bluuebunny/crossref_metadata_2025 huggingface dataset:
Marine geochemical data assimilation in an efficient Earth System Model of global biogeochemical cycling
Authors: Ridgwell A. , Hargreaves J. C. , Edwards N. R. , Annan J. D. , Lenton T. M. , Marsh R. , Yool A. , Watson A.
Published: April 2010

Abstract. We have extended the 3-D ocean based "Grid ENabled Integrated Earth system model" (GENIE-1) to help understand the role of ocean biogeochemistry and marine sediments in the long-term (~100 to 100 000 year) regulation of atmospheric CO2, and the importance of feedbacks between CO2 and climate. Here we describe the ocean carbon cycle, which in its first incarnation is based around a simple single nutrient (phosphate) control on biological productivity. The addition of calcium carbonate preservation in deep-sea sediments and its role in regulating atmospheric CO2 is presented elsewhere (Ridgwell and Hargreaves, 2007). We have calibrated the model parameters controlling ocean carbon cycling in GENIE-1 by assimilating 3-D observational datasets of phosphate and alkalinity using an ensemble Kalman filter method. The calibrated (mean) model predicts a global export production of particulate organic carbon (POC) of 8.9 PgC yr−1, and reproduces the main features of dissolved oxygen distributions in the ocean. For estimating biogenic calcium carbonate (CaCO3) production, we have devised a parameterization in which the CaCO3:POC export ratio is related directly to ambient saturation state. Calibrated global CaCO3 export production (1.2 PgC yr-1) is close to recent marine carbonate budget estimates. The GENIE-1 Earth system model is capable of simulating a wide variety of dissolved and isotopic species of relevance to the study of modern global biogeochemical cycles as well as past global environmental changes recorded in paleoceanographic proxies. Importantly, even with 12 active biogeochemical tracers in the ocean and including the calculation of feedbacks between atmospheric CO2 and climate, we achieve better than 1000 years per (2.4 GHz) CPU hour on a desktop PC. The GENIE-1 model thus provides a viable alternative to box and zonally-averaged models for studying global biogeochemical cycling over all but the very longest (>1 000 000 year) time-scales.
From laboratory manipulations to Earth system models: scaling calcification impacts of ocean acidification
Authors: Ridgwell A. , Schmidt D. N. , Turley C. , Brownlee C. , Maldonado M. T. , Tortell P. , Young J. R.
Published: April 2010

Abstract. The observed variation in the calcification responses of coccolithophores to changes in carbonate chemistry paints a highly incoherent picture, particularly for the most commonly cultured "species", Emiliania huxleyi. The disparity between magnitude and potentially even sign of the calcification change under simulated end-of-century ocean surface chemical changes (higher pCO2, lower pH and carbonate saturation), raises challenges to quantifying future carbon cycle impacts and feedbacks because it introduces significant uncertainty in parameterizations used for global models. Here we compile the results of coccolithophore carbonate chemistry manipulation experiments and review how ocean carbon cycle models have attempted to bridge the gap from experiments to global impacts. Although we can rule out methodological differences in how carbonate chemistry is altered as introducing an experimental bias, the absence of a consistent calcification response implies that model parameterizations based on small and differing subsets of experimental observations will lead to varying estimates for the global carbon cycle impacts of ocean acidification. We highlight two pertinent observations that might help: (1) the degree of coccolith calcification varies substantially, both between species and within species across different genotypes, and (2) the calcification response across mesocosm and shipboard incubations has so-far been found to be relatively consistent. By analogy to descriptions of plankton growth rate vs. temperature, such as the "Eppley curve", which seek to encapsulate the net community response via progressive assemblage change rather than the response of any single species, we posit that progressive future ocean acidification may drive a transition in dominance from more to less heavily calcified coccolithophores. Assemblage shift may be more important to integrated community calcification response than species-specific response, highlighting the importance of whole community manipulation experiments to models in the absence of a complete physiological understanding of the underlying calcification process. However, on a century time-scale, regardless of the parameterization adopted, the atmospheric pCO2 impact of ocean acidification is minor compared to other global carbon cycle feedbacks.
Disentangling the effects of climate and people on Sahel vegetation dynamics
Authors: Seaquist J. W. , Hickler T. , Eklundh L. , Ardö J. , Heumann B. W.
Published: April 2010

Abstract. The Sahel belt of Africa has been the focus of intensive scientific research since the 1960s, spurred on by the chronic vulnerability of its population to recurring drought and the threat of long-term land degradation. But satellite sensors have recently shown that much of the region has experienced significant increases in photosynthetic activity since the early 1980s, thus re-energizing long-standing debates about the role that people play in shaping land surface status, and thus climate at regional scales. In this paper, we test the hypothesis that people have had a measurable impact on vegetation dynamics in the Sahel for the period 1982–2002. We compare potential natural vegetation dynamics predicted by a process-based ecosystem model with satellite-derived greenness observations, and map the agreement between the two across a geographic grid at a spatial resolution of 0.5°. As aggregated data-model agreement is very good, any local differences between the two could be due to human impact. We then relate this agreement metric to state-of-the-art data sets on demographics, pasture, and cropping. Our findings suggest that demographic and agricultural pressures in the Sahel are unable to account for differences between simulated and observed vegetation dynamics, even for the most densely populated areas. But we do identify a weak, positive correlation between data-model agreement and pasture intensity at the Sahel-wide level. This indicates that herding or grazing does not appreciably affect vegetation dynamics in the region. Either people have not had a significant impact on vegetation dynamics in the Sahel or the identification of a human "footprint" is precluded by inconsistent or subtle vegetation response to complex socio-environmental interactions, and/or limitations in the data used for this study. We do not exclude the possibility of a greater human influence on vegetation dynamics over the coming decades with changing land use.
Quantifying the structure of the mesopelagic microbial loop from observed depth profiles of bacteria and protozoa
Authors: Tanaka T. , Rassoulzadegan F. , Thingstad T. F.
Published: April 2010

Abstract. t is widely recognized that organic carbon exported to the ocean aphotic layer is significantly consumed by heterotrophic organisms such as bacteria and zooplankton in the mesopelagic layer. However, very little is known for the trophic link between bacteria and zooplankton or the structure of the microbial loop in this layer. In the northwestern Mediterranean, recent studies have shown that viruses, bacteria, heterotrophic nanoflagellates, and ciliates distribute down to 2000 m with group-specific depth-dependent decreases, and that bacterial production decreases with depth down to 1000 m. Here we show that such data can be analyzed using a simple steady-state food chain model to quantify the carbon flow from bacteria to zooplankton over the mesopelagic layer. The model indicates that a similar amount of bacterial production is allocated to viruses and heterotrophic nanoflagellates, and that heterotrophic nanoflagellates are the important remineralizers.
Carbon dynamics and CO2 air-sea exchanges in the eutrophied coastal waters of the southern bight of the North Sea: a modelling study
Authors: Gypens N. , Lancelot C. , Borges A. V.
Published: April 2010

Abstract. A description of the carbonate system has been incorporated in the MIRO biogeochemical model to investigate the contribution of diatom and Phaeocystis blooms to the seasonal dynamics of air-sea CO2 exchanges in the Eastern Channel and Southern Bight of the North Sea with focus on the eutrophied Belgian coastal waters. For this application the model was implemented in a simplified three-box representation of the hydrodynamics including the open ocean boundary box ‘Western English Channel’ (WCH) and the ‘French Coastal Zone’ (FCZ) and ‘Belgian Coastal Zone’ (BCZ) boxes receiving carbon and nutrients from the rivers Seine and Scheldt, respectively. Results were obtained by running the model for the 1996–1999 period. The predicted partial pressures of CO2 (pCO2) were successfully compared with data recorded over the same period in the central BCZ at station 330 (51°26.05′ N; 002°48.50′ E). Budget calculations based on model simulations of carbon flow rates indicated for BCZ a low annual sink of atmospheric CO2 (−0.17 mol C m−2 y−1). On the opposite surface water pCO2 in WCH was estimated in annual equilibrium with respect to atmospheric CO2. The relative contribution of biological, chemical and physical processes to the modelled pCO2 seasonal variability in BCZ was further explored by running model scenarios with separate closures of biological activities and carbon rivers inputs. The suppression of biological processes reversed direction of the CO2 flux in BCZ that became, on an annual scale, a significant source for atmospheric CO2 (+0.58 mol C m−2 y−1). Overall biological activity had a stronger influence on the modelled seasonal cycle of pCO2 than temperature. Especially Phaeocystis colonies which spring growth was associated with an important sink of atmospheric CO2 that counteracted the temperature-driven increase of pCO2 in spring. On the other hand, river inputs of organic and inorganic carbon were shown to increasing water pCO2 and hence emission of CO2 to the atmosphere. Same calculations conducted in WCH, showed that temperature was the main factor controlling the seasonal pCO2 cycle in these waters. The effect of interannual variations of fresh water discharge (and related nutrient and carbon inputs), temperature and wind speed was further explored by running scenarios with forcings typical of two contrasted years (1996 and 1999). Based on these simulations, the model predicts significant variations in the intensity and direction of the annual air-sea CO2 flux.
Seasonal cycling of phosphorus in the southern bight of the North Sea
Authors: van der Zee C. , Chou L.
Published: April 2010

Abstract. We have investigated the seasonal cycle of nutrients and the phosphorus speciation, i.e. dissolved inorganic and organic phosphorus (DIP and DOP) and particulate inorganic and organic phosphorus (PIP and POP), for 10 stations in the Belgian coastal zone. The Belgian part of the southern North Sea is strongly influenced by the river plumes of the Rhine, Meuse and Scheldt. In winter, high nutrient concentrations are observed, whereas in April-May these have all been consumed during the spring bloom and silica or phosphorus limitation develops. The phosphate concentrations increase rapidly again in summer-fall, whereas nitrate and silicate return to their winter values much later. This shows the efficient phosphorus recycling that takes place in the water column. The DOP concentration exhibits two peaks during a seasonal cycle: one in April-May when the phosphate concentration is at its lowest and a second one in fall when the POP content decreases. This indicates two periods of increased phosphorus recycling activity. The seasonal cycle of the DOP is different from that of dissolved organic nitrogen (DON).
Biogeochemical processes in sediments of the Manfredonia Gulf (Southern Adriatic Sea): early diagenesis of carbon and nutrient and benthic exchange
Authors: Spagnoli F. , Bartholini G. , Marini M. , Giordano P.
Published: April 2010

Abstract. In order to understand the mechanisms responsible of the recycle of carbon and nutrients at the sediment-water interface and to understand the role of sediments in nutrients mass balance in coastal water, cores were collected (pore waters and solid phases) and benthic fluxes (oxygen, dissolved nutrients, dissolved iron and managanese, alkalinity and TCO2) were measured in two stations in the Gulf of Manfredonia (Southern Adriatic Sea). Stations were chosen to include a site, in the offshore part of the gulf, under the influence of western Adriatic current and another site, in the inner part of the gulf, under influence of gyres occurring inside the gulf. Both stations were placed in areas characterized by high sedimentation rate. Fluxes at sediment water interface show higher values in S2 site during the summer. Bio-irrigation seems to be the main transport mechanism characterizing both sites, with more evident effects during summer in S1 site.
Methane emission and consumption at a North Sea gas seep (Tommeliten area)
Authors: Niemann H. , Elvert M. , Hovland M. , Orcutt B. , Judd A. , Suck I. , Gutt J. , Joye S. , Damm E. , Finster K. , Boetius A.
Published: April 2010

Abstract. The North Sea hosts large coal, oil and gas reservoirs of commercial value. Natural leakage pathways of subsurface gas to the hydrosphere have been recognized during geological surveys (Hovland and Judd, 1988). The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea. In this study, we report of an active seep site (56°29.90'N, 2°59.80'E) located in the Tommeliten area, Norwegian Block 1/9, at 75 m water depth. Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere during deep mixing situations. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments and carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the Sulphate-Methane Transition Zone (SMTZ). The SMTZ of Tommeliten is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses give evidence that AOM at the Tommeliten SMTZ is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw-1 biphythanes, 140 ng g-dw-1 fatty acid ai-C15:0), cell numbers (1.5x108 cells cm-3), AOM and SR rates (3 nmol cm-3 d-1 in the SMTZ are 2-3 orders of magnitude lower compared to AOM zones of highly active cold seeps such as Hydrate Ridge or the Gulf of Mexico.
Mini-ribozymes and freezing environment: a new scenario for the early RNA world
Authors: Vlassov A. V.
Published: April 2010

Abstract. The RNA World hypothesis states that the present-day life, which is based on DNA genomes and protein enzymes, was preceded by a simpler life form based primarily on RNA. During this era, the genetic information resided in the sequence of RNA molecules and the phenotype derived from the catalytic properties of RNA. Though it is a widely accepted scenario, a number of problems remain unsolved. One of the biggest questions is how complex RNAs could evolve, survive and replicate under typically assumed ''warm and wet'' conditions, taking into account that the RNA phosphodiester backbone is chemically unstable under these conditions. We suggest that prebiotic conditions associated with freezing could have been of key importance in the early RNA World, and discuss the role of primitive catalytic RNA in the evolution of RNA size and complexity.
C2-C10 hydrocarbon emissions from a boreal wetland and forest floor
Authors: Hellén H. , Hakola H. , Pystynen K.-H. , Rinne J. , Haapanala S.
Published: April 2010

Abstract. Emissions of various C2-C10 hydrocarbons and halogenated hydrocarbons from a boreal wetland and Scots pine forest floor were measured by static chamber technique in south-western Finland. Isoprene was the main non-methane hydrocarbon emitted by the wetland but also small emissions of ethene, propane, propene, 1-butene, 2-methylpropene, butane, pentane and hexane were detected. The isoprene emission from the wetland was observed to follow the commonly used isoprene emission algorithm. The mean emission potential of isoprene was 224 μg m−2 h−1 for the whole season. This is lower than the emission potentials published earlier and probably least partly due to the cold and cloudy weather during the measurements. No emissions of monoterpenes or halogenated hydrocarbons from the wetland were detected. Highest hydrocarbon emissions from the Scots pine forest floor were measured in spring and autumn. Main emitted compounds were monoterpenes. Isoprene emissions were negligible. Highest monoterpene emissions were measured in spring after the snow had melted. Emissions dropped in the summer and increased again in autumn. The total monoterpene emission rates varied from zero to 373 μg m−2 h−1. Probable source for these emissions is decaying plant litter. Also small emissions of chloroform (100–800 ng m−2 h−1), ethene, propane, propene, 2-methylpropene, cis-2-butene, pentane, hexane and heptane were detected.
Aggregate structure and stability linked to carbon dynamics in a south Chilean Andisol
Authors: Huygens D. , Boeckx P. , Van Cleemput O. , Godoy R , Oyarzún C.
Published: April 2010

Abstract. The extreme vulnerability of soil organic carbon to climate and land use change emphasizes the need for further research in different terrestrial ecosystems. We have studied the aggregate stability and carbon dynamics in a chronosequence of three different land uses in a south Chilean Andisols: a second growth Nothofagus obliqua forest (SGFOR), a grassland (GRASS) and a Pinus radiata plantation (PINUS). The aim of this study was to investigate the role of Al as soil organic matter stabilizing agent in this Andisol. In a case study, we linked differences in carbon dynamics between the three land use treatments to physical protection and recalcitrance of the soil organic matter (SOM). In this study, C aggregate stability and dynamics were studied using size and density fractionation experiments of the SOM, δ13C and total carbon analysis of the different SOM fractions, and mineralization measurements. The results showed that electrostatic attractions between and among Al-oxides and clay minerals are mainly responsible for the stabilization of soil aggregates and the physical protection of the enclosed soil organic carbon. Whole soil C mineralization rate constants were highest for SGFOR and PINUS, followed by GRASS. In contrast, incubation experiments of isolated macro organic matter fractions showed that the recalcitrance of the SOM decreased in another order: PINUS > SGFOR > GRASS. We concluded that physical protection of soil aggregates was the main process determining whole soil C mineralization. Land use changes affected soil organic carbon dynamics in this south Chilean Andisol by altering soil pH and consequently available Al.
Non-invasive diagnostics in pathological fossils by magnetic resonance imaging
Authors: Mietchen D. , Keupp H. , Manz B. , Volke F.
Published: April 2010

Abstract. For more than a decade, Magnetic Resonance Imaging (MRI) has been routinely employed in clinical diagnostics because it allows to non-invasively study anatomical structures and physiological processes in vivo and to differentiate between healthy and pathological states, particularly in soft tissue. Here, we demonstrate that MRI can likewise be applied to fossilized biological samples and help in elucidating paleopathological and paleoecological questions: Five anomalous guards of Jurassic and Cretaceous belemnites are presented along with putative paleopathological scenarios directly derived from 3D Magnetic Resonance images with microscopic resolution. These syn vivo deformities of both the mineralized internal rostrum and the surrounding former soft tissue can be traced back in part to traumatic events of predator-prey-interactions, and partly to parasitism. Evidence is presented that the frequently observed anomalous apical collar might be indicative of an inflammatory disease. Finally, the potential of Magnetic Resonance techniques for further paleontological applications is being discussed.
Inhibition of nitrogenase by oxygen in marine cyanobacteria controls the global nitrogen and oxygen cycles
Authors: Berman-Frank I. , Chen Y.-B. , Gerchman Y. , Dismukes G. C. , Falkowski P. G.
Published: April 2010

Abstract. Cyanobacterial N2-fixation supplies the vast majority of biologically accessible inorganic nitrogen to nutrient-poor aquatic ecosystems. The process, catalyzed by the heterodimeric protein complex, nitrogenase, is thought to predate that of oxygenic photosynthesis. Remarkably, while the enzyme plays such a critical role in Earth's biogeochemical cycles, the activity of nitrogenase in cyanobacteria is markedly inhibited in vivo at a post-translational level by the concentration of O2 in the contemporary atmosphere leading to metabolic and biogeochemical inefficiency in N2 fixation. We illustrate this crippling effect with data from Trichodesmium spp. an important contributor of "new nitrogen" to the world's subtropical and tropical oceans. The enzymatic inefficiency of nitrogenase imposes a major elemental taxation on diazotrophic cyanobacteria both in the costs of protein synthesis and for scarce trace elements, such as iron. This restriction has, in turn, led to a global limitation of fixed nitrogen in the contemporary oceans and provides a strong biological control on the upper bound of oxygen concentration in Earth's atmosphere.
Nitric oxide and nitrous oxide emission from Hungarian forest soils; link with atmospheric N-deposition
Authors: Horváth L. , Führer E. , Lajtha K.
Published: April 2010

Abstract. Studies of forest nitrogen (N) budgets generally measure inputs to the atmosphere in wet and dry precipitation and outputs via hydrologic export. Although denitrification has been shown to be important in many wetland ecosystems, emission of nitrogen oxides from forest soils is an important, and often overlooked, component of an ecosystem nitrogen budget. During one year (2002-2003), emissions of nitric oxide (NO) and nitrous oxide (N2O) were measured from Sessile oak and Norway spruce forest soils in northeast Hungary. Accumulation in small static chambers followed by gas chromatography-mass spectrometry detection was used for the estimation of N2O emission flux. Because there are rapid chemical reactions of NO and ozone, small dynamic chambers were used for in situ NO flux measurements. Average soil emissions of NO were 1.2 and 2.1 µgNm-2h-1, and for N2O were 15 and 20 µgNm-2h-1, for spruce and oak soils, respectively. The previously determined nitrogen balance between the atmosphere and the forest ecosystem was re-calculated using these soil emission figures. The total (dry + wet) atmospheric N-deposition to the soil was 1.42 and 1.59gNm-2yr-1 for spruce and oak, respectively, while the soil emissions are 0.14 and 0.20 gNm-2yr-1. Thus, about 10-13% of N compounds deposited to the soil, mostly as NH3/NH4+ and HNO3/NO3-, are transformed in the soil and emitted back to the atmosphere, mostly as a greenhouse gas (N2O).
Global prediction of planktic foraminiferal fluxes from hydrographic and productivity data
Authors: Žarić S. , Schulz M. , Mulitza S.
Published: April 2010

Abstract. Understanding and quantifying the seasonal and spatial distribution of planktic foraminiferal fluxes reflected in sedimentary assemblages is key to interpret foraminifera-based proxies in paleoceanography. Towards this goal we present an empirical model to predict foraminiferal fluxes on a global scale. A compilation of planktic foraminiferal flux and export production data from globally distributed sediment traps together with environmental data of sea-surface temperature and mixed-layer depth from online databases is used to calibrate the model that calculates monthly foraminiferal fluxes for the 18 most common species. The calibrated model is then forced with a global data set of hydrographic and productivity data to predict monthly foraminiferal fluxes worldwide. The predictive skills of the model are assessed by comparing the model output with planktic foraminiferal assemblages from globally distributed surface sediments as well as with measured foraminiferal fluxes of sediment traps not included in the calibration data set. Many general distribution patterns of foraminiferal species recognized from the model output compare favorably with observations from coretops or sediment traps, even though the model still produces problematic results in some places. Among others, meridional gradients in species richness and diversity, increased relative abundances of Neogloboquadrina pachyderma (dex.) in upwelling areas, and peak abundances of Globigerinella siphonifera in oligotrophic subtropical gyres show good agreement between model and coretops. Absolute foraminiferal fluxes are significantly underestimated in most cases, while seasonal variations can be reproduced for some species. Interannual differences in foraminiferal fluxes are not reflected by the model which might partly be due to a lack of actual environmental data for the calibration and model experiments. The limited predictive skills of the model suggest that additional parameters should be considered. Export production should probably be replaced by depth-dependent primary production data reflecting the true food availability for planktic foraminifera. Results might also be improved by adding a dynamic component to the model and linking it to an ecosystem model.
Impact of 40 years poplar cultivation on soil carbon stocks and greenhouse gas fluxes
Authors: Ferré C. , Leip A. , Matteucci G. , Previtali F. , Seufert G.
Published: April 2010

Abstract. Within the JRC Kyoto Experiment in the Regional Park and UN-Biosphere Reserve "Parco Ticino" (North-Italy, near Pavia), the soil carbon stocks and fluxes of CO2, N2O, and CH4 were measured in a poplar plantation in comparison with a natural mesohygrophilous deciduous forest nearby, which represents the pristine land cover of the area. Soil fluxes were measured using the static and dynamic closed chamber techniques for CH4 N2O, and CO2, respectively. We made further a pedological study to relate the spatial variability found with soil parameters. Annual emission fluxes of N2O and CO2 and deposition fluxes of CH4 were calculated for the year 2003 for the poplar plantation and compared to those measured at the natural forest site. N2O emissions at the poplar plantation were 0.15$plusmn;0.1 g N2O m-2 y-1 and the difference to the emissions at the natural forest of 0.07±0.06 g N2O m-2 y-1 are partly due to a period of high emissions after the flooding of the site at the end of 2002. CH4 consumption at the natural forest was twice as large as at the poplar plantation. In comparison to the relict forest, carbon stocks in the soil under the poplar plantation were depleted by 61% of surface (10 cm) carbon and by 25% down the profile under tillage (45 cm). Soil respiration rates were not significant different at both sites with 1608±1053 and 2200±791 g CO2 m-2 y-1 at the poplar plantation and natural forest, respectively, indicating that soil organic carbon is much more stable in the natural forest. In terms of the greenhouse gas budget, the non-CO2 gases contributed minor to the overall soil balance with only 0.9% (N2O) and -0.3% (CH4 of CO2-eq emissions in the natural forest, and 2.7% (N2O) and -0.2% of CO2-eq. emissions in the poplar plantation. The very high spatial variability of soil fluxes within the two sites was related to the morphology of the floodplain area, which was formed by the historic course of the Ticino river and led to a small-scale (tenth of meters) variability in soil texture and to small-scale differences in elevation. Differences of site conditions are reflected by differences of inundation patterns, ecosystem productivity, CO2 and N2O emission rates, and soil contents of carbon and nitrogen. Additional variability was observed during a flooding event and after fertilisation at the poplar site. Despite of this variability, the two sites are comparable as both originate from alluvial deposits. The study shows that changes in soil carbon stocks and related fertility are the most visible phenomena after 40 years of land use change from a pristine forest to a fast growing poplar plantation. Therefore, the conservation and careful management of existing carbon stocks deserves highest priority in the context of the Kyoto Protocol.
Co-evolution of phytoplankton C:N:P stoichiometry and the deep ocean N:P ratio
Authors: Lenton T. M. , Klausmeier C. A.
Published: April 2010

Abstract. There is a long-established, remarkable correspondence between the nitrogen-to-phosphorus ratio N:P~15 of deep ocean water and the ''Redfield ratio'' of N:P~16 required by phytoplankton. Redfield and subsequent workers have suggested that it is due to N-fixing organisms being selected when N:P<16 but being out-competed when N:P>16. Models have shown this mechanism can work, but recent observations reveal that the real system is more complex. First, the C:N:P stoichiometry of phytoplankton varies with growth rate, nutrient and light limitation, species and phylum. Second, although N-fixation is sometimes P-limited and suppressed by N-addition, there is also evidence for Fe-limitation, light-limitation and P and Fe co-limitation of N-fixers. Here we adapt recent models to include non-Redfieldian stoichiometry of phytoplankton and limitation of N-fixers by resources other than P. We show that the deep ocean N:P is set by the N:P threshold that triggers N-fixation, and is not directly related to the N:P ratio of sinking material. However, assuming competitive dynamics set the N:P threshold for N-fixation, it will be close to the N:P requirement of non-fixers (rather than that of N-fixers) and consequently so will the deep ocean N:P ratio. Theoretical limits on the N:P requirements of phytoplankton suggest that since the deep ocean became well oxygenated, its N:P has remained within the range 7.7–32.3. Decreases in phytoplankton C:P and N:P ratios over the past ~1 Gyr are predicted to have driven a decrease in deep ocean N:P, probably via increasing PO4. Even if Fe or light limitation restrict N-fixers to a fraction of the surface ocean, they reach higher densities there, minimising variations in deep ocean N:P. Thus Redfield's mechanism is robust and we expand it to suggest that phytoplankton C:N:P and deep ocean N:P have co-evolved.
Comets, carbonaceous meteorites, and the origin of the biosphere
Authors: Hoover r. b.
Published: April 2010

Abstract. The Biosphere is considered to represent the Earth's crust, atmosphere, oceans, and ice caps and the living organisms that survive within this habitat. This paper considers the significance of comets and carbonaceous meteorites to the origin and evolution of the Biosphere and presents new Field Emission Scanning Electron Microscope (FESEM) images of indigenous microfossils in the Orgueil and Murchison meteorites. The discovery of microbial extremophiles in deep crustal rocks, hydrothermal vents and ancient ice has established that the biosphere is far more extensive than previously recognized. Chemical and molecular biomarkers and microfossils in Archaean rocks indicate that life appeared very early on the primitive Earth and the origin of the biosphere is closely linked with the emergence of life. The role of comets, carbonaceous meteorites, interstellar dust and asteroids in the delivery of water, organics and prebiotic chemicals to Earth during the Hadean (4.5–3.8 Ga) period of heavy bombardment has become more widely recognized. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have established that comets contain complex organic chemicals; that water is the predominant volatile; and that high temperatures (~400 K) can be reached on the black (albedo~0.03) nuclei when near perihelion. The microscopic dust particles in the Tempel 1 ejecta are similar in size to the particulates of the Orgueil meteorite and evidence is mounting that comets may represent the parent bodies of the CI meteorites. Impact craters and pinnacles on comet Wild 2 suggest a thick crust. Episodic outbursts and jets of Halley, Borrelly, Wild 2 and Tempel 1 near perihelion indicate that localized regimes of liquid water may periodically exist beneath the thick crust of many comets. This increases the possibility that microbial life might survive in comets and therefore the widely accepted view that comets are devoid of liquid water and therefore sterile may be invalid. Consequently, the potential role of comets in the possible delivery of viable microorganisms, as well as water and organic chemicals, to Earth merits further consideration. FESEM investigations of CI and CM carbonaceous meteorites have resulted in the detection of well-preserved remains of large, complex and highly differentiated filamentous microfossils, mats, and consortia embedded in freshly fractured interior surfaces of the rock matrix. Energy Dispersive X-ray Spectroscopy (EDS) data indicate that these remains are mineralized and consequently they are interpreted to represent indigenous microfossils rather than recent microbial contaminants. The detection of indigenous microfossils in carbonaceous meteorites suggests that the paradigm of the endogenous origin of life on Earth may also require reconsideration.
Suitability of quantum cascade laser spectrometry for CH4 and N2O eddy covariance measurements
Authors: Kroon P. S. , Hensen A. , Jonker H. J. J. , Zahniser M. S. , van 't Veen W. H. , Vermeulen A. T.
Published: April 2010

Abstract. A quantum cascade laser spectrometer was evaluated for eddy covariance measurements of CH4 and N2O using laboratory tests and three months of continuous measurements. Moreover, an indication was given of CH4 and N2O exchange. All four required criteria for eddy covariance measurements related to continuity, sampling frequency, precision and stationarity were checked. The system had been running continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system was employed for unattended operation of the system. A sampling frequency of 10 Hz was obtained using a 1 GHz PC system. A precision of 2.6 and 0.3 ppb Hz−1/2 was obtained for CH4 and N2O, respectively. However, it proved to be important to calibrate the equipment frequently using a low and a high standard. Drift in the system was removed using a 120 s running mean filter. Average fluxes and standard deviations in the averages of 484±375 ngC m−2s−1 (2.32±1.80 mg m−2h−1) and 39±62 ngN m−2s−1 (0.22±0.35 mg m−2h−1) were observed. About 40% of the total N2O emission was due to a fertilizing event.
Characterizing ecosystem-atmosphere interactions from short to interannual time scales
Authors: Mahecha M. D. , Reichstein M. , Lange H. , Carvalhais N. , Bernhofer C. , Grünwald T. , Papale D. , Seufert G.
Published: April 2010

Abstract. Characterizing ecosystem-atmosphere interactions in terms of carbon and water exchange on different time scales is considered a major challenge in terrestrial biogeochemical cycle research. The respective time series are now partly comprising an observation period of one decade. In this study, we explored whether the observation period is already sufficient to detect cross relationships of the variables beyond the annual cycle as they are expected from comparable studies in climatology. We explored the potential of Singular System Analysis (SSA) to extract arbitrary kinds of oscillatory patterns. The method is completely data adaptive and performs an effective signal to noise separation. We found that most observations (NEE, GPP, Reco, VPD, LE, H, u, P) were influenced significantly by low frequency components (interannual variability). Furthermore we extracted a set of nonlinear relationships and found clear annual hysteresis effects except for the NEE-Rg relationship which turned out to be the sole linear relationship in the observation space. SSA provides a new tool to investigate these phenomena explicitly on different time scales. Furthermore, we showed that SSA has great potential for eddy covariance data processing since it can be applied as novel gap filling approach relying on the temporal time series structure only.
Composition of microbial communities in aerosol, snow and ice samples from remote glaciated areas (Antarctica, Alps, Andes)
Authors: Elster J. , Delmas R. J. , Petit J.-R. , Řeháková K.
Published: April 2010

Abstract. Taxonomical and ecological analyses were performed on micro-autotrophs (cyanobacteria and algae together with remnants of diatom valves), micro-fungi (hyphae and spores), bacteria (rod, cocci and red clusters), yeast, and plant pollen extracted from various samples: Alps snow (Mt. Blank area), Andean snow (Illimani, Bolivia), Antarctic aerosol filters (Dumont d'Urville, Terre Adélie), and Antarctic inland ice (Terre Adélie). Three methods for ice and snow sample's pre-concentration were tested (filtration, centrifugation and lyophilisation). Afterwards, cultivation methods for terrestrial, freshwater and marine microorganisms (micro-autotrophs and micro-fungi) were used in combination with liquid and solid media. The main goal of the study was to find out if micro-autotrophs are commonly transported by air masses, and later stored in snow and icecaps around the world. The most striking result of this study was the absence of culturable micro-autotrophs in all studied samples. However, an unusual culturable pigmented prokaryote was found in both alpine snow and aerosol samples. Analyses of many samples and proper statistical analyses (PCA, RDA- Monte Carlo permutation tests) showed that studied treatments highly significantly differ in both microbial community and biotic remnants composition F=9.33, p=0.001. In addition, GLM showed that studied treatments highly significantly differ in numbers of categories of microorganisms and remnants of biological material F=11.45, p=0.00005. The Antarctic aerosol samples were characterised by having red clusters of bacteria, the unusual prokaryote and yeasts. The high mountain snow from the Alps and Andes contained much more culturable heterotrophs. The unusual prokaryote was very abundant, as were coccoid bacteria, red clusters of bacteria, as well as yeasts. The Antarctic ice samples were quite different. These samples had higher numbers of rod bacteria and fungal hyphae. The microbial communities and biological remnants of analysed samples comprises two communities, without a sharp boundary between them: i) the first community includes ubiquitous organisms including contaminants, ii) the second community represents individuals frequently occurring in remote terrestrial cold or hot desert/semi-desert and/or marginal soil-snow-ice ecosystems.
Detailed validation of the bidirectional effect in various Case 1 waters for application to Ocean Color imagery
Authors: Voss K. J. , Morel A. , Antoine D.
Published: April 2010

Abstract. The radiance viewed from the ocean depends on the illumination and viewing geometry along with the water properties and this variation is called the bidirectional effect, or BRDF of the water. This BRDF depends on the inherent optical properties of the water, including the volume scattering function, and is important when comparing data from different satellite sensors. The current model by Morel et al. (2002) depends on modeled water parameters, thus must be carefully validated. In this paper we combined upwelling radiance distribution data from several cruises, in varied water types and with a wide range of solar zenith angles. We found that the average error of the model, when compared to the data was less than 1%, while the RMS difference between the model and data was on the order of 0.02–0.03. This is well within the statistical noise of the data, which was on the order of 0.04–0.05, due to environmental noise sources such as wave focusing.
Co-limitation by iron, silicate, and light of three Southern Ocean diatom species
Authors: Hoffmann L. J. , Peeken I. , Lochte K.
Published: April 2010

Abstract. The effect of combined iron, silicate, and light co-limitation was investigated in two Southern Ocean diatom species, Chaetoceros dichaeta and Actinocyclus sp. and one cosmopolitan species, Chaetoceros debilis, all isolated in the Southern Ocean (SO). We found species specific differences in the level of nutrient limitation and its effect on physiological and morphological parameters. Growth of all species tested was clearly co-limited by iron and silicate, reflected in a 4 to 40 times higher increase in cell numbers in the high iron, high silicate treatments compared with the controls. However, the effect of iron and silicate availability on chain length and frustules structures was species specific. Most drastic frustule malformation was found under iron and silicate co-limitation in C. dichaeta while Si limitation caused a strong cell elongation in both Chaetoceros species. Additional a significant increase in chain length was observed in these species under high iron conditions. Therefore, species composition in the SO is likely also indirectly affected by these nutrients via different effects on diatom grazing protection. These morphological changes reflect a potential as biological markers in sediments for the growth history of chain forming species. High light conditions, comparable with light intensities found in the upper 28 m of the SO, showed a negative impact on growth of the endemic species C. dichaeta and Actinocyclus sp. This is in contrast to the assumed light limitation of SO diatoms and indicates an adaptation strategy to the deep mixing and resulting low light conditions in the SO. In contrast to that, the cosmopolitan species C. debilis was not negatively affected by increased light intensity, indicating adaptation to a broader light environment. These results suggest that light limitation of SO phytoplankton due to deep wind mixed layers may play a minor role than hitherto assumed.
Climate-driven enrichment of pollutants in peatlands
Authors: Martínez Cortizas A. , Biester H. , Mighall T. , Bindler R.
Published: April 2010

Abstract. Peatlands play an important role for global carbon dynamics, acting as a sink or source depending on climate. Such changes imply a series of additional effects because peatlands are also an important reservoir of atmospherically derived pollutants. Using a multiproxy approach (non-pollen-palynomorphs, δ15N, C/N, Se, Br, I, Hg, Ti), we show a relationship between climate (wetter-drier) and peat decomposition, which affected element concentrations in a Spanish bog during the last 5500 years. Changes in superficial wetness played a critical role in the cycling of elements coupled to carbon dynamics. Dry phases caused increased peat mineralisation, resulting in a 2–3 times increase in concentrations of the analysed elements independent from atmospheric fluxes. Under the present trend of climate change large areas of northern peatlands are expected to be severely affected; in this context our findings indicate that the increase in carbon release, which leads to an enrichment of elements, may enhance the export of stored contaminants (Hg, organohalogens) to the aquatic systems or to the atmosphere.
Precambrian palaeontology in the light of molecular phylogeny – an example: the radiation of the green algae
Authors: Teyssèdre B.
Published: April 2010

Abstract. The problem of the antiquity of the radiation of the green algae (phylum Viridiplantae) has been hotly debated and is still controversial today. A method combining Precambrian paleontology and molecular phylogeny is applied to shed light on this topic. As a critical method, molecular phylogeny is essential for avoiding taxonomic mistakes. As a heuristic method, it helps us to discern to what extent the presence of such and such clade is likely at such and such time, and it may even suggest the attribution of some fossil to a clade whose taxonomic position will be distinctly defined even though it has no previously known representative. Some well characterized Precambrian fossils of green algae are Palaeastrum and Proterocladus at Svanbergfjellet (ca. 750 Ma), Tasmanites and Pterospermella at Thule (ca. 1200 Ma), Spiromorpha at Ruyang (ca. 1200 Ma) and Leiosphaeridia crassa at Roper (ca. 1450 Ma). The position of these fossils in the taxonomy and the phylogeny of the Viriplantae is discussed. The conclusions are that the Chlorophyceae and the Ulvophyceae were separated long before 750 Ma, that the Chlorophyta and the Streptophyta were separated long before 1200 Ma and that the last common ancestor of the Viridiplantae and the Rhodophyta was possibly two billion years old.
Influences of initial plankton biomass and mixed layer depths on the outcome of iron-fertilization experiments
Authors: Fujii M. , Chai F.
Published: April 2010

Abstract. Several in situ iron-enrichment experiments have been conducted, where the response of the phytoplankton community differed. We use a marine ecosystem model to investigate the effect of iron on phytoplankton in response to different initial plankton conditions and mixed layer depths. Sensitivity analysis of the model results to the mixed layer depths reveals that the modeled response to the same iron enhancement treatment differed dramatically according to the different mixed layer depth. The magnitude of the iron-induced biogeochemical responses in the surface water, such as maximum chlorophyll, is inversely correlated with the mixed layer depth, as observed. The significant decrease in maximum surface chlorophyll with mixed layer depth results from the difference in diatom concentration in the mixed layer, which is determined by vertical mixing. Sensitivity of the model to initial mesozooplankton (as grazers on diatoms) biomass shows that column-integrated net community production and export production are strongly controlled by the initial mesozooplankton biomass. Higher initial mesozooplankton biomass yields high grazing pressure on diatoms, which results in less accumulation of diatom biomass. The initial diatom biomass is also important to the outcome of iron enrichment but is not as crucial as the mixed layer depth and the initial mesozooplankton biomass. This modeling study suggests not only mixed layer depth but also the initial biomass of diatoms and its principle grazers are crucial factors in the response of the phytoplankton community to the iron enrichments, and should be considered in designing future iron-enrichment experiments.