ɪn dʒˌiːoʊkˈɛmɪstɹi, pˌeɪliːoʊklˌaɪmɐtˈɑːlədʒi ænd pˌeɪliːoʊsiːnˈɑːɡɹəfi dˈɛltə ˈeɪtiːn ˈoʊ ɔːɹ dˈɛltəˈoʊ ˈeɪtiːn ɪz ɐ mˈɛʒɚɹ ʌvðə ɹˈeɪʃɪˌoʊ ʌv stˈeɪbəl ˈaɪsətˌoʊps ˈɑːksɪdʒən ˈeɪtiːn ˈeɪtiːn ˈoʊ ænd ˈɑːksɪdʒən sˈɪkstiːn sˈɪkstiːn ˈoʊ.
In  geochemistry, paleoclimatology and paleoceanography δ18O or delta-O-18 is a measure of the ratio of stable isotopes  oxygen-18 (18O) and oxygen-16 (16O).