Saharan dust deposited in Lake Bastani, Corsica: The northernmost dust record of the termination of the Holocene African Humid Period?
Résumé
Throughout the Quaternary, variations of the insolation received over Africa have governed the monsoon dynamics in this region, generating a recurrence of intense rainfall periods. These African Humid Periods (AHP) are characterized by a major transformation of the Saharan hydrological cycle, favouring the development of vast fluvial systems and tropical humid ecosystems in the currently hyper-arid Sahara Desert. In the current context of global warming, the mechanisms as well as the environmental responses associated with these periods of rapid changes between two extreme climatic contexts remain crucial to understand. Many studies have investigated the mechanisms associated with the last AHP that occurred in the early Holocene (9 to 5ka), and more particularly its initiation and termination. Despite all these efforts, these climatic transitions remain highly debated (e.g. influence of high latitudes versus regional forcing, vegetation feedback). Here, we propose to improve our understanding of the Holocene AHP by studying Saharan dust deposited in Lake Bastani (Corsica, western Mediterranean) during the last 12ka. Indeed, as dust emissions are function of the aridity of their sources, among other parameters such as wind intensity, Saharan dust fluxes recorded over and out of Africa may represent an indirect way to reconstruct Sahara past hydrological changes. Bastani Lake is a high elevation system with a very restricted watershed and has been described as a natural Saharan dust trap during the last 3ka (Sabatier et al., accepted). In this study, we present a Holocene multi-proxy characterization of the fine-grained sediments recorded in Bastani lake. We develop a multiproxies approach based on mineralogy and major elements composition of the clay fraction as well as microscopic observations and quantification of the biogenic silica, which complicates Saharan dust supply estimation in this system. This effort to decipher the Bastani lake sediments composition will allow us to qualify and quantify the Saharan dust signal from the bulk sediment record (watershed erosion/alteration, biogenic silica productivity) in order to discuss, to our knowledge, the northernmost aeolian response of the Sahara desert hydrological changes of the termination of this key climatic transition.