ABSTRACT
Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale.
ABSTRACT
In modern microbial mats, hydrogen sulfide shows pronounced sulfur isotope (δ34 S) variability over small spatial scales (~50 over <4 mm), providing information about microbial sulfur cycling within different ecological niches in the mat. In the geological record, the location of pyrite formation, overprinting from mat accretion, and post-depositional alteration also affect both fine-scale δ34 S patterns and bulk δ34 Spyrite values. We report µm-scale δ34 S patterns in Proterozoic samples with well-preserved microbial mat textures. We show a well-defined relationship between δ34 S values and sulfide mineral grain size and type. Small pyrite grains (<25 µm) span a large range, tending toward high δ34 S values (-54.5 to 11.7, mean: -14.4). Larger pyrite grains (>25 µm) have low but equally variable δ34 S values (-61.0 to -10.5, mean: -44.4). In one sample, larger sphalerite grains (>35 µm) have intermediate and essentially invariant δ34 S values (-22.6 to -15.6, mean: -19.4). We suggest that different sulfide mineral populations reflect separate stages of formation. In the first stage, small pyrite grains form near the mat surface along a redox boundary where high rates of sulfate reduction, partial closed-system sulfate consumption in microenvironments, and/or sulfide oxidation lead to high δ34 S values. In another stage, large sphalerite grains with low δ34 S values grow along the edges of pore spaces formed from desiccation of the mat. Large pyrite grains form deeper in the mat at slower sulfate reduction rates, leading to low δ34 Ssulfide values. We do not see evidence for significant 34 S-enrichment in bulk pore water sulfide at depth in the mat due to closed-system Rayleigh fractionation effects. On a local scale, Rayleigh fractionation influences the range of δ34 S values measured for individual pyrite grains. Fine-scale analyses of δ34 Spyrite patterns can thus be used to extract environmental information from ancient microbial mats and aid in the interpretation of bulk δ34 Spyrite records.
Subject(s)
Fossils , Microbiota , Sulfides/analysis , Sulfur Isotopes/analysisABSTRACT
This paper deals with cellular-physiological changes in regard to adaptative problems in the pig. As an example for lysosomal catabolism, beta-glucuronidase activity in liver tissue of pigs with different constitution is presented. Male slaughter pigs (n = 120), equally distributed on the breeds Piétrain, German Large White and German Landrace, are used for the investigation. The results show significant variances between, as well as within the breeds. Partly high significant, positive correlations exist between beta-glucuronidase activity and survival rates. The importance of beta-glucuronidase activity and the lysosomes for adaptative constitution and development in the pig is discussed.
