Andrade et al.: Sea level oscillations in shallow waters 245 Tidal and subtidal oscillations in a shallow water system in southern Brazil Sea level oscillations in time scales between hours and days have a great vertical amplitude regarding the low lying coastal gradient of the beaches in the Rio Grande do Sul coast. However, the mechanism of oscillations is poorly understood since the scarcity of observational data makes it impossible to determine the forces that control sea level oscillations. Therefore, hourly sea level and wind time series with a time period of 650 days were examined. It has been found that the mean tidal and subtidal amplitudes were very similar to each other and that a considerable portion of the energy from sea level oscillations was due to astronomical forces. A new perspective was introduced when high and low frequencies were compared, leading to the comprehension that astronomical tides should be considered in coastal studies in southern Brazil. The sea level time series analyzed in this study showed that the maximum amplitude of the high spring tide was 0.53m, and that the subtidal rise caused by the wind reached up to 0.66m. In general, when large tidal and subtidal amplitudes are added, it can generate extreme events of sea level rise on the coast, which constitute a direct threat to coastal communities and habitats.

This paper describes the evolution of a sector of the southern coastal plain of the Pelotas Basin, southern Brazil, between the last Pleistocene sea-level lowstand and the Holocene highstand, based on geomorphology and high-resolution stratigraphy. A fluvial drainage system associated with an incised valley developed during the Last Glacial Maximum (LGM) was identified. Two highresolution 2D and 2.5D geophysical profiles using Ground-Penetrating Radar (GPR) show a Pleistocene fluvial system's former path, starting close to its present mouth inside Mirim Lagoon crossing the coastal barriers and reaching the inner continental shelf, covering some 60 km across the coastal plain. During the LGM, with the sea-level at −120 to −130 m and the coastline positioned close to the shelf edge (distant 200 km from the present coastline), the fluvial system excavated a ~31.5-m deep channel. Two cores, 36 and 32 m long, show that the paleochannel was filled with sedimentary deposits after 19.4 ka BP, and the facies succession represents the transition from fluvial, to estuarine, to the coastal barrier, and finally to inner shelf depositional environments, generated by processes connected to LGM and the Postglacial Marine Transgression (PMT). The study region behaved as a sediment by-pass zone, connecting the adjacent coastal plain's inner portion with the inner continental shelf. The studied area presents an unusual record of the LGM at a coastal plain domain.

Calculation of the coastal sediment budget involves estimation of the timing and intensity of processes of erosion, transport, and deposition, as well as an understanding of local and regional sediment dynamics. The modern sedimentary deposits present in the coastal zone constitute the physical basis of coastal ecosystems. Knowledge of the dynamics of these sediments from the source to sink area, through regional sediment management, is critical to understanding the long-term stability of the coastal zone and the fate of these important natural resources. In this article, the littoral cell concept has been applied to the midcoast of Rio Grande do Sul, a wave-dominated and dissipative-intermediate sandy coast in southern Brazil. To analyze littoral drift variations along the 275 km long study area, the shoreline was divided into 12 cells. Littoral drift rates were estimated and compared using the energy flux method. Wave parameters were obtained from WAVEWATCH III. The sand volume of the coastal dune field (4.20 billion m3) was quantified using satellite imagery and the aeolian transport rates estimated utilizing the sediment budget residual. The net annual longshore transport rates obtained with the Coastal Engineering Research Center equation range from 0.60 to 2.63 million m3 per year. The littoral drift rates obtained with the Van Rijn (2001) and Kamphuis (1991) equations range between 0.15 and 1.00 million m3 per year. Based on the sediment budget and dune field age, the CERC formula seems more appropriate to estimate longshore transport.

ABSTRACT. This paper addresses the characterization of the geomorphology and palaeo-evolution of the La Plata River on the south Brazilian continental shelf,through bathymetric data and sedimentary and palynological analysis from sediment core samples. The analysis allowed us to characterize a transgressive depositionalsequence in the La Plata River palaeo-channel. The palynological sequences revealed continental fresh water environments, that involved into lagoonal and mixohalineenvironments and then into shallow marine environments towards the top, thus characterizing a fluvial-estuarine environment. These new data offer sufficient informationto establish the palaeo-geographic evolution of the La Plata River palaeo-channel and its local influence on the sedimentation of the Rio Grande do Sul Statecontinental shelf.Keywords: palaeo-valley, continental shelf, marine transgression, La Plata River. RESUMO. O presente trabalho trata da evolução e caracterização geomorfológica do paleocanal do rio de La Plata sobre a plataforma continental sul-brasileira.A partir da análise de dados de levantamento batimétrico e da obtenção de testemunhos no paleocanal, coletados para fins de estudo morfológico, sedimentológico epalinológico, foi possível identificar sequências deposicionais transgressivas. Os registros palinológicos evidenciaram ambientes com influência continental de água doce, migrando para lagunar, mixohalino e marinho raso, em direção ao topo dos testemunhos, caracterizando um ambiente fluvio-estuarino. Os resultados obtidoscontribuem para o estabelecimento da evolução paleogeográfica e da influência do paleocanal do rio de La Plata na sedimentação, de parte, da plataforma continentaldo Rio Grande do Sul.Palavras-chave: paleovale, plataforma continental, transgressão marinha, rio de La Plata.

O experimento foi realizado com o objetivo de estudar características estruturais e morfológicas de cinco genótipos de Pennisetum sp. (CE 08 A.D., Venezuela, HV-241, Elefante B e Hexaplóide) sob pastejo no período de seca na Zona da Mata de Pernambuco. Os genótipos foram manejados sob lotação rotacionada (44 dias de descanso e quatro dias de pastejo) ao longo de dois ciclos de pastejo. Os dados foram analisados em delineamento experimental de blocos ao acaso com parcelas subdivididas (os genótipos representaram as parcelas e os ciclos de pastejo, as subparcelas) e quatro repetições. Houve variação nas características estruturais e morfológicas de genótipos de Pennisetum sp. Os genótipos CE 08 A.D. e Elefante B apresentaram maior densidade de lâmina foliar verde, menor porcentagem de material morto e maior densidade de perfilhos basais remanescentes e aéreos novos, com médias de 5,0±0,4 kg de MS/ha/cm, 33,0±0,2%, 22,0±0,2 e 146,0±0,4 perfilhos/m², respectivamente. O HV-241 apresentou alta participação de material morto em sua biomassa aérea (55,6±0,3%), o que pode ser atribuído à alta mortalidade de perfilhos (19,0±0,3 e 114,0±0,4 perfilhos basais e aéreos mortos/m², respectivamente). Os genótipos CE 08 A.D. e Elefante B destacaram-se como promissores para utilização sob pastejo no período de seca. O genótipo HV-241, híbrido de capim-elefante com o milheto, foi mais afetado pelos efeitos do estresse hídrico no período seco do ano.