Cavitron extraction of xylem water suggests cryogenic extraction biases vary across species but are independent of tree water stress

Cryogenic vacuum distillation (CVD) is a widely used technique for extracting plant water from stems for isotopic analysis, but concerns about potential isotopic biases have emerged. Here, we leverage the Cavitron centrifugation technique to extract xylem water and compare its isotopic signature to that of CVD-extracted bulk stem water as well as source water. Conducted under field conditions in tropical northern Australia, our study spans seven tree species naturally experiencing a range of water stress levels. Our findings reveal a significant deuterium bias in CVD-extracted bulk stem water when compared to xylem water (median bias −14.9‰), whereas xylem water closely aligned with source water (median offset −1.9‰). We find substantial variations in deuterium bias among the seven tree species (bias ranging from −19.3‰ to −9.1‰), but intriguingly, CVD-induced biases were unrelated to environmental factors such as relative stem water content and predawn leaf water potential. These results imply that inter-specific differences may be driven by anatomical traits rather than tree hydraulic functioning. Additionally, our data highlight the potential to use a site-specific deuterium offset, based on the isotopic signature of local source water, for correcting CVD-induced biases.     

Impact of aerosols present in Titan's atmosphere on the CASSINI radar experiment

Simulations of Titan's atmospheric transmission and surface reflectivity have been developed in order to estimate how Titan's atmosphere and surface properties could affect performances of the Cassini radar experiment. In this paper we present a selection of models for Titan's haze, vertical rain distribution, and surface composition implemented in our simulations. We collected dielectric constant values for the Cassini radar wavelength (∼2.2 cm) for materials of interest for Titan: liquid methane, liquid mixture of methane-ethane, water ice, and light hydrocarbon ices. Due to the lack of permittivity values for Titan's haze particles in the microwave range, we performed dielectric constant (ε_r) measurements around 2.2 cm on tholins synthesized in laboratory. We obtained a real part of ε_r in the range of 2-2.5 and a loss tangent between 10⁻³ and 5×10⁻². By combining aerosol distribution models (with hypothetical condensation at low altitudes) to surface models, we find the following results: (1) Aerosol-only atmospheres should cause no loss and are essentially transparent for Cassini radar, as expected by former analysis. (2) However, if clouds are present, some atmospheric models generate significant attenuation that can reach −50 dB, well below the sensitivity threshold of the receiver. In such cases, a 13.78 GHz radar would not be able to measure echoes coming from the surface. We thus warn about possible risks of misinterpretation if a “wet atmosphere” is not taken into account. (3) Rough surface scattering leads to a typical response of ∼−17 dB. These results will have important implications on future Cassini radar data analysis.     

The ichthyoplankton assemblage and the environmental variables off the NW and N Iberian Peninsula coasts,in early spring

Ichthyoplankton and mesozooplankton were sampled and fluorescence and physical environmental variables were measured off the NW and N Iberian Peninsula coasts, during April 2005. A total of 51 species of fish larvae, belonging to 26 families, were recorded. Sardina pilchardus, with 43.8% and 58.7% of the total fish egg and larval catches, respectively, dominated the ichthyoplankton assemblage. The study area was divided by a cross-shelf frontal structure into two hydrographic regions that coincided with the Atlantic and Cantabrian geographic regions. Ichthyoplankton abundance was higher in the Cantabrian region while larval diversity was higher in the Atlantic region. This was the main alongshore variability in the structure of the larval fish assemblage. Nevertheless, the stronger variability, related with the presence of a shelf-slope front, was found in the central-eastern Cantabrian region where two major larval fish assemblages, an “outer” and a “coastal”, were distinguished. The Atlantic region, where the shelf-slope front was not found, was inhabited by a single larval fish assemblage. Canonical correspondence analysis revealed that, off the NW and N Iberian Peninsula coasts, the horizontal distribution of larval fish species in early spring may be explained by a limited number of environmental variables. Of these, the most important were the physical variables depth and sea surface temperature.     

INTEGRAL and XMM–Newton observations of the X-ray pulsar IGR J16320−4751/AX J1631.9−4752

We report on observations of the X-ray pulsar IGR J16320−4751 (also known as AX J1631.9−4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ) and XMM–Newton . We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded.     

Acute Disturbance of Lake Pontchartrain Benthic Communities by Hurricane Katrina

In 2005, Hurricane Katrina produced a distinct, acute ecological disturbance of the benthic invertebrate community of Lake Pontchartrain, LA, USA. The bivalve Rangia cuneata and other community dominants were lost from 50% (815 km²) of the lake bottom. The storm surge directly killed benthic organisms and produced salinity stratification that caused episodes of detrimental low dissolved oxygen concentration at depths >3.7 m. Past disturbance of the bottom by shell dredging and intrusion of higher salinity bottom water through deep shipping channels appears to have contributed to the severity of this impact. Colonization by tolerant opportunistic taxa occurred, but low rainfall after Katrina has slowed the recovery of the typical rangia community. A decrease in water transparency and an increase in turbidity and chlorophyll a were associated with the loss of clam biomass. Other hurricanes may have produced less obvious but similar effects on smaller spatial and temporal scales.     

A seismotectonic study of the Southeastern Alaska Region

We compare relocations of recent (1973–2005) and historic (1919–1972) earthquakes to geologic and geophysical (gravity, aeromagnetic, and uplift) information to determine the relationship of seismicity to crustal deformation in southeastern Alaska. Our results suggest that along strike changes in the structure of the Pacific plate may control the location of the ends of rupture zones for large earthquakes along the offshore Queen Charlotte fault system in the southern portion of the study area. There is a marked increase in background seismicity in the northern portion of the study area where the Fairweather fault begins to bend toward the northwest and crustal uplift due to glacial unloading exceeds 20 mm/year. Focal mechanisms indicate that thrust and reverse mechanisms predominate in the region of maximum uplift, as might be expected by the decrease in ice sheet thickness. The diffuse nature of seismicity between the Fairweather and Denali faults in the northern study area suggests a complex interaction between plate/microplate interactions and glacial unloading, making it difficult to determine the optimal fault orientation for failure in moderate magnitude (5.5 to 6.5) earthquakes within this region.     

Exploration of hydrothermal targets on Mars

Based on various lines of geologic, geomorphic, topographic, geophysical, spectral, and elemental evidence, we conclude that hydrothermal environments have certainly existed on Mars and are likely to still exist. Here, we present candidate targets of endogenic- and exogenic-driven hydrothermal environments on Mars based on a set of selection criteria and suggest strategies for the detection of such targets. This includes a re-evaluation of potential targets using both existing and yet-to-be-released remote information provided by the instruments onboard the Mars orbiters and rovers. We also provide terrestrial analogs for possible martian hydrothermal environments to highlight the implications of these targets for potential martian life. This compilation and synthesis of data from martian localities indicating hydrothermal activity is timely and a first step towards prioritizing candidate targets for further investigation, which will likely add more targets to this list. Future in situ exploration will have to focus on the most promising of the hydrothermal targets and investigate them utilizing a novel integrated multi-tier, multi-agent reconnaissance mission architecture.     

The role of arsenic-bearing rocks in groundwater pollution at Zimapán Valley, México

 Interaction of groundwater with As-bearing rocks has been proposed as one of three main sources of arsenic at Zimapán valley, México. The complexity of the geology and hydrogeology of the valley make it difficult to identify the natural causes of arsenic poisoning. Samples from the different rock outcrops and water from wells tapping various rock formations were analyzed. The rocks from mineralized areas contained higher concentrations of arsenic with respect to the same formations in non-mineralized areas. The arsenic minerals arsenopyrite, scorodite, and tennantite were identified in some rock samples. Higher temperature and lower Eh values were found for those wells containing more arsenic. The physicochemical characteristics of these naturally polluted well waters could be produced by arsenopyrite oxidation. The geochemical model PHREEQCI was used to perform the inverse modeling of two wells located along the same fault. Arsenopyrite oxidation and scorodite dissolution appear to be the geochemical processes producing the natural pollution according to the model. The release and transport of arsenic mainly occur through fractures within the cretaceous limestones where the most productive wells are drilled. The presence of arsenic should be expected also in other formations near mineralized zones in the Zimapán Valley. Field determinations of Eh and T could be used to detect potentially polluted wells. Received: 29 April 1999 / Accepted: 18 July 2000     

Known and unknown earthquakes through some European periodicals of the eighteenth century

Since the eighteenth century, pioneer seismologists have used information from the periodical press to compile their lists of European earthquakes. A systematic reading of three eighteenth century periodicals –Gaceta de Madrid (1701–1750), Gazeta de Lisboa (1715–1751) and Mercure de France (1732–1763) – has been carried out in the frame of the EC project ‘Review of Historical Seismicity in Europe (RHISE)’. The retrieval of earthquake records provides data on European and Mediterranean earthquakes. Sources and records are here analysed to verify their reliability and to understand the significance of the earthquake information they supply. Special attention has been paid to earthquakes that affected Italian territory, by means of a comparison between records and space-time, intensity parameters of the Italian seismic catalogue: this comparison shows that about 45% of the earthquakes mentioned by the periodicals are unknown in the Italian catalogue, and that 30% of them are damaging earthquakes.