Dentine oxygen isotopes (δ¹⁸O) as a proxy for odontocete distributions and movements

Abstract

Spatial variation in marine oxygen isotope ratios (δ 18O) resulting from differential evaporation rates and precipitation inputs is potentially useful for characterizing marine mammal distributions and tracking movements across δ 18O gradients. Dentine hydroxyapatite contains carbonate and phosphate that precipitate in oxygen isotopic equilibrium with body water, which in odontocetes closely tracks the isotopic composition of ambient water. To test whether dentine oxygen isotope composition reliably records that of ambient water and can therefore serve as a proxy for odontocete distribution and movement patterns, we measured δ 18O values of dentine structural carbonate (δ 18 OSC) and phosphate (δ 18 OP) of seven odontocete species (n = 55 individuals) from regional marine water bodies spanning a surface water δ 18O range of several per mil. Mean dentine δ 18 OSC (range +21.2 to +25.5‰ VSMOW) and δ 18 OP (+16.7 to +20.3‰) values were strongly correlated with marine surface water δ 18O values, with lower dentine δ 18 OSC and δ 18 OP values in high‐latitude regions (Arctic and Eastern North Pacific) and higher values in the Gulf of California, Gulf of Mexico, and Mediterranean Sea. Correlations between dentine δ 18 OSC and δ 18 OP values with marine surface water δ 18O values indicate that sequential δ 18O measurements along dentine, which grows incrementally and archives intra‐ and interannual isotopic composition over the lifetime of the animal, would be useful for characterizing residency within and movements among water bodies with strong δ 18O gradients, particularly between polar and lower latitudes, or between oceans and marginal basins.

Are stable isotope ratios and oscillations consistent in all baleen plates along the filtering apparatus? Validation of an increasingly used methodology

“…Stable isotopes ratios are expressed following the delta (δ) notation, while the relative variations of stable isotope ratios are expressed as per mil (‰) deviations from the predefined international standards according to the equation: where X isC orN, and R sample and R standard are the heavy‐to‐light isotope ratios (C/ 12 C and 15 N/ 14 N) in the sample and in the reference standards, respectively. These standards are the Vienna Pee Dee Belemnite (V‐PDB) calcium carbonate for 13 C and atmospheric nitrogen (air) for 15 N. The precision and accuracy for δ 13 C and δ 15 N measurements were 0.1 and 0.3‰, respectively.…”

“…In the cases in which such tissues experience continuous growth, a chronologically sequential record of the environment in which the animal has lived is preserved in successive growth layers. This property has been used to infer variations in physiology or habitat use during periods of the life cycle of individuals that otherwise would be impossible to monitor …”

Stable isotope relationships between apatite phosphate (δ18O), structural carbonate (δ18O, δ13C), and collagen (δ2H, δ13C, δ15N, δ34S) in modern human dentine

“…However, some studies have shown that there is no clear need for any pretreatment of the apatite because only high amounts of organic matter influence carbonate δ 13 C and δ 18 O values . Numerous recent studies have shown that pretreatment can have unintended and inconsistent consequences for the isotopic composition of structural carbonate or phosphate . Our results indicate no significant mean offsets between pretreated and untreated dentine.…”

“…Our results indicate no significant mean offsets between pretreated and untreated dentine. However, there was relatively high variability in the offsets among the samples (2.9‰ for δ 18 O values and 2.9‰ for δ 13 C values) . In addition, the great loss of about 50% of the raw dentine material can be considered as being a further drawback of the pretreatment procedure.…”

A simplified silver phosphate extraction method for oxygen isotope analysis of bioapatite

“…Bio‐ and Ca‐phosphate apatites can accommodate a carbonate component (CO 3 2− ) . The oxygen isotopic analysis of the carbonate component is relatively simple and routine . However, the oxygen isotopic composition of carbonate is more prone to isotopic exchange with the environment during post‐mortem diagenetic alteration than that of phosphate (PO 4 3− ), because the P–O bond is stronger than the C–O bond .…”