The Influence of Competing Hydroclimate Processes on Stable Isotope Ratios in Tropical Rainfall

Abstract

In tropical paleoclimate studies, paleo-precipitation is often reconstructed from proxies via the “amount effect,” that is, the empirical inverse relationship between local precipitation amount (P) and the oxygen isotopic composition of precipitation (δ 18 O P ). However, recent research has illustrated numerous microphysical and dynamical controls on δ 18 O P that do not necessarily covary with P, complicating the reconstruction of circulation features like the Intertropical Convergence Zone. Here we introduce a new conceptual and statistical model for δ 18 O P that better captures the physical foundations for δ 18 O P as a tracer of hydrological balance. We find that bulk precipitation microphysics and cloud type exert comparable influences on δ 18 O P . Moisture transport plays an important secondary role in regions of deep atmospheric convection such as the Intertropical Convergence Zone and Indo-Pacific Warm Pool. Our findings help reconcile conflicting interpretations of Intertropical Convergence Zone excursions, and provide a firm physical grounding for more nuanced, accurate interpretations of past hydroclimate using water isotope proxies.