Search results for "ISOTOPE"

Isotope Fractionation of Selenium During Fungal Biomethylation by Alternaria alternata

2011

The natural abundance of stable Se isotopes may reflect sources and formation conditions of methylated Se. We aimed at (1) quantifying the degree of methylation of selenate [Se(VI)] and (hydro)selenite [Se(IV)] by the fungus Alternaria alternata at pH 4 and 7 and (2) determining the effects of these different Se sources and pH values on 82Se/76Se ratios (δ82/76Se) in methylselenides. Alternaria alternata was incubated with Se(VI) and Se(IV) in closed microcosms for 11-15 days and additionally with Se(IV) for 3-5 days at 30 °C. We determined Se concentrations and δ82/76Se values in source Se(VI) and Se(IV), media, fungi, and trapped methylselenides. In Se(VI) incubations, methylselenide vola…

Eurhomalea exalbida (Bivalvia): A reliable recorder of climate in southern South America?

2012

Abstract Due to the lack of suitable high-resolution archives, regional and continental-scale climate dynamics of southern South America are not well understood. Shells of the long-lived, shallow-marine bivalve mollusk, Eurhomalea exalbida (Dillwyn), are likely to contain information on the past water temperatures. As yet, however, no rigorous calibration study has been presented so that growth history traits and the reliability of shell oxygen isotope-based temperature estimates remain unknown. Shell growth patterns and oxygen isotope ratios of four young specimens of E. exalbida from the Falkland Islands (Southwest Atlantic) were analyzed and cross-calibrated with environmental parameters…

Record of 1.82 Ga Andean-type continental arc magmatism in NE Rajasthan, India: Insights from zircon and Sm–Nd ages, combined with Nd–Sr isotope geoc…

2009

Abstract We document a Palaeoproterozoic Andean-type continental arc granitoid emplacement event in the northwestern segment of the Aravalli mountain range, NW India. Our study is focused on the Jasrapur pluton which is dominated by monzogranites with a subordinate amount of granodiorite and quartz monzodiorite. These rocks carry typical continental arc geochemical signatures, such as high-K calc-alkaline, mildly peraluminous, I-type and magnesian features, as well as high Rb and low Nb, Y and Rb/Zr ratios, decoupling between LILE and HFSE, and negative Nb–Ta and Ti anomalies. Conventional geothermobarometric estimates suggest high temperature (~ 800 °C) and pressure (≥ 600 MPa) conditions …

2015

Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes (2H, 13C, 15N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea th…

The trophic structure of the pipefish community (Pisces: Syngnathidae) from a western Mediterranean seagrass meadow based on stable isotope analysis

2004

Syngnathus abaster andSyngnathus typhle (Pisces: Syngnathidae) from a dense Cymodocea nodesa meadow in the western Mediterranean Stagnone di Marsala (Italy) were studied using δ13N and δ15N analysis. Because of the presence of these two species in the same habitat and the specialized parental care by the male, the effect of species and sex on the isotopic composition was also studied to investigate the different feeding strategies between and within species.S. abaster andS. typhle exhibited enriched13C and15N values throughout the sampling period (mean ±SE, δ13C =−10.5±1.8‰ and−10.8±2.0‰, δ15N=11.9±0.7‰ and 10.6±1.0%., respectively), suggesting that these species receive their energy mainly…

Trophic Transfer of Trace Elements in an Isotopically Constructed Food Chain From a Semi-enclosed Marine Coastal Area (Stagnone di Marsala, Sicily, M…

2012

Trace element accumulation is particularly important in coastal and transitional environments, which act as contaminant buffers between the continental and marine systems. We compared trace element transfer to the biota in two locations with different open-sea exposures in a semi-enclosed marine coastal area (Stagnone di Marsala, Sicily, Italy) using isotopically reconstructed food chains. Samples of sediment, macroalgae, seagrasses, invertebrates, fish, and bird feathers were sampled in July 2006 and analysed for stable carbon and nitrogen isotopes (δ(13)C, δ(15)N) and trace elements (arsenic [As], cadmium [Cd], total mercury [THg], and lead [Pb]). Trophic magnification factors were calcul…

Chemical, mineralogical and isotopic characterization of black crusts and airborne particulate matter in the historical urban area of Palermo

2009

A comparison of the impacts of introduced signal crayfish and native noble crayfish in boreal lake ecosystems

2014

Transport and partitioning of 13C-photoassimilate between peach fruiting shoots

2008

We used a non-intrusive method (13CO2 feeding) and a manipulative approach to see whether fruiting shoots in peach trees are autonomous or may import carbon from neighboring shoots under forced conditions, and whether the degree of autonomy is influenced by the source-sink relationship on the shoot. In three experiments, leaf to fruit ratio (L:F) of selected fruiting shoots was moderately (2005 and 2006) or strongly (extreme enforcing 2006) altered to either encourage or discourage movement of carbon from 13C-labeled sending shoots (SFS) to receiving fruiting shoots (RFS), both located on the same main scaffold of V-shaped peach trees. At stage I and III of fruit growth, fruit and shoot tip…

Modeling of 137Cs migration in soils using an 80-year soil archive: role of fertilizers and agricultural amendments

2008

An 80-year soil archive, the 42-plot experimental design at the INRA in Versailles (France), is used here to study long-term contamination by 137Cs atmospheric deposition and the fate of this radioisotope when associated with various agricultural practices: fallow land, KCl, NH4(NO3), superphosphate fertilizers, horse manure and lime amendments. The pertinence of a simple box model, where radiocaesium is supposed to move downward by convectional mechanisms, is checked using samples from control plots which had been neither amended, nor cultivated since 1928. This simple model presents the advantage of depending on only two parameters: α, a proportional factor allowing the historical atmosph…