Holocene paleoenvironmental reconstruction based on the lacustrine evolution of three Cameroonian lakes (SW, Africa)

Lakes are the most attractive and expressive characteristics of a landscape. Lacustrine sediments provide a historical record of the conditions of the surrounding catchment area. The aim of this study is to reconstruct the Holocene lacustrine evolution of 3 lakes located in Yaoundé, Dizangué and Ngaoundéré regions (Cameroon, SW-Africa) using a multiproxy approach including analysis of sediments, diatoms, pollen, with absolute chronologies based on radiocarbon dates. Sediment cores were recovered from a raft using polyvinyl chloride (PVC) pipe. Sediment grains are generally sub-rounded and rounded indicative of both aeolian and fluvial transportation. Pollen and diatom data revealed major hydrological changes and strong fluctuations between wet conditions during the "Medieval Warm Period" (1100 − 800 yrs BP), and dry conditions during the "Little Ice Age" (500 − 300 yrs BP). Four distinct paleoclimatic phases were identified from the diatom assemblage of lakes from Yaoundé and Dizangué (South) and Ngaoundéré (North). The diatom assemblages in Simbock Lake (southern Cameroon) indicate high water levels initially, followed by a transition marked by increased aerophilic species, potentially indicating episodic drying or reduced water supply. Furthermore, a pH and trophic inversion suggests eutrophication due to nutrient influx. In the Ossa Lake complex (southern Cameroon), four phases reveal changes from oligotrophic to eutrophic conditions, with Aulacoseira species dominating, and the evolution of acidic to clear waters. Lake Ngaoundaba in the Adamawa (northern Cameroon) exhibits three phases, indicating stable oligotrophic conditions, episodic drying, and a rise in lake level with increased tychoplanktonic species, particularly Aulacoseira distans . These hydrological changes have controlled the dynamics of tropical rainforests during the Little Ice Age (LIA) and the Medieval Warming (MW) in this part of Africa, resulting in their expansion during periods of heavy rainfall and contraction during periods of reduced rainfall.