The roles of climate and human land-use in the late Holocene rainforest crisis of Central Africa

Type Article
Date 2019-01
Language English
Author(s) Bayon Germain1, 2, Schefuss Enno3, Dupont Lydie3, Borges Alberto V.4, Dennielou BernardORCID1, Lambert Thibault5, Mollenhauer Gesine6, Monin Laurence2, Ponzevera Emmanuel1, Skonieczny Charlotte7, Andre Luc2
Affiliation(s) 1 : IFREMER, Marine Geosci Unit, F-29280 Plouzane, France.
2 : Royal Museum Cent Africa, Dept Earth Sci, B-3080 Tervuren, Belgium.
3 : Bremen Univ, MARUM Ctr Marine Environm Sci, D-28359 Bremen, Germany.
4 : Univ Liege, Chem Oceanog Unit, B-4000 Liege, Belgium.
5 : Univ Lausanne, Inst Earth Surface Dynam, CH-1015 Lausanne, Switzerland.
6 : Alfred Wegener Inst Polar & Marine Res, D-27570 Bremerhaven, Germany.
7 : Univ Paris Saclay, Univ Paris Sud, Lab Geosci Paris Sud, CNRS,UMR 8148, F-91405 Orsay, France.
Source Earth And Planetary Science Letters (0012-821X) (Elsevier Science Bv), 2019-01 , Vol. 505 , P. 30-41
DOI 10.1016/j.epsl.2018.10.016
WOS© Times Cited 3
Keyword(s) neodymium isotopes, suspended particulates, Congo Basin, ENSO, human land-use, deforestation
Abstract

There is increasing evidence that abrupt vegetation shifts and large-scale erosive phases occurred in Central Africa during the third millennium before present. Debate exists as to whether these events were caused by climate change and/or intensifying human activities related to the Bantu expansion. In this study, we report on a multi-proxy investigation of a sediment core (KZR-23) recovered from the Congo submarine canyon. Our aim was to reconstruct climate, erosion and vegetation patterns in the Congo Basin for the last 10,000 yrs, with a particular emphasis on the late Holocene period. Samples of modern riverine suspended particulates were also analyzed to characterize sediment source geochemical signatures from across the Congo watershed. We find that a sudden increase of bulk sediment aluminium-to-potassium (Al/K) ratios and initial radiocarbon ages of bulk organic matter occurred after 2,200 yrs ago, coincident with a pollen-inferred vegetation change suggesting forest retreat and development of savannas. Although hydrogen isotope compositions of plant waxes (δDwax) do not reveal a substantial hydroclimate shift during this period, neodymium isotopes and rare earth elements in detrital fractions indicate provenance changes for the sediment exported from the Congo Basin at that time, hence suggesting a reorganization of spatial rainfall patterns across Central Africa during this event.

Taken together, these findings provide evidence for changing landscapes in Central Africa from about 2,200 yrs ago, associated with synchronous events of vegetation changes and enhanced erosion of pre-aged and highly weathered soils. These events coincided remarkably well with the arrival of Iron Age communities into the rainforest, as inferred from comparison to regional archaeological syntheses. While the human impact on the environment remains difficult to quantify at the scale of the vast Congo Basin, we tentatively propose that strengthening of El Niño-Southern Oscillation (ENSO) variability at that time played a key role in triggering the observed environmental changes, and possibly acted as a driver for the eastward migration of Bantu-speaking peoples across Central Africa.

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Bayon Germain, Schefuss Enno, Dupont Lydie, Borges Alberto V., Dennielou Bernard, Lambert Thibault, Mollenhauer Gesine, Monin Laurence, Ponzevera Emmanuel, Skonieczny Charlotte, Andre Luc (2019). The roles of climate and human land-use in the late Holocene rainforest crisis of Central Africa. Earth And Planetary Science Letters, 505, 30-41. Publisher's official version : https://doi.org/10.1016/j.epsl.2018.10.016 , Open Access version : https://archimer.ifremer.fr/doc/00463/57467/