Impactos ENSO en cuencas atlánticas de Sudamérica

Interannual changes in precipitation cause significant effects on the Pacific watersheds of South America. Large rivers flowing to the Atlantic Ocean as the Paraná and Uruguay are also influenced by ENSO-triggered floods causing significant impacts on the economies of Argentina, Brazil and Uruguay. At the same time, the floodplains of small rivers are also sensitive to strong ENSOs. Floods occur approximately simultaneously in subtropical watersheds of Brazil and high-latitude watersheds of North Patagonia. ENSO-triggered floods were recorded during the years 1941-42, 1982-83 and 1997- 98. Several floods impacted along the Itajaí River affecting the higher (Blumenau city) and lower estuary (Itajaí city). The Guaiba River, at the headlands of Lagoa dos Patos, has repeatedly flooded Porto Alegre. At the Río de la Plata basin, significant increases in the discharges were assigned to the Paraná and the Uruguay rivers. The small basin of the Quequén Grande River without extended floodplains is subject to periodic failure of its margins. The Colorado River, the northern limit of Patagonia, is allochthonous and its watershed was artificial and progressively modified; the ENSO event of 1983 caused an increase in its salinity due to the sudden reactivation of the DesaguaderoCuracó system.Los cambios interanuales en las precipitaciones causan significativos efectos en las cuencas pacíficas de Sudamérica. Los grandes ríos que fluyen hacia el Océano Atlántico como el Paraná y el Uruguay también son influenciados por estas inundaciones originadas por estos eventos ENSO causando significativos impactos en las economías de Argentina, Brasil y Uruguay. Asimismo, las planicies aluviales de los pequeños ríos también son sensibles a los ENSOs fuertes. Las crecidas ocurren casi simultáneamente en las cuencas subtropicales de Brasil como en las cuencas de altas latitudes de Patagonia. Inundaciones gavilladas por eventos ENSO fueron registradas en los años 1941-42, 1982-83 y 1997-98. Varias inundaciones afectaron al río Itajaí afectando las porciones más altas (Blumenau) y bajas del estuario (Itajaí). El río Guaíba, en las cabeceras de la Lagoa dos Patos, ha repetidamente inundado Porto Alegre. En la cuenca del Río de la Plata, incrementos significativos de su descarga fueron originados por los ríos Paraná y Uruguay. La pequeña cuenca del río Quequén Grande sin grandes planicies aluviales está sujeta a periódicos derrumbes de sus albardones. El río Colorado, límite norte de la Patagonia, es alóctono y su cuenca fue progresiva y artificialmente modificada; el ENSO de 1983 causó un aumento de su salinidad debido a la súbita reactivación del sistema DesaguaderoCuracó.Fil: Isla, Federico Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Toldo Junior, Elirio Ernestino. Universidade Federal do Rio Grande do Sul; Brasi

Coastal barriers from Argentina: Buenos Aires, Patagonia and Tierra del Fuego

Barriers, barrier islands and spits characterise low-lying coasts. However, they can grow along erosive coasts where there is a constant supply of sand, gravel, or both. At the Argentine coast, sandy barriers characterise the template coast of Buenos Aires. The availability of gravel at the Patagonian and Tierra del Fuego coasts induces the formation beach-ridge plains that can derived into coarse-grained spits. The morphology of these spits obeys to the basin depth and the availability of sediment. Recurved spits signify that the beach drift is locally modified by the action of waves or sediment-supply shortages. Some spits are today subject to local erosion (cannibalisation) that compensates these sediment deficits. Barriers and spits are ideal to locate harbours, marinas or touristic (resort) villages. However, the freshwater volumes inside their bodies are limited, even in areas where rain-fed aquifers have plenty of capacity. In this sense, resort villages are limited in their urban sprawl and planners should foresee these resource-based limitations

ENSO-triggered floods in South America: correlation between maximum monthly discharges during strong events

ENSO-triggered floods altered completely the annual discharge of many watersheds of South America. Anomalous 9 years as 1941, 1982-83, 1997-98 and 2015-16 signified enormous fluvial discharges draining towards the Pacific Ocean, but also to the Atlantic. These floods affected large cities built on medium-latitudinal Andes (Lima, Quito, Salta), but also those located at floodplains, as Porto Alegre, Blumenau, Curitiba, Asunción, Santa Fe and Buenos Aires. Maximum discharge months are particular and easily distinguished along time series from watersheds located at the South American Arid Diagonal. At watersheds conditioned by precipitations delivered from the Atlantic or Pacific anti-cyclonic centers, the ENSO-triggered floods are more difficult to discern. The floods of 1941 affected 70,000 inhabitants in Porto Alegre. In 1983, Blumenau city was flooded during several days; and the Paraná River multiplied 15 times the width of its middle floodplain. That year, the Colorado River in Northern Patagonia connected for the last time to the Desagûadero Chadileuvú - Curacó system and its delta received saline water for the last time. During strong ENSO years the water balances of certain piedmont lakes of Southern Patagonia are modified as the increases in snow accumulations cause high water levels, with a lag of 13 months. The correlation between the maximum monthly discharges of 1982-83 and 1997-98 at different regions and watersheds indicates they can be forecasted for future floods triggered by same phenomena. South American rivers can be classified therefore into ENSO-affected and ENSO-dominated for those within the Arid Diagonal that are exclusively subject to high discharges during those years.Fil: Isla, Federico Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Coastal urbanization strategies for resort locations, Argentina

Coastal cities have particular spatial urbanization trends conditioned by the dominant activities, meaning tourism, fishing or commerce. Notwithstanding that, there are other issues or restrictions that also conditioned the growing pattern of these villages or cities that can change during their development. In this sense, monocentric patterns (harbor cities) may evolve into a radial model related to main accessing routes. Touristic cities emplaced on barrier systems extended alongshore while their service areas installed at opposite directions where lots are cheaper. Some coastal villages grew exponentially in the last century in Argentina although they had original restrictions in the freshwater availability. Today, they are also conditioned to the recreational qualities of their beaches, or the disposal availability of residential sewages.Coastal cities have particular spatial urbanization trends conditioned by the dominant activities, meaning tourism, fishing or commerce. Notwithstanding that, there are other issues or restrictions that also conditioned the growing pattern of these villages or cities that can change during their development. In this sense, monocentric patterns (harbor cities) may evolve into a radial model related to main accessing routes. Touristic cities emplaced on barrier systems extended alongshore while their service areas installed at opposite directions where lots are cheaper. Some coastal villages grew exponentially in the last century in Argentina although they had original restrictions in the freshwater availability. Today, they are also conditioned to the recreational qualities of their beaches, or the disposal availability of residential sewages.Fil: Isla, Federico Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; ArgentinaFil: Isla, Maria del Pilar. Universidad Nacional de Mar del Plata. Facultad de Arquitectura, Urbanismo y Diseño; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentin

Sediment input from fluvial sources and cliff erosion to the continental shelf of Argentina

The coasts of southern Buenos Aires, Patagonia and Tierra del Fuego are dominated by cliff erosion. Mean rates of cliff retreat are estimated to be about 0.5-0.6 m/year by comparing old photographs with modern satellite images. Considering the height of the Patagonian and Fueguian cliffs (70 to 120 m), the volume of sediment eroded from these cliffs exceeded the volumes provided by the erosion of the cliffs of Buenos Aires (10 to 20 m height). These erosion rates support an estimated delivery of 217 million tons of sediment per year to the continental shelf, exceeding significantly the 22 millions of tons/year transported by the larger Patagonian rivers Negro and Colorado. However, the contribution of these rivers has decreased since the Late Pleistocene changes in the direction of transport of some watersheds. The Chubut and Chico de Santa Cruz rivers suffered reductions of 21-24% in their watershed areas, resulting in reductions of about 33-34% in the volume of water transported to the Atlantic Ocean per year. As the amount of sediment delivered to the Argentine continental shelf by cliff erosion is higher than the fluvial transport, it should be also considered in the balance of beaches fed by longshore transport.O litoral de Buenos Aires, Patagónia e Terra del Fuego é dominado pela erosão de falésias marinhas. As taxas de medias de recuo foram estimados em 0,5-0,6 m/ano, com base na comparação de fotografias aéreas antigas com imagens satelitárias modernas. Considerando a altura das falésias patagónicas e fueguinas (70 a 120 m), o volume de sedimento erodido supera os volumes que provêm das falésias de Buenos Aires (10 a 20 m). Estas taxas de erosão permitiram estimar um aporte de 217 milhões de toneladas por ano de sedimento à plataforma continental, superando os 22 milhões de toneladas/ano transportados pelos rios da Patagónia, Negro e Colorado. Além disso, a contribuição fluvial diminuiu devido às alterações na drenagem que afetaram algumas bacias desde o Pleistoceno Superior. Os rios Chubut e Chico de Santa Cruz sofreram reduções de 21-24% nas áreas de drenagem, o que significou diminuições de 33-44% nas contribuições de água para o Oceano Atlântico. Como o volume de sedimentos proveniente da erosão de falésias e fornecido à plataforma continental argentina supera o do fornecimento fluvial, tal deve ser também considerado na análise do balanço sedimentar das praias alimentadas pela deriva litorânea

Modern diatom assemblages in surface sediments from meso-macrotidal estuaries of Patagonia, Argentina

The composition and distribution of diatom assemblages from surface sediments in the littoral zone of meso and macrotidal estuaries from Patagonia (Argentina) were studied with the aim to recover modern data on diatom distribution applicable to future paleoenvironmental reconstructions in coastal areas of Southern South America. Twenty-seven sites were selected to cover the maximum spatial distribution along the Negro, Chubut, Santa Cruz valleys and San Julián Bay. Salinity, water temperature, pH, sediment grain size and organic matter content were measured. Multivariate methods (cluster, CCA and NMDS analysis) were explored to analyse the relation between biotic and abiotic data. The results showed that the spatial distribution and species composition of diatom assemblages are strongly related to salinity and temperature. The diatom assemblages of riverine conditions (without salt-wedge influence) were characterized by high abundances of the freshwater diatom species Cocconeis placentula, C. euglypta and Aulacoseira granulata, meanwhile high abundances of marine and marine-brackish species such as Paralia sulcata, Rhaphoneis amphiceros, Delphineis surirella and Diploneis interrupta were characteristic of estuarine conditions (i.e. under salt-wedge influence). As temperature is directly related to latitude there are differences between northern and southern Patagonian communities. Different proportions or combinations of the taxa produce the distinction between assemblages. In southern estuaries with lower temperatures, the diatom assemblages are less diverse.Fil: Espinosa, Marcela Alcira. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Isla, Federico Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Quaternary glaciolacustrine deposits around a Triple Junction site: Paleolakes at the foot of the Northern Patagonian Ice field (Argentina and Chile)

The area involved by the triple junction between the South American, Nazca and Antarctic plates activity was affected by Quaternary glaciations. Before 12,800 yrs BP an extended ice field occupied the top of the Patagonian Andes, irradiating glaciers towards the east and the west dominantly. Towards the east, the ice melted in piedmont lakes; towards the west, fjords melted into the Pacific Ocean. The Upper-Pleistocene climate amelioration caused the recession of those glaciers. Some piedmont lakes reversed their Atlantic outflow towards to the Pacific Ocean. The glaciers retreat caused the fluvial reactivations along crustal former faults that were located below the ice. The Patagonian ice field became therefore split into present Northern and Southern fields. At the second largest lake of South America, the Buenos Aires-General Carrera Lake, the water level dropped from about 500 m over present mean sea level to 230 m. Several glaciolacustrine deposits from this area are indicating significant variations caused by climatic changes, volcanism and tectonics, differing in spatial and temporal magnitudes. The triple junction activity involved subduction of the Chile Ridge below the continental South American plate, volcanic activity and faulting. During the glacier melting the Baker River captured three eastern-moving glacial systems towards the southwest, towards the Pacific Ocean. This rapid event is thought to occur 12,800 yrs BP. The lowering of these glaciolacustrine systems should be also interpreted in terms of the tectonic activity in the region and considering other processes operating in the lakes and within the watersheds.Fil: Isla, Federico Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Espinosa, Marcela Alcira. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Sedimentology of the Irene and la toma formations from the neogene of the Claromecó basin, Buenos Aires

La cuenca de Claromecó se ubica entre los positivos de Tandil y Ventania. La Formación Irene fue definida para el ámbito del sudoeste de esta Pampa Interserrana, Buenos Aires, para margas claras diaclasadas y lajadas que alcanzan 7 m de espesor en la Estación Irene del Ferrocarril General Roca. Estas rocas que comprenden lo que fue denominado "Araucanense" están subyaciendo limos arenosos carbonáticos rojizos que corresponden a sedimentos pampeanos de la Formación La Toma. De acuerdo a los contenidos fosilíferos y la presencia de escorias, estos sedimentos que coronan las lomas han sido equiparados a las Formaciones Monte Hermoso y Chapadmalal. Se postula entonces una edad pliocena para la porción aflorante (superior) de la Formación Irene y para la formación La Toma. El paisaje es de lomas coronadas por limos entoscados.The Claromecó Basin is located between the horst of Tandil and Ventania. The Irene formation is defined to the west of the Interserrana ("between ranges") Plain, Buenos Aires Province, for light-coloured carbonatic siltstones with joints that sums 7 m thick at the locality close to Irene Railway Station. These rocks comprising the Araucanense are underlying reddish sandy silts assigned to the Pampian sediments of La Toma Formation. According to the fossiliferous and escoria content, these sediments were similar to those outcropping as Monte Hermoso and Chapadmalal formations. It is therefore assumed a Pliocene age for the upper levels of the Irene Formation, as well as to the La Toma Formation. The hilly landscape is crowned by silt with calcretes.Fil: Isla, Federico Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; ArgentinaFil: Dondas, Alejandro. Provincia de Buenos Aires. Municipalidad de General Pueyrredon. Secretaría de Cultura. Museo Municipal de Ciencias Naturales Lorenzo Scaglia; ArgentinaFil: Oliva, Cristian. Museo Municipal de Ciencias Naturales Carlos Darwin. Punta Alta; Argentin