Dissolved and particulate concentrations of metals (Fe, Al, Mn, Co, Ni, Cu, Zn, Cd, Tl, Pb) and As were monitored over a 5 year period in the Amous River downstream of its confluence with a creek severely affected by acid mine drainage (AMD) originating from a former Pb–Zn mine. Water pH ranged from 6.5 to 8.8. Metals were predominantly in dissolved form, except Fe and Pb, which were in particulate form. In the particulate phase, metals were generally associated with Al oxides, whereas As was linked to Fe oxides. Metal concentrations in the dissolved and/or particulate phase were generally higher during the wet season due to higher generation of AMD. Average dissolved (size < 0.22 μm) metal concentrations (μg/L) were 1 ± 4 (Fe), 69 ± 49 (Al), 140 ± 118 (Mn), 4 ± 3 Co, 6 ± 4 (Ni), 1.3 ± 0.8 (Cu), 126 ± 81 (Zn), 1.1 ± 0.7 (Cd), 0.9 ± 0.5 (Tl), 2 ± 3 (Pb). Dissolved As concentrations ranged from 5 to 134 μg/L (30 ± 23 μg/L). During the survey, the concentration of colloidal metals (5 kDa < size < 0.22 μm) was less than 25% of dissolved concentrations. Dissolved metal concentrations were generally higher than the maximum concentrations allowed in European surface waters for priority substances (Ni, Cd and Pb) and higher than the environmental quality standards for other compounds. Using Diffusion Gradient in Thin Film (DGT) probes, metals were shown to be in potentially bioavailable form. The concentrations in Leuciscus cephalus were below the maximum Pb and Cd concentrations allowed in fish muscle for human consumption by the European Water Directive. Amongst the elements studied, only As, Pb and Tl were shown to bioaccumulate in liver tissue (As, Pb) or otoliths (Tl). Bioaccumulation of metals or As was not detected in muscle. 相似文献
Long slit spectra of the planetary nebula NGC 5189 with its [WC2] type central object and the G2.4+1.4 wind bubble around the evolved Pop. I WO star Sand 4 were obtained in order to investigate the observable effects of different initial masses in stars with otherwise similar spectra. Our preliminary results of a comparative spectroscopic study of these two objects shows that the chemical composition of the two nebuale is completely different, even though their morphology is most probably quite similar. In addition, the PN appears much more chemically homogeneous. These features are clearly associated with the evolutionary paths of the stars. 相似文献
The seasonal variability of sea surface height (SSH) and currents are defined by analysis of altimeter data in the NE Pacific Ocean over the region from Central America to the Alaska Gyre. The results help to clarify questions about the timing of seasonal maxima in the boundary currents. As explained below, the long-term temporal mean of the SSH values must be removed at each spatial point to remove the temporally invariant (and large) signal caused by the marine geoid. We refer to the resulting SSH values, which contain all of the temporal variations, as the ‘residual’ SSH. Our main findings are:
1. The maximum surface velocities around the boundaries of the cyclonic Alaska Gyre (the Alaska Current and the Alaska Stream) occur in winter, at the same time that the equatorward California Current is weakest or reversed (forming the poleward Davidson Current); the maximum surface velocities in the California Current occur in summer. These seasonal maxima are coincident with the large-scale atmospheric wind forcing over each region.
2. Most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the NE Pacific basin, directly connecting the boundaries of the subpolar gyre, the subtropical gyre and the Equatorial Current System.
3. Seasonal variability in the surface velocities of the eastward North Pacific Current (West Wind Drift) is weak in comparison to seasonal changes in the surface currents along the boundaries.
4. There is an initial appearance next to the coast and offshore migration of seasonal highs and lows in SSH, alongshore velocity and eddy kinetic energy (EKE) in the Alaska Gyre, similar to the previously-described seasonal offshore migration in the California Current.
5. The seasonal development of high SSH and poleward current residuals next to the coast appear first off Central America and mainland Mexico in May–June, prior to their appearance in the southern part of the California Current in July–August and their eventual spread around the entire basin in November–December. Similarly, low SSH and equatorward transport residuals appear first off Central America and Mexico in January–February before spreading farther north in spring and summer.
6. The maximum values of EKE occur when each of the boundary currents are maximum.
Article Outline
1. Introduction and background
2. Data and methods
2.1. Altimeter and tide gauge data
2.2. Atmospheric forcing—sea level pressure
2.3. Statistical gridding
3. Results
4. Summary and discussion
4.1. Alaska Gyre
4.2. Connections around the boundaries of the subarctic and subtropical gyres
4.3. Connections to the North Pacific Current
4.4. Offshore ‘propagation’ of the seasonal height and transport signals
4.5. Connections to the equatorial current systems along the boundaries
Acknowledgements
References
1. Introduction and background
This is the first of a two-part analysis of temporal variability of the NE Pacific Ocean’s surface circulation, as measured by satellite altimeters. Here we examine the seasonal variability. In Part 2 (Strub & James, 2002) we analyze the non-seasonal anomalies of the surface circulation over the 1993–1998 period, during which the 1997–1998 El Niño creates the largest signal. Formation of the seasonal cycles discussed here is the first step in creating the non-seasonal anomalies. The seasonal cycles themselves, however, provide new information on the response of the NE Pacific to strong seasonal forcing, on scales not previously addressed. This analysis quantifies the degree of connection, on seasonal time scales, between the boundary currents in the eastern subarctic and subtropical gyres, as well as the connection between the boundaries and the interior NE Pacific. It further shows a connection to the equatorial current system.Numerous papers describe aspects of the seasonal cycles for certain parameters in subregions of our larger domain. Chapters in Robinson and Brink (1998) review some of the past results from the coastal ocean in the regions between the Equator and the Alaska Gyre ( Badan; Hickey and Royer). Fig. 1 presents the climatological surface dynamic height field (relative to 500 m) in the NE Pacific, calculated from the long-term mean climatological temperature and salinity data of Levitus and Gelfeld (1992). The 500 m reference level is used to concentrate on the surface flow seen by altimeters. Although this climatology is overly smooth, it shows the major currents in the area. The broad, eastward North Pacific Current (also called the West Wind Drift) splits into the counterclockwise Alaska Gyre and the equatorward California Current. South of 20°N in summer, the California Current turns westward and flows into the North Equatorial Current, while in winter–spring, part of it continues along the Mexican mainland before turning westward ( Badan; Fiedler and Fiedler). The long-term climatology shows both paths. The North Equatorial Countercurrent (NECC) flows eastward between 5° –10°N to approximately 120°W, but is only weakly seen in the annual climatology from there to the cyclonic flow around the Costa Rica Dome near 8°N, 92°W. The NECC is a shallow current (found in the upper 200 m) and might appear more strongly if a shallower reference were used, but it is also seasonally intermittent. When the Intertropical Convergence Zone (ITCZ) is in its northern location near 10°N (summer), surface divergences and upwelling create a zonal trough in surface height, driving the NECC along the southern side of the trough. When the ITCZ moves south in winter, the NECC weakens or reverses. 相似文献
We present an analysis of the rainfall-evaporation-atmospheric moisture cycle in a semi-arid tropical zone (southwestern Madagascar) to quantify the recycling and mixing processes that occur above an endorheic lake system (Lake Ihotry) during an annual cycle. The study combines an isotope mass balance with a detailed field investigation of the lake system and a previously established daily time-step lake water balance model. The mass balance and Craig-Gordon equations are used to calculate the isotopic composition of the evaporative flux from the lake surface (δE) and to derive a daily time series of the ambient atmospheric water vapour composition above the lake (δAL) during a 8-month dry season. Calculated δAL results from a mixing between regional moisture (δAR) and locally evaporated water (δE), the latter representing 50% of δAL at the end of the dry season. The contribution of recycled moisture to on-lake precipitation during the wet season is estimated to ?16%. We show that, as expected, the deuterium excess is high in recycled precipitation and low in evaporated precipitation, but also that the recycled moisture in an endorheic system may have a low deuterium excess resulting from the low deuterium excess in regional precipitation. In case of a long evaporative season, the atmospheric moisture is not in isotopic equilibrium with the annual composition of precipitation because of the contribution of the recycled vapour to the local atmospheric pool. Our approach demonstrates the importance of water recycling on the atmospheric moisture cycle and precipitation in a tropical semi-arid system, and can be applied to other natural systems, enlarging the potential range of investigation of the atmospheric vapour cycle and rainfall sources in tropical lands. It may also represent a valuable complement to direct water vapour sampling, in yielding the long-term evolution of the atmospheric vapour composition with spatially averaged values and smoothed temporal variations. 相似文献
There is a widespread interest to digitize the precious information contained in the astronomical plate archives, both for
the preservation of their content and for its fast distribution to all interested researchers in order to achieve their better
scientific exploitation. This paper presents the first results of our large-scale project to digitize the archive of plates
of the Italian Astronomical Observatories and of the Specola Vaticana. Similar systems, composed by commercial flat-bed retro-illuminated
scanners plus dedicated personal computers and acquisition and analysis software, have been installed in all participating
Institutes. Ad-hoc codes have been developed to acquire the data, to test the suitability of the machines to our scientific needs, and to reduce
the digital data in order to extract the astrometric, photometric and spectroscopic content. Two more elements complete the
overall project: the provision of high quality BVRI CCD sequences in selected fields with the Campo Imperatore telescopes,
and the distribution of the digitized information to all interested researchers via the Web. The methods we have derived in
the course of this project have been already applied successfully to plates taken by other Observatories, for instance at
Byurakan and at Hamburg. 相似文献
Magma transfer processes at persistently active volcanoes are distinguished by the large magma flux required to sustain the prodigious quantities of heat and gas emitted at the surface. Although the resulting degassed magma has been conjectured to accumulate either deep within the volcanic edifice or in the upper levels of the sub-edifice system, no direct evidence for such active accumulation has been reported. Temporal gravity data are unique in being able to quantify mass changes and have been successfully used to model shallow magma movements on different temporal scales, but have not generally been applied to the investigation of postulated long-term accumulation of magma at greater spatial scales within volcanic systems. Here, we model the critical data acquisition parameters required to detect mass flux at volcanoes, we review existing data from a number of volcanoes that exemplify the measurement of shallow mass changes and present new data from Poas and Telica volcanoes. We show that if a substantial proportion of degassed magma lodges within the sub-edifice region, it would result in measurable annual to decadal gravity increases occurring over spatial scales of tens of kilometres and propose that existing microgravity data from Sakurajima and, possibly, Etna volcanoes could be interpreted in these terms. Furthermore, such repeat microgravity data could be used to determine whether the accumulation rate is in equilibrium with the rate of production of degassed magma as calculated from the surface gas flux and hence identify the build-up of gas-rich magma at depth that may be significant in terms of eruption potential. We also argue that large magma bodies, both molten and frozen, modelled beneath volcanoes from seismic and gravity data, could represent endogenous or cryptic intrusions of degassed magma based on order of magnitude calculations using present-day emission rates and typical volcano lifetimes. 相似文献
