The transition to microbial photosynthesis in hot spring ecosystems

Even casual observations of continental hot springs reveal that photosynthesis has its limits. In an effort to explore the transition to photosynthesis, field measurements of temperature and pH were made at 996 hot spring locations at Yellowstone National Park ranging from 14° to 94 °C and pH from 0.8 to 9.7. In addition, sulfide measurements were made in 426 of these locations showing concentrations up to 8820 μg L^? 1 total sulfide. These data indicate that the previously established upper temperature (73–75 °C) for the transition to photosynthesis is reached in many basic hot springs, but that the transition occurs at lower temperature with decreasing pH below ~ 6.5. As an example, no strong evidence for photosynthesis was found above 45 °C at pH ~ 2. In several locations, photosynthesis appears to be suppressed despite temperatures and pH values that permit photosynthesis elsewhere. Sulfide concentrations may be responsible for the suppression of photosynthesis at these sites. Total sulfide concentrations were observed to decrease downstream in hot spring outflow channels. Abiotic processes (degassing, oxidation, mineral precipitation, etc.) are too slow to account for these decreases, suggesting an explanation from microbial sulfide oxidation that is supported by field experiments. Microbial sulfide oxidation may determine the ultimate suitability of some hot springs for microbial photosynthesis.     

Modeling locally varying anisotropy of CO2 emissions in the United States

In a spatial property modeling context, the variables of interest to be modeled often display complex nonlinear features. Techniques to incorporate these nonlinear features, such as multiple point statistics or cummulants, are often complex with input parameters that are difficult to infer. The methodology proposed in this paper uses a classical vector-based definition of locally varying anisotropy to characterize nonlinear features and incorporate locally varying anisotropy into numerical property models. The required input is an exhaustive field of anisotropy orientation and magnitude. The methodology consists of (1) using the shortest path distance between locations to define the covariance between points in space (2) multidimensional scaling of the domain to ensure positive definite kriging equations and (3) estimation or simulation with kriging or sequential Gaussian simulation. The only additional parameter required when kriging or simulating with locally varying anisotropy is the number of dimensions to retain in multidimensional scaling. The methodology is demonstrated on a CO₂ emissions data set for the United States in 2002 and shows an improvement in cross validation results as well as a visual reproduction of nonlinear features.     

The Hf-Nd isotopic composition of marine sediments

This paper presents new major and trace-element data and Lu-Hf and Sm-Nd isotopic compositions for representative suites of marine sediment samples from 14 drill sites outboard of the world’s major subduction zones. These suites and samples were chosen to represent the global range in lithology, Lu/Hf ratios, and sediment flux in subducting sediments worldwide. The data reported here represent the most comprehensive data set on subducting sediments and define the Hf-Nd isotopic variations that occur in oceanic sediments and constrain the processes that caused them.Using new marine sediment data presented here, in conjunction with published data, we derive a new Terrestrial Array given by the equation, ε_Hf = 1.55 × ε_Nd + 1.21. This array was calculated using >3400 present-day Hf and Nd isotope values. The steeper slope and smaller y-intercept of this array, compared to the original expression (ε_Hf = 1.36 × ε_Nd + 2.89; Vervoort et al., 1999) reflects the use of present day values and the unradiogenic Hf of old continental samples included in the array.In order to examine the Hf-Nd isotopic variations in marine sediments, we have classified our samples into 5 groups based on lithology and major and trace-element geochemical compositions: turbidites, terrigenous clays, and volcaniclastic, hydrothermal and hydrogenetic sediments. Compositions along the Terrestrial Array are largely controlled by terrigenous material derived from the continents and delivered to the ocean basins via turbidites, volcaniclastic sediments, and volcanic inputs from magmatic arcs. Compositions below the Terrestrial Array derive from unradiogenic Hf in zircon-rich turbidites. The anomalous compositions above the Terrestrial Array largely reflect the decoupled behavior of Hf and Nd during continental weathering and delivery to the ocean. Both terrigenous and hydrogenetic clays possess anomalously radiogenic Hf, reflecting terrestrial sedimentary and weathering processes on the one hand and marine inheritance on the other. This probably occurs during complementary processes involving preferential retention of unradiogenic Hf on the continents in the form of zircon and release of radiogenic Hf from the breakdown of easily weathered, high Lu-Hf phases such as apatite.     

Vertical Structure Of Turbulence In Offshore Flow During Rasex

The adjustment of the boundary layer immediately downstream froma coastline is examined based on two levels of eddy correlation data collected on a mast at the shore and six levels of eddy correlation data and profiles of mean variables collected from a mast 2 km offshore during the Risø Air-Sea Experiment. The characteristics of offshore flow are studied in terms of case studies and inter-variable relationships for the entire one-month data set. A turbulent kinetic energy budget is constructed for each case study.The buoyancy generation of turbulence is small compared to shear generation and dissipation. However, weakly stable and weakly unstable cases exhibit completely different vertical structure. With flow of warm air from land over cooler water, modest buoyancy destruction of turbulence and reduced shear generation of turbulence over the less rough sea surface cause the turbulence to rapidly weaken downstream from the coast. The reduction of downward mixing of momentum by the stratification leads to smaller roughness lengths compared to the unstable case. Shear generation at higher levels and advection of stronger turbulence from land often lead to an increase of stress and turbulence energy with height and downward transport of turbulence energy toward the surface.With flow of cool air over a warmer sea surface, a convective internal boundary layer develops downstream from the coast. An overlying relatively thick layer of downward buoyancy flux (virtual temperature flux) is sometimes maintained by shear generation in the accelerating offshore flow.     

Optical dating of tsunami-laid sand from an Oregon coastal lake

Optical ages for five samples of tsunami-laid sand from an Oregon coastal lake were determined using an infrared optical-dating method on K-feldspar separates and, as a test of accuracy, compared to ages determined by AMS ¹⁴C dating of detrital plant fragments found in the same beds. Two optical ages were about 20% younger than calibrated ¹⁴C ages of about 3.1 and 4.3 ka. Correction of the optical ages using measured anomalous fading rates brings them into agreement with the ¹⁴C ages. The approach used holds significant promise for improving the accuracy of infrared optical-dating methods.Luminescence data for the other three samples result in optical age limits much greater than the ¹⁴C ages. These data provide a textbook demonstration of the correlation between scatter in the luminescence intensity of individual sample aliquots and their normalization values that is expected when the samples contain sand grains not adequately exposed to daylight just prior to or during deposition and burial. Thus, the data for these three samples suggest that the tsunamis eroded young and old sand deposits before dropping the sand in the lake.     

Be isotope and B-Be investigations of the historic eruptions of Mt. Vesuvius

Cosmogenic and radioactive ¹⁰Be, stable ⁹Be and B concentrations have been determined for four alkaline lavas from the recent cycle of historical activity at Mt. Vesuvius, in the Central Campania Province (Italy). The goal of this study was to use the Be isotope and Be-B systematics of these lavas in a manner analogous to that used in regions unequivocally related to active subduction, in hopes of being able to document a subduction origin for the Vesuvian lavas. Four lavas measured to date have low ¹⁰Be concentrations as well as low B/Be ratios. While the low ¹⁰Be concentrations could reflect subduction and incorporation of old sediments and/or only contributions from the basaltic part of the subducting plate, the combination of low ¹⁰Be and low B/Be ratios must be interpreted as the absence of a subduction signature in these lavas. Unfortunately, the absence of a subduction signature in the lavas cannot be used unequivocally to argue against recent subduction in the Central Campania region. Subduction of an unusually young, hot slab which has lost its B through prograde metamorphic reactions at shallow levels could explain the absence of a subduction signature, as could extensive crustal contamination. In addition, recent studies in Java show that alkaline lavas in this region of active subduction never show a subduction signature, even when erupting in close proximity to calc-alkaline and tholeiitic lavas which do; by analogy, the Vesuvian lavas studied may have been generated in a part of the sub-arc mantle which either does not experience or does not preserve the chemical signature of subduction modification. The present data set does not allow us to make definitive statements about the role of subduction in the origin of the Central Campania lavas.     

Variability of bedload transport and channel morphology in a braided river hydraulic model

This paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1:50 braided river model. The experiments, each of 90 h duration, were carried out in a 20 × 3m tilting flume. All the experiments started with the same initial conditions. Bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume. The model showed reasonable hydraulic similarity when compared to prototype rivers. Results show that mean bedload transport rates for the 11 runs vary in the range 0·98 to 1·49gs^?1 (mean + 1·21, coefficient of variation 11 per cent). Within-run transport rates commonly vary from close to zero, to two and occasionally three or four times the mean rate. Within the bedload series, several irregular phases of transport intensity can be observed, but time series analysis of the data show little underlying serial structure (an AR(2) autoregressive model is appropriate). Channel patterns are narrow/braided, are established quickly and remain relatively stable throughout the runs, although channel widths increase between 20 and 103 per cent over the 11 runs. Channel behaviour varies from aggradational to transitional between aggradation and degradation. Time-averaged bedload transport rate is weakly correlated with braiding intensity. In general, these results demonstrate that for a given set of controlling variables, bedload transport and channel morphology can be approximately replicated.     

A scenario-based water conservation planning support system (SB-WCPSS)

In this study a water consumption model is built into a scenario-based planning support system (SB-WCPSS). The SB-WCPSS consists of four components—(1) a model input graphic user interface, (2) a community spatial database, (3) a set of drinking water consumption models, and (4) output display. The SB-WCPSS is implemented with a commercial planning support system software package—CommunityViz. The model is applied using data in Cincinnati, Ohio, USA to demonstrate the scenario development. In the application, water consumption consists of land use based indoor, turf, and pool water usages. Climate change is reflected in monthly temperature and precipitation. By specifying anticipated future land uses and associated water consumption rates, temperature, and precipitation, SB-WCPSS users can analyze and compare water consumptions under various scenarios, using maps, graphs, and tables. Parcel-based daily water consumptions were computed and summarized spatially by neighborhood, block group, or land use type. The results demonstrate that water conservation strategies, such as xeriscape, can reduce turf water usage. Indoor water consumption depends on the number of people who use water and how they use water. The study shows that the SB-WCPSS structure is sound and user friendly. Future improvement will be on enhancing various components, such as using parcel-based data and more robust water consumption models. The system may be used by water resource managers and decision makers to adapt water resources (e.g., watersheds and infrastructure) to climate change and demographic and economic development.     

EURD: The Mission and the Stellar Absolute Fluxes of B-Type Stars

We present here stellar spectra of B stars obtained with the EURD spectrograph, one of the three instruments on board MINISAT-01. EURD is a spectrograph specially designed to detect diffuse radiation in thewavelength range between 350 and 1100 Å with 5 Å spectral resolution. EURD main scientific targets are: the spectrum of interstellar medium,atmospheric airglow, decaying neutrinos, Moon and early type stars.