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The surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening, leading to their gradual rise. Recent studies of the Andes indicate that their elevation remained relatively stable for long periods (tens of millions of years), separated by rapid (1 to 4 million years) changes of 1.5 kilometers or more. Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle.

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The elevation of Earth's surface is among the most difficult environmental variables to reconstruct from the geological record. Here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters, constrained by measurements of abundances of 13C-18O bonds in soil carbonates. We use this approach to show that the Altiplano plateau in the Bolivian Andes rose at an average rate of 1.03 +/- 0.12 millimeters per year between approximately 10.3 and approximately 6.7 million years ago. This rate is consistent with the removal of dense lower crust and/or lithospheric mantle as the cause of elevation gain.

In order to generate a reliable and long-lasting stable isotope ratio standard for CO 2 in samples of clean air, CO 2 is liberated from well-characterized carbonate material and mixed with CO 2 -free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO 2 is generated by a conventional acid digestion of powdered carbonate. Evolved CO 2 gas is mixed and equilibrated with a prefabricated gas comprised of N 2 , O 2 , Ar, and N 2 O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high-precision air-CO 2 work (about AE0.015% for d 13 C and AE0.025% for d18 O). To establish a valid d 18O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 478C has been determined with a high level of precision. Using identical procedures, CO 2 -in-air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, d To quantitatively control the extent of isotope-scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L-SVEC, IAEA-CO-1, IAEA-CO-8, CAL-1 and CAL-2) were also processed. As a further control pure CO 2 reference gases (Narcis I and II, NIST-RM 8563, GS19 and GS20) were mixed with CO 2 -free synthetic air. Independently, the pure CO 2 gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB-scale for CO 2 -in-air (e.g. CG-99, based on calibration of pure CO 2 gas) has been carefully established. The systematic high-precision comparison of secondary carbonate and CO 2 reference materials covering a wide range in isotopic composition revealed that assigned d-values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross-contamination errors for high-precision isotope ratio measurements.As a result of the experiments, a new standard reference material (SRM), which consists of two 5-L glass flasks containing air at 1.6 bar and the CO 2 evolved from two different carbonate materials, is available for distribution. These 'J-RAS' SRM flasks ('Jena-Reference Air Set') are designed to serve as a high-precision link to VPDB for improving inter-laboratory comparability.a CopyrightThe isotopic composition and concentration of CO 2 in atmospheric air are useful parameters, required for deriving carbon-flux information between atmospheric, terrestrial, ...

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Stable isotope ratios of the life science elements carbon, hydrogen, oxygen and nitrogen vary slightly, but significantly in major compartments of the earth. Owing mainly to antropogenic activities including land use change and fossil fuel burning, the 13 C/ 12 C ratio of CO 2 in the atmosphere has changed over the last 200 years by 1.5 parts per thousand (from about 0.0111073 to 0.0110906). In between interglacial warm periods and glacial maxima, the 18 O/ 16 O ratio of precipitation in Greenland has changed by as much as 5 parts per thousand (0.001935-0.001925). While seeming small, such changes are detectable reliably with specialised mass spectrometric techniques. The small changes reflect natural fractionation processes that have left their signature in natural archives. These enable us to investigate the climate of past times in order to understand how the Earth's climatic system works and how it can react to external forcing. In addition, studying contemporary isotopic change of natural compartments can help to identify sources and sinks for atmospheric trace gases provided the respective isotopic signatures are large enough for measurement and have not been obscured by unknown processes. This information is vital within the framework of the Kyoto process for controlling CO 2 emissions.

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