In-situ reflectance spectroscopy – analysing techniques for high-resolution pigment logging in sediment cores     

Bert Rein  Frank Sirocko 《International Journal of Earth Sciences》2003,92(1):143-143

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A simple model for potential dewfall in an arid region   总被引：4，自引：0，他引：4  

Adrie F. G. Jacobs  Bert G. Heusinkveld  Simon M. Berkowicz 《Atmospheric Research》2002,64(1-4)

It is not always easy to know, post-facto, whether both dewfall and fog may have occurred over a given evening period. Instrumentation limitations make it difficult to quantify dew deposition since they rely on artificial sensing surfaces that are either visually examined on a daily basis or recorded. In arid to Mediterranean regions, both dew and fog can play significant ecological roles as suppliers of moisture. Long-term observation records of dew and fog in such regions tend to be limited, however, due partly to a lack of interest and limited distribution of well-instrumented meteorological stations. Simple meteorological criteria are suggested here to calculate potential dewfall and to indicate whether fog was likely to have occurred over a given evening. A field campaign was carried out in the NW Negev desert, Israel, in September and October 1997, to collect meteorological data and carry out dewfall measurements.  相似文献   

Effect of elevated CO2 on carbon pools and fluxes in a brackish marsh     

Anne S. Marsh  Daniel P. Rasse  Bert G. Drake  J. Patrick Megonigal 《Estuaries and Coasts》2005,28(5):694-704

The effects of long-term exposure to elevated atmospheric CO₂ (ambient + 340 ppmv) on carbon cycling were investigated for two plant communities in a Chesapeake Bay brackish marsh, one dominated by the C₃ sedgeSchoenplectus americanus and the other by the C₄ grassSpartina patens. Elevated CO₂ resulted in a significant increase in porewater concentrations of DIC at 30 cm depth (p < 0.1). The CO₂ treatment also yielded increases in DOC (15 to 27%) and dissolved CH₄ (12–18%) in the C₃ marsh (means for several depths over the period of June 1998 and June 1999), but not at a significant level. Elevated CO₂ increased mean ecosystem emissions of CO₂ (34–393 g C m⁻² yr⁻¹) and CH₄ (0.21–0.40 g C m⁻² yr⁻¹) in the C₃ community, but the effects were only significant on certain dates. For example, CO₂ enrichment increased C export to the atmosphere in the C₃ community during one of two winter seasons measured (p = 0.09). In the C₄ community, gross photosynthesis responded relatively weakly to elevated CO₂ (18% increase, p > 0.1), and the concomitant effects on dissolved carbon concentrations, respiration, and CH₄ emissions were small or absent. We concluded that elevated CO₂ has the potential to increase dissolved inorganic carbon export to estuaries.  相似文献   

Seasonal and interannual variability of carbon dioxide and water balances of a grassland     

Adrie F. G. Jacobs  Bert G. Heusinkveld  Albert A. M. Holtslag 《Climatic change》2007,82(1-2):163-177

There is great international concern over the increase of atmospheric carbon dioxide and its effect on vegetation and climate, and vice versa. Many studies on this issue are based on climate model calculations or indirect satellite observations. In contrast we present a 12-year study (1994–2005) on the net ecosystem exchange of carbon dioxide (NEE) and precipitation surplus (i.e., precipitation–evaporation) of a grassland area in the centre of the Netherlands. On basis of direct flux observations and a process-based model we study and quantify the carbon uptake via assimilation and carbon release via soil and plant respiration. It appears that nearly year-round the assimilation term dominates, which indicates an accumulation of carbon dioxide. The mean net carbon uptake for the 12-year period is about 3 tonnes C per hectare, but with a strong seasonal and interannual variability depending on the weather and water budget. This variability may severely hamper the accurate quantification of carbon storage by vegetation in our present climates and its projection for future climates.  相似文献   

The East Greenland Current and its contribution to the Denmark Strait overflow   总被引：8，自引：1，他引：8  

Rudels  Bert; Fahrbach  Eberhard; Meincke  Jens; Budeus  Gereon; Eriksson  Patrick 《ICES Journal of Marine Science》2002,59(6):1133-1154

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Recent environmental history of the desert oasis lakes at Ounianga Serir,Chad     

Mike Creutz  Bert Van Bocxlaer  Moussa Abderamane  Dirk Verschuren 《Journal of Paleolimnology》2016,55(2):167-183

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The proper motion VS redshift relation for superluminal radio sources     

Bert W. Rust  Stephen G. Nash  Barry J. Geldzahler 《Astrophysics and Space Science》1989,152(1):141-170

Two models for superluminal radio sources predict sharp lower bounds for the apparent velocities of separation. The light echo model predicts a minimum velocityv _min=2c, and the dipole field model predictsv _min=4.446c. Yahil (1979) has suggested that, if either of these models is correct, thenv _min provides a standard velocity which can be used to determine the cosmological parametersH andq ₀. This is accomplished by estimating a lower envelope for the proper motion vs redshift relation. Yahil also argued that the procedure could easily be generalized to include a nonzero cosmical constant . We derive the formulas relating the proper motion to the redshiftz in a Friedmann universe with a nonzero . We show that the determination of a lower envelope for a given sample of measured points yields an estimate of the angle of inclination _i for each source in the sample. We formulate the estimation of the lower envelope as a constrained maximum likelihood problem with the constraints specified by the expected value of the largest order statistic for the estimated _i . We solve this problem numerically using an off-the-shelf nonlinearly constrained nonlinear optimization program from the NAg library. Assuming =0, we apply the estimation procedure to a sample of 27 sources with measured values , using both the light echo and the dipole field models. The fits giveH=103 km s^–1 Mpc^–1 for the light echo model andH=46 km s^–1 Mpc^–1 for the dipole field model. In both cases the fits giveq ₀=0.4, but the uncertainty in this result is too large to rule out the possibility thatq ₀>0.5. When is allowed to be a free parameter, we obtainH=105 km s^–1 Mpc^–1 for the light echo model andH=47 km s^–1 Mpc^–1 for the dipole field model. In both cases the fits giveq ₀=–1 and /H ₀ ² =6.7, but no significance can be attached to these results because of the paucity of measured data at hight redshifts. For all of the fits, we compute the corresponding estimates of the _i and compare the cumulative distribution of these values with that expected from a sample of randomly oriented sources. In all cases we find a large excess of sources at low-inclination angles (high apparent velocities). The expected selection effect would produce such an excess, but the excess is large enough to suggest a strong contamination of the sample by relativistic beam sources which would only be seen at low inclination angles.Applied Research Corporation  相似文献   

Deep pore water profiles reflect enhanced microbial activity towards tidal flat margins     

Melanie Beck  Jürgen Köster  Bert Engelen  Jan M. Holstein  Antje Gittel  Martin Könneke  Thomas Riedel  Kai Wirtz  Heribert Cypionka  Jürgen Rullkötter  Hans-Jürgen Brumsack 《Ocean Dynamics》2009,59(2):371-383

Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore, tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat areas.  相似文献   

An experimental investigation of spin-up from rest of a stratified fluid     

Jan Bert Flor  John W.M. Bush  Marius Ungarish 《地球物理与天体物理流体动力学》2013,107(4):277-296

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Impact of horizontal eddy diffusivity on Lagrangian statistics for coastal pollution from a major marine fairway     

Bert Viikmäe  Tomas Torsvik  Tarmo Soomere 《Ocean Dynamics》2013,63(5):589-597

Lagrangian trajectory methods are often applied as deterministic transport models, where transport is due strictly to advection without taking into account stochastic elements of particle dispersion, which raises questions about validity of the model results. The present work investigates the impact of horizontal eddy diffusivity for a case study of coastal pollution in the Gulf of Finland, where the pollutants are assumed to originate from a major fairway and are transported to the coast by surface currents. Lagrangian trajectories are calculated using the TRACMASS model from velocity fields calculated by the Rossby Centre circulation model for 1982 to 2001. Three cases are investigated: (1) trajectory calculation without eddy diffusivity, (2) stochastic modelling of eddy diffusivity with a constant diffusion coefficient and (3) stochastic modelling of eddy diffusivity with a time- and space-variable diffusion coefficient. It is found that the eddy diffusivity effect increases the spreading rate of initially closely packed trajectories and the number of trajectories that eventually reach the coast. The pattern of most frequently hit coastal sections, the probability of hit to each such section and the time the pollution spends offshore are virtually invariant with respect to inclusion of eddy diffusivity.  相似文献