An individual-based population dynamic model for estimating biomass yield and nutrient fluxes through an off-shore mussel (Mytilus galloprovincialis) farm     

Daniele Brigolin  Gabriele Dal Maschio  Federico Rampazzo  Michele Giani  Roberto Pastres 《Estuarine, Coastal and Shelf Science》2009

The fluxes of carbon, nitrogen and phosphorus through an off-shore long-line Mytilus galloprovincialis farm during a typical rearing cycle were estimated by combining a simple population dynamic model, based on a new individual model, and a set of field data, concerning the composition of the seston, as well as that of mussel meat and faeces. The individual model, based on an energy budget, was validated against a set of original field data, which were purposely collected from July 2006 to May 2007 in the North-Western Adriatic Sea (Italy) and was further tested using historical data. The model was upscaled to the population level by means of a set of Monte Carlo simulations, which were used for estimating the size structure of the population. The daily fluxes of C, N and P associated with mussel filtration, excretion and faeces and pseudo-faeces production were integrated over the 10-month-long rearing cycle and compared with the total amount of C, N and P removed by harvesting. The results indicate that the individual model compares well with an existing literature model and provides reliable estimations of the growth of mussel specimen over a range of trophic conditions which are typical of the Northern Adriatic Sea coastal area. The results of the budget calculation indicate that, even though the harvest represents a net removal of phosphorus and nitrogen from the ecosystem, the mussel farm increases the retention time of both nutrients in the coastal area, via the deposition of faeces and pseudo-faeces on the sea-bed. In fact, the amount of nitrogen associated with deposition is approximately twice the harvested one and the amount of phosphorus is approximately five times higher. These findings are in qualitative agreement with the results of literature budget and model calculations carried out in a temperate coastal embayment. This agreement suggests that the proper assessment of the overall effect of long-line mussel farming on both the benthic and pelagic ecosystem asks for an integrated modelling approach, which should include the dynamic of early diagenesis processes, as well as of that of nutrients released from the surface sediment.  相似文献   

Hybrid character and pre-eruptive events of Mt Amiata volcano (Italy) inferred from geochronological,petro-geochemical and isotopic data     

Anita Cadoux  Daniele L. Pinti 《Journal of Volcanology and Geothermal Research》2009,179(3-4):169-190

A new geochronological and geochemical study was carried out to better constrain the petrogenesis and eruptive history of Monte Amiata, a large Pleistocene trachydacitic volcano of Southern Tuscany. Previous studies suggested a magma mixing origin between calc-alkaline silicic melts from the Tuscan Magmatic Province (TMP) and potassic mafic melts like those found in the Roman Magmatic Province (RMP). Two eruptive episodes–the first at ca. 300 kyr, the second at ca. 200 kyr–were distinguished from the few available ages. However, both the involvement of a RMP-like melt as mafic end-member and the timing of volcanic activity remained to be ascertained. The K–Ar ages obtained on plagioclase, sanidine and glass separated from Mt Amiata volcanic rocks demonstrate the sanidine is the most suitable phase for K–Ar dating. Sanidine yields ages of 304–293 kyr for the basal trachydacitic unit (BTC), 298–280 kyr in the domes unit (DLC) and unexpected older ages of 312–308 kyr for the more mafic summit lava unit (OLL). A careful re-examination of the literature ages together with those obtained in this study shows that they tend to a common age of ca. 300 kyr whatever the volcanic unit. We interpret this as a reset of the K–Ar chronometer in response to a consequent recharge of the silicic magma reservoir by hot mafic melts. This recharge most probably triggered the first volcanic eruption of Mt Amiata magmas. In our model, we suppose an initially chemically-stratified magma chamber; the input of deep hot mafic melts reset the crystals clock and probably allowed the eruption of the huge amount of trachydacitic crystal mush. We propose that the controversial BTC unit could have emplaced during a non-explosive eruption if we consider either pre-eruption passive degassing or extrusion of the trachydacites as magmatic foam.First Pb isotopic data of mafic enclaves from the trachydacitic units, together with major and trace elements and new Sr and Nd data support the magma mixing as the dominant process at the origin of the Mt Amiata volcanic rocks. The similar LILE/HFSE ratios evidenced in this contribution between the magmatic enclaves of Mt Amiata and RMP volcanic rocks, together with their comparable Sr, Nd and Pb isotopic compositions, definitively argue for the involvement of a RMP-like melt in the mixing. The Mt Amiata is thus indisputably a hybrid volcano between TMP and RMP in terms of petrogenesis and ages.  相似文献   

Anomalously deep earthquakes in northwestern Italy     

Marco Cattaneo  Paolo Augliera  Stefano Parolai  Daniele Spallarossa 《Journal of Seismology》1999,3(4):421-435

It is usually assumed that earthquakes in intraplate regions occur in the upper crust, and northwestern Italy is generally assigned to this kind of normal seismicity. In this work, the depth distribution of the events localized in this area by the Istituto Geofisico Geodetico (IGG) seismic network in the period 1991–1997 is analyzed in detail. In particular, the location capability of the network is discussed, adopting as reference quarry blasts (for the epicentral position) and the locations obtained from a dense temporary network (for the depth estimate). Within the so-obtained error limits, the depth distribution of events show a characteristic pattern: while for most of the area covered by the network the well-located seismicity lies within the first 20 km of depth, in a band following the inner arc of the Western Alps, numerous events have anomalously large focal depths, reaching a maximum of 114 km. These depth determinations cannot be attributed to instabilities of the location procedure: different choices of the propagation models used for the hypocentral determination led to very similar depth values, always significantly larger than the standard values for the surrounding areas. A strong correlation has been found between the 3-dimensional distribution of these foci and the P-wave propagation anomalies obtained from tomographic studies, suggesting a direct link between elastic and rheological properties of lower crust and upper mantle in this area.  相似文献   

Water table variations in Atacama Desert alluvial fans: discussion of “Evidence of short-term groundwater recharge signal propagation from the Andes to the central Atacama Desert: a singular spectrum analysis approach”*     

Benoît Viguier  Hervé Jourde  Véronique Leonardi  Elisabeth Lictevout  Linda Daniele 《水文科学杂志》2020,65(9):1606-1613

ABSTRACT

Using a statistical approach, Scheihing attempts to demonstrate the direct influence of recharge events in the Precordillera and the Andean Piedmont on water table variations in downstream alluvial fans. The author “unquestionably” discards the existence of ephemeral recharge processes in alluvial fans although they are frequently impacted by major floods. However, the author does not consider previous publications about recharge processes in arid alluvial fans, the hydraulic setting of the Pampa del Tamarugal Aquifer (PTA) and anthropogenic pressure changes in the PTA. Because the sustainable management of groundwater resources in drylands depends on a good understanding of hydrogeological processes, we propose a thorough reinterpretation of the short- and long-term PTA water table variations addressed by the author. In this comment, we illustrate the limits of the sole use of a statistical approach for characterizing both recharge processes and factors controlling the water table variations in the Atacama Desert.  相似文献   

Seismic safety of reinforced concrete members and structures     

Hooshang Banon  Daniele Veneziano 《地震工程与结构动力学》1982,10(2):179-193

Based on cyclic load tests of large-scale reinforced concrete elements and assemblages, a probabilistic model of member failure is developed. The model gives the probability of survival at time t as a functional of damage ratio and dissipated energy up to t. After extension to multivariate survival of several members with correlated resistance, the model is used to calculate the safety of reinforced concrete frames subjected to given input motions. Results are in terms of the probability of local failure and of no failure anywhere in the system.  相似文献   

Flexural uplift of a lithospheric slab near the Vema transform (Central Atlantic): Timing and mechanisms     

Enrico Bonatti  Daniele Brunelli  W. Roger Buck  Anna Cipriani  Paola Fabretti  Valentina Ferrante  Luca Gasperini  Marco Ligi   《Earth and Planetary Science Letters》2005,240(3-4):642-655

The Vema Transverse Ridge (VTR) is a prominent, long and narrow topographic anomaly that runs for over 300 km along a sea floor spreading flow line south of the Vema transform at 11° N in the Atlantic. It rises abruptly about 140 km from the axis of the Mid-Atlantic Ridge (MAR) in 10 Myr old crust and runs continuously up to 25 Myr old crust. It reaches over 3 km above the predicted lithospheric thermal contraction level. It is absent in crust younger than 10 Myr; thus, the uplift of the VTR must have ended roughly 10 Ma. The VTR is interpreted as the exposed edge of a flexured and uplifted slab of oceanic lithosphere that was generated at an 80 km long MAR segment. Based on satellite gravimetry imagery this MAR segment was born roughly 50 Ma and increased its length at an average rate of 1.6 mm/yr. Multibeam data show that the MAR-parallel sea floor fabric south of the VTR shifts its orientation by 5° to 10° clockwise in 11–12 Myr old crust, indicating a change at that time of the orientation of the MAR axis and of the position of the Euler rotation pole. This change caused extension normal to the transform, followed between 12 and 10 Ma by flexure of the edge of the lithospheric slab, uplift of the VTR at a rate of 2 to 4 mm/yr, and exposure of a lithospheric section (Vema Lithospheric Section or VLS) at the northern edge of the slab, parallel to the Vema transform. Ages of pelagic carbonates encrusting ultramafic rocks sampled at the base of the VLS at different distances from the MAR axis suggest that the entire VTR rose vertically as a single block within the active transform offset. A 50 km long portion of the crest of the VTR rose above sea level, subsided, was truncated at sea level and covered by a carbonate platform. Subaerial and submarine erosion has gradually removed material from the top of the VTR and has modified its slopes. Spreading half rate of the crust south of the transform decreased from 17.2 mm/yr between 26 and 19 Ma to 16.9 mm/yr between 19 and 10 Ma, to 13.6 mm/yr from 10 Ma to present. The slowing down of spreading occurred close in time to the change in ridge/transform geometry, suggesting that the two events are related. A numerical model relates lithospheric flexure to extension normal to the transform, suggesting that the extent of the uplift depends on the thickness of the brittle layer, consistent with the observed greater uplift of the older lithosphere along the VTR.  相似文献   

A model for silicate melt viscosity in the system CaMgSi₂O₆-CaAl₂Si₂O₈-NaAlSi₃O₈     

James K. Russell  Daniele Giordano 《Geochimica et cosmochimica acta》2005,69(22):5333-5349

Five hundred eighty-five viscosity measurements on 40 melt compositions from the ternary system CaMgSi₂O₆ (Di)-CaAl₂Si₂O₈ (An)-NaAlSi₃O₈ (Ab) have been compiled to create an experimental database spanning a wide range of temperatures (660-2175°C). The melts within this ternary system show near-Arrhenian to strongly non-Arrhenian properties, and in this regard are comparable to natural melts. The database is used to produce a chemical model for the compositional and temperature dependence of melt viscosity in the Di-An-Ab system. We use the Vogel-Fulcher-Tammann equation (VFT: log η = A + B/(T − C)) to account for the temperature dependence of melt viscosity. We also assume that all silicate melts converge to a common viscosity at high temperature. Thus, A is independent of composition, and all compositional dependence resides in the parameters B and C. The best estimate for A is −5.06, which implies a high-temperature limit to viscosity of 10^-5.06 Pa s. The compositional dependence of B and C is expressed by 12 coefficients (b_i=1,2.6, c_j=1,2..6) representing linear (e.g., b_i=1:3) and higher order, nonlinear (e.g., b_i=4:6) contributions. Our results suggest a near-linear compositional dependence for B (<10% nonlinear) and C (<7% nonlinear). We use the model to predict model VFT functions and to demonstrate the systematic variations in viscosity due to changes in melt composition. Despite the near linear compositional dependence of B and C, the model reproduces the pronounced nonlinearities shown by the original data, including the crossing of VFT functions for different melt compositions. We also calculate values of T_g for melts across the Di-An-Ab ternary system and show that intermediate melt compositions have T_g values that are depressed by up to 100°C relative to the end-members Di-An-Ab. Our non-Arrhenian viscosity model accurately reproduces the original database, allows for continuous variations in rheological properties, and has a demonstrated capacity for extrapolation beyond the original data.  相似文献   

Stability of Al- and F-rich titanite in metacarbonate: petrologic and isotopic constraints from a polymetamorphic eclogitic marble of the internal Sesia Zone (Western Alps)   总被引：1，自引：0，他引：1  

Daniele Castelli  Daniela Rubatto 《Contributions to Mineralogy and Petrology》2002,142(6):627-639

Al- and F-rich titanite (3.862O₃ <9.33 wt%, 0.931(F, OH)₁Ti_-1O_-1 substitution within single crystals, particularly at grain boundaries with omphacite and/or phengite. In-situ ion microprobe U-Pb analysis of titanite domains that have various Al and F contents yielded apparent ²⁰⁶Pb/²³⁸U ages scattering between 283 and 153 Ma. Chemical and petrological data are indispensable to interpret this complex age distribution, and the good correlation between ²⁰⁶Pb/²³⁸U ratios and Al content indicates that the Al- and F-rich titanite was formed during pre-Alpine metamorphism (𔕑ᆟ Ma). Progressively younger ages are obtained in domains with decreasing Al and F content, suggesting that partial chemical re-equilibration was responsible for the incomplete isotopic resetting during Alpine metamorphism. Petrological and U-Pb data show that Al- and F-rich titanite should be used with caution to infer high-pressure conditions in polymetamorphic carbonate systems.  相似文献   

Contrasting styles of Mount Vesuvius activity in the period between the Avellino and Pompeii Plinian eruptions,and some implications for assessment of future hazards     

Daniele Andronico  Raffaello Cioni 《Bulletin of Volcanology》2002,64(6):372-391

Intense explosive activity occurred repeatedly at Vesuvius during the nearly 1,600-year period between the two Plinian eruptions of Avellino (3.5 ka) and Pompeii (79 A.D.). By correlating stratigraphic sections from more than 40 sites around the volcano, we identify the deposits of six main eruptions (AP1-AP6) and of some minor intervening events. Several deposits can be traced up to 20 km from the vent. Their stratigraphic and dispersal features suggest the prevalence of two main contrasting eruptive styles, each involving a complex relationship between magmatic and phreatomagmatic phases. The two main eruption styles are (1) sub-Plinian to phreato-Plinian events (AP1 and AP2 members), where deposits consist of pumice and scoria fall layers alternating with fine-grained, vesiculated, accretionary lapilli-bearing ashes; and (2) mixed, violent Strombolian to Vulcanian events (AP3-AP6 members), which deposited a complex sequence of fallout, massive to thinly stratified, scoria-bearing lapilli layers and fine ash beds. Morphology and density variations of the juvenile fragments confirm the important role played by magma-water interaction in the eruptive dynamics. The mean composition of the ejected material changes with time, and shows a strong correlation with vent position and eruption style. The ranges of intensity and magnitude of these events, derived by estimations of peak column height and volume of the ejecta, are significantly smaller than the values for the better known Plinian and sub-Plinian eruptions of Vesuvius, enlarging the spectrum of the possible eruptive scenarios at Vesuvius, useful in the assessment of its potential hazard.  相似文献   

Comment: Tephrochronological dating of varved interglacial lake deposits from Piànico‐Sèllere (Southern Alps,Italy) to around 400 ka. Achim Brauer,Sabine Wulf,Clara Mangili and Andrea Moscariello Journal of Quaternary Science 22: 85–96     

Daniele L. Pinti  Virgile Rouchon  Xavier Quidelleur  Pierre‐Yves Gillot  Sergio Chiesa  Cesare Ravazzi 《第四纪科学杂志》2007,22(4):411-414

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