Evaluation of triple oxygen isotopes in daily East African precipitation as a potential tracer of recycled continental moisture

Like the Amazon for South America, the "continental sea" of the Congo rainforest plays a critical role in the water cycle for Africa. However, its contribution to rainfall relative to oceanic sources is unconstrained, making it difficult to assess feedbacks between changes in forest cover and changes in African rainfall under past or present climate states. Stable isotopes in precipitation, including δ¹⁸O, δ¹⁷O, and δ²H, integrate many processes involved in continental moisture recycling and should therefore theoretically aid in distinguishing between oceanic and continental moisture, but such an application has not yet been developed in such a complex low-latitude setting. Here, we present daily precipitation isotope data collected beginning in May 2018 at 5 sites along a southwest-northeast transect in western Uganda, East Africa. These sites are located directly east of the Congo rainforest, and all sites receive precipitation sourced from both a westerly, recycled source as well as an easterly, oceanic source. Initial results reveal distinct differences in the δ¹⁸O, δ¹⁷O, δ²H, d-excess and Δ¹⁷O in precipitation sourced from easterly vs. westerly locations. Using satellite and reanalysis estimates of winds, land cover, and rainfall, we evaluate whether recycled evapotranspired moisture exhibits a Δ¹⁷O distinct from direct oceanic moisture. Our results will illuminate the potential for precipitation isotopes, particularly triple oxygen isotopes, to serve as a tracer of continental recycling on a broader scale in Africa.