Precession-driven salinity feedback in the western Pacific warm pool: insights from alkenone hydrogen isotopes over the past 450 kyr

Abstract The Western Pacific Warm Pool (WPWP) acts as Earth’s largest tropical heat reservoir; however, the mechanisms that drive orbital-scale sea surface salinity (SSS) variability remain unresolved, as traditional δ¹⁸O-based proxies conflate regional salinity with global ice-volume effects. Here, we present a 450 kyr SSS record from the WPWP using hydrogen isotope composition of alkenones (δD Alk )—a proxy isolating evaporation-precipitation balance—paired with isotope-enabled climate modeling. Our results reveal dominant precessional SSS variability, with maxima during boreal precession minima (P min ) when intensified meridional insolation gradients strengthen Walker Circulation, enhance evaporation, and sustain La Niña-like conditions. The δD Alk record demonstrates that precession-driven ocean-atmosphere feedbacks govern 78% of SSS variability, and reconcile discrepancies in previous δ¹⁸O-based studies showing the significant influence of obliquity. Integration with climate simulations shows that precession-induced trade winds amplify saline water advection and evaporation, establishing a “salinification triad” that dominates WPWP hydroclimate. These findings redefine the WPWP as a precession-paced engine of tropical hydrology, suggesting that the low-latitude tropical hydrology is highly sensitive to insolation intensity and then regulates ENSO-monsoon interactions. By isolating orbital controls on salinity extremes, this work advances frameworks for projecting hydrological responses to anthropogenic warming, critical for regions reliant on monsoon rainfall, emphasizing the vulnerability of tropical hydrological extremes to orbital forcing.