This study reconstructs the history of vegetation and land use over the last 2000 years in southwestern Morocco, based on a multi-proxy approach conducted on sediment core GeoB 6008-1 collected offshore from Cape Ghir. The age–depth model of the core is based on 17 lead-210 datings for the upper levels and 8 radiocarbon (¹⁴C) datings using Accelerator Mass Spectrometry for the older levels, covering the chronological interval from 520 BC to 1977 AD and providing a robust chronological framework.
The study combines three types of analyses. A palynological analysis reconstructs changes in the vegetation environment. A grain-size analysis of sediment particles, combined with End-Member Modeling, identifies sediment sources (fluvial versus aeolian transport). Finally, X-ray fluorescence (XRF) analysis, using the Fe/Ca intensity ratio, compares terrigenous inputs (Fe) to marine carbonate production (Ca), thereby reflecting environmental variations (erosion, river floods, dust inputs, etc.).
The results show that between 650 and 850 AD, the sedimentation rate increased significantly (rising from about 100 to 300 cm per 1,000 years), accompanied by a doubling of pollen flux and the Fe/Ca ratio. These converging signals indicate a substantial increase in terrestrial inputs to the marine environment and suggest a strengthening of erosion processes and fluvial transport to the ocean. At the same time, marked changes are observed in the pollen record: a sharp increase in Cichorioideae, Artemisia, and Plantago pollen—taxa indicative of open or anthropogenically disturbed environments—and a decline in deciduous oak pollen, while evergreen oaks show more limited variations.
These transformations are interpreted as resulting from intensified human pressures, consistent with socio-historical dynamics associated with the arrival and spread of Islam from the 7th century onward, a period marked by the expansion of human settlement, agriculture, and pastoralism in the region. The increase in agropastoral activities, particularly goat herding, likely promoted the degradation of woody vegetation and intensified erosional processes.
After 850 AD and up to the present, sedimentary indicators (sedimentation rate, Fe/Ca) remain relatively stable, suggesting lower variability in terrigenous inputs. In contrast, pollen assemblages continue to indicate degradation of natural vegetation, including signs of expansion of tree crops (olive, argan) and the introduction of exotic species such as eucalyptus over the past 150 years.
Overall, the results highlight the significant impact of socio-economic dynamics on vegetation and regional erosion, as recorded in marine sediment archives.
Ref. McGregor H.V., Dupont L., Stuut J.-B. W & Kuhlmann H., 2009 - Vegetation change, goats, and religion: a 2000-year history of land use in southern Morocco. Quaternary Science Reviews 28, 1434–1448.
Posted by Jean-Paul Peltier.