bluuebunny/crossref_metadata_2025 huggingface dataset:
Centennial black carbon turnover observed in a Russian steppe soil
Authors: Hammes K. , Torn M. S. , Lapenas A. G. , Schmidt M. W. I.
Published: April 2010

Abstract. Black carbon (BC), from incomplete combustion of fuels and biomass, has been considered highly recalcitrant and a substantial sink for carbon dioxide. Recent studies have shown that BC can be degraded. We use soils sampled 100 years apart in a Russian steppe preserve to generate the first whole-profile estimate of BC stocks and turnover in the field. BC stocks (initially 2.5 kg m-2) decreased 25% with cessation of biomass burning. BC turnover in the soil was 293 y (best estimate; range 212–541 y), much faster than inert/passive carbon in soil models. Such results provide a new constraint on theories of soil carbon stabilization. Most importantly, BC cannot be assumed chemically recalcitrant in all soils; other explanations for very old soil carbon are needed.
Organic nutrients and excess nitrogen in the North Atlantic subtropical gyre
Authors: Landolfi A. , Oschlies A. , Sanders R.
Published: April 2010

Abstract. To enable an accurate estimate of total excess nitrogen (N) in the North Atlantic a new tracer, TNxs, is defined which includes the contribution of organic nutrients to the assessment of N:P stoichiometric anomalies. We estimate the spatial distribution of TNxs within the North Atlantic using data from a trans-Atlantic section across 24.5° N conducted in 2004. We then employ three different approaches to infer rates of total excess nitrogen accumulation using pCFC-12 derived ventilation ages (a TNxs vertical integration, a one end-member and a two-end member mixing model). Despite some variability among the different methods the dissolved organic nutrient fraction always contributes to about half of the TNxs accumulation, which is in the order of 9.38±4.18×1011 mol N y−1. Here we suggest that neglecting organic nutrients in stoichiometric balances of the marine N and P inventories can lead to systematic errors when estimating a nitrogen excess or deficit relative to the Redfield ratio in the oceans. For the North Atlantic the inclusion of the organic fraction leads to an upward revision of the N supply by N2 fixation to 10.2±6.9×1011 mol N y−1. This enhanced estimate of nitrogen fixation reconciles the geochemical estimates of N2 fixation derived from excess nitrate and the direct estimates from N2 fixation measurements.
Carbon isotope discrimination of C3 vegetation in Central Asian Grassland as related to long-term and short-term precipitation patterns
Authors: Wittmer M. , Auerswald K. , Tungalag R. , Bai Y. F. , Schäufele R. , Bai C. H. , Schnyder H.
Published: April 2010

Abstract. The relationship between carbon isotope discrimination (13Δ) of C3 vegetation and long-term (30 years) and short-term (growing period) precipitation was investigated. Members of Stipa, a dominant grass genus in the (semi-)arid Asian steppes, and other C3 species were collected along aridity gradients in Inner Mongolia in 2005 (11 sites, 71 samples) and in the Republic of Mongolia in 2006 (40 sites, 45 samples). The data set was expanded with published and unpublished data of Stipa and other C3 species (11 studies covering 8 years, including 64 observations of Stipa, and 103 observations of other C3 species) and C3 community bulk-samples (11 samples). Weather data were geostatistically interpolated for all sampling sites and years. 13Δ of Stipa followed different relationships for the individual years when related to mean annual precipitation due to large anomalies between annual and long-term average precipitation patterns. But, the 13Δ response to rainfall converged when mean annual precipitation was replaced by year-specific mean daily growing period precipitation (PG). Remarkably, the 13Δ-response to PG for C3 species as a whole (including herbaceous dicots, semi-shrubs and grasses) and also the C3 community-level response were virtually identical to that of Stipa. The relation was also valid outside the geographical and climatic range where it was developed, giving proof of its robustness.
A regional high-resolution carbon flux inversion of North America for 2004
Authors: Schuh A. E. , Denning A. S. , Corbin K. D. , Baker I. T. , Uliasz M. , Parazoo N. , Andrews A. E. , Worthy D. E. J.
Published: April 2010

Abstract. Resolving the discrepancies between NEE estimates based upon (1) ground studies and (2) atmospheric inversion results, demands increasingly sophisticated techniques. In this paper we present a high-resolution inversion based upon a regional meteorology model (RAMS) and an underlying biosphere (SiB3) model, both running on an identical 40 km grid over most of North America. Previous papers have utilized inversion regions formed by collapsing biome-similar grid cells into large aggregated regions. The effect of this is that the NEE correction imposed on forested regions on the east coast of the United States might be the same as that imposed on forests on the west coast of the United States while, in reality, there likely exist subtle differences in the two areas, both natural and anthropogenic. Our current inversion framework utilizes a combination of previously employed inversion techniques while allowing carbon flux corrections to be biome independent. Temporally and spatially high-resolution results utilizing biome-independent corrections provide insight into carbon dynamics in North America. In particular, we analyze hourly CO2 mixing ratio data from a sparse network of eight towers in North America for 2004. A prior estimate of carbon fluxes due to gross primary productivity (GPP) and ecosystem respiration (ER) is constructed from the SiB3 biosphere model on a 40 km grid. A combination of transport from the RAMS and the parameterized chemical transport model (PCTM) models is used to forge a connection between upwind biosphere fluxes and downwind observed CO2 mixing ratio data. A Kalman filter procedure is used to estimate weekly corrections to biosphere fluxes based upon observed CO2. RMSE-weighted annual NEE estimates, over an ensemble of potential inversion parameter sets, show a mean estimate 0.57 Pg/yr sink in North America. We perform the inversion with two independently derived boundary inflow conditions and calculate jackknife-based statistics to test the robustness of the model results. We then compare final results to estimates obtained from the CarbonTracker inversion system and the Ameriflux network. Results are promising, showing the ability to correct carbon fluxes from the biosphere models over annual and seasonal time scales, as well as over the different GPP and ER components, and also providing interesting hypotheses for future work.
Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, Acropora: implications for coral-growth rates
Authors: Juillet-Leclerc A. , Reynaud S.
Published: April 2010

Abstract. Skeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL) and high light (HL) for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ18O levels in all nubbins; responses in respiration and δ13C were not clear. The partitioning of the colonies into two groups, one showing a δ13C increase and the other a δ13C decrease with increased light, revealed common behaviors. Samples showing an increase in δ13C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ13C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ18O and δ13C. The high scattering of inter-colony δ18O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. The δ13C responses could also be related to differing algal distributions in different skeletal portions. Our results were compared to observations by Gladfelter on Acropora cervicornis (1982). Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and accretion are two separate growth modes, and accretion is light-enhanced while extension is light-repressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals.
Is global warming already changing ocean productivity?
Authors: Henson S. A. , Sarmiento J. L. , Dunne J. P. , Bopp L. , Lima I. , Doney S. C. , John J. , Beaulieu C.
Published: April 2010

Abstract. Global warming is predicted to alter the ocean's biological productivity. But how will we recognise the impacts of climate change on ocean productivity? The most comprehensive information available on the global distribution of ocean productivity comes from satellite ocean colour data. Now that over ten years of SeaWiFS data have accumulated, can we begin to detect and attribute global warming trends in productivity? Here we compare recent trends in SeaWiFS data to longer-term records from three biogeochemical models (GFDL, IPSL and NCAR). We find that detection of real trends in the satellite data is confounded by the relatively short time series and large interannual and decadal variability in productivity. Thus, recent observed changes in chlorophyll, primary production and the size of the oligotrophic gyres cannot be unequivocally attributed to the impact of global warming. Instead, our analyses suggest that a time series of ~40 yr length is needed to distinguish a global warming trend from natural variability. Analysis of modelled chlorophyll and primary production from 2001–2100 suggests that, on average, the global warming trend will not be unambiguously separable from decadal variability until ~2055. Because the magnitude of natural variability in chlorophyll and primary production is larger than, or similar to, the global warming trend, a consistent, decades-long data record must be established if the impact of climate change on ocean productivity is to be definitively detected.
Exchange of reactive nitrogen compounds: concentrations and fluxes of total ammonium and total nitrate above a spruce forest canopy
Authors: Wolff V. , Trebs I. , Foken T. , Meixner F. X.
Published: April 2010

Abstract. Total ammonium (tot-NH4+) and total nitrate (tot-NO3−) provide a chemically conservative quantity in the measurement of exchange processes of reactive nitrogen compounds ammonia (NH3), particulate ammonium (NH4+), nitric acid (HNO3), and particulate nitrate (NO3−), using the aerodynamic gradient method. Total fluxes were derived from concentration differences of total ammonium (NH3 and NH4+) and total nitrate (HNO3 and NO3−) measured at two levels. Gaseous species and related particulate compounds were measured selectively, simultaneously and continuously above a spruce forest canopy in south-eastern Germany in summer 2007. Measurements were performed using a wet-chemical two-point gradient instrument, the GRAEGOR. Median concentrations of NH3, HNO3, NH4−, and NO3− were 0.57, 0.12, 0.76, and 0.48 μg m−3, respectively. Total ammonium and total nitrate fluxes showed large variations depending on meteorological conditions, with concentrations close to zero under humid and cool conditions and higher concentrations under dry conditions. Mean fluxes of total ammonium and total nitrate in September 2007 were directed towards the forest canopy and were −65.77 ng m−2 s−1 and −41.02 ng m−2 s−1 (in terms of nitrogen), respectively. Their deposition was controlled by aerodynamic resistances only, with very little influence of surface resistances. Including measurements of wet deposition and findings of former studies at the study site on occult deposition (fog water interception), the total N deposition in September 2007 was estimated to 5.86 kg ha−1.
Changes in alpine plant growth under future climate conditions
Authors: Rammig A. , Jonas T. , Zimmermann N. E. , Rixen C.
Published: April 2010

Abstract. Alpine shrub- and grasslands are shaped by extreme climatic conditions such as a long-lasting snow cover and a short vegetation period. Such ecosystems are expected to be highly sensitive to global environmental change. Prolonged growing seasons and shifts in temperature and precipitation are likely to affect plant phenology and growth. In a unique experiment, climatology and plant growth was monitored for almost a decade at 17 snow meteorological stations in different alpine regions along the Swiss Alps. Regression analyses revealed highly significant correlations between mean air temperature in May/June and snow melt-out, onset of plant growth, and plant height. These correlations were used to project plant growth phenology for future climate conditions based on the gridded output of a set of regional climate models runs. Melt-out and onset of growth were projected to occur on average 17 days earlier by the end of the century than in the control period from 1971–2000 under the future climate conditions of the low resolution climate model ensemble. Plant height and biomass production were expected to increase by 77% and 45%, respectively. The earlier melt-out and onset of growth will probably cause a considerable shift towards higher growing plants and thus increased biomass. Our results represent the first quantitative and spatially explicit estimates of climate change impacts on future growing season length and the respective productivity of alpine plant communities in the Swiss Alps.
Individual and interacting effects of pCO2 and temperature on Emiliania huxleyi calcification: study of the calcite production, the coccolith morphology and the coccosphere size
Authors: De Bodt C. , Van Oostende N. , Harlay J. , Sabbe K. , Chou L.
Published: April 2010

Abstract. The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppm V CO2, 380 ppm V CO2 and 750 ppm V CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13°C and 18°C) during the calcification phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that the cell abundance-normalized particulate organic carbon concentration (POC) increased from the present to the future CO2 treatments. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cell abundance-normalized particulate inorganic carbon (PIC) content as well as a lower PIC:POC ratio at future CO2 levels and at 18°C. Coccosphere-sized particles showed a size reduction trend with both increasing temperature and CO2 concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effect of pCO2 and temperature was observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming.
Changes in the spectrum and rates of extracellular enzyme activities in seawater following aggregate formation
Authors: Ziervogel K. , Steen A. D. , Arnosti C.
Published: April 2010

Abstract. Marine snow aggregates are heavily colonized by heterotrophic microorganisms that express high levels of hydrolytic activities, making aggregates hotspots for carbon remineralization in the ocean. To assess how aggregate formation influences the ability of seawater microbial communities to access organic carbon, we compared hydrolysis rates of six polysaccharides in coastal seawater after aggregates had been formed (via incubation on a roller table) with hydrolysis rates in seawater from the same site that had not incubated on a roller table (referred to as whole seawater). Hydrolysis rates in the aggregates themselves were up to three orders of magnitude higher on a volume basis than in whole seawater. The enhancement of enzyme activity in aggregates relative to whole seawater differed by substrate, suggesting that the enhancement was under cellular control, rather than due to factors such as lysis or grazing. A comparison of hydrolysis rates in whole seawater with those in aggregate-free seawater, i.e. the fraction of water from the roller bottles that did not contain aggregates, demonstrated a nuanced microbial response to aggregate formation. Activities of laminarinase and xylanase enzymes in aggregate-free seawater were higher than in whole seawater, while activities of chondroitin, fucoidan, and arabinogalactan hydrolyzing enzymes were lower than in whole seawater. These data suggest that aggregate formation enhanced production of laminarinase and xylanase enzymes, and the enhancement also affected the surrounding seawater. Decreased activities of chondroitin, fucoidan, and arabinoglactan-hydrolyzing enzymes in aggregate-free seawater relative to whole seawater are likely due to shifts in enzyme production by the aggregate-associated community, coupled with the effects of enzyme degradation. Enhanced activities of laminarin- and xylan-hydrolyzing enzymes in aggregate-free seawater were due at least in part to cell-free enzymes. Measurements of enzyme lifetime using commercial enzymes suggest that hydrolytic lifetimes of cell-free enzymes may be sufficiently long to affect carbon remineralization in areas far from their site of production. Aggregate formation may be an important mechanism shaping the spectrum of enzymes active in the ocean, stimulating production of cell-free enzymes and leading to spatial and temporal decoupling of enzyme activity from the microorganisms that produced them.
Global spatial distribution of natural riverine silica inputs to the coastal zone
Authors: Dürr H. H. , Meybeck M. , Hartmann J. , Laruelle G. G. , Roubeix V.
Published: April 2010

Abstract. Silica, SiO2, in dissolved (DSi) and particulate (PSi) form, is both a major product of continental weathering as well as an essential nutrient in terrestrial and aquatic systems. Here we present estimates of the spatial distribution of riverine silica fluxes under natural conditions, i.e. without human influence, to ~140 segments of the global coastal zone. Focussing on the construction of the DSi budget, natural DSi concentration is multiplied with discharge of rivers for each segment for documented basins and segments. Segments with no documentation available are estimated using clustered information based mainly on considerations of local lithology, climate, and lake retention. We approximate fluxes of particulate silica in various forms (PSi) from fluxes of suspended matter, calculated from existing models. Results have been established for silica fluxes, concentrations and yields for drainage basins of the different continents, oceans basins as well as coastal segment basins. For the continental surfaces actually draining into the oceans (exorheic regions, representing 114.7 M km2), 371 M t y−1 of DSi and 8835 M t y−1 of PSi are transported, corresponding to a mean concentration of 9.5 mg l−1 and 226 mg l−1, and to a mean yield of 3.3 t km−2 y−1 and 77 t km−2 y−1, respectively. DSi yields exceeding 6.6 t km−2 y−1, i.e. >2× the global average, represent 17.4% of the global continental ice-free exorheic area but correspond to 56.0% of DSi fluxes. Pacific catchments hold most of the hyper-active areas (>5× global average), suggesting a close connection between tectonic activity and DSi fluxes resulting from silicate weathering. The macro-filters of regional and marginal seas intercept 33% and 46% of the total dissolved and particulate silica fluxes.
Nitrogen fertilization did not affect decay of old lignin and SOC in a 13C-labeled arable soil over 36 years
Authors: Hofmann A. , Heim A. , Gioacchini P. , Miltner A. , Gehre M. , Schmidt M. W. I.
Published: April 2010

Abstract. Retardation of soil organic carbon (SOC) decay after nitrogen addition to litter or soil has been suggested in several recent studies and has been attributed to a retardation in lignin decay. With our study we tested the long-term effect of mineral nitrogen fertilization on the decay of the SOC component lignin in arable soil. To achieve this, we tracked 13C-labeled lignin and SOC in an arable soil that is part of a 36-year field experiment with two mineral nitrogen fertilization levels. We could show that nitrogen fertilization neither retarded nor enhanced the decay of old SOC or lignin over a period of 36 years, proposing that decay of lignin was less sensitive to nitrogen fertilization than previously suggested. However, for fresh biomass there were indications that lignin decay might have been enhanced by nitrogen fertilization, whereas decay of SOC was unaffected. A retardation of SOC decay due to nitrogen addition, as found in other experiments, can therefore only be explained by effects on lignin decay, if lignin was actually measured.
Spatial distribution and functional significance of leaf lamina shape in Amazonian forest trees
Authors: Malhado A. C. M. , Whittaker R. J. , Malhi Y. , Ladle R. J. , ter Steege H. , Aragão L. E. O. C. , Quesada C. A. , Araujo A. M. , Phillips O. L. , Peacock J. , López-González G. , Baker T. R. , Butt N. , Anderson L. O. , Arroyo L. , Almeida S. , Higuchi N. , Killeen T. J. , Monteagudo A. , Neill D. A. , Pitman N. C. A. , Prieto A. , Salomão R. P. , Silva N. , Vásquez-M. R. , Laurance W. F. , Alexiades M. N. , Ramírez A. H.
Published: April 2010

Abstract. Leaves in tropical forests come in an enormous variety of sizes and shapes, each of which can be ultimately viewed as an adaptation to the complex problem of optimising the capture of light for photosynthesis. However, the fact that many different shape "strategies" coexist within a habitat demonstrate that there are many other intrinsic and extrinsic factors involved, such as the differential investment in support tissues required for different leaf lamina shapes. Here, we take a macrogeographic approach to understanding the function of different lamina shape categories. Specifically, we use 106 permanent plots spread across the Amazon rainforest basin to: (1) describe the geographic distribution of some simple metrics of lamina shape in plots from across Amazonia, and; (2) identify and quantify relationships between key environmental parameters and lamina shape in tropical forests. Because the plots are not randomly distributed across the study area, achieving this latter objective requires the use of statistics that can account for spatial auto-correlation. We found that between 60–70% of the 2791 species and 83 908 individual trees in the dataset could be classified as elliptic (=the widest part of a leaf is on an axis in the middle fifth of the long axis of the leaf). Furthermore, the average Amazonian tree leaf is 2.5 times longer than it is wide and has an entire margin. Contrary to theoretical expectations we found little support for the hypothesis that narrow leaves are an adaptation to dry conditions and low nutrient soils. However, we did find strong regional patterns in leaf lamina length-width ratios and several significant correlations with precipitation variables suggesting that water availability may be exerting an as yet unrecognised selective pressure on leaf shape of rainforest trees. Furthermore, we found a strong correlation between the proportion of trees with non-entire laminas (dissected, toothed, etc.) and mean annual temperature once again supporting the well documented association that provides a basis for reconstructing past temperature regimes.
The influence of hypercapnia and macrofauna on sediment nutrient flux – will ocean acidification affect nutrient exchange?
Authors: Wood H. L. , Widdicombe S. , Spicer J. I.
Published: April 2010

Abstract. Rising levels of atmospheric carbon dioxide and the concomitant increased uptake of this by the oceans is resulting in hypercapnia-related reduction of ocean pH. Research focussed on the direct effects of these physicochemical changes on marine invertebrates has begun to improve our understanding of impacts at the level of individual physiologies. However, CO2-related impairment of organisms' contribution to ecological or ecosystem processes has barely been addressed. The burrowing ophiuroid Amphiura filiformis, which has a physiology that makes it susceptible to reduced pH, plays a key role in sediment nutrient cycling by mixing and irrigating the sediment, a process known as bioturbation. Here we investigate the role of A. filiformis in modifying nutrient flux rates across the sediment-water boundary and the impact of CO2-related acidification on this process. A 40 day exposure study was conducted under predicted pH scenarios from the years 2100 (pH 7.7) and 2300 (pH 7.3), plus an additional treatment of pH 6.8. This study demonstrated strong relationships between A. filiformis density and cycling of some nutrients; A. filiformis activity increases the sediment uptake of phosphate and the release of nitrite and nitrate. No relationship between A. filiformis density and the flux of ammonium or silicate were observed. Results also indicated that, within the timescale of this experiment, effects at the individual bioturbator level appear not to translate into reduced ecosystem influence. Rather the effect of hypercapnia and lowered pH on bacteria and microphytobenthos may have been of greater significance in understanding the changes to nutrient fluxes seen here. However, long term survival of key bioturbating species is far from assured and changes in both bioturbation and microbial processes could alter key biogeochemical processes in future, more acidic oceans.
Stoichiometries of remineralisation and denitrification in global biogeochemical ocean models
Authors: Paulmier A. , Kriest I. , Oschlies A.
Published: April 2010

Abstract. Since the seminal paper of Redfield (1934), constant stoichiometric elemental ratios linking biotic carbon and nutrient fluxes are often assumed in marine biogeochemistry, and especially in coupled biogeochemical circulation models to link the global oxygen, carbon and nutrient cycles. However, when looking in more detail, some deviations from the classical Redfield stoichiometry have been reported, in particular with respect to remineralization of organic matter changing with depth or with ambient oxygen levels. We here compare the assumptions about the stoichiometry of organic matter and its remineralization that are used explicitly and implicitly in common biogeochemical ocean models. We find that the implicit assumptions made about the hydrogen content of organic matter can lead to inconsistencies in the modeled remineralization and denitrification stoichiometries. It is suggested that models explicitly state the chemical composition assumed for the organic matter, including its oxygen and hydrogen content.
Improving land surface models with FLUXNET data
Authors: Williams M. , Richardson A. D. , Reichstein M. , Stoy P. C. , Peylin P. , Verbeeck H. , Carvalhais N. , Jung M. , Hollinger D. Y. , Kattge J. , Leuning R. , Luo Y. , Tomelleri E. , Trudinger C. , Wang Y.-P.
Published: April 2010

Abstract. There is a growing consensus that land surface models (LSMs) that simulate terrestrial biosphere exchanges of matter and energy must be better constrained with data to quantify and address their uncertainties. FLUXNET, an international network of sites that measure the land surface exchanges of carbon, water and energy using the eddy covariance technique, is a prime source of data for model improvement. Here we outline a multi-stage process for fusing LSMs with FLUXNET data to generate better models with quantifiable uncertainty. First, we describe FLUXNET data availability, and its random and systematic biases. We then introduce methods for assessing LSM model runs against FLUXNET observations in temporal and spatial domains. These assessments are a prelude to more formal model-data fusion (MDF). MDF links model to data, based on error weightings. In theory, MDF produces optimal analyses of the modelled system, but there are practical problems. We first discuss how to set model errors and initial conditions. In both cases incorrect assumptions will affect the outcome of the MDF. We then review the problem of equifinality, whereby multiple combinations of parameters can produce similar model output. Fusing multiple independent data provides a means to limit equifinality. We then show how parameter probability density functions (PDFs) from MDF can be used to interpret model process validity, and to propagate errors into model outputs. Posterior parameter distributions are a useful way to assess the success of MDF, combined with a determination of whether model residuals are Gaussian. If the MDF scheme provides evidence for temporal variation in parameters, then that is indicative of a critical missing dynamic process. A comparison of parameter PDFs generated with the same model from multiple FLUXNET sites can provide insights into the concept and validity of plant functional types (PFT) – we would expect similar parameter estimates among sites sharing a single PFT. We conclude by identifying five major model-data fusion challenges for the FLUXNET and LSM communities: 1) to determine appropriate use of current data and to explore the information gained in using longer time series; 2) to avoid confounding effects of missing process representation on parameter estimation; 3) to assimilate more data types, including those from earth observation; 4) to fully quantify uncertainties arising from data bias, model structure, and initial conditions problems; and 5) to carefully test current model concepts (e.g. PFTs) and guide development of new concepts.
Oxygen penetration deep into the sediment of the South Pacific gyre
Authors: Fischer J. P. , Ferdelman T. G. , D'Hondt S. , Røy H. , Wenzhöfer F.
Published: April 2010

Abstract. Benthic microbial oxygen consumption rates were investigated during an IODP site survey to the South Pacific Gyre. Primary production, particle fluxes and sedimentation rates are extraordinarily low in this most oligotrophic oceanic region on earth. We studied benthic microbial respiration rates from vertical oxygen profiles in sediments obtained on different spatial scales ex situ (in piston cores and multi cores), and in situ (using a benthic lander with a microelectrode profiler). Along a transect in the area 24 to 46° S and 165 to 117° W, cores at 10 of 11 sites were oxygenated for their entire lengths (as much as 8 m below seafloor), at concentrations >150 μmol L−1 O2. This represents the deepest oxygen penetration ever measured in marine sediments. Microprofiles from the top sediment layer revealed a diffusive oxygen flux to the sediment in the order of 0.2 mmol m−2 d−1. This is in the lower range of previously reported fluxes for oligotrophic sediments but corresponds well to the low surface water primary production. Because of the inert nature of the deeper sediment, oxygen that is not consumed in the surface layer diffuses downward to much greater depth. In deeper zones, a small O2 flux of ~0.1 μmol m−2 d−1 was therefore still present. This flux was constant with depth, indicating extremely low respiration rates. Modeling of the measured oxygen profiles suggests that the sediment is probably oxygenated down to the basalt, indicating an oxygen flux from the sediment into the basaltic basement.
Net community production of oxygen derived from in vitro and in situ 1-D modeling techniques in a cyclonic mesoscale eddy in the Sargasso Sea
Authors: Mouriño-Carballido B. , Anderson L. A.
Published: April 2010

Abstract. A cyclonic eddy was intensively investigated during four cruises carried out in the Sargasso Sea between late June and early August 2004. In this study we compare in vitro incubation estimates of net community production (NCP) with in situ estimates derived from oxygen profiles and a 1-D model. The in vitro NCP rates measured at the center of the eddy showed a shift from slight net autotrophy (7±3 mmol O2 m−2 d−1) to net heterotrophy (−25±5 mmol O2 m−2 d−1) from late June to early August. The model-derived NCP rates also showed a temporal decline (21 to −1 to 13 mmol O2 m−2 d−1), but reported net autotrophy or balance for the sampling period. These results point to methodological artefacts or temporal and submesoscale variability as the mechanisms responsible for the disagreement between the in vitro and the in situ NCP estimates.
Turbulence in a coastal Mediterranean area: surface fluxes and related parameters at Castel Porziano, Italy
Authors: Cieslik S. A. , Gerosa G. , Finco A. , Matteucci G. , Cape N. , Misztal P.
Published: April 2010

Abstract. During the ACCENT/VOCBAS measuring campaign conducted at Castel Porziano, Italy over a Mediterranean macchia ecosystem located near the coastline, a series of micrometeorological observations were made. Sensible and latent heat fluxes, as well as ozone fluxes, are presented. The behaviour of the main meteorological variables such as temperature, humidity, wind speed and direction, is analysed.
Aerosol fluxes and particle growth above managed grassland
Authors: Nemitz E. , Dorsey J. R. , Flynn M. J. , Gallagher M. W. , Hensen A. , Erisman J.-W. , Owen S. M. , Dämmgen U. , Sutton M. A.
Published: April 2010

Abstract. Particle deposition velocities (11–3000 nm diameter) measured above grassland by eddy covariance during the EU GRAMINAE experiment in June 2000 averaged 0.24 and 0.03 mm s−1 to long (0.75 m) and short (0.07 m) grass, respectively. After fertilisation with 108 kg N ha−1 as calcium ammonium nitrate, sustained apparent upward fluxes of particles were observed. Analysis of concentrations and fluxes of potential precursor gases, including NH3, HNO3, HCl and selected VOCs, shows that condensation of HNO3 and NH3 on the surface of existing particles is responsible for this effect. A novel approach is developed to derive particle growth rates at the field scale, from a combination of measurements of vertical fluxes and particle size-distributions. For the first 9 days after fertilization, growth rates of 11 nm particles of 3.5 nm hr−1 and 0.89 nm hr−1 were derived for day and night-time conditions, respectively. This implies total NH4NO3 production rates of 1.1 and 0.44 μg m−3 h−1, respectively. The effect translates into a small error in measured ammonia fluxes (0.06% day, 0.56% night) and a larger error in NH4+ and NO3- aerosol fluxes of 3.6% and 10%, respectively. By converting rapidly exchanged NH3 and HNO3 into slowly depositing NH4NO3, the reaction modifies the total N budget, though this effect is small (<1% for the 10 days following fertilization), as NH3 emission dominates the net flux. It is estimated that 3.8% of the fertilizer N was volatilised as NH3, of which 0.05% re-condensed to form NH4NO3 particles within the lowest 2 m of the surface layer. This surface induced process would at least scale up to a global NH4NO3 formation of ca. 0.21 kt N yr−1 from NH4NO3 fertilisers and potentially 45 kt N yr−1 from NH3 emissions in general.
From laboratory manipulations to earth system models: predicting pelagic calcification and its consequences
Authors: Ridgwell A. , Schmidt D. N. , Turley C. , Brownlee C. , Maldonado M. T. , Tortell P. , Young J. R.
Published: April 2010

Abstract. The variation in pH-dependent calcification responses of coccolithophores paint a highly incoherent picture, particularly for the most commonly cultured "species", Emiliania huxleyi. The disparity between magnitude and even sign of the calcification change at higher CO2 (lower pH), raises challenges to quantifying future carbon cycle changes and feedbacks, by introducing significant uncertainty in parameterizations used for global models. Putting aside the possibility of methodological differences that introduce an experimental bias, we highlight two pertinent observations that can help resolve conflicting interpretations: (1) a calcification "optimum" in environmental conditions (pH) has been observed in other coccolithophore species, and (2) there exists an unambiguous direction to the CO2-calcification response across mesocosm and shipboard incubations. We propose that an equivalence can be drawn between integrated ecosystem calcification as a function of pH (or other carbonate system parameter such as calcite saturation state) and a widely used description of plankton growth rate vs. temperature – the "Eppley curve". This provides a conceptual framework for reconciling available experimental manipulations as well as a quasi-empirical relationship for ocean acidification impacts on carbonate production that can be incorporated into models. By analogy to the Eppley curve temperature vs. growth rate relationship, progressive ocean acidification in the future may drive a relatively smooth ecosystem response through transition in dominance from more to less heavily calcified coccolithophores in addition to species-specific calcification changes. However, regardless of the model parameterization employed, on a century time-scale, the CO2-calcification effect is a minor control of atmospheric CO2 compared to other C cycle feedbacks or to fossil fuel emissions.
Soils of amazonia with particular reference to the rainfor sites
Authors: Quesada C. A. , Lloyd J. , Anderson L. O. , Fyllas N. M. , Schwarz M. , Czimczik C. I.
Published: April 2010

Abstract. The tropical forests of Amazonia occur on a wide variety of different soil types reflecting a rich diversity of geologic and geomorphologic conditions. We here review the existing literature about the main soil groups of Amazonia, describing their genesis, geographical patterns and principal chemical, physical and morphologic characteristics. Original data is also presented with profiles of exchangeable cations, carbon and particle size fraction illustrated for the principal soil types, also emphasizing the high diversity existing within the main soil groups when possible. Maps of geographic distribution of soils occurring under forest vegetation are also introduced, and to contextualize soils into an evolutionary framework, a scheme of soil development is proposed having as its basis a chemical weathering index. We identify a continuum of soil evolution in Amazonia with soil properties varying predictably along this pedogenetic gradient.
Influence of elevated CO2 concentrations on cell division and nitrogen fixation rates in the bloom-forming cyanobacterium Nodularia spumigena
Authors: Czerny J. , Barcelos e Ramos J. , Riebesell U.
Published: April 2010

Abstract. The surface ocean currently absorbs about one-fourth of the CO2 emitted to the atmosphere from human activities. As this CO2 dissolves in seawater, it reacts with seawater to form carbonic acid, increasing ocean acidity and shifting the partitioning of inorganic carbon species towards increased CO2 at the expense of CO32− concentrations. While the decrease in [CO32−] and/or increase in [H+] has been found to adversely affect many calcifying organisms, some photosynthetic organisms appear to benefit from increasing [CO2]. Among these is the cyanobacterium Trichodesmium, a predominant diazotroph (nitrogen-fixing) in large parts of the oligotrophic oceans, which responded with increased carbon and nitrogen fixation at elevated pCO2. With the mechanism underlying this CO2 stimulation still unknown, the question arises whether this is a common response of diazotrophic cyanobacteria. In this study we therefore investigate the physiological response of Nodularia spumigena, a heterocystous bloom-forming diazotroph of the Baltic Sea, to CO2-induced changes in seawater carbonate chemistry. N. spumigena reacted to seawater acidification/carbonation with reduced cell division rates and nitrogen fixation rates, accompanied by significant changes in carbon and phosphorus quota and elemental composition of the formed biomass. Possible explanations for the contrasting physiological responses of Nodularia compared to Trichodesmium may be found in the different ecological strategies of non-heterocystous (Trichodesmium) and heterocystous (Nodularia) cyanobacteria.
CO2 perturbation experiments: similarities and differences between dissolved inorganic carbon and total alkalinity manipulations
Authors: Schulz K. G. , Barcelos e Ramos J. , Zeebe R. E. , Riebesell U.
Published: April 2010

Abstract. Increasing atmospheric carbon dioxide (CO2) through human activities and invasion of anthropogenic CO2 into the surface ocean alters the seawater carbonate chemistry, increasing CO2 and bicarbonate (HCO3
Photosynthetic production of boreal ground vegetation after a forest clear-cut
Authors: Kulmala L. , Pumpanen J. , Vesala T. , Hari P.
Published: April 2010

Abstract. Heather (Calluna vulgaris), rosebay willowherb (Epilobium angustifolium), wavy hair-grass (Deschampsia flexuosa) and raspberry (Rubus idaeus) are typical species on boreal clear-cut sites. According to our study, they all had clear and species-specific annual cycles of photosynthetic activity (Pmax). The maxima of C. vulgaris and E. angustifolium occurred around June and July, while that of R. idaeus occurred as late as in August. The photosynthetic activity of C. vulgaris followed the temperature history closely when the soil moisture was high. Deciduous D. flexuosa also followed the temperature history, unlike E. angustifolium and R. idaeus. During a short drought, some shoots decreased their Pmax levels but none of the species showed congruent reactions within individuals. In general, we noticed that the comparison of Pmax or respiration of different shoots caused less discrepancy when based on ground area than on leaf mass. Using species composition and continuous temperature and light measurements, we upscaled the species-specific process rates and integrated fixed and respired CO2 of ground vegetation during an entire growing season 2005. The photosynthetic production of ground vegetation was 760 g C m−2 y−1 at the fertile site and 300 g C m−2 y−1 at the infertile site. During the snow-free period (18 April–21 November), C. vulgaris respired 68 g C m−2 y−1 and E. angustifolium 7 g C m−2 y−1 at the infertile site. At the fertile site, E. angustifolium and R. idaeus respired 22 and 12 g C m−2 y−1, respectively.
Variations in leaf physiological properties within Amazon forest canopies
Authors: Lloyd J. , Patiño S. , Paiva R. Q. , Nardoto G. B. , Quesada C. A. , Santos A. J. B. , Baker T. R. , Brand W. A. , Hilke I. , Gielmann H. , Raessler M. , Luizão F. J. , Martinelli L. A. , Mercado L. M.
Published: April 2010

Abstract. Vertical profiles in leaf mass per unit leaf area (MA), foliar 13C composition (δ13C) and leaf nitrogen (N), phosphorus (P), carbon (C), potassium (K), magnesium (Mg) and calcium (Ca) concentrations were estimated for 204 rain forest trees growing in 57 sites across the Amazon Basin. Data was analysed using a multilevel modelling approach, allowing a separation of gradients within individual tree canopies (intra-tree gradients) as opposed to stand level gradients occurring because of systematic differences occurring between different trees of different heights (inter-tree gradients). Significant positive intra-tree gradients (i.e. increasing values with increasing sampling height) were observed for MA and [C]DW (the subscript denoting on a dry weight basis) with negative intra-tree gradients observed for δ13C, [Mg]DW and [K]DW. No significant intra-tree gradients were observed for [N]DW, [P]DW or [Ca]DW. Although the magnitudes of inter-tree gradients were not significantly different for MA, δ13C, [C]DW, [K]DW, [N]DW, [P]DW and [Ca]DW, for [Mg]DW there no systematic difference observed between trees of different heights, this being in contrast to the strongly negative intra-tree gradients also found to exist. When expressed on a leaf area basis, significant positive gradients were observed for N, P and K both within and between trees, these being attributable to the positive intra- and inter-tree gradients in MA mentioned above. No systematic intra-tree gradient was observed for either Ca or Mg when expressed on a leaf area basis, but with a significant positive gradient observed for Mg between trees (i.e. with taller trees tending to have a higher Mg per unit area). In contrast to the other variables measured, significant variations in intra-tree gradients for different individuals were found to exist for MA, δ13C and [P] (area basis). This was best associated with the overall average area based [P], this also being considered to be a surrogate for a leaf's photosynthetic capacity, Amax. A new model is presented which is in agreement with the above observations. The model predicts that trees characterised by a low upper canopy Amax should have shallow or even non-existent gradients in Amax, with optimal intra-canopy gradients becoming sharper as a tree's upper canopy Amax increases. Nevertheless, in all cases it is predicted that the optimal within-canopy gradients in Amax should be less than is generally observed for photon irradiance. Although this is consistent with numerous observations, it is also in contrast to previously held notions of optimality.
The effect of soil redistribution on soil organic carbon: an experimental study
Authors: Van Hemelryck H. , Fiener P. , Van Oost K. , Govers G.
Published: April 2010

Abstract. Soil erosion, transport and deposition by water drastically affect the distribution of soil organic carbon (SOC) within a landscape. Furthermore, soil redistribution is assumed to have a large impact on the exchange of carbon (C) between the pedosphere and the atmosphere. There is, however, significant scientific disagreement concerning the relative importance of the key-mechanisms at play. One of the major uncertainties concerns the fraction of SOC that is mineralized when soil is eroded by water, from the moment when detachment takes place until the moment when the SOC becomes protected by burial. In this study, the changes in C-exchange between soil and atmosphere as affected by soil redistribution processes were experimentally quantified. During a laboratory experiment, three types of erosional events were simulated, each of which was designed to produce a different amount of eroded soil material with a different degree of aggregation. During a 98-day period, CO2-efflux was measured in-situ and under field conditions on undisturbed soils with a layer of deposited soil material. Depending on the initial conditions of the soil and the intensity of the erosion process, a significant fraction of eroded SOC was mineralized after deposition (between 14 and 22%). However, results also suggest that deposition produces a dense stratified layer of sediment that caps the soil surface, leading to a decrease in SOC decomposition in deeper soil layers. As a result, the net effect of erosion on SOC can be smaller, depending on the functioning of the whole soil system. In this study, soil redistribution processes contributed an additional emission of 2 to 12% of total C contained in eroded sediment.