Climatic instability in mid and low latitudes during the Holocene: the 4.1 cal. ka climatic event
by
Fabienne Marret
School of Ocean Sciences-University of Wales (Bangor)
Coauthors: James Scourse (School of Ocean Sciences-University of Wales (Bangor)), Jean Maley (CNRS/ISEM and ORSTOM, University of Montpellier)

Millennial-scale climatic variations have punctuated the Holocene, showing abrupt changes from warm to cool or wetter to drier conditions. Amongst these climatic events, there is an increased evidence for an abrupt multicentennial shift of climatic conditions around 3.8/3.7 ka BP (4.1 cal. ka BP) in mid- to low-latitude regions, which had a profound impact on landscape and civilisation history. In the Mediterranean region, subtropical, tropical and equatorial Africa, a number of continental proxies (lake levels, pollen sequences, stable isotopes) record this abrupt change, indicating the onset of dry 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. Up to now, there are very few marine sequences that record with high-resolution this particular climatic shift. We present here new data from the Congo fan with an integrated signal of marine and terrestrial proxies. Around 4.0 cal. ka BP, a major change in surface conditions off the Congo River mouth is observed, with a possible establishment of seasonal upwelling, and lower sea-surface temperatures. In parallel, pollen data indicate an increase of herbaceous, afromontane taxa and charred grass cuticles, suggesting a more open vegetation in the lowland regions with an increase of savannah fires.

Date received: March 29, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caiq-93.