Oxygen isotope composition of North American bobcat (Lynx rufus) and puma (Puma concolor) bone phosphate: implications for provenance and climate reconstruction

Pre-treatment methods for stable oxygen and carbon isotope analyses of structural carbonates of bones in marine teleost fishes

RATIONALE

Although the proportion of structural carbonates in vertebrate bones is low, the values of isotopes, namely stable oxygen (δ18 O) and carbon (δ13 C), in structural carbonates provide environmental and physiological information, which can be beneficial for estimating the palaeontological and ecological parameters of vertebrates. However, a few studies have analysed the isotopes of structural carbonates in modern teleost fishes, and a well-developed protocol for sample preparation is lacking.

METHODS

We examined different pre-treatment methods of preparing bone samples of three marine teleost fishes (Japanese flounder, Pacific bluefin tuna and yellowtail) and investigated the effects of the cleaning methods on the stable isotope values of structural carbonates among vertebrae in the same individual. Isotope values were analysed using isotope ratio mass spectrometry.

RESULTS

Physical cleaning was the most promising pre-treatment method and resulted in δ18 O values that were comparable to those of otoliths. Chemical treatments with NaOH and H2 O2 changed the percentage of structural carbonates in the bone and affected δ18 O and δ13 C values. High-temperature treatments, such as boiling and roasting, altered δ18 O values due to the exchange of oxygen with environmental water or vapour.

CONCLUSIONS

Our results suggest that chemical cleaning methods used to prepare bone phosphate or collagen samples for isotope analyses are not suitable for structural carbonates. Physical cleaning is the appropriate pre-treatment method for analysing the isotopes of structural carbonates. Also, we emphasise that standardising the vertebral number is necessary to make δ13 C values comparable between specimens in the same species.

Tracking cats revisited: Placing terrestrial mammalian carnivores on δ2H and δ18O isoscapes

The relationship between hydrogen and oxygen stable isotopic compositions in environmental water and hair was investigated for both domestic cats (Felis catus) and dogs (Canis lupus familiaris). A strong, but different, covariance was measured between the hydrogen and oxygen stable isotopic compositions of local precipitation and hair keratin from both cats and dogs. These isotopic differences are most likely a result of the differences between the dietary and drinking water needs of cats compared to dogs. Moreover, the δ²H and δ¹⁸O values of hair from captive and wild felids and canids, such as cougars (Puma concolor), bobcats (Lynx rufus), and wolves (Canis lupus) are broadly consistent with these measurements. This evidence indicates that while the water budgets of terrestrial mammalian carnivores need to be considered in isotopic applications, it is clear that felids and canids may be placed on tissue–specific hydrogen and oxygen isotopic landscapes for ecological, provenance, or forensic studies.

The relationship between the phosphate and structural carbonate fractionation of fallow deer bioapatite in tooth enamel

RATIONALE

The species-specific relationship between phosphate (δ¹⁸ O_P values) and structural carbonate (δ¹⁸ O_C values) oxygen isotope ratios has been established for several modern and fossil animal species but until now it has not been investigated in European fallow deer (Dama dama dama). This study describes the relationship between phosphate and structural carbonate bioapatite in tooth enamel of extant fallow deer, which will help us further understand the species' unique environmental and cultural history.

METHODS

The oxygen isotope composition of phosphate (δ¹⁸ O_P value) and structural carbonate (δ¹⁸ O_C value) of hydroxylapatite was determined in 51 modern fallow deer tooth enamel samples from across Europe and West Asia. The δ¹⁸ O_C values were measured on a GV IsoPrime dual-inlet mass spectrometer and the δ¹⁸ O_P values on a temperature-controlled elemental analyser (TC/EA) coupled to a DeltaPlus XL isotope ratio mass spectrometer via a ConFlo III interface.

RESULTS

This study establishes a direct and linear relationship between the δ¹⁸ O_C and δ¹⁸ O_P values from fallow deer tooth enamel (δ¹⁸ O_C  = +9.244(±0.216) + 0.958 * δ¹⁸ O_P (±0.013)). Despite the successful regression, the variation in δ¹⁸ O values from samples collected in the same geographical area is greater than expected, although the results cluster in broad climatic groupings when Koppen-Geiger classifications are taken into account for the individuals' locations.

CONCLUSIONS

This is the first comprehensive study of the relationship between ionic forms of oxygen (phosphate oxygen and structural carbonate) in fallow deer dental enamel. The new equation will allow direct comparison with other herbivore data. Variable δ¹⁸ O values within populations of fallow deer broadly reflect the ecological zones they are found in which may explain this pattern of results in other euryphagic species.

Tales of mystery and imagination in stable isotope geochemistry: celebrating the 75th birthday of Jochen Hoefs

We celebrate the contribution of Jochen Hoefs to the development of stable isotope (bio)geochemistry on the occasion of his 75th birthday.