The Parnaiba River Delta - from modern hydro and morphodynamics to sea level change

This study presents the first findings regarding the hydrography, morphodynamics, hydrodynamics and sea-level change on Parnaíba River (PR) and its delta. The PR is 1,400 km long and located in NE Brazil. It forms an asymmetric wave dominated delta, the Parnaíba River Delta (PRD). The delta region is approximately 100 km wide and has tidal channels forming an estuarine-lagoonal system, west of PR. The delta is located in a transition zone in terms of climatic and oceanographic conditions. Despite the existence of a river dam on its mid-course, the river has a moderate (approximately 91 mg/l, in average) suspended sediment load which is mainly attributed to the geology and the climatic conditions of its drainage basin. Rainfall data from 1965 to 2009 revealed seasonal variations on rainfall and suspended sediment concentration (SSC). Moreover, harmonic analysis of time series revealed a correlation of both, rainfall and SSC, with El Niño-Southern Oscillation (ENSO). The suspended sediment concentration was calculated from a set of 12 multispectral satellite images (CBERS 2-B and LANDSAT TM 5), which were calibrated using in situ measurements. Using averaged river discharge and remote sensed suspended sediment concentration it was possible to estimate the amount of sediment that is transported through the PR to the continental shelf. The PR is the primary sediment source to the adjacent coast and this is evidenced by the shoreline stability and progradation noticed at the vicinities of the river mouth (observed on decadal time scale using satellite images). The river runoff interferes on the direction of the offshore bottom currents on the continental shelf up to 4 km in front of the river mouth. It acts as a hydrodynamic groin preventing sediment bypass. Offshore bathymetry and seismic profiles depicted evidences of past sea level on the continental shelf offshore PRD in the form of incised valley and paleo-channels. Interpretations of architectural elements, seismic facies and seismic boundaries were related to extreme events of sea level such as sea level low- and highstand providing relative age control for the formation and complete burial of the paleo-channels. Relating worldwide reconstructions of sea level curves to the interpretations it is suggested that the valley incision occurred during the Late Pleistocene sea-level drop and lowstand (70,000 – 20,000 years BP). Moreover, the valley infill indicates the flooding of the shelf during deglacial sea-level rise that reached the mid-Holocene highstand around 5,500 years BP

Vulnerabilidade costeira e dinâmica sedimentar - Campo de dunas de Mangue Seco, Guamaré/RN, NE do Brasil.

We determined migration rates of three dunes, based on measurements and comparison of volume variation between June, 2013 and May, 2014. The study area is located in Alegria Wind Farm, in Guamaré municipality, located in the septentrional coast of the state of Rio Grande do Norte, Northeastern Brazil. The research applied a combination of measurements using geodetic GPS and sediment collection, which was used to characterize the dune morphodynamics. We generated MDT's using the interpolation points (kriging) and calculated its volume. The volume gained in June 2013 (132.470 m3). We compared the sediment volumes in consecutive months, and the results showed that there was an increase of the dune between June to July (+ 31.545m3) and August to September 2013 (10.341m3 +), and decreased from July to August 2013 (-7.700m3). Despite the reduction in the period from July to August, the final volume of the dune is higher than the initial. Transversal profiles of the dune show that the volume changes happened because of leeward and windward. The wind speed to start sediment transportation (UCT), showed that these NE winds are more effective, and the increase of the volume of the dunes is related to its occurrence. The MDT generated shows that these are barchan dunes. Between June to September 2013 and from January to May 2014, dunes migrated 6m to SW direction and ~ 5m to NW, which results in a movement of 1.5 m / a month and 1.25 m / a month, respectively. According to the weather station of Macau-RN, the UCT speed and the transversal profiles, the highest speed of migration occurred between June to July and August to September. Morphological variation of the dune is influenced by the variation in the frequency of occurrence of NE winds.Buscamos determinar taxas de migração de três dunas, baseando-se em medições da variação de volume entre junho de 2013 a maio de 2014. A área em estudo localiza-se no Parque Eólico Alegria, município de Guamaré, litoral setentrional do Estado do Rio Grande do Norte, Nordeste/Brasil. Utilizou-se uma combinação de medições de GPS geodésico e coleta de sedimentos para caracterizar sua morfodinâmica. Foi gerado o MDT (Modelo Digital do Terreno), utilizando a krigagem e foi calculado o seu volume. O volume no mês de junho de 2013 foi de 132.470 m3. Comparou-se com os volumes nos meses consecutivos e os resultados mostraram que houve aumento da duna entre junho-julho de 2013 (+31.545m3) e agosto-setembro de 2013 (+10.341m3), e redução entre julho-agosto de 2013 (-7.700m3). Apesar da redução entre julho-agosto, o volume calculado da duna é superior ao volume inicial. Perfis transversais na duna mostram que as modificações ocorreram a sotavento e barlavento. A velocidade do vento para início do transporte sedimentar (Uct), mostrou que estes de NE são mais efetivos, e o aumento no volume das dunas está relacionado à sua ocorrência. O MDT gerado mostra que as dunas são barcanas. Entre junho-setembro de 2013 e janeiro-maio de 2014, as dunas migraram 6 metros para SW e ~5m para NW, o que resulta em 1,5 m/mês e 1,25 m/mês, respectivamente. De acordo com a estação meteorológica de Macau/RN, da velocidade Uct e dos perfis transversais, a maior velocidade de migração ocorreu entre junho-julho e agosto-setembro. A variação morfológica da duna é influenciada pela variação na frequência de ocorrência dos ventos de NE

Assessing Holocene Evolution of the Parnaiba River Delta using Petrophysical, Radiocarbon Dating, and Sedimentological Analysis

The Parnaíba River Delta, located in northeastern Brazil, is one of the few examples of a deltaic depositional system with its pristine characteristics well preserved. This has placed it the spotlight of scientific research for the most diverse areas. The present work aimed to identify changes in the depositional environment based on stratigraphic and sedimentological analysis. Vibracores were collected in several places such as an old mangrove forest, in active tidal channels and supratidal swamp zones. The study included sediment analysis associated with petrophysics (Gamma Ray Spectrometry) and age dating by the radiocarbon method. In the first phase, the gamma-ray spectral analysis and the photographic record of the cores were carried out, followed by the stratigraphic description (color, texture, presence of organic matter, fossil content, sedimentary structures), as well as the identification and selection of material for dating. Subsequently, the cores were sampled at regular intervals, every 4 cm, for grain size, compositional (organic matter and calcium carbonate quantification), and mineralogical analyses. The results obtained showed mineralogical variations, which indicate changes in sedimentary origin. The gamma-spectrometric data tend to show higher values with the decrease of the grain and are associated with the sedimentological, stratigraphic, and mineralogical data, improving the interpretation of the depositional history. The contents of organic matter and calcium carbonate, in general, presented variations related to the grain size, with fine sediments (fine sand, silt and clay) presenting higher contents of organic matter, while carbonate is related to the presence of shells. Datings showed ages ranging from 4057± 22 BP to recent (1950 AD). The integration and joint analysis of the data allowed a better interpretation of the Late Holocene evolution of the old channels of the Parnaiba river that are currently working as a system of tidal channels

Vulnerabilidade costeira e dinâmica sedimentar - Campo de dunas de Mangue Seco, Guamaré/RN, NE do Brasil.

We determined migration rates of three dunes, based on measurements and comparison of volume variation between June, 2013 and May, 2014. The study area is located in Alegria Wind Farm, in Guamaré municipality, located in the septentrional coast of the state of Rio Grande do Norte, Northeastern Brazil. The research applied a combination of measurements using geodetic GPS and sediment collection, which was used to characterize the dune morphodynamics. We generated MDT's using the interpolation points (kriging) and calculated its volume. The volume gained in June 2013 (132.470 m3). We compared the sediment volumes in consecutive months, and the results showed that there was an increase of the dune between June to July (+ 31.545m3) and August to September 2013 (10.341m3 +), and decreased from July to August 2013 (-7.700m3). Despite the reduction in the period from July to August, the final volume of the dune is higher than the initial. Transversal profiles of the dune show that the volume changes happened because of leeward and windward. The wind speed to start sediment transportation (UCT), showed that these NE winds are more effective, and the increase of the volume of the dunes is related to its occurrence. The MDT generated shows that these are barchan dunes. Between June to September 2013 and from January to May 2014, dunes migrated 6m to SW direction and ~ 5m to NW, which results in a movement of 1.5 m / a month and 1.25 m / a month, respectively. According to the weather station of Macau-RN, the UCT speed and the transversal profiles, the highest speed of migration occurred between June to July and August to September. Morphological variation of the dune is influenced by the variation in the frequency of occurrence of NE winds.Buscamos determinar taxas de migração de três dunas, baseando-se em medições da variação de volume entre junho de 2013 a maio de 2014. A área em estudo localiza-se no Parque Eólico Alegria, município de Guamaré, litoral setentrional do Estado do Rio Grande do Norte, Nordeste/Brasil. Utilizou-se uma combinação de medições de GPS geodésico e coleta de sedimentos para caracterizar sua morfodinâmica. Foi gerado o MDT (Modelo Digital do Terreno), utilizando a krigagem e foi calculado o seu volume. O volume no mês de junho de 2013 foi de 132.470 m3. Comparou-se com os volumes nos meses consecutivos e os resultados mostraram que houve aumento da duna entre junho-julho de 2013 (+31.545m3) e agosto-setembro de 2013 (+10.341m3), e redução entre julho-agosto de 2013 (-7.700m3). Apesar da redução entre julho-agosto, o volume calculado da duna é superior ao volume inicial. Perfis transversais na duna mostram que as modificações ocorreram a sotavento e barlavento. A velocidade do vento para início do transporte sedimentar (Uct), mostrou que estes de NE são mais efetivos, e o aumento no volume das dunas está relacionado à sua ocorrência. O MDT gerado mostra que as dunas são barcanas. Entre junho-setembro de 2013 e janeiro-maio de 2014, as dunas migraram 6 metros para SW e ~5m para NW, o que resulta em 1,5 m/mês e 1,25 m/mês, respectivamente. De acordo com a estação meteorológica de Macau/RN, da velocidade Uct e dos perfis transversais, a maior velocidade de migração ocorreu entre junho-julho e agosto-setembro. A variação morfológica da duna é influenciada pela variação na frequência de ocorrência dos ventos de NE