Hamiltonian Stability of Spin–Orbit Resonances in Celestial Mechanics

The behaviour of ‘resonances’ in the spin-orbit coupling in celestial mechanics is investigated in a conservative setting. We consider a Hamiltonian nearly-integrable model describing an approximation of the spin-orbit interaction. The continuous system is reduced to a mapping by integrating the equations of motion through a symplectic algorithm. We study numerically the stability of periodic orbits associated to the above mapping by looking at the eigenvalues of the matrix of the linearized map over the full cycle of the periodic orbit. In particular, the value of the trace of the matrix is related to the stability character of the periodic orbit. We denote by ε_* (p/q) the value of the perturbing parameter at which a given elliptic periodic orbit with frequency p/q becomes unstable. A plot of the critical function ε_* (p/q) versus the frequency at different orbital eccentricities shows significant peaks at the synchronous resonance (for low eccentricities) and at the synchronous and 3:2 resonances (at higher eccentricities) in good agreement with astronomical observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Late Quaternary palaeohydrology of Lake Pergusa (Sicily,southern Italy) as inferred by stable isotopes of lacustrine carbonates

Ten meters of lacustrine deposits retrieved from Lake Pergusa (Sicily, southern Italy) were investigated through stable isotope composition (carbon and oxygen) of authigenic carbonate (calcareous muds) and freshwater shells. The core chronology was established through three AMS dates, and by correlation with a previously dated nearby core. Stable isotope data show that the lake water evolution was mainly dominated by evaporation. Between ca. 20 and 28 ka the recovered sediments have very high δ¹⁸O values, likely corresponding to very dry climatic conditions. The observed rapid oscillations in the δ¹⁸O of the recovered sediments during this period also suggest important climatic fluctuations. More humid conditions dominated during the Holocene period, with the wettest interval occurring between ca. 9000 and 3000 years BP. Late Holocene sediments represent a substantial return to drier conditions. The available pollen data from a nearby core substantially confirm this general climatic trend during the Holocene. The positive correlation between δ¹³C of the calcareous muds and carbonate content suggests that biological activity played a key role in the carbon isotope evolution of dissolved inorganic carbon. However, a clear climatic signal is not evident from the δ¹³C record.     

Phosphorus dynamics in water and sediments in urbanized and non-urbanized rivers in Southern Brazil

Phosphorus flux models show that the removal tends to be a common feature in polluted estuarine systems whereas the release of P to the adjacent coastal area occurs in pristine environments. This study analyzes the distribution of P in water and sediments along six rivers in the south coast of Brazil. Three rivers located inside protected areas were considered non-polluted and used as a control of urbanization. The other three, situated within urbanized areas, were considered as having highly elevated concentrations of P. Results showed a different behavior of P in water and sediments located in urbanized and non-urbanized areas. The concentrations of dissolved organic (P-org) and inorganic (P-inorg) phosphorus in water, and the total phosphorus (P-tot) and polyphosphate (P-poly) in sediments where higher in the urbanized rivers compared to the non-urbanized ones. Both P of punctual origin and of diffuse origin contributed to the maintenance of elevated concentrations and disturbed the natural fluxes along the polluted rivers. The minimum and maximum concentrations in urbanized areas varied from 0.39 to 12.45 (microM) for P-org and 0.00 to 5.92 (microM) for P-inorg in water, and in sediments from 89.90 to 808.16 (microM g(-1)) for P-tot and 0.00 to 76.51 (microM g(-1)) for P-poly. In non-urbanized areas concentrations in water varied from 0.22 to 1.20 (microM) for P-inorg and 4.43 to 5.56 (microM) for P-org, and in sediments from 45.91 to 652.26 (microM g(-1)) for P-tot and 0.00 to 8.61 (microM g(-1)) for P-poly. Using a hierarchical sampling design and a simple model of variation of P (K(d) model) it was possible to demonstrate that urbanized and non-urbanized estuaries may act as sinks or sources of P. The variation of P analysis in different points along each of the six rivers showed that release and removal areas may occur within a same river independently of its urbanization.     

Stress pattern at Campi Flegrei from focal mechanisms of the 1982–1984 earthquakes (southern Italy)

Campi Flegrei is a Holocene volcanic area in the Campanian Plain (Southern Italy) within the Apennine Chain, a neogenic thrust belt built up since the Middle Miocene. The volcanic complex consists of a c. 12-km-diameter caldera containing several monogenetic volcanoes, the youngest of which (Monte Nuovo) erupted in 1538. Since at least Roman times, the area has also been affected by slow vertical movements (bradiseismic activity). Between 1982 and 1985, this slow motion was interrupted by a period of more rapid displacement which caused a maximum uplift of 180 cm in the town of Pozzuoli. To model the local stress field associated with the uplift, the Angelier inversion technique has been applied using the focal mechanisms of forty-nine earthquakes which occurred between April 1982 and December 1984. The results show that doming coupled with a regional extensional strain can account for the seismic phenomena that affected the area.     

Marine geology of the Medriff Corridor, Mediterranean Ridge

Abstract Thirty-one piston and/or gravity cores not exceeding 10 m in length were raised in selected areas of a 300 km-long transect (Medriff Corridor) crossing the Mediterranean Ridge, an accretionary complex subject to continent/continent collision, containing an important evaporitic body (Messinian evaporites), in order to ground-truth the geological make-up. Core location, very accurate with reference to a complex bottom configuration, was preceded by swathe mapping, seismic profiling and side-scan sonar investigations. Most sediment cores have a pelagic facies, with biogenic marls as dominant lithology, and sapropels and tephras as minor, isochronous lithologies. A combination of isochronous lithologies and calcareous plankton biochronology permits high resolution stratigraphic correlations. Pelagic facies sediments are Middle Pleistocene to Holocene in age. Two cores associated with mounds located along thrusts contain a matrix-supported mud breccia of deep provenance, Burdigalian-Langhian in age, similar to that characteristic of the Mediterranean Ridge diapiric belt (Cita et al. 1995 ). Three new brine-filled anoxic basins (Urania, l'Atalante and Discovery) were discovered. The brines originated from submarine dissolution of Messinian evaporites and are different in the various basins. The sedimentary record strongly differs from basin to basin. These brine lakes are very young (35 000 years or less). A drastic change in sedimentation rate recorded in the Discovery Basin suggests that basin collapse was sudden and followed by progressive development of basin anoxia. Some cores were analyzed with a prototype multisensor for P-wave velocity, magnetic susceptibility and density. Sapropels show up as abrupt decreases in P-wave velocity and density, and tephra as sudden increases in magnetic susceptibility. Mud breccia displays P-wave velocities greater than pelagic marls, with peaks related to lithic clasts. Anoxic sediments have high P-wave velocities; peaks are associated with gypsum crystals.     

Using historical maps to analyze two hundred years of land cover changes: case study of Sorrento peninsula (south Italy)

Historical maps are effective sources of geographical information and useful for historical and territorial research. In this study, the examination of landscape dynamics on the basis of historical maps over a period of more than 200 years was conducted. The study area is Sorrento peninsula and part of the near Sarno river basin in South Italy. This study provides a general framework for the assessment of the overall quality and accuracy of historical maps. The application of the methodology used in this specific case study can contribute to a better understanding of the dynamics of the landscape in the long term. The derived knowledge can be applied in the planning of the landscape in order to implement correct conservation strategies. The comparison was made on four maps 1817, 1875, 1960, and 2006. Geodetic accuracy of the sheet maps of 1817 and 1875 offer a right basis for a macro analysis of land cover dynamics, evaluating conversion from one land cover category to another. Main transformation, identified in the period between 1875 and 1960, was the disappearance of vineyards, which covered 25% of the total study area in 1875. Agricultural areas increased in this period to cover 57% of the total area.     

Weighting of Parts in Compositional Data Analysis: Advances and Applications

Mathematical Geosciences - It often occurs in practice that it is sensible to give different weights to the variables involved in a multivariate data analysis—and the same holds for...     

The contrasting geochemical message from the New Caledonia gabbronorites: insights on depletion and contamination processes of the sub-arc mantle in a nascent arc setting

The New Caledonia ophiolite hosts one of the rare examples of crust-mantle sections built in a nascent arc environment, providing the unique opportunity to investigate the first stages of arc magmatism in a subduction setting. The sequence consists of refractory harzburgites, overlain by ultramafic (dunites and wehrlites) and mafic lithologies (gabbronorites). The gabbronorites occur in the upper part of the sequence as decimetre to metre-size sills. They are mainly formed (??55 to 70 vol%) of Ca-rich plagioclase (An up to 96 mol%) and high Mg# (88–92), Al₂O₃-poor (1.5–2.4 wt%) clinopyroxene (8–20 vol%), often rimmed by interstitial or poikilitic orthopyroxene (6–27 vol%). Mg-rich olivine (3–15 vol%, Fo?=?87–89 mol%) occurs as anhedral, resorbed crystals. Whole rock (WR) compositions exhibit high Mg# (86–92) and strikingly low trace element contents. They own LREE-depleted patterns, with nearly flat (0.82?≤?Dy_N/Yb_N?≤?1.00) and low HREE (Yb_N?=?0.2–0.9) and positive Eu anomalies. Clinopyroxene trace element chemistry mirrors the extreme depletion of the WR. By contrast, FME enrichments are observed for WR and clinopyroxene. Geochemical models show that the gabbronorites crystallized from primitive, ultra-depleted melts bearing evidence of fluid contamination processes, but with significantly different geochemical signatures compared to boninitic rocks worldwide, i.e. lower LREE-MREE, and absence of Nb depletion and Zr–Hf enrichments. Nd isotopes (+?8.2?≤?εNd_i?≤?+?13.1), together with radiogenic Pb isotopic ratios, support an origin from a DMM source variably modified by slab fluids. We propose that the geochemical signature of the New Caledonia gabbronorites reflect emplacement of primitive, non-aggregated, magma batches in the lower fore-arc crust, during the first phases of arc formation.     

Quantitative integration of 3D and 4D seismic impedance into reservoir simulation model updating in the Norne Field

The ultimate goal of reservoir simulation in reservoir surveillance technology is to estimate long-term production forecasting and to plan development and management of petroleum fields. However, maintaining reliable reservoir models which honour available static and dynamic data, involve inherent risks due to the uncertainties in space and time of the distribution of hydrocarbons inside reservoirs. Recent applications have shown that these uncertainties can be reduced by quantitative integration of seismic data into the reservoir modelling workflows to identify which areas and reservoir attributes of the model should be updated. This work aims using seismic data to reduce ambiguity in calibrating reservoir flow simulation model with an uncertain petro-elastic model, proposing a circular workflow of inverted seismic impedance (3D and 4D) and engineering studies, with emphasis on the interface between static and dynamic models. The main contribution is to develop an updating procedure for adjusting reservoir simulation response before using it in the production forecasting and enhance the interpretive capability of reservoir properties. Accordingly, the workflow evaluates consistency of reservoir simulation model and inverted seismic impedance, assisted by production history data, to close the loop between reservoir engineering and seismic domains. The methodology is evaluated in a complex, faulted, sandstone reservoir, the Norne benchmark field, where a significant reservoir behaviour understanding (about the static and dynamic reservoir properties) is obtained towards the quantitative integration of seismic impedance data. This leads to diagnosis of the reservoir flow simulation reliability and generation of an updated simulation model consistent with observed seismic and well production history data, as well as a calibrated petro-elastic model. Furthermore, as Norne Field is a benchmark case, this study can be considered to enrich the discussions over deterministic or probabilistic history matching studies.     

Changes in biomass structure and trophic status of the plankton communities in a highly dynamic ecosystem (Gulf of Venice,Northern Adriatic Sea)

The changes in the plankton biomass structure in relation to nutrient inputs were studied in the Gulf of Venice (Northern Adriatic Sea), an area characterized by a very marked trophic state variability. The investigation was carried out at two stations, in March, May and July 2005 and 2006, considering the whole water column. The size structure (from picoplankton to mesozooplankton) of both autotrophs and heterotrophs was analysed. Signals of diluted waters and nutrient inputs were more marked in 2005 than in 2006. In 2005, the total plankton biomass was almost double (87 ± 37 μg·C·l^?1) that in 2006 (44 ± 26 μg·C·l^?1). The variations were determined mainly by phytoplankton, with a 70% decrease, and a shift from a community dominated by microphytoplankton (49 ± 12%) in 2005 to one dominated by bacteria (43 ± 11%) in 2006 was observed. The relationship between the heterotrophic (H) and autotrophic (A) biomass indicated a rapid decline of the H/A ratio with increasing phytoplankton biomass. This study, although temporally limited, is consistent with the results reported for other marine environments and it seems to confirm the importance of nutrient inputs in structuring the biomass of plankton community.