Oxygen isotope fractionation between bird bone phosphate and drinking water

Area of Science:

• Paleoclimatology
• Isotope Geochemistry
• Avian Biology

Background:

• Oxygen isotope analysis of bone phosphate (δ¹⁸Op) offers insights into past environments.
• Existing methods for reconstructing water isotope values (δ¹⁸Ow) in birds have limitations.
• Broiler chickens provide a model for establishing a global relationship between bone and water isotopes.

Purpose of the Study:

• To develop a precise equation correlating bone phosphate oxygen isotope composition (δ¹⁸Op) with local rainfall oxygen isotope values (δ¹⁸Ow).
• To validate the applicability of this equation across diverse avian species and geological time periods.
• To refine paleoclimatic reconstructions using avian fossil records.

Main Methods:

• Measured oxygen isotope compositions (δ¹⁸Op) in broiler chicken bones from 21 global farms.
• Collected local rainfall isotope data (δ¹⁸Ow) from IAEA/WMO stations.
• Applied linear least squares fitting to establish an isotopic fractionation equation.

Main Results:

• A highly significant linear relationship was found: δ¹⁸Ow = 1.119 (±0.040) δ¹⁸Op - 24.222 (±0.644); R² = 0.98.
• The derived equation accurately predicted δ¹⁸Ow for various extant bird species (mallard ducks, buzzards, gulls, ostriches, rheas).
• Application to fossil penguins and basal birds yielded comparable or refined estimates of past water and temperature conditions.

Conclusions:

• The established bone phosphate-water oxygen isotope relationship is broadly applicable to modern birds of diverse ecologies and body masses.
• The equation provides reliable estimates for paleoseawater and paleoprecipitation, aiding paleoclimatic studies.
• Caution is advised when applying the modern bird equation to basal birds due to potential differences in metabolism and body temperature.