Atualizado: 27 de ago. de 2020
Os GTs 2.1 Geodiversidade e Biodiversidade dos Substratos Plataformais e 3.2 Ciclos Biogeoquímicos, Fluxo de CO2 e Acidificação do Oceano Atlântico Tropical, publicaram recentemente dois trabalhos em periódicos conceituados, listado abaixo:
Mapa batimétrico mostrando as principais falhas perfis batimétricos e sísmicos: (a) —Coroa das Lavadeiras b—arenitos de praia, c—Campo de dunes subaquosas de Guamaré, d— Coroa Branca, e—Vale Inciso do Açu, f— Vale Inciso do Apodi; (B) Compartimentos batimétricos da platform continental. Principais falhas: 1—Afonso Bezerra; 2—Carnaubais; 3—Macau; 4—Ubarana; 5—Pescada; 6—Shelf Edge Faults; 7—Areia Branca.
Resumo:
The primary objective of this study is to assess the control of faults of the rift and post-rift stages on the shelf morphology of the Potiguar Basin in northeastern Brazil. This aborted rift basin was generated during the opening of the Equatorial Atlantic in the Aptian. The offshore portion of the continental margin consists of a narrow (~ 40 km) and shallow (~ 70 m below present sea-level) continental shelf with a very steep continental slope (1:11). Our dataset encompasses gravity, bathymetric, shallow seismic and structural data. The results indicate that low sedimentation rates during the Quaternary period contributed to the identification of structural controls in pre-Holocene rocks. The key evidence for fault reactivation on the seafloor is the link between coastal and shelf features associated with pre-Cenozoic structures of the Potiguar Basin. During periods of low sea level, the incision of shelf valleys was readjusted longitudinally and transversally due to the structural controls. Shelf gradient breaks are associated with the occurrences of coplanar ESE– WNW-oriented faults, and uplifted and subsided areas occur in between these fault systems. The results indicate a strong correlation between the margin geometry, modern shelf surface, near-surface expression, and the rift-phase faults, which appear to be reactivated in concordance with the present-day margin stress field. We conclude that neotectonics has influenced both the sediment deposition and morphology of the NE Brazilian Equatorial margin during Quaternary times.
Mudança na SST (°C) e PWS (m2/s2) durante 1964–1975 (a) and 1976–2012 (b). Os contornos em magenta indicam 95% do teste de confidência de Mann– Kendall para a SST; apenas os vetores PWS significativos de acordo com 95% do teste de confidência de Mann–Kendall estão plotados.
Resumo:
A homogeneous monthly data set of sea surface temperature (SST) and pseudo wind stress based on in situ observations is used to investigate the climatic trends over the tropical Atlantic during the last five decades (1964–2012). After a decrease of SST by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial ([1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Surprisingly, the trade wind system also strengthened over the period 1964–2012. Complementary information extracted from other observational data sources confirms the simultaneity of SST warming and the strengthening of the surface winds. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing. Conversely, we suggest that long- term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the Atlantic meridional overtuning circulation and the subtropical cells are required to explain the observations.
Atualizado: 27 de ago. de 2020
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).
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.
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.