Cruz, A. P. S.A. P. S.CruzBasak, C.C.BasakKapuge, A. K. I. U.A. K. I. U.KapugeLI LO2026-02-012026-02-012025-12-24https://www.scopus.com/pages/publications/105025702258https://scholars.lib.ntu.edu.tw/handle/123456789/735702Dissolved neodymium (Nd) isotopes are key tracers for water mass mixing in the open ocean and for land-ocean exchanges in marginal seas. Hydrogenous Nd isotope ratios (expressed as εNd) in cores north of the equator reflect values of the surrounding lithology and tend to vary in accordance with local rainfall records, indicating higher terrestrial input from intensified weathering/runoff. Here, we report fossil fish teeth derived εNd from core MD05-2925 (9.3°S, 151.5°E, 1,661 m) in the western tropical Pacific, south of the equator, and explore its use as an indicator of hydroclimatic and weathering changes over the last 30 kyr. Data presented here reveal a pattern of change in εNd that broadly corresponds to regional precipitation. Core MD05-2925 exhibited a decrease in εNd (∼εNd = −1.6) during Heinrich Stadial 1 (HS1) (a wet period at the core site) that could not be tracked to any immediate local sources. Subsequently, during the Bølling-Allerød (B-A) interstadial, characterized by drier conditions in the Southern Hemisphere, we observe an increase in εNd values (∼εNd = −0.37). We suggest that the decrease in εNd observed during HS1 originates from the Australian coast under an intense rainfall regime, with this unradiogenic Nd being transported northward via the Upper Circumpolar Deep Water. Furthermore, we propose that variations in εNd reflect changes in the local hydrological regime along the southern edge of the Intertropical Convergence Zone. This study highlights the effectiveness of hydrogenous Nd isotopes in nearshore environments as a potential indicator of regional hydrological changes.Pacific OceanPacific Ocean (Tropical)FishGeophysicsIsotopesJurassicRainTropical engineeringTropicsWeatheringHydroclimaticInterstadialsIsotope ratioLocal sourceMarginal seasNeodymium isotopesOpen oceanPrecipitation variabilityWater massWet periodfossil recordhydrological changeintertropical convergence zoneisotopic ratioland-sea interactionmixingneodymium isotopeprecipitation (climatology)rainfallSouthern Hemispheretracerwater massLithology[SDGs]SDG14journal article10.1029/2025gc012711