Mês: agosto 2013

-- inctAmbTropic fase I, Congressos | inctAmbTropic fase I, Formação | inctAmbTropic fase I, GT1.1 | inctAmbTropic fase I

GT1.1 Realiza Nova Expedição ao Atol das Rocas

Entre os dias 27/06/2013 e 27/07/2013 foi realizada a segunda expedição para a Reserva Biológica do Atol das Rocas, como parte das atividades do GT1.1 Respostas da Linha de Costa do inctAmbTropic.  A expedição teve por objetivo obter um conjunto de dados in situ sobre os processos hidrodinâmicos que controlam a geomorfologia das ilhas no interior do atol. Foram obtidos dados de onda, correntes e marés, através do fundeio de 3 ADCP`s no interior do atol e 1 ADCP na porção externa. Além disso, dados da morfologia tridimensal das ilhas recifais e “run up” foram obtidos ao longo do período de estadia no Atol. O trabalho faz parte do doutorado de Mirella Costa que está sendo desenvolvido no IO/USP (http://ldc.io.usp.br), sob a orientação do Prof. Eduardo Siegle.

Esta segunda expedição contou com o apoio do Analista Ambiental, Eduardo Macedo, do ICMBio PARNAMAR Fernando de Noronha e do Prof. Carlos A.F. Schettini (UFPE). Também contribuiram para o sucesso da campanha o Prof. Natan Pereira (UNEB), o doutorando Miguel Loiola (UFBA) e mestrando Tiago Albuquerque (UFBA).

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Trabalho de Campo no Atol das Rocas

A primeira expedição havia ocorrido no segundo semestre de 2012 (out-nov), onde foi medido o mesmo conjunto de dados, contudo durante um período de alta energia, caracterizado pela entrada de ondulações de direção norte. Os resultados da primeira campanha serão apresentados pela doutoranda Mirella na sessão oral “Reef Forms” do 8th IAG International Conference on Geomorphology, a ser realizado em Paris (França) (http://www.geomorphology-iag-paris2013.com).

ABSTRACT

Morphological response of reef island on rocas atoll (South Atlantic Ocean) to Seasonal energetic wave conditions. Costa M., Macedo, E., Siegle E.Reef islands on Rocas Atoll, the only atoll in the South Atlantic Ocean, are located at its leeward side, being protected from waves most part of the year but subjected to the impact of energetic swells from the north from November to February. With the aim of assessing the morphological evolution related to the incoming waves, in situ measurements were conducted in November 2012, covering a series of energetic wave conditions. Waves were measured by an ADCP (Nortek Aquadopp profiler) deployed at 1.2 km distance from the reef island and 0.9 km from the reef rim during 28 days. Simultaneously, the morphology of the entire reef island was surveyed with the use of a Differential Global Positioning System (DGPS). High energy waves with peak periods of about 13 s and significant wave heights of 2 m presented a weekly recurrence followed by a gradual decay. Morphological surveys show that the northwestern side of the island, which has been historically eroded, undergoes larger morphological changes. However, in contrast, there was an increase in volume on the beach island. The tridimensional terrain elevation models clearly show the removal of submerged banks dispersed on the reef rim and their deposition over the beach. This is thought to be due to the intense wave set-up generated by waves breaking on the leeward reef edge, moving the sediments in the opposite direction to that of the overall gravity-driven outflow. The results suggest that the sediment redistribution by seasonal northern swells contribute to sediment accretion on the reef island, thereby reducing the long-term erosion of this portion of the island.

#AtoldasRocas #Congressos #GT11 #PraiasArenosas

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A Sedimentação na Plataforma Central do Brasil

Já encontra-se disponível “on line” o mais recente trabalho publicado no âmbito do inctAmbTropic. O trabalho intitulado “The narrow, shallow, low-accommodation shelf of central Brazil:  sedimentology, evolution, and human uses”   tem como autores Dominguez, JML, Silva, RP, Nunes, AS, Freire, AFM.  O trabalho está publicado na revista Geomorphology (Impact Factor: 2,552, 5-Year Impact Factor: 3,066).

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Atividade Pesqueira na Borda da Plataforma Continental Central do Brasil

O trabalho apresenta uma síntese e modelo conceitual da sedimentação na plataforma continental central do Brasil  e é  a primeira publicação a apresentar informações detalhadas para esta região.  O trabalho é uma contribuição do GT2.1 Geodiversidade e Biodiversidade dos Substratos do inctAmbTropic.

ABSTRACT

The continental shelf off the coast of central Brazil, extending from 10 to 16°S, is unusually narrow (~ 20 km) and rests on the São Francisco craton. The shelf break is located between the 45 and 50 m isobaths and coincides with major hinge-lines of the marginal basins. The shelf was exposed for most of the Quaternary period, particularly during the last 1 my, when the average sea level was −62 m. Submarine geomorphology is strongly influenced by this extended sub-aerial exposure and reduced subsidence, resulting in widespread incisions on the shelf. During the limited episodes of shelf inundation, as is the case today, a few meters of non-framework grain assemblages dominated by coralline algae accumulated on the outer shelf, while quartz sands were restricted to water depths of less than 10–15 m. Mud accumulation on this unusually shallow shelf is aided by additional accommodation space provided by incisions and canyon heads indenting the shelf. Artisanal fisheries, targeting high-value commercial species associated with hard bottoms located on the outer shelf and shelf break, are the most important human use of this shelf. Data used in this study have been compiled from theses and previously conducted surveys and consist of four piston cores, 509 km of chirp subbottom profiles and side scan recordings, and 711 bottom grab samples that have been analyzed for various textural and compositional aspects.

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Conceptual model for sedimentation in the narrow, shallow shelf off central Brazil. Highstand sedimentation — during the few, brief highstand episodes, the shelf and coastal zone were flooded. Highstand coastal bays formed at the upstream end of incised valleys and were later infilled. On the shelf these incised valleys were partially infilled with fine-grained sediments. On the rest of the shelf, the reduced siliciclastic influx favored an essentially carbonate sedimentation, of non-framework rhodoalgal, oligophotic grain assemblages. Framework builders (hermatipic corals) developed on the very shallow areas bordering the coastline. Fonte: Dominguez, J.M.L., et al., The narrow, shallow, low-accommodation shelf of central Brazil: Sedimentology, evolution, and human uses, Geomorphology (2013), http://dx.doi.org/10.1016/j.geomorph.2013.07.004

Chama-se a atenção que  a base de dados gerada para este trabalho está disponibilizada na forma de Dados Suplementares no portal do periódico Geomorphology, publicado pela Editora Elsevier, incluindo arquivos no formato kml para visualização da distribuição espacial do dados no Google Earth.

#Geodiversidade #GT21 #HabitatsMarinhos #PlataformaContinental