Sedimentary Processes on the NW Iberian Continental Shelf since the Little Ice Age

• Published in: Estuarine, Coastal and Shelf Science
• Main Authors: Martins, V., Figueira, R.C.L., França, E.J., Ferreira, P.A.L., Martins, P., Santos, J.F., Dias, J.M.A., Laut, L.M., Soares, A.M.M., Ferreira da Silva, E., Rocha, F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2012
• Subjects: NW Iberian Continental Shelf; North Atlantic Oscillation; Anthropic influence; Multiproxy approach; Late little ice age; North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/10773/9013; https://doi.org/10.1016/j.ecss.2012.03.004

The OMEX core CD110 W90, retrieved from the Douro Mud Patch (DMP) off the River Douro in the north of Portugal, records the period since the beginning of Little Ice Age (LIA). The core chronology is based upon the data attributes for 210 Pb, 137 Cs and a 14 C dating from a level near the core base. Geochemical, granulometric, microfaunal (benthic foraminifera) and compositional data suggest the occurrence of precipitation changes which may have been, at least partially, influenced by the North Atlantic Oscillation (NAO), that contributes to the regulation of the oceaneatmosphere dynamics in the North Atlantic. Southwesterly Atlantic storm track is associated with the negative phases of the NAO, when the Azores High is anomalously weak, higher oceanographic hydrodynamism, downwelling events and increased rainfall generally occurs. Prevalence of these characteristics during the LIA left a record that corresponds to phases of major floods. During these phases the DMP received a higher contribution of relatively coarse-grained terrigenous sediments, enriched in quartz particles, which diluted the contribution of other minerals, as indicated by reduced concentrations of several lithogenic chemical elements such as: Al, As, Ba, Ce, Co, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Rb, Sc, Sn, Th, V and Y. The presence of biogenic carbonate particles also underwent dilution, as revealed by the smaller abundance of foraminifera and correlative lower concentrations of Ca and Sr. During this period, the DMP also received an increased contribution of organic matter, indicated by higher values of lignin remains and a benthic foraminifera high productivity index, or BFHP, which gave rise to early diagenetic changes with pyrite formation. Since the beginning of the 20th century this contribution diminished, probably due to several drier periods and the impact of human activities in the river basins, e.g. construction of dams, or, on the littoral areas, construction of hard-engineering structures and sand extraction activities. ...