Morphology, grain-size and faunistic composition of the macrotidal beaches of Tierra del Fuego Morfología, tamaño de grano y composición faunística de las playas macromareales de Tierra del Fuego

Morphodynamic models have been applied to macrotidal beaches. They are based on unimodal grain sizes and average dynamic parameters as the wave height and period at the breaker zone. Bimodal gravel beaches do not fit to these models because a) grain size is subject to spatial segregations (gravel and granules at the upper beach zones and fine sand at the lower-tide terrace), and b) wave dynamics vary temporarily during the tidal cycle: the beach has a reflective behaviour during high tide and dissipative during low tide. Superimposed to these morphodynamical constraints, along the Atlantic coast of Tierra del Fuego inherited factors control the coastal morphology. In low-lying coasts (South-American Plate portion), the Holocene sea-level fluctuation permitted the construction of beach ridge plains. On high-relief coasts (Scotia Microplate), the same fluctuation have little enough sediment available, and therefore pocket beaches developed between capes and sand accumulations at river outlets. Two areas were found of interest by their heavy mineral content: the Rio Chico beach-ridge plain, and the coastline between Ewan and Ladrillero estuaries. With regard to the molluscan beach composition, rocky bottom specimens dominate at the capes.<br>Los modelos morfodinámicos han sido aplicados a playas macromareales basados en granulometrías unimodales y parámetros dinámicos estables como la altura de ola y período estimados en la rompiente. Las playas bimodales de grava no se consideran en estos modelos debido a que las granulometrías están sujetas a segregaciones espaciales (gravas y gránulos en los sectores superiores de la playa, y arena fina en los sectores inferiores) y variaciones temporales en la dinámica de las olas condicionadas por la marea (la playa tiene una dinámica reflectiva durante marea alta y disipativa durante marea baja). Sobreimpuestos a estas limitaciones morfodinámicas, en la costa atlántica de Tierra del Fuego se dan factores heredados que controlan la morfología costera. En costas bajas (porción de la Placa Sudamericana), la fluctuación holocena del nivel del mar permitió la construcción de planicies de cordones de playas. En las costas de alto relieve (Microplaca de Scotia), la misma fluctuación no tuvo suficiente sedimento disponible y se desarrollaron playas de bolsillo entre cabos y acumulaciones de arena en las desembocaduras de ríos. Dos áreas resultaron de interés por su contenido en minerales pesados: la planicie de cordones de playa del Río Chico y el sector comprendido entre los estuarios de los ríos Ewan y Ladrillero. En relación a la composición faunística de las playas, los moluscos que prefieren fondos rocosos son más abundantes en los cabos

Hydrological processes interconnecting the two largest watersheds of South America from multi-decadal to inter-annual time scales: A critical review

The hydrological aspects of the Amazon and the La Plata basins are interconnected through southward moisture transport performed by the Low-Level Jet east of the Andes and the South Atlantic Convergence Zone. Remote effects of sea surface temperature variability in the Pacific and the Atlantic are of varied periodicities, from multi-decadal to inter-annual time scales. Major oscillations thus far detected are Atlantic Multi-decadal Oscillation, Pacific Multi-decadal Oscillation, North Atlantic Oscillation, Atlantic Dipole, Antarctic Oscillation, and the El Niño Southern Oscillation. In the multi-decadal, inter-decadal and decadal time scales, the effects of climate variability over the hydrological processes that interconnect the Amazon and La Plata watersheds are felt predominantly in the South American Monsoon season, while on the inter-annual scale the effects vary along the year. The hydrological memory in Amazonian soils is also responsible for the inter-annual variability of hydrology of the Amazon Basin. Due to the effects of soil water on evapotranspiration, the hydrological memory can affect the supply of moisture to the La Plata Basin, influencing the inter-annual variability of this basin. The implications of the observed oscillations to the hydrological and climatological variability in the two basins are discussed and synthesized in this article. Hypotheses for future research are formulated. © 2019 Royal Meteorological Societ