Two phases of the Holocene East African Humid Period: Inferred from a high-resolution geochemical record off Tanzania

During the Holocene, the most notably climatic change across the African continent is the African Humid Period (AHP), however the pace and primary forcing for this pluvial condition is still ambiguous, particularly in East Africa. We present a high-resolution marine sediment record off Tanzania to provide insights into the climatic conditions of inland East Africa during the Holocene. Major element ratios (i.e., log-ratios of Fe/Ca and Ti/Ca), derived from X-Ray Fluorescence scanning, have been employed to document variations in humidity in East Africa. Our results show that the AHP is represented by two humid phases: an intense humid period from the beginning of the Holocene to 8 ka (AHP I); and a moderate humid period spanning from 8 to 5.5 ka (AHP II). On the basis of our geochemical record and regime detection, the termination of the AHP initiated at 5.5 ka and ceased around 3.5 ka. Combined with other paleoclimatic records around East Africa, we suggest that the humid conditions in this region responded to Northern Hemisphere (NH) summer insolation. The AHP I and II might have been related to an eastward shift of the Congo Air Boundary and warmer conditions in the western Indian Ocean, which resulted in additional moisture being delivered from the Atlantic and Indian Oceans during the NH summer and autumn, respectively. We further note a drought event throughout East Africa north of 10°S around 8.2 ka, which may have been related to the southward migration of the Intertropical Convergence Zone in response to the NH cooling event.