Pollen-inferred climatic fluctuations in Ethiopia during the last 3000 years

Abstract

Although lake levels fluctuations are known from Ethiopia during the late Holocene, few continuous paleoclimatic records are available from the high plateau. A 3000 yr high resolution pollen record from the Arsi Mountain in Arussi province of southeastern Ethiopia, provides information on recent changes in the vegetation, above the upper tree line, at 3600 m elevation. The organic sediment was deposited into the Dega Sala swamp ca. 3000 yr B.P., on top of a coarse gravel reepresenting a solifuxion deposit linked to neoglacial. The surrounding vegetation was established as that of the Ericaceous belt, with Ericaceae shrub dominant. The pollen diagram registers significant changes in the relative frequencies of the local herbaceous pollen component versus the arboreal taxa from the upper forest limit. Allowing the high altitude of the site, such changes indicate downward movements of the vegetation belts that are due mainly to temperature variations. An estimated cooling of 2°C is registered at 560±120 yr B.P. (AMS date), contemporaneous with the Little Ice Age. The successive upward regrowth of the forest is rather indicative of a recent warming than linked to recolonization of the forest following anthropogenic deforestation, unlikely at altitude above potential cultivation.