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

Abstract

Recently, δ 17O and its excess (Δ′17O) have become increasingly significant “triple-oxygen-isotope” indicators of distinctive hydrological processes in hydrology and climatology. This situation mirrors the research regarding δ 18O and δ 2H in the 1960s towards a solid theoretical base and a surge in application examples and field studies worldwide. Currently, systematic global measurements for δ 17O in precipitation are still lacking. As a result, attempts have been made to define a Global δ 17O/δ 18O 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′17O 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 17O/δ 18O GMWL based on four-year monthly records from 66 GNIP stations, (b) formulate local δ 17O/δ 18O meteoric water lines (LMWL) for these stations’ areas, and (c) evaluate regional and seasonal variations of Δ′17O in precipitation. The GMWL for δ 17O/δ 18O was determined to be δ′17O = 0.5280 ± 0.0002 δ′18O + 0.0153 ± 0.0013, in keeping with the consensus value. Furthermore, our results suggested that using a line-conditioned 17O-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.