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991.
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X-ray images of sediment core allow recognition of fine-scaled sedimentary structures which traditional epoxy casts or lacquer peels are unable to resolve. The X-ray imaging system SCOPIX has the additional advantage of acquiring high-resolution digital pictures suitable for further analysis by advanced image processing techniques. Because of the frequent presence of both physical and biogenic sedimentary structures in undisturbed sediment cores, two image analysis procedures have been established which simplify the information contained in the images (in term of structures and facies), and allow a quantitative characterization of the observed structures. This form of parametrization of the image structure constitutes an additional source of information for a better interpretation of the physical processes responsible for the generation of the sedimentary structures. 相似文献
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996.
997.
C. Rabouille H. Stahl F. Bassinot A. Tengberg J. Brunnegard P. Hall K. Kiriakoulakis J. -L. Reyss L. Dezileau P. Crassous P. Roos R. S. Lampitt 《Progress in Oceanography》2001,50(1-4)
Fluxes contributing to the particulate carbonate system in deep-sea sediments were investigated at the BENGAL site in the Porcupine Abyssal Plain (Northeast Atlantic). Deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0.37±0.1 mmol C m−2 d−1. Dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers, is 0.4±0.1 mmol C m−2 d−1. Burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14C dating on foraminifera (0.66±0.1 mmol C m−2 d−1). Burial plus dissolution was three times larger than particle deposition flux which indicates that steady-state is not achieved in these sediments. Mass balances for other components (BSi, 210Pb), and calculations of the focusing factor using 230Th, show that lateral inputs play only a minor role in this imbalance. Decadal variations of annual particle fluxes are also within the uncertainty of our average. Long-term change in dissolution may contribute to the imbalance, but can not be the main reason because burial alone is greater than the input flux. The observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past. A box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady-state is in the order of 3 kyr. Thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates. We estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries. 相似文献
998.
The analysis is performed on the basis of comparison of the hydrological characteristics of prestrait regions of the Sea of
Marmara. It is shown that, in summer, the Black-Sea waters are weakly mixed with the Mediterranean waters and the levels of
salinity in the prestrait regions differ by 0.6–0.9‰. In winter, the indicated difference increases and the level of salinity
near the entrance of Dardanelles reaches 29‰ and exceeds the level observed near the entrance of Bosporus by 5.5‰. In the
analyzed regions, we observe local temperature maxima and minima near the interface of two water masses. This is explained
by the presence of strong seasonal variations of temperature for the Black-Sea waters and their absence for the Mediterranean
waters. The physical mechanisms responsible for the seasonal variations of the intensity of transformations of the Black-Sea
waters are discussed.
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Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 49–55, March–April, 2007. 相似文献
999.
Changes in climatic parameters and in temperature and precipitation extremes in northern Eurasia in the late 20th century are analyzed. A spatial distribution of temperature and precipitation anomalies and of a set of indices of climate extremes is presented. Changes in climate extremes show a tendency toward a milder climate, mainly in winter. At the same time, the frost-free period has substantially decreased in the eastern, northern, and central parts of European Russia. In some regions during summer, there is an increase in the frequency of extreme events such as heavy rains, droughts, and sharp cooling. It is shown that the geographic pattern of present-day climate anomalies is linked to variations in the large-scale atmospheric circulation. The main mechanism of the current warming in northern Eurasia is a winter intensification of zonal flow linked to the increased frequency of positive anomalies of the North Atlantic Oscillation index. 相似文献
1000.
Multi-AUV Control and Adaptive Sampling in Monterey Bay 总被引:3,自引:0,他引:3
Edward Fiorelli Naomi Ehrich Leonard Pradeep Bhatta Derek A. Paley Ralf Bachmayer David M. Fratantoni 《Oceanic Engineering, IEEE Journal of》2006,31(4):935-948
Operations with multiple autonomous underwater vehicles (AUVs) have a variety of underwater applications. For example, a coordinated group of vehicles with environmental sensors can perform adaptive ocean sampling at the appropriate spatial and temporal scales. We describe a methodology for cooperative control of multiple vehicles based on virtual bodies and artificial potentials (VBAP). This methodology allows for adaptable formation control and can be used for missions such as gradient climbing and feature tracking in an uncertain environment. We discuss our implementation on a fleet of autonomous underwater gliders and present results from sea trials in Monterey Bay in August, 2003. These at-sea demonstrations were performed as part of the Autonomous Ocean Sampling Network (AOSN) II project 相似文献