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Tracking bottom waters in the Southern Adriatic Sea applying seismic oceanography techniques (2012)

Carniel, S. ; Bergamasco, A. ; Book, J. W. ; [weitere]

Elsevier Science Limited

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Publikationsdatum: 2017-04-04

Beschreibung: We present the first results from the Seismic Oceanography (SO) cruise ADRIASEISMIC where we successfully imaged thermohaline fine structures in the shallow water environment (50-150 m) of the southern Adriatic Sea during March 2009 using a compact two GI-gun seismic source. The SO observations are complemented with traditional oceanographic and micro-structure measurements and show that SO can operate over almost the entire water column except (in our experimental layout) for the uppermost 50 m. After processing to enhance the signal-to-noise ratio, the seismic reflection data have a vertical resolution of ~10 m and a horizontal resolution of ~100 m and provide a laterally continuous map of significant thermohaline boundaries that cannot be achieved with conventional physical oceanography measurements alone. ADRIASEISMIC specifically targeted structures in shallow waters, namely along the western margin of the southern Adriatic Sea, between the Gargano peninsula and the Bari canyon, and imaged the Northern Adriatic Dense Water (NAdDW), a bounded cold and relatively dense water mass flowing from the northern Adriatic Sea. The seismic data acquired in Bari canyon and offshore of the Gargano promontory show many regions of strongly reflecting shallow structures, and the incorporation of XBTs measurements with these data demonstrate that they can be interpreted in terms of temperature structures and gradients. In the Gargano region several warm water intrusive structures are mapped along with the offshore transitional edge of cold waters of strong NAdDW influence. In Bari Canyon, waters with NAdDW influence are further mapped extending over the shelf and off the slope into a 5 km long tongue extending offshore between depths of 200-300 m. More generally, even though neither cascading nor open-ocean deep convection process appeared to be evident during March 2009, the SO approach was able to map details of thermal features not resolved by even closely spaced XBT measurements.

Beschreibung: Published

Beschreibung: 30-38

Beschreibung: 3.7. Dinamica del clima e dell'oceano

Beschreibung: JCR Journal

Beschreibung: restricted

Schlagwort(e): seismic oceanography ; Adriatic Sea ; 03. Hydrosphere::03.02. Hydrology::03.02.02. Hydrological processes: interaction, transport, dynamics

Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Materialart: article

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Infection of the gonads of Glaucosoma hebvaicum by the nematode Philometva lateolabracis: occurrence and host response (2002)

Hesp, S. A. ; Hobbs, R. P. ; Potter, I. C.

Oxford, UK : Blackwell Publishing Ltd

Journal of fish biology 60 (2002), S. 0

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ISSN: 1095-8649

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: The prevalence of infection of the West Australian dhufish Glaucosoma hebraicum off the lower west coast of Australia by Philometra lateolabracis was greater among females than males, which contrasts with the situation with Pagrus auratus in waters off New Zealand. Live P. lateolabracis were represented solely by females and were found only in the gonads of fish of mature size (L50 at first maturity = c. 300 mm) caught between December and April and thus during the spawning period of dhufish. Since the gonads were largest during that period, they, and particularly ovaries, would provide an abundant food source in the form of blood. The prevalence of the parasite (live + dead individuals) increased with host body size to reach a maximum of c. 80% in the 700–799 mm length class of females and c. 50% in the largest length class of males. During the spawning period of G hebraicum, P. lateolabracis developed from small, non-gravid females to large gravid females, representing an increase in mass of more than 200 times. The maximum length of P. lateolabracis (470 mm) in G hebraicum is the greatest yet recorded for this species. Gonadosomatic indices provided no evidence that infection by P. lateolabracis leads to a conspicuous atrophy of the ovaries, which contrasts with the situation with the gonads of some of the teleosts infected by Philometra species, and presumably reflects, in part, the small volume of the ovary occupied by P. lateolabracis (c. 3%) and the low intensity of infection (mean = 2.0, maximum = 7). Although the presence of live P. lateolabracis did not stimulate an obvious tissue response by the ovaries during the spawning period of G. hebraicum, both the dead and any live parasites that remain after spawning become encapsulated in fibrous tissue.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1095-8649.2002.tb01692.x

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Lower crustal reflectivity from waveform inversion (1993)

Failly, M. ; Singh, S. C. ; Hobbs, R. W.

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 115 (1993), S. 0

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ISSN: 1365-246X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: Deep seismic reflection profiles show that the lower part of the continental crust often contains many strong subhorizontal reflections. Based on forward modelling, these reflections are interpreted as a sequence of alternating high- and low-velocity layers. A waveform inversion provides an optimum model by minimizing the misfit between observed data and synthetic seismograms. However, it is very difficult to invert for the whole data set, partly because of the large computation time needed in modelling and partly because the high amplitude reflected energy in the upper crust dominates the misfit function.To overcome these difficulties we propose a three-step strategy for inverting the deeper part of seismic reflection data over a narrow aperture in which the velocity structure can be assumed to be 1-D. First, both source wavelet and recorded wavefield are propagated in the plane-wave domain downwards to a particular depth for a given 1-D medium. Because the source-receiver distances are short for deep reflections it is assumed that these reflections are at normal incidence. It is also assumed that the near-surface velocity is known or has been estimated using other inversion schemes. The downward propagation algorithm takes account of nearsurface effects, such as multiple reflections and attenuation. Second, starting from a known background-velocity model, a non-linear iterative waveform inversion is applied to the propagated data set. The method is based on minimizing the difference, sample by sample, between observed and calculated wavefields in a least-squares sense. The forward modelling, which consists of calculating the data from the model, uses a reflectivity method to compute the synthetic seismogram in the plane-wave domain. The model perturbation is calculated with the help of the conjugate gradients method. The non-linear inversion gives the short wavelengths of impedance contrast, which is a function of density and velocity, in the lower crust.Third, an interpretational step is tried in order to recover the medium wavelengths of velocity. The algorithm is tested on synthetic data and then applied to a part of the WAM data set, south-west of England. A good fit to the real data with the optimum model predicts that the velocity contrast of the layers in the lower crust varies from 0.2 km s-1 to 0.5 km s-1 and the thickness from at least 0.075 km to 1 km.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-246X.1993.tb01195.x

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Complex structure along a Mesozoic sea-floor spreading ridge: BIRPS deep seismic reflection, Cape Verde abyssal plain (1994)

McBride, J. H. ; White, R. S. ; Henstock, T. J. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 119 (1994), S. 0

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ISSN: 1365-246X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: As part of an intensive study of a small area of oceanic lithosphere, the British Institutions Reflection Profiling Syndicate (BIRPS) acquired closely spaced deepseismic-reflection profiles over the Early Cretaceous crust of the Cape Verde abyssal plain off West Africa. The survey consisted of profiles spaced at 4 km arranged into strike lines parallel to the old sea-floor spreading axis (‘isochron’ profiles) and orthogonal dip lines oriented in the original direction of spreading (‘flow’ profiles). A large-capacity, well-tuned airgun source and very quiet shooting conditions ensured a high signal-to-noise ratio for deep reflection. Devising a strategy for mitigating contamination from ‘wrap-around’ multiples arriving from previous shots enabled us to use the minimum possible shot-point interval (50 m) allowed for collecting long (18 s) records. Data processing was oriented towards a medium with low root-mean-square velocity, steeply dipping structure, and pervasive low apparent velocity noise from diffraction at the top of the igneous crust. The contrast between the isochron and flow profiles is striking. Isochron profiles are typically highly reflective throughout the igneous crust, consisting of bright, bidirectionally dipping reflection sets that extend in places from the top of the igneous basement down to the interpreted Moho reflection. These reflections do not offset intracrustal or top-basement structure and thus are not interpreted as faults: an igneous intrusive origin seems more likely. Flow profiles are more sparsely reflective but show individual steeply dipping reflections best developed in the upper igneous crust, continuing down in places to the Moho. Dipping reflections on the flow profiles are interpreted as major normal faults since they are clearly associated with offsets of the top of the basement as well as truncation of horizontal reflections within the igneous crust. The dominant dip of these reflections is to the west towards the spreading ridge axis. Reflections from the vicinity of the Moho, while well developed in some places, are not particularly prominent across the survey area. Moho reflections appear to show a different structural relation to crustal features on the isochron and flow profiles: on isochron profiles, dipping reflections occasionally flatten out into, and may merge with, the Moho reflection; on flow profiles, as dipping crustal reflections approach the Moho reflection, they are usually abruptly cut off by it without extending deeper. This survey shows how oceanic crustal structure can vary rapidly over relatively small areas, provides convincing evidence that a structurally complex fabric dominates oceanic igneous crust, and gives a conclusive observation of faults that penetrate the entire oceanic crust.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb00134.x

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Stochastic characterization and seismic response of upper and middle crustal rocks based on the Lewisian gneiss complex, Scotland (1994)

Levander, A. ; England, R. W. ; Smith, S. K. ; [weitere]

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 119 (1994), S. 0

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ISSN: 1365-246X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: We have developed statistical models of upper and middle crustal seismic velocity heterogeneity based on geologic maps and petrophysical data from the Lewisian gneiss complex, Scotland. the level of heterogeneity we have measured is relevant to seismic exploration of the crystalline crust using conventional reflection and refraction techniques. We digitized two 1:10560 geologic maps of Laxfordian (Archean) age Lewisian rocks on a 26.8m grid. Both maps are believed to be representative of the upper and middle crust in north-western Scotland, and both are believed to provide cross-sectional views of parts of the crust. the digital maps were characterized by the statistics of their lithologic populations and by their 2-D spatial autocorrelation functions. Different lithologies were assigned seismic velocities appropriate for the mid-crust using petrophysical data. Three lithologies are dominant: silicic gneisses (Vp∼6.2 km s−1), mafic amphibolites (Vp— 6.75 kms−1), and intermediate composition schists (Vp—6.5kms−1). Both maps have self-affine spatial fabrics.The first map covers the core of a syncline. Its autocorrelation function defines a medium with a fractal dimension of 2.78, a horizontal characteristic length of about 244m and a vertical correlation of about 133m (aspect ratio is 2:1). It has an essentially trimodal velocity (lithology) population consisting of 37 per cent silicicgneiss, 43 per cent mafic amphibolites, and 20 per cent schists. This map is representative of 30-40 per cent of Laxfordian rocks. the second map is a plan view which can be rotated 90° about an axis perpendicular to strike to give a cross-section. This map is characterized by a fractal dimension of 2.55, with a horizontal correlation length of about 111m and a vertical correlation of about 38m (aspect ratio 3:1). It has a nearly bimodal population consisting of 77 per cent silicic gneisses and 22 per cent mafic amphibotites. It is representative of 60-70 per cent of Laxfordian rocks.Lastly we examine the seismic response of an upper to middle crust based on our statistical models using acoustic and elastic 2-D finite-difference synthetic seismograms. Short-offset shot records demonstrate that a Lewisian upper crust produces scattered waves which significantly disrupt signals reflecting from deeper levels. Measurements of transmission scattering Q, and coda decay rates confirm that seismic scattering in Lewisian-type crust is strong. the migrated CMP response of a Lewisian crustal model shows the characteristic ‘salt and pepper’ pattern often observed in the upper crust, and described, incorrectly, as ‘transparent'. We suggest that ‘translucent’ is a more appropriate descriptor.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb00925.x

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Restoration Ecology: Repairing the Earth's Ecosystems in the New Millennium (2001)

Hobbs, R. J. ; Harris, J. A.

Boston, MA, USA : Blackwell Science Inc

Restoration ecology 9 (2001), S. 0

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ISSN: 1526-100X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: The extent of human-induced change and damage to Earth's ecosystems renders ecosystem repair an essential part of our future survival strategy, and this demands that restoration ecology provide effective conceptual and practical tools for this task. We argue that restoration ecology has to be an integral component of land management in today's world, and to be broadly applicable, has to have a clearly articulated conceptual basis. This needs to recognize that most ecosystems are dynamic and hence restoration goals cannot be based on static attributes. Setting clear and achievable goals is essential, and these should focus on the desired characteristics for the system in the future, rather than in relation to what these were in the past. Goal setting requires that there is a clear understanding of the restoration options available (and the relative costs of different options). The concept of restoration thresholds suggests that options are determined by the current state of the system in relation to biotic and abiotic thresholds. A further important task is the development of effective and easily measured success criteria. Many parameters could be considered for inclusion in restoration success criteria, but these are often ambiguous or hard to measure. Success criteria need to relate clearly back to specific restoration goals. If restoration ecology is to be successfully practiced as part of humanity's response to continued ecosystem change and degradation, restoration ecologists need to rise to the challenges of meshing science, practice and policy. Restoration ecology is likely to be one of the most important fields of the coming century.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1526-100x.2001.009002239.x

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Establishment of Perennial Shrub and Tree Species in Degraded Eucalyptus salmonophloia (Salmon Gum) Remnant Woodlands: Effects of Restoration Treatments (2000)

Yates, C. J. ; Hobbs, R. J. ; Atkins, L.

Boston, MA, USA : Blackwell Science Inc

Restoration ecology 8 (2000), S. 0

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ISSN: 1526-100X

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Woodlands dominated by Eucalyptus salmonophloia (salmon gum) occur throughout the fragmented landscape of the southwestern Australian wheatbelt. These remnants are often degraded by livestock grazing and weed invasion and in many cases there is little or no understorey remaining and little or no regeneration of the dominant tree E. salmonophloia. There is a growing interest in developing techniques for restoring remnant woodlands. This study describes techniques for establishing seedlings of the dominant tree and perennial understorey species in E. salmonophloia (salmon gum) woodlands degraded by livestock grazing. The study tests the hypothesis that, in addition to the exclusion of livestock, management of weeds and reintroduction of plant species, restoration of plant species diversity will require techniques which mimic large-scale disturbances, reduce soil compaction, and restore soil water infiltration to suitable rates. Five-month-old seedlings of the dominant tree E. salmonophloia and four commonly associated woody shrubs (Acacia hemiteles, Atriplex semibaccata, Maireana brevifolia, and Melaleuca pauperiflora) were planted into areas that differed with respect to grazing (–rabbit/ −livestock and +rabbit/–livestock), tree canopy disturbance (+/–competition with tree canopy) and amelioration of soil compaction (+/–deep ripping). Following three growing seasons and two summers, the exclusion of rabbits had no significant effect on the survival and growth of planted species. As a consequence grazing treatments are pooled for the purposes of presenting the impacts of removing competition with adult trees and soil deep ripping. The removal of competition with adult E. salmonophloia trees significantly improved the survival of E. salmonophloia seedlings but did not improve survival of understorey species. Deep ripping the soil significantly improved the survival of both E. salmonophloia and the shrub A. hemiteles but did not improve the survival of other understorey species. In contrast to seedling survival, the removal of adult E. salmonophloia trees and deep ripping soil significantly increased the growth of all species. The results indicate that increasing levels of intervention will increase the chances of successfully restoring tree and understorey species diversity in degraded E. salmonophloia woodlands.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1526-100x.2000.80020.x

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Community and population dynamics of serpentine grassland annuals in relation to gopher disturbance (1985)

Hobbs, R. J. ; Mooney, H. A.

Springer

Oecologia 67 (1985), S. 342-351

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ISSN: 1432-1939

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary This study examines the effects of soil disturbance by gophers on patterns of species abundance in an annual grassland community on serpentine soil. We assessed production, dispersal and storage of seed, germination, survivorship and growth of the most abundant species in undisturbed vegetation and on gopher mounds. Fewer seeds of the dominant species were dispersed onto gopher mounds due to the limited movement of seeds from within the closed vegetation. Species with taller flowering stalks were more likely to colonise gopher mounds. The timing of gopher disturbance in relation to the timing of seed fall determined which species could colonise mounds. Lower numbers of seeds falling onto gopher mounds resulted in lower seedling densities of several species compared with undisturbed areas. Survivorship of the commonest species differed between undisturbed areas and gopher mounds formed at different times of year. This resulted in characteristic spectra of species abundance on the different microhabitats, giving rise to distinct spatial patterning in the community. Plants growing on gopher mounds were generally larger and produced more seed than plants in undisturbed vegetation. We suggest that continued gopher disturbance is a factor allowing several species, including perennial grasses, to persist in this community.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00384939

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Invasion of an annual grassland in Northern California by Baccharis pilularis ssp. consanguinea (1987)

Williams, K. ; Hobbs, R. J. ; Hamburg, S. P.

Springer

Oecologia 72 (1987), S. 461-465

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ISSN: 1432-1939

Schlagwort(e): Baccharis pilularis ; Episodic invasion ; Shrub stablishment ; Community change ; El Niño

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary We studied the invasion of a California annual grassland by the shrub, Baccharis pilularis ssp. consanguinea (DC) C.B. Wolf. A series of aerial photographs indicated that the shrub had been present at the study site for 35–45 years but spread very little until the early 1970's. A period of slow expansion was followed by rapid outward spread of the shrub population and large increases in shrub density. Detailed demographic studies showed a period of rapid population increase from 1978 to 1983, with the highest stablishment rates in 1982–83. Establishment was strongly correlated with annual and spring rainfall amounts. An iniiall period of slow outward spread is thought to have profided foci for rapid spread during years of high rainfall.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00377580

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Harvester ant foraging and plant species distribution in annual grassland (1985)

Hobbs, R. J.

Springer

Oecologia 67 (1985), S. 519-523

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ISSN: 1432-1939

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The harvester antVeromessor andrei Mayr is a major seed predator on annual grassland growing on serpentine soil at Jasper Ridge, N. California. Ants forage intensively during morning and evening sessions in areas surrounding nests. Activity is at its most intense in early summer, coinciding with peak seed release for most annual plant species. Ants show strong preferences for seeds of non-dominant species, notablyMicroseris douglasii (DC.) Sch.-Bip., but preferences alter over the season in response to seed availability. Seeds of the dominant annual species,Lasthenia californica DC ex Lindley are not foraged until later in the summer when seeds of other species are less abundant. Seedling densities and species compositions on ant nests differ markedly from surrounding areas with species relative abundances being similar to those found on gopher mounds. An exclosure experiment in areas adjacent to nests indicated that ants significantly reduced the densities of species with preferred seeds. Ants may therefore significantly affect plant distribution and abundance within the serpentine grassland.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00790023

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