Epistemic and ethical trade-offs in decision analytical modelling

Designing decision analytical models requires making choices that can involve a range of trade-offs and interactions between epistemic and ethical considerations. Such choices include determining the complexity of a model and deciding what types of risk will be assessed. Here, we demonstrate how model design choices can involve trade-offs between the epistemic benefits of representational completeness and simplicity, which interact with ethical considerations about fairness and human life. We illustrate this point by focusing on modeling studies that assess flood risks in New Orleans, Louisiana. Addressing the ethical and epistemic implications of model design choices can help clarify the scope of factors necessary to inform ethically sound and economically efficient decision-making.     

A high temperature equation of state for the H2O-CaCl2 and H2O-MgCl2 systems

An equation of state (EOS) is developed for salt-water systems in the high temperature range. As an example of the applications, this EOS is parameterized for the calculation of density, immiscibility, and the compositions of coexisting phases in the CaCl₂-H₂O and MgCl₂-H₂O systems from 523 to 973 K and from saturation pressure to 1500 bar. All available volumetric and phase equilibrium measurements of these binaries are well represented by this equation. This EOS is based on a Helmholtz free energy representation constructed from a reference system containing hard-sphere and polar contributions plus an empirical correction. For the temperature and pressure range in this study, the electrolyte solutes are assumed to be associated. The water molecules are modeled as hard spheres with point dipoles and the solute molecules, MgCl₂ and CaCl₂, as hard spheres with point quadrupoles. The free energy of the reference system is calculated from an analytical representation of the Helmholtz free energy of the hard-sphere contributions and perturbative estimates of the electrostatic contributions. The empirical correction used to account for deviations of the reference system predictions from measured data is based on a virial expansion. The formalism allows generalization to aqueous systems containing insoluble gases (CO₂, CH₄), alkali chlorides (NaCl, KCl), and alkaline earth chlorides (CaCl₂, MgCl₂). The program of this model is available as an electronic annex (see EA1 and EA2) and can also be downloaded at: http://www.geochem-model.org/programs.htm.     

Apatite-rich pyrometamorphic rocks from Suweileh area,Jordan

Representative samples from the upper Cretaceous pyrometamorphic rocks from Suweileh area were investigated by using XRD, XRF, SEM/EDS, and microprobe techniques. Suweileh area is characterized by the presence of varicolored marble (dominated by green apatite-rich rocks) overlying bituminous marl and silicified limestone-phosphorite beds. The bituminous rocks are enriched with P, S, and F in addition to reduced sensitive trace elements that were inherited later by their metamorphic equivalents. The rocks were affected by severe tectonism that produced intensive fracturing which facilitated the chemical leaching. The mineralogy of the varicolored marble from Suweileh area is equivalent to Daba-Siwaqa and Maqarin areas in central and north Jordan. High-temperature and low-temperature groups of minerals were recognized. The first group is the result of pyrometamorphism produced from the spontaneous combustion of bituminous marl. The metamorphism was contemporaneous with tectonism of the Rift Valley. The second secondary group of minerals is the result of alteration by high alkaline waters followed by precipitation along the weakness zones. A hyperalkaline circulating water similar to the current issuing waters from Maqarin (north Jordan) was responsible for leaching and precipitation of anions and trace elements. A similar scenario was reported in north and central Jordan. The calculated structural formula of fluorapatite is Ca_5.02 (P_2.325, Si_0.22, S_0.0833) O₁₂ F_0.975. The apatite structure incorporates S and Si (inherited from the bituminous precursor) that substitute for P in the tetrahedral positions.     

A comparison of satellite winds and surface buoy winds in the northeast Pacific: Research note

Abstract

Cloud‐motion winds measured from organized and disorganized cumulus cloud fields are compared with winds measured at collocated buoys in the northeast Pacific Ocean. Findings suggest that an automated tracking algorithm using GOES satellite imagery can measure cloud‐level winds at these latitudes. Comparisons with buoy wind measurements show that the influence of boundary‐layer stability should be included in estimates of surface winds from cloud‐motion data.     

Aeolian sediment transport and morphologic change on a managed and an unmanaged foredune

Sediment transport and short‐term morphologic change were evaluated at a site where sand fences are deployed and the beach is raked (Managed Site) and a site where these human adjustments are not practiced (Unmanaged Site). Data were gathered across the seaward portion of a low foredune when winds blew nearly shore‐normal at mean speeds 8.9 to 9.3 m s^‐1. Data from traps revealed sediment transport rates at unvegetated portions of the foredune crest (40.2 to 43.5 kg m^‐1 h^‐1) were greater than on the backshore (4.9 to 11.2 kg m^‐1 h^‐1) due to onshore decreases in surface moisture and speed‐up of the wind passing over the foredune. Data from erosion pins indicate sediment input to the dune was 1.48 m³ m^‐1 alongshore at the Managed Site and 1.25 m³ m^‐1 at the Unmanaged Site. The Unmanaged Site had deposition at the dune toe, erosion at mid‐slope, and deposition at the crest. Deposition occurred at mid‐slope on the Managed Site near a partially buried (0.58 m high) fence with a porosity of about 65%. Deposition at partially buried wrack on the upper backshore and dune toe at the Unmanaged Site was about twice as great as deposition in this zone at the Managed Site. Results indicate that: (1) the seaward slope of the foredune can be a more important source of sand to the lee of the crest than the beach; (2) wrack near the toe can decrease transport into the foredune; (3) a scour zone can occur on the foredune slope above the wrack line; (4) a fence placed in this location can promote deposition and offset scour, but fences can restrict delivery of sediment farther inland. Evaluation of alternative configurations of fences and strategies for managing wrack is required to better determine the ways that humans modify foredunes. Copyright © 2012 John Wiley & Sons, Ltd.     

Salinity history of coastal marshes reconstructed from diatom remains

Sediment cores were collected from three Louisiana coastal marsh ponds, dated with radioisotopes, and analyzed for diatom remains to determine if long-term salinity changes were evident in the sediment record. A diatom-based salinity index formulated from a statistical comparison of available salinity data and changing diatom assemblages demonstrated that diatom remains appear to preserve salinity signals in coastal brackish and salt marsh environments. The salinity index was applied to sediment cores spanning the late 1600s to the 1990s and provided a more complete record of salinity than field data, which were temporally and spatially incomplete. The salinity reconstructions indicated that salinity has increased at two sites and decreased at a third since the early 1900s. The salinity changes are less than 1‰ per decade in all cases, and may be due to natural variability as depicted by the wide range of salinities observed between the late 1600s and 1900. Salinity regimes may be very localized (<2 km from a hydrologic source), indicating single-site studies may not be applicable to regional inferences. This study demonstrates that diatoms can be used to reconstruct past salinity in coastal marsh environments and can provide a useful tool with which to study the changing hydrology of river-influenced ecosystems.     

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

We developed an algorithm for calculating habitat suitability for seagrasses and related submerged aquatic vegetation (SAV) at coastal sites where monitoring data are available for five water quality variables that govern light availability at the leaf surface. We developed independent estimates of the minimum light required for SAV survival both as a percentage of surface light passing though the water column to the depth of SAV growth (PLW _min) and as a percentage of light reaching reaching leaves through the epiphyte layer (PLL _min). Value were computed by applying, as inputs to this algorithm, statistically dervived values for water quality variables that correspond to thresholds for SAV presence in Chesapeake Bay. These estimates ofPLW _min andPLL _min compared well with the values established from a literature review. Calcultations account for tidal range, and total light attenuation is partitioned into water column and epiphyte contributions. Water column attenuation is further partitioned into effects of chlorophylla (chla), total suspended solids (TSS) and other substances. We used this algorithm to predict potential SAV presence throughout the Bay where calculated light available at plant leaves exceededPLL _min. Predictions closely matched results of aerial photographic monitoring surveys of SAV distribution. Correspondence between predictions and observations was particularly strong in the mesohaline and polythaline regions, which contain 75–80% of all potential SAV sites in this estuary. The method also allows for independent assessment of effects of physical and chemical factors other than light in limiting SAV growth and survival. Although this algorithm was developed with data from Chesapeake Bay, its general structure allows it to be calibrated and used as a quantitative tool for applying water quality data to define suitability of specific sites as habitats for SAV survival in diverse coastal environments worldwide.     

Equations of state for the NaCl-H2O-CH4 system and the NaCl-H2O-CO2-CH4 system: Phase equilibria and volumetric properties above 573 k

An equation of state (EOS) based on thermodynamic perturbation theory is presented for the NaCl-H₂O-CH₄ system. This equation consistently reproduces PvTX properties and phase equilibria with an accuracy close to that of data in the temperature, pressure and concentration ranges from 648 K to 873 K, 0 to 2500 bar and up to 2.37 mol % NaCl. Good agreement with recent ternary immiscibility data from 673 K to 873 K suggests that the EOS may provide accurate predictions for NaCl concentrations as high as 40 mol %. We could not find any experimental data above 873 K that can be used to validate the predictions of the EOS inside the ternary. However, parameters for the mixed ternary system were established from parameters evaluated for pure and binary systems and accurate combination rules. Therefore, predictions in the ternary should be reliable to the high temperatures and pressures where the EOS for the lower order systems are valid (about 1300 K and 5000 bar). Using the same combining approach, an EOS for the quaternary NaCl-H₂O-CO₂-CH₄ is constructed on the basis of parameters from our earlier model for the NaCl-H₂O-CO₂ system and the present NaCl-H₂O-CH₄ model. This suggests that predictions of the quaternary EOS are reliable also to about 1300 K and 5000 bar.     

Conditions of core formation in the earth: Constraints from Nickel and Cobalt partitioning

The abundances of Ni and Co in the Earth’s mantle are depleted relative to chondrites due to terrestrial core formation. Recently, the observed mantle depletions of these elements have been explained by liquid metal-liquid silicate equilibrium during core formation in a high pressure, high temperature magma ocean on the early Earth. However, different magma ocean models, which would be expected to give consistent results, have proposed vastly different pressures (24 to 59 GPa), temperatures (2200 to >4000 K) and oxygen fugacities (−0.15 to −2.4 ΔIW) for the Earth’s magma ocean. In an attempt to resolve the contradictory results from different magma ocean models and determine the thermodynamic conditions appropriate for core formation in the Earth, experiments were conducted to better constrain the influences of temperature and C on the partitioning behaviors of Ni and Co. Results of experiments at 7 GPa with temperatures of 1923-2673 K show that the metal-silicate partition coefficients for both Ni and Co decrease with increasing temperature, with the effect being more significant for Ni. Little change in the partitioning behaviors of either Ni or Co with varying C-content of the metallic liquid was found. By combining the new temperature data with previous results from pressure and oxygen fugacity studies, we parameterized the partitioning behavior of Ni and Co and applied the parameterizations to core formation in a terrestrial magma ocean. Multiple combinations of pressure, temperature, and oxygen fugacity can explain the observed mantle depletions of Ni and Co, and all of the very different previously proposed magma ocean conditions are generally consistent with valid solutions. By using the FeO content of the Earth’s mantle as an additional constraint on the oxygen fugacity, magma ocean conditions of 30-60 GPa, > 2000 K, and −2.2 ΔIW are suggested. Similar systematic approaches and studies of other moderately siderophile elements could further constrain the magma ocean conditions on the early Earth.     

Heat capacity calculations for Al2O3 corundum and MgSiO3 ilmenite

We have used Kieffer's vibrational model to calculate heat capacities and entropies for Al₂O₃ corundum and MgSiO₃ ilmenite, using available vibrational and elastic data for these phases. The calculated heat capacity for corundum is within 1–2 percent of the experimental values between 100 K and 1,800 K, while that for MgSiO₃ ilmenite is within 1–2 percent of the experimental data between 350 K and 500 K. We have calculated the heat capacity for MgSiO₃ ilmenite from 50 K to 1,800 K, which extends the range of available heat capacity data for this phase. The results of this calculation suggest that there may be differences in the vibrational properties of corundum and MgSiO₃ ilmenite. Finally, we have used the results of our calculation to obtain a transition entropy of near -18.8 J/mol.K for the MgSiO₃ pyroxene-ilmenite reaction.