Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.     

An Attempt to Close the Daytime Surface Energy Balance Using Spatially-Averaged Flux Measurements

Single-tower eddy-covariance measurements represent the complete surface flux of a scalar only under idealized conditions. Therefore, we often find an underestimation of energy fluxes expressed as a lack of energy balance closure at many sites. In this study, a multi-tower approach to measure atmospheric energy fluxes based on spatial averaging is evaluated and possible mechanisms causing a lack of energy balance closure are analysed, focussing on daytime data only. It is shown that the multi-tower technique is also unable to measure the entire flux for our site, likely because the assumption of horizontal homogeneity is violated. Heterogeneity-induced and buoyancy-driven quasi-stationary circulations are probably the dominant processes causing the underestimation of energy fluxes. A dependence of the energy balance residual on stability is found, with residuals close to zero for stable stratification, a maximum under unstable to near-neutral conditions and still relatively large residuals for stronger instability. Assuming the processes transporting energy and CO₂ are similar, the implications on long-term CO₂ flux measurements are analysed. Accordingly, the resulting selective systematic error of cumulative net ecosystem exchange estimates for agricultural regions such as ours can be of the order of more than 100%, since mainly the fluxes during periods of net CO₂ uptake are underestimated while periods of net CO₂ release are much less affected by this bias. Further investigations about this issue are highly warranted.     

Dissolution kinetics and the weathering of mafic minerals

Fayalite, hypersthene, basalt, and obsidian were dissolved in buffered solutions (25°C; pH 4.5 and 5.5) under air, N₂ or O₂ atmospheres, in order to follow the kinetics of dissolution. Each dissolved more rapidly at lower pH values, dissolving most rapidly in the initial few days, followed by slower dissolution for periods up to six months. Dissolution was more rapid when air was excluded. In oxygen atmospheres an Fe(OH)₃ precipitate armors mineral surfaces, thus inhibiting further dissolution, and further affects the solution by scavenging dissolved silica and cations. Dissolution reactions include initial exchange between cations and H⁺, incongruent dissolution of silicate structures, oxidation of Fe²⁺ in solution, precipitation of Fe(OH)₃, and scavenging of dissolved silica and cations by Fe(OH)₃. Dissolution kinetics may explain weathering of mafic rocks and minerals at the Earth's surface, the formation of Fe-oxide coatings on mineral grains, weathering of submarine mafic rocks and intrastratal solution of mafic minerals in buried sandstones. Early Precambrian weathering would have been more rapid before the appearance of large amounts of oxygen in the atmosphere, and continental denudation rates may have been higher than at present because of this effect and the predominance of mafic igneous rocks at an early stage of continent formation and growth.     

Late Mesozoic crustal extension along the southern Eurasian margin: evidence from volcanic rocks of the Bangong-Nujiang Suture zone, Tibet

The Mesozoic was a period of marginal basin formations, closures and reactivations along segments of the southern Eurasian margin. Remnants of some of these events are now preserved as exposures of Juras-sic-Cretaceous ophiolites and ophiolitic mélanges, thick sequences of Jurassic flysch deposits and Middle Cretaceous sedimentary and volcanic formations along the Bangong-Nujiang Suture Zone (BNS).