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Introdução do livro À descoberta da Ria Formosa

Publication . Moura, Delminda; Mendes, Isabel; Aníbal, Jaime

A Ria Formosa localiza-se na região mais meridional de Portugal, no litoral sul do Algarve e é uma das zonas húmidas socioeconómica e ecologicamente mais importantes de Portugal continental. Em 1978, a importância ecológica da Ria Formosa foi consagrada através do Decreto-lei 45/78 de 2 de maio, com o estatuto de Reserva Natural. No entanto, quase uma década depois, o estatuto foi alterado para Parque Natural da Ria Formosa (PNRF) pelo Decreto-lei 373/87 de 9 de dezembro. Esta alteração teve como objetivo compatibilizar a proteção deste importante sistema lagunar, com as atividades socioeconómicas que aí se desenvolvem. Os reconhecidos méritos de raridade, valor científico, ecológico e social da Ria Formosa, fazem com que esteja integrada na Rede Nacional de Áreas Protegidas, que lhe concede o estatuto legal de proteção para garantir a preservação da biodiversidade e serviços ecossistémicos bem como do seu património geológico e paisagístico.

2021Book part

Open access

Formation history and material budget of holocene shelf mud depocenters in the Gulf of Cadiz

Publication . Hanebuth, Till J.J.; King, Mary Lee; Lobo, Francisco J.; Mendes, Isabel

Mud depocenters (MDCs) are common elements on modern continental shelves and act as a major shallow-marine sink for fluviogenic material. These most proximal depocenters, thus, play a major role in material cycling and carbon availability on global and regional scales, though individual formation history, dependence on external forcing mechanisms, and material composition makes each of them a unique case. This study establishes a chronostratigraphic framework and deciphers the depositional dynamics for the two main MDCs on the continental shelf in the eastern Gulf of Cadiz, as a prime example, with the goal to calculate a regional sediment and carbon budget. Based on the analysis of 2040 km of subbottom profiles and 18 sediment cores, the fine-grained depocenters began to grow during maximum flooding around 6.5 cal ka BP. Sedimentation rates ranged between 2 and 35 cm/ka until 2.7 cal ka BP and increased significantly around the Roman Warm Period (30-200 cm/ka), caused by regional humidification as well as mining and agricultural activities. After 1.0 cal ka BP, sedimentation rates rose further (20-3000 cm/ka), due to land clearing in coincidence with erosion-favoring aridity during the Islamic period and the Medieval Climate Anomaly. Unprecedented sediment accumulation started with the Industrial Era. The total sediment volume of the two MDCs is 5.80 km(3) with a dry mass of 12,971 Mt. 85 Mt of organic matter and 3637 Mt of carbonate make this depocenter an important shallow-marine sink, with a total of 521 Mt carbon as a significant player in the regional terrestrial-marine carbon cycle.

2021Journal article

Restricted access

Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: stratigraphic architecture and controlling factors in a low fluvial supply setting

Publication . Carrión-Torrente, Álvaro; Lobo, Francisco José; Puga-Bernabéu, Ángel; Luján, María; Mendes, Isabel; Hanebuth, Till J. J.; Lebreiro, Susana; García, Marga; Reguera, María Isabel; Antón, Laura; Van Rooij, David; Cerrillo-Escoriza, Javier

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gila & SIM;o-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.

2023-09Journal article

Open access