We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (δ13C‐DIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000 m in the northeastern Atlantic Ocean. The between‐lab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11‰ (1σ). The multi‐lab average δ13C‐DIC value reported for the deep seawater sample was consistent within 0.1‰ with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the between‐lab standard deviation to 0.06‰. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/uncertainty target proposed by the Global Ocean Observing System (±0.05‰) is attainable, but only if an aqueous phase reference material for δ13C‐DIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a “Certified” or internally consistent “consensus” value for δ13C‐DIC can be assigned to various batches.

The Europan Molecular Indicators of Life Investigation (EMILI) is an instrument concept being developed for the Europa Lander mission currently under study. EMILI will meet and exceed the scientific and technical/resource requirements of the organic composition analyzer identified as a core instrument on the Lander. EMILI tightly couples two complementary analytical techniques, based on 1) liquid extraction and processing with capillary electrophoresis and 2) thermal and chemical extraction with gas chromatography, to robustly detect, structurally characterize, and quantify the broadest range of organics and other Europan chemicals over widely-varying concentrations. Dual processing and analysis paths enable EMILI to perform a thorough characterization of potential molecular biosignatures and contextual compounds in collected surface samples. Here we present a summary of the requirements, design, and development status of EMILI with projected scientific opportunities on the Europa Lander as well as on other potential life detection missions seeking potential molecular biosignatures in situ.

Replicate sampling along stratigraphic horizons in one outcrop of Ordovician limestones of the Nashville Dome reveals considerable variation in d 13 C, d 18 O, and Sr concentration among seemingly identical samples. Ten vertical transects were sampled, each consisting of samples taken at 10 cm intervals from 2 m below to 1 m above the M4-M5 sequence boundary of Patzkowsky (1997, 1998). The 10 transects were each 2 m apart. The resulting 10 replicate and thus seemingly interchangeable samples from each horizon have ranges of d 13 C as great as 2.4% and ranges of d 18 O as great as 2.8%, and Sr concentrations that vary by as much as a factor of four. Variance is great both just below and just above surfaces of subaerial exposure. As a result, maxima in variance in d 13 C, as well as or (in some cases) instead of minima in mean d 13 C, can be used to test such surfaces for exposure. Maxima in variance and minima in mean d 13 C may be found either below a surface of subaerial exposure in the meteorically altered sediment, or above that surface in the transgressive lag where reworked pre-exposure sediment is mixed with unaltered post-exposure sediment.The large variances and ranges found in this study, and the dissimilarity of geochemical profiles from the 10 vertical transects, indicate that single samples of stratigraphic horizons, and thus single vertical transects, can yield misleading characterizations of stratigraphic variation of geochemical parameters. Instead, replicate sampling along horizons better characterizes isotopic and elemental variation through stratigraphic sections than does existing single-sample strategies, and it will be more useful in future testing of surfaces of subaerial exposure. For example, the replicate geochemical data used in this project confirm the presence of three surfaces of subaerial exposure, whereas only two had been recognized as exposure surfaces before. Data from replicate samples also make unnecessary the use of arbitrary criteria for inferring exposure, such as the predetermined numerical cutoffs used by Railsback et al. (2003).

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