资源环境科技发展态势分析平台

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 (delta O-18(P)). However, recent research has illustrated numerous microphysical and dynamical controls on delta O-18(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 delta O-18(P) that better captures the physical foundations for delta O-18(P) as a tracer of hydrological balance. We find that bulk precipitation microphysics and cloud type exert comparable influences on delta O-18(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.

Plain Language Summary The oxygen isotopic composition of tropical precipitation is a powerful tool for "fingerprinting" the history of evaporation, condensation, and transport that water was subjected to in the atmosphere before it reached the ground as precipitation. For this reason, the oxygen isotopic composition of precipitation is commonly employed as a water cycle tracer, both in modern-day contexts and in geologic archives. Translating oxygen isotope ratios into metrics of circulation and climate is not always straightforward, however, due to the range of processes that can affect precipitation. Here we introduce a novel conceptual and statistical framework for interpreting oxygen isotope ratios in tropical precipitation by deconvolving its multiple competing influences. We find that the relative importance of each factor varies geographically. Moisture source is particularly important around the Indo-Pacific Warm Pool, while cloud type exerts strong influence in regions where stratiform clouds are abundant. These results help to reconcile conflicting interpretations of how the Intertropical Convergence Zone and other key features of tropical circulation respond to climate forcings, which are critical questions for past climate reconstructions as well as future climate projections.