RESUMEN
RATIONALE: Chemical lipid extraction or using alternative tissues such as fish fin as opposed to muscle may alter isotopic ratios and influence interpretations of δ13 C, δ15 N, and previously unassessed δ34 S values in stable isotope analyses (SIA). Our objectives were to determine if lipid extraction alters these isotope ratios in muscle, if lipid normalization models can be used for lipid-rich salmonids, and if fin isotope ratios are comparable with those of muscle in adult salmonids. METHODS: In six adult salmonid species (n = 106) collected from Lake Ontario, we compared three isotope ratios in lipid-extracted (LE) muscle with bulk muscle, and LE muscle with fin tissue, with paired t-tests and linear regressions. We compared differences between δ13 C values in LE and bulk muscle with predicted values from lipid normalization models and the log-linear model of best fit and determined model efficiency. RESULTS: The δ15 N values in LE muscle increased (<1) relative to bulk muscle for most salmonids, with relationships nearing 1:1. There were either no differences or strong 1:1 relationships in δ34 S values between species-specific bulk and LE muscle. One lipid normalization model had greater model efficiency (97%) than the model of best fit (94%). Fin had higher δ13 C values than LE muscle while δ15 N trends varied (<1); however, both isotope ratios had either no or weak linear relationships with fin and LE muscle within species. The δ34 S values in fin were similar to those in LE muscle and had strong 1:1 relationships across species. CONCLUSIONS: We recommend using the lipid normalization model to adjust for δ13 C values in lipid-rich muscle (C:N >3.4). LE muscle could be used without δ15 N or δ34 S adjustments, but the minimal increase in δ15 N values may affect SIA interpretation. With high unexplained variability among adult species in fin-muscle δ13 C and δ15 N relationships, species-specific fin-muscle adjustments are warranted. No fin-muscle tissue adjustment would be required for δ34 S values.
Asunto(s)
Aletas de Animales/química , Isótopos de Carbono/aislamiento & purificación , Fraccionamiento Químico/métodos , Lípidos/química , Músculos/química , Isótopos de Nitrógeno/aislamiento & purificación , Isótopos de Azufre/aislamiento & purificación , Animales , Isótopos de Carbono/análisis , Carne/análisis , Isótopos de Nitrógeno/análisis , Salmonidae , Isótopos de Azufre/análisisRESUMEN
The minor extent of sulfur isotope fractionation preserved in many Neoarchean sedimentary successions suggests that sulfate-reducing microorganisms played an insignificant role in ancient marine environments, despite evidence that these organisms evolved much earlier. We present bulk, microdrilled, and ion probe sulfur isotope data from carbonate-associated pyrite in the ~2.5-billion-year-old Batatal Formation of Brazil, revealing large mass-dependent fractionations (approaching 50 per mil) associated with microbial sulfate reduction, as well as consistently negative Δ(33)S values (~ -2 per mil) indicative of atmospheric photochemical reactions. Persistent (33)S depletion through ~60 meters of shallow marine carbonate implies long-term stability of seawater sulfate abundance and isotope composition. In contrast, a negative Δ(33)S excursion in lower Batatal strata indicates a response time of ~40,000 to 150,000 years, suggesting Neoarchean sulfate concentrations between ~1 and 10 µM.