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.