Quantifying the Fingerprint of Oceanic Moisture Source Conditions in Deuterium and 17O Excess Parameters of Precipitation

The deuterium excess (d-excess) and more recently developed O-17 excess (Delta ' O-17) of precipitation are isotopic tracers that are sensitive to oceanic moisture source (OMS) conditions. However, other regional and local processes also affect precipitation d-excess and Delta ' O-17 and may modify or overprint their OMS signals. Here, I leverage the new atmospheric moisture flow data set to diagnose the OMS regions and conditions globally and show that OMS temperature and relative humidity together explain 41% of the variability in monthly mean precipitation d-excess in low- and mid-latitudes. Based on a few sites currently having paired d-excess and Delta ' O-17 data, I also show that the contrasting sensitivity between d-excess and Delta ' O-17 to OMS temperature, which is initially predicted by theory, is distinguishable from precipitation observations under annual mean conditions. This study contributes to disentangling the complex controls on precipitation d-excess and Delta ' O-17 by quantifying the crucial role of OMS dynamics.