Letter from the vatican: 26 April 2015

This narrative deals with the author's experiences while attending a human trafficking panel at the Pontifical Academy of Social Sciences (PASS) in the Casina Pio IV, Vatican City, 7–21 April 2015.     

CORN HYBRID SELECTION AND CLIMATIC VARIABILITY: GAMBLING WITH NATURE?

Farmer adaptation to climatic variability is explored via an analysis of corn hybrid selection in southern Ontario. Corn hybrid varieties are available for a wide range of conditions, including accumulated heat, measured as Corn Heat Units (chus). Hybrids with higher chu ratings generally have higher yields, so long as there is sufficient heat for them to mature. Farmers choose their hybrid varieties prior to the growing season, in the face of uncertainty about the chus that will accumulate at their location. Farmers in the sample counties showed a consistent tendency to adjust their hybrid selection on the basis of the previous year's growing conditions. After the high chu year of 1991, farmers chose significantly more longer-maturing and potentially higher-yielding, but riskier varieties. After the lower chu years of 1992 and 1993, farmers' hybrid selections became markedly more conservative. L'étude de I'adaptation des fermiers aux changements climatiques se fait par une analyse de /'hybridation du maïs au sud de l'Ontario. Les variétés de maïs hybrides conviennent à différentes conditions climatiques in-cluant la chaleur accumulée, mesurée en Unitées de Chaleur de Maïs (ucms). Les hybrides ayant une valeur ucm plus élevée donnent généralement un rendement plus élevéà condition qu'ils bénéficient d'assez de chaleur pour mûrir. Les fermiers des comtés sélectionnés ont démontré une tendance persistante à baser leurs sélections d'hybrides en fonction des conditions de crois-sance de I'année précédente. Depuis 1991, année ayant connu un taux élevé d'UCM, les fermiers ont opté pour un type d'hybride à croissance prolongée, au potentiel de rendement plus élevé mats également plus risqué. Les années 1992 et 1993 ayant connu un niveau ucm moins élevé, les fermiers ont alors sélectionné des hybrides plus traditionnels.     

Precipitation of lead–zinc ores in the Mississippi Valley‐type deposit at Trèves,Cévennes region of southern France

The Trèves zinc–lead deposit is one of several Mississippi Valley‐type (MVT) deposits in the Cévennes region of southern France. Fluid inclusion studies show that the ore was deposited at temperatures between approximately 80 and 150°C from a brine that derived its salinity mainly from the evaporation of seawater past halite saturation. Lead isotope studies suggest that the metals were extracted from local basement rocks. Sulfur isotope data and studies of organic matter indicate that the reduced sulfur in the ores was derived from the reduction of Mesozoic marine sulfate by thermochemical sulfate reduction or bacterially mediated processes at a different time or place from ore deposition. The large range of δ³⁴S values determined for the minerals in the deposit (12.2–19.2‰ for barite, 3.8–13.8‰ for sphalerite and galena, and 8.7 to ?21.2‰ for pyrite), are best explained by the mixing of fluids containing different sources of sulfur. Geochemical reaction path calculations, based on quantitative fluid inclusion data and constrained by field observations, were used to evaluate possible precipitation mechanisms. The most important precipitation mechanism was probably the mixing of fluids containing different metal and reduced sulfur contents. Cooling, dilution, and changes in pH of the ore fluid probably played a minor role in the precipitation of ores. The optimum results that produced the most metal sulfide deposition with the least amount of fluid was the mixing of a fluid containing low amounts of reduced sulfur with a sulfur‐rich, metal poor fluid. In this scenario, large amounts of sphalerite and galena are precipitated, together with smaller quantities of pyrite precipitated and dolomite dissolved. The relative amounts of metal precipitated and dolomite dissolved in this scenario agree with field observations that show only minor dolomite dissolution during ore deposition. The modeling results demonstrate the important control of the reduced sulfur concentration on the Zn and Pb transport capacity of the ore fluid and the volumes of fluid required to form the deposit. The studies of the Trèves ores provide insights into the ore‐forming processes of a typical MVT deposit in the Cévennes region. However, the extent to which these processes can be extrapolated to other MVT deposits in the Cévennes region is problematic. Nevertheless, the evidence for the extensive migration of fluids in the basement and sedimentary cover rocks in the Cévennes region suggests that the ore forming processes for the Trèves deposit must be considered equally viable possibilities for the numerous fault‐controlled and mineralogically similar MVT deposits in the Cévennes region.