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International audienceBiome reconstruction from pollen and plant macrofossil data provides an objective method to reconstruct past vegetation. Biomes for Africa and the Arabian peninsula have been mapped for 6000 years sp and provide a new standard for the evaluation of simulated palaeovegetation distributions. A test using modern pollen data shows the robustness of the biomization method, which is able to predict the major vegetation types with a high confidence level. The application of the procedure to the 6000 years data set (pollen and plant macrofossil analyses) shows systematic differences from the present that are consistent with the numerous previous regional and continental interpretations, while providing a more extensive and more objective basis for such interpretations. Madagascar, eastern, southern and central Africa show only minor changes in terms of biomes, compared to present. Major changes in biome distributions occur north of 15 degrees N, with steppe in many low-elevation sites that are now desert, and temperate xerophytic woods/scrub and warm mixed forest in the Saharan mountains. These shifts in biome distributions, imply significant changes in climate, especially precipitation, between 6000 years and present, reflecting a change in monsoon extent combined with a southward expansion of Mediterranean influence

Funder: NERC RONO: NE/D012996/1The African Humid Period of the early to mid-Holocene (12,000?5000 years ago) had dramatic ecological and societal consequences, including the expansion of vegetation and civilization into the ?green Sahara.? While the humid period itself is well documented throughout northern and equatorial Africa, mechanisms behind observed regional variability in the timing and magnitude of the humid period remain disputed. This paper presents a new hydrogen isotope record from leaf waxes (?Dwax) in a 15,000-year sediment core from Lake Tana, Ethiopia (12?N, 37?E) to provide insight into the timing, duration, and intensity of the African Humid Period over northeastern Africa. ?Dwax at Lake Tana ranges between ?80? and ?170?, with an abrupt transition from D-enriched to D-depleted waxes between 13,000?11,500 years before present (13?11.5 ka). A similarly abrupt transition from D-depleted to D-enriched waxes occurs ca 8.5?8 ka and is followed by generally D-enriched waxes throughout the late Holocene. Trends in ?Dwax covary with changes in Northern Hemisphere summer insolation and reflect increased precipitation at Lake Tana during the AHP; however, the transition from D-depleted to D-enriched waxes occurs earlier at Lake Tana (ca 8 ka, vs 5 ka) than in many other regional records, and the amplitude of D-depletion during the AHP is larger at Lake Tana as well. We attribute this early enrichment to a reduction of moisture derived from westerly sources (the Congo Basin and Atlantic Ocean) which we suggest are D-depleted relative to moisture sourced from the east (Indian Ocean) and the north (Red Sea and Mediterranean Sea). Our new record highlights the importance of both the northward migration of the tropical rain belt as well as east-west migration of the Congo Air Boundary to precipitation source and amount during the African Humid Period.authorsversionPeer reviewe