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

Abstract

AbstractIn 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 (δ18OP). However, recent research has illustrated numerous microphysical and dynamical controls on δ18OP 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 δ18OP that better captures the physical foundations for δ18OP as a tracer of hydrological balance. We find that bulk precipitation microphysics and cloud type exert comparable influences on δ18OP. 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.