VARIABILIDADE CLIMÁTICA E SEDIMENTAÇÃO RECENTE NA PLATAFORMA CONTINENTAL SOB INFLUENCIA DO RIO GUADIANA

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Natural and human-induced Holocene paleoenvironmental changes on the Guadiana shelf (northern Gulf of Cadiz)

Publication . Mendes, Isabel; Dias, J. A.; Schönfeld, J.; Ferreira, Óscar; Rosa, F.; Gonzalez, R.; Lobo, F. J.

Three contrasting sedimentary environments on the continental shelf off the Guadiana River (northern Gulf of Cadiz) were integrated in a chronological framework and analysed in terms of sedimentology and benthic foraminiferal assemblages to understand the Holocene paleoenvironmental evolution. The analysed environments differ in terms of their depositional regimes and benthic foraminiferal assemblages. However, a dominant fluvial origin of the sand fraction was observed in all three environments. Holocene sedimentary processes were mainly controlled by natural (sea level changes and climate variations) and human-induced processes (e.g. deforestation, agriculture) along four evolutionary stages. The three older stages were mainly influenced by natural processes, such as sea level variations and fluvial inputs, whereas the most recent stage reflects a combination of climatic- and human-induced processes. A deepening of sedimentary environments related to a period of rapid sea level rise, strongly influenced by river discharges occurred from c. 11,500 to c. 10,000 cal. yr BP. A reduction in sediment export to the shelf, as a result of the continuous and rapid sea level rise and enhanced estuary infilling reflects the second stage, from c. 10,000 to c. 5000 cal. yr BP. The beginning of the third stage, from c. 5000 to c. 1500–1000 cal. yr BP, is marked by a sea-level slowdown and the relatively stable climate and environmental conditions. The fourth stage, from c. 1500–1000 cal. yr BP to Recent times, reflects the intensification of human-induced processes and climatic variability in the Guadiana River basin. This stage also reflects modern depositional conditions, with the formation of a proximal prodeltaic wedge and a distal muddy body.

2012Journal article

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The continental shelf off the Guadiana estuary

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The continental shelf off the Guadiana estuary

Publication . Mendes, Isabel; Rosa, Francisca; Moura, Delminda; Mendes, I.; Gomes, Ana; Aníbal, Jaime

The Continental shelf is the seafloor area around a large land mass where the sea is relatively shallow compared with the open ocean.This major physiographic domain is comprised between the shoreline and the shelf break located at variable water depths (generally, around 200 m water depth) and variable extensions (average width of about 80 km). The continental shelf off the Guadiana estuary is the area in front of the Guadiana River mouth,which is influenced by the discharges of the Guadiana River Basin.This area is located in the southern border between Portugal and Spain, in the middle part of the northern Gulf of Cadiz continental shelf, southwestern Iberian Peninsula.

2017Book part

Open Access

Living, dead and fossil benthic foraminifera on a river dominated shelf (northern Gulf of Cadiz) and their use for paleoenvironmental reconstruction

Publication . Mendes, Isabel; Dias, J. A.; Schönfeld, J.; Ferreira, Óscar; Rosa, F.; Lobo, F. J.

Same-area comparison between patterns of Recent (living) and Holocene benthic foraminiferal assemblage composition is essential to validate their utility as proxies for paleoenvironmental reconstructions. Such reconstructions have scarcely been attempted in shelf environments. In this study, we compared living (stained), dead and Holocene benthic foraminiferal assemblages from the Gulf of Cadiz continental shelf off the Guadiana River. On average, 99% of the living benthic foraminiferal species were preserved in the dead assemblage and 95% in the fossil record. Several common species were assessed as indicators for certain environmental factors, including river discharge, supply of terrestrial organic matter, heavy metal concentrations, oxygen levels, substrate properties, hydrodynamic energy levels, sea-level rise and human impact. The paleoenvironmental reconstruction depicted five stages of Holocene environmental evolution of the Guadiana shelf over the last 11500 Cal yr BP. The characteristics of the stages, and the transitions between them, were in particular driven by changes in sea-level, influx of terrestrial organic matter and limits of productivity.

2013Journal article

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