Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil

Observations of thermohaline properties and currents were undertaken in the Curimataú River estuary (6°18′S), Rio Grande do Norte state (RN), Brazil, during consecutive neap–spring tidal cycles in the austral autumn rainy season. Highly asymmetric neap tide along channel velocities (−0.4 to 0.9 m s⁻¹) and highly stratified conditions were generated by an increase of the buoyancy energy from the freshwater input (R _iE≈5.6). During the spring-tidal cycle the river discharge decreased and the longitudinal velocity components were higher, less asymmetrical (−0.8 to 1.1 m s⁻¹) and semidiurnal, associated with moderately stratified conditions (R _iE≈0.1) due to the increase of the kinetic tidal energy forcing mechanism. The overall salinity variation from surface to bottom during two tidal cycles was from 20.5 to 36.3 and 29 to 36.7 in the neap and spring tide experiments, respectively; in the last experiment, the tropical water (TW) mass intrusion was enhanced. The net salt transport reversed from down to up estuary during the neap and spring tide experiments, respectively, varied from 6.0 to –2.0 kg m⁻¹ s⁻¹, an indication of changes in the main forcing of the estuary dynamics. Evaluation of a classical steady analytical model, in comparison with nearly steady experimental vertical profiles of velocity, shows an agreement classifiable as reasonably fair.     

Raman characteristics of hydrocarbon and hydrocarbon inclusions

The Raman spectrograms of hydrocarbon standard samples show that: (1) the Raman spectrogram of normal paraffin has very strong peaks of methyl and methylene (from 2700 cm-1 to 2970 cm-1); (2) branch methyl has the particular peak of 748 cm-1±; (3) six cyclic has the particular peak of 804 cm-1±; (4) phenyl has two particular peaks of 988 cm-1± and 3058 cm-1± and the 988 cm-1± peak is stronger than the 3058 cm-1± peak; and (5) hexene has three alkenyl spectrum peaks of 1294 cm-1±, 1635 cm-1± and 2996 cm-1±, with the 1635 cm-1± peak being the strongest, showing that the number of carbon in hy-drocarbon does not affect its Raman spectrogram, and the hydrocarbon molecular structure and base groups affect its Raman spectrogram, the same hydrocarbons (such as normal paraffin) have the same Raman spectrogram; the types (such as CH4, C2H6, C3H8) and the content of hydrocarbon in oil inclu-sions are not estimated by their characteristic Raman peaks. According to the Raman spectrograms of hydrocarbon compositions, the Raman spectrogram of hydrocarbon inclusion can be divided into five types: saturated hydrocarbon Raman spectrogram, fluoresce Raman spectrogram, saturated hydro-carbon bitumen Raman spectrogram, bitumen Raman spectrogram, and ethane Raman spectrogram. And according to the characteristics of Raman spectrogram, hydrocarbon inclusions can be divided into five types: saturated hydrocarbon inclusion, less saturated hydrocarbon (oil or gas) inclusion, saturated hydrocarbon bitumen inclusion, bitumen inclusion, and methane water inclusion.     

Cluster analysis of soil CO<Subscript>2</Subscript> data from Mt. Etna (Italy) reveals volcanic influences on temporal and spatial patterns of degassing

Soil CO₂ concentration data were collected periodically from July 2001 to June 2005 from sampling site grids in two areas located on the lower flanks of Mt. Etna volcano (Paternò and Zafferana Etnea–Santa Venerina). Cluster analysis was performed on the acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources. In both areas three clusters were recognised, whose average CO₂ concentration values throughout the whole study period remained significantly different from one another. The clusters with the lowest CO₂ concentrations showed time-averaged values ranging from 980 to 1,170 ppm vol, whereas those with intermediate CO₂ concentrations showed time-averaged values ranging from 1,400 to 2,320 ppm vol, and those with the highest concentrations showed time-averaged values between 1,960 and 55,430 ppm vol. We attribute the lowest CO₂ concentrations largely to a biogenic source of CO₂. Conversely, the highest CO₂ concentrations are attributed to a magmatic source, whereas the intermediate values are due to a variable mixing of the two sources described above. The spatial distribution of the CO₂ values related to the magmatic source define a clear direction of anomalous degassing in the Zafferana Etnea–Santa Venerina area, which we attribute to the presence of a hidden fault, whereas in the Paternò area no such oriented anomalies were observed, probably because of the lower permeability of local soil. Time-series analysis shows that most of the variations observed in the soil CO₂ data from both areas were related to changes in the volcanic activity of Mt. Etna. Seasonal influences were only observed in the time patterns of the clusters characterised by low CO₂ concentrations, and no significant interdependence was found between soil CO₂ concentrations and meteorological parameters. The largest observed temporal anomalies are interpreted as release of CO₂ from magma batches that migrated from deeper to shallower portions of Etna’s feeder system. The pattern of occurrence of such episodes of anomalous gas release during the observation period was quite different between the two studied areas. This pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano’s feeder system after June 2003, interpreted as magma accumulation into a shallow (<8 km depth) reservoir.     

Correlation between plasmid DNA damage induced by PM10 and trace metals in inhalable particulate matters in Beijing air

Based on the study of Beijing PM₁₀ bioreactivity with the newly developed plasmid DNA assay method, and analysis for trace elements of PM₁₀, the cause of plasmid DNA damage by PM₁₀ was investigated. The study showed that plasmid DNA oxidative damages by PM₁₀ are of difference in different seasons at various areas. The concentrations of TM50 of PM₁₀ in whole samples respectively collected at urban and comparison sites during winter were 900 μg mL⁻¹ and 74 μg mL⁻¹, while those in their corresponding soluble fractions were 540 μg mL⁻¹ and 86 μg mL⁻¹. In contrast, TM50 contents of PM₁₀ from summer whole samples at urban areas and comparison sites were 116 μg mL⁻¹ and 210 μg mL⁻¹, whereas those in their soluble fractions were 180 μg mL⁻¹ and 306 μg mL⁻¹. The difference of bioreactivity of Beijing PM₁₀ resulted from the variation of trace elements. The oxidative damage of plasmid DNA caused by Pb, Zn, As in PM₁₀ (whole sample) was relatively strong. TM50 and Mn, V, Zn display stronger correlation in the soluble fraction. It implies that Zn could be the major trace element in Beijing PM₁₀ which contributes to oxidative damage to plasmid DNA.     

Early Paleozoic subduction of the Paleo-Asian Ocean: Geochronological and geochemical evidence from the Dashizhai basalts,Inner Mongolia

Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns (i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high TiO₂, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sr(i)=0.7028−0.7032, ε_Nd(t)=+9.8−+11.2, ε_Hf(t)=+16.1−+18.4). Group 2 has lower TiO₂, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sr(i)=0.7037−0.7038, ε_Nd(t)=+5.7−+7.3, ε_Hf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation” volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions of different volcano-sedimentary associations. Supported by National Basic Research Program of China (Grant No. 2006CB403504)     

Puhimau Thermal Area: A Window into the Upper East Rift Zone of Volcano, Hawaii?

We report the results of two soil CO₂ efflux surveys by the closed chamber circulation method at the Puhimau thermal area in the upper East Rift Zone (ERZ) of volcano, Hawaii. The surveys were undertaken in 1996 and 1998 to constrain how much CO₂ might be reaching the ERZ after degassing beneath the summit caldera and whether the Puhimau thermal area might be a significant contributor to the overall CO₂ budget of . The area was revisited in 2001 to determine the effects of surface disturbance on efflux values by the collar emplacement technique utilized in the earlier surveys. Utilizing a cutoff value of 50 g m⁻² d⁻¹ for the surrounding forest background efflux, the CO₂ emission rates for the anomaly at Puhimau thermal area were 27 t d⁻¹ in 1996 and 17 t d⁻¹ in 1998. Water vapor was removed before analysis in all cases in order to obtain CO₂ values on a dry air basis and mitigate the effect of water vapor dilution on the measurements. It is clear that Puhimau thermal area is not a significant contributor to CO₂ output and that most of CO₂ (8500 t d⁻¹) is degassed at the summit, leaving only magma with its remaining stored volatiles, such as SO₂, for injection down the ERZ. Because of the low CO₂ emission rate and the presence of a shallow water table in the upper ERZ that effectively scrubs SO₂ and other acid gases, Puhimau thermal area currently does not appear to be generally well suited for observing temporal changes in degassing at .     

Chemical and isotopic compositions of thermal springs,fumaroles and bubbling gases at Tacaná Volcano (Mexico–Guatemala): implications for volcanic surveillance

This study presents baseline data for future geochemical monitoring of the active Tacaná volcano–hydrothermal system (Mexico–Guatemala). Seven groups of thermal springs, related to a NW/SE-oriented fault scarp cutting the summit area (4,100m a.s.l.), discharge at the northwest foot of the volcano (1,500–2,000m a.s.l.); another one on the southern ends of Tacaná (La Calera). The near-neutral (pH from 5.8 to 6.9) thermal (T from 25.7°C to 63.0°C) HCO₃–SO₄ waters are thought to have formed by the absorption of a H₂S/SO₂–CO₂-enriched steam into a Cl-rich geothermal aquifer, afterwards mixed by Na/HCO₃-enriched meteoric waters originating from the higher elevations of the volcano as stated by the isotopic composition (δD and δ¹⁸O) of meteoric and spring waters. Boiling temperature fumaroles (89°C at ~3,600m a.s.l. NW of the summit), formed after the May 1986 phreatic explosion, emit isotopically light vapour (δD and δ¹⁸O as low as −128 and −19.9‰, respectively) resulting from steam separation from the summit aquifer. Fumarolic as well as bubbling gases at five springs are CO₂-dominated. The δ¹³C_CO2 for all gases show typical magmatic values of −3.6 ± 1.3‰ vs V-PDB. The large range in ³He/⁴He ratios for bubbling, dissolved and fumarolic gases [from 1.3 to 6.9 atmospheric ³He/⁴He ratio (R _A)] is ascribed to a different degree of near-surface boiling processes inside a heterogeneous aquifer at the contact between the volcanic edifice and the crystalline basement (⁴He source). Tacaná volcano offers a unique opportunity to give insight into shallow hydrothermal and deep magmatic processes affecting the CO₂/³He ratio of gases: bubbling springs with lower gas/water ratios show higher ³He/⁴He ratios and consequently lower CO₂/³He ratios (e.g. Zarco spring). Typical Central American CO₂/³He and ³He/⁴He ratios are found for the fumarolic Agua Caliente and Zarco gases (3.1 ± 1.6 × 10¹⁰ and 6.0 ± 0.9 R _A, respectively). The L/S (5.9 ± 0.5) and (L + S)/M ratios (9.2 ± 0.7) for the same gases are almost identical to the ones calculated for gases in El Salvador, suggesting an enhanced slab contribution as far as the northern extreme of the Central American Volcanic Arc, Tacaná.     

Seasonal and inter-annual variability in alkalinity in Liverpool Bay (53.5° N, 3.5° W) and in major river inputs to the North Sea

A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA) and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO _x decreased by 25 ± 4 μmol kg⁻¹ and DIC by 106 ± 16 μmol kg⁻¹. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of TA increased by 33 ± 8 μmol kg⁻¹ (2009) and 33 ± 15 μmol kg⁻¹ (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al. (2009) suggested that denitrification may enhance the CO₂ uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake of CO₂ into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show that patterns of seasonal change in concentrations of TA in river inputs differ between river systems.     

Sorption of Eu<Superscript>3+</Superscript>onto nano-size silica-water interfaces

The sorption of Eu species onto nano-size silica-water interfaces is investigated at pH range of 1―8.5 and the initial Eu concentrations (C_Eu) of 2×10⁻⁵, 2×10⁻⁴ and 2×10⁻³ M using fluorescence spectroscopy. The sorption rate of Eu is initially low, but significantly increases at pH > 4. For the initial C_Eu of 2×10⁻⁵, 2×10⁻⁴ and 2×10⁻³ M, the dissolved Eu species are completely sorbed onto silica-water interfaces at pH = 4.75, −5.8 and 6.6, respectively, with the respective sorption densities of −1.58×10⁻⁸, 1.58×10⁻⁷ and 1.58×10⁻⁶ mol/m². The sorbed Eu species at pH < 6 is aquo Eu³⁺, which is sorbed onto silica-water interfaces as an outer-sphere complex at pH < 5, but may be sorbed as an inner-sphere bidentate complex at 5 < pH < 6, due to the decrease of the N_H2O to −6 at pH = 6. At pH = 6 – 8, Eu(OH)²⁺, Eu(CO₃)⁺and Eu(CO₃)₂ ⁻ form in the solutions, and Eu(CO₃)⁺is dominant at pH = −7.5. These ions may be sorbed onto silica-water interfaces as inner-sphere bidentate complexes or multi-nuclear pre-cipitates.     

Major-ion bulk deposition around an active volcano (Mt. Etna, Italy)

Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO₄) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano (pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks. Variation of the deposition rates during the March 2001–March 2003 period, coupled with previous measurements from 1997 to 2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO₂ flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of HF, HCl and SO₂ emitted by the summit crater's plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day⁻¹ which is two orders of magnitude higher than that typical of quiescent degassing phases.     

Fluid mixing as the mechanism of formation of the Dajing Cu-Sn-Ag-Pb-Zn ore deposit,Inner Mongolia

Dajing Cu-Sn-Ag-Pb-Zn ore deposit, in the Inner Mongolia Autonomous Region of China, is a fissure-filling hydrothermal ore deposit. The δD values of quartz-hosted inclusion water are centered at −100%.– −130%.. The δ³⁴S values of sulfide ore minerals and δ¹³ C values of carbonate gangue minerals vary from −0.3%. to 2.6%. and from −2.9%. to −7.0%., respectively. Integrated isotopic data point to two major contributions to the mineralizing fluid that include a dominant meteoric-derived groundwater, and sulfur and carbon species from hypogene magma. Linear trends are exhibited on the gaseous H₂O versus CO₂ plot, and plots of CO, N₂, CH₄, and C₂H₆. It is shown by quantitative simulation that magma degassing cannot explain the linear trends. Hence, these linear trends are interpreted in terms of mixing of CO₂-rich magmatic fluid with meteoric-derived groundwater. The groundwater circulated in Paleozoic sedimentary rocks and absorbed CO, N₂, CH₄, C₂H₆ and radiogenic Ar from organic matter. Cooling effects resulting from mixing have caused the precipitation of ore minerals.     

Strombolian explosive styles and source conditions: insights from thermal (FLIR) video

Forward Looking Infrared Radiometer (FLIR) cameras offer a unique view of explosive volcanism by providing an image of calibrated temperatures. In this study, 344 eruptive events at Stromboli volcano, Italy, were imaged in 2001–2004 with a FLIR camera operating at up to 30 Hz. The FLIR was effective at revealing both ash plumes and coarse ballistic scoria, and a wide range of eruption styles was recorded. Eruptions at Stromboli can generally be classified into two groups: Type 1 eruptions, which are dominated by coarse ballistic particles, and Type 2 eruptions, which consist of an optically-thick, ash-rich plume, with (Type 2a) or without (Type 2b) large numbers of ballistic particles. Furthermore, Type 2a plumes exhibited gas thrust velocities (>15 m s⁻¹) while Type 2b plumes were limited to buoyant velocities (<15 m s⁻¹) above the crater rim. A given vent would normally maintain a particular gross eruption style (Type 1 vs. 2) for days to weeks, indicating stability of the uppermost conduit on these timescales. Velocities at the crater rim had a range of 3–101 m s⁻¹, with an overall mean value of 24 m s⁻¹. Mean crater rim velocities by eruption style were: Type 1 = 34 m s⁻¹, Type 2a = 31 m s⁻¹, Type 2b = 7 m s⁻¹. Eruption durations had a range of 6–41 s, with a mean of 15 s, similar among eruption styles. The ash in Type 2 eruptions originates from either backfilled material (crater wall slumping or ejecta rollback) or rheological changes in the uppermost magma column. Type 2a and 2b behaviors are shown to be a function of the overpressure of the bursting slug. In general, our imaging data support a broadening of the current paradigm for strombolian behavior, incorporating an uppermost conduit that can be more variable than is commonly considered.     

Uncertainty analysis of CO<Subscript>2</Subscript> flux components in subtropical evergreen coniferous plantation

We present an uncertainty analysis of ecological process parameters and CO₂ flux components (R _eco, NEE and gross ecosystem exchange (GEE)) derived from 3 years’ continuous eddy covariance measurements of CO₂ fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to analyze the random error of CO₂ fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO₂ flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters and CO₂ flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters. Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary least square method (OLS). (3) The differences between simulated R_eco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m⁻²·a⁻¹), 34.33% (79 g C·m⁻²·a⁻¹) and 5.4% (92 g C·m⁻²·a⁻¹). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m⁻²·a⁻¹), 2.1% (5.7 g C·m⁻²·a⁻¹), and 0.26% (4.3 g C·m⁻²·a⁻¹), respectively, which suggested that the optimization methods are more important than the ecological models in influencing uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO₂ flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the timescale, the smaller the uncertainty. The relative uncertainties of R_eco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale. Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No. 2002CB412502)     

Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data

Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002, when a submarine gas eruption began in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo, and Panarelli, about 2.5 km east of Panarea Island. The gas eruption decreased to a state of low degassing by July 2003. Before 2002, the activity of Panarea volcano was characterized by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of Panarea volcano using the global positioning system (GPS) velocity field obtained by the combination of continuous and episodic site observations of the Panarea GPS network in the time span 1995–2007. We present a combined model of Okada sources, which explains the GPS results acquired in the area from December 2002. The kinematics of Panarea volcano show two distinct active crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural evidence. Subsidence on order of several millimeters/year is affecting the entire Panarea volcano, and a shortening of 10⁻⁶ year⁻¹ has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes in the regional stress field as suggested by the geophysical and volcanological events which occurred in 2002 in the Southern Tyrrhenian area.     

SO2 Emission from Active Volcanoes Measured Simultaneously by COSPEC and mini-DOAS

We measured SO₂ emission rate from six volcanoes in Latin America (Santa Ana, El Salvador; San Cristóbal and Masaya, Nicaragua; Arenal and Poás, Costa Rica; Tungurahua and Sierra Negra, Ecuador) and from Mt. Etna, Italy, using two different remote sensing techniques: COSPEC (COrrelation SPECtrometer) and miniDOAS (miniaturized Differential Optical Absorption Spectroscopy). One of the goals of this study was to evaluate the differences in SO₂ emission rates obtained by these two methods. The observed average SO₂ emission rates measured during this study were 2688 t·d⁻¹ from Tungurahua in July 2006, 2375 t·d⁻¹ in September 2005 and 480 t·d⁻¹ in February 2006 from Santa Ana, 1200 t·d⁻¹ in May 2005 from Etna, 955 t·d⁻¹ in March 2006 and 1165 t·d⁻¹ in December 2006 from Masaya, 5400 t·d⁻¹ of March 7, 2006 and 265 t·d⁻¹ in March 2006 from San Cristobal, 113 t·d⁻¹ in April 2006 from Arenal, 104 t·d⁻¹ in April 2006 from Poás and 11 t·d⁻¹ in July 2006 from Sierra Negra volcano. Most of the observed relative differences of SO₂ emission measurements from COSPEC and miniDOAS were lower than 10%.     

Holocene tephrochronology record of large explosive eruptions in the southernmost Patagonian Andes

For regionally widespread Holocene tephra layers in southernmost Patagonia, correlations based on both chemical and chronological data indicate their derivation from five large-volume (>1 km³) explosive eruptions of four different volcanoes in the southernmost Andes. Bulk-tephra and tephra-glass major and trace-element chemistry and Sr isotopic ratios unambiguously distinguish different source volcanoes, and imply that two of the regionally widespread tephra (MB₁ and MB₂) were derived from Mt. Burney (52°S), one (R₁) from Reclus (51°S), one (A₁) from Aguilera (50°S) and one (H₁) from Hudson volcano (46°S). The H₁ tephra derived from the Hudson volcano, which is located at the southern end of the Andean Southern Volcanic Zone (SVZ; 33–46°S), contains distinctive greenish andesitic glass with FeO > 4.5 wt.% and TiO₂ > 1.2 wt.%. In contrast, rhyolitic glass in tephra derived from the eruptions of Mt. Burney, Reclus and Aguilera volcanoes, which are located in the Andean Austral Volcanic Zone (AVZ; 49–55°S), is clear and transparent and has significantly lower FeO and TiO₂. Tephra derived from these three AVZ volcanoes all contain plagioclase, orthopyroxene, minor clinopyroxene and amphibole. Biotite occurs only in the Aguilera A₁ tephra, which also has the highest bulk-tephra and tephra-glass K₂O and Rb contents. Averages of new and published ¹⁴C ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated ¹⁴C age of the R₁ eruption of Reclus volcano to 12,685 ± 260 years BP, the MB₁ and MB₂ eruptions of Mt. Burney to 8,425 ± 500 and 3,830 ± 390 years BP, the Hudson H₁ eruption to 6,850 ± 160 years BP, and the A₁ eruption of Aguilera volcano to 3,000 ± 100 years BP. The volume of the largest of these eruptions, H₁ of the Hudson volcano, is estimated as >18 km³. The volume of the Reclus R₁ eruption is estimated at >10 km³, the Aguilera A₁ eruption at between 4 and 9 km³, and the younger Mt. Burney MB₂ eruption at ≥2.8 km³. The volume of the older MB₁ Mt. Burney eruption is the least well constrained, but must have been larger than the younger MB₂ eruption. The data indicate that the frequency of explosive activity of volcanic centers in the AVZ is lower than in the southern SVZ.     

Vertical hydraulic exchange and the contribution of hyporheic community respiration to whole ecosystem respiration in the River Lahn (Germany)

To quantify the contribution of hyporheic community respiration to whole running-water ecosystem respiration in a cultural landscape setting, we studied the vertical hydraulic exchange in riffle–pool sequences of the River Lahn (Germany). We used flow through curves from four tracer experiments to estimate flow velocities in the surface and subsurface water. Generally, vertical exchange velocities were higher in riffle sections and a high temporal variability was observed (range of values 0.11–1.08 m day⁻¹). We then used (1) the exchange velocities and (2) time series of dissolved oxygen concentration in surface and subsurface water to calculate hyporheic respiration. Hyporheic respiration was estimated in a range of 10–50 mg O₂ m⁻³ day⁻¹ for the upper sediment layer (first 20 cm). It was much lower in the deeper sediment layer (20–40 cm), ranging from 0 to 10 mg O₂ m⁻³ day⁻¹ (volumes are volumes of interstitial water; the average porosity was 20%). We determined primary production and respiration of the biofilm growing on the sediment by modelling dissolved oxygen concentration time series for a 2,450 m long stream reach (dissolved oxygen concentrations with diurnal variations from 8 to 16 mg L⁻¹). Modelled respiration rates ranged from 2 to 21 g O₂ m² day⁻¹. All information was integrated in a system analysis with numerical simulations of respiration with and without sediments. Results indicated that hyporheic respiration accounted for 6 to 14% of whole ecosystem respiration. These values are much lower than in other whole system respiration studies on more oligotrophic river systems.     

Geochemistry of the volcano-hydrothermal system of El Chichón Volcano, Chiapas, Mexico

 The 1982 eruption of El Chichón volcano ejected more than 1 km³ of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former lava dome, a vigorously boiling crater spring now discharges  / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg of SO₄), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰, δ¹⁸O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg), less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO₄, vs 3550 mg/kg) with δ³⁴S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately 100 kg/s of 71  °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished data). Relative N₂, Ar and He gas concentrations suggest extensional tectonics for the El Chichón volcanic centre. The ³He/⁴He and ⁴He/²⁰Ne ratios in gases from the crater fumaroles (7.3R_a, 2560) and Agua Caliente hot springs (5.3R_a, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichón have a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO₄–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures. Received: 21 July 1997 / Accepted: 4 December 1997