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Human activities within the context of a drying trend triggered the megafaunal extinctions in Madagascar and Mascarene Islands., Madagascar and the Mascarene Islands of Mauritius and Rodrigues underwent catastrophic ecological and landscape transformations, which virtually eliminated their entire endemic vertebrate megafauna during the past millennium. These ecosystem changes have been alternately attributed to either human activities, climate change, or both, but parsing their relative importance, particularly in the case of Madagascar, has proven difficult. Here, we present a multimillennial (approximately the past 8000 years) reconstruction of the southwest Indian Ocean hydroclimate variability using speleothems from the island of Rodrigues, located ∼1600 km east of Madagascar. The record shows a recurring pattern of hydroclimate variability characterized by submillennial-scale drying trends, which were punctuated by decadal-to-multidecadal megadroughts, including during the late Holocene. Our data imply that the megafauna of the Mascarenes and Madagascar were resilient, enduring repeated past episodes of severe climate stress, but collapsed when a major increase in human activity occurred in the context of a prominent drying trend.

The “4.2 ka event” is frequently described as a major global climate anomaly between 4.2 and 3.9 ka, which defines the beginning of the current Meghalayan age in the Holocene epoch. The “event” has been disproportionately reported from proxy records from the Northern Hemisphere, but its climatic manifestation remains much less clear in the Southern Hemisphere. Here, we present highly resolved and chronologically well-constrained speleothem oxygen and carbon isotopes records between ∼6 and 3 ka from Rodrigues Island in the southwestern subtropical Indian Ocean, located ∼600 km east of Mauritius. Our records show that the 4.2 ka event did not manifest itself as a period of major climate change at Rodrigues Island in the context of our record's length. Instead, we find evidence for a multi-centennial drought that occurred near-continuously between 3.9 and 3.5 ka and temporally coincided with climate change throughout the Southern Hemisphere.

The 4.2 ka BP event is widely described as a 200–300 years long interval of major climate anomaly (typically, arid and cooler conditions potentially across the globe), which defines the beginning of the current Meghalayan age in the Holocene epoch. The 4.2 ka event however, has been disproportionately reported from proxy records situated at low-mid latitudes in the Northern Hemisphere. Consequently, the climatic manifestation of the 4.2 ka event in both spatial and temporal domains is still much less clear in Southern Hemisphere. This is particularly the case for the southwest sector of the southern Indian Ocean. Here we present high-resolution and chronologically well-constrained speleothem oxygen and carbon isotopes records of hydroclimate variability between ~ 6 and 3 ka ago from Rodrigues Island, located in the southwest subtropical Indian Ocean, ~ 600 km east of Mauritius. Our records reveal a major shift to drier condition at circa 4 ka BP, which culminated into a multicentennial period of drought (i.e., megadrought) that lasted continuously from ~ 3.9 to 3.5 ka BP. The inferred hydroclimatic conditions between 4.0 and 4.2 ka BP, are however not distinctly distinguishable from the region’s mean hydroclimatic state over the length of our record. Because the precipitation variability at Rodrigues is distinctly modulated by meridional movement of the Inter-Tropical Convergence Zone and the El Nino Southern Oscillation dynamics, our proxy data may ultimately provide critical constraints in our understanding the timing and dynamical forcing of the 4.2 ka event.