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941.
Bouchra Nechad Aida Alvera-Azcaràte Kevin Ruddick Naomi Greenwood 《Ocean Dynamics》2011,61(8):1205-1214
In situ measurements of total suspended matter (TSM) over the period 2003–2006, collected with two autonomous platforms from
the Centre for Environment, Fisheries and Aquatic Sciences (Cefas) measuring the optical backscatter (OBS) in the southern
North Sea, are used to assess the accuracy of TSM time series extracted from satellite data. Since there are gaps in the remote
sensing (RS) data, due mainly to cloud cover, the Data Interpolating Empirical Orthogonal Functions (DINEOF) is used to fill
in the TSM time series and build a continuous daily “recoloured” dataset. The RS datasets consist of TSM maps derived from
MODIS imagery using the bio-optical model of Nechad et al. (Rem Sens Environ 114: 854–866, 2010). In this study, the DINEOF
time series are compared to the in situ OBS measured in moderately to very turbid waters respectively in West Gabbard and
Warp Anchorage, in the southern North Sea. The discrepancies between instantaneous RS, DINEOF-filled RS data and Cefas data
are analysed in terms of TSM algorithm uncertainties, space–time variability and DINEOF reconstruction uncertainty. 相似文献
942.
Béatrice Allard Michaël Danger Loïc Ten-Hage Gérard Lacroix 《Aquatic Sciences - Research Across Boundaries》2011,73(1):113-126
The effects of food web structure on the quantity and biochemical composition of seston, zooplankton and recently deposited
sediment in experimental freshwater mesocosms were examined. Food web structure was manipulated by addition of zooplanktivorous
fish. Biochemical characterisations were carried out using lipid biomarkers (sterols, fatty acids, chlorophyll-derived compounds
and long-chain alkanediols). Fish addition decreased zooplankton biomass and increased seston biomass and deposited sediment
through a trophic cascade. Fish presence strongly influenced the biochemical characteristics of seston and sediment. In contrast,
food web structure had a minor impact on the lipid biomarker composition of zooplankton. Although the relative abundance of
sterols in the different compartments did not differ strongly between treatments, sterol profiles in seston and sediment depended
on food web structure. The predominance of Δ7-sterols in seston and sediment in the fish treatment indicated a major contribution of Chlorophyceae. In contrast, the distribution
of sterols in seston and sediment in the fishless treatment, dominated by cholesterol, indicated a major zooplanktonic input.
The distribution of fatty acids and the relative abundance of chlorophyll-derived compounds and long-chain alkanediols agreed
with the predominant contribution of phytoplankton or zooplankton to seston and sediment in the two treatments. The relative
abundance of bacterial biomarkers suggested that the contribution of bacteria was rather low. The high relative abundance
of polyunsaturated fatty acids (PUFAs) and the absence of stanols in sediments suggested low microbial reworking of organic
matter in the recently accumulated sediments. The trophic cascade, generated by the addition of fish, increased the relative
abundance of PUFAs in deposited organic matter, thus enhancing sediment quality and potential degradability. 相似文献
943.
Katrina J. Butkas Yvonne Vadeboncoeur M. Jake Vander Zanden 《Aquatic Sciences - Research Across Boundaries》2011,73(1):153-169
Studies of aquatic invertebrate production have been primarily conducted at the level of individual taxa or populations. Advancing
our understanding of the functioning and energy flow in aquatic ecosystems necessitates scaling-up to community and whole-lake
levels, as well as integrating across benthic and pelagic habitats and across multiple trophic levels. In this paper, we compare
a suite of non-cohort based methods for estimating benthic invertebrate production at subpopulation, habitat, and whole-lake
levels for Sparkling Lake, WI, USA. Estimates of the overall mean benthic invertebrate production (i.e. whole-lake level)
ranged from 1.9 to 5.0 g DM m−2 y−1, depending on the method. Production estimates varied widely among depths and habitats, and there was general qualitative
agreement among methods with regards to differences in production among habitats. However, there were also consistent and
systematic differences among methods. The size-frequency method gave the highest, while the regression model of Banse and
Mosher (Ecol Monogr 50:355–379, 1980) gave the lowest production estimates. The regression model of Plante and Downing (Can J Fish Aquat Sci 46:1489–1498, 1989) had the lowest average coefficients of variation at habitat (CV = 0.17) and whole-lake (CV = 0.08) levels. At the habitat
level, variance in production estimates decreased with sampling effort, with little improvement after 10–15 samples. Our study
shows how different production estimates can be generated from the same field data, though aggregating estimates up to the
whole-lake level does produce an averaging effect that tends to reduce variance. 相似文献
944.
Narges Afsari Forogh Sodoudi Fataneh Taghizadeh Farahmand Mohammad Reza Ghassemi 《Journal of Seismology》2011,15(2):341-353
Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities
in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath
the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset
includes teleseismic data (M
b ≥ 5.5, epicentral distance from 30° to 95°) recorded at 12 three-component short-period stations of Kermanshah, Isfahan and
Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at the Moho
boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P
wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity
such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver
function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan
Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth
decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat
Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed
a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho
boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ
increases to 4.3 km/s beneath the Moho. 相似文献
945.
A temporary accelerometer network has been installed in Tarcento (Friuli, NE Italy), a small town heavily hit by the 1976–1977
Friuli earthquake sequence, as a part of an ongoing research project aimed at ground motion simulation and generation of shakemaps
in the near-field of an earthquake. The network operated from October 2008 to April 2010 and consisted of three K2 accelerographs
with internal Episensor, distributed over a linear array of about 1.5 km length. Tarcento town had been chosen, at the end
of the 1970s, as the ideal site for a pilot microzonation study, the first of this kind in Italy, in which a substantial number
of field (and laboratory) tests were carried out in order to assess the mechanical properties of local alluvium deposits and
their complex (3D) geometrical configuration. The data from the temporary network, illustrated herein, allow for proper verification
and review of some of the quantitative predictions formulated in the 1980 study. As argued in the discussion section, we also
believe that the data are apt to provide valuable information of more general interest on the complex seismic response of
alluvium-filled valleys, and we show therein how the observations can be interpreted in the light of presently available parametric
simulation studies and simplified criteria for handling basin amplification effects. 相似文献
946.
Soil particle-size distributions (PSD) have been used to estimate soil hydraulic properties. Various parametric PSD models
have been proposed to describe the soil PSD from sparse experimental data. It is important to determine which PSD model best
represents specific soils. Fourteen PSD models were examined in order to determine the best model for representing the deposited
soils adjacent to dams in the China Loess Plateau; these were: Skaggs (S-1, S-2, and S-3), fractal (FR), Jaky (J), Lima and
Silva (LS), Morgan (M), Gompertz (G), logarithm (L), exponential (E), log-exponential (LE), Weibull (W), van Genuchten type
(VG) as well as Fredlund (F) models. Four-hundred and eighty samples were obtained from soils deposited in the Liudaogou catchment.
The coefficient of determination (R
2), the Akaike’s information criterion (AIC), and the modified AIC (mAIC) were used. Based upon R
2 and AIC, the three- and four-parameter models were both good at describing the PSDs of deposited soils, and the LE, FR, and
E models were the poorest. However, the mAIC in conjunction with R
2 and AIC results indicated that the W model was optimum for describing PSD of the deposited soils for emphasizing the effect
of parameter number. This analysis was also helpful for finding out which model is the best one. Our results are applicable
to the China Loess Plateau. 相似文献
947.
Aggeliki Adamaki Eleftheria E. Papadimitriou George M. Tsaklidis Vassilios Karakostas 《Acta Geophysica》2011,59(4):748-769
Aftershock rates seem to follow a power law decay, but the assessment of the aftershock frequency immediately after an earthquake,
as well as during the evolution of a seismic excitation remains a demand for the imminent seismic hazard. The purpose of this
work is to study the temporal distribution of triggered earthquakes in short time scales following a strong event, and thus
a multiple seismic sequence was chosen for this purpose. Statistical models are applied to the 1981 Corinth Gulf sequence,
comprising three strong (M = 6.7, M = 6.5, and M = 6.3) events between 24 February and 4 March. The non-homogeneous Poisson process outperforms the simple Poisson process
in order to model the aftershock sequence, whereas the Weibull process is more appropriate to capture the features of the
short-term behavior, but not the most proper for describing the seismicity in long term. The aftershock data defines a smooth
curve of the declining rate and a long-tail theoretical model is more appropriate to fit the data than a rapidly declining
exponential function, as supported by the quantitative results derived from the survival function. An autoregressive model
is also applied to the seismic sequence, shedding more light on the stationarity of the time series. 相似文献
948.
Anne A. Petrenko Andrea M. Doglioli Francesco Nencioli Marion Kersalé Ziyuan Hu Francesco d’Ovidio 《Ocean Dynamics》2017,67(3-4):513-533
The main objective of the LAgrangian Transport EXperiment (LATEX) project was to study the influence of coastal mesoscale and submesoscale physical processes on circulation dynamics, cross-shelf exchanges, and biogeochemistry in the western continental shelf of the Gulf of Lion, Northwestern Mediterranean Sea. LATEX was a five-year multidisciplinary project based on the combined analysis of numerical model simulations and multi-platform field experiments. The model component included a ten-year realistic 3D numerical simulation, with a 1 km horizontal resolution over the gulf, nested in a coarser 3 km resolution model. The in situ component involved four cruises, including a large-scale multidisciplinary campaign with two research vessels in 2010. This review concentrates on the physics results of LATEX, addressing three main subjects: (1) the investigation of the mesoscale to submesoscale processes. The eddies are elliptic, baroclinic, and anticyclonic; the strong thermal and saline front is density compensated. Their generation processes are studied; (2) the development of sampling strategies for their direct observations. LATEX has implemented an adaptive strategy Lagrangian tool, with a reference software available on the web, to perform offshore campaigns in a Lagrangian framework; (3) the quantification of horizontal mixing and cross-shelf exchanges. Lateral diffusivity coefficients, calculated in various ways including a novel technique, are in the range classically encountered for their associated scales. Cross-shelf fluxes have been calculated, after retrieving the near-inertial oscillation contribution. Further perspectives are discussed, especially for the ongoing challenge of studying submesoscale features remotely and from in situ data. 相似文献
949.
Maialen Irazoqui Apecechea Martin Verlaan Firmijn Zijl Camille Le Coz Herman Kernkamp 《Ocean Dynamics》2017,67(6):729-749
The impact of the self-attraction and loading effect (SAL) in a regional 2D barotropic tidal model has been assessed, a term with acknowledged and well-understood importance for global models but omitted for boundary-forced, regional models, for which the implementation of SAL is non-trivial due to its non-local nature. In order to understand the impact of the lack of SAL effects in a regional scale, we have forced a regional model of the Northwest European Continental Shelf and the North Sea (continental shelf model (CSM)) with the SAL potential field derived from a global model (GTSM), in the form of a pressure field. Impacts have been studied in an uncalibrated setup and with only tidal forcing activated, in order to isolate effects. Additionally, the usually adopted simple SAL parameterization, in which the SAL contribution to the total tide is parameterized as a percentage of the barotropic pressure gradient (typically chosen 10%), is also implemented and compared to the results obtained with a full SAL computation. A significant impact on M2 representation is observed in the English Channel, Irish Sea and the west (UK East coast) and south (Belgian and Dutch Coast) of the North Sea, with an impact of up to 20 cm in vector difference terms. The impact of SAL translates into a consistent M2 amplitude and propagation speeds reduction throughout the domain. Results using the beta approximation, with an optimal domain-wide constant value of 1.5%, show a somewhat comparable impact in phase but opposite direction of the impact in amplitude, increasing amplitudes everywhere. In relative terms, both implementations lead to a reduction of the tidal representation error in comparison with the reference run without SAL, with the full SAL approach showing further impacted, improved results. Although the overprediction of tidal amplitudes and propagation speeds in the reference run might have additional sources like the lack of additional dissipative processes and non-considered bottom friction settings, results show an overall significant impact, most remarkable in tidal phases. After showing evidence of the SAL impact in regional models, the question of how to include this physical process in them in an efficient way arises, since SAL is a non-local effect and depends on the instantaneous water levels over the whole ocean, which is non-trivial to implement. 相似文献
950.
Nitrate interleaving structures were observed below the mixed layer during a cruise to the Kuroshio Extension in October 2009. In this paper, we investigate the formation mechanisms for these vertical nitrate anomalies, which may be an important source of nitrate to the oligotrphoc surface waters south of the Kuroshio Extension Front. We found that nitrate concentrations below the main stream of the Kuroshio Extension were elevated compared to the ambient water of the same density (σ ?? = 23.5–25). This appears to be analogous to the “nutrient stream” below the mixed layer, associated with the Gulf Stream. Strong turbulence was observed above the vertical nitrate anomaly, and we found that this can drive a large vertical turbulent nitrate flux \(>\mathcal {O}\) (1 mmol N m?2 day?1). A realistic, high-resolution (2 km) numerical simulation reproduces the observed Kuroshio nutrient stream and nitrate interleaving structures, with similar lateral and vertical scales. The model results suggest that the nitrate interleaving structures are first generated at the western side of the meander crest on the south side of the Kuroshio Extension, where the southern tip of the mixed layer front is under frontogenesis. Lagrangian analyses reveal that the vertical shear of geostrophic and subinertial ageostrophic flow below the mixed layer tilts the existing along-isopycnal nitrate gradient of the Kuroshio nutrient stream to form nitrate interleaving structures. This study suggests that the multi-scale combination of (i) the lateral stirring of the Kuroshio nutrient stream by developed mixed layer fronts during fall to winter, (ii) the associated tilting of along-isopycnal nitrate gradient of the nutrient stream by subinertial shear, which forms vertical interleaving structures, and (iii) the strong turbulent diffusion above them, may provide a route to supply nutrients to oligotrophic surface waters on the south side of the Kuroshio Extension. 相似文献