Climatic instability in west equatorial Africa during the Mid- and Late Holocene

Millennial-scale climatic variations have punctuated the Holocene characterised by abrupt changes from warm to cool or wetter to drier conditions. Amongst these climatic events, there is increased evidence for an abrupt multicentennial shift of climatic conditions around 3.8/3.7 kyr BP (4.1 cal. kyr BP) in mid- to low-latitude regions which had a profound impact on landscape and population migration. In the Mediterranean region, subtropical, tropical and equatorial Africa, a number of continental proxies (lake-levels, pollen sequences, stable isotopes) record this abrupt change towards drier conditions. However, regionalism in climatic conditions is reflected in the vegetation records, possibly in relation to orographic conditions and the influence of sea-surface conditions. Hitherto there have been very few marine sequences that record this particular climatic shift at high-resolution. We present here new data from the Congo deep-sea fan containing integrated marine and terrestrial proxies. Around 5-4 cal. kyr BP, shifts in surface conditions off the Congo River mouth are observed, with possible establishment of seasonal coastal upwelling, and lower sea-surface temperatures. In parallel, pollen data indicate fluctuations of herbaceous, afromontane taxa and charred grass cuticles, suggesting more open vegetation in the lowland regions and an increase in cloud forest and/or afromontane vegetation at higher altitudes within the Congolese region. (c) 2006 Elsevier Ltd and INQUA. All rights reserved.