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791.
S. Bianchelli C. Gambi D. Zeppilli R. Danovaro 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):420-433
Metazoan meiofaunal abundance, total biomass, nematode size and the richness of taxa were investigated along bathymetric gradients (from the shelf break down to ca. 5000-m depth) in six submarine canyons and on five adjacent open slopes of three deep-sea regions. The investigated areas were distributed along >2500 km, on the Portuguese to the Catalan and South Adriatic margins. The Portuguese and Catalan margins displayed the highest abundances, biomass and richness of taxa, while the lowest values were observed in the Central Mediterranean Sea. The comparison between canyons and the nearby open slopes showed the lack of significant differences in terms of meiofaunal abundance and biomass at any sampling depth. In most canyons and on most slopes, meiofaunal variables did not display consistent bathymetric patterns. Conversely, we found that the different topographic features were apparently responsible for significant differences in the abundance and distribution of the rare meiofaunal taxa (i.e. taxa accounting for <1% of total meiofaunal abundance). Several taxa belonging to the temporary meiofauna, such as larvae/juveniles of Priapulida, Holothuroidea, Ascidiacea and Cnidaria, were encountered exclusively on open slopes, while others (including the Tanaidacea and Echinodea larvae) were found exclusively in canyons sediments. Results reported here indicate that, at large spatial scales, differences in deep-sea meiofaunal abundance and biomass are not only controlled by the available food sources, but also by the region or habitat specific topographic features, which apparently play a key role in the distribution of rare benthic taxa. 相似文献
792.
This paper studies the causes and mechanisms of the formation of extreme anomalies in the tropospheric temperature associated
with the North Atlantic Oscillation (NAO). Our approach is based on understanding that, in the annual cycle, continental-scale
tropospheric temperature anomalies (planetary waves with longitudinal wave numbers of 1–3) can both intensify under the direct
action of heat inflow as an energy source for these anomalies (radiation cooling/heating) and weaken as a result of the destructive
action of heat inflow under temperature advections with the opposite (to the heat inflow) sign [4, 5]. According to the monthly
mean data of the NCEP/NCAR reanalysis over the 40-year period, seasonal air temperature anomalies have been studied at the
level 850 hPa (T
850) in different regions of Eurasia. It has been confirmed that the negative NAO phase in winter is favorable for preserving
negative T
850 anomalies in the east of the continent at this time of year, whereas the positive NAO phase is favorable for negative T
850 anomalies in the west. However, it has been revealed that this dependence was critically violated during the winter seasons
approximately two years before an extreme event. This was explained by the fact that, in those years, the NAO influence on
winter T
850 anomalies was limited. This paper formally considers a certain mechanism of anomalous heat inflow as an energy source for
these anomalies with functions of the formation (intensification) of negative T
850 anomalies in winter and positive T
850 anomalies in summer, as well as with a function of the limitation of the influence of the predominant dynamic mode on some
regions of the continent. It is shown that, in the 1960s, T
850 anomalies with negative NAO indices in the east of the continent were governed by a hypothetic mechanism of heat inflow as
an energy source for anomalies; in 1980s, at prolonged positive NAO indices, T
850 anomalies in the west of the continent could also be governed by this mechanism. This paper, within the accepted degree of
detail, demonstrates the process of limitation of the NAO influence in some years (1966, 1967, 1987, and 1988), which leads
to an unbalance of the anomalies and a possible extreme phenomenon. It is demonstrated that, in some seasons, the anomalies
were not governed by the hypothetic mechanism of the heat inflow under the action of large NAO changes and a complete upset
of the annual cycle of anomalies. Determining the first indicators of the unbalance, which can lead to extreme anomalies,
is shown to be difficult if it is based only on an analysis of winter seasons (as is the case with most of the works) without
invoking the annual trends of the tropospheric temperature and the NAO index. 相似文献
793.
Jae-Hun Park Kathleen A. Donohue D. Randolph Watts Luc Rainville 《Journal of Oceanography》2010,66(5):709-717
The distribution of deep near-inertial waves (NIWs) is investigated using data mainly from an array of 46 near-bottom acoustic
current meter sensors spanning a 600 km × 600 km region as part of the Kuroshio Extension System Study during 2004–2006. The
deep NIW distribution is interpreted in the context of both upper-layer and near-bottom mapped circulations. The wintertime-mean
mixed-layer NIW energy input, modeled from observed wind stress, has the same range of values north and south of the Kuroshio
Extension in this region. Yet, the wintertime-mean deep NIW energy distribution reveals a sharp factor-of-5 decrease from
north to south of the Kuroshio jet. This direct observational evidence shows that the Kuroshio Extension blocks the equatorward
propagation of NIWs. The NIW energy that does reach the sea floor within the subset of wintertime observations in the subtropical
gyre arrives with patchy spatial and temporal distribution. Elevated NIW energy in deep water is associated with anticyclones
in the deep barotropic flow and unassociated with upper layer eddies. 相似文献
794.
V. I. Man’kovskii G. A. Tolkachenko E. B. Shibanov O. V. Martynov E. N. Korchemkina D. V. Yakovleva I. A. Kalinskii 《Physical Oceanography》2010,20(3):207-230
We present the results of measurements of optical characteristics of waters (the beam attenuation coefficient, volume scattering
function, sea water reflectance, and Secchi depth) and optical characteristics of the atmosphere (aerosol optical thickness,
content of vapors, and the ?ngstr?m exponent) carried out in September 2008 on the oceanographic platform near Katsiveli.
We carried out the comparative analysis of hydrooptical characteristics measured in various years. The optical type of sea
waters in the period of observations is determined. 相似文献
795.
A. G. Zatsepin E. G. Morozov V. T. Paka A. N. Demidov A. A. Kondrashov A. O. Korzh V. V. Kremenetskiy S. G. Poyarkov D. M. Soloviev 《Oceanology》2010,50(5):643-656
During cruise 54 of the R/V Akademik Mstislav Keldysh to the southwestern Kara Sea (September 6 to October 7, 2007), a large amount of hydrophysical data with unique spatial resolution
was obtained on the basis of measurements using different instruments. The analysis of the data gave us the possibility to
study the dynamics and hydrological structure of the southwestern Kara Sea basin. The main elements of the general circulation
are the following: the Yamal Current, the Eastern Novaya Zemlya Current, and the St. Anna Trough Current. All these currents
are topographically controlled; they flow over the bottom slopes along the isobaths. The Yamal Current begins at the Kara
Gates Strait and turns to the east as part of the cyclonic circulation. Then, it turns to the north and propagates along the
Yamal coast over the 100-m isobath. The Eastern Novaya Zemlya Current (its core is located over the eastern slope of the Novaya
Zemlya Trough) flows to the northeast. Near the northern edge of Novaya Zemlya, it encounters the St. Anna Trough Current,
separates from the coast, and flows practically to the east merging with the continuation of the Yamal Current. A strong frontal
zone is formed in the region where the two currents merge above the threshold that separates the St. Anna Trough from the
Novaya Zemlya Trough and divides the warm and saline Arctic waters from the cooler and fresher waters of the southwestern
part of the Kara Sea. This threshold, whose depth does not exceed 100–150 m, is a barrier that prevents the spreading of the
Barents Sea and Arctic waters to the southwestern part of the Kara Sea basin through the St. Anna Trough. 相似文献
796.
A review of the climatological characteristics of landfalling Gulf hurricanes for wind, wave, and surge hazard estimation 总被引:1,自引:0,他引:1
The climatological characteristics of landfalling Gulf of Mexico hurricanes are presented, focusing on the basic parameters needed for accurately determining the structure and intensity of hurricanes for ocean response models. These include the maximum sustained wind, radius of maximum winds, the Holland-B parameter, the peripheral or far-field pressure, the surface roughness and coefficient of drag, and the central pressure for historical hurricanes in the Gulf.Despite evidence of a slight increase in the annual number of named storms over the past 50 years, presently there is no statistically significant trend in tropical storms, hurricanes, or major hurricanes in the Gulf of Mexico. In addition, the long-term variability of tropical cyclones in the Gulf reflects the observed variability in the Atlantic basin as a whole. Analyses of hurricane winds from multiple sources suggest the presence of a bias toward overestimating the strength of winds in the HURDAT dataset from 7% to 15%. Results presented comparing HURDAT with other sources also show an overestimation of intensity at landfall, with an estimated bias of ~10%.Finally, a review of recent studies has shown that hurricane frequencies and intensities appear to vary on a much more localized scale than previously believed. This exacerbates the sampling problem for accurate characterization of hurricane parameters for design and operational applications. 相似文献
797.
Jeffrey Poort Oleg M. Khlystov Lieven Naudts Albert D. Duchkov Hitoshi Shoji Shin’ya Nishio Marc De Batist Akihiro Hachikubo Masato Kida Hirotsugu Minami Andrey Y. Manakov Marina V. Kulikova Alexey A. Krylov 《Geo-Marine Letters》2012,32(5-6):407-417
Thermal measurements and hydrate mapping in the vicinity of the K-2 mud volcano in Lake Baikal have revealed a particular type of association of thermal anomalies (29–121?mW?m–2) near hydrate-forming layers. Detailed coring within K-2 showed that hydrates are restricted to two distinct zones at sub-bottom depths exceeding 70–300?cm. Temperature data from stations with hydrate recovery and degassing features all display low thermal gradients. Otherwise, the thermal gradients within the mud volcano are generally increased. These findings imply a more complicated thermal regime than often assumed for mud volcanoes, with important roles for both fluids and hydrates. The coexistence of neighbouring low and high thermal anomalies is interpreted to result from discharging and recharging fluid activity, rather than hydrate thermodynamics. It is suggested that hydrates play a key role in controlling the fluid circulation pattern at an early stage. At a later stage, the inflow of undersaturated lake water would favour the dissolution of structure I hydrates and the formation of structure II hydrates, the latter having been observed on top of structure I hydrates in the K-2 mud volcano. 相似文献
798.
Ananiev R. A. Dmitrevsky N. N. Roslyakov A. G. Chernykh D. V. Moroz E. A. Zarayskaya Y. A. Semiletov I. P. 《Oceanology》2022,62(1):127-132
Oceanology - The emission of natural gas from the seafloor to the surface in shelf areas of the Arctic seas is of increasing interest among researchers. Recently, various types of acoustic... 相似文献
799.
Gorchakov G. I. Kopeikin V. M. Karpov A. V. Gushchin R. A. Datsenko O. I. Buntov D. V. 《Izvestiya Atmospheric and Oceanic Physics》2022,58(5):466-475
Izvestiya, Atmospheric and Oceanic Physics - Measurements of electric currents of saltation in the wind-sand flux and currents caused by the wind transport of dust aerosol particles have been... 相似文献
800.
P. Cobo C. Ranz A. Fernández M. Cuesta D.K. Anthony M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95
Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic
pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling
sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are
normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst.
However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer
radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude,
Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum
length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate
the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform
radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be
measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest
pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated
by its application to a sediment wedge model. 相似文献