bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the precipitation in southwestern part of Greece with X-band Doppler radar, 2-D video disdrometer and rain gauges
Authors: Defer E. , Anagnostou M. 
Published: April 2010

Abstract. We document precipitation in the southwestern part of Greece with the National Observatory of Athens (NOA) X-band radar, NOA 2D video disdrometer and a network of rain gauges. The observations were collected between February and April 2004. Time evolution of the drop size distribution (DSD) is presented for the 9 March 2004 case where rain rate (computed on 1-min period) was measured up to 80 mm/h and reflectivity at the location of the disdrometer exceeded 40 dBZ. We then present the differences of DSD as function of the rain rate for the studied case as well as for the entire observations of the field experiment. It shows that higher the rain rate is, larger the range of the DSD and higher the concentration of the raindrops are.
A Low-Cost Versatile Broadband (DC to K-Band) Planar 50Ω Termination
Authors: Olbrich M. O. , Biebl E. M. 
Published: April 2010

Abstract. Numerous standard RF circuits like directional couplers, hybrids, amplitude modulators, oscillators, etc. require a 50Ω termination. Additionally, in several measurement scenarios, ports have to be terminated. Such terminations are preferable of the same waveguide type as the circuits to avoid degradation of their performance. In general, standard fabrication steps are desired as they are cost-effective. The straightforward solution is a 50Ω resistor shunted to ground by means of a via. Partial wraparound SMD resistors in a 0402 size have low parasitics making them applicable up to K-band. However, for RF, this combination suffers from the considerable inductive parasitics of the via. Different approaches to avoid the vias, with varying disadvantages exist. We analyzed the approach of broadband matching the non ideal viaresistor combination to 50Ω by means of a filter structure. The realization uses only standard design and fabrication methods. The design procedure can easily be adapted to arbitrary substrates and fabrication technologies. The assembled 50Ω termination was measured using TRL calibration with a VNA. Therefore its characteristics are determined in the intended plane and it can be directly included into a planar 50Ω circuit. The measured terminations showed a VSWR better than 1.34 within the whole band from DC to K-band, and within 57% of the band (including the 24GHz ISM band) the VSWR is better than 1.22.
Digital Component Separator for future W-CDMA-LINC Transmitters implemented on an FPGA
Authors: Gerhard W. , Knöchel R. 
Published: April 2010

Abstract. This paper presents the implementation of a Digital-Component-Separator (DCS) for a LINC-transmitter (linear amplification using nonlinear components) on an FPGA (field programmable gate array). It investigates and estimates the bandwidth requirements for such a LINC system. The influence of bandwidth limitations on a digitally based LINC-transmitter for W-CDMA utilization is studied by simulations. Furthermore a LINC transmitter is proposed which employs a flexible image-reject- or a direct up-conversion-architecture for transmission of single or combined multi-carrier/channel W-CDMA signals using the phase-modulation approach. The sampling frequency can be chosen at a value up to 32 times (122.88MHz) the symbol rate of the W-CDMA chip rate of 3.84Mbits/s. Measurement results for a LINC transmitter are presented and discussed.
Inventories of N2O and NO emissions from European forest soils
Authors: Kesik M. , Ambus P. , Baritz R. , Brüggemann N. , Butterbach-Bahl K. , Damm M. , Duyzer J. , Horváth L. , Kiese R. , Kitzler B. , Leip A. , Li C. , Pihlatie M. , Pilegaard K. , Seufert S. , Simpson D. , Skiba U. , Smiatek G. , Vesala T. , Zechmeister-Boltenstern S. 
Published: April 2010

Abstract. Forest soils are a significant source for the primary and secondary greenhouse gases N2O and NO. However, current estimates are still uncertain due to the still limited number of field measurements and the herein observed pronounced variability of N trace gas fluxes in space and time, which are due to the variation of environmental factors such as soil and vegetation properties or meteorological conditions. To overcome these problems we further developed a process-oriented model, the PnET-N-DNDC model, which simulates the N trace gas exchange on the basis of the processes involved in production, consumption and emission of N trace gases. This model was validated against field observations of N trace gas fluxes from 19 sites obtained within the EU project NOFRETETE, and shown to perform well for N2O (r2=0.68, slope=0.76) and NO (r2=0.78, slope=0.73). For the calculation of a European-wide emission inventory we linked the model to a detailed, regionally and temporally resolved database, comprising climatic properties (daily resolution), and soil parameters, and information on forest areas and types for the years 1990, 1995 and 2000. Our calculations show that N trace gas fluxes from forest soils may vary substantial from year to year and that distinct regional patterns can be observed. Our central estimate of NO emissions from forest soils in the EU amounts to 98.4, 84.9 and 99.2 kt N yr−1, using meteorology from 1990, 1995 and year 2000, respectively. This is <1.0% of pyrogenic NOx emissions. For N2O emissions the central estimates were 86.8, 77.6 and 81.6 kt N yr−1, respectively, which is approx. 14.5% of the source strength coming from agricultural soils. An extensive sensitivity analysis was conducted which showed a range in emissions from 44.4 to 254.0 kt N yr−1 for NO and 50.7 to 96.9 kt N yr−1 for N2O, for year 2000 meteorology. The results show that process-oriented models coupled to a GIS are useful tools for the calculation of regional, national, or global inventories of biogenic N trace gas emissions from soils. This work represents the most comprehensive effort to date to simulate NO and N2O emissions from European forest soils.
On the application and interpretation of Keeling plots in paleo climate research – deciphering δ13C of atmospheric CO2 measured in ice cores
Authors: Köhler P. , Fischer H. , Schmitt J. , Munhoven G. 
Published: April 2010

Abstract. The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide (pCO2) and of δ13C of CO2 over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. Carbon uptake by the ocean cannot longer be neglected for less abrupt changes as occurring during glacial cycles. We introduce an equation for the calculation of long-term changes in the isotopic signature of atmospheric CO2 caused by an injection of terrestrial carbon to the atmosphere, in which the ocean is introduced as third reservoir. This is a paleo extension of the two reservoir mass balance equations of the Keeling plot approach. It gives an explanation for the bias between the isotopic signature of the terrestrial release and the signature deduced with the Keeling plot approach for long-term processes, in which the oceanic reservoir cannot be neglected. These deduced isotopic signatures are similar (−8.6‰) for steady state analyses of long-term changes in the terrestrial and marine biosphere which both perturb the atmospheric carbon reservoir. They are more positive than the δ13C signals of the sources, e.g. the terrestrial carbon pools themselves (−25‰). A distinction of specific processes acting on the global carbon cycle from the Keeling plot approach is not straightforward. In general, processes related to biogenic fixation or release of carbon have lower y-intercepts in the Keeling plot than changes in physical processes, however in many case they are indistinguishable (e.g. ocean circulation from biogenic carbon fixation).
Nitrogen assimilation and short term retention in a nutrient-rich tidal freshwater marsh – a whole ecosystem 15N enrichment study
Authors: Gribsholt B. , Struyf E. , Tramper A. , De Brabandere L. , Brion N. 
Published: April 2010

Abstract. We conducted two (May 2002 and September 2003) pulse additions of 15NH4+ to the flood water inundating a tidal freshwater marsh fringing the nutrient-rich Scheldt River (Belgium) and traced the fate of ammonium in the intact ecosystem. Here we report in detail the 15N uptake into the various marsh components (leaves, roots, sediment, leaf litter and invertebrate fauna), and the 15N retention on a scale of 15 days. We particularly focus on the contributions of the rooted macrophytes and the microbial community in the sediment and on plant litter. Assimilation and short term retention of 15NH4+ was low on both occasions. Only 4–9% of the added 15N trace was assimilated, corresponding to 13–22% and 8–18% of the processed 15N (i.e. not exported as 15NH4+ in May and September, respectively. In May nitrogen assimilation rate (per hour inundated) was >3 times faster than in September. Macrophytes (above- and below ground) were of limited importance for short term 15N retention accounting for <6% of the total 15NH4+ processed by the marsh. The less dominant herbaceous species were more important (on an area basis) than the dominant reed (Phragmites australis). The microbial community colonizing the sediment and litter surfaces were responsible for most nitrogen assimilation and short-term retention in the marsh. The large reactive surface area available for microbial colonization together with direct plant uptake, are the crucial components for nitrogen assimilation, retention and transformation in nutrient-rich tidal freshwater marshes.
The significance of nitrogen fixation to new production during early summer in the Baltic Sea
Authors: Ohlendieck U. , Gundersen K. , Meyerhöfer M. , Fritsche P. , Nachtigall K. , Bergmann B. 
Published: April 2010

Abstract. Rates of dinitrogen (N2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June–July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m-2 (1998) and 33 mmol N m-2 (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12–26% more new N than other annual estimates (mid July–mid October) from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasize the need for multiple stations and seasonal sampling strategies in biochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28–150% of N needed to meet the rate of C incorporation by primary production. Since the molar C:N rate incorporation ratio (C:NRATE) in filamentous cyanobacterial cells was almost twice as high as the molar C:N mass ratio (C:NMASS) in both years, we suggest that the diazotrophs incorporated excess C on a short term basis (for carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4–24) in 1998 and 18% (range 2–45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be attributed to regenerated incorporation of dissolved organic N (DON) and ammonium generated from larger diazotroph cyanobacteria. Therefore, N excretion from filamentous cyanobacteria may significantly contribute to the pool of regenerated nutrients used by the non-diazotroph community in summer. Higher average concentrations of regenerated N (ammonium) coincided with higher rates of N2 fixation found during the 1999 transect and a higher level of 15N-enrichment in cells <5 µm. A variable but significant fraction of total N2 fixation (1–10%) could be attributed to diazotrophy in cells between 5–20 µm.
Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay
Authors: Laës A. , Blain S. , Laan P. , Ussher S. J. , Achterberg E. P. , Tréguer P. , de Baar H. J. W. 
Published: April 2010

Abstract. Dissolved iron (DFe; <0.2μm) and dissolved manganese (DMn; <0.2μm) concentrations were determined in the water column of the Bay of Biscay (eastern North Atlantic Ocean) in March 2002. The samples were collected along a transect traversing from the European continental shelf over the continental slope. The highest DFe and DMn concentrations (2.39 nM and 6.10 nM, respectively) were observed in the bottom waters on the shelf at stations closest to the coast. The release of trace metal from resuspended particles and the diffusion from pore waters resulted in elevated DFe and DMn concentrations in the Bottom Boundary Layer (BBL). In the slope region, the highest total dissolvable iron (TDFe), DFe and DMn values (24.6 nM, 1.58 nM and 2.12 nM, respectively) were observed close to the bottom at depth of ca. 600–700 m. Internal wave activity and slope circulation are thought to be at the origin of this phenomenon. These processes were also very likely the cause of elevated concentrations (DFe: 1.27 nM, DMn: 2.34 nM) measured in surface waters of stations located in the same area. At stations off the continental slope, the vertical distribution of both metals were typical of open ocean conditions, indicating that inputs from the continental margin did not impact the metal distributions in the offshore waters.
Identification of the accretion rate for annually resolved archives
Authors: De Ridder F. , de Brauwere A. , Pintelon R. , Schoukens J. , Dehairs F. 
Published: April 2010

Abstract. The past environment is often reconstructed by measuring a given proxy (e.g. δ18O) in an environmental archive, i.e. a species which gradually accumulates mass and records the current environment during this mass formation (e.g. corals, shells, trees, etc...). When such an environmental proxy is measured, its values are known as a function of distance. However, to relate the data to environmental variations, the date associated with each measurement, i.e. the time base, should be known. This is not straightforward solved, since species usually do not grow at constant rates. In this paper, we investigate this problem for annually resolved archives, which exhibit a certain periodicity. Such signals are often found in clams or corals. Due to variations in accretion rate the data along the distance axis have a disturbed periodic profile. A method is developed to extract information about the accretion rate, such that the original (periodic) signal as function of time can be recovered. Simultaneously the exact shape of the periodic signal is estimated. The final methodology is quasi-independent of choices made by the investigator. Every step in the procedure is described in detail and finally, the method is exemplified on a real world example.
On the application and interpretation of Keeling plots in paleo climate research – deciphering δ13C of atmospheric CO2 measured in ice cores
Authors: Köhler P. , Schmitt J. , Fischer H. 
Published: April 2010

Abstract. The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide (pCO2) and of δ13C of CO2 over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. Our analysis shows that features seen in pCO2 and δ13C during the industrial period can be interpreted with respect to the Keeling plot. However, only a maximum of approximately half of the signal can be explained by this method. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. For less abrupt changes as occurring during glacial cycles carbon uptake by the ocean cannot longer be neglected. We introduce an equation for the calculation of the effective isotopic signature of long-term changes in the carbon cycle, in which the ocean is introduced as third reservoir. This is a paleo extention of the two reservoir mass balance equations of the Keeling plot approach. Steady state analyses of changes in the terrestrial and marine biosphere lead to similar effective isotopic signatures (−8.6 per mil) of the carbon fluxes perturbing the atmosphere. These signatures are more positive than the δ13C signals of the sources, e.g. the terrestrial carbon pools themselves (~−25 per mil). In all other cases the effective isotopic signatures are larger (−8.2 per mil to −0.7 per mil), and very often indistinguishable in the light of the uncertainties. Therefore, a back calculation from well distinct fluctuations in pCO2 and δ13C to identify their origin using the Keeling plot approach seems not possible.
An importance of diazotrophic cyanobacteria as a primary producer during Cretaceous Oceanic Anoxic Event 2
Authors: Ohkouchi N. , Kashiyama Y. , Kuroda J. , Ogawa N. O. , Kitazato H. 
Published: April 2010

Abstract. In Livello Bonarelli black shale deposited during Cretaceous Oceanic Anoxic Event 2 (OAE-2, ca. 94 Ma), nitrogen isotopic compositions of bulk sediments are in a narrow range from −2.7 to −0.7. We also determined molecular distribution and nitrogen isotopic compositions of geoporphyrins extracted from the black shale. The nitrogen isotopic compositions of C32 Ni deoxophylloerythroetioporphyrin (DPEP) and total Ni porphyrins are −3.5 and −3.3, respectively, leading us to the estimation that the mean nitrogen isotopic composition of photoautotrophic cell was around +1 during the formation of Bonarelli black shale. This value is suggestive of N2-fixation a dominant process for these photoautotrophs when assimilating nitrogen. Furthermore, Ni-chelated C32 DPEP, derived mainly from chlorophyll a was the highest concentration. Based on these evidence, we conclude that diazotrophic cyanobacteria were major primary producers during that time. The cyanobacteria may be key photoautotrophs during the formation of black shale type sediments intermittently observed throughout the later half of the Earth's history, and hence may have played a crucial role in the evolution of geochemical cycles.
Nitrous oxide water column distribution during the transition from anoxic to oxic conditions in the Baltic Sea
Authors: Walter S. , Breitenbach U. , Bange H. W. , Nausch G. , Wallace D. W. R. 
Published: April 2010

Abstract. In January 2003, a major inflow of cold and oxygen-rich North Sea Water in the Baltic Sea terminated an ongoing stagnation period in parts of the central Baltic Sea. In order to investigate the role of North Sea Water inflow to the Baltic Sea with regard to the production of nitrous oxide (N2O), we measured dissolved and atmospheric N2O at 26 stations in the southern and central Baltic Sea in October 2003. At the time of our cruise, water renewal had proceeded to the eastern Gotland Basin, whereas the western Gotland Basin was still unaffected by the inflow. The deep water renewal was detectable in the distributions of temperature, salinity, and oxygen concentrations as well as in the distribution of the N2O concentrations: Shallow stations in the Kiel Bight and Pomeranian Bight were well-ventilated with uniform N2O concentrations near equilibrium throughout the water column. In contrast, stations in the deep basins, such as the Bornholm and the Gotland Deep, showed a clear stratification with deep water affected by North Sea Water. Inflowing North Sea Water led to changed environmental conditions, especially enhanced oxygen (O2) or declining hydrogen sulfide (H2S) concentrations, thus, affecting the conditions for the production of N2O. Pattern of N2O profiles and correlations with parameters like oxygen and nitrate differed between the basins. The dominant production pathway seems to be nitrification rather than denitrification. No indications for advection of N2O by North Sea Water were found. A rough budget revealed a significant surplus of in situ produced N2O after the inflow. However, due to the permanent halocline, it can be assumed that the formed N2O does not reach the atmosphere. Hydrographic aspects therefore are decisive factors determining the final release of produced N2O to the atmosphere.
Climate-human-environment interactions: resolving our past
Authors: Dearing J. A. 
Published: April 2010

Abstract. The paper reviews how we can learn from the past about climate-human-environment interactions at the present time, and in the future. It focuses on data sources for environmental change at local/regional and regional/global spatial scales, and shows the scope and limitations of each. It reviews alternative methods for learning from the past, including the increasing use of simulation models. The use of multiple records (observational, palaeoenvironmental, archaeological, documentary) in local case-studies is exemplified in a study from China, where independent records help unravel the complexity of interactions and provide a basis for assessing the resilience and sustainability of the landscape system. Holocene global records for Natural Forcings (e.g. climate and tectonics), Human Society and Ecosystems are reviewed, and the problems of reconstructing global records of processes that are only recorded at local scales examined. Existing regional/global records are used to speculate about the veracity of anthropogenic forcing of global climate, with specific consideration of the Ruddiman theory. The paper concludes that a full understanding of causes of earth system change through (at least) the Holocene can come only through the most rigorous reconstructions of climate, human activities and earth processes, and importantly their interactions, at all locations and at all scales. It follows that we need to promote inter-scale learning: regionalisation and generalisation of existing data would be useful first steps. There is now a need to develop long-term simulation models that can help anticipate complex ecosystem behaviour and environmental processes in the face of global environmental change – and resolving our past is an essential element in that endeavour.