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Oxygen isotopic variations in modern cetacean teeth and bones: implications for ecological, paleoecological, and paleoclimatic studies

Ciner, Burcu, Wang, Yang, Parker, William
Science bulletin 2016 v.61 pp. 92-104
Orcinus orca, Physeter macrocephalus, bones, data collection, ears, equations, fossils, habitat preferences, marine sediments, migratory behavior, oxygen, phosphates, seawater, stable isotopes, teeth, water temperature, whales
The oxygen isotope ratios (δ18O) preserved in marine sediments have been widely used to reconstruct past ocean temperatures. However, there remain significant uncertainties associated with this method, owing to assumptions about the δ18O of ancient seawater which affects the temperature inferred from sediment δ18O records. In this study, oxygen isotope compositions of phosphate in teeth and bones from five different modern cetacean species, including sperm whale, pygmy sperm whale, short-finned pilot whale, killer whale, and Cuvier’s beaked whale, and three fossil whales were determined. The data were used to assess whether the oxygen isotope ratios of biogenic phosphate (δ18Op) from cetaceans are a reliable proxy for the oxygen isotopic composition of ocean water (δ18Ow). The δ18Op values of modern cetaceans range from 15.5‰ to 21.3‰, averaging (19.6‰± 0.8‰) (n = 136). Using a greatly expanded global cetacean δ18Op dataset, the following regression equation is derived for cetaceans: δ18Ow = 0.95317 (±0.03293) δ18Op – 17.971 (±0.605), r = 0.97253. The new equation, when applied to fossil teeth and bones, yielded reasonable estimates of ancient seawater δ18Ow values. Intra-tooth isotopic variations were observed within individual teeth. Among the selected species, the killer whale (O. orca) has the lowest δ18Op values and the largest intra-tooth δ18Op variation, reflecting its habitat preference and migratory behavior. The results show that oxygen isotope analysis of phosphate in cetacean teeth and dense ear bones provides a useful tool for reconstructing the oxygen isotopic composition of seawater and for examining environmental preferences (including migratory behavior) of both modern and ancient whales.