bluuebunny/crossref_metadata_2025 huggingface dataset:
Historical and simulated ecosystem carbon dynamics in Ghana: land use, management, and climate
Authors: Tan Z. , Tieszen L. L. , Tachie-Obeng E. , Liu S. , Dieye A. M.
Published: April 2010

Abstract. We used the General Ensemble biogeochemical Modeling System (GEMS) to simulate responses of natural and managed ecosystems to changes in land use, management, and climate for a forest/savanna transitional zone in central Ghana. Model results show that deforestation for crop production during the last century resulted in a substantial reduction in ecosystem carbon (C) stock from 135.4 Mg C ha−1 in 1900 to 77.0 Mg C ha−1 in 2000, and in soil organic C stock within the top 20 cm of soil from 26.6 Mg C ha−1 to 21.2 Mg C ha−1. If no land use change takes place from 2000 through 2100, low and high climate change scenarios (increase in temperature and decrease in precipitation over time) will result in losses of soil organic C stock by 19% and 25%, respectively. A low nitrogen (N) fertilization rate is the principal constraint on current crop production. An increase in N fertilization under the low climate change scenario would increase crop yield by 14% with 30 kg N ha−1 and by 38% with 60 kg N ha−1, leading to an increase in the average soil C stock by 12% and 29%, respectively, in all cropland by 2100. The results suggest that the climate changes in the future from current climate conditions will not necessarily become a determinant control on ecosystem C fluxes and crop production, while a reasonable N fertilization rate is critical to achieve food security and agricultural sustainability in the study area through the 21st century, and current cropping systems could be optimized to make full use of the rainfall resource.
Stable isotopes as ecological tracers: an efficient method for assessing the contribution of multiple sources to mixtures
Authors: Bugalho M. N. , Barcia P. , Caldeira M. C. , Cerdeira J. O.
Published: April 2010

Abstract. Stable isotopes are increasingly being used as tracers of ecological processes potentially providing relevant information to environmental management issues. An application of the methodology consists in relating the stable isotopic composition of a sample mixture to that of sources. The number of stable isotopes, however, is usually lower than that of potential sources existing in an ecosystem, which creates mathematical difficulties in correctly tracing sources. We discuss a linear programming model which efficiently derives information on the contribution of sources to mixtures for any number of stable isotopes and any number of sources by addressing multiple sources simultaneously. The model identifies which sources are present in all, present in a subset of the samples or absent from all samples simultaneously and calculates minimum and maximum values of each source in the mixtures. We illustrate the model using a data set consisting on the isotopic signatures of different plant sources ingested by primary consumers in tropical riverine habitat in Asia. The model discussed may contribute to extend the scope of stable isotopes methodology to a range of new problems dealing with multiple sources and multiple tracers. For instance, in food web studies, if particular organic matter sources disappear or decrease in availability (e.g. climate change scenarios) the model allows simulation of alternative diets of the consumers providing potentially relevant information for managers and decision makers.
Modeling carbon dynamics in two adjacent spruce forests with different soil conditions in Russia
Authors: Kurbatova J. , Li C. , Varlagin A. , Xiao X. , Vygodskaya N.
Published: April 2010

Abstract. Net ecosystem carbon exchange (NEE) were measured with eddy covariance method for two adjacent forests located at the southern boundary of European taiga in Russia in 1999–2004. The two spruce forests shared similar vegetation composition but differed in soil conditions. The wet spruce forest (WSF) possessed a thick peat layer (60 cm) with a high water table seasonally close to or above the soil surface. The dry spruce forest (DSF) had a relatively thin organic layer (5 cm) with a deep water table (>60 cm). The measured NEE fluxes (2000 and −1440 kg C ha−1 yr−1 for WSF and DSF, respectively) indicated that WSF was a source while DSF a sink of atmospheric carbon dioxide during the experimental years. A process-based model, Forest-DNDC, was employed in the study to interpret the observations. The modeled NEE fluxes were 1800 and −2200 kg C ha−1 yr−1 for WSF and DSF, respectively, which were comparable with the observations. The modeled data indicated that WSF and DSF had similar rates of photosynthesis and plant autotrophic respiration but differed in soil heterotrophic respiration. The simulations resulted in a hypothesis that the water table fluctuation at WSF could play a key role in determining the negative C balance in the ecosystem. A sensitivity test was conducted by running Forest-DNDC with varied water table scenarios for WSF. The results proved that the NEE fluxes from WSF were highly sensitive to the water table depth. When the water table dropped, the length of flooding season became shorter and more organic matter in the soil profile suffered from rapid decomposition that converted the ecosystem into a source atmospheric C. The conclusion from this modeling study could be applicable for a wide range of wetland and forest ecosystems that have accumulated soil organic C while face hydrological changes under certain climatic or land-use change scenarios.
Vertical structure and diurnal variability of ammonia exchange potential within an intensively managed grass canopy
Authors: Herrmann B. , Mattsson M. , Jones S. , Cellier P. , Milford C. , Sutton M. A. , Schjoerring J. K. , Neftel A.
Published: April 2010

Abstract. Stomatal ammonia compensation points (χs) of grass species on a mixed fertilized grassland were determined by measurements of apoplastic NH4+ and H+ in the field. Calculated χs-values were compared with in-canopy atmospheric NH3 concentrations (χa) measured by micrometeorological techniques. Leaf apoplastic NH4+ did not significantly differ between intact leaves from different heights above the ground. Bulk leaf NH4+ and especially NO3− slightly increased at the bottom of the canopy and these concentrations were very high in senescent plant litter. Calculated χs-values were below atmospheric χa at all canopy levels measured, indicating that the grassland was characterized by NH3 deposition before cutting. This was confirmed by the χa profile, showing the lowest χa close to the ground (15 cm above soil surface) and an increase in χa with canopy height, especially during the night. Neither χs nor χa could be measured close to the soil surface, the litter NH4+ material indicated a high potential for NH3 emission tough. A diurnal course in apoplastic NH4+ was seen in the regrowing grass growing after cutting, with highest concentration around noon. Both apoplastic and tissue NH4+ increased in young grass compared to tall grass. Following cutting, in-canopy gradients of atmospheric χa showed NH3 emission but since calculated χs-values of the cut grass were still lower than atmospheric NH3 concentrations, the emissions could not entirely be explained by stomatal NH3 loss. High tissue NH4+ in the senescent plant material indicated that this fraction constituted an NH3 source. After fertilization, NH4+ increased both in apoplast and leaf tissue with the most pronounced increase in former compared to the latter. The diurnal pattern in apoplastic NH4+ was even more pronounced after fertilization and calculated χs-values were generally higher, but remained below atmospheric NH3.
A multi-species coccolith volume response to an anthropogenically-modified ocean
Authors: Halloran P. R. , Hall I. R. , Colmenero-Hidalgo E. , Rickaby R. E. M.
Published: April 2010

Abstract. Major questions surround the species-specific nature of coccolithophore calcification in response to rising atmospheric CO2 levels. Here we present CaCO3 particle volume distribution data from the coccolith size-fraction of a rapidly accumulating North Atlantic sediment core. These data appear to indicate that coccoliths produced by the larger coccolithophore species present at this location increase in mass in parallel with anthropogenic CO2 release. This finding has significant implications for the realistic representation of an assemblage-wide coccolithophore CO2-calcification response in numerical models.
Methane emissions from the upwelling area off Mauritania (NW Africa)
Authors: Kock A. , Gebhardt S. , Bange H. W.
Published: April 2010

Abstract. Coastal upwelling regions have been indentified as sites of enhanced CH4 emissions to the atmosphere. The coastal upwelling area off Mauritania (NW Africa) is one of the most biologically productive regions of the world's ocean but its CH4 emissions have not been quantified so far. More than 1000 measurements of atmospheric and dissolved CH4 in the surface layer in the upwelling area off Mauritania were performed as part of the German SOPRAN (Surface Ocean Processes in the Anthropocene) study during two cruises in March/April 2005 (P320/1) and February 2007 (P348). During P348 enhanced CH4 saturations of up to 179% were found close to the coast and were associated with upwelling of South Atlantic Central Water. An area-weighted, seasonally adjusted estimate yielded overall annual CH4 emissions in the range from 0.7 to 1.4 Gg CH4. Thus the upwelling area off Mauritania represents a regional hot spot of CH4 emissions but seems to be of minor importance for the global oceanic CH4 emissions.
Evaluation of satellite based indices for primary production estimates in a sparse savanna in the Sudan
Authors: Sjöström M. , Ardö J. , Eklundh L. , El-Tahir B. A. , El-Khidir H. A. M. , Pilesjö P. , Seaquist J.
Published: April 2010

Abstract. One of the more frequently applied methods for integrating controls on primary production through satellite data is the Light Use Efficiency (LUE) approach. Satellite indices such as the Enhanced Vegetation Index (EVI) and the Shortwave Infrared Water Stress Index (SIWSI) have previously shown promise as predictors of primary production in several different environments. In this study, we evaluate EVI and SIWSI derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensor against in-situ measurements from central Sudan in order to asses their applicability in LUE-based primary production modelling within a water limited environment. Results show a strong correlation between EVI against gross primary production (GPP), demonstrating the significance of EVI for deriving information on primary production with relatively high accuracy at similar areas. Evaluation of SIWSI however, reveal that the fraction of vegetation apparently is to low for the index to provide accurate information on canopy water content, indicating that the use of SIWSI as a predictor of water stress in satellite data-driven primary production modelling in similar semi-arid ecosystems is limited.
Deposition of nitrogen and phosphorus on the Baltic Sea: seasonal patterns and nitrogen isotope composition
Authors: Rolff C. , Elmgren R. , Voss M.
Published: April 2010

Abstract. Atmospheric deposition of nitrogen and phosphorus on the Baltic Proper was estimated monthly at two coastal stations and two isolated islands in 2001 and 2002. Yearly nitrogen deposition ranged between 387 and 727 mg N m−2 yr−1 (average ~617) and was composed of ~10% organic N and approximately equal amounts of ammonium and nitrate. Winter nitrate peaks at the isolated islands possibly indicated ship emissions. Load weighted δ15N of deposited N was 3.7‰ and 0.35‰ at the coastal stations and the isolated islands respectively. Winter δ15N was ~3‰ lighter than in summer, reflecting winter dominance of nitrate. The light isotopic composition of deposited nitrogen may cause overestimates of nitrogen fixation in basin-wide isotopic budgeting, whereas relatively heavy deposition of ammonium during summer instead may cause underestimates of fixation in budgets of the upper mixed layer. δ15N in atmospherically deposited nitrate and ammonium was estimated by regression to –7.9 and 13.5‰ respectively. Phosphorus deposition showed no clear seasonal pattern and was considerably lower at the isolated islands. Organic P constituted 20–40% of annual P deposition. P deposition is unlikely to be a major source for cyanobacterial blooms but may potentially prolong an ongoing bloom.
Drivers of interannual variability in Net Ecosystem Exchange in a semi-arid savanna ecosystem, South Africa
Authors: Archibald S. , Kirton A. , van der Merwe M. , Scholes R. J. , Williams C. A. , Hanan N.
Published: April 2010

Abstract. Inter-annual variability in primary production and ecosystem respiration was explored using eddy-covariance data at a semi-arid savanna site in the Kruger Park, South Africa. New methods of extrapolating night-time respiration to the entire day and filling gaps in eddy-covariance data in semi-arid systems were developed. Net ecosystem exchange (NEE) in these systems occurs as pulses associated with rainfall events, a pattern not well-represented in current standard gap-filling procedures developed primarily for temperate flux sites. They furthermore do not take into account the decrease in respiration at high soil temperatures. An artificial neural network (ANN) model incorporating these features predicted measured fluxes accurately (MAE 0.42 g C/m2/day), and was able to represent the seasonal patterns of photosynthesis and respiration at the site. The amount of green leaf area (indexed using satellite-derived estimates of fractional interception of photosynthetically active radiation fAPAR), and the timing and magnitude of rainfall events, were the two most important predictors used in the ANN model. These drivers were also identified by multiple linear models (MLR), with strong interactive effects. The annual integral of the filled NEE data was found to range from −138 to +155 g C/m2/y over the 5 year eddy covariance measurement period. When applied to a 25 year time series of meteorological data, the ANN model predicts an annual mean NEE of 75 (±105) g C/m2/y. The main correlates of this inter-annual variability were found to be variation in the amount of absorbed photosynthetically active radiation (APAR), length of the growing season, and number of days in the year when moisture was available in the soil.
Bacterial diversity in Himalayan glacial ice and its relationship to dust
Authors: Zhang S. , Hou S. , Wu Y. , Qin D.
Published: April 2010

Abstract. Concentrations and community diversity of bacteria from 50 segments of a 108.83 m ice core drilled from the East Rongbuk (ER) Glacier (28.03° N, 86.96° E, 6518 m above sea level) on the northeast slope of Mt. Qomolangma (Everest), covering the period 950–1963 AD, were investigated by epifluorescence microscope, DGGE and Shannon-Weaver index analysis. There are four general periods of bacterial diversity, corresponding to four phases of dust abundance revealed by Ca2+ concentrations. It is indicated that higher bacterial community diversity is associated with warm periods, while lower bacterial community diversity with cold periods. However, a previously suggested positive correlation between bacterial and Ca2+ concentrations was not indicated by our observations. In fact, a weakly negative correlation was found between these two parameters. Our results suggest that bacterial community diversity, rather than concentrations, might be a suitable biological proxy for the reconstruction of past climatic and environmental changes preserved in glacial ice.
Carbon and oxygen isotope analysis of leaf biomass reveals contrasting photosynthetic responses to elevated CO2 near geologic vents in Yellowstone National Park
Authors: Sharma S. , Williams D. G.
Published: April 2010

Abstract. In this study we explore the use of natural CO2 emissions in Yellowstone National Park (YNP) in Wyoming, USA to study responses of natural vegetation to elevated CO2 levels. Radiocarbon (14C) analysis of leaf biomass from a conifer (Pinus contortus; lodgepole pine) and an invasive, non-native herb (Linaria dalmatica; Dalmation toadflax) was used to trace the inputs of vent CO2 and quantify assimilation-weighted CO2 concentrations experienced by individual plants near vents and in comparable locations with no geologic CO2 exposure. The carbon and oxygen isotopic composition and nitrogen percent of leaf biomass from the same plants was used to investigate photosynthetic responses of these plants to naturally elevated atmospheric CO2 concentrations. The coupled shifts in carbon and oxygen isotope values suggest that dalmation toadflax responded to elevated CO2 exposure by increasing stomatal conductance with no change in photosynthetic capacity and lodgepole pine apparently responded by decreasing stomatal conductance and photosynthetic capacity. Lodgepole pine saplings exposed to elevated levels of CO2 likewise had reduced leaf nitrogen concentrations compared to plants with no enhanced CO2 exposure, further suggesting that this widespread and dominant conifer down-regulated photosynthetic capacity under elevated CO2 levels near geologic vents.
Inter-comparison of ammonia fluxes obtained using the relaxed eddy accumulation technique
Authors: Hensen A. , Nemitz E. , Flynn M. J. , Blatter A. , Jones S. K. , Sørensen L. L. , Hensen B. , Pryor S. , Jensen B. , Otjes R. P. , Cobussen J. , Loubet B. , Erisman J. W. , Gallagher M. W. , Neftel A. , Sutton M. A.
Published: April 2010

Abstract. The exchange of NH3 between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the determination of fluxes at one height permits multiple systems to be deployed to quantify vertical flux divergence (either due to effects of chemical production or advection). During the Braunschweig integrated experiment four different continuous-sampling REA systems were operated during a period of about 10 days and were compared against a reference provided by independent application of the Aerodynamic Gradient Method (AGM). The experiment covered episodes before, after cutting and fertilising and provided a wide range of fluxes −60–3600 ng NH3 m−2 s−1 for testing the REA systems. The REA systems showed moderate to good correlation with the AGM estimates, with r2 values for the linear regressions between 0.3 and 0.82. For the period immediately after fertilization, the REA systems showed average fluxes 20% to 70% lower than the reference. At periods with low fluxes REA and AGM can agree within a few %. Overall, the results show that the continuous REA technique can now be used to measure NH3 surface exchange fluxes. While REA requires greater analytical precision in NH3 measurement than the AGM, a key advantage of REA is that auto-referencing periods can be introduced to remove bias between sampling inlets. However, while the data here indicate differences consistent with advection effects, further improvements in sampling precision are needed to allow measurement of flux divergence. Wet chemical techniques will be developed further since they use the sticky and reactive properties of NH3 that impedes development of cheaper optical systems.
Evidence for surface organic matter modulation of air-sea CO2 gas exchange
Authors: Calleja M. Ll. , Duarte C. M. , Prairie Y. T. , Agustí S. , Herndl G. J.
Published: April 2010

Abstract. Air-sea CO2 exchange depends on the air-sea CO2 gradient and the gas transfer velocity (k), computed as a simple function of wind speed. Large discrepancies among relationships predicting k from wind suggest that other processes may also contribute significantly to modulate CO2 exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the ocean surface organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (k) was evaluated by direct measurements of air-sea CO2 fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO2 fluxes, for a given air-sea CO2 partial pressure gradient and wind speed below 5 m s−1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These findings suggest that consideration of the role of organic matter in modulating air-sea CO2 exchange can improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean.
Temporal variations in microbial activities and carbon turnover in subtidal sandy sediments
Authors: Böer S. I. , Arnosti C. , van Beusekom J. E. E. , Boetius A.
Published: April 2010

Abstract. Temporal dynamics and vertical patterns in bacterial abundances and activities were studied in a shallow subtidal sand flat in the Sylt-Rømø Basin (North Frisian Wadden Sea, Germany.) Extracellular enzymatic activities, bacterial carbon production and community respiration showed strong (factor of 4–5) temporal variations that were mostly related to seasonal temperature change, but also to changes in substrate availability. These temporal patterns in activity were barely reflected in bacterial (200–400 mmol C m−2) and microphytobenthic biomass (800–1500 mmol C m−2) or the sedimentary carbohydrate inventory (1300–2900 mmol C m−2), suggesting that grazing controls the standing stocks of the microphytobenthic and bacterial assemblages. Despite their exposure to strong hydrodynamic forces such as tidal currents and wind-induced wave surge, the subtidal sandy sediments showed persistent vertical gradients in bacterial abundances, bacterial carbon production and extracellular enzymatic activities at all times. The vertical distribution of these parameters was tightly coupled to that of the microphytobenthos, dominated by diatoms. Despite the low organic carbon content typical for surge-exposed sandy sediments, high extracellular enzymatic activities and bacterial carbon production rates indicate a very active heterotrophic bacterial community, with a gross secondary productivity of 30–180 mmol C m−2, and a biomass turnover time of 2–18 days. Our data suggest that this high activity is supported by the rapid flux of carbohydrates from microphytobenthic primary productivity. Accordingly, the potential activities of enzymes hydrolyzing carbohydrates cover most of the total bacterial carbon demand during all seasons.
Imminent ocean acidification projected with the NCAR global coupled carbon cycle-climate model
Authors: Steinacher M. , Joos F. , Frölicher T. L. , Plattner G.-K. , Doney S. C.
Published: April 2010

Abstract. Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm), and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185%. Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally soon and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.
The importance of ocean transport in the fate of anthropogenic CO2
Authors: Cao L. , Eby M. , Ridgwell A. , Caldeira K. , Archer D. , Ishida A. , Joos F. , Matsumoto K. , Mikolajewicz U. , Mouchet A. , Orr J. C. , Plattner G.-K. , Schlitzer R. , Tokos K. , Totterdell I. , Tschumi T. , Yamanaka Y. , Yool A.
Published: April 2010

Abstract. We assess uncertainties in projected oceanic uptake of anthropogenic CO2 associated with uncertainties in model ocean transport using a suite of climate/carbon-cycle models. In response to a CO2 pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO2 from 278 to 556 ppm), the fraction of CO2 emitted absorbed by the ocean (model mean ±2σ) is 37±8%, 56±10%, and 81±4% in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of excess CO2 on timescales from decades to about a century is strongly correlated with simulated present-day uptake of chlorofluorocarbons (CFCs) and anthropogenic CO2, while the amount of excess CO2 absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. The rates of surface-to-deep ocean transport are determined for individual models from the instantaneous doubling CO2 experiments, and they are used to calculate oceanic uptake of CO2 in response to emission pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO2 from a number of model simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rate across models on the oceanic uptake of anthropogenic CO2 is of similar magnitude as that of climate-carbon cycle feedbacks in a single model associated with changes in temperature, circulation, and marine biology, emphasizing the importance of ocean transport in the fate of anthropogenic CO2.
Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements
Authors: Milford C. , Theobald M. R. , Nemitz E. , Hargreaves K. J. , Horvath L. , Raso J. , Dämmgen U. , Neftel A. , Jones S. K. , Hensen A. , Loubet B. , Cellier P. , Sutton M. A.
Published: April 2010

Abstract. Quantification of ammonia (NH3) land-atmosphere exchange is required for atmospheric modelling and assessment of nitrogen deposition, yet flux measurement methods remain highly uncertain. To address this issue, a major inter-comparison of ammonia fluxes over intensively managed grassland was conducted during the GRAMINAE Integrated Experiment held in Braunschweig, Germany. In order to provide a robust dataset of ammonia exchange with the vegetation, four independent continuous flux gradient systems were operated. Three independently operated continuous wet denuders systems (AMANDA) were compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system. Measurements were made at two distances from an adjacent livestock farm, allowing effects of advection to be quantified in a real landscape setting. Data treatment included filtering for instrument failure, disturbed wind sectors and unsuitable micrometeorological conditions, with corrections made for storage and advection errors. The inter-comparison demonstrated good agreement in measured ammonia concentrations and fluxes (<20% difference) for some periods, although the performance of the ammonia analyzers was variable, with much poorer agreement on particular days. However, by using four systems, the inter-comparison was able to provide a robust mean estimate of continuous ammonia fluxes through the experiment. The observed fluxes were: a) small bi-directional fluxes prior to cutting (−64 to 42 ng NH3 m−2 s−1), b) larger diurnally-varying emissions following cutting (−49 to 703 ng NH3 m−2 s−1) and c) much larger emissions following fertilizer application (0 to 3820 ng NH3 m−2 s−1). The results are a salutary reminder of the uncertainty in unreplicated ammonia flux measurements, while the replication of the present study provides a uniquely robust dataset for the evaluation of ammonia exchange processes. It is clear that consistently reliable determination of ammonia concentrations remains the major measurement challenge.
Can we use hourly CO2 concentration data in inversions? Comparing high resolution WRF-VPRM simulations with coastal tower measurements of CO2
Authors: Ahmadov R. , Gerbig C. , Kretschmer R. , Körner S. , Rödenbeck C. , Bousquet P. , Ramonet M.
Published: April 2010

Abstract. In order to better understand the effects that mesoscale transport has on atmospheric CO2 distributions, we have used the WRF model coupled to the diagnostic biospheric model VPRM, which provides high-resolution biospheric CO2 fluxes based on MODIS satellite indices. We have run WRF-VPRM for the period from 16 May to 15 June in 2005 covering the intensive period of the CERES experiment, using the CO2 fields from the global model LMDZ for initialization and lateral boundary conditions. The comparison of modeled CO2 concentration time series against observations at the Biscarosse tower and against output from two global models – LMDZ and TM3 – clearly reveals that WRF-VPRM can capture the measured CO2 signal much better than the global models with lower resolution. Also the diurnal variability of the atmospheric CO2 field caused by recirculation of nighttime respired CO2 is simulated by WRF-VRPM reasonably well. Analysis of the nighttime data indicates that with high resolution modeling tools such as WRF-VPRM a large fraction of the time periods that are impossible to utilize in global models, can be used quantitatively and help constraining respiratory fluxes. The paper concludes that we need to utilize a high-resolution model such as WRF-VPRM to use continental observations of CO2 concentration data with more spatial and temporal coverage and to link them to the global inversion models.
Similar patterns of community organization characterize distinct groups of different trophic levels in the plankton of the NW Mediterranean Sea
Authors: Raybaud V. , Tunin-Ley A. , Ritchie M. E. , Dolan J. R.
Published: April 2010

Abstract. Planktonic populations were sampled over a 4 week period in the NW Mediterranean, at a site subject to little vertical advection during the Dynaproc 2 cruise in 2004. The characteristics of the phytoplankton, the tintinnid community and the zooplankton have recently been described (Lasternas et al., 2008; Dolan et al., 2009; Raybaud et al., 2008). Based on these studies we compared the characteristics of 3 well-circumscribed groups of different trophic levels: Ceratium of the phytoplankton, herbivorous tintinnids of the microzooplankton, and large (>500 μm) omnivorous and carnivorous copepods of the metazoan zooplankton. In all three groups, diversity as H' or species richness, was less variable than concentration of organisms. Plotting time against species accumulation, the curves approached plateau values for Ceratium spp, tintinnids and large copepods but only a small number of species were consistently present (core species) and these accounted for most of the populations. For Ceratium core species numbered 10, for tintinnids 11 species, and for large copepods, core species numbered 4 during the day and 16 at night. Ceratium, tintinnids and large copepods showed some similar patterns of community structure in terms of species abundance distributions. Ceratium species were distributed in a log-normal pattern. Tintinnid species showed a log-series distribution. Large copepods communities were highly dominated with night samples showed much higher abundances and greater species richness than day samples. However, species abundance distributions were similar between day and night and were mostly log-normal. The paradox of the plankton, describing phytoplankton communities as super-saturated with species, extends to the microzooplankton and zooplankton.
Distributions of surface water CO2 and air-sea flux of CO2 in coastal regions of the Canadian Beaufort Sea in late summer
Authors: Murata A. , Shimada K. , Nishino S. , Itoh M.
Published: April 2010

Abstract. To quantify the air-sea flux of CO2 in a high-latitude coastal region, we conducted shipboard observations of atmospheric and surface water partial pressures of CO2 (pCO2) and total dissolved inorganic carbon (TCO2) in the Canadian Beaufort Sea (150° W–127° W; 69° N–73° N) in late summer 2000 and 2002. Surface water pCO2 was lower than atmospheric pCO2 (2000, 361.0 μatm; 2002, 364.7 μatm), and ranged from 250 to 344 μatm. Accordingly, ΔpCO2, which is the driving force of the air-sea exchange of CO2 and is calculated from differences in pCO2 between the sea surface and the overlying air, was generally negative (potential sink for atmospheric CO2), although positive ΔpCO2 values (source) were also found locally. Distributions of surface water pCO2, as well as those of ΔpCO2 and CO2 flux, were controlled mainly by water mixing related to river discharge. The air-sea fluxes of CO2 were −15.0 and −16.8 mmol m−2 d−1 on average in 2000 and 2002, respectively, implying that the area acted as a moderate sink for atmospheric CO2. The air-to-sea net CO2 flux in an extended area of the western Arctic Ocean (411 000 km2) during the ice-free season (=100 days) was calculated as 10.2±7.7 mmol m−2 d−1, equivalent to a regional CO2 sink of 5.0±3.8 Tg C. The estimated buffer factor was 1.5, indicating that the area is a high-capacity CO2 sink. These CO2 flux estimates will need to be revised because they probably include a bias due to the vertical gradients of physical and chemical properties characteristic in the region, which have not yet been adequately considered.
Evolution of the potential distribution area of french mediterranean forests under global warming
Authors: Gaucherel C. , Guiot J. , Misson L.
Published: April 2010

Abstract. This work aims at understanding future spatial and temporal distributions of tree species in the Mediterranean region of France under various climates. We focused on two different species (Pinus Halepensis and Quercus Ilex) and compared their growth under the IPCC-B2 climate scenario in order to quantify significant changes between present and future. The influence of environmental factors such as atmospheric CO2 increase and topography on the tree growth has also been quantified. We modeled species growths with the help of a process-based model (MAIDEN), previously calibrated over measured ecophysiological and dendrochronological series with a Bayesian scheme. The model was fed with the ARPEGE – MeteoFrance climate model, combined with an explicit increase in CO2 atmospheric concentration. The main output of the model gives the carbon allocation in boles and thus tree production. Our results show that the MAIDEN model is correctly able to simulate pine and oak production in space and time, after detailed calibration and validation stages. Yet, these simulations, mainly based on climate, are indicative and not predictive. The comparison of simulated growth at end of 20 and 21 centuries, show a shift of the pine production optimum from about 650 to 950 m due to 2.5°K temperature increase, while no optimum has been found for oak. With the direct effect of CO2 increase taken into account, both species show a significant increase in productivity (+26 and +43% for pine and oak, respectively) at the end of the 21 century. While both species have complementary growth mechanisms, they have a good chance to extend their spatial distribution and their elevation in the Alps during the 21 century under the IPCC-B2 climate scenario. This extension is mainly due to the CO2 fertilization effect.
Introduction to the special section Bio-optical and biogeochemical conditions in the South East Pacific in late 2004: the BIOSOPE program
Authors: Claustre H. , Sciandra A. , Vaulot D.
Published: April 2010

Abstract. The objectives of the BIOSOPE (BIogeochemistry and Optics SOuth Pacific Experiment) project was to study, during the austral summer, the biological, biogeochemical and bio-optical properties of different trophic regimes in the South East Pacific: the eutrophic zone associated with the upwelling regime of the Chilean coast, he mesotrophic area associated with the plume of the Marquises Islands in the HNLC (High Nutrient Low Chlorophyll) waters of this subequatorial area, and the extremely oligotrophic area associated with the central part of the South Pacific Gyre (SPG). At the end of 2004, a 55-day international cruise with 32 scientists on board took place between Tahiti and Chile, crossing the SPG along a North-West South-East transect. This paper describes in detail the objective of the BIOSOPE project, the implementation plan of the cruise, the main hydrological entities encountered along the ~8000 km South East pacific transect and ends with a general overview of the papers published in this Biogeosciences special issue.
Contrasting distribution of aggregates >100 μm in the upper kilometre of the South-Eastern Pacific
Authors: Guidi L. , Gorsky G. , Claustre H. , Picheral M. , Stemmann L.
Published: April 2010

Abstract. Large sinking particles transport organic and inorganic matter into the deeper layers of the oceans. From 70 to 90% of the superficial particulate material is disaggregated within the upper 1000 m. This decrease with depth indicates that remineralization processes are intense during sedimentation. Generally, the estimates of vertical flux rely on the sediment trap data but difficulties inherent in their design, limit the reliability of this information. During the BIOSOPE study in the southeastern Pacific, 76 vertical casts using the Underwater Video Profiler (UVP) and deployments of a limited number of drifting sediment traps provided an opportunity to fit the UVP data to sediment trap flux measurements. We applied than the calculated UVP flux in the upper 1000 m to the whole 8000 km BIOSOPE transect. Comparison between the large particulate material (LPM) abundance and the estimated fluxes from both UVP and sediment traps showed different patterns in different regions. On the western end of the BIOSOPE section the standing stock of particles in the superficial layer was high but the export between 150 and 250 m was low. Below this layer the flux values increased. High values of about 30% of the calculated UVP maximum superficial flux were observed below 900 m at the HNLC station. The South Pacific Gyre exported about 2 mg m−2 d−1. While off Chilean coast 95% of the superficial matter was remineralized or advected in the upper kilometer, 20% of the superficial flux was observed below 900 m near the Chilean coast. These results suggest that the export to deep waters is spatially heterogeneous and related to the different biotic and abiotic factors.
The effect of a reciprocal peat transplant between two contrasting Central European sites on C cycling
Authors: Novak M. , Zemanova L. , Buzek F. , Jackova I. , Adamova M. , Komarek A. , Vile M. A. , Wieder R. K. , Stepanova M.
Published: April 2010

Abstract. An 18-month reciprocal peat transplant experiment was conducted between two peatlands in the Czech Republic. Both sites were 100% Sphagnum-covered, with no vascular plants, and no hummocks and hollows. Atmospheric depositions of sulfur were up to 10 times higher at the northern site Velke jerabi jezero (VJJ), compared to the southern site Cervene blato (CB). Forty-cm deep peat cores, 10 cm in diameter, were used as transplants and controls in five replicates. Our objective was to evaluate whether CO2 and CH4 production potentials in Sphagnum peat bogs are governed mainly by organic matter quality, or by environmental conditions. Production rates and δ13C values of CO2 and CH4 were measured in the laboratory at time t=18 months. All measured parameters converged to those of the host site, indicating that, at least in the short-term perspective, environmental conditions were a more important control of greenhouse gas emissions than organic carbon quality. Since sulfate reducers outcompete methanogens, we hypothesized that the S-polluted site VJJ should have lower methane emissions than CB. In fact, the opposite was true, with higher methane emissions from VJJ. As a first step in an effort to link C isotope composition of emitted gases and residual peat substrate, we determined whether multiple vertical δ13C profiles in peat agree. A high degree of within-site homogeneity in δ13C was found. The δ13C value increased downcore at both CB and VJJ. However, 20 cm below surface, a reversal to lower δ13C downcore was seen at VJJ. Based on 210Pb dating, peat at 20 cm depth at VJJ was only 15 years old. Increasing δ13C values in VJJ peat accumulated between 1880–1990 could not be caused by assimilation of atmospheric CO2 gradually enriched in the light isotope 12C due to fossil fuel burning.
A possible role of ground-based microorganisms on cloud formation in the atmosphere
Authors: Ekström S. , Nozière B. , Hultberg M. , Alsberg T. , Magnér J. , Nilsson E. D. , Artaxo P.
Published: April 2010

Abstract. The formation of clouds is an important process for the atmosphere, the hydrological cycle, and climate, but also a difficult one to predict because some aspects of the transformations of aerosol particles into cloud droplets are still not well understood. In this work, we show that microorganisms might affect cloud formation without leaving the Earth's surface by releasing biological surfactants (or biosurfactants) in the environment, that make their way into atmospheric aerosols and should significantly enhance their conversion into of cloud droplets. In the first part of this work, the cloud-nucleating efficiency (or "CCN" efficiency) of standard biosurfactants was characterized by osmolality and surface tension measurements and found to be better than for any aerosol material studied so far, including inorganic salts. These results identify molecular structures that give to organic compounds exceptional CCN properties. In the second part, atmospheric aerosols sampled at different locations (temperate & tropical, forested & marine ones) were found to all have a surface tension below 30 mN/m, which can only be accounted for by the presence of biosurfactants. The results also showed that these biosurfactants were concentrated enough to significantly affect the surface tension of these aerosols and enhance their CCN efficiency. The presence of such strong biosurfactants in aerosols would be consistent with the recent identification of organic fractions of higher CCN efficiency than ammonium sulfate in aerosols. And a role of microorganisms at the Earth's surface on clouds could also explain previously reported correlations between algae bloom and cloud cover. Our results also suggest that biosurfactants might be common in aerosols and thus of global relevance. If their impact on cloud formation is confirmed by future studies, this work would have identified a new role of microorganisms at the Earth's surface on the atmosphere, and a new component of the Earth's system and climate.
Organic carbon sequestration and discharge from a deciduous forest catchment in Korea
Authors: Kim S. J. , Kim J. , Kim K.
Published: April 2010

Abstract. Soil infiltration and surface discharge of precipitation are critical processes that affect the sequestration and discharge of dissolved organic carbon (DOC) and particulate organic carbon (POC) in forested catchments. Both DOC and POC are highly concentrated in the soil surface in most forest ecosystems and their discharge may not be negligible particularly under the monsoon climate. In East Asia, however, there are little data available to evaluate the role of such processes in forest carbon budget. In this paper, we address two basic questions: 1) how does stream discharge respond to storm events in a forest catchment? and 2) how much DOC and POC are discharged from the catchment particularly during the summer monsoon period? To answer these questions, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge, groundwater level) and conducted hydrochemical analyses (including DOC, POC, and six tracers) for a deciduous forest catchment in Gwangneung National Arboretum in west-central Korea. Based on the end-member mixing analysis of the six storm events during the summer monsoon in 2005, the surface discharge was estimated as 30 to 80% of the total runoff discharge. The stream discharge responded to precipitation within 12 h during these storm events. The annual discharge of DOC and POC from the catchment was estimated as 0.04 and 0.05 t C ha−1 yr−1, respectively. Approximately 70% of the annual organic carbon efflux occurred during the summer monsoon period. Overall, the annual discharge of organic carbon was estimated to be 4 to 14% of the net ecosystem carbon exchange (NEE) obtained by eddy covariance technique at the same site. Considering the current trends of increasing intensity and amount of summer rainfall and the large interannual variability in NEE, ignoring the organic carbon discharge from forest ecosystems would result in an overestimation (underestimation) of the strength of forests as a carbon sink (source) in the monsoon East Asia.
Trends and regional distributions of land and ocean carbon sinks
Authors: Sarmiento J. L. , Gloor M. , Gruber N. , Beaulieu C. , Jacobson A. R. , Fletcher S. M. , Pacala S. , Rodgers K.
Published: April 2010

Abstract. We show here a new estimate of the variability and long-term trends in the net land carbon sink from 1960 onwards calculated from the difference between fossil fuel emissions, the observed atmospheric growth rate, and the ocean uptake obtained by recent ocean model simulations forced with reanalysis wind stress and heat and water fluxes. The net land carbon sink appears to have increased by −0.88 (−0.77 to −1.04) Pg C yr−1 after ~1988/1989 from a relatively constant mean of −0.27 Pg C yr−1 before then to −1.15 Pg C yr−1 thereafter (the sign convention is negative out of the atmosphere). This result is significant at the 1% critical level. The increase in net land uptake is partially compensated by a reduction in the expected oceanic uptake, which we estimate from model simulations as about 0.35 (0.26 to 0.49) Pg C yr−1. This implies that the atmospheric growth rate must have decreased by about −0.53 (−0.51 to −0.55) Pg C yr−1 (equivalent to −0.25 ppm yr−1) below what would have been projected if the ocean uptake had continued to grow at the rate expected from a constant climate model and if the net land uptake had continued at its pre-1988/1989 level. A regional synthesis and assessment of the land carbon sources and sinks over the post 1988/1989 period reveals broad agreement that the northern hemisphere land is a major sink of atmospheric CO2, but there remain major discrepancies with regard to the sign and magnitude of the net flux to and from tropical land.