Effect of diurnal and seasonal temperature variation on Cussac cave ventilation using co2 assessment

Cussac cave was investigated to assess the cave air temperature variations and to understand its ventilation regime. This cave is located in an active karst system in the south west part of France. It has a single entrance and is considered as a cold air trap. In this study, air mass exchanges were probed. Measurements of temperature and Pco₂ with a 30-min frequency were made in several locations close to the cave entrance. Speed of the air flow was also measured at the door of cave entrance. Results show that cave air Pco₂ varies from 0.18 to 3.33 %. This cave appears to be a CO₂ source with a net mass of 2319 tons blown in 2009. Carbon-stable isotope of CO₂ (¹³Cco₂) ranges from −20.6 ‰ in cold season to −23.8 ‰ in warm season. Cave air is interpreted as a result of a mix between external air and an isotopically depleted air, coming from the rock environment. The isotopic value of the light member varies through time, from −23.9 to −22.5 ‰. Furthermore, this study ascertains that the cave never stops in communicating with the external air. The ventilation regime is identified. (1) In cold season, the cave inhales at night and blows a little at the warmest hours. However, in warm season, (2) cave blows at night, but (3) during the day, a convection loop takes place in the entrance area and prevents the external air from entering the cave, confirming the cold air trap.

     

Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...     

Instrumental Seismicity of the Western Alps: A Revised Catalogue

—The western Alpine regions have been instrumented since the beginning of the century, and the number of seismological stations largely increased since 1980. This dense network has allowed an important improvement in the hypocentral determination, even for low magnitude events. This condition was a good opportunity to perform a synthesis of 32 years of instrumental seismicity in the Western Alps and southeast of France (1962–1993) and to attempt an improvement of the older event location with the assistance of the more recent locations.¶The revised catalogue of seismicity is built using station corrections and regional crustal models. After the elimination of non-natural events, the catalogue is composed of 6697 events. Another improvement corresponds to the revision of magnitudes. We performed several tests to evaluate the reliability of our results location of quarry events and rock bursts, epicentral correlation with geological features, coherence in depth with interpreted seismic profile (ECORS line), Moho isobaths. A first use of this catalogue is presented for the Haute-Ubaye region in the southwestern Alps.     

CO2-H2O mixtures in the geological sequestration of CO2. I. Assessment and calculation of mutual solubilities from 12 to 100°C and up to 600 bar

Evaluating the feasibility of CO₂ geologic sequestration requires the use of pressure-temperature-composition (P-T-X) data for mixtures of CO₂ and H₂O at moderate pressures and temperatures (typically below 500 bar and below 100°C). For this purpose, published experimental P-T-X data in this temperature and pressure range are reviewed. These data cover the two-phase region where a CO₂-rich phase (generally gas) and an H₂O-rich liquid coexist and are reported as the mutual solubilities of H₂O and CO₂ in the two coexisting phases. For the most part, mutual solubilities reported from various sources are in good agreement. In this paper, a noniterative procedure is presented to calculate the composition of the compressed CO₂ and liquid H₂O phases at equilibrium, based on equating chemical potentials and using the Redlich-Kwong equation of state to express departure from ideal behavior. The procedure is an extension of that used by King et al. (1992), covering a broader range of temperatures and experimental data than those authors, and is readily expandable to a nonideal liquid phase. The calculation method and formulation are kept as simple as possible to avoid degrading the performance of numerical models of water-CO₂ flows for which they are intended. The method is implemented in a computer routine, and inverse modeling is used to determine, simultaneously, (1) new Redlich-Kwong parameters for the CO₂-H₂O mixture, and (2) aqueous solubility constants for gaseous and liquid CO₂ as a function of temperature. In doing so, mutual solubilities of H₂O from 15 to 100°C and CO₂ from 12 to 110°C and up to 600 bar are generally reproduced within a few percent of experimental values. Fugacity coefficients of pure CO₂ are reproduced mostly within one percent of published reference data.     

Apport d'informations qualitatives pour l'estimation des teneurs en milieux hétérogènes : cas d'une pollution de sols par des hydrocarbures aromatiques polycycliques (HAP)

Grade estimates are often of weak precision in the case of heterogeneous media, due to their high variability, even at small scale. Qualitative information is then useful to improve the quality of the estimates, without prohibitive additional costs. How can we sample such variables, and detect the ones that are of interest for the estimation of grades? The general methodology is presented and then illustrated for the estimation of the benzo(a)pyren (a polycyclic aromatic hydrocarbon, PAH) concentration in soils, sampled on a former coking plant. To cite this article: N. Jeannée, C. de Fouquet, C. R. Geoscience 335 (2003).To cite this article: N. Jeannée, C. de Fouquet, C. R. Geoscience 335 (2003).     

Future productivity and phenology changes in European grasslands for different warming levels: implications for grassland management and carbon balance

Background

Europe has warmed more than the global average (land and ocean) since pre-industrial times, and is also projected to continue to warm faster than the global average in the twenty-first century. According to the climate models ensemble projections for various climate scenarios, annual mean temperature of Europe for 2071–2100 is predicted to be 1–5.5 °C higher than that for 1971–2000. Climate change and elevated CO₂ concentration are anticipated to affect grassland management and livestock production in Europe. However, there has been little work done to quantify the European-wide response of grassland to future climate change. Here we applied ORCHIDEE-GM v2.2, a grid-based model for managed grassland, over European grassland to estimate the impacts of future global change.

Results

Increases in grassland productivity are simulated in response to future global change, which are mainly attributed to the simulated fertilization effect of rising CO₂. The results show significant phenology shifts, in particular an earlier winter-spring onset of grass growth over Europe. A longer growing season is projected over southern and southeastern Europe. In other regions, summer drought causes an earlier end to the growing season, overall reducing growing season length. Future global change allows an increase of management intensity with higher than current potential annual grass forage yield, grazing capacity and livestock density, and a shift in seasonal grazing capacity. We found a continual grassland soil carbon sink in Mediterranean, Alpine, North eastern, South eastern and Eastern regions under specific warming level (SWL) of 1.5 and 2 °C relative to pre-industrial climate. However, this carbon sink is found to saturate, and gradually turn to a carbon source at warming level reaching 3.5 °C.

Conclusions

This study provides a European-wide assessment of the future changes in productivity and phenology of grassland, and their consequences for the management intensity and the carbon balance. The simulated productivity increase in response to future global change enables an intensification of grassland management over Europe. However, the simulated increase in the interannual variability of grassland productivity over some regions may reduce the farmers’ ability to take advantage of the increased long-term mean productivity in the face of more frequent, and more severe drops of productivity in the future.