Triple Oxygen Isotopes: Fundamental Relationships and Applications

摘要

The element oxygen has three stable isotopes: O-16, O-17, and O-18. For a defined process, a change in O-18/O-16 scales with the corresponding change in O-17/O-16, or the fractionation factors (18)alpha and (17)alpha have a relationship of theta = ln(17)alpha/ln(18 alpha), in which the triple oxygen isotope exponent theta is relatively fixed but does vary with reaction path, temperature, and species involved. When the small variation is of interest, the distinction of three concepts-theta, S (a slope through data points in delta O-17-delta O-18 space), and C (an arbitrary referencing number for the degree of O-17 deviation)-becomes important. Triple oxygen isotope variations can be measured by modern instruments and thus offer an additional line of information on the underlying reaction processes and conditions. Analytical methods and Earth science applications have recently been developed for air oxygen, carbon dioxide, water, silicates, oxides, sulfates, carbonates, and phosphates.