Explore the vast range of titles available.

Southern African (SA) hydroclimate is largely shaped by the interactions of atmospheric circulations, e.g., Hadley Circulation, and oceanic elements, like the Benguela Upwelling System (BUS), Agulhas System, and Antarctic Circumpolar frontal system. Large-scale changes to the Meridional Temperature Gradient (MTG) influence both the atmospheric and oceanic components of the hydroclimate system, and thus impact hydroclimate over SA. We present a leaf wax hydroclimate record from ODP 1084, in the BUS, which reveals that changes in the isotopic signature of precipitation over SA coincide with a strengthening of the MTG across the Mid-Pleistocene Transition (MPT). We use HadCM3 simulations to demonstrate the sensitivity of winter rainfall to shifts in the MTG during the MPT. Given the ongoing impacts of climate change on water resources in SA, awareness of the relationship between rainfall and shifts in Hadley Circulation could provide insight into past water availability and aid regional adaptation efforts. Leaf wax isotopes and climate modeling show that Southern African rainfall and vegetation zones shifted in response to a stronger Meridional Temperature Gradient during the Mid-Pleistocene Transition.

Future projections of southwestern African hydroclimate are highly uncertain. However, insights from past warm climates, like the Pliocene, can reveal mechanisms of future change and help benchmark models. Using leaf wax hydrogen isotopes to reconstruct precipitation (δDp) from Namibia over the past 5 million years, we find a long‐term depletion trend (−50‰). Empirical mode decomposition indicates this trend is linked to sea surface temperatures (SSTs) within the Benguela Upwelling System, but modulated by Indian Ocean SSTs on shorter timescales. The influence of SSTs on reconstructed regional hydroclimate is similar to that observed during modern Benguela Nin∼$\\tilde{n}$ o events, which bring extreme flooding to the region. Isotope‐enabled simulations and PlioMIP2 results suggest that capturing a Benguela Nin∼$\\tilde{n}$ o‐like state is key to accurately simulating Pliocene, and future, regional hydroclimate. This has implications for future regional climate, since an increased frequency of Benguela Nin∼$\\tilde{n}$ os poses risk to the ecosystems and industries in the region. Plain Language Summary Rainfall in southwestern Africa will likely be impacted by human‐caused climate change, but climate models disagree on whether the region will get wetter or drier as the planet warms. Previous studies, which used plant pollen preserved in ocean sediment, tell us that southwestern Africa was wetter during the Pliocene, a warm period approximately 5.3 to 2.5 million‐years‐ago, and got drier over time as Earth cooled. This drying is thought to be caused by a concurrent decrease in temperatures within the eastern South Atlantic Ocean. In this study we measure hydrogen isotopes in ancient plant matter and use statistical tools which indicate that rainfall patterns in southwestern Africa are also impacted by changes in Indian Ocean temperatures. This combined Atlantic and Indian Ocean influence is similar to events that we observe in modern times where areas of arid southwestern Africa get short bouts of very strong rainfall when the coastal waters warm. The area that gets strong rainfall depends on where the warm water occurs along the western coast and whether there's also warmer‐ or colder‐than‐normal water in the Indian Ocean. If the Pliocene ocean temperature patterns resembled these events, we may need to do further studies to determine whether they will become more common in the future. Key Points Plio‐Pleistocene changes in the hydrogen stable isotopic signature of leaf waxes from Southern Africa are linked to Benguela temperatures Higher frequency shifts in the record are likely driven by Indian Ocean temperatures via a mechanism observed in the modern Isotope‐enabled simulations suggest that capturing this mechanism may be key to accurately simulating past and future regional hydroclimate

Southwestern North America (SWNA), like many subtropical regions, is predicted to become drier in response to anthropogenic warming. However, during the Pliocene, when carbon dioxide was above pre‐industrial levels, multiple lines of evidence suggest that SWNA was much wetter. While existing explanations for a wet Pliocene invoke increases in winter rain, recent modeling studies hypothesize that summer rain may have also played an important role. Here, we present the first direct evidence for an intensified mid‐Pliocene monsoon in SWNA using leaf wax hydrogen isotopes. These new records provide evidence that the mid‐Pliocene featured an intensified and expanded North American Monsoon. Using proxies and isotope‐enabled model simulations, we show that monsoon intensification is linked to amplified warming on the southern California margin relative to the tropical Pacific. This mechanism has clear relevance for understanding present‐day monsoon variations, since we show that intervals of amplified subtropical warming on the California margin, as are seen during modern California margin heat waves, are associated with a stronger monsoon. Because marine heat waves are predicted to increase in frequency, the future may bring intervals of “Pliocene‐like” rainfall that co‐exist with intensifying megadrought in SWNA, with implications for ecosystems, human infrastructure, and water resources. Plain Language Summary The middle Pliocene, an interval approximately 3 million years ago, has long puzzled climate scientists. Despite having higher‐than‐preindustrial carbon dioxide levels, which should result in drier conditions in subtropical regions, some subtropical regions were wet during the Pliocene. In southwestern North America, there were large permanent lakes and plant and animal species that cannot exist in arid regions. We used measurements of hydrogen isotopes in ancient plant matter to show that wet conditions in the Pliocene southwest resulted from a stronger monsoon. This stronger monsoon was caused by changes in subtropical and tropical ocean temperatures in the eastern Pacific. This study presents the first direct evidence that monsoon changes caused wet conditions in the middle Pliocene. It also has relevance for the present, since we find evidence that present‐day changes in subtropical ocean temperatures can amplify the monsoon, via a mechanism that strongly resembles what happened in the Pliocene. Our study suggests that further studies of the Pliocene can shed light on how future monsoon changes may influence wildfire, landscapes, and water resources across the southwest. Key Points Leaf wax hydrogen isotopes preserved in ocean sediments reveal evidence of a stronger mid‐Pliocene monsoon in southwestern North America Isotope‐enabled simulations show that a stronger monsoon resulted from a diminished east Pacific subtropical‐tropical temperature gradient This mechanism is relevant to understanding present‐day monsoon variability in response to California margin marine heat waves

In the recent decade, a number of extreme weather events have highlighted the vulnerability and unpreparedness of communities in Southern Africa (SA) to anthropogenic climate-change related weather events. Such occurrences are only expected to increase in frequency, however projections of the future mean state of hydroclimate in SA are uncertain; there is broad agreement of earth system models that Africa as a whole will become hotter and drier by 2100, however, projected changes to regional hydroclimate are ambiguous. Insights from past intervals of warm climates, like the Pliocene, or intervals of rapid climate change, like the Mid-Pleistocene Transition, can reveal mechanisms of future change and help benchmark models. In this work, I conduct a comprehensive examination of Southern African hydroclimate dynamics using a combination of organic biogeochemistry, statistical methods, and modeling approaches. I use leaf wax hydrogen and carbon isotopes to reconstruct precipitation and vegetation changes in Southern Africa. I employ a variety of statistical methods to identify long term and short term (sub-million-year) modes of variability in those records, and I utilize climate models, like the isotope-enabled Community Atmosphere Model and the Hadley Center Climate Model to evaluate the climate dynamics driving these precipitation and vegetation changes. Finally, I analyze a set of Community Earth System Model simulations to evaluate the influence of model resolution on the model’s ability to simulate Southern African hydroclimate.The work presented herein (1) contributes to our understanding of the processes driving long and short term changes in Southern African hydroclimate, (2) emphasizes the similarities of past mechanisms to those observed in the modern, and prompts us to consider whether the relatively short-lived drought events we see in the modern have the potential to become longer-lived features of the future climatology, and (3) revisits the debate for increased model resolution versus improved model parametrization.