The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes

The Canadian Centre for Climate Modelling and Analysis (CCCma) has developed the fourth generation of the Canadian Atmospheric Global Climate Model (CanAM4). The new model includes substantially modified physical parameterizations compared to its predecessor. In particular, the treatment of clouds, cloud radiative effects, and precipitation has been modified. Aerosol direct and indirect effects are calculated based on a bulk aerosol scheme. Simulation results for present-day global climate are analyzed, with a focus on cloud radiative effects and precipitation. Good overall agreement is found between climatological mean short- and longwave cloud radiative effects and observations from the Clouds and Earth's Radiant Energy System (CERES) experiment. An analysis of the responses of cloud radiative effects to variations in climate will be presented in a companion paper.

[Traduit par la rédaction] Le Centre canadien de la modélisation et de l'analyse climatique (CCmaC) a mis au point la quatrième génération du modèle canadien de circulation générale de l'atmosphère (CanAM4). Le nouveau modèle comprend des paramétrisations physiques passablement modifiées comparativement à son prédécesseur. En particulier, le traitement des nuages, des effets radiatifs des nuages et des précipitations a été modifié. Les effets directs et indirects des aérosols sont calculés à l'aide d'un schéma d'aérosols en bloc. Nous analysons des résultats de simulation pour le climat général du jour présent en mettant l'accent sur les effets radiatifs des nuages et les précipitations. Nous trouvons un bon accord général entre la moyenne climatologique des effets radiatifs des nuages pour les courtes et les grandes longueurs d'onde et les observations de l'expérience CERES (Clouds and Earth's Radiant Energy System). Une analyse de la réponse des effets radiatifs des nuages aux variations du climat sera présentée dans un article connexe.     

Water contents of Roberts Victor xenolithic eclogites: primary and metasomatic controls

A suite of eclogites from the Roberts Victor kimberlite has been extensively characterized in terms of petrology and geochemical compositions (Gréau et al. in Geochim Cosmochim Acta 75(22):6927–6954, 2011; Huang et al. in Lithos 142–143:161–181, 2012a). In the present study, the water contents of eclogitic garnet and omphacite were analyzed by Fourier transform infrared spectrometry. Garnet does not contain measureable OH in any sample. The water content of omphacite in the studied eclogites ranges from 211 to 1,496 ppm. Mantle metasomatism has modified the water content of some of the eclogites, while others retain water contents characteristic of their original environment. The OH contents of the metasomatized eclogites may be mainly controlled by the H₂O fugacity and mineral compositions. The OH contents of the non-metasomatized samples are interpreted to be more sensitive to their mantle equilibration temperature, pressure, and the local fugacities of H₂O and O₂. The calculated water content of the metasomatic medium is similar to that of carbonatitic–kimberlitic melts/fluids. Eclogites contain more water than peridotites recorded in the literature (341 ± 161 vs 122 ± 54 ppm) and represent an important water reservoir in the lithospheric mantle wherever they occur. This is an important parameter to be considered in the interpretation of mantle processes and geophysical data such as seismic wave speeds and electrical conductivity, and in geodynamic modeling.     

A three-dimensional analytical tool for modeling reactive transport

In this note, we present a public domain analytical reactive transport modeling tool (ART3D, version 2.0). The tool is developed in FORTRAN and can be used for solving a system of a set of partial differential equations coupled with a first-order reaction network. ART3D uses a novel analytic solution technique proposed by Clement. The new software includes options for performing Monte Carlo simulations and automated parameter estimation.     

Morphometric comparisons between automated and manual karst depression inventories in Apalachicola National Forest,Florida, and Mammoth Cave National Park,Kentucky, USA

Karst depression catalogs are critical to assessing the hydrology and geohazards of an area; yet, the delineation of these features within a landscape can be a difficult, time-consuming and subjective task. This study evaluates the efficacy of karst depression inventorying using an automated fill-difference method operating on high-resolution lidar-derived digital elevation models (DEMs). The resulting catalog is compared with existing karst depression inventories for two low-development areas of the USA, Mammoth Cave National Park (MACA) and Apalachicola National Forest (ANF), where karst depressions have been mapped previously using a manual closed-contour approach. The automated fill method captures 93 and 85 % of these previously mapped karst depressions at MACA and ANF, respectively. Field observations and topographic analysis suggest that the omitted features were likely misclassified within the existing catalogs. The automated routine returns 797 and 3377 additional topographic depressions, at MACA and ANF, respectively, which are not included in the existing catalogs. While the geology of ANF is mostly homogenous Quaternary deposits, the newly identified, typically smaller-scale depressions found within MACA tend to be disproportionally located in non-carbonate-dominated formations, where the development of karst may be restricted by geologic heterogeneity. Within both areas, the size distributions of the two inventories are statistically identical for features larger than ~10³ m² in area or ~3 m in depth. For individual depressions captured by both methods at MACA, the automated fill-difference routine tends to return a slightly larger estimate of depression size and aggregate small depressions into larger ones. Conversely, at ANF, some low-relief depressions may be disaggregated by the fill-difference technique, with a trend toward smaller estimated depression areas when the automated method is employed. The automated fill-difference method, operating on high-resolution lidar-derived DEMs, can reproduce and expand the existing inventories of karst depressions, while minimizing false detections that may be inherent within pre-existing catalogs.     

Trace-metal content of the Pueblo Viejo precious-metal deposits and their relation to other high-sulfidation epithermal systems

We provide here information on the distribution of copper, zinc, lead, gold, silver, barium, arsenic, antimony, mercury, selenium and tellurium in the Moore and Monte Negro high-sulfidation epithermal deposits in the Pueblo Viejo district, Dominican Republic. Moore and Monte Negro are funnel-shaped zones of advanced argillic alteration and precious-metal mineralization which extend to depths of about 350 m below the present surface. The uppermost part of the Moore deposit has been removed by erosion, whereas the Monte Negro deposit is covered by rocks containing low, but still anomalous gold grades. At Moore, concentrations of all elements except copper increase upward through the deposit. At Monte Negro, all elements except barium and zinc show a similar upward increase in concentration to a point near the top of the deposit from which they decrease upward. This difference reflects the fact that the top of the Moore deposit has been removed by erosion. Because the deposits are funnel-shaped and average metal concentrations increase by almost an order of magnitude upward, most of the metals are concentrated in the upper parts of the deposits. The upward increase in concentration of most metals is gradual and similar in magnitude to the prograde temperature dependence in solubilities of many metal complexes, suggesting that the metals were deposited by cooling. By contrast, concentrations of mercury and, to a lesser extent, tellurium increase more abruptly in the upper part of the deposits. This change probably reflects boiling of the hydrothermal solutions and partitioning of mercury and tellurium into a rising vapor phase, and it suggests that host rocks overlying the deposits will be anomalous in mercury and tellurium. Comparison to the Broadlands, New Zealand, hydrothermal system supports these inferred depositional processes. It shows that the behavior of arsenic and antimony at Broadlands was different from that at Pueblo Viejo, possibly because the elements were complexed differently in the two ore fluids. Comparison of trace-element abundances at Pueblo Viejo to other high-sulfidation epithermal systems shows differences in base-metal, arsenic and mercury abundances which may be related to the depths at which the deposits formed. The results of this study highlight the application and need for quantitative trace-element data from epithermal deposits.     

Metamorphic incongruent solution,diffusion and pressure solution stripes

The formation of pressure solution stripes is discussed on the basis of previosly published observations and of local chemical equilibria between solution and solid phases. Chemically driven mineral reactions can be localized at early sites of nucleation and be enhanced by stresses to create patterns of cleavage stripes. These reactions cause transport of material over distances greater than single grains. They provide suitable sites and suitable chemistry for later incongruent pressure solution, potentially a much faster process than congruent pressure solution discussed in previous literature. Neither reaction nor straightforward incongruent pressure solution explains the solution of quartz, commonly observed at cleavage stripes. Quartz pressure solution is explicable on certain assumptions about diffusivities and the effects of stresses. This involves interaction between quartz and the established incongruent solution of other minerals, an overall process termed ‘interdependent pressure solution’. Electrical potential differences will be greatest during early mineral reactions, a feature which may provide a means to corroborate the chemical role in initiating ‘pressure solution stripes’.