Introduction: We have studied the petrography and Fe-isotope composition of seven chondrules, four from the Allende (CV3) carbonaceous chondrite and three from the Chainpur (LL3.4) ordinary chondrite. Three textural-chemical chondrule types are represented within this sample set: (1) BO, (2) RP and (3) PO/POP. These textural differences allow us to exa mine the Fe-isotope composition in materia...

Sulfur compounds in intermediate valence states, for example elemental sulfur, thiosulfate, and tetrathionate, are important players in the biogeochemical sulfur cycle. However, key understanding about the pathways of oxidation involving mixed-valance state sulfur species is still missing. Here we report the sulfur and oxygen isotope fractionation effects during the oxidation of tetrathionate (...

Oxygen and hydrogen isotope signatures of animal tissues are strongly correlated with the isotope signature of local precipitation and as a result, isotope signatures of tissues are commonly used to study resource utilization and migration in animals and to reconstruct climate. To better understand the mechanisms behind these correlations, we manipulated the isotope composition of the drinking ...

Watershed-scale carbon budgets remain poorly understood, in part due to inadequate simulation tools to assess in-stream carbon fate and transport. A new numerical model termed ISOtope-based FLuvial Organic Carbon (ISOFLOC) is formulated to simulate the fluvial organic carbon budget in watersheds where hydrologic, sediment transport, and biogeochemical processes are coupled to control benthic an...

The application of stable isotopes in speleothem records requires an understanding of the extent to which speleothem calcite isotopic compositions refl ect the compositions of the cave waters from which they precipitate. To test for equilibrium precipitation, modern speleothem calcite was grown on glass plates, so that the carbon and oxygen isotope composition of the calcite and the water from ...

We present a framework for interpreting the carbon isotopic composition of sedimentary rocks, which in turn requires a fundamental reinterpretation of the carbon cycle and redox budgets over Earth's history. We propose that authigenic carbonate, produced in sediment pore fluids during early diagenesis, has played a major role in the carbon cycle in the past. This sink constitutes a minor compon...

Weekly water samples were taken to measure stable isotope composition (d13C and d15N) of particulate organic matter (POM) in Lake Wauberg, Florida, from June 1994 to May 1995. The average d13C of POM was 219.3%, consistent with an autochthonous origin from phytoplankton production, and exhibited a seasonal pattern that coincided with changes in water temperature, pH, CO2 concentration, and phyt...

The stable isotopic compositions of nitrogen and carbon in animal tissues reflect diet. However, factors other than diet can also affect these stable isotope ratios, leading to misinterpretations of diet composition. To test the hypothesis that variation in metabolic rate alters the isotopic compositions of tissues, deer mice (Peromyscus maniculatus (Wagner, 1845)) were kept at three temperatur...

The stable carbon isotope (13)C is used as a universal tracer in plant eco-physiology and studies of carbon exchange between vegetation and atmosphere. Photosynthesis fractionates against (13)CO(2) so that source sugars (photosynthates) are on average (13)C depleted by 20‰ compared with atmospheric CO(2). The carbon isotope distribution within sugars has been shown to be heterogeneous, with rel...

Natural-abundance stable isotope ratios provide a wealth of ecological information relating to food web structure, trophic level, and location. The correct interpretation of stable isotope data requires an understanding of spatial and temporal variation in the isotopic compositions at the base of the food web. In marine pelagic environments, accurate interpretation of stable isotope data is ham...