Comparative study of sampling methods and in situ and laboratory analysis for shallow-water submarine hydrothermal systems

A primary aim for sampling of submarine hydrothermal vents is to minimize inclusion of ambient seawater. Here, we compare the results of three different sampling methods (air displacement, two-valve bottle, and syringes) for shallow submarine systems. Mixing of hydrothermal fluid with seawater is unavoidable; however, calculations based on linear mixing models allow estimation of the hydrothermal fluid end-member composition. The results show that sampling with a two-valve bottle and syringes are the best options because they allow collection of samples with a large proportion of hydrothermal fluid. Additionally, we compare the results of in situ and laboratory analyses of the fluid samples, and demonstrate that determination of chemical composition in situ is the best option for some components, as re-equilibration affects some component concentrations (i.e. bicarbonate). Conversely, silica determination in situ usually underestimates the concentration in the fluid, as it does not account for polymeric silica. Other components can be measured either in the field or in the laboratory.     

Composition and applied sedimentology of salt from brines of the Mamfe Basin, Cameroon

Salts produced using brines of the Mamfe Basin were analysed by XRD for their mineral composition and ICP-MS for minor element composition. Halite (NaCl) and dolomite (CaMg (CO₃)₂) constitute the major minerals with minor impurities from Mo and Cd in the chlorides and Sc and Cu in the carbonates. The mineral composition is evidence of dissolution of evaporites with parent brine of marine origin. Other elements analysed are suggested to be adsorbed to these salts and result from water–rock interaction. The elements partitioned based on their correlation to other elements are suggested to derive from sulphates including barite for Ba, sulphides for Pb, Zn, silicates for Zr, Mn and oxides for V, Cr. The electrical conductance of the brines is related to the salt yield by the equation; M = 9 × 10^− 4E− 3.27, and it can be used to estimate salt yield throughout the year. Over 1200 tons of salt consisting dominantly of grade I halite are lost annually as brines across the basin. Purification is required for some minor elements including Ba, Pb, Hg and Cd for use as a condiment. A genetic relation between the parent brine, sulphide minerals and organic matter-rich sediments is proposed.     

Comparison of soil solution chemistry sampled by centrifugation, two types of suction lysimeters and zero-tension lysimeters

The choice of sampling method for soil solution is of great importance. In this paper soil solution chemistry sampled by centrifugation, two types of suction lysimeters and zero-tension lysimeters have been studied with the purpose of investigating systematic differences between them. The samples were taken at 4 depths from an acidified forest soil as well as from adjacent lime and ash treated soils. A centrifugation drainage method was compared with two types of suction lysimeters (‘Rhizon’ and ‘Prenart’) and zero-tension lysimeters. About half of the 27 variables measured showed a significant difference between the sampling methods used. Typically the centrifuged samples had lower pH (4.0 vs. 4.4), Ca (21 μM vs. 30 μM) and Mg (25 μM vs. 34 μM) concentrations and higher Cl (330 μM vs. 230 μM) and DOC (4.4 mM vs. 3.2 mM) concentrations than the Rhizon lysimeters. Also the other lysimeters showed significant differences compared to the centrifuged samples for about half the number of analytes. Centrifuged samples had higher concentrations of all analytes except NO₃ and PO₄ compared to zero-tension lysimeters and also for all analytes except NO₃ and Al compared to Prenart lysimeters. Among the environmental factors considered depth showed an influence to some extent, while sampling occasion had a great significant impact on the difference between the centrifugation method and the Rhizon lysimeters. Factors like individual pits or soil treatment did not show any influence on the difference between the methods.     

Geologic correlation between the Neoproterozoic Sergipano belt (NE Brazil) and the Yaoundé belt (Cameroon, Africa)

The Yaoundé belt (Cameroon) and the Sergipano belt (NE Brazil) belonged to a major and continuous Neoproterozoic orogen at the northern margin of the ancient Congo-São Francisco craton. The Yaoundé belt comprises schists, quartzites, gneisses and migmatitic gneisses grouped into three domains; the low-grade Mbalmayo Group in south and the medium- to high-grade Yaoundé and Bafia Group in north. The Sergipano belt is divided into six domains, the three southernmost of which are mostly made up of clastic and chemical metasedimentary rocks whereas the others are more diverse with a migmatite–gneiss complex, and two metavolcanicplutonic complexes. In general, the two belts show structural vergence and decrease of metamorphic grade towards the craton; three main deformation phases are recognized in the Sergipano belt in contrast with two described in the Yaoundé belt. The minimum age of Pan-African-Brasiliano collision in the Sergipano belt is constrained at 628 ± 12 Ma on syn-collision granites, whereas in the Yaoundé belt collision took place between 620 and 610 Ma, i.e. the age of granulite facies metamorphism. Sm–Nd isotope geochemistry and U–Pb age dating indicate that most clastic metasedimentary rocks in both belts were derived from sources to the north and, to a lesser degree, from the cratons to the south.     

Changes in the circulation of Tampa Bay due to Hurricane Frances as recorded by ADCP measurements and reproduced with a numerical Ocean model

Hurricane Frances is shown to greatly alter the hydrodynamics within Tampa Bay, Florida, and the exchange of water with the Gulf of Mexico in both observational data and a realistic numerical circulation model of the Tampa Bay estuary. Hurricane Frances hit Tampa Bay on September 5, 2004 with surface winds peaking twice near 22 m s⁻¹. There were three stages to the hydrodynamic effect of Frances on Tampa Bay. The first stage included the approach of Frances up to the first wind peak. The winds were to the south and southeast. During this stage sea level was maintained below mean sea level (MSL) and the residual current (demeaned, detided) was weak. The second stage began as the winds turned to the east and northeast, as the eye passed near the bay, and ended as the second wind peak appeared. During this stage the residual currents were strongly positive (into the bay), raising sea level to 1.2 m above MSL at St. Petersburg. The measured residual circulation peaked at over +0.7 m s⁻¹ near the surface. The model shows this velocity peak yielded a maximum volume flux into the bay of +44,227 m³ s⁻¹, displacing a total volume of 1.5 billion m³ in just a few hours, about 42% of the bay volume. In the third stage a strong negative flow developed as the wind and sea level relaxed to near normal levels. The ADCP measured a peak outflow of −0.8 m s⁻¹ during this time. Model results indicate a maximum flux of −37,575 m³ s⁻¹, and that it took about 50 h to drain the extra volume driven into the bay by Hurricane Frances.     

The effect of multiple stressors on salt marsh end-of-season biomass

It is becoming more apparent that commonly used statistical methods (e.g. analysis of variance and regression) are not the best methods for estimating limiting relationships or stressor effects. A major challenge of estimating the effects associated with a measured subset of limiting factors is to account for the effects of unmeasured factors in an ecologically realistic matter. We used quantile regression to elucidate multiple stressor effects on end-of-season biomass data from two salt marsh sites in coastal Louisiana collected for 18 yr. Stressor effects evaluated based on available data were flooding, salinity air temperature, cloud cover, precipitation deficit, grazing by muskrat, and surface water nitrogen and phosphorus. Precipitation deficit combined with surface water nitrogen provided the best two-parameter model to explain variation in the peak biomass with different slopes and intercepts for the two study sites. Precipitation deficit, cloud cover, and temperature were significantly correlated with each other. Surface water nitrogen was significantly correlated with surface water phosphorus and muskrat density. The site with the larger duration of flooding showed reduced peak biomass, when cloud cover and surface water nitrogen were optimal. Variation in the relatively low salinity occurring in our study area did not explain any of the variation inSpartina alterniflora biomass.