Alfalfa was labeled in the field with 99 atom % 13CO2 and cut either the same day (C1) or 30 d after labeling (C30). The C1 alfalfa contained 84% of the 13C label in cell contents, whereas C30 alfalfa contained 47% of the 13C label in cell contents. In two separate trials, C1 and C30 alfalfa were dosed to two or four Suffolk ewes fed natural abundance alfalfa diets. Carbon isotope ratios (13C/1...

The Palaeocene-Eocene thermal maximum (PETM) is characterized by a global negative carbon isotope excursion (CIE) and widespread dissolution of seafloor carbonate sediments. The latter feature supports the hypothesis that the PETM and CIE were caused by the rapid release of a large mass (greater than 2000Gt C) of 12C-enriched carbon. The source of this carbon, however, remains a mystery. Possib...

Abstract. Oxygen and hydrogen isotope ratios in polar precipitation are widely used as proxies for local temperature. In combination, oxygen also provide information on sea surface temperature at the oceanic moisture source locations where originates. Temperature reconstructions obtained from ice-core records generally rely linear approximations of relationships among temperature, water-isotope...

Kinetic isotope effects related to the breaking of chemical bonds drive sulfur isotope fractionation during dissimilatory sulfate reduction (DSR), whereas oxygen isotope fractionation duringDSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explo...

the upper cretaceous carbonate sequence of ab-deraz formation is well exposed in the kopet- dagh basin. this formation comprises marly limestone and three chalky limestone units. chalky limestone of ab-deraz formation is mainly composed of calcareous dinoflagellate (pithonellid calcispher), cocolithofore and planktonic foraminifera. carbon and oxygen stable isotopes analysis of the third chalky...

Acetate turnover in the methanogenic freshwater anoxic sediments of Lake Vechten, The Netherlands, and in anoxic sediments from the Tamar Estuary, United Kingdom, and the Grosser Jasmunder Bodden, Germany, the latter two dominated by sulfate reduction, was determined. Stable isotopes and radioisotopes, inhibitors (chloroform and fluoroacetate), and methane flux were used to provide independent ...

Mass-independent fractionation of sulfur isotopes (S-MIF) results from photochemical reactions involving short-wavelength UV light. The presence of these anomalies in Archean sediments [(4-2.5 billion years ago, (Ga)] implies that the early atmosphere was free of the appropriate UV absorbers, of which ozone is the most important in the modern atmosphere. Consequently, S-MIF is considered some o...

Carbon and oxygen isotope ratios of fossil horse tooth enamel from Nebraska and Texas show evidence for late Neogene environmental changes in the Great Plains. The earliest unambiguous C4 dietary signal among Texas equids coincides with the age of the classic late Hemphillian–age Coffee Ranch fauna, which we suggest is ∼6.6 Ma based on volcanic ash correlations. C4 vegetation was present in the...

Abstract. Tracer-aided hydrological models integrating water isotope modules into the simulation of runoff generation are useful tools to reduce uncertainty modeling in cold basins that featured by complex processes and multiple components. However, there is little guidance on strategy field sampling for analysis run tracer-aided models, which especially important large mountainous Tibetan Plat...

Detailed carbon isotope records have water enriched in i•C into the deep North Atlantic been obtained from benthic foraminifera in the during glacial periods alters the carbon isotopic North Atlantic (CHN 82 Sta 24 Core 4PC, 42øN, 32øW, signal of Atlantic cores relative to the global 3427 m, 244 kyr) and central equatorial Pacific mean [Streeter and Shackleton, 1979; Duplessy et (KNR 73 Sta 4 C...