Timing of the southward retreat of the ITCZ at the end of the Holocene Humid Period in Southern Arabia: Data-model comparison

New pollen data from Omani mangroves (Kwar-al-Jaramah [22.49° N - 59.76° E] and Filim [20.61° N - 58.17° E]), in addition to previously published paleohydrological records from Southern Arabia improve our understanding of the timing and amplitude of the southward retreat of the Indian monsoon influence in Southern Arabia along a north-south transect. Comparison with simulations performed with the IPSL climate model, considering both snapshot experiments and transient simulations from 6000 cal yr BP to the present, confirm the latitudinally time-transgressive nature of the humid-arid transition at the end of the Holocene Humid Period. This occurred in two steps, respectively dated at around 5000 and 2700 cal yr BP. At around 5000 cal yr BP, the southward ITCZ shift was orbitally-driven and led to the abrupt aridification at Kwar-al-Jaramah and the progressive increase of dryness at Filim as the mean position of the ITCZ was centered ca 22.30°N. At 2700 cal yr BP, aridity was fully in place over all of southern Arabia due to increased climate variability. More intense rainy events during the last millennium, however, may have contributed to the discrete hydrological improvement without any impact on the regional vegetation which has remained desert to the present day.