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Northwest Africa transitioned from a wet/vegetated landscape toward drier/sparser conditions sometime between the late‐Pliocene and the late‐Pleistocene. However, our understanding of the precise timing and nature of this transition is hampered by a paucity of paleo‐records which bridge these two intervals. Here we report new plant‐wax isotope as well as dust and opal flux records from the relatively brief interval ∼1.1–1.0 million years ago (Ma) to evaluate the astronomical timescale controls of Northwest African hydroclimate and vegetation during the Mid‐Pleistocene Transition (MPT) and, in context with published records, the drivers of long‐term climate and ecological trends over the Plio‐Pleistocene. The tempo and amplitude of the Northwest African monsoon rainfall swings closely track low latitude insolation forcings over the last 5 Ma. However, we demonstrate that a pronounced mean state decline in monsoon strength likely occurred following the MPT most likely instigated by increasing Atlantic meridional sea surface temperature gradients or declines in the strength of the meridional overturning circulation. The northward extent of vegetation does not track changes in monsoon strength over the Plio‐Pleistocene and thus may be more strongly influenced by changes in monsoon rainfall extent or ecosystem disturbances. Progressively diminished dust fluxes following a decline in monsoon strength after 1.0 Ma is consistent with reduced production and subsequent depletion of fine‐grained sediments in the Sahara. Synchroneity between dust and opal fluxes across timescales suggests nutrient delivery to the surface ocean via dust plays a key role in marine primary productivity off the coast of Northwest Africa. Key Points: Northwest African monsoon intensity declined substantially sometime between 1.0 and 0.5 MaRainfall penetration or disturbances may be more consequential than monsoon strength for ecosystem biogeography over 105–106 yearsSedimentary dust and opal fluxes drop following monsoon intensity decline, linking dust production, dust flux, and marine productivity [ABSTRACT FROM AUTHOR]

Mineral dust aerosol concentrations in the atmosphere varied greatly on glacial–interglacial timescales. The greatest changes in global dust activity occurred in response to changes in orbital parameters (which affect dust emission intensity through glacial activity) and the lifetime of dust in the atmosphere (caused by changes in the global hydrological cycle). Long-term changes in the surface dust deposition rate are registered in geological archives such as loess, peats, lakes, marine sediments, and ice. Data provided by these archives are crucial for guiding simulations of dust and for better understanding the natural global dust cycle. However, the methods employed to derive paleo-dust deposition rates differ markedly between archives and are subject to different sources of uncertainty. Here, we present Paleo ± Dust, an updated compilation of bulk and <10 µ m paleo-dust deposition rates with quantitative 1σ uncertainties that are inter-comparable among archive types. Paleo ± Dust incorporates a total of 285 pre-industrial Holocene (pi-HOL) and 209 Last Glacial Maximum (LGM) dust flux constraints from studies published until December 2022, including, for the first time, peat records. We also recalculate previously published dust fluxes to exclude data from the last deglaciation and thus obtain more representative constraints for the last pre-industrial interglacial and glacial end-member climate states. Based on Paleo ± Dust, the global LGM:pi -HOL ratio of <10 µ m dust deposition rates is 3.1 ± 0.7 (1σ). We expect Paleo ± Dust to be of use for future paleoclimate dust studies and simulations using Earth system models of high to intermediate complexity. Paleo ± Dust is publicly accessible at 10.1594/PANGAEA.962969 (Cosentino et al., 2024). [ABSTRACT FROM AUTHOR]

Savanna ecosystems were the landscapes for human evolution and are vital to modern Sub-Saharan African food security, yet the fundamental drivers of climate and ecology in these ecosystems remain unclear. Here we generate plant-wax isotope and dust flux records to explore the mechanistic drivers of the Northwest African monsoon, and to assess ecosystem responses to changes in monsoon rainfall and atmospheric pCO2. We show that monsoon rainfall is controlled by low-latitude insolation gradients and that while increases in precipitation are associated with expansion of grasslands into desert landscapes, changes in pCO2 predominantly drive the C3/C4 composition of savanna ecosystems. Plant-wax isotope and dust flux records reveal that the long-term variability of the Northwest African monsoon is controlled by tropical solar radiation gradients. Grasslands expand into the Sahara during strong monsoons, but the ultimate composition of the ecosystem is controlled by CO2. [ABSTRACT FROM AUTHOR]