Volcanic Emanations Research Articles

The solubility of CaF2 in seawater of normal and increased salinity (associated with genesis of fluorite in sedimentary rocks)

The solubility of crystalline and precipitated calcium fluoride in seawater and brines of the first stages of its evaporative concentration (before the beginning of gypsum and halite setting) was experimentally studied. It was established that in the entire studied range of salinity, seawater and its derivatives are strongly undersaturated by the calcium fluoride, which excludes its spontaneous precipitation in drying isolated sea basins. A necessary condition for the formation of sedimentary fluorite is the entry into the drying sea basins of significant amounts of dissolved fluorine from external sources, which can be river runoff, volcanic emanations, and hydrothermal solutions.

Atmospheric Deposition around the Industrial Areas of Milazzo and Priolo Gargallo (Sicily–Italy)—Part B: Trace Elements

The concentrations of trace elements in atmospheric bulk depositions (wet plus dry) were investigated from two highly industrialised areas of Sicily (southern Italy) from June 2018 to July 2019, in order to recognise the main natural and anthropogenic sources. A side objective of this study was to improve the common sampling procedures and analytical methods used for monitoring trace elements in atmospheric deposition. The trace element VWM (Volume-Weighted Mean) concentrations ranged from less than 0.01 μg L−1 for trace elements such as Cs, Tl, and U, up to 24 μg L−1 for minor elements (Al, Zn, Sr), in the filtered aliquot, while they reached concentrations up to 144 μg L−1 for the same elements, in the unfiltered aliquot. Therefore, significant differences in concentrations between these two aliquots were found, particularly for Al, Fe, Ti, Zn, Cr, Pb, Se, Cs, and U. This implies that filtering operations may produce a consistent underestimation of concentrations of certain ‘constituents’ of the atmospheric deposition. Natural (marine spray, local and regional geogenic input, volcanic emanations) and anthropogenic sources (industrial emissions, auto vehicular traffic, and diffuse background pollution) which influence rainwater chemistry were identified. Enrichment factors (EFs), with respect to the upper crust composition, provided clear evidence of the different sources above mentioned: Ti, Fe, Al, Cs, Cr, Rb, and Co have low EFs (<1), and are referable to the (local and/or regional) geogenic input, while Se, Sb, Zn, B, Cd, Cu, Mo, Sr, As, with high EFs (>10), highlight the influence of marine and/or industrial sources. The study produced a novel dataset on the atmospheric deposition rate of several trace elements, which had never been studied in the investigated areas. Finally, a comparison of trace element deposition rates in the studied areas with the atmospheric deposition reported for 53 different sites, belonging to 20 different European nations, was made. The comparison showed that some elements, such as Al, V, Zn, and Mo had higher median deposition fluxes in the Sicilian sites than in European monitoring sites.

О возможной природе сталактитоподобных образований в агатах Ольского плато (Северо-Восток России)

The features of the stalactite-like formations relationship with onyxes in the geodes of the Ola basalt plateau agates are considered. It is shown that such formations are formed from the gel in the arc parts of cavities and flow down in the shape of icicles under the influence of gravity. "Stalactites" intersect previously formed layers of opal, chalcedony, quartz. The onyx layers. consisting of the silica group (SiO2,) minerals, can be dissolved only with the participation of F or HF. This is especially important in the case of poured basalts, since they contain no silica (SiO2) minerals, and silicon crystallizes in a different coordination (SiO4, Si3O8) in feldspars, olivine, etc. Geode filling with silica can be explained by the passage of gaseous HF and F from volcanic emanations through the thickness of silicon-containing rocks, with partial Si dissolution and formation of gaseous silicon tetrafluoride (SiF4), which fills cavities (bubbles) in basalt lavas. Subsequently, when meteoric water seeps into the cavity, silicon tetrafluoride is hydrolyzed to form orthosilicic acid, which is transformed into silica gel; the latter polymerizes to form chalcedony. Simultaneously, the remains of F either evaporate through cracks or accumulate in the cavity arch, again dissolving basalt in the vault of the geode (cycle repetition), with the formation of a viscous gel-like substance containing fluorine, which flows down in jets and polymerizes, thus creating stalactite-like structures. The author uses the photographs of agates found by B. M. Sedov in his numerous hikes to the Ola basalt plateau. The photographs were published in the wonderful book, "Agates from Upstream of the Ola River (Russia)" by B. M. Sedov.

Isotopic constraints on selenium degassing from basaltic magma and near-surface capture by fumarolic deposits: Implications for Se redistribution onto the Earth's surface

Volcanic emanations from cooling basaltic lava represent a diffuse and relatively poorly constrained source of metallic and non-metallic compounds to the Earth's surface. These compounds become incorporated in fumarolic minerals and redeposit at the surface of lava flows before entering the environmental cycle. The semi-volatile and chalcophile element selenium (Se) can be either vital or toxic to animals and humans. Thus, understanding the pathways of Se capture and relative concentrations in fumaroles is imperative for estimating their contributions to soils and aquifers in volcanically active regions, with implications for animal and human health. In this study, we report Se concentrations and Se stable isotope composition in a sample suite comprising degassed and undegassed basaltic rocks and various fumarolic deposits (thenardite, Na-K sulfate, gypsum, fluoride, and native sulfur) fed from degassing lava flows at Piton de la Fournaise volcano, Réunion Island. Erupted basaltic lavas (136–58 ng·g−1 Se) lost up to more than half of their pre-eruptive Se due to subaerial degassing and retained a heavier isotope composition (δ82/76Se = 0.11 ± 0.17‰, 2 s.d.) compared to less undegassed volcanic glass (138 ng·g−1 Se and δ82/76Se = −0.19 ± 0.04‰, 2 s.e.). Fumarolic deposits that formed over a temperature range of ~800–100 °C and captured Se from the degassing lava show higher to very high Se concentrations ranging from 0.54 μg·g−1 to 1578 μg·g−1 and significant Se isotope fractionation (δ82/76Se = +0.6 to −2.08‰). We propose two separate models that can explain the relative concentration and Se isotope composition of the deposits: 1) A compound oxidation state-dependent Se incorporation into the various fumarolic minerals, or 2) Temperature-dependent Rayleigh condensation from a cooling gas triggered by compound saturation. The Rayleigh condensation model can entirely explain the Se concentration and isotope composition of the fumaroles and predicts that up to 80% of the Se released from the lava is likely to be captured by precipitation to form solid phases within the lava pile, most dramatically in the coldest deposits below the sublimation temperature of SeO2 (< 315 °C). In contrast, mineral-dependent isotope pathways cannot fully explain our data, including the lighter Se isotope compositions in the more oxidized compounds compared to more reduced ones. Such a mineralogical effect cannot be excluded but further investigations and experimental studies are required in order to scrutinize and invoke its role. Finally, the environmental impact of these degassing-induced secondary products will be dependent on the relative compound water solubilities resulting in either Se mobilization towards aquifers or accumulation onto developing soils and plants. Such studies could prove useful for developing risk assessments in volcanically active regions on our planet, and for reaching a better understanding of the global continent-ocean Se isotope budget and signature.

The origin of Miocene evaporites in the Tuz Gölü basin (Central Anatolia, Turkey): Implications from strontium, sulfur and oxygen isotopic compositions of the Ca-Sulfate minerals

Sulfur, oxygen and strontium isotope compositions of the sulfate minerals (gypsum and anhydride) of the Miocene evaporites in the Tuz Gölü basin which is the largest, closed and inner basin of Turkey located in the Central Anatolia, were investigated to evaluate the origin of the sulfates and interpret the precipitation paleoenvironment. The isotopic, mineralogical and chemical properties and composition of the samples collected from drillings were investigated. The δ34SCDT and δ18OSMOW values of the sulfate minerals range from 18.78 to 35.90‰ and 7.55–22.57‰, respectively. Most of the δ34S values are similar to marine (Messinian) water. In addition, the 87Sr/86Sr ratios of the minerals vary from 0.707803 to 0.708209.Most of the δ34S and δ18O values and 87Sr/86Sr ratios of the investigated samples in the Tuz Gölü basin are similar to those of the isotopic values of the Messinian marine sulfates indicating that the minerals were precipitated mostly from marine water. The 34S and 18O values of some samples are higher than those of the evaporites precipitated from the Miocene seawater and indicate that the evolution of the sufates in the basin was also controlled by the recycling-dissolution of the predeposited marine sulfates (Oligocene-Eocene), arid conditions and bacterial sulfate reduction (BSR) processes. Additionally, the low δ18O values and 87Sr/86Sr ratios with high Sr content of some samples other than those of the Miocene marine sulfates may have been caused by the influence of volcanic emanations, hydrothermal fluid, re-oxidation of sulfur and partially the contribution of the external or internal nonmarine water to the basin (e.g., meteoric water or groundwater/surface water). The Ca-sulfate minerals with high Sr contents and low 87Sr/86Sr ratios may have precipitated under the seawater-dominated hydrothermal fluid mixing conditions.

Evaluation of possible impact on human health of atmospheric mercury emanations from the Popocatépetl volcano.

The contribution of Hg from volcanic emanations is decisive for assessing global mercury emissions given the impact of this highly toxic contaminant on human health and ecosystems. Atmospheric Hg emissions from Popocatépetl volcano and their dispersion were evaluated carrying out two gaseous elemental mercury (GEM) surveys during a period of intense volcanic activity. Continuous GEM measurements were taken for 24h using a portable mercury vapor analyzer (Lumex RA-915M) at the Altzomoni Atmospheric Observatory (AAO), 11km from the crater. In addition, a long-distance survey to measure GEM was conducted during an automobile transect around the volcano, covering a distance of 129km. The evaluation of the GEM data registered in the fixed location showed that heightened volcanic activity clearly intensifies the concentration of atmospheric Hg, extreme values around 5ngm-3. Highest concentrations of GEM recorded during the mobile survey were about 10ngm-3. In both surveys, the recorded concentrations during most of the measurement time were below 2ngm-3, but measurements were taken at a considerable distance from the crater, and GEM is subject to dilution processes. During both surveys, recorded GEM did not exceed the 200ngm-3 concentration recommended by the WHO (Air quality guidelines for Europe, 2000) as the regulatory limits for Hg in the atmospheric environment for long-term inhalation. Because this study was carried out in inhabited areas around the volcano during a period of intense volcanic activity, it can be concluded that the Popocatépetl does not represent a risk to human health in terms of Hg.

Volcanically modulated pyrite burial and ocean–atmosphere oxidation

It is widely assumed that changes in the rate of biological O2 supply to the atmosphere played little, if any, role in driving the Great Oxidation Event (GOE) because extensive biological O2 production via oxygenic photosynthesis significantly predates atmospheric oxygenation on Earth. Moreover, the C isotope record seemingly precludes a dramatic increase in O2-liberating burial of organic C in the late Archean. However, organic C burial is not the only way in which the biosphere may oxidize the Earth's atmosphere. Biologically mediated burial of reduced mineral phases may also yield net oxidation. For example, reducing power can be transferred from organic matter to H2S via anaerobic respiration and ultimately stored in sedimentary pyrite (FeS2). Changes in pyrite burial may thus impact Earth's oxidation trajectory. Here, we revisit the earliest recognized episode of sulfide-rich (euxinic), pyrite-precipitating conditions in Earth's ocean, ∼200–300 million years prior to the GOE, as preserved in the ∼2.7–2.6 billion-year-old (Ga) Roy Hill Shale of the Jeerinah Formation. Applying Fe speciation and trace metal proxies to drillcore samples from two sites, we characterize both spatial and temporal heterogeneity in the accumulation of H2S in the otherwise Fe-rich Hamersley Basin. We argue that extensive pyrite burial in these locally euxinic environments was the consequence of enhanced volcanic emanations of SO2 to the atmosphere rather than oxidative weathering of crustal sulfides. Because SO2 reduction and burial as pyrite is chemically analogous to CO2 reduction and burial as organic matter, we further posit that this alternative oxidation pathway contributed to Earth's protracted oxygenation during the GOE. Our results thus highlight the need for continued study of the interplay between solid-Earth, volcanic, and biological processes and their joint modulation of oceanic and atmospheric composition.

Insights into the Hadean Earth from Experimental Studies of Zircon

Abstract Geologists investigate the evolution of the atmosphere, crust, and mantle through time by direct study of the rock record. However, the Hadean eon (&amp;gt;3.85 Ga) has been traditionally viewed as inaccessible due to the absence of preserved rocks. The discovery of &amp;gt;4.0 Ga detrital zircons from Western Australia in the 1980s – coupled with the development of new micro-analytical capabilities – made possible new avenues of early Earth research. The prevailing view that emerged is that the early Earth may have contained a stable hydrosphere, water-saturated or (near water-saturated) granitic magmas, and volcanic emanations dominated by neutral gas species (e.g., CO2, H2O, and SO2). The Hadean Earth may have been capable of supporting life ∼200 Ma after accretion and perhaps earlier. Many of these models are formulated – or have been subsequently supported – by laboratory experiments of zircon. Important petrological variables such as temperature, pressure, oxygen fugacity, and component activities (e.g., SiO2/TiO2-activities) can be controlled. These experiments are fundamental for extrapolation to ‘deep time’ because they provide a means to understand primary chemistry preserved in ancient zircons. This review paper specifically focuses on zircon experimental studies (oxygen isotope fractionations, Ti-thermometry, and redox sensitive element incorporation into zircon), which have influenced our view of the very early Earth.

The oxidation state of Hadean magmas and implications for early Earth’s atmosphere

Magmatic outgassing of volatiles from Earth's interior probably played a critical part in determining the composition of the earliest atmosphere, more than 4,000 million years (Myr) ago. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen and sulphur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure (fugacity) of oxygen. Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH(4), H(2), H(2)S, NH(3) and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H(2)O, CO(2), SO(2) and N(2) (refs 1-4). Direct constraints on the oxidation state of terrestrial magmas before 3,850 Myr before present (that is, the Hadean eon) are tenuous because the rock record is sparse or absent. Samples from this earliest period of Earth's history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching ∼4,400 Myr (refs 5-8). Here we report a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts that is based on the incorporation of cerium into zircon crystals. We find that the melts have average oxygen fugacities that are consistent with an oxidation state defined by the fayalite-magnetite-quartz buffer, similar to present-day conditions. Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from mantle-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day mantle-derived lavas as early as ∼4,350 Myr before present. These results suggest that outgassing of Earth's interior later than ∼200 Myr into the history of Solar System formation would not have resulted in a reducing atmosphere.

Oceanic spreading center–generated basaltic crust and associated sulfidic and carbonate-rich hydrothermal deposits in the Archean (ca. 3 Ga), North Spirit Lake greenstone belt, Ontario, Canada

Detailed mapping of a portion of the North Spirit Lake greenstone belt reveals a basal basaltic volcanic unit (ca. 3 Ga) with a komatiitic component and strong major and trace element geochemical affinity with typical mid-ocean ridge basalts (e.g., N-MORB). The overlying transitional unit includes basaltic tuffs, which have close geochemical affinity to the underlying basalts, and to N-MORB. Interbedded with and overlying the tuffs is a thin, laterally continuous sulfide-rich unit with chert interbeds, which is in turn overlain by interbedded carbonate, chert, and iron-rich sedimentary rocks. The chemical sedimentary rocks of the transitional unit display rare-earth element (REE) patterns and positive Eu anomalies consistent with derivation from fluids associated with submarine hydrothermal vent fields. The sulfide unit is interpreted to represent proximal hydrothermal vent deposits derived from black smoker activity near a spreading center. The overlying carbonate and chert mounds and beds are interpreted as hydrothermal deposits formed at lower temperatures in a more distal setting relative to the spreading center. The carbonate deposits may have formed in an environment analogous to that of the Lost City hydrothermal field (Kelley et al., 2001), where abundant chimneys, dendrites, and beds of carbonate are produced ∼15 km from the mid-Atlantic rift axis. The basal volcanic unit consequently is interpreted as ocean-floor basalts formed at an Archean spreading center, with the basaltic tuffs representing the last volcanic emanations, and with the chemical sediments representing hydrothermal-vents deposits both proximal and distal to the spreading center. The capping siliciclastic unit likely is part of an accretionary wedge, possibly representing ocean closure after a protracted seafloor spreading episode. The sedimentary rocks were derived, in part, from a weathered tonalite-trondhjemite-granodiorite source. The supracrustal rocks of the North Spirit Lake greenstone belt provide an unusually clear window into some tectonic activity on the primitive Earth, including evidence for the existence of ocean-floor basalts, proximal and distal hydrothermal activity, and possibly a protracted cycle of ocean opening and destruction.

Reply to comment by K. Caldeira et al. on “Modern-age buildup of CO2and its effects on seawater acidity and salinity”

Reply to comment by K. Caldeira et al. on “Modern-age buildup of CO₂and its effects on seawater acidity and salinity”

Titanium complexation in hydrothermal systems

The solubility of rutile in aqueous solutions of HCl, HF, H2SO4, NaOH, and NaF was determined at 500°C, 1000 bar, and hydrogen fugacity from 8 × 10−12 to 10.3 bar (Mn3O4/Mn2O3 and Ni/NiO buffers, dissolution of an Al batch weight). The experimentally determined solubility values were used to calculate the constants of the following equilibria at 500°C and 1 kbar pressure: TiO2(rutile) + H2O + HCl0 = Ti(OH)3Cl0 (pK = 4.89); TiO2(rutile) + 2HCl0 = Ti(OH)2Cl 2 0 (pK = 4.69), TiO2(rutile) + HS O 4 − + H+ = Ti(OH)2SO 4 0 (pK = 1.98), TiO2(rutile) + 2HSO 4 − + 2H+ = Ti(SO4) 2 0 + 2H2O (pK = −1.50), TiO2(rutile) + 2H2O + OH− = Ti(OH) 5 − (pK = 3.17), TiO2(rutile) + 2H2O + 2OH− = Ti(OH) 6 2− (pK = 1.46), TiO2(rutile) + 2H2O + F− = Ti(OH)3F0 + OH− (pK = 5.86), TiO2(rutile) + 2HF0 = Ti(OH)2F 2 0 (pK = 2.99), and TiO2(rutile) + 2H2O + F− = Ti(OH)4F− (pK = 3.69). Based on the results obtained on the composition of volcanic emanations whose Ti concentrations were determined, we evaluated the constants of the equilibria TiO2(rutile) + H2O + HCl0 = Ti(OH)3Cl0 (pK = 2.74) and TiO2(rutile) + HSO 4 − + H+ = Ti(OH)2SO 4 0 (pK = 3.40) at 25°C. The electrostatic model of electrolyte ionization was used to calculate the ionization constants and the Gibbs free energy values for the following Ti species in aqueous fluids at the parameters of postmagmatic processes: Ti(OH) 3 + , Ti(OH) 4 0 , Ti(OH) 5 − , Ti(OH) 6 2− , Ti(OH)3F0, Ti(OH)2F 2 0 , Ti(OH)4F−, Ti(OH)3Cl0, Ti(OH)2Cl 2 0 , Ti(OH)2SO 4 0 , and Ti(SO4) 2 0 . As follows from our data on Ti complexation with Cl, F, and SO4, fluids the most favorable for Ti migration are aqueous acid F-rich solutions with Ti concentrations of no higher than a few fractions of a milligram per kilogram of water.

The chemical variability at the surface of Mars: Implication for sediment formation and rock weathering

Compositional data analysis was performed on chemical compositions of martian surface materials in order to unravel scenarios of past and present weathering and to evaluate the role of meteoritic accumulation. The observed chemical variability is analyzed by means of principal component analysis. Potential reservoirs that may have contributed primary material to soil formation are assessed. Chemical alteration in the course of in situ weathering is described in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts. The interplay of localized chemical alteration and global scale re-distribution and mixing of fines material is documented through the identification of different soil forming branches. These branches emanate from distinct compositional domains, which comprise basaltic and basalt-andesitic primary materials, and they converge to a global dust composition, which represents the product of chemical and physical disintegration and subsequent global mixing. Mass balance considerations applied to localized weathering phenomena are in line with findings from experimental acid–sulfate weathering on olivine-bearing basalts and the persistence of secondary silica in evaporitic rocks. In addition the composition and oxidation state of involved volcanic gases is deduced. Our findings corroborate the past activity of volcanic exhalation products in combination with liquid water. We conclude that average martian crust is dominated by basaltic materials at its topmost level and that the amount of meteoritic accumulation may contribute about 6 wt% to the martian fines. From the meteoritic contribution minimum soil formation rates of 60 ± 20 cm / Gyr are derived. Sequestration of atmospheric oxygen during weathering of primary materials may account for the oxygen deficiency of the martian atmosphere. A 4–14-m-thick layer of oxidized martian fines may account for the estimated deficit of 1.7 × 10 18 mol O 2 in the martian atmosphere depending on the primary oxidation state of volatile volcanic emanations.

Characterization of gas chemistry and noble-gas isotope ratios of inclusion fluids in magmatic-hydrothermal and magmatic-steam alunite

Chemical and isotope data were obtained for the active gas and noble gas of inclusion fluids in coarse-grained samples of magmatic-hydrothermal and magmatic-steam alunite from well-studied deposits (Marysvale, Utah; Tambo, Chile; Tapajós, Brazil; Cactus, California; Pierina, Peru), most of which are discussed in this Volume. Primary fluid inclusions in the alunite typically are less than 0.2 μm but range up to several micrometers. Analyses of the active-gas composition of these alunite-hosted inclusion fluids released in vacuo by both crushing and heating indicate consistent differences in the compositions of magmatic-hydrothermal and magmatic-steam fluids. The compositions of fluids released by crushing were influenced by contributions from significant populations of secondary inclusions that trapped largely postdepositional hydrothermal fluids. Thermally released fluids gave the best representation of the fluids that formed primary alunite. The data are consistent with current models for the evolution of magmatic-hydrothermal and magmatic-steam fluids. Magmatic-steam fluids are vapor-dominant, average about 49 mol% H 2O, and contain N 2, H 2, CH 4, CO, Ar, He, HF, and HCl, with SO 2 the dominant sulfur gas (average SO 2/H 2S=202). In contrast, magmatic-hydrothermal fluids are liquid-dominant, average about 88 mol% H 2O, and contain N 2, H 2, CO 2, and HF, with H 2S about as abundant as SO 2 (average SO 2/H 2S=0.7). The low SO 2/H 2S and N 2/Ar ratios, and the near-absence of He in magmatic-hydrothermal fluids, are consistent with their derivation from degassed condensed magmatic fluids whose evolution from reduced-to-oxidized aqueous sulfur species was governed first by rock and then by fluid buffers. The high SO 2/H 2S and N 2/Ar with significant concentrations of He in magmatic-steam fluids are consistent with derivation directly from a magma. None of the data supports the entrainment of atmospheric gases or mixing of air-saturated gases in meteoric water in either magmatic-hydrothermal or magmatic-steam fluids. Thus, the oxidation of SO 2 to aqueous sulfate in the magmatic-steam fluids did not result from mixing with atmospheric oxygen. Both of the fluid types are characterized by high H 2 contents that range from 0.2 mol% to the extraordinarily large amounts (66 mol%) observed in some magmatic-steam fluids. Modeling of gas speciation using SOLVGAS requires most of the gas species to have been in disequilibrium at the time of their trapping in the fluid inclusions. The origin of such extreme H 2 concentrations, although problematic, is thought to be largely related to accumulation of H 2 from the reaction of water with ferrous iron during the rise of magma and probably even after exsolution of fluid from a magma. The large contents of reduced gases in the inclusion fluids are far in excess of those observed in volcanic emanations, and are thought to reflect the close “sampling position” of the host alunite relative to the location of the magma. Isotope ratios of He and Ne indicate largely crustal sources for these gases in the alunite parental fluids derived from Tertiary magmas, but a greater mantle component for the gases in alunite parental fluids derived from Proterozoic magmas.

Cenozoic marine geochemistry of thallium deduced from isotopic studies of ferromanganese crusts and pelagic sediments

Cenozoic records of Tl isotope compositions recorded by ferromanganese (Fe–Mn) crusts have been obtained. Such records are of interest because recent growth surfaces of Fe–Mn crusts display a nearly constant Tl isotope fractionation relative to seawater. The time-series data are complemented by results for bulk samples and leachates of various marine sediments. Oxic pelagic sediments and anoxic marine deposits can be distinguished by their Tl isotope compositions. Both pelagic clays and biogenic oozes are typically characterized by ϵ 205Tl greater than +2.5, whereas anoxic sediments have ϵ 205Tl of less than −1.5 ( ϵ 205Tl is the deviation of the 205Tl/ 203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 10 4). Leaching experiments indicate that the high ϵ 205Tl values of oxic sediments probably reflect authigenic Fe–Mn oxyhydroxides. Time-resolved Tl isotope compositions were obtained from six Fe–Mn crusts from the Atlantic, Indian, and Pacific oceans and a number of observations indicate that these records were not biased by diagenetic alteration. Over the last 25 Myr, the data do not show isotopic variations that significantly exceed the range of Tl isotope compositions observed for surface layers of Fe–Mn crusts distributed globally ( ϵ 205Tl=+12.8±1.2). This indicates that variations in deep-ocean temperature were not recorded by Tl isotopes. The results most likely reflect a constant Tl isotope composition for seawater. The growth layers of three Fe–Mn crusts that are older than 25 Ma show a systematic increase of ϵ 205Tl with decreasing age, from about +6 at 60–50 Ma to about +12 at 25 Ma. These trends are thought to be due to variations in the Tl isotope composition of seawater, which requires that the oceans of the early Cenozoic either had smaller output fluxes or received larger input fluxes of Tl with low ϵ 205Tl. Larger inputs of isotopically light Tl may have been supplied by benthic fluxes from reducing sediments, rivers, and/or volcanic emanations. Alternatively, the Tl isotope trends may reflect the increasing importance of Tl fluxes to altered ocean crust through time.

The mass balance of dissolved thallium in the oceans

This study provides a comprehensive and quantitative discussion of the inventory and mass balance of dissolved thallium (Tl) in the oceans. The calculations are based on a critical evaluation of recently published analytical data. Thallium is estimated to have a mean seawater concentration of 65 pmol/kg and this implies a total oceanic inventory of about 8.76×10 4 Mmol Tl. The five primary sources of dissolved Tl in the oceans are rivers, hydrothermal fluids, eolian contributions from volcanic emanations and mineral aerosols, and benthic fluxes from continental margin sediments. Combined, these sources generate a Tl flux of between 1.4 and 12 Mmol/year, with a best estimate of 5.2 Mmol/year. Based on this, an oceanic residence time of 7–63 ky is calculated for Tl, with a best estimate of 17 ky. The two main oceanic sinks of Tl are scavenging from seawater by the authigenic phases of pelagic clays and uptake of Tl during low-temperature alteration of oceanic crust. These sinks remove about 1.6–7.7 Mmol/year of Tl, with a best estimate of 4.2 Mmol/year. This indicates an oceanic residence time of 11–56 ky, with a best estimate of 21 ky. The mass balance yields input and output fluxes which are identical, within the uncertainties, and this is in accord with a budget that is in steady state.

The importance of volcanic emissions for the global atmospheric mercury cycle

Abstract Mercury is a highly volatile, bioaccumulating toxic trace metal with a long (∼1 yr) atmospheric residence time. Hg is strongly enriched in volcanic emanations, and volcanoes are the only natural sources of direct Hg emission to the free troposphere and stratosphere. However, there is considerable uncertainty over the annual emission rate of mercury from volcanoes. Previous estimates, based on limited measurements from volcanic plumes, span three orders of magnitude (∼100–103 Mg Hg/yr), or from Here we critically evaluate published data from volcanic plumes, and combine this with information from natural archives to show unequivocally the significance of volcanoes for the global biogeochemical mercury cycle. ‘Low’ global volcanic flux estimates ( 103 Mg) explosive eruptions overwhelm the total atmospheric burden several times per century, and account for ∼15% of total volcanic Hg emissions.

Variation in the chemical composition of Obuki Spring, Tamagawa Hot Springs (1951-2000)

A change in the chemical composition of Obuki Spring, a typical chloride-sulfate acid hot spring in Japan, has been revealed by continuous observation for more than 40 years. The concentration of SO 4 2 - increased markedly from 1972 (∼1 g/l) to 1978 (∼3 g/l), then decreased gradually from 1978 to 1990 (∼1 g/ 1). Variations in the Cl - concentration were apparently within a smaller range than those of the SO 4 2 - concentration. The concentrations of numerous cations increased during 1972-1990, as did the SO 4 2- concentrations. This variation is thought to be the result of a mechanism involving a second source, namely, volcanic emanations of a sulfur-rich composition, which were temporarily added to emanations from the first source; the first source has continuously supplied volcanic emanations to the original acid hydrothermal solution at Obuki Spring, and the second source is responsible for the increase in SO 4 2-, Cl - , and acidity. Variations in the concentrations of most other components can be explained as the result of changes in the interaction between the acid hydrothermal solution and the surrounding rocks; the latter changes were themselves the consequence of increases in acidity.

ANALYSIS OF AIRBORNE PARTICULATE MATTER COLLECTED AFTER AN ERUPTION EPISODE OF THE POPOCATÉPETL VOLCANO

Samples of airborne particulate matter were collected in four sites along an east-west line from the Popocatépetl volcano after the eruption episode of June 30, 1997. The Popocatépetl volcano, with variable activity since it was known, is currently under low but continuous activity prolonged for almost one decade, with occasional moderate eruption episodes producing mainly fumes, ashes and volcanic dusts. The main objective of this study is to determine whether or not some elements have increased their presence in the atmosphere as a result of the volcanic activity, and also if some others, not usually found in urban aerosols, have appeared because of the same reason. In addition, the information obtained will be a source of scientific data for health risk assessment of the population exposed to volcanic emanations. The sample collection was performed on alternate days from July 10 to August 13 1997 in Puebla and Atlixco in Puebla State. Tlalpan within Mexico City, and Salazar in the State of Mexico. Two samples a day were taken in two periods: 7-19 h and 19-7 h. The samplers separated particles into two particle size fractions. PM25 and PM15. Elemental concentrations were determined by PIXE and the results obtained showed increased concentrations of mainly Ti and Fe in all sampling sites, thus indicating a long range transportation of volcanic dusts in both particle size fractions. Concentrations of Ti were found clearly above the average values of urban areas such as Mexico City, and although this element can be considered of low toxicity, the biological, metabolic and toxic effects on human beings are still under investigation.

Models for Distribution of Terrestrial Noble Gases and Evolution of the Atmosphere

Noble gases provide unique clues to the structure of the Earth and the degassing of volatiles into the atmosphere. Since the noble gases are highly depleted in the Earth, their isotopic compositions are prone to substantial changes due to radiogenic additions, even from scarce parent elements and low-yield nuclear processes. On a global scale, noble gas isotopic variations reflect planetary differentiation processes that generate fractionations between these volatiles and parent elements. It has long been recognized that the atmosphere is not primary (i.e., solar) and so is not simply a remnant of the solar nebula. From similarities with volcanic emanations, a secondary origin of the atmosphere was proposed, that is, atmospheric volatiles are derived from degassing of the solid Earth (Brown 1949; Suess 1949; Rubey 1951). The characteristics of the atmosphere therefore reflect the acquisition of volatiles by the solid Earth during formation (see Pepin and Porcelli 2002, this volume), as well as the history of degassing from the mantle. The precise connection between volatiles now emanating from the Earth and the long-term evolution of the atmosphere are key subjects of modeling efforts. Major advances in understanding the behavior of terrestrial volatiles have been made based upon observations on the characteristics of noble gases that remain within the Earth. Various models seek to define different components and reservoirs in the planetary interior, how materials are exchanged between them, and how the noble gases are progressively transferred to the atmosphere. These models are evaluated here after a review of the available constraints on noble gas distributions and fluxes. Note that the crust is largely ignored here, because it is not a major noble gas reservoir because of reworking and thus extensive degassing (Ballentine and Burnard 2002, this volume). In this review, emphasis is placed on the specific …