Browsing by Author "Ewague, A"

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    Ancient steroids: human faecal signals and environmental data from a Holocene sediment record of the Yagour Plateau, High Atlas, Morocco
    (European General Assembly, 2022-05-27) Cornelissen, HL; Lupein, R; Fletcher, WJ; Hughes, PD; Bell, BA; Rhoujjati, A; Ewague, A; Fink, D
    The analysis of steroids (stanols and stanols compounds) preserved within Holocene sediment records represents a novel approach to establish past periods of human and herbivore occupation in the Atlas mountains of Morocco. These organic compounds are faecally produced by omnivorous and ruminant mammals; the concentrations and ratios of the compounds are used in this study as proxies for past dynamics of human presence. In this study, stanol analysis is employed in tandem with multiproxy sedimentological, palaeoecological and geochronological data of a lake-margin sediment core to evaluate Holocene human presence around the high-elevation wetland system of the Yagour Plateau, in the High Atlas mountains (31.31°N, 7.60°W, 2460 m.a.s.l.). The site is a vital resource for modern pastoral communities, providing fodder for livestock during seasonal dry periods. Cultural institutions known as Agdals regulate access to this wetland and have been established since early-historic times at least. The Yagour Plateau is well-known for its remarkable abundance of undated petroglyphs, which may relate to the territorial delineation of these Agdals. However, direct dating of archaeological remains is rare and the timing of human presence on the High Atlas rangelands is not well known. Information gained on the dynamics of human presence of remote, high-elevation sites in the High Atlas may be helpful in improving the understanding of the relationships between Holocene climatic, anthropogenic and ecological signals. Here, we present new data from 25 stanol samples spanning the last 13 kyr, complemented by two multiproxy records that include pollen, charcoal and non-pollen palynomorphs. The temporal context of these proxy records is underpinned by high-resolution age-depth radiocarbon chronology. We observe elevated stanol ratios from 6.2 cal ka BP to modern times, likely indicating intermittent human presence on the plateau since the Mid-Holocene. High coprostanol concentrations between 4.9 to 4.0 cal ka BP are similar to modern levels and indicate peak human presence. Faecal biomarkers match well with pollen-based anthropogenic indicators, particularly Plantago pollen abundance. This study supports a significant human presence on the Yagour Plateau from the Mid-Holocene onwards, contributing to the study of long-term human presence and climate dynamics in a sensitive mountain region at the boundary of the Atlantic and Saharan climate systems. © Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License.
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    Rapid environmental changes of the Late-glacial and Holocene in a sediment record from the Yagour Plateau, High Atlas, Morocco
    (Copernicus GmbH, 2021-04-19) Cornelissen, HL; Fletcher, WJ; Hughes, PD; Bell, BA; Rhoujjati, A; Ewague, A; Fink, D
    The High Atlas mountains of Morocco represent a climatological frontier between the Atlantic and Saharan realms as well as a site of major Pleistocene glacier expansion. However, Late-glacial and Holocene environmental change is weakly constrained, leaving open questions about the influence of high- and low-latitude climate forcing and the expression of North Atlantic rapid climate changes. High elevation lakes on the sandstone plateaux of the High Atlas have been recognised as archives of Late Quaternary environmental change but remain little explored. Here, we present findings from new sedimentological, palaeoecological and geochronological investigation of a lake marginal sediment core recovered in June 2019 from the Ifard Lake located on the Yagour Plateau. The plateau is a distinctive sandstone upland located to the southeast of Marrakech in the High Atlas (31.31°N, 7.60°W, 2460 m.a.s.l.). The lake is located within a small, perched catchment area, offering an opportunity to isolate catchment effects and investigate atmospheric deposition of organic and inorganic tracers of past environmental change. The core stratigraphy reveals shifts between inorganic sands and lake muds with fluctuations in grain sizes and sediment reddening. The differences in these stratigraphic layers are most likely linked to hydrological changes associated with changing snowpack conditions and local catchment erosion dynamics. The core chronology is well-constrained by AMS radiocarbon dating of pollen concentrates, with the core sequence spanning the last ca. 14,000 years. The driving agents of environmental change on the plateau are inferred using a multiproxy approach, combining sedimentological analyses (particle-size by laser granulometry, elemental analysis by core-scanning XRF, C/H/N/S analysis), palynology (pollen, spores, non-pollen palynomorphs) and contiguous macrocharcoal analysis. High-resolution, well-constrained proxies therefore permit novel regional insights into past environmental and climatic changes at centennial timescales. A prime working hypothesis is that the imprint of wider palaeoclimatic changes of both the North Atlantic region and Saharan realm (African Humid Period, AHP) is detected at this site. Key climatic periods such as the Younger Dryas and multi-centennial cooling episodes around 8000 and 4200 years ago are distinctly characterised in the record by finer grain sizes and the accumulation of pollen-rich material and charcoal. These responses are thought to be governed by regional climate forcing and local snowmelt moisture supply to the Yagour Plateau. An increase in fine sediment supply, magnetic susceptibility and Fe content in the upper part of the core may be related to enhanced atmospheric dust deposition following the end of the AHP. Whilst taking anthropological influences on the local environment into account, this study will contribute to the detection of long-term and rapid climate changes in a sensitive mountain region at the rim of the Atlantic and Saharan climate systems.