The Southwestern Atlantic Ocean: present and past marine sedimentation

Marine Geology is one of the most recently developed branches of the geological sciences, which began to actively evolve after the mid XX century when the “modern” research techniques for obtaining really trustworthy data from the ocean floor and subbottom appeared, such as high resolution bathymetry, seismic, sea-bottom profilers, submarine photography and sea-floor sampling. In the Southwestern Atlantic continental margin the first great impulse occurred in the 1950´s and 1960´s by the agreement achieved between the Lamont-Doherty Earth Observatory (LDEO) of the Columbia University (USA) and the Argentina Hydrographic Survey (SHN). It was a pioneering work at a global scale as it represented a leading case for developing marine seismic technologies at sea useful for understanding the major oceanic sedimentary processes and the subbottom structure (e.g., Ahrens et al., 1971). Also in the 1960’s, another major agreement between CONICET (Argentina) and Woods Hole Oceanographic Institution (USA) allowed the acquisition by the Argentine government of the former research vessel Atlantis (later named, under Argentine flag, as “El Austral” and presently “Dr. Bernardo Houssay”), which was the first ship specifically built for oceanographic research and one of the most famous and internationally recognized because of its contribution to the knowledge of the ocean floors between 1939 and the latest 1950´s, including the findings that initially supported the continental drift´s theory. Following that, several national initiatives helped to advance in the development of marine geological sciences in the region. Among the most important we can mention: the REMAC Project in Brazil in the 1960’s and 1970’s -that allowed the participation of several Brazilian universities as well as North American research institutions-, the agreement between the SHN and the Uruguayan Oceanographic, Hydrographic and Meteorological Survey (SOHMA) in the 1970 ´s and 1980´s under the framework of the Administrative Commission for the Río de la Plata (CARP), the agreement between SOHMA and the Rio Grande do Sul University (URGS, Brazil) in the 1980´s and 1990´s, and the Projects MARGEN in Argentina and REVIZEE in Brazil - that began in the 1980´s-. The highly significant results that arose from those agreements and national projects impulsed the Argentina-Brazil-Uruguay geological communities to focus on the importance of deeply studying the ocean environments in the region and the needs to organize working teams aimed at developing research programs on the subject

Seasonal and spatial variations of saltmarsh benthic foraminiferal communities from North Norfolk, England

Time series foraminiferal data were obtained from samples collected from three sites at Brancaster Overy Staithe, Burnham Overy Staithe and Thornham on the North Norfolk coast over a 1-year period. At each collection point, six environmental variables—temperature, chlorophyll, sand, mud, pH and salinity—were also measured. The principle aim of this study was to examine the benthic foraminiferal fauna in regard to the temporal variability of foraminiferal abundance, seasonal trend, dominant species, species diversity and the impact of environmental variables on the foraminiferal communities in the top 1 cm of sediment over a 1-year time series. The foraminiferal assemblages at the three sites were dominated by three species: Haynesina germanica, Ammonia sp. and Elphidium williamsoni. Foraminiferal species showed considerable seasonal and temporal fluctuation throughout the year at the three investigated sites. The foraminiferal assemblage at the three low marsh zones showed a maximum abundance in autumn between September and November and a minimum abundance observed between July and August. There were two separate peaks in the abundance of Ammonia sp. and E. williamsoni, one in spring and another in autumn. In contrast, H. germanica showed a single peak in its abundance in autumn. A generalized additive modelling approach was used to explain the variation in the observed foraminiferal abundance and to estimate the significant impact of each of the environmental variables on living foraminiferal assemblages, with taxa abundance as the dependent variable. When included in the model as predictors, most of the environmental variables contributed little in explaining the observed variation in foraminiferal species abundance. However, the hypotheses for differences amongst sites, salinity and pH were significant and explained most of the variability in species relative abundance

Paleoproductivity changes during the Holocene in the inner shelf of Cabo Frio, southeastern Brazilian continental margin: Benthic foraminifera and sedimentological proxies

Sedimentological and benthic foraminifera analyses carried out on a core (length 4.15 in, collected at 22 degrees 56`31 `` S and 41 degrees 58`48 `` W, at a water depth of 43 in) sampled from the inner shelf of Cabo Frio, southeastern Brazilian continental margin, allowed identification of different hydrodynamic and productivity regimes related to sea-level fluctuations and/or climatic changes, during the last 9.4 ka cal BP. Prior to 7.0 ka cal BP, a less intense hydrodynamic and lower productivity regime occurred at lower sea levels and under drier climatic conditions. Between 7.0 and 5.0 ka cal BP, relatively stronger local oceanic circulation and relatively high productivity were observed, in a scenario of rising sea levels and more humid conditions. From 5.0 to 3.0 ka cal BP, bottom currents weakened and input of nutrients increased, with productivity levels similar to the previous phase at lower sea level and in a drier climate. From 3.0 ka cal BP up to the present, stronger hydrodynamic conditions and a higher productivity regime are linked to the establishment of the upwelling process in Cabo Frio. From 2.5 ka cal BP to the present, upwelling enhancement has been recognized, resulting from the combined action of NE winds and the intensification of the meandering pattern of the Brazil Current (BC). (C) 2008 Elsevier Ltd and INQUA. All rights reserved

Estudios tafonómicos en foraminíferos bentónicos como proxy de \ud hidrodinámica y sedimentología en el gradiente Río de La Plata – Océano \ud Atlántico Sur Occidental

Los foraminíferos bentónicos representan un excelente proxy geológico, ya que sus \ud caparazones son incorporados en el sedimento y pasan a comportarse como granos \ud sedimentares durante los eventos de transporte y erosión, permitiendo así, el registro \ud de condiciones y eventos que ocurren en los océanos. De este modo, son usados para \ud describir patrones de hidrodinámica y evaluar índices de deposición, erosión y \ud retrabajamiento del sedimento en los ambientes marinos. Concretamente, las regiones \ud costeras representan zonas de alta complejidad ambiental, debido a que en ellas se \ud da la mezcla de agua tanto de origen continental como marino, y a su vez, al efecto de \ud la descarga fluvial que aporta material particulado del continente para el océano. El \ud Río de la Plata (RdLP) representa el cuarto mayor estuario del mundo y el segundo del \ud continente americano, lo cual convierte al sistema RdLP-Océano Atlántico en un \ud complejo gradiente estuarino de interés en estudios sedimentológicos con posteriores \ud aplicaciones paleo-climáticas y paleo-ecológicas del Cuaternario Superior. En el \ud presente estudio, se registra a partir de las asociaciones muertas, para la región del \ud estuario entrada de agua marina hasta la zona del frente termohalino. Dichas \ud asociaciones se caracterizaron por especies típicas de plataforma y aguas frías. La \ud región marina del RdlP registró los mayores porcentajes de abrasión y fragmentación \ud de caparazones, indicando una zona de alta energía. Por otro lado, en la región más \ud oceánica las asociaciones muertas reflejaron un transporte en dirección norte, \ud influenciado por la pluma del RdlP. Cabe resaltar la presencia en esta región de una \ud isla barrera, vestigio de una paleo-costa producto de una regresión Holocénica. Este \ud local se caracterizó por un aumento de la abrasión y fragmentación mostrando la gran \ud hidrodinámica presente. En todos los casos existió correlación entre las señales \ud tafonómicas y los datos geo-químicos (sedimentología, pH, oxígeno disuelto, carbono \ud orgánico y nitrógeno total

Ecosystem health of Montevideo coastal zone: A multi approach using some different benthic indicators to improve a ten-year-ago assessment

A study on the benthic ecosystem health was performed to assess the environmental quality of Montevideo coastal zone, in view of the construction of a new sanitation system. Data were compared to previous research undertaken 10 years ago, and biochemical composition of organic matter, heavy metals, organic matter, phytopigments, benthic diatoms, macrofauna community structure and a biotic index (AMBI) were used as proxies. Results indicate an environmental quality-gradient, with the worst conditions within the inner stations of Montevideo Bay and an improvement towards the adjacent coastal zone. Higher levels of chromium, lead, phaeopigments, organic biopolymers and poor benthic macrofauna and diatom communities, characterised the hypertrophic innermost portion of Montevideo Bay. Data indicated a clear deterioration of the adjacent coastal zone comparatively to that observed 10 years ago. The complementary use of approaches not applied before (benthic diatoms and organic biopolymers) with those formerly applied improve our assessment of the trophic status and the environmental health of the area. (C) 2010 Elsevier B.V. All rights reserved.Programa de Desarrollo Tecnologico[PDT 63-028]Programa de Desarrollo TecnologicoIntendencia Municipal de MontevideoIntendencia Municipal de MontevideoSNI-ANIISNI-ANIIPEDECIBAPEDECIB