The spatial hydrological structure of the western tropical Pacific derived from δ18O and δD signatures

•Surface water features fall into two zones separated at 155° E along the longitude transect.•The water source contributions at station CTD03were confirmed by an isotope fractionation model.•Correlations between Chl a and δ18O (d-excess) reveal the potential impact of biogenic processes. Lack the connection between the air-sea interaction and deep hydrological processes hinders to clarify the response of Western Pacific warm pool (WPWP) to recent global warming. In this paper, δ18O, δD, combined with other properties of seawater collecting during the 37th and 47th Chinese Research Expedition cruises, were measured to trace the potential hydrological processes in the tropical Pacific Ocean. The change in δ18O and d-excess signatures of surface water revealed that two different zones were separated at 155° E along the transect. This coincided with the spatial evaporation–precipitation pattern of the Pacific Walker circulation (PWC). At station CTD03, 18O-enriched water (salinity ∼ 35 psu, δ18O ∼ 0.20‰ in average) at a depth of 100 ∼ 150 m was potentially attributed to the recirculation of the Kuroshio Extension Flow (KEF). In contrast, the deep water with low δ18O (− 0.60‰ in average from 2000 m to 5680 m) indicated the dominant Lower Circumpolar Pacific Water (LCPW). These contributions of water mass sources to the hydrological structure of western Pacific warm pool (WPWP) were confirmed by a mass balance model. Furthermore, significant linear correlations between chlorophyll and δ18O, as well as chlorophyll and d-excess within the upper 200 m at station CTD03, indicated that the seawater δ18O signature could be impacted by biogenic fractionation. The research highlights the validity of δ18O and d-excess to indicate both hydrological processes and watermass structure in WPWP. Further proofs based on investigation and experiments are required.