Global and local meteoric water lines for δ(17)O/δ(18)O and the spatiotemporal distribution of Δ′(17)O in Earth’s precipitation

Recently, δ(17)O and its excess (Δ′(17)O) have become increasingly significant “triple-oxygen-isotope” indicators of distinctive hydrological processes in hydrology and climatology. This situation mirrors the research regarding δ(18)O and δ(2)H in the 1960s towards a solid theoretical base and a surge in application examples and field studies worldwide. Currently, systematic global measurements for δ(17)O in precipitation are still lacking. As a result, attempts have been made to define a Global δ(17)O/δ(18)O Meteoric Water Line (GMWL), often by using regional or local datasets of varying systematicity. Different definitions of the global reference slope (λ(ref)) for determining Δ′(17)O values have been proposed, by ongoing debate around a proposed consensus value of 0.528. This study used worldwide samples archived in the IAEA Global Network of Isotopes in Precipitation (GNIP) to (a) derive a δ(17)O/δ(18)O GMWL based on four-year monthly records from 66 GNIP stations, (b) formulate local δ(17)O/δ(18)O meteoric water lines (LMWL) for these stations’ areas, and (c) evaluate regional and seasonal variations of Δ′(17)O in precipitation. The GMWL for δ(17)O/δ(18)O was determined to be δ′(17)O = 0.5280 ± 0.0002 δ′(18)O + 0.0153 ± 0.0013, in keeping with the consensus value. Furthermore, our results suggested that using a line-conditioned (17)O-excess is a viable alternative over the global λ(ref) in the context of regional hydrology and paleoclimatology interpretations; however, without challenging the global λ(ref) as such.