Showing papers by "Tyler B. Coplen published in 1998"

The relative contributions of summer and cool-season precipitation to groundwater recharge, Spring Mountains, Nevada, USA

Abstract: A comparison of the stable-isotope signatures of spring waters, snow, snowmelt, summer (July thru September) rain, and cool season (October thru June) rain indicates that the high-intensity, short-duration summer convective storms, which contribute approximately a third of the annual precipitation to the Spring Mountains, provide only a small fraction (perhaps 10%) of the recharge to this major upland in southern Nevada, USA. Late spring snowmelt is the principal means of recharging the fractured Paleozoic-age carbonate rocks comprising the central and highest portion of the Spring Mountains. Daily discharge measurements at Peak Spring Canyon Creek during the period 1978–94 show that snowpacks were greatly enhanced during El Nino events.

Sulphur isotope data consistency improved

Abstract: The standard used for reporting relative sulphur isotope-abundance data has, historically, been troilite (FeS) derived from the Canon Diablo meteorite, CDT However, the isotopic inhomogeneity of this material — the variability in its sulphur-34/sulphur-32 isotope ratio is at least 04‰ — greatly exceeds the achievable analytical uncertainty of 005‰ (ref 1) Accordingly, the International Union of Pure and Applied Chemistry (IUPAC) has recommended the setting up of a VCDT scale, which is expected to improve agreement between laboratories in measuring this ratio, δ34S

History of the recommended atomic-weight values from 1882 to 1997: A comparison of differences from current values to the estimated uncertainties of earlier values (Technical Report)

Abstract: International commissions and national committees for atomic weights (mean relative atomic masses) have recommended regularly updated, best values for these atomic weights as applicable to terrestrial sources of the chemical elements. Presented here is a historically complete listing starting with the values in F. W. Clarke's 1882 recalculation, followed by the recommended values in the annual reports of the American Chemical Society's Atomic Weights Commission. From 1903, an International Commission published such reports and its values (scaled to an atomic weight of 16 for oxygen) are here used in preference to those of national committees of Britain, Germany, Spain, Switzerland, and the U.S.A. We have, however, made scaling adjustments from Ar(O) to Ar(C) where not negligible. From 1920, this International Commission constituted itself under the International Union of Pure and Applied Chemistry (IUPAC). Since then, IUPAC has published reports (mostly biennially) listing the recommended atomic weights, which are reproduced here. Since 1979, these values have been called the “standard atomic weights” and, since 1969, all values have been published with their estimated uncertainties. Few of the earlier values were published with uncertainties. Nevertheless, we assessed such uncertainties on the basis of our understanding of the likely contemporary judgement of the values' reliability. While neglecting remaining uncertainties of 1997 values, we derive “differences” and a retrospective index of reliability of atomic-weight values in relation to assessments of uncertainties at the time of their publication. A striking improvement in reliability appears to have been achieved since the commissions have imposed upon themselves the rule of recording estimated uncertainties from all recognized sources of error.