Volatile organic sulfur compounds as biomarkers complementary to methane: Infrared absorption spectroscopy of CH3SH enables insitu measurements on Earth and Mars

As universal products of biological processes, volatile organic sulfur compounds such as methyl mercaptan (CH₃SH) may be essential in the search for signs of life on Mars and in exoplanet atmospheres. Methyl mercaptan is implicated in the origin of life at sites of low-temperature hydrothermal activity driven by serpentinization. Serpentinization may occur on Mars, in icy satellite oceans, and in other small wet bodies to a greater extent than on Earth, with important implications for life. We characterized absorption features in pure laboratory sample spectra of CH₃SH using the Carbon Isotope Laser Spectrometer (CILS), an infrared $(3.27\mathrm{\mu }\mathrm{m})$ tunable diode laser spectrometer with capabilities nearly identical to those of the Tunable Laser Spectrometer (TLS) instrument on the Mars Science Laboratory. The molecular species proves detectable by CILS and TLS at the sensitivities approaching the level of parts per trillion with pre-concentration. These measurements demonstrate the possibility for detection of methyl mercaptan, with implications for its possible use as an in situ biosignature for Earth-based and extraterrestrial exploration.     

LIDAR Validation Using GIS: A Case Study Comparison between Two LIDAR Collection Methods

Abstract

In the summer of 2000, the Annapolis Valley of Nova Scotia, Canada was selected for a high‐resolution elevation survey utilizing LIDAR (Light Detection And Ranging). Two different LIDAR systems were used to acquire data for the area. The vertical accuracy specification for the survey called for heights to be within an average of 15 cm of measured GPS heights and 95% of the data to be within 30 cm. Prior to the application of these data to geoscientific problems, extensive validation procedures were employed. High precision GPS and traditional surveys were conducted to collect height validation checkpoints. Two validation methods were developed in a GIS environment that involved comparing the checkpoints to the original LIDAR points and to an interpolated “bald earth” DEM. A systematic height error between flight lines for one of the LIDAR methods was detected that related to the calibration procedures used in the survey. This study highlights the differences between laser systems, calibration and deployment methodologies and emphasizes the necessity for independent validation data.     

Simulating artificial cities in a GIS environment: urban growth under alternative regulation regimes

This paper reports on an attempt to combine neo-classical urban economic theory with complex systems methods. The innovative feature of our model from the point of view of conventional economic theory lies in its explicit treatment of spatial relationships and time sequence. From the perspective of raster or cellular GIS models of urban processes, the work is innovative in that it replaces the more usual heuristic cell-transition rules with micro-economic theory. The mix of modelling paradigms is not unproblematic, however, and we discuss the challenges encountered at this research frontier. These notwithstanding, our hybrid model has the potential to be used as a GIS-based laboratory for exploring micro-economic propositions, particularly those relating to urban processes that are path dependent. The version of the model reported simulates spatially equilibriated path dependent futures of a city governed by local development decisions that are at partial equilibria in the neo-classical sense. Two simulations are described which permit visual and economic exploration of (a) an explicitly spatial version of the economic theory of externalities and (b) a new theory of densification. The dual paradigm (Cellular Automata-neo-classical economics) leads to an interesting class of simulations in terms of stability. Economically our simulated cities become increasingly efficient, in terms of private and social product. The long-run economic equilibrium is achieved by many individually efficient negotiations based only on local information. There is no parallel long-run spatial equilibrium however. The spatial configuration of land uses is constantly shifting as a result of randomness in the land use bidding process. The spatial instability is, however, limited by the self-organised drive for greater overall economic efficiency. In economic terms, the model's spatial instability represents random re-allocation of land-use within a set of Pareto-efficient spatial configurations - an intriguing result that we intend to follow up in future work.     

Mapping gamma radiation and its uncertainty from weathering products in a Tasmanian landscape with a proximal sensor and random forest kriging

The radionuclides of potassium (⁴⁰ K), uranium (²³⁸U) and thorium (²³²Th) emit from the land surface gamma radiation that is characteristic of the underlying rocks and the distribution of their weathering products in the landscape. We measured the radiation along widely separated transects using a mobile proximal sensor over a 10 000‐ha region of Tasmania. We supplemented the transect data with information from soil and geological maps and dense data from LandSat and SPOT imagery, a digital elevation model and terrain attributes on a grid at 30‐m intervals so as to map the radionuclides. We used a sequence of steps, starting with a spatial bootstrap and random forests to predict emissions across the study area and at sampling points excluded from the bootstrap samples. The predictions at the sampling points were compared with the observed values to obtain residuals, which were then used to krige them at all points on the 30 m grid. We combined the random forest and kriging predictions on the 30‐m grid to obtain our random forest kriging predictions. Repeating the procedure 100 times provided confidence limits on our results and predictions. The resulting maps of the radionuclides accord well with what we know of the soil, lithology and topography of the region from other sources. Alluvial deposits with large amounts of potassium extend from the foot slopes of the Great Western Tiers and along the flood plains of the Meander River, providing evidence of previous widespread weathering and deposition of the material. The fertile Red Ferrosols (roughly equivalent to Ferralic Nitisols in the World reference base (WRB) classification) on the extensive Tertiary basalt plateau emit little gamma radiation as a result of deep weathering and of potassium movement and accumulation down its talus slopes. The maps show the complexity of the region in terms of soil, lithology and terrain, and they show the merits of gamma radiometry for mapping and understanding the distribution of materials in such regions. Copyright © 2013 John Wiley & Sons, Ltd.     

Sealevel history recorded in the Pleistocene carbonate sequence in IODP Hole 310‐M0005D,off Tahiti

Material cored during the Integrated Ocean Drilling Program (IODP) Expedition 310 ‘Tahiti Sea Level’ revealed that the fossil reef systems around Tahiti are composed of two major stratigraphic sequences: (i) a last deglacial sequence; and (ii) an older Pleistocene sequence. The older Pleistocene carbonate sequence is composed of reef deposits associated with volcaniclastic sediments and was preserved in Hole 310‐M0005D drilled off Maraa. Within an approximately 70‐m‐thick older Pleistocene sequence (33.22–101.93 m below seafloor; 92.85–161.56 m below present sealevel) in this hole, 11 depositional units are defined by lithological changes, sedimentological features, and paleontological characteristics and are numbered sequentially from the top of the hole downward (Subunits P1–P11). Paleowater depths inferred from nongeniculate coralline algae, combined with those determined by using corals and larger foraminifers, suggest two major sealevel rises during the deposition of the older Pleistocene sequence. Of these, the second sealevel rise is associated with an intervening sealevel drop. It is likely that the second sealevel rise corresponds to that during Termination II (TII, the penultimate deglaciation, from Marine Isotope Stages 6 to 5e). Therefore, the intervening sealevel drop can be correlated with that known as the ‘sealevel reversal’ during TII. Because there are limited data on the Pleistocene reef systems in the tropical South Pacific Ocean, this study provides important information about Pleistocene sealevel history, the evolution of coral reef ecosystems, and the responses of coral reefs to Quaternary climate changes.     

The effects of oil exploration and production in the Fladen Ground: composition and concentration of hydrocarbons in sediment samples collected during 2001 and their comparison with sediment samples collected in 1989

Due to the potentially accumulative nature of the Fladen Ground, an area of intense oil activity in the North Sea, a survey was carried out in 1989 to map the distribution of contamination in relation to these oil activities. All the sediments collected were screened by ultraviolet fluorescence (UVF) for polycyclic aromatic hydrocarbons (PAHs) and selected samples were analysed for n-alkanes (by GC-FID), PAHs and biomarkers (by GC-MSD). This survey was repeated in 2001, with all the 1989 sites being resampled. All of these sediments were analysed for UVF oil equivalents, PAHs, n-alkanes and biomarkers. The concentrations of these parameters decreased between 1989 and 2001, with average decreases ranging from 43% to 88%. In addition, no significant difference was found, for all the parameters, between near field (<5 km from an oil installation) and far field (>5 km from an oil installation) sites in 2001 indicating that the Fladen Ground is approaching a 'steady state' or background concentration for contamination.     

Seasonal anecdysis and moulting synchrony in field populations of Palaemon elegans (Rathke)

A population of Palaemon elegans studied during 1978–1980 showed a characteristic moult cycle structure according to season, comprising a winter anecdysis, ‘epidemic’ spring moulting and synchrony of moult cycle development. The initiation of moulting in the spring was temperature-dependent, an estimated environmental temperature of 7–8 °C being necessary to allow moulting. Developmental synchrony during the moult cycle was observed following the initial spring moults, and it is thought that the degree and duration of moult synchrony is temperature-dependent. Synchrony is lost during the summer. Despite seasonal climatic differences between years, little difference in the time of appearance of berried females was seen. It is thought that oogenesis is controlled primarily by photoperiodic rather than temperature-dependent mechanisms. During egg development the moult cycle of ovigerous females was prolonged during intermoult stages and, during late vitellogenesis, premoult stages were prolonged.     

Different levels of mussel (Mytilus edulis) DNA strand breaks following chronic field and acute laboratory exposure to polycyclic aromatic hydrocarbons

Levels of polycyclic aromatic hydrocarbons (PAHs) including benzo[a]pyrene (B[a]P) were at least seven-fold higher in mussels sampled from a polluted site (Loch Leven, in Scotland, UK) compared to a nearby clean reference site (Loch Etive) throughout the year 2000. Levels of DNA strand breaks (alkaline COMET assay) using both gill and digestive gland nuclei were similar at both sites despite the difference in contaminant load (total PAH). In contrast, mussels collected from a reference site (Port Quin, Cornwall, UK) had an increase in DNA strand breaks in digestive gland cells following laboratory exposure to B[a]P-dosed Isochrysis galbana. However, after 14 days high dose (20 ppb-exposed diet) animals had returned to levels similar to the controls. There was no evidence of increased necrosis or apoptosis after treatments. The results from these two studies suggest that an adaptive response may prevent ongoing DNA damage in mussels exposed to high levels of B[a]P and PAH contamination.     

Implications from a field study regarding the relationship between polycyclic aromatic hydrocarbons and glutathione S-transferase activity in mussels

An aluminium smelter on the west coast of Scotland discharges an aqueous effluent containing polycyclic aromatic hydrocarbons (PAHs) at the head of Loch Leven. The loch also supports two mussel (Mytilus edulis) farms. Data are presented on burdens of PAHs in the soft tissues of mussels and the effect of these contaminants on glutathione S-transferase (GST) activity in mussel hepatopancreas. GST activity is shown to be correlated with total PAH burden and also with the concentrations of certain individual PAHs. These field data show that high molecular weight PAHs are closely correlated to GST activity, whereas low molecular weight PAHs are not. This suggests that 5- and 6-ring PAHs have a more pronounced role than 2- to 4-ring compounds in inducing GST activity in mussels from Loch Leven. It is proposed that it may be more appropriate to link GST activity with 5- and 6-ring compounds only, rather than with the total PAH burden.