bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of CO2 fluxes via eddy covariance measurements with model predictions in a dominant subtropical forest ecosystem
Authors: Yan J.-H. , Zhou G.-Y. , Li Y.-L. , Zhang D.-Q. , Otieno D. , Tenhunen J.
Published: April 2010

Abstract. CO2 fluxes were measured continuously for twelve months (2003) using eddy covariance technique at canopy layer in a dominant subtropical forest in South China. Our results showed that daytime maximum CO2 fluxes of the whole ecosystem varied from −15 to −20 μmol m−2 s−1. The peaks of CO2 fluxes appeared earlier than the peaks of solar radiation. Contribution of CO2 fluxes in a subtropical forest in the dry season was 53% of the annual total from the whole forest ecosystem. Daytime CO2 fluxes were very large in October, November and December, which was therefore an important stage for uptake of CO2 by the forest ecosystem from the atmosphere. Using the estimates of biomass, soil carbon and parameters of leaf photosynthesis from other studies at the same forest, we ran a process-based model, CBM (stands for CSIRO Biosphere Model) for this site, and compared the predicted fluxes of CO2 with measurements. We obtained reasonable agreement. The mean difference between the simulated and measured daytime CO2 fluxes from the year-round (8249 records) was −0.2 μmol m−2 s−1 and implied well within measurement accuracy. Based on estimates of forest ecosystem respiration, NEE was calculated −242 and −276 gCm−2 year−1 for measured and modelled, respectively. In previous study, NPP for this forest stand was 694 gCm−2 year−1 during 2003/04 and litterfall was 424 gCm−2 year−1. We therefore calculated NEE as −270 gCm−2 year−1 and very similar to the values obtained by measured and modelled CO2 fluxes in this study.
Biosphere-atmosphere exchange of CO2 in relation to climate: a cross-biome analysis across multiple time scales
Authors: Stoy P. C. , Richardson A. D. , Baldocchi D. D. , Katul G. G. , Stanovick J. , Mahecha M. D. , Reichstein M. , Detto M. , Law B. E. , Wohlfahrt G. , Arriga N. , Campos J. , McCaughey J. H. , Montagnani L. , Paw U K. T. , Sevanto S. , Williams M.
Published: April 2010

Abstract. The biosphere-atmosphere flux of CO2 responds to climatic variability at time scales from seconds to years and longer. Quantifying the strength of the interaction between the flux and climate variables at multiple frequencies is necessary to begin understanding the climatic controls on the dynamics of the terrestrial carbon cycle. Orthonormal wavelet transformation (OWT) can quantify the interaction between flux and microclimate at multiple frequencies while expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the measured climate-flux interaction. The variability of the net ecosystem exchange of CO2 (NEE), gross ecosystem productivity (GEP) and ecosystem respiration (RE), and their co-variability with dominant climatic drivers, are explored with a global dataset consisting of 253 eddy covariance research sites. Results demonstrate that the NEE and GEP wavelet spectra are similar amongst plant functional types (PFT) at weekly and shorter time scales, but significant divergence appeared among PFT at the biweekly and longer time scales, at which NEE and GEP are relatively less variable than climate. The RE spectra rarely differ among PFT across time scales. On average, RE spectra had greater low frequency (monthly to interannual) variability than NEE, GEP and climate. The low frequency Fourier coefficients of eight sites with more than eight years of data were compared against CANOAK ecosystem model simulations. Both measurements and theory demonstrate that "multi-annual" spectral peaks in flux may emerge at low (4+ years) time scales. Biological responses to climate and other internal system dynamics provide the likely explanation for observed multi-annual variability, but data records must be lengthened and measurements of ecosystem state must be made, and made available, to disentangle the mechanisms responsible for these patterns.
Impacts of elevated CO2 on phytoplankton community composition and organic carbon dynamics in nutrient-depleted Okhotsk Sea surface waters
Authors: Yoshimura T. , Nishioka J. , Suzuki K. , Hattori H. , Kiyosawa H. , Watanabe Y. W.
Published: April 2010

Abstract. Impacts of the increasing CO2 in seawater (i.e. ocean acidification) on phytoplankton physiology may have various and potentially adverse effects on phytoplankton dynamics and the carbon cycle. We conducted a CO2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the phytoplankton assemblage and dynamics of organic carbon. During the 14-day incubation of nutrient-depleted surface water with a natural phytoplankton assemblage under 150, 280, 480, and 590 μatm pCO2, the relative abundance of fucoxanthin-containing phytoplankton such as diatoms and prymnesiophytes decreased with increasing pCO2. The amount of DOC accumulation also decreased with increasing pCO2, while differences in POC accumulation between the treatments were small and did not show a clear trend with the pCO2. Change in the phytoplankton community composition under different CO2 conditions will alter the organic carbon dynamics as found in the present experiment. Compared to results in the literature from nutrient-replete conditions indicating a potential enhancement of phytoplankton production with elevated CO2, the present results indicated a different physiological response of phytoplankton under nutrient-depleted conditions. These results indicate that the continuing increase in atmospheric CO2 can significantly affect the structure of marine ecosystems and carbon cycle in nutrient-depleted subpolar surface waters.
Impact of dust deposition on Fe biogeochemistry at the Tropical Eastern North Atlantic Time-series Observatory site
Authors: Ye Y. , Völker C. , Wolf-Gladrow D. A.
Published: April 2010

Abstract. A one-dimensional model of iron speciation and biogeochemistry, coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model, is applied for the Tropical Eastern North Atlantic Time-series Observatory (TENATSO) site. Aimed at investigating the role of organic complexation and dust particles in Fe speciation and bioavailability, the model is extended in this study by a more complex description of the origin and fate of organic ligands and of particle aggregation and sinking. Model results show that the profile of dissolved iron is strongly influenced by the abundance of organic ligands. Modelled processes controlling the source and fate of ligands can well explain the abundance of strong ligands. However, a restoring of total weak ligands towards a constant value is required for reproducing the observed nutrient-like profile of weak ligands, indicating that decay time of weak ligands might be too long for a 1d-model. High dust deposition brings not only considerable input of iron into surface waters but also fine inorganic particles for particle aggregation and Fe scavenging. Simulated profiles of dissolved iron show high sensitivity to re-dissolution of colloidal and particulate iron. The colloidal to soluble iron ratio is underestimated assuming that colloidal iron is mainly composed of inorganic colloids. That strongly argues for introducing organic colloids into the model in future work.
Strain-specific responses of Emiliania huxleyi to changing seawater carbonate chemistry
Authors: Langer G. , Nehrke G. , Probert I. , Ly J. , Ziveri P.
Published: April 2010

Abstract. Four strains of the coccolithophore Emiliania huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 μatm to ~1200 μatm. Growth rate, particulate organic carbon content, and particulate inorganic carbon content were measured, and organic and inorganic carbon production calculated. The four strains did not show a uniform response to carbonate chemistry changes in any of the analysed parameters and none of the four strains displayed a response pattern previously described for this species. We conclude that the sensitivity of different strains of E. huxleyi to acidification differs substantially and that this likely has a genetic basis. We propose that this can explain apparently contradictory results reported in the literature.
An upgraded carbon-based method to estimate the anthropogenic fraction of dissolved CO2 in the Atlantic Ocean
Authors: Vázquez-Rodríguez M. , Padin X. A. , Ríos A. F. , Bellerby R. G. J. , Pérez F. F.
Published: April 2010

Abstract. An upgrade of classical methods to calculate the anthropogenic carbon (Cant) signal based on estimates of the preformed dissolved inorganic carbon (CT
Seasonal pH and aragonite saturation horizons in the Gulf of Alaska during the North Pacific Survey, 1956–1957
Authors: McKinnell S. , Christian J. R.
Published: April 2010

Abstract. The extent of global change in carbon system parameters can only be evaluated by comparing present with past measurements. In the northern North Pacific, where aragonite saturation horizons are among the shallowest in the world, historical measurements of carbonate parameters vary from rare to nonexistent. However, during the summer of 1956 and winter of 1957, an extensive survey of the oceanography of the Northeast Pacific, under the auspices of the Canadian Committee on Oceanography, was conducted by the Fisheries Research Board of Canada. Approximately 2500 measurements of pH at depths from surface to 2000 m were taken throughout the Gulf of Alaska, in addition to measurements of nutrient and hydrographic properties. After conversion to the contemporary total pH scale, these data revealed significant seasonal and latitudinal differences in pH in the upper 200 m. Estimates of aragonite saturation indicate that undersaturated water was a common feature of the surface mixed layer north of 51° N latitude in the winter of 1957. The North Pacific Survey data were compared with the results of a summer 2007 survey of the west coast of North America where pH levels were ~0.1 pH units lower (at a reference density of 26.2σθ than was found in the summer of 1956.
Influence of hydrological fluxes on bio-geochemical processes in a peatland
Authors: Bougon N. , Aquilina L. , Auterives C. , Vandenkoornhuyse P.
Published: April 2010

Abstract. Factors influencing the dynamics of nitrate and sulphate concentration observed in a south Normandy peatland were determined experimentally. The effects of high or low nitrate input, and oxic or anoxic conditions on microbial activity were investigated in bioreactors, using peat samples from field sites influenced by different hydrologic regimes. Site S, unlike site G, was characterized by the presence of hydrogeological gradients inducing water fluxes from river to peat during most of the hydrological cycle. Peat samples from both sites were subjected to similar experimental conditions to distinguish between the chemical effects (NO3-, O2) and the physical effects (hydrologic regimes). [Cl-], [SO42-] and [NO3-] were monitored for 240 h. Nitrate was significantly reduced in most experiments: (1) Removal of 70% of the initial nitrate content after 51 h under anoxic conditions; (2) Complete nitrate reduction after 240 h in soil from the S site. This reduction was interpreted as heterotrophic denitrification. Sulphate monitoring revealed that 400 mg/L were produced in peat from site S under aerobic conditions. Sulphate changes under anaerobiosis were not significant or, for samples from G, under any conditions. Clear differences in chloride content (deviance analysis, P<0.05), sulphate concentration and nitrate consumption dynamics (deviance analysis, P<0.0001) were observed between the G and S sites. Our results demonstrate that the rates of nitrate removal and sulphate production differ between peat samples from sites subjected to different hydrological regimes, even under similar redox and nitrate conditions. This experimental approach highlights the effect of hydrological fluxes leading to modifications of microbial activity which are likely related to changes in microbial diversity.
Rate of Iceland Sea acidification from time series measurements
Authors: Olafsson J. , Olafsdottir S. R. , Benoit-Cattin A. , Danielsen M. , Arnarson T. S. , Takahashi T.
Published: April 2010

Abstract. The Iceland Sea is one part of the Nordic Seas. Cold Arctic Water prevails there and the deep water is an important source of North Atlantic Deep Water. We have evaluated time series observations of measured pCO2 and total CO2 concentration from discrete seawater samples during 1985–2008 for changes in response to increasing atmospheric carbon dioxide. The surface pH in winter decreases 0.0024 yr−1, which is 50% faster than those at two subtropical time series stations, BATS and ESTOC. In the deep water regime (>1500 m), the rate of pH decline is ¼ of that observed in surface waters. The surface calcium carbonate saturation states (Ω) are about 1.5 for aragonite and 2.5 for calcite, and are about ½ those for subtropical waters. During the period 1985–2008, the degree of saturation (Ω) decreased at a rate of 0.0072 yr−1 for aragonite and 0.012 yr−1 for calcite. The aragonite saturation horizon is currently at 1750 m and rising at 4 m yr−1. Based on local hypsography, each year causes 800 km2 of sea floor, previously bathed in saturated waters, to be exposed to undersaturation conditions.
Mapping landscape scale variations of forest structure, biomass, and productivity in Amazonia
Authors: Saatchi S. , Malhi Y. , Zutta B. , Buermann W. , Anderson L. O. , Araujo A. M. , Phillips O. L. , Peacock J. , ter Steege H. , Lopez Gonzalez G. , Baker T. , Arroyo L. , Almeida S. , Higuchi N. , Killeen T. , Monteagudo A. , Neill D. , Pitman N. , Prieto A. , Salomão R. , Silva N. , Vásquez Martínez R. , Laurance W. , Ramírez H. A.
Published: April 2010

Abstract. Landscape and environmental variables such as topography, geomorphology, soil types, and climate are important factors affecting forest composition, structure, productivity, and biomass. Here, we combine a network of forest inventories with recently developed global data products from satellite observations in modeling the potential distributions of forest structure and productivity in Amazonia and examine how geomorphology, soil, and precipitation control these distributions. We use the RAINFOR network of forest plots distributed in lowland forests across Amazonia, and satellite observations of tree cover, leaf area index, phenology, moisture, and topographical variations. A maximum entropy estimation (Maxent) model is employed to predict the spatial distribution of several key forest structure parameters: basal area, fraction of large trees, fraction of palms, wood density, productivity, and above-ground biomass at 5 km spatial resolution. A series of statistical tests at selected thresholds as well as across all thresholds and jackknife analysis are used to examine the accuracy of distribution maps and the relative contributions of environmental variables. The final maps were interpreted using soil, precipitation, and geomorphological features of Amazonia and it was found that the length of dry season played a key role in impacting the distribution of all forest variables except the wood density. Soil type had a significant impact on the wood productivity. Most high productivity forests were distributed either on less infertile soils of western Amazonia and Andean foothills, on crystalline shields, and younger alluvial deposits. Areas of low elevation and high density of small rivers of Central Amazonia showed distinct features, hosting mainly forests with low productivity and smaller trees.
The sensitivity of microbial processes in Icelandic soils to increasing temperatures
Authors: Guicharnaud R. , Arnalds O. , Paton G. I.
Published: April 2010

Abstract. Temperature change is acknowledged to have a significance effect on soil biological processes and the corresponding sequestration of carbon and the cycling of key nutrients. Soils at high latitudes are likely to be particularly impacted by increases in temperature. In this study, the response of a range of soil microbial parameters (respiration, nutrient availability, microbial biomass carbon, arylphosphatase and dehydrogenase activity) to temperature changes was measured in sub-arctic soils collected from across Iceland. Sample sites reflected two soil temperature regimes (cryic and frigid) and two land uses (pasture and arable). The soils were sampled from the field frozen, equilibrated at −20°C and then incubated for two weeks at −10°C, −2°C, +2°C and +10°C. Respiration and enzymatic activity were temperature dependent. Microbial biomass carbon and nitrogen mineralisation did not change with temperature. The main factor controlling soil respiration at −10°C was the concentration of dissolved organic carbon. At −10°C, dissolved organic carbon accounted for 88% of the fraction of labile carbon which was significantly greater than that recorded at +10°C when dissolved organic carbon accounted for as low as 42% of the labile carbon fraction. Heterotrophic microbial activity is governed by both substrate availability and the temperature and this has been described by the Q10 factor. Elevated temperatures in the short term may have little effect on the size of the microbial biomass but will have significant impacts on the release of carbon through respiration. These results demonstrate that gradual changes in temperature across large areas at higher latitudes will have considerable impacts in relation to global soil carbon dynamics.
Regionalization of turbulent fluxes by combining aircraft measurements with footprint analysis
Authors: El-Madany T. , Geiß H. , Schmidt A. , Klemm O.
Published: April 2010

Abstract. This paper presents a method for the regionalization of turbulent fluxes by combining airborne flux measurements and footprint analysis. Eddy covariance measurements were performed with a small environmental research aircraft in May 2008 over the "Münsterland" region in northwest Germany. This region is dominated by agricultural patches that are typically a few hectares in size. An analytic footprint model was tested and applied to relate the fluxes, as measured on the aircraft during day time conditions, to different vegetation types on the ground. The geo referenced footprint areas were merged with high resolution land use data (30×30 m), resulting in a quantification of different land use types inside the respective footprints. The fluxes of the sampled area in the Münsterland of 1510 km2 were scaled up to the area of the "Westfälische Bucht" (6054 km2), since the land use composition are comparable to a large extent. The mean fluxes calculated of 99 flight segments and used for the regionalization were found −0.69 mg m−2 s−1 for carbon dioxide and +0.17 g m−2 s−1 for water vapor.
Soil carbon stocks in ecoregions of Africa
Authors: Henry M. , Valentini R. , Bernoux M.
Published: April 2010

Abstract. The African continent plays a growing role in the carbon (C) cycle. However, Africa is one of the weakest links in our understanding of the global carbon cycle particularly when considering the soil compartment. Most of the soil organic carbon (SOC) estimates concern the global size of the soil C reservoir without indication on its distribution, or if given, limited to the contribution of a large ecosystems or region. The aim of the study is i) to assess the original soil C stocks (SOC) of Africa for the different countries and Ecoregions, and ii) to compare SOC estimates from different soil properties databases and digital maps. Four recent global digital soil maps and five soil properties databases were used to estimate the SOC for different soil layers in Africa. Those databases hold between 1799 and 4043 soil profiles which are considered to represent the soil units showed on a 0.5 by 0.5 degree soil maps of Africa. SOC of Africa ranged 133 420–184 116 Tg for 0–100 cm soil layer. The most recent databases estimated 166 397 Tg C which corresponded to 9% of the global SOC stock and 68% of the terrestrial C pool of Africa. Average SOC ranges 0.4–8.2 kg m−2 at national scale and 1.53–6.61 kg m−2 for ecoregions. Using different soil database or spatial data leads to up to 30% of difference. These quantities indicate a great potential to develop sink activities through soil C sequestration activities.
Mean vertical velocities and flow tilt angles at a fetch-limited forest site in the context of carbon dioxide vertical advection
Authors: Dellwik E. , Mann J. , Bingöl F. , Larsen K. S.
Published: April 2010

Abstract. An analysis of flow angles from a fetch-limited beech forest site with clearings is presented. Flow angles and vertical velocities from two types of sonic anemometers as well as a ground based remote sensing lidar were analysed. Instead of using rotations, where zero-flow angles were assumed for neutral flow, the data from the instruments were interpreted in relation to the terrain. Uncertainties regarding flow distortion and limited sampling time (statistical uncertainty) were evaluated and found to be significant. Especially for one of the sonic anemometers, relatively small changes in the flow distortion correction could change the sign of mean vertical velocities taken during stable atmospheric stratification relative to the neutral flow. Despite the uncertainties, it was possible to some extent to relate both positive and negative mean flow angles to features in the terrain. Conical and linear scans with a remote sensing lidar were evaluated for estimation of vertical velocities and flow angles. The results of the vertical conical scans were promising, and yielded negative flow angles for a sector where the forest is fetch-limited. However, more data and analysis is needed for a complete evaluation of the technique. The horizontal linear scans showed the variability of the mean wind speed field. A vertical velocity was calculated from different focusing distances, but this estimate yielded unrealistically high vertical velocities, due to neglect of the transversal wind component. The vertical advection term was calculated using the measured mean flow angles at the mast and profile measurements of carbon dioxide, but it is not recommended to use in relation with the flux measurement as the vertical velocity measured at the mast is most likely not representative for the whole forest.
A kinetic analysis of leaf uptake of COS and its relation to transpiration, photosynthesis and carbon isotope fractionation
Authors: Seibt U. , Kesselmeier J. , Sandoval-Soto L. , Kuhn U. , Berry J. A.
Published: April 2010

Abstract. Carbonyl sulfide (COS) is an atmospheric trace gas that holds great promise for studies of terrestrial carbon and water exchange. In leaves, COS follows the same pathway as CO2 during photosynthesis. Both gases are taken up in enzyme reactions, making COS and CO2 uptake closely coupled at the leaf scale. The biological background of leaf COS uptake is a hydrolysis reaction catalyzed by the enzyme carbonic anhydrase. Based on this, we derive and test a simple kinetic model of leaf COS uptake, and relate COS to CO2 and water fluxes at the leaf scale. The equation was found to predict realistic COS fluxes compared to observations from field and laboratory chambers. We confirm that COS uptake at the leaf level is directly linked to stomatal conductance. As a consequence, the ratio of deposition velocities (uptake rate divided by ambient mole fraction) for leaf COS and CO2 fluxes can provide an estimate of Ci/Ca the ratio of intercellular to atmospheric CO2, an important plant gas exchange parameter that cannot be measured directly. The majority of published deposition velocity ratios for leaf studies on a variety of species fall in the range of 1.5 to 4, corresponding to Ci/Ca ratios of 0.5 to 0.8. In addition, we utilize the coupling of Ci/Ca and photosynthetic ˆ13C discrimination to derive an estimate of 2.8±0.3 for the global mean ratio of deposition velocities. This corresponds to a global vegetation sink of COS in the order of 900±100 Gg S yr−1. COS can now be implemented in the same model framework as CO2 and water vapour. Atmospheric COS measurements can then provide independent constraints on CO2 and water cycles at ecosystem, regional and global scales.
Contrasting effects of temperature and winter mixing on the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean
Authors: Dumousseaud C. , Achterberg E. P. , Tyrrell T. , Charalampopoulou A. , Schuster U. , Hartman M. , Hydes D. J.
Published: April 2010

Abstract. Future climate change due to the increase in atmospheric CO2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary productivity and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic Ocean for the period between 2005 and 2007. Monthly observations were made between the English Channel and the Bay of Biscay using a ship of opportunity program. During the colder winter of 2005/2006, the maximum depth of the mixed layer reached 500 m in the Bay of Biscay, whilst during the warmer (by 2.6±0.5°C) winter of 2006/2007 the mixed layer depth reached only 300 m. The inter-annual differences in late winter concentrations of nitrate (2.8±1.1 μmol l−1) and dissolved inorganic carbon (22±6 μmol l−1), with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO2 fluxes (ranging from +4.5 to −5.5 mmol m−2 d−1) showed an increased oceanic CO2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences.
A one-month study of the zooplankton community at a fixed station in the Ligurian Sea: the potential impact of the species composition on the mineralization of organic matter
Authors: Mousseau L. , Lefevre D. , Narcy F. , Nival P. , Andersen V.
Published: April 2010

Abstract. The cruise project was designed to study temporal variations of the ecosystem during the summer-autumn transition and focused on the part played by zooplankton as top-down controllers, and the relative importance of top-down versus bottom-up controls. Zooplankton should play a key role both in the vertical transfer of particulate organic matter and in the mineralisation of organic matter. Although the importance of species diversity is well recognized, the impact of diversity on carbon fluxes is rarely considered. Trophic roles of zooplankton range from strict herbivory to strict carnivory, with all possible combinations (i.e. omnivory) between these two extremes. Feeding strategies are also very diverse, for example, active predators, passive filter feeders or suspension feeders co-exist (Bamstedt at al., 2000). As the metabolic cost of these different trophic roles and ways of feeding should be different, a physiological diversity must be considered in any assessment of the role of zooplankton in the flux of organic matter (e.g. Longhurts and Harrison, 1989). At a minimum,, species and functional diversities contribute to the diversity of exported organic matter (Steinberg et al., 2000; Madin et al., 2001). Fecal pellets, the organic matter egested by zooplankton, differ in form, size and weight, and hence in their sedimentation and degradation rates (Turner, 2002). The downward flux of organic matter thus depends on not only on physical and chemical processes but also on biological variables. The area sampled, located in the central part of the Ligurian Sea is next to the DYFAMED site, a time-series station monthly monitored for several years now. The zone is considered to be oligotrophic and protected from strong advective processes (Andersen and Prieur, 2000). The two cruises DYNAmic of the rapid PROCess (DYNAPROC 1 in May 1995 and DYNAPROC 2, the present study) were devoted to factors controlling the vertical flux of matter on short time scales. The aim of the work presented here was to estimate, at a fixed station in the Ligurian Sea (NW Mediterranean Sea),the impact of zooplankton on organic matter fluxes. We determined the species composition and then for the dominant species of the community, we estimated rates of, oxygen consumption, carbon dioxide production and ammonium excretion. Our sampling period, the summer-autumn transition featuring strong wind events, offered contrasting situations for primary and export production (Marty et al., 2008). We thus have the opportunity to estimate how the zooplankton, from a species-specific point of view, react to these changes.
Vertical patterns of soil carbon, nitrogen and carbon: nitrogen stoichiometry in Tibetan grasslands
Authors: Yang Y. H. , Fang J. Y. , Guo D. L. , Ji C. J. , Ma W. H.
Published: April 2010

Abstract. Vertical patterns of soil organic carbon (SOC), total nitrogen (TN) and C:N stoichiometry are crucial for understanding biogeochemical cycles in high-altitude ecosystems, but remain poorly understood. In this study, we investigated vertical distributions of SOC and TN as well as their stoichiometric relationships in alpine grasslands on the Tibetan Plateau using data of 405 profiles surveyed from 135 sites across the plateau during 2001–2004. Our results showed that, both SOC and TN in alpine grasslands decreased with soil depth, while C:N ratio did not exhibit significant change along soil profile. The associations of SOC and TN content (amount per area) with environmental factors diminished with soil depth. Soil carbon content was nearly proportional to nitrogen content with a slope of 1.04 across various various grassland types. The slope did not differ significantly between alpine steppe and alpine meadow or between alpine grasslands and global ecosystems, and also did not reveal significant differences among various soil depth intervals, suggesting that soil carbon-nitrogen coupling is irrespective of ecosystem types and soil depths.
Satellites reveal an increase in gross primary production in a greenlandic high arctic fen 1992–2008
Authors: Tagesson T. , Mastepanov M. , Tamstorf M. P. , Eklundh L. , Schubert P. , Ekberg A. , Sigsgaard C. , Christensen T. R. , Ström L.
Published: April 2010

Abstract. Arctic wetlands play a key role in the terrestrial carbon cycle. Recent studies have shown a greening trend and indicated an increase in CO2 uptake in boreal and sub- to low-arctic areas. Our aim was to combine satellite-based normalized difference vegetation index (NDVI) with ground-based flux measurements of CO2 to investigate a possible greening trend and potential changes in gross primary production (GPP) between 1992 and 2008 in a high arctic fen area. The study took place in Rylekaerene in the Zackenberg Research Area (74°28' N 20°34' W), located in the National park of North Eastern Greenland. We estimated the light use efficiency (ε) for the dominant vegetation types from field measured fractions of photosynthetic active radiation (FAPAR) and ground-based flux measurements of GPP. Measured FAPAR were correlated to satellite-based NDVI. The FAPAR-NDVI relationship in combination with ε was applied to satellite data to model GPP 1992–2008. The model was evaluated against field measured GPP. The model was a useful tool for up-scaling GPP and all basic requirements for the model were well met, e.g., FAPAR was well correlated to NDVI and modeled GPP was well correlated to field measurements. The studied high arctic fen area has experienced a strong increase in GPP between 1992 and 2008. The area has during this period also experienced a substantial increase in local air temperature. Consequently, the observed greening trend is most likely due to ongoing climatic change possibly in combination with CO2 fertilization, due to increasing atmospheric concentrations of CO2.
Estimation of nighttime ecosystem respiration over a paddy field in China
Authors: Hossen M. S. , Hiyama T. , Tanaka H.
Published: April 2010

Abstract. Accurate estimation of terrestrial ecosystem respiration is crucial for developing regional- to global-scale carbon budget databases. This study evaluated nighttime ecosystem respiration under low turbulence conditions at a paddy field in China during the 2004 growing season. Data from turbulent flux with storage change and alternatively from CO2 concentration profiles measured from the surface to 32 m height were investigated and compared. Conditions were separated into windy and calm using a friction velocity (u∗) threshold. On calm nights, the vertical gradient of CO2 concentration was higher near the canopy level and decreased with height. No differences were detected in terms of quantity and seasonality between the eddy covariance-observed nighttime ecosystem respiration (Re) and the alternatively calculated Re under calm conditions. Nighttime underestimation of paddy ecosystem respiration was low, even under calm conditions. Under stable atmospheric conditions, nighttime "loss" of CO2 flux may result mainly from CO2 being stored in air below the sensor height, and CO2 drainage loss could be small because advection is small. Because the addition of measurement-height storage change is preferable for reducing nighttime underestimation, u∗ filtering and low turbulence data elimination are not required for the paddy ecosystem. Alternatively, under low turbulence conditions, nighttime flux can be calculated from concentration profiles, but actual measurement of the nocturnal boundary layer height is very important. For gap-filling of nighttime CO2 flux data for a paddy ecosystem, development of multiple regression functions based on the crop biomass/leaf area index in association with field water status is preferable to a single regression function using air/soil temperature.
A global database of soil respiration data
Authors: Bond-Lamberty B. , Thomson A.
Published: April 2010

Abstract. Soil respiration – RS, the flux of autotropically- and heterotrophically-generated CO2 from the soil to the atmosphere – remains the least well-constrained component of the terrestrial C cycle. Here we introduce the SRDB database, a near-universal compendium of published RS data, and make it available to the scientific community both as a traditional static archive and as a dynamic community database that will be updated over time by interested users. The database encompasses all published studies that report one of the following data measured in the field (not laboratory): annual RS, mean seasonal RS, a seasonal or annual partitioning of RS into its sources fluxes, RS temperature response (Q10), or RS at 10 °C. Its orientation is thus to seasonal and annual fluxes, not shorter-term or chamber-specific measurements. To date, data from 818 studies have been entered into the database, constituting 3379 records. The data span the measurement years 1961–2007 and are dominated by temperate, well-drained forests. We briefly examine some aspects of the SRDB data – mean annual RS fluxes and their correlation with other carbon fluxes, RS variability, temperature sensitivities, and the partitioning of RS source flux – and suggest some potential lines of research that could be explored using these data. The SRDB database described here is available online in a permanent archive as well as via a project-hosting repository; the latter source leverages open-source software technologies to encourage wider participation in the database's future development. Ultimately, we hope that the updating of, and corrections to, the SRDB will become a shared project, managed by the users of these data in the scientific community.
Technical Note: A combined soil/canopy chamber system for tracing δ13C in soil respiration after a 13CO2 canopy pulse labelling
Authors: Barthel M. , Sturm P. , Gentsch L. , Knohl A.
Published: April 2010

Abstract. In this study we present a combined soil/canopy chamber system that allows the investigation of carbon flow through the atmosphere-plant-soil system via a 13CO2 canopy labelling approach – especially when using short vegetation such as tree saplings. The developed chamber system clearly separates soil and canopy compartment in order to (a) prevent physical diffusion of 13C tracer into the soil chamber during a 13CO2 canopy pulse labelling (b) study stable isotope processes in soil and canopy individually and independently. In combination with novel laser spectrometry, measuring CO2 (Aerodyne Research Inc.) and H2O (Los Gatos Research Inc.) isotopologue mixing ratios at a rate of 1 Hz, we were able to trace the label transport from leaves to roots in small beech saplings (Fagus sylvatica L.) without interference due to contamination of the soil matrix and/or canopy re-labelling via tracer returning from soil respiration. A very tight coupling between above- (photosynthesis) and belowground (soil respiration) processes was found, where newly assimilated carbon fixed from the 13CO2 atmosphere re-appeared in soil respiration 2 h after it has been photosynthetically fixed. We were able to demonstrate that leaf metabolism acts on substrate for soil respiration on a diurnal timescale, with input of fresh photosynthates during daytime and starch re-mobilisation during nighttime. Long-term fluctuations in the δ13C of soil respiration, as observed under reduced water availability, could not be described by any biological or instrumental mechanism, as they did occur in an atypical ca. 15 hourly rhythm – potential mechanisms driving these fluctuations are hypothesized.
The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004
Authors: González-Dávila M. , Santana-Casiano J. M. , Rueda M. J. , Llinás O.
Published: April 2010

Abstract. The accelerated rate of increase in the atmospheric carbon dioxide (CO2) and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic properties of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon CO2 concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The experimental values for the partial surface pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, CANT. CT at constant salinity, NCT, increased at a rate of 1 μmol kg−1 yr−1 in the first 200 m, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the ESTOC site has also become more acidic, −0.0018±0.0003 units yr−1 over the first 100 m, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. The rate of change is to be observed over the first 1000 m, where at 300, 600, and 1000 m the NCT increases at a rate of 0.69, 0.61 and 0.48 μmol kg−1 yr−1, respectively. The vertical distribution of the carbonate system variables are affected by the water mass structure and, to a different extent, controlled by the production/decomposition of organic matter, the formation/dissolution of carbonates, and differences in their respective pre-formed values. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, with a total of 35% at the bottom. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented by way of a reference site to follow CANT changes in the North Atlantic Sub-tropical gyre.
No change in topsoil carbon levels of Great Britain, 1978–2007
Authors: Chamberlain P. M. , Emmett B. A. , Scott W. A. , Black H. I. J. , Hornung M. , Frogbrook Z. L.
Published: April 2010

Abstract. Soil is an important store of carbon (C) and there has been recent concern that accelerated loss of carbon from the soil may be reinforcing climate change. There is therefore a need to both track current trends in soil C storage and to identify how soil can contribute to carbon emission reduction targets. Countryside Survey (CS) is an integrated national monitoring program in which vegetation, topsoil, water and land use measurements are made across Great Britain (GB). The soil component of CS is unique as topsoil C concentrations have been measured at three time points (1978, 1998 and 2007) together with topsoil bulk density (2007 only), vegetation composition (all years), and land use (i.e. Broad Habitat, 1998, 2007). The combined dataset allows estimates of change in topsoil C stock over time and the influence of land use change on topsoil C to be investigated. Results indicate that although there was a small increase (8%) in topsoil C concentration between 1978 and 1998 and small decrease (6.5%) between 1998 and 2007, there was no significant change in GB topsoil C concentration (in g kg−1), density (in t ha−1) or stock (in Tg) between 1978 and 2007. Within individual habitats some consistent trends were observed and by examining plots which had consistent vegetation composition since 1978 we demonstrate that land use change was not responsible for the few significant changes that were found. These results are comparable with the few other estimates of recent topsoil C concentration and stock changes in W. Europe, with the exception of a previous study in England and Wales which reported significant topsoil C losses of up to 50% over a similar period. Possible reasons for the contradictory findings are discussed. An extra 220–730 Tg of C would be stored in topsoil C stocks if all GB soils were optimised at the top 5–25% C densities as recorded for each habitat in 2007.
Factors controlling the temporal variability of mass and trace metal downward flux at 1000 m depth at the DYFAMED site (Northwestern Mediterranean Sea)
Authors: Heimbürger L.-E. , Migon C. , Losno R. , Miquel J.-C. , Leblond N. , Cossa D.
Published: April 2010

Abstract. Mass fluxes and trace metal (TM) fluxes were measured from samples collected in 2003 to 2005 from sediment traps deployed at 1000 m depth at the DYFAMED (DYnamique des Flux Atmosphériques en MEDiterranée) time-series station (central Ligurian Sea, 2350 m depth). A highly significant correlation is observed between all TM fluxes, whatever the nature and emission source of the TM (e.g., crustal such as Al, Fe, Co, or anthropogenic such as Zn, Cd, Pb) and the mass flux. Because these TMs originate from different emission sources, and, therefore, their atmospheric deposition to the sea surface varies with different seasonal patterns, it is suggested that fluxes of particulate organic carbon determine fluxes of TMs, and not the contrary. The seasonal sequence of the transfer of TMs to sea floor (winter convection, spring bloom and nutrient depletion of surface waters in summer and autumn) is briefly examined to highlight the concomitant temporal variability of mass and TM fluxes. This suggests that the TM downward transfer is totally controlled by the seasonal variability of biogenic carbon production, itself depending upon the intensity of winter convection. This may be a peculiarity of marine regions such as the Ligurian Sea, where hydrodynamical features (and, therefore, spring blooms) are strongly constrained by climatic and meteorological conditions (winter temperature, wind events, rain events).
Effect of ocean acidification on the early life stages of the blue mussel (Mytilus edulis)
Authors: Gazeau F. , Gattuso J.-P. , Dawber C. , Pronker A. E. , Peene F. , Peene J. , Heip C. H. R. , Middelburg J. J.
Published: April 2010

Abstract. Several experiments have shown a decrease of growth and calcification of organisms at decreased pH levels but relatively few studies have focused on early life stages which are believed to be more sensitive to environmental disturbances such as hypercapnia. Here, we present experimental data demonstrating that the growth of planktonic mussel (Mytilus edulis) larvae is significantly affected by a decrease of pH to a level expected for the end of the century. Even though there was no significant effect of a 0.25–0.34 pH unit decrease on hatching and mortality rates during the first 2 days of development nor during the following 13-day period prior to settlement, final shells were, respectively, 4.5±1.3 and 6.0±2.3% smaller at pHNBS~7.8 than at a control pHNBS of ~8.1. Moreover, a decrease of 12.0±5.4% of shell thickness was observed. More severe impacts were found with a decrease of ~0.5 pHNBS unit during the first 2 days of development which could be attributed to a decrease of calcification due toslight undersaturation of seawater with respect to aragonite. Indeed, important effects on both hatching and D-veliger shell growth were found. Hatching rates were 24±4% lower while D-veliger shells were 12.7±0.9% smaller at pHNBS~7.6 than at a control pHNBS of ~8.1. Although these results show that blue mussel larvae are still able to develop a shell in seawater undersaturated with respect to aragonite, decreases of hatching rates and shell growth suggest a negative impact of ocean acidification on the future survival of bivalve populations potentially leading to significant ecological and economical losses.
Mortality as a key driver of the spatial distribution of aboveground biomass in Amazonian forests: results from a Dynamic Vegetation Model
Authors: Delbart N. , Ciais P. , Chave J. , Viovy N. , Malhi Y. , Le Toan T.
Published: April 2010

Abstract. Dynamic Vegetation Models (DVMs) simulate energy, water and carbon fluxes between the ecosystem and the atmosphere, between the vegetation and the soil, and between plant organs. They also estimate the potential biomass of a forest in equilibrium having grown under a given climate and atmospheric CO2 level. In this study, we evaluate the above ground woody biomass (AGWB) and the above ground woody Net Primary Productivity (NPPAGW) simulated by the DVM ORCHIDEE across Amazonian forests, by comparing the simulation results to a large set of ground measurements (220 sites for biomass, 104 sites for NPPAGW). We found that the NPPAGW is on average overestimated by 63%. We also found that the fraction of biomass that is lost through mortality is 85% too high. These model biases nearly compensate each other to give an average simulated AGWB close to the ground measurement average. Nevertheless, the simulated AGWB spatial distribution differs significantly from the observations. Then, we analyse the discrepancies in biomass with regards to discrepancies in NPPAGW and those in the rate of mortality. When we correct for the error in NPPAGW, the errors on the spatial variations in AGWB are exacerbated, showing clearly that a large part of the misrepresentation of biomass comes from a wrong modelling of mortality processes. Previous studies showed that Amazonian forests with high productivity have a higher mortality rate than forests with lower productivity. We introduce this relationship, which results in strongly improved modelling of biomass and of its spatial variations. We discuss the possibility of modifying the mortality modelling in ORCHIDEE, and the opportunity to improve forest productivity modelling through the integration of biomass measurements, in particular from remote sensing.