Evidence for sea spray effect on oxygen stable isotopes in bone phosphate - Approximation and correction using...

Palaeobiodiversity research based on stable isotope analysis in coastal environments can be severely hampered by the so-called "sea spray" effect. This effect shifts the isotopic signal of terrestrial individuals towards too marine values. It is commonly agreed upon that sea spray influences sulphur stable isotopes. However, we were able to approximate a remarkable sea spray effect also in carbon and oxygen stable isotopes of bone carbonate previously. In the present study we could approximate a minimum sea spray effect of about 13.9% even present in oxygen isotope values of bone phosphate, which was validated by Gaussian Mixture Model (GMM) clustering. This approximated value is by some magnitudes smaller than the minimum sea spray effect approximated for both δ¹³C_carb and δ¹⁸O_carb, and quite close to the sea spray detected for δ³⁴S_coll in a previous study. It may therefore be interpreted as purer minimum sea spray signal compared to the approximation in bone carbonate. Furthermore, detection of sea spray in δ¹⁸O_phos can serve as additional validation of the effect present in bone carbonate, which is more prone to diagenetic alteration compared to bone phosphate. Moreover, the presence of the sea spray effect in both δ¹⁸O_carb and δ¹⁸O_phos demonstrates that sea spray can be taken up by terrestrial mammals not only via food (δ¹⁸O_carb) but also via drinking water (δ¹⁸O_phos). Finally, this study once more confirmed that calculation of δ¹⁸O_phos from δ¹⁸O_carb values using a fixed oxygen isotope spacing (Δδ¹⁸O) can be highly misleading, especially in coastal environments affected by sea spray.