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41.
The objective of this paper was to explore the potentialities of sequential statistical estimation methods to assimilate ocean color observations in a primary production model coupled to a 3D hydrodynamic model. The study site was the gulf of Fos—Rhone delta region on the French Mediterranean coast. The high rate of primary production generally observed in this area is mainly due to strong nutrient inputs of the Rhone River. The assimilation method is derived from the singular evolutive extended Kalman filter (SEEK), which uses an error subspace represented by multivariate empirical orthogonal functions (EOF). SeaWiFS chlorophyll data were assimilated by the ecosystem model during a simulation performed under realistic meteorological conditions for the year 2001. An ‘adaptive’ computing method of the EOF was applied in order to lower the instabilities of the filter. Data assimilation system permitted to reduce the mean absolute error between model and data from 1.51 to 0.77 mg m−3 thanks to the SEEK filter, showing a substantial 49% gain. Efficiency of the SEEK filter was then investigated considering several areas of interest inside the modelled domain. Finally, impact of the assimilation scheme on non-observed variables was illustrated and discussed. Throughout this experimentation the data assimilation system showed its potential regarding operational systems. 相似文献
42.
Silvina Stutz C. Marcela Borel Sonia L. Fontana Laura del Puerto Hugo Inda Felipe García-Rodriguez Marcela S. Tonello 《Journal of Paleolimnology》2010,44(3):761-775
We analyzed pollen, non-pollen palynomorphs (NPPs), calcareous microfossils, plant macrofossils, diatoms, chrysophyte cysts,
opal phytoliths and organic matter content in a 123-cm sediment sequence from Nahuel Rucá Lake, a shallow, freshwater system
in the southeastern Pampa grasslands, Argentina. Three stages in the lake evolution were identified. Before 3,680 cal year BP,
only pollen, NPPs (dinoflagellate cysts and acritarchs) and ostracods were recovered, suggesting brackish/saline conditions
in the lake and nearby areas. Freshwater conditions are, however, indicated by Myriophyllum, Pediastrum and Zygnemataceae. The brackish/saline conditions could have been caused by marine influence during a Holocene sea level
high stand that affected the area ca. 6,000 year BP. Between 3,680 and 390 cal year BP, macrophyte pollen and plant macrofossils
indicate increasingly freshwater conditions in the lake and the adjacent area. Diatom and ostracod assemblages, however, suggest
brackish and oligotrophic conditions, giving way to freshwater and meso-eutrophic conditions toward the end of this period.
The relationship between submersed macrophytes (Myriophyllum, Potamogeton, Ceratophyllum, Chara) and planktonic algae (Chlorophyta and diatoms), suggests a shift in the lake from a clear to a turbid state. This turbid
state is more evident after 390 cal year BP. High values of Pediastrum, Scenedesmus and diatoms (Cyclotella meneghiniana, Aulacoseira granulata, A. muzzanensis) observed during this stage could have reduced light penetration, with consequent loss of submersed plants. Pollen and plant
macrofossils in the uppermost 20 cm indicate a shallow, freshwater lake similar to present, though an increase in brackish/freshwater
diatoms suggests an increase in salinity, perhaps related to periodic droughts. Opal phytoliths yield a regional paleoclimatic
reconstruction that agrees closely with inferences made using pollen, mammals and sediment characteristics. 相似文献
43.
44.
Giovanni Fontana Conall Mac Niocaill Richard J. Brown R. Stephen J. Sparks Matthew Field 《Bulletin of Volcanology》2011,73(8):1063-1083
Palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic
and volcaniclastic deposits in kimberlite pipes in southern Africa. Lithic clasts were sampled from a variety of lithofacies
from three pipes for which the internal geology is well constrained (the Cretaceous A/K1 pipe, Orapa Mine, Botswana, and the
Cambrian K1 and K2 pipes, Venetia Mine, South Africa). The sampled deposits included massive and layered vent-filling breccias
with varying abundances of lithic inclusions, layered crater-filling pyroclastic deposits, talus breccias and volcaniclastic
breccias. Basalt lithic clasts in the layered and massive vent-filling pyroclastic deposits in the A/K1 pipe at Orapa were
emplaced at >570°C, in the pyroclastic crater-filling deposits at 200–440°C and in crater-filling talus breccias and volcaniclastic
breccias at <180°C. The results from the K1 and K2 pipes at Venetia suggest emplacement temperatures for the vent-filling
breccias of 260°C to >560°C, although the interpretation of these results is hampered by the presence of Mesozoic magnetic
overprints. These temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall
within the proposed stability field for common interstitial matrix mineral assemblages within vent-filling volcaniclastic
kimberlites. The temperatures are also comparable to those obtained for pyroclastic deposits in other, silicic, volcanic systems.
Because the lithic content of the studied deposits is 10–30%, the initial bulk temperature of the pyroclastic mixture of cold
lithic clasts and juvenile kimberlite magma could have been 300–400°C hotter than the palaeomagnetic estimates. Together with
the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites, the palaeomagnetic results indicate
that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic
deposits. This study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures
of different kimberlite facies. 相似文献
45.
Richard J. Brown S. Manya I. Buisman G. Fontana M. Field C. Mac Niocaill R. S. J. Sparks F. M. Stuart 《Bulletin of Volcanology》2012,74(7):1621-1643
The Igwisi Hills volcanoes (IHV), Tanzania, are unique and important in preserving extra-crater lavas and pyroclastic edifices. They provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes. Cosmogenic 3He dating of olivine crystals from IHV lavas and palaeomagnetic analyses indicates that they are Upper Pleistocene to Holocene in age. This makes them the youngest known kimberlite bodies on Earth by >30?Ma and may indicate a new phase of kimberlite volcanism on the Tanzania craton. Geological mapping, Global Positioning System surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices, craters and lavas. The volcanoes stand <40?m above the surrounding ground and are comparable in size to small monogenetic basaltic volcanoes. Pyroclastic cones consist of diffusely layered pyroclastic fall deposits comprising scoriaceous, pelletal and dense juvenile pyroclasts. Pyroclasts are similar to those documented in many ancient kimberlite pipes, indicating overlap in magma fragmentation dynamics between the Igwisi eruptions and other kimberlite eruptions. Characteristics of the pyroclastic cone deposits, including an absence of ballistic clasts and dominantly poorly vesicular scoria lapillistones and lapilli tuffs, indicate relatively weak explosive activity. Lava flow features indicate unexpectedly high viscosities (estimated at >102 to 106?Pa?s) for kimberlite, attributed to degassing and in-vent cooling. Each volcano is inferred to be the result of a small-volume, short-lived (days to weeks) monogenetic eruption. The eruptive processes of each Igwisi volcano were broadly similar and developed through three phases: (1) fallout of lithic-bearing pyroclastic rocks during explosive excavation of craters and conduits; (2) fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent; and (3) effusion of degassed viscous magma as lava flows. These processes are similar to those observed for other small-volume monogenetic eruptions (e.g. of basaltic magma). 相似文献
46.
Daniele Penna Marco Borga Daniele Norbiato Giancarlo Dalla Fontana 《Journal of Hydrology》2009,364(3-4):311-327
47.
In this paper the scaling hypotheses are applied to annual maximum series of rainfall depth for different rainfall duration to derive the depth–duration–frequency (DDF) curve. It is shown that, based on the empirically observed scaling properties of rainfall and some general assumptions about the cumulative distribution function for the annual maximum of the rainfall depth, it is possible to derive a simple DDF relationship. This general framework provides a basis for the generation of maps that can be used to infer DDF curves at any point of a particular area. Data from a dense raingauge network in a mountainous region in north-eastern Italy (the Trentino Province) are used to clarify the methodology for the construction and regionalization of the DDF relationship. The geographical variation of short-duration (i.e., less than 60 xmin) rainfall extremes is also evaluated by using the same framework. It is found that depth–duration ratios, defined as the ratios of the t-min to the 60-min rainfall depths of the same return period, may be considered independent of return period and geographical location for any storm duration less than 60 min. 相似文献
48.
New trends in marine chemical ecology 总被引：1，自引：0，他引：1
A. Ianora M. Boersma R. Casotti A. Fontana J. Harder F. Hoffmann H. Pavia P. Potin S. A. Poulet G. Toth 《Estuaries and Coasts》2006,29(4):531-551
This essay is the outcome of a colloquium convened in November 2005 at the Benthos Laboratory of the Stazione Zoologica Anton
Dohrn in Ischia, Italy, on chemical ecology and the role of secondary metabolites in the structuring and functioning of marine
biodiversity. The participants of the workshop are part of the European Network of Excellence MarBEF (Marine Biodiversity
and Ecosystem Function), a consortium of 56 European marine institutes to integrate and disseminate knowledge and expertise
on marine biodiversity. Here we review some of the new trends and emerging topics in marine chemical ecology. The first section
deals with microbial chemical interactions. Microbes communicate with each other using diffusible molecules such as N-acylhomoserine
lactones (AHL). These are regulators in cell-density-dependent gene regulation (quorum sensing) controlling microbial processes.
In chemical interactions with higher organisms, microbes can act either as harmful pathogens that are repelled by the host’s
chemical defense or as beneficial symbionts. These symbionts are sometimes the true producers of the host’s secondary metabolites
that have defensive and protective functions for their hosts. We also describe how allelochemicals can shape phytoplankton
communities by regulating competition for available resources, and also interactions among individuals of the same species.
Compounds such as the diatom-derived unsaturated aldehydes have been demonstrated to act as info chemicals, and they possibly
function as a diffusible bloom-termination signal that triggers an active cell death and bloom termination at sea. The same
molecules have also been shown to interfere with the reproductive capacity of grazing animals deterring future generations
of potential predators. Such compounds differ from those that act as feeding deterrents since they do not target the predator
but its offspring. Many of the neurotoxins produced by dinoflagellates act as feeding deterrents, and laboratory experiments
have shown that ingestion of these algae by some microzooplankton and macrozooplankton can cause acute, responses such as
death, incapacitation, altered swimming behavior, and reduced fecundity and egg-hatching success. These effects may rarely
occur in nature because of low individual grazing rates on dinoflagellate cells and grazing on other food sources such as
microflagellates and diatoms. We also consider the nutritional component of marine plant-herbivore interactions, especially
in the plankton, and the information available on the effects of growing conditions of algae on the production of toxic metabolites.
Species producing saxitoxins seem to consistently produce the highest amounts of toxins (on a per cell basis) in the exponential
phase of growth, and there is a decrease in their production under nitrogen, but not under phosphorus stress, where the production
actually increases. We try to explain the circumstances under which organisms defend themselves chemically and argue that
the most likely explanatory model for the production of secondary metabolites used for defense in planktonic organisms is
the carbon nutrient balance hypothesis, which predicts that most algae produce their toxins mainly under conditions where
carbon is in excess and nitrogen (or other nutrients) is limiting. We also discuss chemically mediated macroalgal-herbivore
interactions in the benthos and the large variation in concentration of seaweed defense metabolites at different spatial and
temporal scales. Seaweeds have been shown to produce a large variety of secondary metabolites with highly variable chemical
structures such as terpenoids, acetogenins, amino acid derivates, and polyphenols. Many of these compounds probably have multiple
simultaneous functions for the seaweeds and can act as allelopathic, antimicrobial, and antifouling or ultraviolet-screening
agents, as well as herbivore deterrents. We also provide examples of interactions between marine benthic invertebrates, especially
sponges, molluscs, and cnidarians, that are mediated by specific secondary metabolites and discuss the role of these in shaping
benthic communities. 相似文献
49.
Stefano Conti Daniela Fontana Claudio Corrado Lucente Gian Andrea Pini 《International Journal of Earth Sciences》2014,103(1):281-295
The Montardone mélange (Mm) is a chaotic, block-in-matrix unit outcropping in the Montebaranzone syncline in the northern Apennines. The Mm occurs in the uppermost part of the Termina Fm, the Middle–Late Miocene interval of a succession deposited in a wedge-top slope basin (Epiligurian succession). The Mm is closely associated with bodies of authigenic carbonates, characterized by negative values of δ13C (from ?18.22 to ?39.05 ‰ PDB) and chemosynthetic benthic fauna (lucinid and vesicomyid bivalves). In this paper, we propose that the Mm is a mud volcano originated by the post-depositional reactivation and rising of a stratigraphically lower mud-rich mass transport body (Canossa–Val Tiepido sedimentary mélange or olistostrome) triggered by fluid overpressure. We base our conclusion on (1) the Mm pierces the entire Termina Fm and older Epiligurian units and represents the direct continuation of the underlying Canossa–Val Tiepido mélange; (2) the geometry and facies distribution of the Montebaranzone sandstone body, which are compatible with a confined basin controlled by the rising of the Mm; (3) the systematic presence of large-scale (lateral extension 300–400 m) seep-carbonates associated with the mélange, suggesting a persistent gas-enriched fluid vent from the ascending overpressured mud; (4) blocks and clasts sourced from the Mm, hosted by the authigenic carbonates, conveyed by ascending mud and gas-enriched fluids. The Mm represents one of the few fossil examples of reactivation of a basin-scale sedimentary mélange (olistostrome); a three-stage model showing mechanisms of Mm raising is proposed. 相似文献