NOAA/WDS Paleoclimatology - Isotopic reconstruction of the African Humid Period and Congo Air Boundary migration at Lake Tana, Ethiopia

The African Humid Period of the early to mid-Holocene (12,000e5000 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 (dDwax) 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. dDwax at Lake Tana ranges between 80‰ and 170 ‰, with an abrupt transition from D-enriched to D-depleted waxes between 13,000 e11,500 years before present (13e11.5 ka). A similarly abrupt transition from D-depleted to D-enriched waxes occurs ca 8.5e8 ka and is followed by generally D-enriched waxes throughout the late Holocene. Trends in dDwax 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 Ddepletion 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 Ddepleted 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.