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1040 NATURE | VOL 405 | 29 JUNE 2000 | www.nature.com nonlinear fracture mechanics theories approximate, through tractions that resist crack opening, the net effects of various bridging mechanisms, such as bridging and frictional sliding between ®rstorder lamellae and microcracking. Our micromechanical model predicts that the magnitudes of the bridging(More)
Several studies have used the temperature dependence of gas solubilities in water to derive paleotemperatures from noble gases in groundwaters. We present a general method to infer environmental parameters from concentrations of dissolved atmospheric noble gases in water. Our approach incorporates statistical methods to quantify uncertainties of the deduced(More)
The characteristic feature of the physical structure of Lac Pavin is a distinct and permanent chemically induced density increase between about 60 and 70 m depth. This chemocline separates the seasonally mixed mixolimnion from the monimolimnion, which is characterized by elevated temperature and salinity as well as complete anoxia. Previously published(More)
A unique data set of 50 years of monthly temperature profiles from Lake Zurich, a normally ice-free lake located on the Swiss Plateau, allowed the one-dimensional numerical k-« lake model ’’SIMSTRAT’’ to be calibrated (1948– 1957) and validated (1958–1997). Hindcasts of temperature profiles agree excellently with the measured data. Both interannual and(More)
Dissolved noble gases in groundwater are used to reconstruct paleotemperature, but also yield information about "excess air", a component of dissolved gases in excess of solubility equilibrium, derived from dissolution of trapped air in the ground. A good characterization of the excess air component is necessary not only to obtain reliable noble gas(More)
We present elemental and isotopic measurements of noble gases (He, Ne, Ar, Kr, and Xe), oxygen and nitrogen of firn air from two sites. The first set of samples was taken in 1998 at the summit of the Devon Ice Cap in the eastern part of Devon Island. The second set was taken in 2001 at NGRIP location (North Greenland). He and Ne are heavily enriched(More)
The hydrogeological system of an ecologically sensitive alpine floodplain in the Valle di Blenio, Switzerland, was investigated using hydrochemical and 3H-3He dating methods. Water samples from six wells and from different surface locations were analyzed. The analysis of the concentrations of major ions in conjunction with age determination by the(More)
We determined in situ reductive transformation rates of tetrachloroethene (PCE) in a contaminated aquifer by combining compound-specific carbon stable isotope analysis (CSIA) of the contaminants with tracer-based ((3)H-(3)He) groundwater dating. With increasing distance from the source, PCE was gradually transformed to trichloroethene (TCE),(More)
The formation of an excess of dissolved gas (“excess air”) in quasi-saturated media was studied by analyzing and interpreting dissolved noble gas concentrations in laboratory column experiments. Using quartz sand filled columns of 1 m length, two different experimental designs were realized. In the first, groundwater recharge was simulated by a(More)