Climate changes since the mid-Holocene in the Middle Atlas, Morocco

Abstract

© Author(s) 2015. The Holocene climate is known to be rather stable although with few abrupt changes that lasted few decades. The present study is related the climate changes and their environmental impacts during the last 6000 years from a fossil record collected in the Middle Atlas, Morocco. Reconstruction of three climate variables (January temperature (Tjan), annual precipitation (P ann ) and a precipitation seasonal index (SI)) was based on pollen data and analyzed various bio and geo-chemical elements. Then we evaluated the relationships between all the environmental variables. Climate over the last 6000 years was rather stable with a smooth trend of aridity towards the present. Tjan has varied within about 2°C range and P ann within less than 100 mm yr -1 . Despite such overall climate stability, after ca. 3750 cal BP some important changes were observe in the ecosystem composition, the carbon isotopic contents of organic matter in lake sediments (δ 13 C), the total organic carbon and nitrogen amount and the carbon to nitrogen ratio (C / N). These environmental changes are related to the transition in the conifer forest between the Atlas cedar, which expanded after 3750 cal BP, and the pine forest. These vegetation changes have impacted the sedimentation type and composition into the lake. Between 5500 and 5000 cal BP an abrupt change is recorded in all bio and geo-chemical indicators as well as in the pollen data. The multi-proxy analysis, taking into account the climate variables, tends to indicate that it was mainly a decrease in temperature without a significant change in the overall amount of precipitation. In summary, the present study confirms the overall climate stability over the last 6000 years and highlights the presence of short and abrupt climate events.