bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro formation of Ca-oxalates and the mineral glushinskite by fungal interaction with carbonate substrates and seawater
Authors: Kolo K. , Claeys Ph.
Published: April 2010

Abstract. This study investigates the in vitro formation of Ca-oxalates and glushinskite through fungal interaction with carbonate substrates and seawater. In the first experiment, thin-sections prepared from dolomitic rock samples of Terwagne Formation (Carboniferous, Viséan, northern France) served as substrates. The thin sections placed in Petri dishes were exposed to fungi grown from naturally existing airborne spores. In the second experiment, fungal growth and mineral formation was monitored using only standard seawater (SSW) as substrate. Fungal growth media consisted of a high protein/carbohydrates and sugar diet with demineralised water for irrigation. Fungal growth process reached completion under uncontrolled laboratory conditions. The fungal interaction and attack on the carbonate substrates resulted in the formation of Ca-oxalates (weddellite CaC2O4·2(H2O), whewellite (CaC2O4·(H2O)) and glushinskite MgC2O4·2(H2O) associated with the destruction of the original substrate and its replacement by the new minerals. The seawater substrate resulted also in the formation of glushinskite and Ca-oxalates. Both of Ca and Mg were mobilized from the experimental substrates by fungi. The newly formed minerals and textural changes caused by fungal attack on the carbonate substrate were investigated using light and scanning electron microscopy (SEM-EDX), x-ray diffraction (XRD) and Raman spectroscopy. The results document the role of microorganisms in biomineralization, neo-mineral formation and sediment diagenesis. They also reveal the capacity of living fungi to interact with liquid substrates and precipitate new minerals. This work is the first report on the in vitro formation of the mineral glushinskite through fungal-carbonate and sea water substrates interactions processes.
Geophysical and geochemical signatures of Gulf of Mexico seafloor brines
Authors: Joye S. B. , MacDonald I. R. , Montoya J. P. , Peccini M.
Published: April 2010

Abstract. Geophysical, temperature, and discrete depth-stratified geochemical data illustrate differences between an actively venting mud volcano and a relatively quiescent brine pool in the Gulf of Mexico along the continental slope. Geophysical data, including laser-line scan mosaics and sub-bottom profiles, document the dynamic nature of both environments. Temperature profiles, obtained by lowering a CTD into the brine fluid, show that the venting brine was at least 10°C warmer than the bottom water. At the brine pool, two thermoclines were observed, one directly below the brine-seawater interface and a second about one meter below the first. At the mud volcano, substantial temperature variability was observed, with the core brine temperature being either slightly (~2°C in 1997) or substantially (19°C in 1998) elevated above bottom water temperature. Geochemical samples were obtained using a device called the "brine trapper" and concentrations of dissolved gases, major ions and nutrients were determined using standard techniques. Both brines contained about four times as much salt as seawater and steep concentration gradients of dissolved ions and nutrients versus brine depth were apparent. Differences in the concentrations of calcium, magnesium and potassium between the two brine fluids suggests that the fluids are derived from different sources or that brine-sediment reactions are more important at the mud volcano than the brine pool. Substantial concentrations of methane and ammonium were observed in both brines, suggesting that fluids expelled from deep ocean brines are important sources of methane and dissolved inorganic nitrogen to the surrounding environment.
Greenhouse gas emissions from Indian rice fields: calibration and upscaling using the DNDC model
Authors: Pathak H. , Li C. , Wassmann R.
Published: April 2010

Abstract. Crop growth simulation models provide a means to quantify the effects of climate, soil and management on crop growth and biogeochemical processes in soil. The Denitrification and Decomposition (DNDC) model was evaluated for its ability to simulate methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) emissions from Indian rice fields with various management practices. The model was calibrated and validated for field experiments in New Delhi, India. The observed yield, N uptake and greenhouse gas (GHG) emissions were in good agreement with the values predicted by the model. The model was then applied for estimation of GHG emissions from rice fields in India using a newly compiled soil/climate/land use database. Continuous flooding of rice fields (42.25 million ha) resulted in annual net emissions of 1.07–1.10, 0.038–0.048 and 21.16–60.96 Tg of CH4-C, N2O-N and CO2-C, respectively, with a cumulated global warming potential (GWP) of 130.93–272.83 Tg CO2 equivalent. Intermittent flooding of rice fields reduced annual net emissions to 0.12–0.13 Tg CH4-C and 16.66–48.80 Tg CO2-C while N2O emission increased to 0.056–0.060 Tg N2O-N. The GWP, however, reduced to 91.73–211.80 Tg CO2 equivalent. The study suggests that the model can be applied for studying the GHG related issues in rice cropping systems of India.
Comparison of modelled and monitored deposition fluxes of sulphur and nitrogen to ICP-forest sites in Europe
Authors: Westling O. , Fagerli H. , Hellsten S. , Knulst J. C. , Simpson D.
Published: April 2010

Abstract. The EMEP MSC-W Eulerian chemical transport model, and its predictions of deposition of acidifying and eutrophying pollutants over Europe, play a key role in the development of emission control strategies for the UNECE and EU. It is important that this model is tested against observational data. Such model evaluation is usually conducted using observations from the EMEP monitoring network, which includes around 70 sites with wet deposition measurements in a variety of landscapes. Here we compare the results of the EMEP model with a completely independent data-set, that of the EU/ICP Forest (Level II) monitoring network. Modelled data from 1997 and 2000 were compared with observed deposition data from 160 ICP-Forest plots. In general, similarities between modelled and observed deposition in this study were reasonably good (r2 values between 0.5-0.8 for most components and years, with mean values across all sites being within 30%), despite the uncertainty in comparing measured plot data with modelled grid data. EMEP tends to give somewhat lower values for the average, median and percentile SO2-4, NO-3 and NH+4, wet deposition in the whole deposition gradient compared to ICP, but differences in mean values were within 20% in 1997 and 30% in 2000. Modelled and observed concentrations of SO2-4, NO -3 and NH4+ in precipitation are very similar as average (differences of 0-14%), median and percentiles, and the correlation between modelled and observed data is rather high r2=0.50-0.78). Many of the sites showing large discrepancies between EMEP and ICP data were found to have unusually high inter-annual variability in the precipitation amounts registered by ICP, suggesting that some differences may be due to sampling procedures or complex topographic effects. A simple precipitation variability index (PVI) was devised to flag sites with large variability, and many outliers in the chemical comparison were shown to be such sites. The largest discrepancies were seen between EMEP and ICP precipitation amounts and for this component the correlation was very poor (r2=0.04-0.23 with all data, and 0.23-0.27 with PVI-filtered data). Although more work is needed to understand these discrepancies, the overall conclusion is that the EMEP model performs rather well in reproducing patterns of S and N deposition to European forests.
The fate of new production from N2 fixation
Authors: Mulholland M. R.
Published: April 2010

Abstract. While we now know that marine N2 fixation is a significant source of new nitrogen (N) in the marine environment, little is known about the fate of this production, despite the importance of diazotrophs to global carbon and nutrient cycles. Specifically, does new production from N2 fixation fuel autotrophic or heterotrophic growth, facilitate carbon (C) export from the euphotic zone, or contribute primarily to microbial productivity and respiration in the euphotic zone? For Trichodesmium, the diazotroph we know the most about, the transfer of recently fixed N2 (and C) appears to be primarily through dissolved pools. The release of N appears to vary among and within populations and, probably as a result of the changing physiological state of cells and populations. The net result of trophic transfers appears to depend on the complexity of the colonizing community and co-occurring organisms. In order to understand the impact of diazotrophy on carbon flow and export in marine systems, we need a better assessment of the trophic flow of elements in Trichodesmium communities dominated by different species, various free and colonial morphologies, and in various defined physiological states. Nitrogen and carbon fixation rates themselves vary by orders of magnitude within and among studies highlighting the difficulty in extrapolating global rates of N2 fixation from direct measurements. Because the stoichiometry of N2 and C fixation does not appear to be in balance with the stoichiometry of particles, and the relationship between C and N2 fixation rates is also variable, it is equally difficult to derive global rates of one from the other. A better understanding of the physiology and physiological ecology of Trichodesmium and other marine diazotrophs is necessary to understand and predict the effects of increased or decreased diazotrophy in the context of the carbon cycle and global change.
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.
DON as a source of bioavailable nitrogen for phytoplankton
Authors: Bronk D. A. , See J. H. , Bradley P. , Killberg L.
Published: April 2010

Abstract. Relative to inorganic nitrogen, concentrations of dissolved organic nitrogen (DON) are often high, even in regions believed to be nitrogen-limited. The persistence of these high concentrations led to the view that the DON pool was largely refractory and therefore unimportant to plankton nutrition. What DON is utilized was believed to fuel bacterial production. More recent work, however, indicates that rates into and out of the DON pool can be large, and that the constancy in concentration is a function of tightly coupled production and consumption processes. Evidence is also accumulating that indicates phytoplankton, including a number of harmful species, may obtain a substantial part of their nitrogen nutrition from organic compounds. Ongoing research is investigating ways to discriminate between autotrophic and heterotrophic utilization, as well as a number of mechanisms such as cell surface enzymes and photochemical decomposition, that could facilitate phytoplankton use of DON components.
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.
Effects of climate warming and declining species richness in grassland model ecosystems: acclimation of CO2 fluxes
Authors: Vicca S. , Serrano-Ortiz P. , De Boeck H. J. , Lemmens C. M. H. M. , Nijs I. , Ceulemans R. , Kowalski A. S. , Janssens I. A.
Published: April 2010

Abstract. To study the effects of warming and declining species richness on the carbon balance of grassland communities, model ecosystems containing one, three or nine species were exposed to ambient and elevated (ambient +3°C) air temperature. In this paper, we analyze measured ecosystem CO2 fluxes to test whether ecosystem photosynthesis and respiration had acclimated to warming after 28 months of continuous heating, and whether the degree of acclimation depended on species richness. At first sight, we found no signs of acclimation in photosynthesis or respiration. However, because plant cover was significantly higher in the heated treatment, normalization for plant cover revealed down-regulation of both photosynthesis and respiration. Although CO2 fluxes were larger in communities with higher species richness, species richness did not affect the degree of acclimation to warming. These results imply that models need to take into account thermal acclimation to simulate photosynthesis and respiration in a warmer world.
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.
The impact of lateral carbon fluxes on the European carbon balance
Authors: Ciais P. , Borges A. V. , Abril G. , Meybeck M. , Folberth G. , Hauglustaine D. , Janssens I. A.
Published: April 2010

Abstract. To date, little has been written about the important role played by processes transporting carbon laterally over continents, and from continents to oceans. These processes have an impact on the CO2 budgets and on the carbon budgets at local, regional and continental scales. We estimated the impact on the European carbon balance of the transport of carbon by the trade of wood and food products, by the emission and oxidation of reactive reduced carbon species, and by rivers and freshwater systems up to estuaries. The analysis is completed by new estimates of the carbon fluxes of coastal seas. The magnitude of the CO2 and carbon fluxes caused by lateral transport over Europe is comparable to current estimates of carbon gain by European ecosystems. At the continental level, we estimate a CO2 sink over Europe of 140 TgC yr−1 and a carbon sink of 50 TgC yr−1 being caused by lateral transport processes.
The definition of life in the context of its origin
Authors: Zhuravlev Y. N. , Avetisov V. A.
Published: April 2010

Abstract. Current life is a complex multilevel phenomenon that is so diverse in its manifestations that a short and exhaustive definition of life is hardly possible. The high complexity of life, as well as a poor understanding of what life is in essence, are the obstacles to the elaboration of such a definition. Important characteristics of life, such as whole system-, ecosystem-, and information-defined characteristics have been included in the definition of life only recently. Ecosystem-defined characteristics have been absent in models of the pre-biotic state for a long time. However, without an ecosystem context, the concept of the emergence of life cannot be complete. Interconnections between living and non-living components of a primordial evolving system are decisive for the period of transition from chemical to biological evolution. Information-defined characteristics of life are often reduced to storage and the expression of genetic information, yet, the operation of such perfect processes in pre-biotic and transitional systems is unlikely. Genetic information, as defined in terms of the Shannon theory of communication, represents only a certain "informational channel" specified with respect to the expression of the structural genes. However, recent findings concerning the molecular mechanisms of the differential regulation of gene activity, and in the genomics, postgenomics and proteomics control mechanisms, suppose a richer diversity of informational flows in the organism. Moreover, considering life in more general context, other types of informational channels related, in particular, to the differentiation of higher taxa, hiatus, and expansion processes, should be kept in mind. In many publications devoted to the origin of life, the terms "living", "life", and "living organism" are freely interchanged that proves the vagueness of insights about the different levels of living system. This report considers some variants of the definition of life that have been recently suggested and are based on present-day knowledge of the structures and functions of life. The contradictory demands of a definition, that needs to be complete and short at the same time, are emphasized. A definition characterizing life as a state, a structure, and a process, is proposed.
Small-scale spatial structure in plankton distributions
Authors: Tzella A. , Haynes P. H.
Published: April 2010

Abstract. The observed filamental nature of plankton populations suggests that stirring plays an important role in determining their spatial structure. If diffusive mixing is neglected, the various interacting biological species within a fluid parcel are determined by the parcel time history. The induced spatial structure has been shown to be a result of competition between the time evolution of the biological processes involved and the stirring induced by the flow as measured, for example, by the rate of divergence of the distance of neighbouring fluid parcels. In the work presented here we examine a simple biological model based on delay-differential equations, previously seen in Abraham (1998) including nutrients, phytoplankton and zooplankton, coupled to a strain flow. Previous theoretical investigations made on a differential equation model (Hernández-Garcia et al., 2002) imply that the latter two should share the same small-scale structure. The generalization from differential equations to delay-differential equations, associated with the addition of a maturation time to the zooplankton growth, should not make a difference, provided sufficiently small spatial scales are considered. However, this theoretical prediction is in contradiction with the results of Abraham (1998) where the phytoplankton and zooplankton structures remain uncorrelated at all length scales. A new set of numerical experiments is performed here which show that these two regimes coexist. On larger scales , there is a decoupling of the spatial structure of the zooplankton distribution on the one hand, and the phytoplankton and nutrient on the other. On the other hand, at small enough length scales, the phytoplankton and zooplankton share the same spatial structure as expected by the theory involving no maturation time.
The role of air-sea exchange in the marine nitrogen cycle
Authors: Jickells T.
Published: April 2010

Abstract. This contribution to the Spot-On volume considers the magnitude and composition of atmospheric nitrogen inputs to the oceans and then goes on to consider the impacts of these inputs. Effects in open ocean and coastal areas are probably different. Offshore atmospheric inputs may produce a small enhancement of overall ocean productivity and hence CO2 drawdown. In coastal waters atmospheric inputs contribute significantly to overall eutrophication pressure, but evidence that they trigger algal blooms is limited. Management of atmospheric inputs to coastal waters to mitigate eutrophication pressures requires that emissions be managed over a wide area reflecting the efficient long range transport of atmospheric nitrogen. Strategies for management of oxidised and reduced nitrogen deposition will be different reflecting their different rates of deposition.
Thermal stability of soil organic matter responds to long-term fertilization practices
Authors: Leifeld J. , Franko U. , Schulz E.
Published: April 2010

Abstract. We used differential scanning calorimetry (DSC) to infer thermal properties of soil organic matter (SOM) in the static fertilization experiment in Bad Lauchstädt, Germany, which has been established in 1902. Four treatments (null N, change from null to manuring in 1978 NM, change from manuring to null in 1978 MN, and permanent manure and mineral fertilization since 1902 M) were sampled in 2004. Soil organic carbon contents were highest for M (2.4%), lowest for N (1.7%), and similar for MN and NM (2.2%). DSC thermograms were characterized by three peaks at around 354, 430, and 520°C, which were assigned to as thermally labile and stable SOM and combustion residues from lignite, respectively. DSC peak temperatures were relatively constant among treatments, but peak heights normalized to the organic C content of the soil were significantly different for labile and stable SOM. Labile C was higher for M>MN=NM=N, and stable C decreased in the order N=NM>MN=M, showing that agricultural depletion of SOM increases the share of thermally stable C. Lignite-derived C was not affected by management, suggesting a homogeneous deposition across treatments.
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.
Modeling impacts of management alternatives on soil carbon storage of farmland in Northwest China
Authors: Zhang F. , Li C. , Wang Z. , Wu H.
Published: April 2010

Abstract. Long-term losses of soil organic carbon (SOC) have been observed in many agriculture lands in Northwest China, one of the regions with the longest cultivation history in the world. The decline of SOC contents not only impaired the soil fertility but also increased the amount of carbon dioxide (CO2) emitted from terrestrial ecosystems into the atmosphere. However, quantifying the SOC losses at regional scale has long been remaining unsolved. A process-based model, Denitrification-Decomposition or DNDC, was adopted in the study to quantify impacts of farming management practices on SOC dynamics for a selected region, Shaanxi Province. The selected domain, with 3 million hectares of cropland across different climatic and farming management regimes, is representative for the major agricultural areas in Northwest China. The DNDC model was tested against long-term SOC dynamics observed at five agricultural sites in China. The agreement between the observed and modeled results indicate that DNDC was capable of capturing patterns and magnitudes of SOC changes across the climate zones, soil types, and management regimes in China. To quantify SOC dynamics for Shaanxi, we constructed a GIS database to hold all of the DNDC-required input information (e.g., weather, soil properties, crop acreage, and farming practices) for all the farmland in the studied domain. Sensitivity tests indicated the spatial heterogeneity of soil properties, especially initial SOC content, was the major source of uncertainty for the modeled SOC dynamics at regional scale. The Most Sensitive Factor (MSF) method was employed in the study to quantify the uncertainties produced from the upscaling process. The results from the regional simulations for Shaanxi indicated that (1) the overall 3 million hectares of farmland in the province was a source of atmospheric CO2 with 0.5 Tg C yr−1 lost in 2000 under the current farming management conditions, (2) an increase in the rate of crop residue incorporation from 15% to 50% or 90% converted the farmland from the C source to a C sink with 0.7 or 2.1 Tg C yr−1 sequestered, respectively, and (3) applying farmyard manure at a rate of 500 kg C ha−1 also converted the cropland into a weak C sink with 0.18 Tg C sequestered in the farmland in Shaanxi. In the studied domain, crop residue and farmyard manure used to be the major sources of soil nutrients during the centuries-long cultivation history but were gradually abandoned since 1950s when synthetic fertilizers became available. The results from this modeling study suggest that recovery of the traditional farming practices (i.e., residue incorporation and manure amendment) be a feasible approach to substantially improve the soil C status in the farmland of Shaanxi. The values of C gain or loss from this study for Shaanxi could vary if the modeled domain shifts to other provinces in Northwest China although the general conclusion may remain.
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.
Coastal versus open-ocean denitrification in the Arabian Sea
Authors: Naqvi S. W. A. , Naik H. , Pratihary A. , D’ Souza W. , Narvekar P. V. , Jayakumar D. A. , Devol A. H. , Yoshinari T. , Saino T.
Published: April 2010

Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and mid-shelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N2O) production: in the open-ocean suboxic zone, an accumulation of secondary nitrite (NO2−) is invariably accompanied by depletion of N2O whereas in the coastal suboxic zone high NO2− and very high N2O concentrations frequently co-occur, indicating, respectively, net consumption and net production of N2O by denitrifiers. The extents of heavier isotope enrichment in the combined nitrate and nitrite (NO3−+NO2−) pool and in N2O in reducing waters appear to be considerably smaller in the coastal region, reflecting more varied sources/sinks and/or different isotopic fractionation factors.
Modelling an alkenone-like proxy record in the NW African upwelling
Authors: Giraud X.
Published: April 2010

Abstract. A regional biogeochemical model is applied to the NW African coastal upwelling between 19° N and 27° N to investigate how a water temperature proxy is produced at the sea surface and recorded in the slope sediments. The biological model has two phytoplankton groups, to distinguish an alkenone producer group (considered as coccolithophores) from other phytoplankton. The Regional Ocean Modelling System (ROMS) is used to simulate the ocean circulation, and takes advantage of the Adaptive Grid Refinement in Fortran (AGRIF) package to set up an embedded griding system. The results show that the alkenone-like temperature records in the sediments are between 1.1 and 2.1°C colder compared to the annual mean SSTs. Despite the seasonality of the coccolithophorid production, this temperature difference is not mainly due to a seasonal bias, nor to the lateral advection of phytoplankton and phytodetritus from the cold water domain to most offshore locations, but to the production depth of the coccolithophores. If core-top sediment alkenone-derived temperatures are effectively recording the annual mean SSTs, the quantitative alkenone production in the water column must be inhomogeneous among the coccolithophore population and depend on physiological factors (growth rate, nutrient stress).
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.
Culturable bacteria in Himalayan ice in response to atmospheric circulation
Authors: Zhang S. , Hou S. , Ma X. , Qin D. , Chen T.
Published: April 2010

Abstract. Only recently has specific attention been given to culturable bacteria in Tibetan glaciers, but their relation to atmospheric circulation is less understood yet. Here we investigate the seasonal variation of culturable bacteria preserved in a Himalayan ice core. High concentration of culturable bacteria in glacial ice deposited during the pre-monsoon season is attributed to the transportation of continental dust stirred up by the frequent dust storms in Northwest China during spring. This is also confirmed by the spatial distribution of culturable bacteria in Tibetan glaciers. Culturable bacteria deposited during monsoon season are more diverse than other seasons because they derive from both marine air masses and local or regional continental sources. We suggest that microorganisms in Himalayan ice can be used to reconstruct atmospheric circulation.
Towards a more harmonized processing of eddy covariance CO2 fluxes: algorithms and uncertainty estimation
Authors: Papale D. , Reichstein M. , Canfora E. , Aubinet M. , Bernhofer C. , Longdoz B. , Kutsch W. , Rambal S. , Valentini R. , Vesala T. , Yakir D.
Published: April 2010

Abstract. Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more that 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. These data are usually acquired using the same method but they need a set of corrections that are often differently applied to each site and in a subjective way. In this paper a new standardized set of corrections are proposed and the uncertainties introduced by these corrections are assessed for 8 different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production) and TER (Terrestrial Ecosystem Respiration) are also discussed and a quantitative analysis presented . The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning inter-annual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.
Nitrous oxide in the North Atlantic Ocean
Authors: Walter S. , Bange H. W. , Breitenbach U. , Wallace D. W. R.
Published: April 2010

Abstract. In order to investigate the role of the North Atlantic Ocean as a source of atmospheric nitrous oxide and to decipher the major formation pathways of nitrous oxide, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and subpolar North Atlantic in October/November 2002, March/April 2004, and May 2002, respectively. Nitrous oxide was close to equilibrium or slightly supersaturated in the surface layers suggesting that the North Atlantic acts as a weak source of nitrous oxide to the atmosphere. Depth profiles showed supersaturation throughout the water column with a distinct increasing trend from the subpolar to the tropical region. Lowest nitrous oxide concentrations, near equilibrium and with an average of 11.0±1.7 nmol L−1, were found in the subpolar North Atlantic where the profiles showed no clear maxima. Highest values up to 37.3 nmol L−1 occurred in the tropical North Atlantic with clear maxima at approximately 400 m. A positive correlation of nitrous oxide with nitrate, as well as excess nitrous oxide with AOU, was only observed in the subtropical and tropical regions. Therefore, we conclude that the formation of nitrous oxide occurs in the tropical region rather than in the subpolar region of the North Atlantic and suggest nitrification is the dominant formation pathway in the subtropical and tropical regions.
Predicting the global warming potential of agro-ecosystems
Authors: Lehuger S. , Gabrielle B. , Larmanou E. , Laville P. , Cellier P. , Loubet B.
Published: April 2010

Abstract. Nitrous oxide, carbon dioxide and methane are the main biogenic greenhouse gases (GHG) contributing to the global warming potential (GWP) of agro-ecosystems. Evaluating the impact of agriculture on climate thus requires a capacity to predict the net exchanges of these gases in an integrated manner, as related to environmental conditions and crop management. Here, we used two year-round data sets from two intensively-monitored cropping systems in northern France to test the ability of the biophysical crop model CERES-EGC to simulate GHG exchanges at the plot-scale. The experiments involved maize and rapeseed crops on a loam and rendzina soils, respectively. The model was subsequently extrapolated to predict CO2 and N2O fluxes over an entire crop rotation. Indirect emissions (IE) arising from the production of agricultural inputs and from cropping operations were also added to the final GWP. One experimental site (involving a wheat-maize-barley rotation on a loamy soil) was a net source of GHG with a GWP of 350 kg CO2-C eq ha−1 yr−1, of which 75% were due to IE and 25% to direct N2O emissions. The other site (involving an oilseed rape-wheat-barley rotation on a rendzina) was a net sink of GHG for –250 kg CO2-C eq ha−1 yr−1, mainly due to a higher predicted C sequestration potential and C return from crops. Such modelling approach makes it possible to test various agronomic management scenarios, in order to design productive agro-ecosystems with low global warming impact.
Analyzing the causes and spatial pattern of the European 2003 carbon flux anomaly in Europe using seven models
Authors: Vetter M. , Churkina G. , Jung M. , Reichstein M. , Zaehle S. , Bondeau A. , Chen Y. , Ciais P. , Feser F. , Freibauer A. , Geyer R. , Jones C. , Papale D. , Tenhunen J. , Tomelleri E. , Trusilova K. , Viovy N. , Heimann M.
Published: April 2010

Abstract. Globally, the year 2003 is associated with one of the largest atmospheric CO2 rises on record. In the same year, Europe experienced an anomalously strong flux of CO2 from the land to the atmosphere associated with an exceptionally dry and hot summer in Western and Central Europe. In this study we analyze the magnitude of this carbon flux anomaly and key driving ecosystem processes using simulations of seven terrestrial ecosystem models of different complexity and types (process-oriented and diagnostic). We address the following questions: (1) how large were deviations in the net European carbon flux in 2003 relative to a short-term baseline (1998–2002) and to longer-term variations in annual fluxes (1980 to 2005), (2) which regions exhibited the largest shift in carbon fluxes during the growing season 2003, and (3) which processes controlled the carbon balance anomaly . In Western and Central Europe, the anomaly in net ecosystem productivity (NEP) over growing season 2003 was outside the 1σ bound of the carbon flux anomalies for 1980–2005. The estimated growing season anomaly ranged between –29 and –196 Tg C for Western Europe and between 13 and –94 Tg C for Central Europe depending on the model used. All models responded to a dipole pattern of the climate anomaly in 2003. In Western and Central Europe NEP was reduced due to heat and drought. Over Western Russia NEP was decreased in response to lower than normal temperatures and high precipitation. While models agree on changes in simulated NEP and gross primary productivity anomalies in 2003 over Western and Central Europe, models diverge in the estimates of anomalies in ecosystem respiration. Except for two process models which simulate respiration increase, most models simulated a decrease in ecosystem respiration in 2003. The diagnostic models showed a weaker decrease in ecosystem respiration than the process-oriented models. Based on the multi-model simulations we estimated the total carbon flux anomaly over the 2003 growing season in Europe to range between –0.02 and –0.27 Pg C relative to the net flux in 1998–2002.