Absolute measurements and computed values for Martian irradiance between 10.5 and 12.5 μm

The combination of seasonal and orbital changes in Martian insolation result in complex latitude dependent surface temperature variations that effect the total radiance of the planet as seen from the earth. These surface temperature variations have been calculated, based upon a computer simulation of the thermal environment of the planet. The temperature variations are then integrated to yield the total radiance of the planet as seen from the earth as a function of time. The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm. The average brightness temperature of the Mars disk determined from these measurements was 254°K with a 1 σ error of 4°K.     

Sea State and Rain: A Second Take on Dual-Frequency Altimetry

TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at K_u- and C-band. Thus, each gives two measurements of the normalized backscatter, σ⁰, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the K_u- and C-band σ⁰ values give an indication of rain. This study investigates differences between the two instruments using data from Jason's verification phase. Jason's K_u-band estimates of wave height are ∼1.8% less than TOPEX's, whereas its σ⁰ values are higher. When these effects have been removed the root mean square (rms) mismatch between TOPEX and Jason's K_u-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in σ⁰ with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the σ⁰ measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of-0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high σ⁰ regime, anomalous data can be caused by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data.     

Correlation of strain with anisotropy of magnetic susceptibility (AMS)

Existing correlations between strain and anisotropy of low-field magnetic susceptibility (AMS) have been re-assessed using a single parameter to express both anisotropies. TheP parameter (Hrouda, 1982) shows potential as a powerful single expression of the intensity of strain and of AMS. Previous correlations are improved by use of this parameter. Cautious optimism is justified for correlations between strain and susceptibility in a certain strain window between a lower limit (excluding the incomplete overprint of predeformation anisotropy) and an upper limit (excluding the effects of saturation anisotropy). For successful correlations the influence of stress-controlled recrystallisation should be minimal and the mineralogical sources of susceptibility must predate deformation.     

Equilibrium dihedral angles in the system H2O−CO2−NaCl-calcite,and implications for fluid flow during metamorphism

Fluid-calcite-calcite dihedral angles have been measured for fluids in the system H₂O−CO₂−NaCl, between 1 and 2 kbar, and 550–750° C. It is found that the calcite-calcite-H₂O dihedral angle decreases steadily with addition of NaCl from a value of about 80° (pure water) to 44° (60 wt% NaCl). The CO₂−H₂O system displays a well-defined minimum at , with a dihedral angle of 50°, in contrast to those of pure CO₂ and H₂O which are 90° and 80° respectively. Experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the CO₂−H₂O−NaCl system, which can be approximately correlated with the compositions of the two fluid phases. Such bimodality was only observed for immiscible fluids in the H₂O−NaCl system if the quench rate exceeded about 200°C per min. This is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching. The fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with close to 0.5. Fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly H₂O-rich or CO₂-rich, and of low salinity. All other fluid compositions in the H₂O−CO₂−NaCl-calcite system will occupy isolated pores, the largest of which will grow at the expense of the smallest. Escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture. In contrast, previous experimental studies of quartz-fluid dihedral angles between 950° and 1100° C (Watson and Brenan 1987) predict that quartz-dominated lithologies will permit pervasive flow of H₂O−NaCl fluids, but not of H₂O−CO₂ fluids. Documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites, psammites and limestones which support the results of the experimental studies are discussed.     

A discrete element approach to elastic properties of layered geomaterials

Discrete element methods (DEMs) are used for layered geomaterials to investigate the dependency of traditional engineering constants on material properties and loading conditions. Shear deformations and compression tests parallel and perpendicular to layering are conducted on samples of varying kerogen volume fractions, confining pressures, porosities, and layer geometries. The goal of this article is to develop a method to better characterize oil shale (a transversely isotropic layered geomaterial) while eliminating high experimental costs. The DEM simulations conducted in this study demonstrate strong dependencies of Young's modulus, Poisson's ratio, and shear modulus on kerogen volume fraction and porosity. Furthermore, a rule of thumb for layer thickness and particle resolution is proposed for simulation design. Results agree well with robust effective medium theories, solidify the ability of DEM to model the mechanical properties of layered heterogenous materials, and encourage the use of DEM to study more complicated layered media and material failure. Copyright © 2011 John Wiley & Sons, Ltd.     

Synergies and tradeoffs in how managers,scientists, and fishers value coral reef ecosystem services

Managing ecosystems in a changing environment faces the challenge of balancing diverse competing perspectives on which ecosystem services – nature's benefits – to prioritize. Consequently, we measured and compared how different stakeholders (managers, scientists and fishers) prioritize specific coral reef ecosystem services. Managers’ priorities were more aligned with scientists’ priorities but all stakeholder groups agreed that fishery, education, and habitat were high priorities. However, stakeholder groups differed in the extent to which they prioritized certain services. Fishers tended to assigned greater estimates to fishery and education, managers to culture, and scientists to coastal protection. Furthermore, using network analysis to map the interactions between stakeholders’ priorities, we found distinct synergies and trade-offs in how ecosystem services were prioritized, representing areas of agreement and conflict. In the fishers’ network, trade-offs emerged between two services, both of a higher priority, such as fishery and habitat. Conversely, in the scientists’ network, trade-offs emerged between services of a higher and lower priority, such as habitat and culture. The trade-offs and synergies that emerged in the managers’ network overlap with both fishers’ and scientists’ suggesting a potential brokering role that managers can play in balancing both priorities and conflicts. We suggest that measuring ecosystem service priorities can highlight key areas of agreement and conflict, both within and across stakeholder groups, to be addressed when communicating and prioritizing decisions.     

An assessment of the utility of regional diatom‐based tidal‐level transfer functions

In order to understand natural sea‐level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom‐based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom‐based tidal‐level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site‐specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal‐level transfer functions, may be more appropriate. Copyright © 2011 John Wiley & Sons, Ltd.