Diurnal to interannual rainfall δ^(18)O variations in northern Borneo driven by regional hydrology

The relationship between climate variability and rainfall oxygen isotopic (δ^(18)O) variability is poorly constrained, especially in the tropics, where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate. Here we present a daily-resolved, 5-yr-long timeseries of rainfall δ^(18)O from Gunung Mulu National Park, located in northern Borneo (4°N, 114°E) in the heart of the West Pacific Warm Pool, and compare it to local and regional climatic variables. Daily rainfall δ^(18)O values range from +0.7‰ to −18.5‰ and exhibit a weak but significant inverse relationship with daily local precipitation amount (R=−0.19, p<0.05), consistent with the tropical amount effect. Day-to-day δ^(18)O variability at Mulu is best correlated to regional precipitation amount averaged over the preceding week (R=−0.64, p