Abstract
The fluctuating climatic conditions of the Saharo-Arabian desert belt are increasingly important for both palaeoclimatic and palaeoanthropological debates. Currently, Saharo-Arabia acts as a vast biogeographic barrier between the Afrotropical and Palaearctic realms. On orbital timescales, northward incursions of the African (ASM) and Indian (ISM) Summer Monsoons activated fluvio-lacustrine systems and led to the formation of grassland habitats. The formation of these habitats has been considered a crucial factor in&#160;Homo sapiens&#160;dispersals into the Saharo-Arabian deserts and beyond. The so-called &#8220;northern route&#8221; favours a terrestrial dispersal through green palaeohydrological corridors. However, a maritime &#8220;southern route&#8221; during the sea-level low-stand of Glacial Termination-II (T-II) has also been proposed. The precise phasing between the onset of wetter conditions and rising sea-levels may thus be a crucial factor for testing these alternative hypotheses. Here, we present a precisely dated high-resolution (<100 yrs) stalagmite record from Mukalla Cave, Yemen, at a key location on the &#8220;southern route&#8221;. Wetter conditions in Southern Arabia prevailed from ~127.7 to ~121.1 ka BP and occurred when sea-levels were already higher than at present, revealing a phase-lag of several thousand-years between sea-level rise and the onset of pluvial conditions. This lag is likely related to the colder conditions of Heinrich Stadial-11, which supressed the interhemispheric pressure gradient and the ASM and ISM throughout T-II despite rising insolation. &#948;18Oca&#160;values indicate rainfall intensity during the ~127.7 to ~121.1 ka BP interval 1) followed low-latitude insolation, and 2) was the greatest in the last 130,000 years. &#160;Additionally, a mixed C3/C4 grassland environment, as revealed by stalagmite &#948;13Cca&#160;values, was present in the now desert interior of Yemen. Combined with archaeological evidence, we discuss the potential implications our results have for&#160;H. sapiens&#160;biogeographical shifts and dispersal processes across Saharo-Arabia during early MIS 5.&#160;
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