Pluvial periods in northern Arabia over the last 10 million years

Green periods are becoming an increasingly important facet of both understanding the climatic evolution of Arabia, and permitting mammal dispersals between Africa and Eurasia. Recent research from central Arabia has shown that recurrent phases of increased monsoonal rainfall extended back into the Miocene. However, the latitudinal extent of the tropical rainbelt and green environments, especially at potential dispersal entry points into Arabia, remains uncertain. Here, we provide information on the timing of northern Arabian pluvial periods over the last 10.5 million years. We applied U-Pb dating to a new set of 50 speleothems from 5 caves, showing that periods of enhanced rainfall occurred between ~1.2 to ~1.7 Ma, ~2.8 to ~3.7 Ma, ~4 to ~7.5 Ma and ~9.8-10.5 Ma. Speleothem fluid inclusion water δ¹⁸O and δD stable- sotopes plot in excellent agreement with monsoonal precipitation sources, indicating the tropical rainbelt migrated to at least 29°N over Arabia in Mio-Pleistocene green phases. Absence of speleothem deposition in northern Arabia following the Mid-Pleistocene Transition (1.2 Ma) indicate monsoonal rainfall did not reach high latitudes in sufficient amounts, and reveal a time-transgressive reduction in the northward extent of monsoonal rainfall. These highlight the role of enhanced glacial-boundary conditions as a suppressant to the northern extent of rainfall during green Arabia periods. Whilst Mid-Late Pleistocene lacustrine evidence indicates increased rainfall compared to modern climates, our data suggest that mammal (especially hominin) dispersals in this region took place during relatively drier pluvial periods compared to the Mio-Pliocene.