Heterogeneous bubble nucleation and disequilibrium H2O exsolution in Vesuvius K-phonolite melts

This study focuses on constraining bubble nucleation and H₂O exsolution processes in alkalic K-phonolite melts, using “white pumice” of the 79 AD eruption of Vesuvius as starting material. The first set of experiments consisted of H₂O solubility runs at 1153 to 1250 K and pressures between 50 and 200 MPa, to constrain equilibrium water concentrations along the decompression pathways. The decompression experiments were equilibrated with H₂O at 150 MPa and 1173 and 1223 K, and then decompressed at 3 to 17 MPa/s before rapid quenching. Experiments nucleated bubbles within the first 50 MPa pressure drop, producing maximum bubble number densities (N_V), corrected to melt volume, of 3.8 × 10¹⁴ m^− 3 at 1173 K and 4.3 × 10¹³ m^− 3 at 1223 K. Most bubbles were not visibly attached to crystals, except for a subset attached to pyroxenes primarily in the 1173 K experiments. When compared with prior bubble nucleation studies, the reduced nucleation ΔP and relatively low N_V observed indicate predominantly a heterogeneous nucleation mechanism. Melt–vapor–crystal wetting angles measured in 1173 K experiments from bubbles attached to pyroxene crystals are 36 to 69°, which are similar to those measured on titanomagnetite crystals in calc-alkaline dacite melts. The 1223 K experiments have porosities and water concentrations that largely track equilibrium, despite the rapid decompression rate. The 1173 K experiments deviate strongly from equilibrium trends in both porosity and water concentration, and slower H₂O diffusion rates are likely the cause of the inhibited bubble growth. Bubble number densities from 79 AD Vesuvius natural EU2 pumice are relatively high (2 to 4 × 10¹⁵ m^− 3; [Gurioli, L., Houghton, B.F., Cashman, K.V., Cioni, R., 2005. Complex changes in eruption dynamics during the 79 AD eruption of Vesuvius. Bull. Volcanol. 67: 144–159.]) when corrected to vesicularity. In comparison, corrected N_V's from homogeneous and heterogeneous bubble nucleation experiments from this study and prior work are at least factor of 5 lower, indicating perhaps that the natural magmas initially nucleated bubbles in the presence of CO₂. The disequilibrium H₂O exsolution seen in the 1173 K experiments indicates that inhibited bubble growth could lead to delayed exsolution in the conduit in cooler K-phonolite magmas.     

Volcanic emissions of metals and halogens from White Island (New Zealand) and Erebus volcano (Antarctica) determined with chemical traps

Volcanic emission rates of As, Sb, Pb, Hg, Se, Cl, and F were determined at Erebus volcano, Antarctica and White Island, New Zealand, using chemical traps. The trace metal fluxes were determined by combining the species to S ratios in the solutions with SO₂ emission rates measured by correlation spectrometry at the two volcanoes. At Erebus volcano, fluxes for the metals Pb and Hg were 2.0 × 10^− 4 and 8.1 × 10^− 6 kg s^− 11, respectively. Fluxes for Cl, F, As, Sb and Se (0.35, 0.15, 2.5 × 10^− 4, 1.2 × 10^− 5, and 4.5 × 10^− 6 kg s^− 1, respectively) agreed within error limits for values determined previously by the LiOH impregnated filter method [Zreda-Gostynska, G., Kyle, P., Finnegan, D., Prestbo, K., 1997. Volcanic gas emissions from Mount Erebus and their impact on the Antarctic environment. Journal of Geophysical Research, 102(B7): 15039–15055.], demonstrating the utility of the chemical trap method. A fall in the As/S ratio from 7 × 10^− 4 in 1997/1999 to 3 × 10^− 4 in 2000 at Erebus coincided with a change in the frequency and style of eruptive activity that may have been due to injection of magma into the system. At White Island, chemical trap data indicated fluxes of Cl = 0.90, F = 0.0079, Pb = 2.7 × 10^− 4, Hg = 1.1 × 10^− 5, As = 1.3 × 10^− 4, Sb = 1.9 × 10^− 5 and Se = 1.5 × 10^− 5 kg s^− 1. Samples collected 600 m downwind of the active crater were comparable to samples collected adjacent to the main gas vent, showing that this method can still be used at some distance from a degassing vent.     

Permeability and pore-connectivity variation of pumices from a single pyroclastic flow eruption: Implications for partial fragmentation

The relationship between permeability and vesicularity in volcanic rocks has been used to infer the degassing behavior of hydrous magma. Recent data on natural samples from various eruptions show a wide variation, fitting a power–law relationship of the percolation models with low (< 30%) critical vesicularity (Ф_C). In this study, we present data on permeability and pore-connectivity of juvenile rhyolitic pumice clasts in a pyroclastic flow around Onikobe volcano, NE Japan, and investigate their relationship with vesicularity developed in a single eruption event. The permeability of the pumices having a relatively low abundance of microlites and microphenocrysts shows a trend increasing by 4 orders of magnitude (from 10^− 13.8 to 10^− 10.1 m²) in a high and narrow vesicularity range (from 72 to 80%). This trend intersects at a high angle with the fit to the permeability–vesicularity data in the previous studies that has a low Ф_C, and is located on the extension of the trend for the products of isotropic decompression experiments. The two-dimensional (2D) connectivities of pores for the pumices were also measured from thin sections. From the point of view of percolation theory, connectivity provides information about the probability of percolation. They showed a steep increase from ca. 0 to 0.7 in an almost similar vesicularity range, as compared to their permeabilities. We attribute the increase in 2D connectivity to the increasing amount of ruptured bubble walls, which might have provided less-tortuous paths through larger apertures for gas flow. This, in turn, would cause an effective increase in the permeability. Aggregates of bubble-wall-shaped glass shards were found in the pumices, and their amount and degree of welding are higher in the pumices that have a higher abundance of microlites and microphenocrysts. These pumices have relatively high permeability and 2D connectivity at low vesicularity, which is accounted for by the existence of large irregularly shaped pores. These textural characteristics suggest that a series of partial fragmentation processes, including local rupturing of bubble walls and subsequent foam-collapse with permeable gas flow, might have occurred before the ultimate bulk fragmentation, thus resulting in the increase in permeability. We suggest that the 2D connectivity of pores is a useful parameter to quantify the degree of fragmentation of bubble walls and has the potential for use to assess their permeability.     

Reconstruction and analysis of sub-plinian tephra dispersal during the 1530 A.D. Soufrière (Guadeloupe) eruption: Implications for scenario definition and hazards assessment

The last magmatic eruption of Soufrière of Guadeloupe dated at 1530 A.D. (Soufrière eruption) is characterized by an onset with a partial flank-collapse and emplacement of a debris-avalanche that was followed by a sub-plinian VEI 2–3 explosive short-lived eruption (Phase-1) with a column that reached a height between 9 and 12 km producing about 3.9 × 10⁶ m³ DRE (16.3 × 10⁶ m³ bulk) of juvenile products. The column recurrently collapsed generating scoriaceous pyroclastic flows in radiating valleys up to a distance of 5–6 km with a maximum interpolated bulk deposit volume of 11.7 × 10⁶ m³ (5 × 10⁶ m³ DRE). We have used HAZMAP, a numerical simple first-order model of tephra dispersal [Macedonio, G., Costa, A., Longo, A., 2005. A computer model for volcanic ash fallout and assessment of subsequent hazard. Comput. Geosci. 31, 837–845] to reconstruct to a first approximation the potential dispersal of tephra and associated tephra mass loadings generated by the sub-plinian Phase 1 of the 1530 A.D. eruption. We have tested our model on a deterministic average dry season wind profile that best-fits the available data as well as on a set of randomly selected wind profiles over a 5 year interval that allows the elaboration of probabilistic maps for the exceedance of specific tephra mass load thresholds. Results show that in the hypothesis of a future 1530 A.D. scenario, populated areas to a distance of 3–4 km west–southwest of the vent could be subjected to a static load pressure between 2 and 10 kPa in case of wet tephra, susceptible to cause variable degrees of roof damage. Our results provide volcanological input parameters for scenario and event-tree definition, for assessing volcanic risks and evaluating their impact in case of a future sub-plinian eruption which could affect up to 70 000 people in southern Basse-Terre island and the region. They also provide a framework to aid decision-making concerning land management and development. A sub-plinian eruption is the most likely magmatic scenario in case of a future eruption of this volcano which has shown, since 1992, increasing signs of low-energy seismic, thermal, and acid degassing unrest without significant deformation.     

Respiration and denitrification in permeable continental shelf deposits on the South Atlantic Bight: Rates of carbon and nitrogen cycling from sediment column experiments

Nitrogen (N) cycling and respiration rates were measured in sediment columns packed with southeastern United States continental shelf sands, with high permeability (4.66×10⁻¹¹ m²) and low organic carbon (0.05%) and nitrogen (0.008%). To simulate porewater advection, natural shelf seawater was pumped through columns of different lengths to achieve fluid residence times of approximately 3, 6, and 12 h. Experiments were conducted seasonally at in situ temperature. Fluid flow was uniform in nearly all columns, with minimal dead zones and channeling. Significant respiration (O₂ consumption and ∑CO₂ production) occurred in all columns, with highest respiration rates in summer. Most (78–100%) remineralized N was released as N₂ in the majority of cases, including columns with oxic porewater throughout, with only a small fraction released as NO₃⁻ from some oxic columns. A rate of 0.84–4.83×10¹⁰ mol N yr⁻¹, equivalent to 1.06–6.09×10⁻⁶ mmol N cm⁻² h⁻¹, was calculated for benthic N₂ production in the South Atlantic Bight, which can account for a large fraction of new N inputs to this shelf region. Metal and sulfate reduction occurred in long residence time columns with anoxic outflow in summer and fall, when respiration rates were highest. Because permeable sediments dominate continental shelves, N₂ production in high permeability coastal sediments may play an important role in the global N cycle.     

Metal concentrations in sediments from tourist beaches of Miri City,Sarawak, Malaysia (Borneo Island)

Forty-three sediment samples were collected from the beaches of Miri City, Sarawak, Malaysia to identify the enrichment of partially leached trace metals (PLTMs) from six different tourist beaches. The samples were analyzed for PLTMs Fe, Mn, Cr, Co, Cu, Ni, Pb, Sr and Zn. The concentration pattern suggest that the southern side of the study area is enriched with Fe (1821–6097 μg g⁻¹), Mn (11.57–90.22 μg g⁻¹), Cr (51.50–311 μg g⁻¹), Ni (18–51 μg g⁻¹), Pb (8.81–84.05 μg g⁻¹), Sr (25.95–140.49 μg g⁻¹) and Zn (12.46–35.04 μg g⁻¹). Compared to the eco-toxicological values, Cr > Effects range low (ERL), Lowest effect level (LEL), Severe effect level (SEL); Cu > Unpolluted sediments, ERL, LEL; Pb > Unpolluted sediments and Ni > ERL and LEL. Comparative results with other regions indicate that Co, Cr, Cu, Ni and Zn are higher, indicating an external input rather than natural process.     

Stability of buoyancy opposed mixed convection in a vertical channel and its dependence on permeability

Non-Darcy mixed convective flow of water due to external pressure gradient and buoyancy opposed forces are considered in a vertical channel filled with porous medium, which can be either isotropic or anisotropic. The linear theory of stability analysis has been used to numerically investigate the dependence of the transition behavior of the fully developed basic flow on the permeability of the medium. Numerical experiments indicate that mainly two main instability modes appear: Rayleigh–Taylor (R–T) and buoyant instability. For Darcy numbers (Da) ?10⁻⁹, R–T instability dominates within the entire Reynolds number (Re) range considered here. It was also found that for the same Re, the fully developed base flow is highly unstable (stable) for porous media with high (low) permeability. Further, it was seen that the disturbance isotherm cells migrate from the channel walls toward the centerline when permeability is reduced. Reducing the permeability by one order of magnitude (corresponding to a decrease of Darcy number from 10⁻⁶ to 10⁻⁷) increases base flow stability approximately 20-fold. For higher Reynolds numbers, buoyant, mixed and shear instability of the basic flow were found when Da was increased from 10⁻⁷ to 10⁻³. However, for cases in which permeability and porosity behaved as suggested by Carman–Kozeny relation (CKR), buoyant stability was the only mode of instability. Critical values of the Rayleigh (Ra) and Darcy (Da) numbers in the R–T mode of instability were related to each other by the hyperbolic function RaDa = −2.465.     

Spatio-temporal assessment of perfluorinated compounds in the Brisbane River system,Australia: Impact of a major flood event

Perfluorinated chemicals including PFOA and PFOS have been widely used in consumer products and have become ubiquitous pollutants widely distributed in the aqueous environment. Following a major flood event in 2011, water samples were collected along a spatial gradient of the Brisbane River system to provide an initial estimate of the release of PFASs from flooded urban areas. PFOA (mean concentrations 0.13–6.1 ng L⁻¹) and PFOS (mean concentrations 0.18–15 ng L⁻¹) were the most frequently detected and abundant PFASs. Mean total PFASs concentrations increased from 0.83 ng L⁻¹ at the upstream Wivenhoe Dam to 40 ng L⁻¹ at Oxley Creek, representing an urban catchment. Total masses of PFOA and PFOS delivered into Moreton Bay from January to March were estimated to be 5.6 kg and 12 kg respectively. From this study, urban floodwaters appear to be a previously overlooked source of PFASs into the surrounding environment.     

Magmatic degassing at Erta 'Ale volcano,Ethiopia

Here we report measurements of the chemical composition and flux of gas emitted from the central lava lake at Erta 'Ale volcano (Ethiopia) made on 15 October 2005. We determined an average SO₂ flux of ∼ 0.69 ± 0.17 kg s^− 1 using zenith sky ultraviolet spectroscopy of the plume, and molar proportions of magmatic H₂O, CO₂, SO₂, CO, HCl and HF gases to be 93.58, 3.66, 2.47, 0.06, 0.19 and 0.04%, respectively, by open-path Fourier transform infrared (FTIR) spectrometry. Together, these data imply fluxes of 7.3, 0.7, 0.008, 0.03 and 0.004 kg s^− 1 for H₂O, CO₂, CO, HCl and HF, respectively. These are the first FTIR spectroscopic observations at Erta 'Ale, and are also some of the very few gas measurements made at the volcano since the early 1970s (Gerlach, T.M., 1980b. Investigation of volcanic gas analyses and magma outgassing from Erta 'Ale lava lake, Afar, Ethiopia. Journal of Volcanology and Geothermal Research, 7(3–4): 415–441). We identify significant increases in the proportion of H₂O in the plume with respect to both CO₂ and SO₂ across this 30-year interval, which we attribute to the depletion of volatiles in magma that sourced effusive eruptions during the early 1970s and/or to fractional magma degassing between the two active pit craters located in the summit caldera.     

Matrix bound phosphine in sediments of the yellow sea and its coastal areas

Matrix bound phosphine (MBP), a kind of chemically reduced phosphorus, has received limited attention in prevailing modeling of the phosphorus biogeochemical cycle. MBP has been found to occur in marine sediments. MBP in the sediments of the Yellow Sea and its coastal areas was measured by gas chromatography from 2004 to 2007. MBP levels in surface sediments were 0.19–38.24 ng kg⁻¹ in the shelf of the Yellow Sea, 0.34–17.15 ng kg⁻¹ in the Jiaozhou Bay, 2.11–71.79 ng kg⁻¹ in the Sanggou Bay and 0.28–319.32 ng kg⁻¹ in the rivers around the Jiaozhou Bay. High levels of MBP occurred in the northern and middle areas of the Yellow Sea. Obvious seasonal variation of MBP was observed in surface sediments of the Sanggou Bay, with the highest MBP level occurring in summer and the lowest in winter. MBP in surface sediments of the inner Jiaozhou Bay was higher than those in the outer region. MBP levels increased with depth in the top 5–10 cm sediments of the Jiaozhou Bay and on the intertidal flats. Environmental factors such as type of sediments, temperature, organic matter and human activity were found to affect the concentrations and distribution of MBP in marine sediments.     

Occurrence,distribution and partitioning of nonionic surfactants and pharmaceuticals in the urbanized Long Island Sound Estuary (NY)

This work deals with the environmental distribution of nonionic surfactants (nonylphenol and alcohol ethoxylates), their metabolites (NP, nonylphenol; NPEC, nonylphenol ethoxycarboxylates; and PEG, polyethylene glycols) and a selection of 64 pharmaceuticals in the Long Island Sound (LIS) Estuary which receives important sewage discharges from New York City (NYC). Most target compounds were efficiently removed (>95%) in one wastewater treatment plant monitored, with the exception of NPEC and some specific drugs (e.g., hydrochlorothiazide). Concentrations of surfactants (1.4–4.5 μg L⁻¹) and pharmaceuticals (0.1–0.3 μg L⁻¹) in seawater were influenced by tides and sampling depth, consistent with salinity differences. Surfactants levels in suspended solids samples were higher than 1 μg g⁻¹, whereas only most hydrophobic or positively charged pharmaceuticals could be found (e.g., tamoxifen, clarithromycin). Maximum levels of target compounds in LIS sediments (PEG at highest concentrations, 2.8 μg g⁻¹) were measured nearest NYC, sharply decreasing with distance from major sewage inputs.     

Inter-annual and seasonal variations in the air–sea CO2 balance in the central Baltic Sea and the Kattegat

We estimated the net annual air–sea exchange of carbon dioxide (CO₂) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO₂ (pCO₂^w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (−) and sources (+) of CO₂ within the −4.2 to +5.2 mol m⁻² yr⁻¹ range. On average, for the 1994–2008 period, the East Gotland Sea was a source of CO₂ (1.64 mol m⁻² yr⁻¹), the Bornholm Sea was a source (2.34 mol m⁻² yr⁻¹), and the Kattegat was a sink (−1.16 mol m⁻² yr⁻¹). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity (k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO₂^w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO₂ flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth.     

Fumarole compositions and mercury emissions from the Tatun Volcanic Field,Taiwan: Results from multi-component gas analyser,portable mercury spectrometer and direct sampling techniques

Gas emissions from Tatun volcanic group, northern Taiwan, were studied for the first time using a multi-component gas analyser system (Multi-GAS) in combination with Giggenbach flask methods at fumaroles and mud pools at Da-you-keng (DYK) and Geng-tze-ping (GZP). CO₂/S molar ratios observed at DYK ranged from 3–17, similar ratios were observed using a Multi-GAS sensor box of 8–16. SO₂ at GZP was low, higher concentrations were observed at DYK where SO₂/H₂S ratios were close to 1 for both methods. A lower CO₂/H₂S ratio was measured via Giggenbach flask sampling (7.2) than was found in the plume using the gas sensor at GZP (9.2). This may reflect rapid oxidation of H₂S as it mixes with background air. Gaseous elemental mercury (GEM) levels were observed in the fumarole gases using a portable mercury spectrometer. These are the first such measurements of mercury at Tatun. Mean GEM concentrations in the fumarole plumes were ∼ 20 ng m^− 3, with much higher concentrations observed close to the ground (mean [GEM] 130 and 290 ng m^− 3 at DYK and GZP, respectively). The GEM in the fumarole plume was elevated above concentrations in industrial/urban air in northern Taiwan and the increase in GEM observed when the instrument was lowered suggests high levels of mercury are present in the surrounding ground surface. The GEM/CO₂ (10^− 8) and GEM/S (10^− 6) ratios observed in the fumarole gases were comparable to those observed at other low-temperature fumaroles. Combining the Hg/CO₂ ratio with a previous CO₂ flux value for the area, the annual GEM flux from the Tatun field is estimated as 5–50 kg/year.     

Early spring turbulent mixing in an ice-covered Arctic fjord during transition to melting

Observations are presented of currents, hydrography and turbulence in a jet-type tidally forced fjord in Svalbard. The fjord was ice covered at the time of the experiment in early spring 2004. Turbulence measurements were conducted by both moored instruments within the uppermost 5 m below the ice and a microstructure profiler covering 3–60 m at 75 m depth. Tidal choking at the mouth of the fjord induces a tidal jet advecting relatively warmer water past the measurement site and dominating the variability in hydrography. While there was no strong correlation with the observed hydrography or mixing and the phase of the semidiurnal tidal cycle, the mean structure in dissipation of turbulent kinetic energy, work done under the ice and the mixing in the water column correlated with the current when conditionally sampled for tidal jet events. Observed levels of dissipation of turbulent kinetic energy per unit mass, 1.1×10⁻⁷ W kg⁻¹, and eddy diffusivity, 7.3×10⁻⁴ m² s⁻¹, were comparable to direct measurements at other coastal sites and shelves with rough topography and strong forcing. During spring tides, an average upward heat flux of 5 W m⁻² in the under-ice boundary layer was observed. Instantaneous (1 h averaged) large heat flux events were correlated with periods of large inflow, hence elevated heat fluxes were associated with the tidal jet and its heat content. Vertical heat fluxes are derived from shear-probe measurements by employing a novel model for eddy diffusivity [Shih et al., 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics 525, 193–214]. When compared to the direct heat flux measurements using the eddy correlation method at 5 m below the ice, the upper 4–6 m averaged heat flux estimates from the microstructure profiler agreed with the direct measurements to within 10%. During the experiment water column was stably, but weakly, stratified. Destabilizing buoyancy fluxes recorded close to the ice were absent at 5 m below the ice, and overall, turbulence production was dominated by shear. A scaling for dissipation employing production by both stress and buoyancy [Lombardo and Gregg, 1989. Similarity scaling of viscous and thermal dissipation in a convecting boundary layer. Journal of Geophysical Research 94, 6273–6284] was found to be appropriate for the under-ice boundary layer.     

Short-term dispersion and turbulence in a complex-shaped estuarine embayment

Initial dispersion of material in complex-shaped embayments is examined using observations and scaling based in Crail Bay, Pelorus Sound, New Zealand in autumn of 2005. These observations show the highly variable nature of dispersive transport in an embayment with multiple headlands. Acoustic current profiler-derived typical flow speeds were around 0.05 m s⁻¹ which resulted in drifter-derived short-term (<6 h) horizontal eddy diffusivities of the order of 1 m² s⁻¹ which is somewhat larger than the empirical paradigm. Microstructure estimates of the turbulent kinetic energy dissipation rate were in the range 10⁻⁹–10⁻⁷ m² s⁻³, with some evidence that sidewalls influence the variability and that headlands increase the dissipation rate by at least and order of magnitude. A new parameter relating horizontal diffusivity to circulation and the tide is proposed. This and other scaling comparisons indicate that the headlands in Crail Bay create similar effects to those studied in other systems. However, the long decay times estimated for eddies here implies that they likely interact with other headlands, unlike some previously studied examples.     

Origin and evolution of two contrasting thermal groundwaters (CO2-rich and alkaline) in the Jungwon area,South Korea: Hydrochemical and isotopic evidence

In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20–33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ¹⁸O and δD values (> 1‰ lower in δ¹⁸O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO₂-rich water (P_CO2 = 0.1 to 2 atm) is characterized by lower pH (5.7–6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water (P_CO2 = 10^− 4.1–10^− 4.6 atm) has higher pH (9.1–9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO₂-rich water is influenced by a local supply of deep CO₂ (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca²⁺, Na⁺, Mg²⁺, K⁺, HCO₃⁻ and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water–rock (granite) interaction under the negligible inflow of CO₂. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO₂-rich water resulted from the input of CO₂ in Na–HCO₃ waters and subsequent rock leaching.     

Low-temperature hydrothermal alteration of intra-caldera tuffs,Miocene Tejeda caldera,Gran Canaria,Canary Islands

The Miocene Tejeda caldera on Gran Canaria erupted ~ 20 rhyolite–trachyte ignimbrites (Mogán Group 14–13.3 Ma), followed by ~ 20 phonolitic lava flows and ignimbrites (Fataga Group 13–8.5 Ma). Upper-Mogán tuffs have been severely altered immediately within the caldera margin, whereas extra-caldera Mogán ignimbrites, and overlying Fataga units, are apparently unaltered. The altered intra-caldera samples contain minerals characteristic of secondary fluid–rock interaction (clays, zeolites, adularia), and relics of the primary mineral assemblage identified in unaltered ignimbrites (K-feldspar, plagioclase, pyroxene, amphibole, and groundmass quartz). Major and trace-element data indicate that Si, Na, K, Pb, Sr, and Rb, were strongly mobilized during fluid–rock interaction, whereas Ti, Zr, and Nb behaved in a more refractory manner, experiencing only minor mobilization. The δ¹⁸O values of the altered intra-caldera tuffs are significantly higher than in unaltered extra-caldera ignimbrites, consistent with an overall low-temperature alteration environment. Unaltered extra-caldera ignimbrites have δD values between − 110‰ and − 173‰, which may reflect Rayleigh-type magma degassing and/or post-depositional vapour release. The δD values of the altered intra-caldera tuffs range from − 52‰ to − 131‰, with ambient meteoric water at the alteration site estimated at ca. − 15‰. Interaction and equilibration of the intra-caldera tuffs with ambient meteoric water at low temperature can only account for whole-rock δD values of around − 45‰, given that ?D_clay–water is ca. − 30‰ at 100 °C, and decreases in magnitude at higher temperatures. All altered tuff samples have δD values that are substantially lower than − 45‰, indicating interaction with a meteoric water source with a δD value more negative than − 15‰, which may have been produced in low-temperature steam fumaroles. Supported by numerical modeling, our Gran Canaria data reflect the near-surface, epithermal part of a larger, fault-controlled hydrothermal system associated with the emplacement of the high-level Fataga magma chamber system. In this near-surface environment, fluid temperatures probably did not exceed 200–250 °C.     

Nutrient availability in support of Karenia brevis blooms on the central West Florida Shelf: What keeps Karenia blooming?

Identifying nutrient sources, primarily nitrogen (N) and phosphorus (P), sufficient to support high biomass blooms of the red tide dinoflagellate, Karenia brevis, has remained problematic. The West Florida Shelf is oligotrophic, yet populations >10⁶ cells L⁻¹ frequently occur and blooms can persist for months. Here we examine the magnitude and variety of sources for N and P that are available to support blooms. Annual average in situ or background concentrations of inorganic N in the region where blooms occur range 0.02–0.2 μM while inorganic P ranges 0.025–0.24 μM. Such concentrations would be sufficient to support the growth of populations up to ∼3×10⁴ cells L⁻¹ with at least a 1 d turnover rate. Organic N concentrations average 1–2 orders of magnitude greater than inorganic N, 8–14 μM while organic P concentrations average 0.2–0.5 μM. Concentrations of organic N are sufficient to support blooms >10⁵ cells L⁻¹ but the extent to which this complex mixture of N species is utilizable is unknown. Other sources of nutrients included in our analysis are aerial deposition, estuarine flux, benthic flux, zooplankton excretion, N₂-fixation, and subsequent release of organic and inorganic N by Trichodesmium spp., and release of N and P from dead and decaying fish killed by the blooms. Inputs based on atmospheric deposition, benthic flux, and N₂-fixation, were minor contributors to the flux required to support growth of populations >2.6×10⁴ cells L⁻¹. N and P from decaying fish could theoretically maintain populations at moderate concentrations but insufficient data on the flux and subsequent mixing rates does not allow us to calculate average values. Zooplankton excretion rates, based on measured zooplankton population estimates and excretion rates could also supply all of the N and P required to support populations of 10⁵ and 10⁶ cells L⁻¹, respectively, but excretion is considered as “regenerated” nutrient input and can only maintain biomass rather than contribute to “new” biomass. The combined estuarine flux from Tampa Bay, Charlotte Harbor, and the Caloosahatchee River can supply a varying, but at times significant level of N and P to meet growth and photosynthesis requirements for populations of approximately 10⁵ cells L⁻¹ or below. Estimates of remineralization of dead fish could supply a significant proportion of bloom maintenance requirements but the rate of supply must still be determined. Overall, a combination of sources is required to maintain populations >10⁶ cells L⁻¹.     

Pelagic production and respiration in the Gulf of Papua during May 2004

The metabolic balance between production and respiration in plankton communities of the Gulf of Papua was investigated in May 2004. Water samples taken at 19 stations were allocated to groups on the basis of physico-chemical characteristics. Oxygen consumption and production in flasks incubated in the dark and in the light was determined by micro-Winkler titration. Dark bottle respiration in samples influenced by the estuarine plume averaged 3.09±1.92 (SD) mmol O₂ m⁻³ d⁻¹ and production within surface light bottles averaged 7.63±3.36 (SD)  mmol O₂ m⁻³ d⁻¹. Corresponding values in stations more typical of the central Gulf of Papua were 1.68±1.30 (SD) mmol O₂ m⁻³ d⁻¹ and 1.08±2.25 (SD) mmol O₂ m⁻³ d⁻¹. Despite a shallow (<10 m) euphotic zone within the plume stations, phytoplankton production in the surface layers was sufficiently high to subsidise total water column respiration. Integrating production and respiration over the water column resulted in a calculation of net community production (NCP) of 626±504 (SD) mg C m⁻² d⁻¹, and community respiration (CR) of 712±492 mg C m⁻² d⁻¹ at the plume stations, with an average P:R ratio of 1.97. In the offshore group NCP was 157±450 (SD) mg C m⁻² d⁻¹ and CR was 1620±1576 mg C m⁻² d⁻¹. The average P:R ratio was 1.27. Three of the 7 stations allocated to the offshore group were net heterotrophic. In contrast to earlier studies in the area indicating that the Gulf of Papua waters is heterotrophic [Robertson, A.I., Dixon, P., Alongi, D.M., 1998. The influence of fluvial discharge on pelagic production in the Gulf of Papua, Northern Coral Sea. Estuarine, Coastal and Shelf Science 46, 319–331], our data indicate that in May 2004 the Gulf was in positive metabolic balance, but by only ∼120 mg C m⁻² d⁻¹. We conclude that waters of the Gulf of Papua under riverine influence are net autotrophic, but that within the central Gulf there is a fine metabolic balance alternating between autotrophy and heterotrophy.     

Effects of an estuarine plume-associated bloom on the carbonate system in the lower reaches of the Pearl River estuary and the coastal zone of the northern South China Sea

We observed a phytoplankton bloom downstream of a large estuarine plume induced by heavy precipitation during a cruise conducted in the Pearl River estuary and the northern South China Sea in May–June 2001. The plume delivered a significant amount of nutrients into the estuary and the adjacent coastal region, and enhanced stratification stimulating a phytoplankton bloom in the region near and offshore of Hong Kong. A several fold increase (0.2–1.8 μg Chl L⁻¹) in biomass (Chl a) was observed during the bloom. During the bloom event, the surface water phytoplankton community structure significantly shifted from a pico-phytoplankton dominated community to one dominated by micro-phytoplankton (>20 μm). In addition to increased Chl a, we observed a significant drawdown of pCO₂, biological uptake of dissolved inorganic carbon (DIC) and an associated enhancement of dissolved oxygen and pH, demonstrating enhanced photosynthesis during the bloom. During the bloom, we estimated a net DIC drawdown of 100–150 μmol kg⁻¹ and a TAlk increase of 0–50 μmol kg⁻¹. The mean sea–air CO₂ flux at the peak of the bloom was estimated to be as high as ∼−18 mmol m⁻² d⁻¹. For an average surface water depth of 5 m, a very high apparent biological CO₂ consumption rate of 70–110 mmol m⁻² d⁻¹ was estimated. This value is 2–6 times higher than the estimated air–sea exchange rate.