Climate projections over CORDEX Africa domain using the fifth-generation Canadian Regional Climate Model (CRCM5)

Following the CORDEX experimental protocol, climate simulations and climate-change projections for Africa were made with the new fifth-generation Canadian Regional Climate Model (CRCM5). The model was driven by two Global Climate Models (GCMs), one developed by the Max-Planck-Institut für Meteorologie and the other by the Canadian Centre for Climate Modelling and Analysis, for the period 1950–2100 under the RCP4.5 emission scenario. The performance of the CRCM5 simulations for current climate is discussed first and compared also with a reanalysis-driven CRCM5 simulation. It is shown that errors in lateral boundary conditions and sea-surface temperature from the GCMs have deleterious consequences on the skill of the CRCM5 at reproducing specific regional climate features such as the West African Monsoon and the annual cycle of precipitation. For other aspects of the African climate however the regional model is able to add value compared to the simulations of the driving GCMs. Climate-change projections for periods until the end of this century are also analysed. All models project a warming throughout the twenty-first century, although the details of the climate changes differ notably between model projections, especially for precipitation changes. It is shown that the climate changes projected by CRCM5 often differ noticeably from those of the driving GCMs.     

Modeling stream-aquifer interactions in a shallow aquifer, Choele Choel Island, Patagonia, Argentina

A groundwater/surface-water interaction model was developed for the shallow alluvial aquifer of the Choele Choel Island in Patagonia, Argentina. In this semiarid climate, agriculture is sustained by an irrigation/drainage system. During the irrigation season, seepage losses through unlined distribution canals in irrigated fields contribute to elevated groundwater levels, jeopardizing fruit productivity in some areas. Moreover, high stream stages during the irrigation season interfere with groundwater drainage. The model utilized MODFLOW and its stream package, and was successfully calibrated for a historical irrigation season. Modeling results indicate that drainage through streams is significantly higher than drainage through artificial drains. The stream/aquifer relationship proved very responsive to water table rises caused by irrigation. This response manifested as changes in the gaining/losing character of stream reaches. A synthetic run aimed at isolating the effect of streamflow changes on groundwater levels showed that the effect of higher streamflows dissipates toward the interior of the island, disappearing completely at the island center. Even though some results were qualitative, the model helped to provide a better understanding of the coupled system to elucidate some of the causes of a rising water table on the island.

Mesoproterozoic evolution of the R��o de la Plata Craton in Uruguay: at the heart of Rodinia?

Mesoproterozoic volcanosedimentary units and tectonic events occurring in the Río de la Plata Craton (RPC) are reviewed. A belt consisting of volcanosedimentary successions exhibiting greenschist-facies metamorphism is exposed in the eastern RPC (Nico Pérez Terrane) in Uruguay. The Parque UTE Group consists of basic volcanics and gabbros at the base (1,492?±?4?Ma, U?CPb on zircon), carbonates in its middle part and interbedded carbonates, shales and acid volcanics (1,429?±?21?Ma, U?CPb on zircon) at the top. The Mina Verdún Group is made up of rhyolites and acid pyroclastics at its base and top, and Conophyton-bearing limestones and massive dolostones in the middle. A U?CPb LA-ICP MS zircon age of 1,433?±?6?Ma is reported here for lapilli-tuffs at the base of the Mina Verdún Group (Cerro de las Víboras Formation). This age shows that the Mina Verdún Group immediately postdates the Parque UTE Group, a fact supported by carbon isotope chemostratigraphy. Both units were deformed and metamorphosed between 1.25 and 1.20?Ga, as shown by K?CAr and Ar?CAr ages. This tectonic event affected most of the RPC and led to the accretion of the Nico Pérez Terrane to the remainder of the RPC along the Sarandí del Yí megashear. We report a U?CPb LA-ICP MS zircon age (upper intercept) of 3,096?±?45?Ma for metatonalites of the La China Complex (Nico Pérez Terrane), which yield a lower intercept age of 1,252?Ma. A proto-Andean, Mesoproterozoic belt is envisaged to account for abundant Mesoproterozoic detrital zircon ages occurring in Ediacaran sandstones of the RPC. If the RPC is fringed at both sides by Mesoproterozoic, Grenville-aged belts it is likely that it occupied a rather central position in Rodinia. A possible location between Laurentia and the Kalahari Craton, and to the south of Amazonia, is suggested.     

The Ksar Ghilane 002 shergottite—The 100th registered Martian meteorite fragment

We report on the discovery of a new shergottite from Tunisia, Ksar Ghilane (KG) 002. This single stone, weighing 538 g, is a coarse‐grained basaltic shergottite, mainly composed of maskelynitized plagioclase (approximately 52 vol%) and pyroxene (approximately 37 vol%). It also contains Fe‐rich olivine (approximately 4.5 vol%), large Ca‐phosphates, including both merrillites and Cl‐apatites (approximately 3.4 vol%), minor amounts of silica or SiO₂‐normative K‐rich glass, pyrrhotite, Ti‐magnetite, ilmenite, and accessory baddeleyite. The largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm. Pyroxenes (Fs_26–96En_5–50Wo_2–41). They typically range from cores of about Fs₂₉En₄₁Wo₃₀ to rims of about Fs₆₈En₁₄Wo₁₇. Maskelynite is Ab_41–49An_39–58Or_1–7 in composition, but some can be as anorthitic as An₉₃. Olivine (Fa_91–96) occurs mainly within symplectitic intergrowths, in paragenesis with ilmenite, or at neighboring areas of symplectites. KG 002 is heavily shocked (S5) as indicated by mosaic extinction of pyroxenes, maskelynitized plagioclase, the occurrence of localized shock melt glass pockets, and low radiogenic He concentration. Oxygen isotopes confirm that it is a normal member of the SNC suite. KG 002 is slightly depleted in LREE and shows a positive Eu anomaly, providing evidence for complex magma genesis and mantle processes on Mars. Noble gases with a composition thought to be characteristic for Martian interior is a dominant component. Measurements of ¹⁰Be, ²⁶Al, and ⁵³Mn and comparison with Monte Carlo calculations of production rates indicate that KG 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35–65 cm radius. KG 002 strongly resembles Los Angeles and NWA 2800 basaltic shergottites in element composition, petrography, and mineral chemistry, suggesting a possible launch‐pairing. The similar CRE ages of KG 002 and Los Angeles may suggest an ejection event at approximately 3.0 Ma.     

Groundwater capture processes under a seasonal variation in natural recharge and discharge

 "Capture" is the increase in recharge and the decrease in discharge that occurs when pumping is imposed on an aquifer system that was in a previous state of approximate dynamic equilibrium. Regional groundwater models are usually used to calculate capture in a two-step procedure. A steady-state solution provides an initial-head configuration, a set of flows through the boundaries for the modeled region, and the initial basis for the capture calculation. The transient solutions provide the total change in flows through the boundaries. A difference between the transient and steady-state solutions renders the capture calculation. When seasonality is a modeling issue, the use of a single initial hydraulic head and a single set of boundary flows leads to miscalculations of capture. Instead, an initial condition for each season should be used. This approach may be accomplished by determining steady oscillatory solutions, which vary through the seasons but repeat from year to year. A regional groundwater model previously developed for a portion of the San Pedro River basin, Arizona, USA, is modified to illustrate the effect that different initial conditions have on transient solutions and on capture calculations. Received, September 1996 · Revised, October 1997 · Accepted, October 1997     

Asbestiform and non-asbestiform morphologies in a talc and vermiculite mine from the province of Córdoba (Argentina): a case study

In this work, a talc and vermiculite mine from the province of Córdoba (Argentina) was investigated with special emphasis on the occurrence of asbestiform and non-asbestiform phases. The meta-ultramafic rock was studied by a multimethodological approach, complementing field studies with petrographic-mineralogical, compositional and morphological analyses. Samples were examined by stereomicroscopy, polarizing light microscopy, SEM–EDS, XRD, DSC-TGA and FTIR. Complementary, compositional and textural analyses were performed with FE-SEM–EDS and EPMA. Talc-rich veins with a laminar and fibrous appearance were at first recognized. However, the fibrous morphology observed both in the field and by microscopy is due to an apparent habit because of the sample orientation. To avoid erroneous interpretations, studies by secondary electron images (SEM) are fundamental to carrying out this type of analysis. Tremolite was identified in different zones of the outcrop; however, only ~40% of the crystals located in the vermiculite zone have dimensions to be considered as asbestiform fibres in the range of respirable particles. In these types of complex deposits affected by superimposed metamorphic, igneous and deformational events, multimethodological approaches are necessary to develop models of occurrence of asbestiform morphologies that may be applicable to other with similar characteristics.     

Non-extensivity analysis of seismicity within four subduction regions in Mexico

The non-extensivity approach based on the Tsallis entropy has been applied to seismicity that occurred from 1988 to 2010 along the Mexican South Pacific coast. We analyzed four different regions, characterized by different subduction patterns. Our results indicate a possible correlation between the non-extensive parameters and the seismicity pattern associated with the inclination angle of each subduction region.     

Climate simulation over CORDEX Africa domain using the fifth-generation Canadian Regional Climate Model (CRCM5)

The new fifth-generation Regional Climate Model (CRCM5) was driven by ERA reanalyses for the period 1984–2008 over the African continent following the CORDEX experimental protocol. Overall the model succeeds in reproducing the main features of the geographical distribution and seasonal cycle of temperature and precipitation, the diurnal cycle of precipitation, and the West African Monsoon (WAM). Biases in surface temperature and precipitation are discussed in relation with some circulation defects noted in the simulation. In the African regions near the equator, the model successfully reproduces the double peak of rainfall due to the double passage of the tropical rainbelt, although it better simulates the magnitude and timing of the second peak of precipitation. CRCM5 captures the timing of the monsoon onset for the Sahel region but underestimates the magnitude of precipitation. The simulated diurnal cycle is quite well simulated for all of the regions, but is always somewhat in advance for the timing of rainfall peak. In boreal summer the CRCM5 simulation exhibits a weak cold bias over the Sahara and the maximum temperature is located too far south, resulting in a southward bias in the position of the Saharan Heat Low. The region of maximum ascent in the deep meridional circulation of the Hadley cell is well located in the CRCM5 simulation, but it is somewhat too narrow. The core of the African Easterly Jet is of the right strength and almost at the right height, but it is displayed slightly southward, as a consequence of the southward bias in the position of the Saharan Heat Low and the thermal wind relationship. These biases appear to be germane to the WAM rainfall band being narrower and not moving far enough northward, resulting in a dry bias in the Sahel.