Functioning of intertidal flats inferred from temporal and spatial dynamics of O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and pH in their surface sediment   总被引：1，自引：1，他引：0  

Stefan Jansen  Eva Walpersdorf  Ursula Werner  Markus Billerbeck  Michael E Böttcher  Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332

In this article, we describe the dynamics of pH, O₂ and H₂S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment. In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms, as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this way create specific niches for various types of microorganisms.  相似文献   

Analysis of burnt schist outcrops in the alps: Relation to historical archaeology and Hannibal's crossing in 218 B.C.     

William C. Mahaney  Michael W. Milner  Rana Sodhi  Ronald I. Dorn  Sal Boccia  Roelf P. Beukens  Pierre Tricart  Stphane Schwartz  Eva Chamorro‐Perrez  Ren W. Barendregt  Volli Kalm  Randy W. Dirszowsky 《Geoarchaeology》2007,22(7):797-816

Identification of the exact route followed by Hannibal during his invasion of Italia in the Second Punic War is one of the major questions of antiquity and one that historians/archaeologists have long studied. One of the many clues in the ancient literature that can help answer this question is the mention of fired rock, the result of a conflagration Hannibal is reputed to have employed to reduce the size of boulders in a blocking rockslide some distance down from the high col on the Italian side. The only route with evidence of fired rock along the roadway leading into Italia follows the Col du Clapier, one of the possible northern routes discussed by historians. Radiocarbon dating of calcined rocks is not possible, but whereas Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS), Field Emission Scanning Electron Microscope (FESEM‐EDS), backscatter electron scanning microscopy (BSE), High Resolution Transmission Electron Microscope (HRTEM), and Raman Spectroscopic data do not provide an age for the burnt rock, compositional evidence of the conflagration derived from these analyses may shed light on Hannibal's actual route. © 2007 Wiley Periodicals, Inc.  相似文献   

An Overview of Surface-Based Precipitation Observations at Environment and Climate Change Canada     

Eva Mekis  Norman Donaldson  Janti Reid  Alex Zucconi  Jeffery Hoover  Qian Li 《大气与海洋》2018,56(2):71-95

The objective of this paper is to provide an overview of the present status and procedures related to surface precipitation observations at Environment and Climate Change Canada (ECCC). This work was done to support the ongoing renewal of observation systems and networks at the Meteorological Service of Canada. The paper focusses on selected parameters, namely, accumulated precipitation, precipitation intensity, precipitation type, rainfall, snowfall, and radar reflectivity. Application-specific user needs and requirements are defined and captured by World Meteorological Organization (WMO) Expert Teams at the international level by Observing Systems Capability Analysis and Review (OSCAR) and WMO Integrated Global Observing System (WIGOS), and by ECCC user engagement initiatives within the Canadian context. The precipitation-related networks of ECCC are separated into those containing automatic instruments, those with human (manual) observers, and the radar network. The unique characteristics and data flow for each of these networks, the instrument and installation characteristics, processing steps, and limitations from observation to data distribution and storage are provided. A summary of precipitation instrument-dependent algorithms that are used in ECCC's Data Management System is provided. One outcome of the analysis is the identification of gaps in spatial coverage and data quality that are required to meet user needs. Increased availability of data, including from long-serving manual sites, and an increase in the availability of precipitation type and snowfall amount are identified as improvements that would benefit many users. Other recognized improvements for in situ networks include standardized network procedures, instrument performance adjustments, and improved and sustained access to data and metadata from internal and external networks. Specific to radar, a number of items are recognized that can improve quantitative precipitation estimates. Increased coverage for the radar network and improved methods for assessing and portraying radar data quality would benefit precipitation users.  相似文献   

A model study of dickite intercalated with formamide and N-methylformamide     

Eva Scholtzová  Lubomir Benco  Daniel Tunega 《Physics and Chemistry of Minerals》2008,35(6):299-309

Local geometry and orientation of intercalated molecules of formamide (FA) and N-methylformamide (NMFA) in the clay mineral dickite (D) was studied by means of Density Functional Theory (DFT) calculations. Ten configurations with different orientation of the intercalated molecule were investigated for both D_FA and D_NMFA intercalates. Four groups of relaxed structures sorted by the calculated total electronic energy were found in both cases. The experimental geometry of the D_FA intercalate was denoted as the most stable structure from the investigated models. The differences in the total electronic energy of all D_FA configurations are within the interval of ∼92 kJ/mol. On one hand FA forms intercalates specifically and a close relation between the orientation of the FA molecules in the interlayer space and the stability of a particular configuration has been observed. On the other hand, N-methylformamide forms intercalated structures non-specifically. Small differences in the total energy, not larger than 18 kJ/mol, are observed for different orientations of the NMFA molecules The reorientation of the intercalated molecules has only a small effect on the stabilization of the D_NMFA intercalate what is in contrast with the D_FA intercalate. It was also observed that the experimental D_NMFA configuration is not the most stable. A small variation of the total electronic energy of different configurations correlates with small changes of the orientation of the dipole moment of the intercalated NMFA molecule.  相似文献   

Combination of multi-mission altimetry data along the Mekong River with spatio-temporal kriging     

Eva Boergens  Sven Buhl  Denise Dettmering  Claudia Klüppelberg  Florian Seitz 《Journal of Geodesy》2017,91(5):519-534

River water-level time series at fixed geographical locations, so-called virtual stations, have been computed from single altimeter crossings for many years. Their temporal resolution is limited by the repeat cycle of the individual altimetry missions. The combination of all altimetry measurements along a river enables computing a water-level time series with improved temporal and spatial resolutions. This study uses the geostatistical method of spatio-temporal ordinary kriging to link multi-mission altimetry data along the Mekong River. The required covariance models reflecting the water flow are estimated based on empirical covariance values between altimetry observations at various locations. In this study, two covariance models are developed and tested in the case of the Mekong River: a stationary and a non-stationary covariance model. The proposed approach predicts water-level time series at different locations along the Mekong River with a temporal resolution of 5 days. Validation is performed against in situ data from four gauging stations, yielding RMS differences between 0.82 and 1.29 m and squared correlation coefficients between 0.89 and 0.94. Both models produce comparable results when used for combining data from Envisat, Jason-1, and SARAL for the time period between 2002 and 2015. The quality of the predicted time series turns out to be robust against a possibly decreasing availability of altimetry mission data. This demonstrates that our method is able to close the data gap between the end of the Envisat and the launch of the SARAL mission with interpolated time series.  相似文献   

A closing Ligurian Sea?     

N. Bethoux  J. Fréchet  F. Guyoton  F. Thouvenot  M. Cattaneo  C. Eva  M. Nicolas  M. Granet 《Pure and Applied Geophysics》1992,139(2):179-194

Two earthquakes occurred in the Ligurian Sea in December 1989 and April 1990. Both were widely felt along the French and Italian Rivieras, thus reminding us of the seismic risk in this region. The significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks. Using different techniques (absolute and relative hypocentral locations, doublet analysis and waveform modeling), we computed accurate hypocentral locations and estimated the location-error range for earthquakes in this area. We also computed the focal mechanisms for both mainshocks, and we present here a synthesis that integrates previous data. The reactivation in compression of the Ligurian Sea sphenochasm is confirmed, which would eventually result in the closing of an aborted oceanic domain. As the seismic activity is clearly restricted to the northern margin, we suggest it locally results from the lateral expulsion of the south-western Alps along the Apulian indenter.  相似文献   

Manganese mineralization in andesites of Brestovačka Banja,Serbia: evidence of sea-floor exhalations in the Timok Magmatic Complex     

Aleksandar Pačevski  Vladica Cvetković  Kristina Šarić  Miodrag Banješević  Heidi Eva Hoefer  Aleksandar Kremenović 《Mineralogy and Petrology》2016,110(4):491-502

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Tips and tricks in designing management procedures   总被引：2，自引：2，他引：2  

Rademeyer  Rebecca A.; Plaganyi  Eva E.; Butterworth  Doug S. 《ICES Journal of Marine Science》2007,64(4):618-625

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Population structure of Merluccius merluccius along the Iberian Peninsula coast     

Castillo  Ana G.F.; Alvarez  Paula; Garcia-Vazquez  Eva 《ICES Journal of Marine Science》2005,62(8):1699-1704

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Boundary perturbation formalism for Poisson's equation     

Slavko Chalupka  Jaroslava Sisákova  Eva Vargová 《Studia Geophysica et Geodaetica》1992,36(4):325-328

Summary A formalism for solving Poisson's equation in near spherical geometries by a perturbation technique is presented. The formalism should be easy to implement numerically.  相似文献