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Browsing by Author "Rosa, Francisca Manuel Prudêncio"

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  • Climatic variability and recent sedimentation in the Continental Shelf off the Guadiana River
    Publication . Rosa, Francisca Manuel Prudêncio; Dias, João Manuel Alveirinho; Ferreira, Óscar
    The current work investigates the main depositional events that occurred on the continental shelf adjacent to the Guadiana River mouth (northern Gulf of Cadis, southwestern Iberian Peninsula) during the late Pleistocene and the Holocene, and relates them with main forcing mechanisms, namely climate change, mean sea-level rise and the impact of human activities in the region. An integrated approach based on several palaeoindicators was conducted in four sediment cores collected on the shelf, including sedimentological (sediment grain-size, sand fraction composition and morphoscopy of quartz grains) and micropalaeontological (benthic foraminifera) data, integrated into a temporal framework obtained from AMS (Accelerated Mass Spectometry) radiocarbon (14C) datings. One of these cores was located on the inner shelf and the other three on the mid-shelf mud body. Data analysis and integration allowed to recognize the specific evolution of the depositional patterns in each one of these shelf domains and to interpret the evolution of the mud body. Moreover, the higher resolution of the muddy deposits enabled to reconstruct with greater detail the history of the region. During the phase of fast sea-level rise that marked the late Pleistocene and the beginning of the Holocene, both shelf domains revealed a transgressive trend, with the rise in sea level constituting the main controlling factor of the type and amount of sediments that reached the shelf, and also of the main benthic foraminiferal species that colonized the middle shelf environment. As the mean sea level approached its present-day position around mid- Holocene, the climatic mechanisms became preponderant in determining the evolution of the depositional and ecological patterns across the shelf until ca. 2,500 years ago. Profound changes were observed during the last ca. 2,500-1,500 years, with higher amounts of sediments, mostly fine-grained, starting to reach the shelf and the onset of a clear modification on the benthic foraminifera of the mud body. The Roman and Islamic occupation of southern Iberia seemed to have been the main cause behind these changes, as they led to intensive land-use activities that enhanced soil erosion along the Guadiana Basin. Since then, and until modern times, the depositional record of the shelf and of the mud body, in particular, showed that the coupled-action of the anthropogenic impact with the more recent climate variations, these largely modulated by the North Atlantic Oscillation (NAO), has been the main forcing agent for the environmental changes occurring in the study area.
    2014Doctoral thesis Open access Show more