Carolina Pereira Silvestre

Opal phytolith and isotopic studies of "Restinga" communities of Maricá, Brazil, as a modern reference for paleobiogeoclimatic reconstruction

The Marica restinga, located in the eastern part of the Rio de Janeiro State (Brazil), corresponds to one of the few remaining preserved areas of the states coastal plain. This paper reports on a study of the Marica restinga plant communities and also presents an identification of the main plant species present in each community, with the objective of establishing reference collections, by the methods of the proxies opal phytoliths and stable carbon isotopes, for paleoenvironmental reconstructions of this coastal area during the Quaternary. Six plant communities, distributed perpendicularly to the coast line over sandy barriers, lagoonal plain, lagoon margin and weathered basement were identified: halophile-psamophile, scrub, herbaceous swamp, slack, shrubby vegetation and dry forest. In general, the plant species analyzed in each community presented low productivity of opal phytoliths, as only the Poaceae, Cyperaceae and Arecaceae families produce a great amount and diversity of morphotypes of opal phytoliths. The results of the analysis of stable carbon isotopes in sediments indicated a predominance of C3 or a mixture of C3 and C4 plants, presenting a close correlation with the results found in plants collected in each community. In conclusion, it was verified that the carbon isotope analysis associated with that of the opal phytoliths are good proxies for the reconstruction of vegetation in the study area.

Variações morfológicas nas praias oceânicas de Niterói (RJ, Brasil) em resposta a incidência de ondas de tempestades (Morphological variations of ocean beaches of Niterói (RJ) in response to storms wave incidence)

As praias da enseada de Itaipu em Niteroi (RJ) vem sendo modificadas devido a rapida urbanizacao que ocorreu apos a decada de 1970 com a construcao da ponte Rio-Niteroi. As praias de Piratininga, Sossego, Camboinhas e Itaipu sao dinâmicas e importantes para a protecao do litoral, frente as ondas de tempestades que podem alcancar 3 metros na arrebentacao. O presente estudo apresenta dados de topografia praial e de condicoes de mar obtidos durante e apos a ocorrencia de ressacas entre 2013 e 2014. Os resultados ressaltam o carater altamente dinâmico das praias oceânicas de Niteroi e a vulnerabilidade destas as grandes ondas de tempestades. O comportamento distinto dessas praias e o resultado da energia diferenciada das ondas incidentes ao longo da costa. Essas praias se estreitam rapidamente em resposta a ocorrencia de ressacas, restabelecendo-se logo a seguir quando do retorno as condicoes de tempo bom. A praia de Piratininga e a mais dinâmica, tendo variado entre 34 m e 87 m de largura no inverno. Tambem e a mais urbanizada e apresenta problemas com a destruicao de estruturas de engenharia construidas praticamente dentro do pos-praia. Foi observado uma grande mobilidade de sedimentos ao longo do arco praial em resposta a acao das correntes de deriva litorânea, no caso de Piratininga e Camboinhas, e entre a parte emersa e submersa. A B S T R A C T The beaches of the Itaipu embayment in Niteroi (Rio de Janeiro) have been modified due to rapid urbanization in the 1970s after the construction of the Rio-Niteroi bridge. The beaches of Piratininga, Sossego, Camboinhas and Itaipu are dynamic and important to protect the coast against the impact of stormy waves that can reach three meters in the breaking zone. This study presents beach topography data and sea conditions data obtained during and after storm surges between 2013 and 2014. The results highlight the highly dynamic nature of the ocean beaches of Niteroi and their vulnerability to large stormy waves. The distinct behavior of these beaches is the result of the differentiated energy of the incident waves along the coast. These beaches quickly narrow in response to storm surge and they recompose immediately with the return of good weather conditions. Piratininga beach is the most dynamic, ranging between 34 and 87 meters wide in the winter. It is also the most urbanized and it has problems with the destruction of engineering structures built practically into the backshore. These beaches exhibit high mobility of sediments longitudinally in response to action of longshore currents, especially Piratininga and Camboinhas, and between the unsubmerged and the submerged portion. Keywords: beach, coastal dynamic, geomorphology, Itaipu Embayment.