increase in cloud droplet density and changes in cloud droplet size. These increases in particle size observed in PASE promote additional cooling due to direct scattering from the aerosol. These potential impacts on the radiation balance in the TWR are enhanced by the high solar irradiance and ocean albedo of the TWR. Finally because of the large area involved there is a large factional impact on earth’s radiation budget. The TWR region near Christmas Island appears to be similar to the TWR that persists in August and September, from southwest of the Galapagos to at least Christmas Island. Transport in the TWR between the Galapagos and Christmas involves very little precipitation which could have removed the aerosol thus explaining at least in part the high concentrations of CCN (≈300 at 0.5% supersaturation) observed in PASE. As expected the chemistry of sulfur in the trade winds was found to be initiated by the emission of DMS into the convective boundary layer (BL, the lowest of three layers). However, the efficiency with which this DMS is converted to SO2 has been brought into further question by this study. This unusual result has come about as result of our using two totally different approaches for addressing this long standing question. In the first approach, based on accepted kinetic rate constants and detailed steps for the oxidation of DMS reflecting detailed laboratory studies, a DMS to SO2 conversion efficiency of 60–73% was determined. This range of values lies well within the uncertainties of previous studies. However, using a completely different approach, involving a budget analysis, a conversion value of 100% was estimated. The latter value, to be consistent with all other sulfur studies, requires the existence of a completely independent sulfur source which would emit into the atmosphere at a source strength approximately half that measured for DMS under tropical Pacific conditions. At this time, however, there is no credible scientific observation that identifies what this source might be. Thus, the current study has opened for future scientific investigation the major question: is there yet another major tropical marine source of sulfur? Of equal importance, then, is the related question, is our global sulfur budget significantly in error due to the existence of an unknown marine source of sulfur? Pivotal to both questions may be gaining greater insight about the intermediate DMS oxidation species, DMSO, for which rather unusual measurements have been reported in previous marine sulfur studies. The 3 pptv bromine deficit observed in PASE must be lost over the lifetime of the aerosol which is a few days. This observation suggests that the primary BrO production rate is very small. However, considering the uncertainties in these observations and the possible importance of secondary production of bromine radicals through aerosol surface reactions, to completely rule out the importance of bromine chemistry under tropical conditions at this time cannot be justified. This point has been brought into focus from prior work that even at levels of 1 pptv, the effect of BrO oxidation on DMS can still be quite significant. Thus, as in the case of DMS conversion to SO2, future studies will be needed. In the latter case there will need to be a specific focus on halogen chemistry. Such studies clearly must involve specific measurements of radical species such as BrO.

The Sulfur Budget in Magmas: Evidence from Melt Inclusions, Submarine Glasses, and Volcanic Gas Emissions

Research Article| January 01, 2011 The Sulfur Budget in Magmas: Evidence from Melt Inclusions, Submarine Glasses, and Volcanic Gas Emissions Paul J. Wallace; Paul J. Wallace Deprtment of Geological Sciences, University of Oregon Eugene, Oregon 97403-1272, U.S.A., pwallace@uoregon.edu Search for other works by this author on: GSW Google Scholar Marie Edmonds Marie Edmonds Department of Earth Sciences University of Cambridge Cambridge, CB2 3EQ, United Kingdom, medm06@esc.cam.ac.uk Search for other works by this author on: GSW Google Scholar Author and Article Information Paul J. Wallace Deprtment of Geological Sciences, University of Oregon Eugene, Oregon 97403-1272, U.S.A., pwallace@uoregon.edu Marie Edmonds Department of Earth Sciences University of Cambridge Cambridge, CB2 3EQ, United Kingdom, medm06@esc.cam.ac.uk Publisher: Mineralogical Society of America First Online: 09 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2011) 73 (1): 215–246. https://doi.org/10.2138/rmg.2011.73.8 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul J. Wallace, Marie Edmonds; The Sulfur Budget in Magmas: Evidence from Melt Inclusions, Submarine Glasses, and Volcanic Gas Emissions. Reviews in Mineralogy and Geochemistry 2011;; 73 (1): 215–246. doi: https://doi.org/10.2138/rmg.2011.73.8 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search The major magmatic volatile components—H2O, CO2, S, Cl, and F— play an important role in the formation, evolution, and eruption of magma. Knowledge of magmatic concentrations and fluxes of these volatiles is thus important for understanding explosive eruptive behavior of volcanoes, recycling of volatiles in subduction zones, formation of magmatic-hydrothermal ore deposits, fluxes of volcanic gases to Earth’s atmosphere, and potential climatic impacts of large volcanic eruptions. Over the past 30 years, new analytical techniques for measuring volatiles in melt inclusions and glasses from volcanic rocks and new developments in remote sensing technology used for quantifying... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

High‐resolution dimethyl sulfide and dimethylsulfoniopropionate time series profiles in decaying summer first‐year sea ice at Ice Station Polarstern, western Weddell Sea, Antarctica

High‐resolution profiles of ice dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) concentrations were measured together with a suite of ancillary physical and biological properties during a time series of decaying summer‐level first‐year sea ice throughout December 2004 during the Ice Station Polarstern drift experiment (western Weddell Sea, Antarctica). Ice DMSP and DMS concentrations were always maximum at the bottom of the ice sheet (636–2627 and 292–1430 nM, respectively) where the highest chlorophyll a levels were also found (15–30 μg L−1). Throughout the observation period, the autotrophic surface community (32–205 μg C L−1) was dominated by Phaeocystis sp. while the bottom community (1622–3830 μg C L−1) mainly consisted of pennate diatoms. This illustrates that, although being known for lower DMSP‐to‐chlorophyll a ratios than Phaeocystis sp., diatoms dominated the overall DMSP production because of their much larger biomass. Decreasing DMSP concentrations and increasing DMS‐to‐DMSP ratios in the bottom layers with time suggested active DMSP‐to‐DMS conversion in a slowly degrading environment. Drastic temporal brine volume and brine salinity changes associated with the decaying sea ice cover are shown to directly impact (1) the migration of DMSP and DMS through the brine network, (2) the DMSP‐to‐DMS conversion processes within the ice interior, and (3) the physiological response of the ice algae. First‐order flux estimates show that decaying summer‐level first‐year sea ice alone can significantly contribute to the regional sulfur budget of the Weddell Sea with an estimated average loss rate of 5.7 μmol DMS(P) m−2 d−1) toward the atmosphere and the ocean.

Comparisons of watershed sulfur budgets in southeast Canada and northeast US: new approaches and implications

Most of eastern North America receives elevated levels of atmospheric deposition of sulfur (S) that result from anthropogenic SO2 emissions from fossil fuel combustion. Atmospheric S deposi- tion has acidified sensitive terrestrial and aquatic ecosystems in this region; however, deposition has been declining since the 1970s, resulting in some recovery in previously acidified aquatic ecosystems. Accurate watershed S mass balances help to evaluate the extent to which atmospheric S deposition is retained within ecosystems, and whether internal cycling sources and biogeochemical processes may be affecting the rate of recovery from decreasing S atmospheric loads. This study evaluated S mass balances for 15 sites with watersheds in southeastern Canada and northeastern US for the period 1985 to 2002. These 15 sites included nine in Canada (Turkey

Excess volatiles supplied by mingling of mafic magma at an andesite arc volcano

We present the results of a study of volcanic gases at Soufrière Hills Volcano, Montserrat, which includes the first spectroscopic measurements of the major gas species CO2 and H2S at this volcano using a Multisensor Gas Analyzer System (MultiGAS) sensor. The fluxes of CO2 and H2S were 640–2750 t/d and 84–266 t/d, respectively, during July 2008, during a prolonged eruptive pause. The flux of CO2 is similar to estimates for the entire arc from previous geochemical studies, while the measured H2S flux significantly alters our interpretation of the sulphur budget for this volcano. The fluxes of both sulphur and carbon show considerable excesses over that which can be supplied by degassing of erupted magma. We demonstrate, using thermodynamic models and published constraints on preeruptive volatile concentrations, that the gas composition and fluxes are best modeled by mixing between (1) gases derived from isobaric quenching of mafic magma against cooler andesite magma at depth and (2) gases derived from shallower rhyolitic interstitial melt within the porpyritic andesite. The escape of deep‐derived gases requires pervasive permeability or vapor advection extending to several kilometers depth in the conduit and magma storage system. These results provide more compelling evidence for both the contribution of unerupted mafic magma to the volatile budget of this andesitic arc volcano and the importance of the intruding mafic magma in sustaining the eruption. From a broader perspective, this study illustrates the importance and role of underplating mafic magmas in arc settings. These magmas play an important role in triggering and sustaining eruptions and contribute in a highly significant way to the volatile budget of arc volcanoes.

Effects of storm flow samplings on the evaluation of inorganic nitrogen and sulfate budgets in a small forested watershed

AbstractTo investigate the effects of storm flow samplings on the evaluation of DIN and SO42− budgets, we conducted storm flow samplings and discrete interval (weekly) samplings of stream water, throughfall, and stemflow. This investigation lasted for three years and took place in a small forested watershed in western Japan. Annual exports were calculated by the sum of the load (ΣLtotal)‐ sum of the discharge (ΣQtotal) relationships obtained by storm flow samplings. These were then compared to calculated ones that were based on LQ relationships obtained by discrete interval sampling. The results of discrete interval sampling showed that the relationships of DIN or SO42− concentration to the discharge amount found in stream water differed from those of storm flow sampling. This was especially notable in years with higher annual precipitation and subsequent higher annual discharges. Also, exports of DIN and SO42− during storm flow periods accounted for 83% and 78% of annual exports on 3‐year averages, respectively. These results confirmed that storm flow samplings are essential for estimating annual exports of DIN and SO42−. Annual exports that were calculated based on just discrete interval sampling (46% and 17%, respectively) overestimated DIN and SO42− from discrete interval and storm flow samplings on a 3‐year average. These overestimates were pronounced in years of higher discharge, and critically affected the rates of net‐retention or export of DIN and SO42−. The relationship of smaller input than output of DIN was reversed if storm flow sampling was included. Copyright © 2009 John Wiley & Sons, Ltd.

Experimental evidence for sulfur-rich martian magmas: Implications for volcanism and surficial sulfur sources

It has been proposed that sulfur outgassing by volcanism on Mars contributes to the sulfur budget and volatile cycle at and near the surface (Farquhar et al., 2000; Halevy et al., 2007). However, it remains unclear if shergottites and martian magmas are sulfide saturated or under-saturated, and therefore how much sulfur they can contribute via volcanism. Expressions derived from experimental studies allow prediction of S contents, though they are not calibrated for shergottitic liquids, which are FeO-rich and Al 2O 3-poor compared to the terrestrial experimental dataset upon which the models have been based. We have carried out new experiments designed to test current S saturation models, and then show that existing calibrations are not suitable for high FeO and low Al 2O 3 compositions characteristic of shergottitic liquids. The new results show that existing models either under-predict by a factor of 2, or over-predict by a factor of 2–3, the S contents of sulfide saturated shergottitic liquids. Primitive shergottite magmas are capable of dissolving no more than ~ 4000 ppm S at sulfide saturation. Melting of the martian mantle, and subsequent volcanism provides more than enough sulfur for the sulfate-rich soil and layered deposits recognized on the surface of Mars.

Concentrations, sulfur isotopic compositions and origin of organosulfur compounds in pore waters of a highly polluted raised peatland

Sulfur cycling in peatlands plays a key role in their response to atmospheric deposition of acid sulfate; however, the role of dissolved organic sulfur species has received little attention. In this study, we assess the quantitative importance of dissolved organic sulfur species in a heavily polluted peatland and their role in sulfur cycling. Surface and pore waters from a raised peat bog have been analyzed for dissolved organic and inorganic species. Except in the surface water, organically bound sulfur dominates over sulfate sulfur and the organosulfur is predominantly in the humic fraction, which is not GC amenable. Two organosulfur compounds are present in the GC amenable fraction at all depths; a compound containing a benzene ring, sulfone and amide groups dominates while a compound closely similar to either benzothiazole or 1,2-benzisothiazole is present at 100–1000 times lower concentrations. Other organosulfur species were detected in some samples by GC–AED (gas chromatography–atomic emission detection) at similar or yet lower concentrations but not identifiable with GC–MS. In the shallowest parts of the peat, sulfur isotopic data on the humic and non-humic dissolved organic sulfur fractions show a pronounced difference, implying different sources for these organosulfur compounds. Humic organosulfur is 34S enriched, indicating a source for this component from breakdown of plant materials, which have similar δ34S (0.1‰ and 4.2‰). By contrast, the non-humic organosulfur is more 34S depleted at shallow depths (−11.7‰ in surface water), indicating an origin from reaction of bacterially produced sulfide (−9.9‰ in surface water) with dissolved organic material. Deeper in the peat the non-humic organosulfur becomes more 34S enriched (up to +6.8‰), which may result from either: (i) reactions between organic material and more 34S enriched sulfide; or (less likely) (ii) a shift to production of non-humic organosulfur by breakdown of humic compounds or plant material in the peat matrix.These data highlight the importance of organosulfur species relative to inorganic species in peatland groundwaters. Organosulfur species comprise the bulk of the dissolved sulfur budget and are involved in the bacterial cycling of sulfur in the peatland ecosystem.

Surge in sulphur and halogen degassing from Ambrym volcano, Vanuatu

Volcanoes provide important contributions to atmospheric budgets of SO2 and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18-270 kg s -1 of SO2, and 62-110 gs -1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8-14 and ~27-50 kg s -1 , respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO2 output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.

Long term changes of chemical weathering products in rivers heavily impacted from acid mine drainage: Insights on the impact of coal mining on regional and global carbon and sulfur budgets

The long term impacts of acid mine drainage (AMD) on stream chemistry and regional carbon and sulfur budgets were explored using watersheds of Pennsylvania underlain by extensive coal deposits. Areas of these watersheds have been mined for 200 yr, yet mining activity decreased to < 2% of peak by the late 1900s. A unique aspect of this study was the coupling of 100 yr of data on stream chemistry measurements with detailed coal mining data, which allowed for new budgets of the impact of mining on regional and global budgets. The Lackawanna River and upper Schuylkill River, both ~ 900 km 2 watersheds, witnessed dramatic changes in pH, alkalinity, calcium, magnesium and sulfate. Sulfate fluxes from these watersheds, for instance, were 4–12 times higher in the 1940s than they are currently. Fluxes of sulfate and magnesium from the Susquehanna River at Danville, the major tributary to the Chesapeake Bay, are currently 32 and 70% of what they were in the 1940s, while alkalinity fluxes have doubled and pH has recovered 0.8 pH units. The direct impact on regional carbon budgets through the degassing of CO 2 from carbonates was intense during the height of AMD but the long term regional impact is modest, resulting in the loss of ~ 3.1 Tg of carbon to the atmosphere over the last century. During the 1940s, the export of AMD derived sulfate to the 29,000 km 2 portion of the Susquehanna River studied here was twice as large as the current input from SO x deposition to the entire 71,000 km 2 Susquehanna watershed. This is surprising, comparing the small spatial footprint of AMD to the large footprint of the entire Susquehanna watershed. Normalizing these export rates to coal production data we estimate that global sulfur releases from AMD could account for 28–40% of riverine sulfate derived from pyrite oxidation, and be equal to ~ 20% of anthropogenic S from atmospheric deposition. This study emphasizes the potential importance of AMD to global S budgets, particularly since coal mining is predicted to increase by 50% in the coming century.

Sulfur content at sulfide saturation in oxidized magmas

Research Article| May 01, 2009 Sulfur content at sulfide saturation in oxidized magmas Pedro J. Jugo Pedro J. Jugo * 1Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada *E-mail: pjugo@laurentian.ca. Search for other works by this author on: GSW Google Scholar Author and Article Information Pedro J. Jugo * 1Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada *E-mail: pjugo@laurentian.ca. Publisher: Geological Society of America Received: 28 Sep 2008 Revision Received: 11 Dec 2008 Accepted: 19 Dec 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (5): 415–418. https://doi.org/10.1130/G25527A.1 Article history Received: 28 Sep 2008 Revision Received: 11 Dec 2008 Accepted: 19 Dec 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Pedro J. Jugo; Sulfur content at sulfide saturation in oxidized magmas. Geology 2009;; 37 (5): 415–418. doi: https://doi.org/10.1130/G25527A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Accurate estimates of the sulfur content in silicate melts at sulfide saturation are required to explain magmatic processes such as the origin and budget of sulfur in some volcanic eruptions and the transfer of Cu, Au, and other precious metals from the mantle to the crust via partial melting of the mantle. A model that links S speciation, S content at sulfide saturation (SCSS), S content at anhydrite saturation (SCAS), and changes in oxygen fugacity (fO2) is presented. The model predicts an exponential increase in the SCSS with increasing fO2 from fayalite-magnetite-quartz (FMQ) because of the contribution of sulfate species in the melt. The predicted SCSS ranges from 1300 ppm (at FMQ − 1) to 1500 ppm (at FMQ + 0.5) for mid-oceanic-ridge basalts (MORB), is up to 7500 ppm (at FMQ + 2) for backarc and oceanic-island basalts, and can be as high as 1.4 wt% (at FMQ + 2.3) for island arc basalts. For the mantle wedge above subducting slabs, the SCSS ranges from 1500 ppm (at FMQ + 0.4) to 4500 ppm (at FMQ + 1.7). Disequilibrium experiments show textural evidence that is consistent with the model predictions. Thus, sulfide-undersaturated magmas can be formed at relatively low degrees of melting in metasomatized mantle sources without the need to invoke sulfide elimination by oxidation at high fO2. Estimates of the amount of S that can be transported by silicate melts need to account for the enhanced capacity of silicate melts to dissolve S when sulfate species are present, even if sulfides are the stable S-bearing phase. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Apparent downwind depletion of volcanic SO2 flux—lessons from Masaya Volcano, Nicaragua

A series of 707 measurements at Masaya in 2005, 2006, and 2007 reveals that SO2 emissions 15km downwind of the active vent appear to be ~33% to ~50% less than those measured only 5km from the vent. Measurements from this and previous studies indicate that dry deposition of sulfur from the plume and conversion of SO2 to sulfate aerosols within the plume each may amount to a maximum of 10% loss, and are not sufficient to account for the larger apparent loss measured. However, the SO2 measurement site 15km downwind is located on a ridge over which local trade winds, and the entrained plume, accelerate. Greater wind speeds cause localized dilution of the plume along the axis of propagation. The lower concentrations of SO2 measured on the ridge therefore lead to calculations of lower fluxes when calculated at the same plume speed as measurements from only 5km downwind, and is responsible for the apparent loss of SO2. Due to the importance of SO2 emission rates with respect to hazard mitigation, petrologic studies, and sulfur budget calculations, measured fluxes of SO2 must be as accurate as possible. Future campaigns to measure SO2 flux at Masaya and similar volcanoes will require individual plume speed measurements to be taken at each flux measurement site to compensate for dilution and subsequent calculation of lower fluxes. This study highlights the importance of a comprehensive understanding of a volcano’s interaction with its surroundings, especially for low, boundary layer volcanoes.

Modelling of air quality and atmospheric deposition in Hungary

Annual average atmospheric concentrations and depositions of sulfur and nitrogen species, as well as trace metals in Hungary and its surrounding regions were estimated by model computations. Spatial and temporal variations of the distributions are presented in the paper. The temporal variation of atmospheric sulfur budget was calculated based on a simple atmospheric box model. In the case of atmospheric lead, the cumulative atmospheric depositions were also estimated for a sixty years long period until 2015 using historical emission factors for the past decades as well as emission scenarios for the future. It was found that Hungary belongs to the moderately polluted regions in Europe. A model hierarachy was developed in order to perform multi-scale modelling studies on the air pollution processes at different spatial and temporal scales in Hungary. A set of environmental indicators was defined to characterize the actual state of the atmospheric environment.

Seasonal and event variations in δ34S values of stream sulfate in a Vermont forested catchment: Implications for sulfur sources and cycling

Stable sulfur (S) isotope ratios can be used to identify the sources of sulfate contributing to streamwater. We collected weekly and high-flow stream samples for S isotopic analysis of sulfate through the entire water year 2003 plus the snowmelt period of 2004. The study area was the 41-ha forested W-9 catchment at Sleepers River Research Watershed, Vermont, a site known to produce sulfate from weathering of sulfide minerals in the bedrock. The δ 34S values of streamwater sulfate followed an annual sinusoidal pattern ranging from about 6.5‰ in early spring to about 10‰ in early fall. During high-flow events, δ 34S values typically decreased by 1 to 3‰ from the prevailing seasonal value. The isotopic evidence suggests that stream sulfate concentrations are controlled by: (1) an overall dominance of bedrock-derived sulfate ( δ 34S ~ 6–14‰); (2) contributions of pedogenic sulfate ( δ 34S ~ 5–6‰) during snowmelt and storms with progressively diminishing contributions during base flow recession; and (3) minor effects of dissimilatory bacterial sulfate reduction and subsequent reoxidation of sulfides. Bedrock should not be overlooked as a source of S in catchment sulfate budgets.

Pre-1991 sulfur transfer between mafic injections and dacite magma in the Mt. Pinatubo reservoir

Before the 1991–1992 activity, a large andesite lava dome belonging to the penultimate Pinatubo eruptive period (Buag ∼ 500 BP) formed the volcano summit. Buag porphyritic andesite contains abundant amphibole-bearing microgranular enclaves of basaltic–andesite composition. Buag enclaves have lower K 2O and incompatible trace element (LREE, U, Th) contents than mafic pulses injected in the Pinatubo reservoir during the 1991–1992 eruptive cycle. This study shows that Buag andesite formed by mingling of a hot, water-poor and reduced mafic magma with cold, hydrous and oxidized dacite. Depending on their size, enclaves experienced variable re-equilibration during mixing/mingling. Re-equilibration resulted in hydration, oxidation and transfer of mobile elements (LILE, Cu) from the dacite to the mafic melts and prompted massive amphibole crystallization. In Buag enclaves, S-bearing phases (sulfides, apatite) and melt inclusions in amphibole and plagioclase record the evolution of sulfur partition among melt, crystal and fluid phases during magma cooling and oxidation. At high temperature, sulfur is partitioned between andesitic melt and sulfides (Ni-pyrrhotite). Magma cooling, oxidation and hydration resulted in exsolution of a S–Cl–H 2O vapor phase at the S-solubility minimum near the sulfide–sulfate redox boundary. Primary magmatic sulfide (pyrrhotite) and xenocrystic sulfide grains (pyrite), recycled together with olivines and pyroxenes from old mafic intrusives, were replaced by Cu-rich phases (chalcopyrite, cubanite) and, partially, by Ba–Sr sulfate. Sulfides degassed and transformed into residual spongy magnetite in response to fS 2 drop during final magma ascent and decompression. Our research suggests that a complete evaluation of the sulfur budget at Pinatubo must take into account the en route S assimilation from the country rocks. Moreover, this study shows that the efficiency of sulfur transfer between mafic recharges and injected magmas is controlled by the extent and rate of mingling, hydrous flushing and melt oxidation. Vigorous mixing/mingling and transformation of the magmatic recharge into a spray of small enclaves is required in order to efficiently strip their primary S-content that otherwise remains locked in the sulfides. Hydrous flushing increases the magma oxidation state of the recharges and modifies their primary volatile concentrations that cannot be recovered by the study of late-formed mineral phases and melt inclusions. Conversely, S stored in both late-formed Cu-rich sulfides and interstitial rhyolitic melt represents the pre-eruptive sulfur budget immediately available for release from mafic enclaves during their decompression.

Primary igneous anhydrite: Progress since its recognition in the 1982 El Chichón trachyandesite

Primary igneous anhydrite was first identified in 1982 El Chichón pumices. Analysis of the sulfur budget for the eruption provided compelling evidence that the pre-eruptive magma contained a significant gas phase at ∼ 7 km depth in order to account for the “excess gas release” of ∼ 5–9 million tons of SO 2 to the stratosphere by the eruption. Primary igneous anhydrite and a larger “excess gas release” of ∼ 20 million tons of SO 2 were noted for the significantly larger eruption of Mount Pinatubo in 1991, for which a separate gas phase at ∼ 7–9 km depth was also required by the sulfur budget. Pumices from both eruptions have mineral assemblages dominated by plagioclase and hornblende, with minor biotite, and show evidence for co-nucleation and mutual inclusions of anhydrite and apatite. Both magmas were also very water-rich and highly oxidized, with oxygen fugacities $1 log unit above the synthetic Ni–NiO buffer. Furthering the similarities between these two eruptions, ion-microprobe analyses of sulfur isotopic compositions of anhydrites in pumices from El Chichón and Mount Pinatubo both showed that individual crystals are isotopically homogeneous, but inter-crystalline variations in δ 34S are well beyond analytical error. This study reviews the history of thought regarding primary igneous anhydrite. Ten volcanic and plutonic analogues to the El Chichón and Mount Pinatubo magmas are discussed. All were similarly water-rich and highly oxidized magmas. Hornblende is the dominant mafic phenocryst in all but one plutonic example; in that case so much early anhydrite precipitated that no calcium remained to form hornblende. Biotite is very abundant in that exceptional plutonic case, and is present in six of the other examples with primary igneous anhydrite. Sphene is known as an indicator mineral of high magmatic oxygen fugacity; it was present in the 1982 El Chichón pumices, and in 6 of the other anhydrite-bearing samples. Hornblende and biotite phenocrysts are also characteristic of the intermediate-to-felsic plutonic rocks that typically host porphyry–Cu deposits. Such magmas are also known to be water-rich and highly oxidized. A close spatial and petrogenetic connection exists between magmas with primary igneous anhydrite and magmatic–hydrothermal ore deposits.

Nature and significance of small volume fall deposits at composite volcanoes: Insights from the October 14, 1974 Fuego eruption, Guatemala

The first of four successive pulses of the 1974 explosive eruption of Fuego volcano, Guatemala, produced a small volume (∼0.02 km3 DRE) basaltic sub-plinian tephra fall and flow deposit. Samples collected within 48 h after deposition over much of the dispersal area (7–80 km from the volcano) have been size analyzed down to 8 φ (4 µm). Tephra along the dispersal axis were all well-sorted (σ φ = 0.25–1.00), and sorting increased whereas thickness and median grain size decreased systematically downwind. Skewness varied from slightly positive near the vent to slightly negative in distal regions and is consistent with decoupling between coarse ejecta falling off the rising eruption column and fine ash falling off the windblown volcanic cloud advecting at the final level of rise. Less dense, vesicular coarse particles form a log normal sub-population when separated from the smaller (Mdφ < 3φ or < 0.125 mm), denser shard and crystal sub-population. A unimodal, relatively coarse (Mdφ = 0.58φ or 0.7 mm σ φ = 1.2) initial grain size population is estimated for the whole (fall and flow) deposit. Only a small part of the fine-grained, thin 1974 Fuego tephra deposit has survived erosion to the present day. The initial October 14 pulse, with an estimated column height of 15 km above sea level, was a primary cause of a detectable perturbation in the northern hemisphere stratospheric aerosol layer in late 1974 to early 1975. Such small, sulfur-rich, explosive eruptions may substantially contribute to the overall stratospheric sulfur budget, yet leave only transient deposits, which have little chance of survival even in the recent geologic record. The fraction of finest particles (Mdφ = 4–8φ or 4–63 µm) in the Fuego tephra makes up a separate but minor size mode in the size distribution of samples around the margin of the deposit. A previously undocumented bimodal–unimodal–bimodal change in grain size distribution across the dispersal axis at 20 km downwind from the vent is best accounted for as the result of fallout dispersal of ash from a higher subplinian column and a lower “co-pf” cloud resulting from pyroclastic flows. In addition, there is a degree of asymmetry in the documented grain-size fallout pattern which is attributed to vertically veering wind direction and changing windspeeds, especially across the tropopause. The distribution of fine particles (<8 µm diameter) in the tephra deposit is asymmetrical, mainly along the N edge, with a small enrichment along the S edge. This pattern has hazard significance.

Regional and global trends in sulfate aerosol since the 1980s

In the last two decades anthropogenic SO2 emissions have decreased across Europe and North America but have increased across Asia. Long‐term surface observations suggest that atmospheric sulfate concentrations have followed trends in sulfur emissions more closely across Asia, than across the USA and Europe. We use a global model of chemistry and aerosol to understand changes in the regional sulfur budget between 1985 and 2000. For every 1% decrease in SO2 emissions over Europe and the USA the modelled sulfate column burden decreased by 0.65%, while over Asia a 1% increase in SO2 resulted in a 0.88% increase in sulfate. The different responses can be explained by the availability of oxidant in cloud. We find that because emissions have moved southward to latitudes where in‐cloud oxidation is less oxidant limited, the 12% reduction in global SO2 emissions between 1985 and 2000 caused only a 3% decrease in global sulfate.

Agricultural acid sulfate soils: a potential source of volatile sulfur compounds?

Environmental context. Acid sulfate soils are important contributors to global environmental problems. Agricultural acid sulfate soils have recently been shown to emit sulfur dioxide, an important gas in global issues of acid rain, cloud formation and climate change. This emission is surprising because these soils tend to be wet and the gas is extremely water-soluble. The potential origins of this gas are not yet understood within the context of acid sulfate soils. Our new study reports the measurement of two potential precursors of sulfur dioxide, dimethylsulfide and ethanethiol, from both a natural and an agricultural acid sulfate soil in eastern Australia. Abstract. Most agricultural soils are generally considered to be a sink for sulfur gases rather than a source; however, recent studies have shown significant emissions of sulfur dioxide and hydrogen sulfide from acid sulfate soils. In the current study, acid sulfate soil samples were taken in northern New South Wales from under sugarcane cropping, as well as from an undisturbed nature reserve. Using gas chromatography/flame photometric detection in conjunction with headspace solid-phase microextraction, we have now determined that these soils are a potential source of the low molecular weight volatile sulfur compounds, dimethylsulfide and ethanethiol. Although the mechanism for their production remains unclear, both compounds are important in the transfer and interconversions of atmospheric and terrestrial sulfur. Therefore, these novel findings have important implications for refining local and regional atmospheric sulfur budgets, as well as for expanding our understanding of sulfur cycling within acid sulfate soils and other sediments.