75 resultados para 040400 GEOPHYSICS
Resumo:
The coastal systems, are often subjected to high anthropogenic pressure, which makes it necessary to develop new techniques to assess the environmental impacts caused by such human activity. This paper presents the first results obtained during the development and implementation of a new equipment of submarine geophysics survey oriented to integrated coastal zone management (ICZM). It is based on the drag of a submarine in contact with the sea-bottom. The submarine is equipped with an electromagnetic sensor which allows the measurement of the magnetic susceptibility and electrical conductivity of the surface sediments continuously and to a depth of sediment of 40 cm. This system, once improved, will allow us to obtain valuable information for monitoring the environmental quality of coastal areas.
Resumo:
We present a 55-year-long record (1928-1982) of Sr/Ca in a Bermuda coral (Diploria strigosa), which we use to reconstruct local twentieth century climate features. The clearest climate signal emerges for the late-year Sr/Ca. Although the coral was collected in shallow water (12 m), the correlation with station data is highest for temperatures at 50 m depth (r = -0.70), suggesting that local temperatures at the collection site are not representative for the sea surface temperatures in the adjacent open ocean. The most striking feature of the coral record is the persistent and significant correlation (r = -0.50) with the North Atlantic Oscillation (NAO) index. Field correlations of fall Sr/Ca with the winter sea level pressure (SLP) show the typical spatial NAO pattern. The stable relationship with the NAO shows that Sr/Ca in Bermuda corals is a suitable tool for the reconstruction of North Atlantic climate variability.
Resumo:
The study was inspired by information on Paleozoic andesites, dacites, and diabases on the Belkovsky Island in the 1974 geological survey reports used to reconstruct tectonic evolution of the continental block comprising the New Siberian Islands and the bordering shelf. We did not find felsic volcanics or Middle Paleozoic intrusions in the studied area of the island. Igneous rocks are mafic subvolcanic intrusions including dikes, randomly shaped bodies, explosion breccias, and peperites. They belong to the tholeiitic series and are similar to Siberian traps in petrography and trace-element compositions, with high LREE and LILE and prominent Nb negative anomalies. The island arc affinity is due to continental crust contamination of mantle magma and its long evolution in chambers at different depths. K-Ar biotite age (252+/-5 Ma) of magmatism indicates that it was coeval to the main stage of trap magmatism in the Siberian craton at the Permian-Triassic boundary. The terrane including the New Siberian Islands occurred on the periphery of the Siberian trap province where magmatism acted in rifting environment. Magma intruded into semiliquid wet sediments at shallow depths shortly after their deposition. Therefore, the exposed Paleozoic section in Belkovsky Island may include Permian or possibly Lower Triassic sediments of younger ages than it was believed earlier.