Integral view of Holocene precipitation and vegetation changes in the Nile catchment area as inferred from its delta sediments

Abstract

Listen

Translate article

We compare geochemical and pollen data of several well-dated, high-resolution cores to provide an integral Holocene overview of Nile outflow, sedimentation, and vegetation in and around the Nile delta. We show that the focus point of the Nile plume varied considerably, as indicated by planktonic foraminifer Globigerinoides ruber oxygen isotopes tracing Nile discharge differences in an east–west delta transect. At 13–11.5 cal kyr BP, Nile discharge was low and runoff was predominantly directed to the western part of the delta. Sediment arriving in the delta during that period was dominated by Ethiopian Highland (∼Blue Nile) material, shown by high Ti/Al values of the bulk sediment, indicating dry conditions in the source area of the Blue Nile. Nile discharge increased from ∼11.5 cal kyr BP, and was high across the whole delta from ∼10–6.5 cal kyr BP. During this time, the Ti/Al values decreased within most Nile-delta sediments, suggesting that the relative contribution of Blue-Nile sediment decreased. This was likely due to an increased vegetation cover causing diminished erosion in the Ethiopian Highlands. Nile discharge gradually decreased from ∼6.5 cal kyr BP to present. This decrease was more abrupt in the Western Province of the delta and became more gradual towards the east as the shrinking Nile runoff was directed there. The gradual decrease in precipitation in the Nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower Nile catchment. Our findings suggest a nonlinear response of northeast African vegetation to precipitation from the middle to late Holocene.