Africa’s hydroclimate and environments from the Miocene (~23–5 million years ago) to present-day have been shaped by dynamic interactions among ocean circulation, tectonic evolution, atmospheric chemistry, and hydroclimatic processes. Understanding these shifts offers vital context for reconstructing ancient environments and the evolution of tropical ecosystems. However, persisting challenges remain in explaining the decoupling of global climate signals from regional hydrology, especially in Africa, a continent central to human evolution and biodiversity.

This dissertation integrates climate modeling, proxy analyses, and novel isotope measurements to investigate: (1) how multiple equilibrium states in ocean circulation, particularly the Atlantic Meridional Overturning Circulation (AMOC), contribute to the decoupling of atmospheric CO₂ and regional climate signals during the Middle Miocene Climate Transition (MMCT); (2) the impact of tectonic uplift and valley formation within the East African Rift System (EARS) on Miocene rainfall patterns, moisture transport, and water-isotope signals, and the influence of AMOC on African hydroclimate; and (3) the seasonal and spatial controls on modern rainwater isotopic composition across tropical Africa, improving proxy calibration for paleoclimate reconstructions.

Chapter 2 focuses on the global perspective, investigating how multiple equilibrium states in ocean circulation, particularly the AMOC, contribute to the decoupling of atmospheric CO₂ and regional climate signals during the MMCT. MMCT simulations, using the isotope-enabled Community Earth System Model (iCESM), reveal that initial ocean conditions induce divergent equilibrium states that modulate AMOC strength, sea surface temperature gradients, and precipitation. These findings provide a mechanistic explanation for the frequent asynchrony observed between global pCO₂ and regional SST proxies (UK'37) during the Miocene.

Chapter 3 zooms into Africa to identify the driving mechanisms of flora and faunal changes during the Late Cenozoic (23–15 million years ago), by examining the impact of tectonic uplift and valley formation within the EARS on Miocene rainfall patterns, moisture transport, and water-isotope signals. High-resolution paleoclimate modeling demonstrates how sequential tectonic uplift amplifies orographic precipitation, intensifies low-level jets, generates rain-shadow effects, and modulates water-isotope signatures; these simulated results can be validated against regional proxy archives (e.g., leaf-wax δD, paleosol carbonates δ18O, tooth enamel δ18O), which are very limited for this time interval in eastern Africa. Sensitivity experiments in this chapter also explore the additional influence of AMOC state in controlling continental climate variance.

Chapter 4 then shifts the focus to modern hydroclimate, presenting new stable water isotope datasets from tropical Africa collected at multiple sites. By analyzing biweekly rainwater isotope records, this chapter disentangles the seasonal and spatial controls on meteoric water isotopes and challenges canonical interpretations of the “amount effect.” The data emphasize the significance of shifts in moisture source, convective activity, and dynamic atmospheric boundaries as primary drivers of isotopic variability. This new observation could help refine proxy calibration for hydroclimate reconstructions.

By synthesizing isotope-enabled Earth System Modeling, proxy archives, and modern stable isotope datasets, this work advances understanding of global to regional climate driving mechanisms, tectonic-hydroclimate feedbacks, and controls on African rainwater isotope variability. Africa’s dynamic tectonics and climatic transitions during the Miocene uniquely shaped rainfall patterns and water isotope signals, offering key insights into the evolving climate system we are facing today.