Late Holocene Paleoclimatic Changes in Western Central Africa Inferred from Mineral Abundance in Dated Sediments from Lake Ossa (Southwest Cameroon)

Abstract

Minerals derived from catchment soils were determined using FTIR spectroscopy in the well-dated core OW4 from Lake Ossa, a lowland rainforest area in Cameroon. This quantification provides a hydrologic record indicating that the magnitude of runoff events, and by inference, rainfall pattern, has varied during the Late Holocene. The comparison between minerogenic inputs and vegetation changes improves the understanding of the inferred climate dynamics. Since at least 5400 cal yr B.P., the paleomonsoon rainfall intensity decreased, as shown by a general decrease in mineral fluxes. This observation is consistent with a gradual weakening of the boreal summer insolation in tropical latitudes. However, the major vegetational change lags behind the onset of the decrease in mineral fluxes. From 2800 to ca 1000 cal yr B.P., the forest receded: the amount of rainforest taxa decreased and is replaced by pioneer trees and Poaceae, when the mineral fluxes attained their lowest values. This episode of maximum dryness is attributed to an abrupt climatic event of global significance which is superimposed onto the paleomonsoon variability. It is related to a cold event, which in turn produced a change in the lower atmospheric circulation that was characterized by a strengthening of northern trade winds, probably correlated with sea-surface temperature variations in the eastern tropical Atlantic area.

Biogeochemical variability during the past 3.6 million years recorded by FTIR spectroscopy in the sediment record of Lake El'gygytgyn, Far East Russian Arctic

“…Because the excitation of polar bonds in molecules by IR radiation is wavenumberspecific depending on the structural and atomic composition of the molecules, it is possible to gather information about organic and minerogenic components from one single measurement. The technique has been applied to sediment to assess the concentration of silicate minerals (Sifeddine et al, 1994;Bertaux et al, 1996Bertaux et al, , 1998Wirrmann et al, 2001) and carbonates (Mecozzi et al, 2001), as well as to characterise humic substances (Braguglia et al, 1995;Belzile et al, 1997;Calace et al, 1999Calace et al, , 2006Mecozzi and Pietrantonio, 2006). FTIRS has also successfully been applied in palaeolimnological studies to quantify biogeochemical properties such as biogenic silica, total organic carbon, total inorganic carbon, and total nitrogen (Vogel et al, 2008;Rosén et al, 2010).…”

Latitudinal Linkages in Late Holocene Moisture‐Balance Variation

“…Lake-status and pollen records from the Atlantic side of intertropical Africa typically show dry conditions between 3000 -2800 and 2000 years BP (Stager and Anfang-Sutter 1999;Vincens et al 1999;Wirrmann et al 2001;Giresse et al 2004), often with a clear aridity maximum around 2800 -2500 years BP (Reynaud-Farrera et al 1996;Maley and Brenac 1998). Peak late Holocene aridity in West Africa is thus coeval with a weakened Asian monsoon and North Atlantic cold event 2.…”

Western equatorial African forest-savanna mosaics: a legacy of late Holocene climatic change?

“…ecotone during the past few millennia (Fontes, 1978;White, 1992White, , 2001King et al, 1997). Indirect evidence for a climatic rather than an anthropogenic origin for these savannas is provided by regional palaeoclimatic data from Lakes Barombi-Mbo (Giresse et al, 1994;Maley and Brenac, 1998) and Ossa (Reynaud-Farrera et al, 1996;Wirrmann et al, 2001;Nguetsop et al, 2004;Giresse et al, 2005) in Cameroon, and Lakes Sinnda (Vincens et al, 1998) and Kitina (Elenga et al, 1996) in the Congo, which are situated at the northern and southern limits of the Guineo-Congolian rainforest, respectively. Unlike the savannas formed during the coolest and driest conditions of the Last Glacial Maximum (Maley and Brenac, 1998), which were subsequently recovered by rainforest expansion, palaeoclimatogical data indicate that the late-Holocene savannas correspond with a period of aridity and marked lakelevel reduction.…”