Climatic controls on central African hydrology during the past 20,000 years

Abstract

Past hydrological changes in Africa have been linked to various climatic processes, depending on region and timescale. Long-term precipitation changes in the regions of northern and southern Africa influenced by the monsoons are thought to have been governed by precessional variations in summer insolation. Conversely, short-term precipitation changes in the northern African tropics have been linked to North Atlantic sea surface temperature anomalies, affecting the northward extension of the Intertropical Convergence Zone and its associated rainbelt. Our knowledge of large-scale hydrological changes in equatorial Africa and their forcing factors is, however, limited. Here we analyse the isotopic composition of terrigenous plant lipids, extracted from a marine sediment core close to the Congo River mouth, in order to reconstruct past central African rainfall variations and compare this record to sea surface temperature changes in the South Atlantic Ocean. We find that central African precipitation during the past 20,000 years was mainly controlled by the difference in sea surface temperatures between the tropics and subtropics of the South Atlantic Ocean, whereas we find no evidence that changes in the position of the Intertropical Convergence Zone had a significant influence on the overall moisture availability in central Africa. We conclude that changes in ocean circulation, and hence sea surface temperature patterns, were important in modulating atmospheric moisture transport onto the central African continent.

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

“…Paleohydrological and paleoclimatological investigations covering the last 10,000 yr interglacial period (Holocene) have pointed out that the region has undergone alternating wet and drought periods leading, for the rainforest, to either its expansion during wet intervals or its contraction during drought periods with set up of savanna (Ngomanda et al, 2007(Ngomanda et al, , 2009. The long term precipitation changes in monsoon regime during the past 20,000 yrs in Central Africa are mostly related to changes in ocean circulation and sea surface temperature patterns, which are important to modulate atmospheric moisture transport (Schefusz et al, 2005;Weldeab et al, 2005). The influence on this alternating regime on a long term period (i.e.…”

An abrupt change in the African monsoon at the end of the Younger Dryas

“…[20] A multiproxy study of a core from a highaccumulation-rate site off the mouth of the Congo River provides an outstanding record of changes in river discharge and basin-scale climatic conditions over a large area of equatorial Africa [Schefuss et al, 2005] (Figure 5). The dD of terrestrial plant waxes, a proxy for water balance in the Congo basin, and surface water d 18 O, which at the core site is strongly influenced by the Congo River, both indicate the abrupt onset of drier conditions with reduced Congo River discharge during the YD, followed over the next 1500 years by a gradual transition to wetter conditions ( Figure 5).…”

Paleohydrological changes during the last deglaciation in Northern Brazil

“…The δD of leaf wax lipids produced by land plants, such as triacontanic acid (nC 30 ) and other long chain fatty acids (Eglinton and Hamilton, 1967), although dependent on the δD of meteoric waters (Sachse et al, 2006), is also affected by evaporation and transpiration processes (Sauer et al, 2001;Liu and Huang, 2005). As a matter of fact, the δD of leaf wax lipids has been recently used to track humidity changes in tropical Africa from marine sediments (Schefuß et al, 2005). In a first approximation, the fractionation factor between the δD values of lipids from land plants and the calculated δD values of water allows us to estimate evapotranspiration.…”