Monthly seawater pH and alkalinity measurements were collected between January 1996 and December 2000 at 10°30′N, 64°40′W as part of the CARIACO (CArbon Retention In A Colored Ocean) oceanographic time series. One key objective of CARIACO is to study temporal variability in Total CO2 (TCO2) concentrations and CO2 fugacity (fCO2) at this tropical coastal wind-driven upwelling site. Between 1996 and 2000, the difference between atmospheric and surface ocean CO2 concentrations ranged from about − 64.3 to + 62.3 μatm. Physical and biochemical factors, specifically upwelling, temperature, primary production, and TCO2 concentrations interacted to control temporal variations in fCO2. Air–sea CO2 fluxes were typically depressed (0 to + 10 mmol C m−2 day−1) in the first few months of the year during upwelling. Fluxes were higher during June–November (+ 10 to 20 mmol C m−2 day−1). Fluxes were generally independent of the slight changes in salinity normally seen at the station, but low positive flux values were seen in the second half of 1999 during a period of anomalously heavy rains and land-derived runoff. During the 5 years of monthly data examined, only two episodes of negative air–sea CO2 flux were observed. These occurred during short but intense upwelling events in March 1997 (−10 mmol C m−2 day−1) and March 1998 (− 50 mmol C m−2 day−1). Therefore, the Cariaco Basin generally acted as a source of CO2 to the atmosphere in spite of primary productivity in excess of between 300 and 600 g C m−2 year−1. 相似文献
Magnetic susceptibility in rocks is the sum of the contributions of different magnetic particles (paramagnetic, diamagnetic and ferromagnetic s.l.). These contributions can be measured at variable temperatures or at variable fields (hysteresis loops). Both are time‐consuming techniques that cannot be routinely used in magnetic fabrics analysis. In this study, we propose a simplified method to determine the ferro‐ and paramagnetic contributions to the susceptibility, based on the discrete measurement of susceptibility at two different fields (near 0 and 2.5 T). The results obtained in samples from the Southern Pyrenees and Ebro Basin indicate that the ferromagnetic contribution vary considerably within homogeneous susceptibility values and within the expected range of paramagnetic values. Standard bulk susceptibilities higher than 200 10?6 SI contribute significantly to the ferromagnetic fraction (>50% on average). 相似文献
The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics
which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies and could
be flown within the Cosmic Vision time frame. The mission proposes to perform a set of precision gravitation experiments from
the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: (1) test of the gravity
force law in the Solar System up to and beyond the orbit of Saturn; (2) precise investigation of navigation anomalies at the
fly-bys; (3) measurement of Eddington’s parameter at occultations; (4) mapping of gravity field in the outer solar system
and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13
AU, with the following components: (a) a high-precision accelerometer, with bias-rejection system, measuring the deviation
of the trajectory from the geodesics, that is also giving gravitational forces; (b) Ka-band transponders, as for Cassini,
for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; (c) optional laser equipment, which
would allow one to improve the range and Doppler measurement, resulting in particular in an improved measurement (with respect
to Cassini) of the Eddington’s parameter. In this baseline concept, the main spacecraft is designed to operate beyond the
Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and
fly-by phases allow the mission to achieve its baseline scientific objectives [(1) to (3) in the above list]. In addition
to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend
the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in
the outer Solar System [(4) in the above list].
相似文献
The Regional Atmospheric Modeling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES), developed and evaluated here,
is used to explore the effects of three-dimensional canopy heterogeneity, at the individual tree scale, on the statistical
properties of turbulence most pertinent to mass and momentum transfer. In RAFLES, the canopy interacts with air by exerting
a drag force, by restricting the open volume and apertures available for flow (i.e. finite porosity), and by acting as a heterogeneous
source of heat and moisture. The first and second statistical moments of the velocity and flux profiles computed by RAFLES
are compared with turbulent velocity and scalar flux measurements collected during spring and winter days. The observations
were made at a meteorological tower situated within a southern hardwood canopy at the Duke Forest site, near Durham, North
Carolina, U.S.A. Each of the days analyzed is characterized by distinct regimes of atmospheric stability and canopy foliage
distribution conditions. RAFLES results agreed with the 30-min averaged flow statistics profiles measured at this single tower.
Following this intercomparison, two case studies are numerically considered representing end-members of foliage and midday
atmospheric stability conditions: one representing the winter season with strong winds above a sparse canopy and a slightly
unstable boundary layer; the other representing the spring season with a dense canopy, calm conditions, and a strongly convective
boundary layer. In each case, results from the control canopy, simulating the observed heterogeneous canopy structure at the
Duke Forest hardwood stand, are compared with a test case that also includes heterogeneity commensurate in scale to tree-fall
gaps. The effects of such tree-scale canopy heterogeneity on the flow are explored at three levels pertinent to biosphere-atmosphere
exchange. The first level (zero-dimensional) considers the effects of such heterogeneity on the common representation of the
canopy via length scales such as the zero-plane displacement, the aerodynamic roughness length, the surface-layer depth, and
the eddy-penetration depth. The second level (one-dimensional) considers the normalized horizontally-averaged profiles of
the first and second moments of the flow to assess how tree-scale heterogeneities disturb the entire planar-averaged profiles
from their canonical (and well-studied planar-homogeneous) values inside the canopy and in the surface layer. The third level
(three-dimensional) considers the effects of such tree-scale heterogeneities on the spatial variability of the ejection-sweep
cycle and its propagation to momentum and mass fluxes. From these comparisons, it is shown that such microscale heterogeneity
leads to increased spatial correlations between attributes of the ejection-sweep cycle and measures of canopy heterogeneity,
resulting in correlated spatial heterogeneity in fluxes. This heterogeneity persisted up to four times the mean height of
the canopy (hc) for some variables. Interestingly, this estimate is in agreement with the working definition of the thickness of the canopy
roughness sublayer (2hc–5hc). 相似文献
The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (36 %). 相似文献
Mining operations in Palawan, Philippines, resulted in cinnabar (HgS) mine tailings being used to build a 600 m long peninsula in Honda Bay. Samples collected from the peninsula as well as sediments from the surrounding waters had elevated mercury levels as high as 570 ppm. Natural processes are transporting mercury as much as 10 km from the peninsula, mainly in a coastwise direction, and preferentially associated with fine-grained, organic-rich sediments. Depth of penetration into sediments exceeds 10 cm near the source. As the HgS is transported away from the peninsula, it is rapidly altered to more bioavailable forms; 50% conversion occurs within a distance of only 10–40 m. 相似文献
In the western sector of the Ebro Basin two types of structures deform the Quaternary terraces and pediments developed by the Ebro River and its tributaries: (1) folds up to 10 km long in the lower levels of fluvial terraces and (2) normal listric faults that produce tilting and rollover anticlines of the Quaternary deposits. Both types of structures are linked to the geometrical and lithological features of the Tertiary beds that underlie the Quaternary deposits. Quaternary folds, whose axes are parallel to the strike of the Tertiary beds, are the result of reactivation of Tertiary large-scale (60 km long) folds due to diapirism of their gypsum cores, where the gypsum units reach a maximum thickness of 3 000 m. This reactivation produced flexural-slip in some beds on the limbs of the folds, bringing about the folding of the overlying Quaternary terraces. The mechanism of Quaternary folding involves layer-parallel shear in alternating Tertiary units and folding linked to detachments and reverse layer-parallel faults. Normal listric faults are widespread throughout the studied area. They are partly parallel to low dipping Tertiary beds and are the result of a NNE-SSW tectonic extension, compatible with minor structures and focal mechanisms of recent earthquakes. The relationship between the two kinds of Quaternary structures indicates that diapirism of the gypsum cores of the anticlines was activated by extensional tectonics. 相似文献
Thermal waters from Galicia, Spain, range from CO2-rich, low-pH to high-pH, sulfide-rich waters, going through intermediate waters. In order to explain the variations of their chemical composition, we present a discussion of the major factors governing the water composition. We eiscuss especially the isochemical recrystallization of a granite. It is shown that the equilibrium mineral association of the water-alkali granite system is unique. For chalco-alkaline granites, two different associations are possible, depending on the chemical composition of the granite. The effect of an addition of CO2 is also discussed.
Some criteria allowing a distinction between fully equilibrated and non-equilibrated waters are presented.
Finally, the composition of Galician waters is explained by different initial CO2 contents and by different values of the degree of the granite-water reaction progress (ξ).
Résumé
Les eaux thermales de Galice (Espagne) vont des eaux riches en CO2 aux eaux typiquement alcalines en passant par différents intermédiaires. Pour comprendre l'évolution de la composition chimique de ces eaux, nous avons été conduits à discuter, de façon plus générale, des facteurs majeurs qui fixent la composition minéralogique résultant d'une recristallisation isochimique du granite. Nous avons pu montrer que les granites alcalins se transformaient toujours en la même association minérale, tandis que les granites calcoalcalins pouvaient donner naissance à deux associations d'équilibre différentes. L'apport de CO2 au système eau-roche peut faire passer d'une association minérale à l'autre, et, si le CO2 est en grande quantité, à une association contenant un minéral de moins et du CO2 en excès. On propose également, pour les solutions géothermales, des critères d'équilibre ou de non équilibre, basés sur la composition en éléments majeurs. La variation de composition des eaux de Galice peut alors s'interpréter par des teneurs variables en CO2 et des degrés d'avancement différents de la réaction d'interaction eau-granite. 相似文献