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101.
Bally G Mesnage V Deloffre J Clarisse O Lafite R Dupont JP 《Marine pollution bulletin》2004,49(3):163-173
A seasonal field study was carried out in the Seine estuary to determine the chemistry of sediment porewaters using the 'peeper' technique and changes in the elevation of the mudflats using the 'Altus' technique. This approach allowed us to evaluate the release of nutrients and to link these releases to the sediment hydrodynamics. Our results show that nutrient and organic matter cycling in a Seine estuary mudflat exhibits a seasonal behaviour, which is mainly influenced by variations in hydrodynamics. Sediments, rich organic matter, were input during floods and they were mineralized during summer and autumn, releasing nutrients and dissolved organic carbon into the sediment porewaters. The nutrient release, including ammonium, is mainly linked to the mineralization of organic matter, while the release of phosphate is delayed. The delay could be the result of phosphate association with organic matter and/or its co-precipitation with calcium and iron. 相似文献
102.
Carbon and water cycling in a Bornean tropical rainforest under current and future climate scenarios
Tomoomi Kumagai Gabriel G. Katul Amilcare Porporato Taku M. Saitoh Mizue Ohashi Tomoaki Ichie Masakazu Suzuki 《Advances in water resources》2004,27(12):1844
We examined how the projected increase in atmospheric CO2 and concomitant shifts in air temperature and precipitation affect water and carbon fluxes in an Asian tropical rainforest, using a combination of field measurements, simplified hydrological and carbon models, and Global Climate Model (GCM) projections. The model links the canopy photosynthetic flux with transpiration via a bulk canopy conductance and semi-empirical models of intercellular CO2 concentration, with the transpiration rate determined from a hydrologic balance model. The primary forcing to the hydrologic model are current and projected rainfall statistics. A main novelty in this analysis is that the effect of increased air temperature on vapor pressure deficit (D) and the effects of shifts in precipitation statistics on net radiation are explicitly considered. The model is validated against field measurements conducted in a tropical rainforest in Sarawak, Malaysia under current climate conditions. On the basis of this model and projected shifts in climatic statistics by GCM, we compute the probability distribution of soil moisture and other hydrologic fluxes. Regardless of projected and computed shifts in soil moisture, radiation and mean air temperature, transpiration was not appreciably altered. Despite increases in atmospheric CO2 concentration (Ca) and unchanged transpiration, canopy photosynthesis does not significantly increase if Ci/Ca is assumed constant independent of D (where Ci is the bulk canopy intercellular CO2 concentration). However, photosynthesis increased by a factor of 1.5 if Ci/Ca decreased linearly with D as derived from Leuning stomatal conductance formulation [R. Leuning. Plant Cell Environ 1995;18:339–55]. How elevated atmospheric CO2 alters the relationship between Ci/Ca and D needs to be further investigated under elevated atmospheric CO2 given its consequence on photosynthesis (and concomitant carbon sink) projections. 相似文献
103.
We invert 2D surface gravity data constrained both by geological and seismic information. We use a number of pre-processing tools in order to reduce the general multi-body inversion into several single-body inversions, whereby we can reduce the overall complexity of the inversion task. This is done with as few assumptions as possible. Furthermore, for a single-body inversion we uncouple the determination of the shape of the causative sources from the determination of their mass density contrast to the surroundings. The inversion for the geometrical shape of the source body is done in steps. Firstly, a rough 3D shape of the source is modelled—a model consisting of the vertical mass columns of equal height. The horizontal extension is implied by the surface gravity signal. Subsequently, the shape of each source body is modified to obtain a better fit to the surface gravity data. In each modification step, the overall change of the shape of the source body is followed by an update of the mass density contrast to the surroundings. The technique was applied to a set of gravity data from the Eastern Goldfield area in Western Australia. The area has been widely studied in the past. In 1999, two seismic profiles that cross-sect the area were measured. Furthermore, an extensive geological modelling for the area has been conducted. The practical goal of this work was to verify the geological interpretation using the potential field data (mainly the gravity data although magnetic data were also available) and only weakly constrained by the seismic information. The result was the reconstruction of the ‘rough’ 3D geometry of the source bodies and the estimation of a constant mass density contrast to the surroundings. A possible extension of this technique for detailed studies of the geological model is briefly discussed. 相似文献
104.
An Investigation of Higher-Order Closure Models for a Forested Canopy 总被引:11,自引:10,他引:1
Gabriel Katul 《Boundary-Layer Meteorology》1998,89(1):47-74
Simultaneous triaxial sonic anemometer velocity measurements vertically arrayed at six levels within and above a uniform pine forest were used to examine two parameterization schemes for the triple-velocity correlation tensor employed in higher-order closure models. These parameterizations are the gradient-diffusion approximation typically used in second-order closure models, and the full budget for the triple-velocity correlation tensor typically employed in third-order closure models. Both second- and third-order closure models failed to reproduce the measured profiles of the triple-velocity correlation within and above the canopy. However, the Reynolds stress tensor profiles (including velocity variances) deviated greatly from the measurements only within the lower levels of the canopy. It is shown that the Reynolds stresses are most sensitive to the parameterization of the triple-velocity correlation in these lower canopy regions where local turbulent production is negligible and turbulence is mainly sustained by the flux transport term. The failure of the third-order closure model to reproduce the measured third moments in the upper layers of the canopy-top contradicts conclusions from a previous study over shorter vegetation but agrees with another study for a deciduous forest. Whether the third-order closure model failure is due to the zero-fourth-cumulant closure approximation is therefore considered. Comparisons between measured and predicted quadruple velocity correlations suggest that the zero-fourth-cumulant approximation is valid close to the canopy-atmosphere in agreement with recent experiments. 相似文献
105.
The local effect of intermittency on the inertial subrange energy spectrum of the atmospheric surface layer 总被引:1,自引:0,他引:1
Jozsef Szilagyi Gabriel G. Katul Marc B. Parlange John D. Albertson Anthony T. Cahill 《Boundary-Layer Meteorology》1996,79(1-2):35-50
Orthonormal wavelet expansions are applied to atmospheric surface layer velocity measurements. The effect of intermittent events on the energy spectrum of the inertial subrange is investigated through analysis of wavelet coefficients. The local nature of the orthonormal wavelet transform in physical space makes it possible to identify a relationship between the inertial subrange slope of the local wavelet spectrum and a simple indicator (i.e. the local variance of the signal) of local intermittency buildup. The slope of the local wavelet energy spectrum in the inertial subrange is shown to be sensitive to the presence of intermittent events. During well developed intermittent events (coherent structures), the slope of the energy spectrum is somewhat steeper than -5/3, while in less active regions the slope is found to be flatter than -5/3. When the slopes of local wavelet spectra are ensemble averaged, a slope of -5/3 is recovered for the inertial subrange. 相似文献
106.
107.
Thierry Sempere Gabriel Carlier Pierre Soler Michel Fornari Víctor Carlotto Javier Jacay Oscar Arispe Didier Nraudeau Jos Crdenas Silvia Rosas Nstor Jimnez 《Tectonophysics》2002,345(1-4)
Integrated studies and revisions of sedimentary basins and associated magmatism in Peru and Bolivia (8–22°S) show that this part of western Gondwana underwent rifting during the Late Permian–Middle Jurassic interval. Rifting started in central Peru in the Late Permian and propagated southwards into Bolivia until the Liassic/Dogger, along an axis that coincides with the present Eastern Cordillera. Southwest of this region, lithospheric thinning developed in the Early Jurassic and culminated in the Middle Jurassic, producing considerable subsidence in the Arequipa basin of southern Peru. This 110-Ma-long interval of lithospheric thinning ended 160 Ma with the onset of Malm–earliest Cretaceous partial rift inversion in the Eastern Cordillera area.The lithospheric heterogeneities inherited from these processes are likely to have largely influenced the distribution and features of younger compressional and/or transpressional deformations. In particular, the Altiplano plateau corresponds to a paleotectonic domain of “normal” lithospheric thickness that was bounded by two elongated areas underlain by thinned lithosphere. The high Eastern Cordillera of Peru and Bolivia results from Late Oligocene–Neogene intense inversion of the easternmost thinned area. 相似文献
108.
Diana Zúñiga M. Mar Flexas Anna Sanchez-Vidal Johan Coenjaerts Antoni Calafat Gabriel Jordà Jordi García-Orellana Joan Puigdefàbregas Miquel Canals Manuel Espino Francesc Sardà Joan B. Company 《Progress in Oceanography》2009,82(4):239-251
Within the framework of the multidisciplinary RECS project and with the aim of describing the particle flux transfer from the continental shelf to the deep basin, an array of five mooring lines equipped with a total of five pairs of PPS3/3 sequential-sampling sediment traps and RCM-7/8 current meters were deployed 30 m above the bottom from March 2003 to March 2004 inside and outside the Blanes Canyon. One mooring line was located in the upper canyon at 600 m depth, one in the canyon axis at 1700 m depth and other two close to the canyon walls at 900 m depth. A fifth mooring line was deployed in the continental open slope at 1500 m water depth.The highest near-bottom downward particle flux (14.50 g m−2 d−1) was recorded at the trap located in the upper canyon (M1), where continental inputs associated with the presence of the Tordera River are most relevant. On the other hand, the downward fluxes (4.35 g m−2 d−1) in the canyon axis (M2) were of the same order as those found in the western flank (M3) of the canyon. Both values were clearly higher than the value (1.95 g m−2 d−1) recorded at the eastern canyon wall (M4). The open slope (M5) mass flux (5.42 mg m−2 d−1) recorded by the sediment trap located outside the canyon system was three orders of magnitude lower than the other values registered by the inner canyon stations. The relevance of our data is that it explains how the transport pathway in the canyon occurs through its western flank, where a more active and persistent current toward the open ocean was recorded over the entire year of the experiment.Off-shelf sediment transport along the canyon axis showed clear differences during the period of the study, with some important events leading to strong intensifications of the current coupled with large transport of particle fluxes to the deepest parts of the canyon. Such events are primarily related to increases in river discharge and the occurrence of strong storms and cascading events during the winter.In summary, in this study it is shown that the dynamics of the water masses and the currents in the study area convert the sharp western flank of the Blanes Canyon in a more active region that favors erosion processes than the eastern flank, which has a smoother topography and where the absence of erosional conditions yields to steadier sedimentary processes. 相似文献
109.
Araceli Zamora-Camacho Juan Manuel Espíndola Gabriel Reyes-Dávila 《Pure and Applied Geophysics》2007,164(1):39-52
Volcán de Colima, the most active volcano in Mexico, had a climactic episode on 20 November, 1998. On this date, a dome formed
on the small summit crater during the previous few days, collapsed generating block-and-ash flows. The event was preceded
by almost twelve months of seismic activity, which continued afterwards for several more months. We analyzed the main seismic
activity, which occurred from 20 March, 1998 to 31 March, 1999. The seismicity was dominated by volcano-tectonic earthquakes
before the climax, and subsequently by hybrid and long-period earthquakes. We determined the frequency of events for the entire
period, and located most of the volcano-tectonic events. To assess the possibility that these earthquakes were generated by
the same source, they were tested for their similitude through cross correlation in the time domain. Six groups of similar
events, or earthquake families, were generated. The members of these families appeared before the 20 November event, apparently
ceasing afterwards. We examined the location of the families' events with respect to an existing gravity model in which an
anomalous body of negative density contrast suggests the presence of the magma chamber. Most of the family events occur on
top of the anomalous body, which suggests they were associated with the passage of magma through the feeding conduits of the
volcano. 相似文献
110.