Abstract
Abstract. The present study aims at reconstructing past climate changes and their environmental impacts on plant ecosystems during the last 6000 years in the Middle Atlas, Morocco. Mean January temperature (Tjan), annual precipitation (Pann), winter (Pw) and summer (Ps) precipitation, and a seasonal index (SI) have all been quantified from a fossil pollen record. Several bio- and geo-chemical elements have also been analysed to evaluate the links between past climate, landscape, and ecosystem changes. Over the last 6000 years, climate has changed within a low temperature and precipitation range with a trend of aridity and warming towards the present. Tjan has varied within a ca. 2 °C range, and Pann within less than 100 mm yr−1. The long-term changes reconstructed in our record between 6 ka cal BP and today are consistent with the aridity trend observed in the Mediterranean basin. Despite the overall limited range of climate fluctuation, we observe major changes in the ecosystem composition, the carbon isotopic contents of organic matter (δ13C), the total organic carbon and nitrogen amount, and the carbon to nitrogen ratio (C / N) after ca. 3750 cal BP. The main ecosystem changes correspond to a noticeable transition in the conifer forest between the Atlas cedar, which expanded after 3750 cal BP, and the pine forest. These vegetation changes impacted the sedimentation type and its composition in the lake. Between 5500 and 5000 cal BP, we observe an abrupt change in all proxies which is coherent with a decrease in Tjan without a significant change in the overall amount of precipitation.
Highlights
The amplitude of climate change during the Holocene (11 700 cal BP to the present) is known to be globally less extreme than during the last glacial period (Bianchi and McCave, 1999; Bond et al, 2001; Debret et al, 2007)
This study marks a new contribution to the knowledge of past climates and environmental history in north Africa mountainous areas
Annual precipitation and January mean temperature have respectively varied within a range of 100 mm and 2 to 3 ◦C
Summary
The amplitude of climate change during the Holocene (11 700 cal BP to the present) is known to be globally less extreme than during the last glacial period (Bianchi and McCave, 1999; Bond et al, 2001; Debret et al, 2007). M. Nourelbait et al.: Climate change and ecosystems dynamics. The Holocene climate stability allowed sustainable vegetation dynamics with long-term ecosystem changes, plant species expansions and migrations, and an increase of species diversity over all latitudes (Rohde, 1992). The Holocene period has recorded some abrupt and cold events such as the one at 8.2 ka cal BP Alley and Agustsdottir, 2005) which recorded a depletion of about 4 ◦C in winter temperature in the eastern Mediterranean (Weninger et al, 2009) The Holocene period has recorded some abrupt and cold events such as the one at 8.2 ka cal BP (e.g. Alley and Agustsdottir, 2005) which recorded a depletion of about 4 ◦C in winter temperature in the eastern Mediterranean (Weninger et al, 2009)
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