Temperature and Precipitation reconstructions in Central Africa and recently developed organic biomarkers (TAPIOCA) – TAPIOCA

Africa has been recognized by the IPCC group as one of the most vulnerable region to climate change. Past abrupt climatic and environmental events that have punctuated the recent history of the African provide insights on rapid climate dynamics in the future and are of prime interest to test the ability of models to capture the transient response of the African monsoon and vegetation to both external forcing and internal feedbacks. These changeovers have furthermore crucial impact on sustainability and cultural development of African Societies. However, up to now, humans have been viewed as passive agents in these transitions. Very recently, it was controversially suggested that humans might have play an active role in regime shifts in unbalanced ecosystems. The TAPIOCA project aims at providing detailed investigation of the two last abrupt changes in Western Central Africa: the African Humid Period (AHP) and Late Holocene Rainforest Crisis (LHRC).
The most prominent environmental change over the last 20 ka was the AHP, characterized by the greening of the Sahara 15 ka ago and its later desertification after 6 ka. This climatic “optimum” was triggered by a gradual increase in Northern Hemisphere summer insolation, but many issues remain unresolved about this major perturbation (e.g. timing, stepwise or abrupt transitions, spatial expression) and the role of nonlinear land surface and vegetation feedbacks. A second major vegetation change occurred in Western Central Africa approximately 3000 years ago, forest–savannah mosaic including pioneer trees replaced the mature forests. The origin of the LHRC is still a matter of debate, the anthropogenic hypothesis (deforestation due to Bantu expansion) challenging the more accepted climatic hypothesis to explain this disruption.
Most of the existing continental records of these events are based on qualitative climate indicators and the lack of quantitative reconstructions of key climatic parameters such as temperature hinders comprehensive data-model comparisons. Particularly pollen-based records are potentially confounded by human activities. To fully decipher the drivers and mechanisms controlling monsoon variability, vegetation response and human-environment interactions, there is a crucial need of new records of climate proxies independent of vegetation changes as well as new tracers of human footprints.
The collaborative TAPIOCA project will provide high-resolution, quantitative time series of temperature, precipitation and vegetation type based on well-calibrated organic and isotopic biomarkers. These innovative proxies will be combined with markers of human activities (e.g., fire), and with inorganic isotopic tracers of erosion, provenance and chemical weathering to investigate key lacustrine archives yielding continuous records for the last 20 kyr. This cutting-edge geochemical toolbox will be coupled with regional archeological syntheses to paint climate changes and a prehistory of expansion and technical development of African Societies with the final objectives of testing two main hypotheses:
• Continental temperature changes that have modulated climate sensitivity at a regional scale have been largely minimized leading to an underestimation of the land-ocean thermal contrast during the deglaciation up to the Holocene;
• Human impact on the Central Africa ecosystem has been underestimated as inducing tipping points in environmental evolution over the last 8 ka.
In the frame of international collaborations, we will investigate the Barombi and Mbalang lakes. Located in Cameroon, these lacustrine archives have already shown their potential to deliver continuous and high-resolution sedimentary sequences. While the TAPIOCA consortium already retrieved a sedimentary sequence in the Barombi Mbo lake, a coring campaign of the Mbalang in planed in this project.