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Carbon and oxygen isotope analysis of ostracods living in the near-constant conditions of spring-fed ponds in southern England allowed accurate determination of the ostracod’s calcite-water 13C/12C and 18O/16O fractionations. The 13C/12C fractionations of two species, Candona candida and Pseudocandona rostrata, correspond to values expected for isotopic equilibrium with the pond’s dissolved inorganic carbon at the measured temperature (11°C) and pH (6.9), whilst those of a third species, Herpetocypris reptans, would represent equilibrium at a slightly higher pH (7.1).The 18O/16O fractionations confirm two previous studies in being larger, by up to 3‰, than those ‘traditionally’ regarded as representing equilibrium. When the measured fractionations are considered in the context of more recent work, however, they can be explained in terms of equilibrium if the process of calcite formation at the ostracod lamella occurs at a relatively low pH (≤7) irrespective of the pH of the surrounding water. The pH of calcite formation, and therefore the calcite-water 18O/16O fractionation, may be species and stage (adult versus juvenile) specific, and related to the rate of calcification. [Copyright &y& Elsevier]

Stable isotope analyses at high-resolution intervals along the growth axis of a shell of the land snail Limicolaria kambeul chudeaui Germain, collected in Ethiopia, show a cyclic pattern of d 18 O variation. The cycles have regular periodicity but vary in amplitude. The shape and amplitude of the shell d 18 O cycles is consistent with seasonal changes in the amount and isotopic composition of the rainfall, coupled with temperature and evaporative effects. The number of cycles (|10) corresponds to the estimated lifespan of Limicolaria. Generally constant d 13 C values suggest unvarying diet, environmental CO2 influences, and metabolism through- out the snail’s life, except for one interval of large variations in both d 13 C and d 18 O that may be related to the onset of reproductive activity. If similar results can be obtained for fossil shells, they may provide a high-resolution record of past seasonal climate variability. [ABSTRACT FROM AUTHOR]

Large ranges of 13C/12C and 18O/ 16O ratios are found among modem ostracods from lakes in Jamaica and Mexico. If their calcite carapaces grew in isotopic equilibrium with the lake water, then the main period of carapace formation was probably in the cooler and/or wetter months. Differences in δ13C and δ18 O values between ostracods from different sites relate to spatial variations in the composition of the lake water, and differences between species at the same site probably reflect differences in organic photosynthesis or decay among the micro-habitats occupied by the species. There nevertheless remain significant variations in both δ13C and δ18O among modern valves of the same species at the same site; a consequence of the temporal and spatial variation in lake water and the fact that ostracods form their carapace over a short period. Individual valves from a 1-cm section of a sediment core show that the isotopic effects of changes in the rainfall versus evaporation status of a lake over a period of c. 102 years can be of a similar magnitude to changes recorded by bulk, fine-grained carbonate throughout the late Quaternary. These findings emphasize the need for caution when using isotopic data for single ostracod valves in palaeoclimatic studies. [ABSTRACT FROM PUBLISHER]

Filter packs have been used to collect sulphur and oxygen from air for isotope analysis from many areas of the world. Here we discuss their use to determine the sulphur isotope systematics of SO2 and the sulphur and oxygen systematics of sulphate particles from volcanic vents. Our field data suggest that fractionation of sulphur isotopes occurs during the collection of SO2 from concentrated volcanic gas plumes on alkali-impregnated filter papers. The collection of volcanogenic HCl on the same filters may play a role in this fractionation. Comparison with previous studies, which sampled areas of cleaner atmosphere, suggests that isotopic fractionation only becomes significant where elevated filter loadings occur (e.g., when sampling gas streams with SO2 concentrations greater than ∼1μmolm−3), although this requires further investigation. Previous studies also suggest that for volcanic sulphate particle samples collected at the same time, oxygen isotopes are fractionated while sulphur isotopes are not. Minimising the filter loading reduces these effects, but there is a trade-off with the amount of SO2 or required for isotopic measurements. Despite the convenience of the filter pack technique these fractionation effects limit the use of filter packs for determining δ 34S for SO2 in volcanic gases and δ 18O and δ 17O for the sulphate in volcanic particles, and they will certainly not be useful for determining small variations in the source isotopic signature of the sulphur in the SO2 or the oxygen in the being measured. This highlights the importance of collecting SO2 quantitatively for isotopic analysis. These effects may also have implications if using similar methods to collect SO2 in other environments, especially where concentrations are high. [Copyright &y& Elsevier]

Abstract: Sewage contamination in shallow lake sediments is of concern because the pathogens, organic matter and nutrients contribute to the deterioration of the water-bodies'' health and ecology. Sediment cores from three shallow lakes (Coneries, Church and Clifton Ponds) within Attenborough nature reserve located downstream of sewage treatment works were analysed for TOC, C/N, δ13C, δ15N, bacterial coliforms and faecal sterols. 210Pb and 137Cs activities were used to date the sediments. Elemental analysis suggests that the source of organic matter was algal and down profile changes in δ13C indicate a possible decrease in productivity with time which could be due to improvements in sewage treatment. δ15N for Coneries Pond are slightly higher than those observed in Church or Clifton and are consistent with a sewage-derived nitrate source which has been diluted by non-sewage sources of N. The similarity in δ15N values (+12‰ to +10‰) indicates that the three ponds were not entirely hydrologically isolated. Analysis by gas chromatography/mass spectrometry (GC/MS) reveals that Coneries Pond had sterol concentrations in the range 20 to 30μg/g (dry wt.), whereas, those from Clifton and Church Ponds were lower. The highest concentrations of the human-sourced sewage marker 5β-coprostanol were observed in the top 40cm of Coneries Pond with values up to 2.2μg/g. In contrast, Church and Clifton Pond sediments contain only trace amounts throughout. Down-profile comparison of 5β-coprostanol/cholesterol, 5β-coprostanol/(5β-coprostanol+5α-cholestanol) and 5β-epicoprostanol/coprostanol as well as 5α-cholestanol/cholesterol suggests that Coneries Pond has received appreciable amounts of faecal contamination. Examination of 5β-stigmastanol (marker for herbivorous/ruminant animals) down core concentrations suggests a recent decrease in manure slurry input to Coneries Pond. The greater concentration of β-sitosterol in sediments from Church and Clifton Ponds as compared to Coneries is attributed in part to their greater diversity and extent of aquatic plants and avian faeces. [Copyright &y& Elsevier]