Oxidation of methane at the CH4/H2O-(CO2) transition zone in the external part of the Central Alps, Switzerland: Evidence from stable isotope investigations

With the aim of understanding the mechanisms that control the metamorphic transition from the CH4- to the H2O-(CO2)-dominated fluid zone in the Helvetic domain of the Central Alps of Switzerland, fluid inclusions in quartz, illite ``crystallinity'' index, vitrinite reflectance, and the stable isotope compositions of vein and whole rock minerals and fluids trapped in quartz were investigated along four cross-sections. Increasing temperature during prograde metamorphism led to the formation of dry gas by hydrocarbon cracking in the CH4-zone. Fluid immiscibility in the H2O-CH4-(CO2)-NaCl system resulted in cogenetic, CH4- and H2O-dominated fluid inclusions. In the CH4-zone, fluids were trapped at temperatures <= 270 +/- 5 degrees C. The end of the CH4-zone is markedby a sudden increase of CO2 content in the gas phase of fluid inclusions. At temperatures > 270 +/- 5 degrees C, in the H2O-zone, the total amount of volatiles within the fluid decreased below 1 mol% with no immiscibility. This resulted m total homogenization temperatures of H2O-(CO2-CH4)-NaCl inclusions below 180 degrees C. Hydrogen isotope compositions of methane in fluid inclusion have delta D values of less than -100 parts per thousand in the CH4-zone, typical for an origin through cracking of higher hydrocarbons, but where the methane has not equilibrated with the pore water. delta D values of fluid inclusion water are around -40 parts per thousand., in isotopic equilibrium with phyllosilicates of the whole rocks. Within the CH4 to H2O(CO2) transition zone, delta D(H2O) values in fluid inclusions decrease to -130 parts per thousand interpreted to reflect the contribution of deuterium depleted water from methane oxidation. In the H2O-zone, delta D(H2O) values increase again towards an average of -30 parts per thousand which is again consistent with isotopic equilibrium with host-rock phyllosilicates. delta C-13 values of methane in fluid inclusions from the CH4-zone are around -27 parts per thousand in isotopic equilibrium with calcite in veins and whole rocks. The delta C-13(CH4) values decrease to less than -35 parts per thousand at the transition to the H2O-zone and are no longer in equilibrium with the carbonates in the whole rocks. delta C-13 values of CO, are variable but too low to be in equilibrium with the wall rock fluids, compatible with a contribution of CO2 from closed system oxidation of methane. Differences in isotopic composition between host-rock and Alpine fissure carbonate are generally small, suggesting that the amount of CO2 produced by oxidation of methane was small compared to the C-budget in the rocks and local pore fluids were buffered by the wall rocks during precipitation of calcite within the fissures. (c) 2006 Elsevier B.V. All rights reserved.

Daily energy expenditure in free-living conditions in obese and non-obese children: comparison of doubly labelled water (2H2(18)O) method and heart-rate monitoring.

OBJECTIVE: To compare the heart-rate monitoring with the doubly labelled water (2H2(18)O) method to estimate total daily energy expenditure in obese and non-obese children. DESIGN: Cross sectional study of obese and normal weight children. SUBJECTS: 13 prepubertal children: six obese (4M, 2F, 9.1 +/- 1.5 years, 47.3 +/- 9.7 kg) and seven non-obese (3M, 4F, 9.3 +/- 0.6 years, 31.8 +/- 3.2 kg). MEASUREMENTS: Total daily energy expenditure was assessed by means of the doubly labelled water method (TEEDLW) and of heart-rate monitoring (TEEHR). RESULTS: TEEHR was significantly (P < 0.05) higher than TEEDLW in obese children (9.47 +/- 0.84 MJ/d vs 8.99 +/- 0.63 MJ/d) whereas it was not different in non-obese children (8.43 +/- 2.02 MJ/d vs 8.42 +/- 2.30 MJ/d, P = NS). The difference of TEE assessed by HR monitoring in the obese group averaged 6.2 +/- 4.7%. At the individual level, the degree of agreement (difference between TEEHR and TEEDLW +/- 2s.d.) was low both in obese (-0.36, 1.32 MJ/d) and in non-obese children (-1.30, 1.34 MJ/d). At the group level, the agreement between the two methods was good in nonobese children (95% c.i. for the bias:-0.59, 0.63 MJ/d) but not in obese children (0.04, 0.92 MJ/d). Duration of sleep and energy expenditure during resting and physical activity were not significantly different in the two groups. Patterns of heart-rate (or derived energy expenditure) during the day-time were similar in obese and non-obese children. CONCLUSION: The HR monitoring technique provides an estimation of TEE close to that assessed by the DLW method in non-obese prepubertal children. In comparison with DLW, the HR monitoring method yields a greater TEE value in obese children.

European climate variations over the past half-millennium reconstructed from groundwater

Temperature reconstructions for recent centuries are the basis of estimations of the natural variability in the climate system before and during the onset of anthropogenic perturbation. Here we present, for the first time, an independent and physically based reconstruction of mean annual temperature over the past half millennium obtained from groundwater in France. The reconstructed noble gas temperature (NGT) record suggests cooler than present climate conditions throughout the 16th-19th centuries. Periods of warming occur in the 17th-18th and 20th century, while cooling is reconstructed in the 19th century. A noticeable coincidence with other temperature records is demonstrated. Deuterium excess varies in parallel with the NGT, and indicates variation in the seasonality of the aquifer recharge; whereas high excess air in groundwater indicates periods with high oscillations of the water table.