bluuebunny/crossref_metadata_2025 huggingface dataset:
Biodiversity for multifunctional grasslands: equal productivity in high-diversity low-input and low-diversity high-input systems
Authors: Weigelt A. , Weisser W. W. , Buchmann N. , Scherer-Lorenzen M.
Published: April 2010

Abstract. Modern grassland management seeks to provide many ecosystem services and experimental studies in resource-poor grasslands have shown a positive relationship between plant species richness and a variety of ecosystem functions. Thus, increasing species richness might help to enhance multifunctionality in managed grasslands if the relationship between species richness and ecosystem functioning is equally valid in high-input grassland systems. We tested the relative effects of low-input to high-input management intensities and low to high plant species richness. Using a combination of mowing frequencies (1, 2 or 4 cuts per season) and fertilization levels (0, 100 and 200 kg N ha−1 a−1), we studied the productivity of 78 experimental grassland communities of increasing plant species richness (1, 2, 4, 8 or 16 species with 1 to 4 functional groups) in two successive years. Our results showed that in both years higher diversity was more effective in increasing productivity than higher management intensity: the 16-species mixtures had a surplus of 452 g m−2 y−1 in 2006 and 504 g m−2 y−1 in 2007 over the monoculture yields whereas the high-input management resulted in only 315 g m−2 y−1 higher productivity in 2006 and 440 g m−2 y−1 in 2007 than the low-input management. In addition, high-diversity low-input grassland communities had similar productivity as low-diversity high-input communities. The slopes of the biodiversity – productivity relationships significantly increased with increasing levels of management intensity in both years. We conclude that the biological mechanisms leading to enhanced biomass production in diverse grassland communities are as effective for productivity as a combination of several agricultural measures. Our results demonstrate that high-diversity low-input grassland communities provide not only a high diversity of plants and other organisms, but also ensure high forage yields, thus granting the basis for multifunctional managed grasslands.
Impact of seawater pCO2 changes on calcification and on Mg/Ca and Sr/Ca in benthic foraminifera calcite (Ammonia tepida): results from culturing experiments
Authors: Dissard D. , Nehrke G. , Reichart G. J. , Bijma J.
Published: April 2010

Abstract. Evidence is accumulating of increasing concentrations of dissolved carbon dioxide in the ocean and associated acidification impacts on calcifying organisms. Among these organisms, benthic and planktonic foraminifera are responsible for a large amount of the globally precipitated calcium carbonate. Therefore, their response to an acidifying ocean may have important consequences for future inorganic carbon cycling. To assess the sensitivity of benthic foraminifera to changing carbon dioxide levels and subsequent alteration in seawater carbonate chemistry, we cultured specimens of the shallow water species Ammonia tepida at two concentrations of atmospheric CO2 (120 and 2000 ppm) and two temperatures (10°C and 15°C). Shell weights and elemental compositions were determined. Results indicate that shell weights decrease with decreasing [CO32−], and increase with decreasing temperature. Changes in [CO32−] or total dissolved inorganic carbon do not affect the Mg partition coefficient. On the contrary, Sr incorporation is enhanced under increasing [CO32−]. Implications of these results for the paleoceanographic application of foraminifera are also discussed.
Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development
Authors: Breitbarth E. , Gelting J. , Walve J. , Hoffmann L. J. , Turner D. R. , Hassellöv M. , Ingri J.
Published: April 2010

Abstract. Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA) and reveal several origins of Fe(II) to the water column. Photoreduction of Fe(III)-complexes and deposition by rain are main sources of Fe(II) (up to 0.9 nmol L−1) in light penetrated surface waters. Indication for organic Fe(II) complexation resulting in prolonged residence times in oxygenated water was observed. Surface dwelling heterocystous cyanobacteria where mainly responsible for Fe(II) consumption in comparison to other phytoplankton. The significant Fe(II) concentrations in surface waters apparently play a major role in cyanobacterial bloom development in the Baltic Sea and are a major contributor to the Fe requirements of diazotrophs. Second, Fe(II) concentrations up to 1.44 nmol L−1 were observed at water depths below the euphotic zone, but above the oxic anoxic interface. Finally, all Fe(III) is reduced to Fe(II) in anoxic deep water. However, only a fraction thereof is present as ferrous ions (up to 28 nmol L−1) and was detected by the CL-FIA method applied. Despite their high concentrations, it is unlikely that ferrous ions originating from sub-oxic waters could be a temporary source of bioavailable iron to the euphotic zone since mixed layer depths after strong wind events are not deep enough in summer time.
Nutrient budgets for large Chinese estuaries and embayment
Authors: Liu S. M. , Hong G.-H. , Ye X. W. , Zhang J. , Jiang X. L.
Published: April 2010

Abstract. Nutrient concentrations among the Chinese rivers and bays vary 10–75 fold depending on nutrient elements. The silicic acid levels in South China rivers are higher than those from North China rivers and the yields of dissolved silicate increased from the north to the south of China, indicating the effect of climate on weathering. The nutrient levels in Chinese rivers are higher than those from the large and less-disturbed world rivers such as Amazon and Zaire, but comparable to the values for European and North American polluted and eutrophic rivers like the Loire and Po. This may be ascribed to both of extensive leaching and influences from agricultural and domestic activities over the drainage basins of Chinese rivers. DIN:PO3−4 ratios in most of Chinese rivers and bays are higher (up to 2800) than the other rivers in the world. The atomic ratios of DIN to PO43− in the major Chinese rivers and embayment decrease in exponential trend with increase in the atomic ratios of PO43− to Si(OH)4, indicating that primary production in coastal environments changes with the nutrients transport when the urbanization develops to a certain extent, and the potential limited nutrient elements can be changed from phosphorus to nitrogen limitation, which can modify aquatic food webs and then the ocean ecosystem. A simple steady-state mass-balance box model was employed. The output shows that the estuaries and embayment behave as a sink or source of nutrients. For the major Chinese estuaries, both residual and mixing flow transport nutrients off the estuaries, and nutrient transport fluxes in summer is 3–4 fold that in winter except comparable for NH4+. These fluxes are 1.0–1.7 fold that estimated by timing riverine nutrient concentrations and freshwater discharge. For the major Chinese embayment, nutrient elements are transported to China Seas except PO43− and Si(OH)4 in Sanggou Bay and Jiaozhou Bay. Seasonally, nutrients transport fluxes off the bays in the summer are 2.2–7.0 fold that in the winter. In the embayment, the exchange flow dominated the water budgets, resulting in average system salinity approaching the China seas salinity where river discharge is limited. The major Chinese estuaries and embayment transport 1.0–3.1% of nitrogen, 0.2–0.5% of phosphorus and 3% of silicon necessary for phytoplankton growth for the China Seas. This demonstrates regenerated nutrients in water column and sediments and nutrients transport fluxes between the China Seas and open ocean play an important role for phytoplankton growth. Atmospheric deposition may be another important source of nutrients for the China Seas.
Growth phase dependent hydrogen isotopic fractionation in alkenone-producing haptophytes
Authors: Wolhowe M. D. , Prahl F. G. , Probert I. , Maldonado M.
Published: April 2010

Abstract. Several recent works have investigated use of the hydrogen isotopic composition of C37 alkenones (δDK37s), lipid biomarkers of certain haptophyte microalgae, as an independent paleosalinity proxy. We discuss herein the factors impeding the success of such an application and identify the potential alternative use of δDK37s measurements as a proxy for non-thermal, physiological stress impacts on the U37K' paleotemperature index. Batch-culture experiments with the haptophyte Emiliania huxleyi (CCMP 1742) were conducted to determine the magnitude and variability of the isotopic contrasts between individual C37 alkenones, an analytical impediment to the use of δDK37s in any paleoceanographic context. Further experiments were conducted with Emiliania huxleyi (CCMP 1742) and Gephyrocapsa oceanica (PZ3-1) to determine whether, and to what extent, δDK37s varies between the physiological extremes of nutrient-replete exponential growth and nutrient-depleted senescence, the basis for our proposed use of the measurement as an indicator of stress. Emiliania huxleyi exhibited an isotopic contrast between di- and tri-unsaturated C37 alkenones (αK37:3−K37:2≈0.97) that is nearly identical to that reported recently by others for environmental samples. Furthermore, this contrast appears to be constant with growth stage. The consistency of the offset across different growth stages suggests that a single, well-defined value for αK37:3−K37:2 exists and that its use in an isotope mass-balance will allow accurate determination of δD values for individual alkenones without having to rely on time- and labor-intensive chemical separations. The isotopic fractionation between growth medium and C37 alkenones was observed to increase dramatically upon the onset of nutrient-depletion-induced senescence, suggesting that δDK37s may serve as an objective tool for recognizing and potentially correcting, at least semi-quantitatively, for the effects of nutrient stress on U37K'
Using satellite-derived backscattering coefficients in addition to chlorophyll data to constrain a simple marine biogeochemical model
Authors: Kettle H.
Published: April 2010

Abstract. Biogeochemical models of the ocean carbon cycle are frequently validated by, or tuned to, satellite chlorophyll data. However, ocean carbon cycle models are required to accurately model the movement of carbon, not chlorophyll and due to the high variability of the carbon to chlorophyll ratio in phytoplankton, chlorophyll is not a robust proxy for carbon. Using inherent optical property (IOP) inversion algorithms it is now possible to also derive the amount of light backscattered by the upper ocean (bb) which is related to the amount of particulate organic carbon (POC) present. Using empirical relationships between POC and bb, a 1-d biogeochemical model is used to simulate bb at 490 nm thus allowing the model to be compared with either remotely-sensed chlorophyll or bb data. Here I test the hypothesis that using bb in conjunction with chlorophyll data can help to constrain more model parameters than using chlorophyll alone. This is done by tuning the parameters of the biogeochemical model with a genetic algorithm, so that the model is fitted to either chlorophyll or to both chlorophyll and bb data at three sites in the Atlantic with very different characteristics. There are several IOP algorithms available for estimating bb. Four of these are investigated and three of them used for model tuning. The effect of the different bb datasets on the behaviour of the tuned model is examined to ascertain whether the uncertainty in bb is significant. The results show that the addition of bb data can have a large effect on the modelled detritus and that differences in the IOP algorithms are not particularly significant.
Turbulence characteristics in grassland canopies and implications for tracer transport
Authors: Nemitz E. , Loubet B. , Lehmann B. E. , Cellier P. , Neftel A. , Jones S. K. , Hensen A. , Ihly B. , Tarakanov S. V. , Sutton M. A.
Published: April 2010

Abstract. In-canopy turbulence is a required input to study pollutant cycling and chemistry within plant canopies and to link concentrations and sources. Despite the importance of grasslands worldwide, most previous work has focused on forests and crops. Here, turbulence parameters in a mature agricultural grassland canopy were measured with a combination of a small ultrasonic anemometer, hotwire anemometry and a radon (Rn) tracer technique, as part of a measurement to study ammonia (NH3) exchange with grassland. The measurements are used to derive vertical profiles of basic turbulent parameters, for quadrant-hole analysis of the two-parametric frequency distributions of u'−w' and to derive in-canopy eddy diffusivities as input for models of in-canopy tracer transport. The results are in line with previous measurements on taller canopies, but shows increased decoupling between in-canopy flow and above-canopy turbulence. The comparison of sonic anemometry and Rn measurements implies that Lagrangian time-scales must decrease sharply at the ground, with important implications for estimating the magnitude of ground-level and soil emissions from concentration measurements. Atmospheric stability above and within the canopy has little influence on the standard deviation of vertical wind component inside the canopy. Use of the turbulence parameters in an analytical Lagrangian framework, which is here validated for heat transfer, suggests that measured in-canopy profiles of NH3 are consistent with a ground-level source, presumably from senescent plant parts, which is recaptured by the overlying canopy.
Impact of changes in river nutrient fluxes on the global marine silicon cycle: a model comparison
Authors: Bernard C. Y. , Laruelle G. G. , Slomp C. P. , Heinze C.
Published: April 2010

Abstract. The availability of dissolved silica in the ocean provides a major control on the growth of siliceous phytoplankton. Diatoms in particular account for a large proportion of oceanic primary production. The original source of the silica is rock weathering, followed by transport of dissolved and biogenic silica to the coastal zone. This model study aims at assessing the sensitivity of the global marine silicon cycle to variations in the river input of silica and other nutrients on timescales ranging from several centuries to millennia. We compare the performance of a box model for the marine Si cycle to that of a global biogeochemical ocean general circulation model (HAMOCC2 and 5). Results indicate that the average global ocean response to changes in river input of Si is surprisingly similar in the models on time scales up to 150 kyrs. While the trends in export production and opal burial are the same, the box model shows a delayed response to the imposed perturbations compared to the general circulation model. Results of both models confirm the important role of the continental margins as a sink for silica at the global scale. While general circulation models are indispensable when assessing the spatial variation in opal export production and biogenic Si burial in the ocean, this study demonstrates that box models provide a good alternative when studying the average global ocean response to perturbations of the oceanic silica cycle (especially on longer time scales).
Response of Halimeda to ocean acidification: field and laboratory evidence
Authors: Robbins L. L. , Knorr P. O. , Hallock P.
Published: April 2010

Abstract. Rising atmospheric pCO2 levels are changing ocean chemistry more dramatically now than in the last 20 million years. In fact, pH values of the open ocean have decreased by 0.1 since the 1800s and are predicted to decrease 0.1–0.4 globally in the next 90 years. Ocean acidification will affect fundamental geochemical and biological processes including calcification and carbonate sediment production. The west Florida shelf is a natural laboratory to examine the effects of ocean acidification on aragonite production by calcareous green algae. Scanning electron microscopy (SEM) of crystal morphology of calcifying organisms reveals ultrastructural details of calcification that occurred at different saturation states. Comparison of archived and recent specimens of calcareous green alga Halimeda spp. from the west Florida shelf, demonstrates crystal changes in shape and abundance over a 40+ year time span. Halimeda crystal data from apical sections indicate that increases in crystal concentration and decreases in crystal width occurred over the last 40+ years. Laboratory experiments using living specimens of Halimeda grown in environments with known pH values were used to constrain historical observations. Percentages of organic and inorganic carbon per sample weight of pooled species did not significantly change. However, individual species showed decreased inorganic carbon and increased organic carbon in more recent samples, although the sample sizes were limited. These results indicate that the effect of increased pCO2 and decreased pH on calcification is reflected in the crystal morphology of this organism. More data are needed to confirm the observed changes in mass of crystal and organic carbon.
Calcium carbonate saturation in the surface water of the Arctic Ocean: undersaturation in freshwater influenced shelves
Authors: Chierici M. , Fransson A.
Published: April 2010

Abstract. In the summer of 2005, we sampled surface water and measured pH and total alkalinity (AT) underway aboard IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. We investigated variability of carbonate system parameters, focusing particularly on carbonate concentration [CO32−] and calcium carbonate saturation states, as related to freshwater addition, biological processes and physical upwelling. Measurements on AT, pH at 15°C, salinity (S) and sea surface temperature (SST), were used to calculate total dissolved inorganic carbon (DIC), [CO32−] and saturation of aragonite (ΩAr) and calcite (ΩCa) in the surface water. The same parameters were measured in the water column of the Bering Strait. Some surface waters in the Canadian Arctic Archipelago (CAA) and on the Mackenzie shelf (MS) were found to be undersaturated with respect to aragonite (ΩAr<1). In these areas, surface water was low in AT and DIC (<1500 μmol kg−1) relative to seawater and showed low [CO32−]. The low saturation states were probably due to the effect of dilution due from freshwater addition by sea ice melt (CAA) and river runoff (MS). High AT and DIC and low pH, corresponded with the lowest [CO32−], ΩAr and ΩCa, observed near Cape Bathurst and along the South Chukchi Peninsula. This was linked to physical upwelling of subsurface water with elevated CO2. Highest surface ΩAr and ΩCa of 3.0 and 4.5, respectively, were found on the Chukchi Sea shelf and in the cold water north of Wrangel Island, which is heavily influenced by high CO2 drawdown and lower DIC from intense biological production. In the western Bering Strait, the cold and saline Anadyr Current carries water that is enriched in AT and DIC from enhanced organic matter remineralization, resulting in the lowest ΩAr (~1.2) of the area.
Impacts of hypoxia on the structure and processes in the pelagic community (zooplankton, macro-invertebrates and fish)
Authors: Ekau W. , Auel H. , Pörtner H.-O. , Gilbert D.
Published: April 2010

Abstract. Dissolved oxygen (DO) concentration in the water column is an environmental parameter that is crucial for the successful development of many pelagic organisms. Hypoxia tolerance and threshold values are species- and stage-specific and can vary enormously. While some fish species may suffer from oxygen values of less than 3 ml L−1 and show impact on growth, development and behaviour, other organisms such as euphausiids may survive DO levels as low as 0.1 ml L−1. A change in the average or the minimum or maximum DO in an area may have significant impacts on the survival of certain species and hence on the species composition in the ecosystem with consequent changes in trophic pathways and productivity. Evidence of the deleterious effects of oxygen depletion on species of the pelagic realm is scarce, particularly in terms of the effect of low oxygen on development, recruitment and patterns of migration and distribution. While planktonic organisms have to cope with different DOs and find adaptive mechanisms, nektonic species may avoid areas of inconvenient DO and develop adapted migrational strategies. Planktonic organisms may only be able to escape vertically, above or beneath the Oxygen Minimum Zone (OMZ). In shallow areas only the surface layer can serve as a refuge, in deep waters many organisms have developed vertical migration strategies to use, pass and cope with the OMZ. This paper elucidates the role of DO for different taxa in the pelagic realm and the consequences of low oxygen for foodweb structure and system productivity.
Mesoscale modeling of the CO2 interactions between the surface and the atmosphere applied to the April 2007 CERES field experiment
Authors: Sarrat C. , Noilhan J. , Lacarrère P. , Dolman A. J. , Gerbig C. , Elbers J. A. , Vellinga O. S. , Gioli B. , Miglietta F. , Neininger B. , Lauvaux T. , Ciais P. , Ramonet M. , Ceschia E. , Bonnefond J. M.
Published: April 2010

Abstract. The paper describes a numerical interpretation of the April 2007 CarboEurope Regional Experiment Strategy (CERES) campaign, devotedto the study of CO2 cycle at the regional scale. The four consecutive clear sky days with intensive observations of CO2 concentration, fluxes at the the surface and in the boundary layer have been simulated with the Meso-NH mesoscale model. Aircraft observations of CO2 have been used to identify surface modelling errors and to calibrate the CO2 components of the surface model. After this calibration, the paper describes a systematic comparison of the model outputs with all the data collected during CERES, in April 2007. As a conclusion, an example of CO2 budgeting from the mesoscale model is given.
Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation
Authors: Gilgen A. K. , Buchmann N.
Published: April 2010

Abstract. Water is an important resource for plant live. Since climate scenarios for Switzerland predict an average reduction of 20% in summer precipitation until 2070, understanding ecosystem responses to water shortage, e.g. in terms of plant productivity, is of major concern. Thus, we tested the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude. We assessed the effects of drought on above- and below-ground productivity, stand structure (LAI and vegetation height) and resource use (carbon and water). Drought responses of community above-ground productivity differed among the three sites but scaled positively with total annual precipitation at the sites (R2=0.85). Annual community above-ground biomass productivity was significantly reduced by summer drought at the alpine site receiving the least amount of annual precipitation, while no significant decrease (rather an increase) was observed at the pre-alpine site receiving highest precipitation amounts in all three years. At the lowland site (intermediate precipitation sums), biomass productivity significantly decreased in response to drought only in the third year, after showing increased abundance of a drought tolerant weed species in the second year. No significant change in below-ground biomass productivity was observed at any of the sites in response to simulated summer drought. However, community carbon isotope ratios increased under drought conditions, indicating an increase in water use efficiency. We conclude that there is no general drought response of Swiss grasslands, but that sites with lower annual precipitation seem to be more vulnerable to summer drought than sites with higher annual precipitation, and thus site-specific adaptation measures will be needed especially in regions with low annual precipitation.
Nitrous oxide production in boreal soils with variable organic matter content at low temperature – snow manipulation experiment
Authors: Maljanen M. , Virkajärvi P. , Hytönen J. , Öquist M. , Sparrman T. , Martikainen P. J.
Published: April 2010

Abstract. Agricultural soils are the most important sources for the greenhouse gas nitrous oxide (N2O), which is produced and emitted from soil also at low temperatures. The processes behind emissions at low temperatures are still poorly known. To simulate the effects of a reduction in snow depth on N2O emission in warming climate, snow pack was removed from three different agricultural soils (sand, mull, peat). Removal of snow lowered soil temperature and increased the extent and duration of soil frost which led to enhanced N2O emissions during freezing and thawing events in sand and mull soils. The cumulative emissions during the first year when snow was removed over the whole winter were 0.25, 0.66 and 3.0 g N2O-N m−2 yr−1 in control plots of sand, mull and peat soils, respectively. Without snow cover the respectively cumulative emissions were 0.37, 1.3 and 3.3 g N2O-N m−2 yr−1. Shorter snow manipulation during the second year did not increase the annual emissions. Only 20% of the N2O emission occurred during the growing season. Thus, highlighting the importance of the winter season for this exchange and that the year-round measurements of N2O emissions from boreal soils are integral for estimating their N2O source strength. N2O accumulated in the frozen soil during winter and the soil N2O concentration correlated with the depth of frost but not with the winter N2O emission rates per se. Also laboratory incubations of soil samples showed high production rates of N2O at temperatures below 0°C, especially in the sand and peat soils.
Reconstructing the Nd oceanic cycle using a coupled dynamical – biogeochemical model
Authors: Arsouze T. , Dutay J.-C. , Lacan F. , Jeandel C.
Published: April 2010

Abstract. The decoupling of behaviour observed between Nd isotopic composition (Nd IC, also referred as εNd) and Nd concentration has led to the notion of a "Nd paradox". While εNd behaves in a quasi-conservative way in the open ocean, leading to its broad use as a water-mass tracer, Nd concentration displays vertical profiles that increase with depth together with a deep water enrichment along the global thermohaline circulation, non-conservative behaviour typical of nutrients affected by scavenging in surface waters and remineralisation at depth. In addition, recent studies suggested that the only way to reconcile both concentration and Nd IC oceanic budgets, is to invoke a "Boundary Exchange" process (BE, defined as the co-occurrence of transfer of elements from the margin to the sea with removal of elements from the sea by Boundary Scavenging) as a source-sink term. However, these studies did not simulates the real input/output fluxes of Nd to the ocean, and therefore did prevent from crucial information to apprehend the "Nd paradox". In this study, we investigate this paradox on a global scale using for the first time a fully prognostic coupled dynamical/biogeochemical model and an explicit representation of the sources and sinks to simulate the Nd oceanic cycle. Sources considered are dissolved river fluxes, atmospheric dusts and margin sediment re-dissolution. Sinks are scavenging by settling particles. This model satisfyingly simulate the global Nd oceanic cycle, and produces realistic distribution of Nd concentration and isotopic composition, though a slight overestimation of Nd concentrations in the deep Pacific Ocean, likely revealing an underestimation of the particle fields by the biogeochemical model. Our results underlines that 1) vertical cycling (scavenging/remineralisation) is absolutely necessary to satisfyingly simulate both concentration and εNd, and 2) BE is the dominant Nd source to the ocean. The estimated BE flux (1.1×1010 g(Nd)/yr) is much higher than both dissolved river discharge (2.6×108 g(Nd)/yr) and atmospheric inputs (1.0×108 g(Nd)/yr) that play negligible role in the water column but are necessary to reconcile Nd IC in surface and subsurface. This leads to a recalculated residence time of Nd in the ocean of 360 yrs. The BE flux requires the dissolution of only 3 to 5% of the annually flux of material weathered on the continent and deposited via the solid river discharge on the continental margin.
Changes in mobility and solubility of the redox sensitive metals Fe, Mn and Co at the seawater-sediment interface following CO2 seepage
Authors: Ardelan M. V. , Steinnes E.
Published: April 2010

Abstract. The impact of CO2 seepage on the solubility and distribution of the redox-sensitive metals iron, manganese, and cobalt in seawater and sediment pore water has been studied in experiments in laboratory-scale 0.6 m3 chambers. The mobility and solubility of Fe, Mn and Co were investigated in seawater, membrane filtered seawater, and DGT samplers deployed in water and sediment during a 26 day CO2 seepage study. During the first phase of the experiment of CO2 seepage (0–16 days), total acid-leachable (pH≈1) and "dissolved" (<0.2 μm) concentrations of Fe, Mn and Co (DFe, DMn and DCo) in the seawater increased significantly; the ratios of concentrations of DFe, DMn and DCo in the CO2 chamber to the corresponding values in the control chamber (RDFe, RDMn and RDCo) were as high as 6, 65 and 58, respectively. The second phase of experiment consisted of an additional 10 days of incubation, where the concentrations of all the metals studied still increased but at reduced rates for DMn and DCo. The highest values of RDFe, RDMn and RDCo were about 3 for all metals during this part of the experiment. DGT (diffusive gradients in thin film) labile fractions denoted FeDGT, MnDGT and CoDGT were, respectively 50, 25 and 22 times higher in the CO2 seepage chamber than in the control chamber in the first phase of the experiment. During the second phase, all DGT labile metal concentrations still increased considerably, most notably for Fe. The ratio of FeDGT in the CO2 chamber to that in the control (RDGT-Fe) was still high, about 5, in the second phase of the experiment, whereas the increase in MnDGT and CoDGT slowed down. Our results indicate that acidification following CO2 seepage enhances the mobility and solubility of Fe Mn and Co in sediment and overlying water with contribution of changing in redox conditions and seepage related re-suspension.
Biogeochemistry of a low-activity cold seep in the Larsen B area, western Weddell Sea, Antarctica
Authors: Niemann H. , Fischer D. , Graffe D. , Knittel K. , Montiel A. , Heilmayer O. , Nöthen K. , Pape T. , Kasten S. , Bohrmann G. , Boetius A. , Gutt J.
Published: April 2010

Abstract. First videographic indication of an Antarctic cold seep ecosystem was recently obtained from the collapsed Larsen B ice shelf, western Weddell Sea (Domack et al., 2005). Within the framework of the R/V Polarstern expedition ANTXXIII-8, we revisited this area for geochemical, microbiological and further videographical examinations. During two dives with ROV Cherokee (MARUM, Bremen), several bivalve shell agglomerations of the seep-associated, chemo syntheticclam Calyptogena sp. were found in the trough of the Crane and Evans glacier. The absence of living clam specimens indicates that the flux of sulphide and hence the seepage activity is diminished at present. This impression was further substantiated by our geochemical observations. Concentrations of thermogenic methane were moderately elevated with 2 μM in surface sediments of a clam patch, increasing up to 9 μM at a sediment depth of about 1 m in the bottom sections of the sediment cores. This correlated with a moderate decrease in sulphate from 28 mM at the surface down to 23.4 mM, an increase in sulphide to up to 1.43 mM and elevated rates of the anaerobic oxidation of methane (AOM) of up to 600 pmol cm−3 d−1 at about 1 m below the seafloor. Molecular analyses indicate that methanotrophic archaea related to ANME-3 are the most likely candidates mediating AOM in sediments of the Larsen B seep (Domack et al., 2005; EOS 86, 269–276).
The consumption of atmospheric methane by soil in a simulated future climate
Authors: Curry C. L.
Published: April 2010

Abstract. A recently developed model for the consumption of atmospheric methane by soil (Curry, 2007) is used to investigate the global magnitude and distribution of methane uptake in a simulated future climate. In addition to solving the one-dimensional diffusion-reaction equation, the model includes a parameterization of biological CH4 oxidation that is sensitive to soil temperature and moisture content, along with simple scalings for land cultivation and wetland fractional coverage. Under the SRES emission scenario A1B, the model projects an 8% increase in the global annual mean CH4 soil sink by 2100, over and above the 15% increase expected from increased CH4 concentration alone. While the largest absolute increases occur in cool temperate and subtropical forest ecosystems, the largest relative increases in consumption (>40%) are seen in the boreal forest, tundra and polar desert environments of the high northern latitudes. Methane uptake at mid- to high northern latitudes increases year-round in 2100, with a 68% increase over present-day values in June. This increase is primarily due to enhanced soil diffusivity resulting from increased evaporation and reduced snow cover. At lower latitudes, uptake is enhanced mainly by elevated soil temperatures and/or reduced soil moisture stress, with the dominant influence determined by the local climate.
Greenhouse gas fluxes in a drained peatland forest during spring frost-thaw event
Authors: Pihlatie M. K. , Kiese R. , Brüggemann N. , Butterbach-Bahl K. , Kieloaho A.-J. , Laurila T. , Lohila A. , Mammarella I. , Minkkinen K. , Penttilä T. , Schönborn J. , Vesala T.
Published: April 2010

Abstract. Fluxes of greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured during a two month campaign at a drained peatland forest in Finland by the eddy covariance (EC) technique (CO2 and N2O), and automatic and manual chambers (CO2, CH4 and N2O). In addition, GHG concentrations and soil parameters (mineral nitrogen, temperature, moisture content) in the peat profile were measured. The aim of the measurement campaign was to quantify the GHG fluxes before, during and after thawing of the peat soil, a time period with potentially high GHG fluxes, and to compare different flux measurement methods. The forest was a net CO2 sink during the two months and the fluxes of CO2 dominated the GHG exchange. The peat soil was a small sink of atmospheric CH4 but a small source of N2O. Both CH4 oxidation and N2O production took place in the top-soil whereas CH4 was produced in the deeper layers of the peat. During the thawing of the peat distinct peaks in CO2 and N2O emissions were observed. The CO2 peak followed tightly the increase in soil temperature, whereas the N2O peak occurred with an approx. one week delay after soil thawing. CH4 fluxes did not respond to the thawing of the peat soil. The CO2 and N2O emission peaks were not captured by the manual chambers and hence we conclude that automatic chamber measurements or EC are necessary to quantify fluxes during peak emission periods. Sub-canopy EC measurements and chamber-based fluxes of CO2 and N2O were comparable, although the fluxes of N2O measured by EC were close to the detection limit of the EC system. We conclude that if fluxes are high enough, i.e. greater than 5–10 μg N m−2 h−1, the EC method is a good alternative to measure N2O and CO2 fluxes at ecosystem scale, thereby minimizing problems with chamber enclosures and spatial representativeness of the measurements.
Contribution of root and rhizosphere respiration to the annual variation of carbon balance of a boreal Scots pine forest
Authors: Korhonen J. F. J. , Pumpanen J. , Kolari P. , Juurola E. , Nikinmaa E.
Published: April 2010

Abstract. A large part of gross primary production (GPP) is consumed in root and rhizosphere respiration (Rr). To measure Rr, a group of evergreen coniferous Scots pine (Pinus sylvestris) trees were girdled in a 45-year-old even aged forest in Hyytiälä, Southern Finland. In the girdling, phloem and bark were removed from breast height around the trees. We measured soil CO2 effluxes with a dynamic chamber at the girdled plot and at a non-girdled control plot in close vicinity. Before the girdling, effluxes were 22% higher at the plot to be girdled compared to the control plot. We scaled the measurements so that before girdling the effluxes representing total soil respiration (Rs) were at the same level. We compared the Rr and Rd to GPP measured with eddy covariance system. Our results show that Rr has higher seasonal variation than Rd, and also spatial variability was higher for Rr. The annual Rr:Rs and Rr:GPP-ratios were 0.36 and 0.21, respectively. Rr:Rd varied seasonally and in late summer and in autumn Rr exceeded Rd. Rr followed GPP with a delay of several weeks. During winter and spring Rr was very low, even when GPP and soil temperature had significantly risen. We conclude that Rr and Rd have different response to the environment and that for Rr the substrate availability is a more important explaining variable than soil temperature.
Coupling of surface pCO2 and dissolved oxygen in the northern South China Sea: impacts of contrasting coastal processes
Authors: Zhai W. , Dai M. , Cai W.
Published: April 2010

Abstract. We examined the relationship between CO2 partial pressure (pCO2) and dissolved oxygen (DO) based on a cruise conducted in July 2004 to the northern South China Sea, spanning from estuarine plume, coastal upwelling and deep basin areas. Distinct relationships between pCO2 and DO saturation were identified in different regimes. In coastal upwelling areas and the Pearl River estuary, biological drawdown of pCO2 and production of O2 were simultaneously observed. The two properties were coupled with each other primarily via photosynthesis and respiration. The stoichiometric relationship of the two properties however, was quite different in these two environments due to different values of the Revelle factor. In the offshore areas, apart from the estuary and upwelling, the dynamics of pCO2 and DO were mainly influenced by air-sea exchange during water mixing. Given the fact that air-sea re-equilibration of O2 is much faster than that of CO2, the observed pCO2-DO relationship deviated from that of the theoretical prediction based on the Redfield relationship in the offshore areas.
Belowground carbon pools and dynamics in China's warm temperate and sub-tropical deciduous forests
Authors: Xiao C. W. , Janssens I. A. , Sang W. G. , Wang R. Z. , Xie Z. Q. , Pei Z. Q. , Yi Y.
Published: April 2010

Abstract. We report the first estimates of pools and dynamics of microbes, roots, plant litter and soil organic carbon (SOC) in three dominant types of China's vast deciduous forest area: Betula platyphylla, Quercus liaotungensis, and Quercus aliena varacuteserrata. Organic matter degradation rates overshadowed litter inputs as the main determinant of the soil carbon stocks. Across the three forests, rates of litter decomposition were also indicative for turnover rates of SOC. Litter and SOC decay was faster in the sub-tropical than in the warm-temperate forests. Among the latter, SOC turnover was highest in the forest producing the higher-quality litter. Microbial biomass was, as expected, correlated with SOC content. Microbial activity, in contrast, was highest at the sub-tropical forest, despite the lower SOC availability, lower fraction of labile SOC, and lower soil microbial biomass. These results may contribute to increased understanding of controls over belowground carbon cycling in deciduous forests.
Selective preservation of organic matter in marine environments – processes and impact on the fossil record
Authors: Zonneveld K. A. F. , Versteegh G. J. M. , Kasten S. , Eglinton T. I. , Emeis K.-C. , Huguet C. , Koch B. P. , de Lange G. J. , de Leeuw J. W. , Middelburg J. J. , Mollenhauer G. , Prahl F. G. , Rethemeyer J. , Wakeham S. G.
Published: April 2010

Abstract. The present paper is the result of a workshop sponsored by the Research Centre Ocean Margins, the International Graduate College EUROPROX and the Alfred Wegener Institute for Polar Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments.
Nitrate and dissolved nitrous oxide in groundwater within cropped fields and riparian buffers
Authors: Kim D.-G. , Isenhart T. M. , Parkin T. B. , Schultz R. C. , Loynachan T. E.
Published: April 2010

Abstract. Transport and fate of dissolved nitrous oxide (N2O) in groundwater and its significance to nitrogen dynamics within agro-ecosystems are poorly known in spite of significant potential of N2O to global warming and ozone depletion. Increasing denitrification in riparian buffers may trade a reduction in nitrate (NO3−) transport to surface waters for increased N2O emissions resulting from denitrification-produced N2O dissolved in groundwater being emitted into the air when groundwater flows into a stream or a river. This study quantifies the transport and fate of NO3− and dissolved N2O moving from crop fields through riparian buffers, assesses whether groundwater exported from crop fields and riparian buffers is a significant source of dissolved N2O emissions, and evaluates the Intergovernmental Panel on Climate Change (IPCC) methodology to estimate dissolved N2O emission. We measured concentrations of NO3−; chloride (Cl−); pH; dissolved N2O, dissolved oxygen (DO), and organic carbon (DOC) in groundwater under a multi-species riparian buffer, a cool-season grass filter, and adjacent crop fields located in the Bear Creek watershed in central Iowa, USA. In both the multi-species riparian buffer and the cool-season grass filter, concentrations of dissolved N2O in the groundwater did not change as it passed through the sites, even when the concentrations of groundwater NO3− were decreased by 50% and 59%, respectively, over the same periods. The fraction of N lost to leaching and runoff (0.05) and the modified N2O emission factor, [ratio of dissolved N2O flux to N input (0.00002)] determined for the cropped fields indicate that the current IPCC methodology overestimates dissolved N2O flux in the sites. A low ratio between dissolved N2O flux and soil N2O emission (0.0003) was estimated in the cropped fields. These results suggest that the riparian buffers established adjacent to crop fields for water quality functions (enhanced denitrification) decreased NO3− and were not a source of dissolved N2O. Also, the flux of dissolved N2O from the cropped field was negligible in comparison to soil N2O emission in the crop fields.
Ultraphytoplankton distribution and upper ocean dynamics in the eastern Mediterranean during winter
Authors: Denis M. , Thyssen M. , Martin V. , Manca B. , Vidussi F.
Published: April 2010

Abstract. The vertical distribution of ultraphytoplankton (<10 μm) was determined in the upper 200 m of the eastern Mediterranean during the winter season. Four clusters were resolved by flow cytometry on the basis of their optical properties and identified as Synechococcus, Prochlorococcus, pico- (<3 μm) and nanoeukaryotes (3–10 μm). Synechococcus was the most abundant population (maximum abundance of about 37 000 cells cm−3) and contributed up to 67.7% to the overall ultraphytoplanktonic carbon biomass, whereas the contribution of Prochlorococcus never exceeded 6.5%. The maximum integrated carbon biomass was 1763, 453, 58 and 571 mg C m−2 for nanoeukaryotes, picoeukaryotes, Prochlorococcus and Synechococcus, respectively. Water mass properties were analyzed on the basis of temperature and salinity distributions in order to account for the general circulation and locate the main hydrodynamic structures (fronts, gyres, transition between western and eastern basins). Relationships were established between the ultraphytoplankton distribution and the hydrological characteristics of the main hydrodynamic structures. Significant relationships were found between Synechococcus abundance and density, resulting from the impact of a gyre in southern Adriatic and a thermohaline front in the Ionian Sea. A significant relationship was also found between picoeukaryotes and salinity in the comparison of western and eastern Mediterranean. Relationships were only significant for the most abundant clusters. As the first investigation of ultraphytoplankton winter distribution in the eastern Mediterranean, the present study will significantly contribute to a better knowledge of the ultraphytoplankton structure over seasons and of its dependence on hydrological features.
Current and future CO2 emissions from drained peatlands in Southeast Asia
Authors: Hooijer A. , Page S. , Canadell J. G. , Silvius M. , Kwadijk J. , Wösten H. , Jauhiainen J.
Published: April 2010

Abstract. Forested tropical peatlands in Southeast Asia store at least 42 000 Million metric tonnes (Mt) of soil carbon. Human activity and climate change threatens the stability of this large pool which has been decreasing rapidly over the last few decades owing to deforestation, drainage and fire. In this paper we estimate the carbon dioxide (CO2) emissions resulting from drainage of lowland tropical peatland for agricultural and forestry development which dominates the perturbation of the carbon balance in the region. Present and future emissions from drained peatlands are quantified using data on peatland extent and peat thickness, present and projected land use, water management practices and decomposition rates. Of the 27.1 Million hectares (Mha) of peatland in Southeast Asia, 12.9 Mha had been deforested and mostly drained by 2006. This latter area is increasing rapidly as a result of increasing land development pressures. Carbon dioxide (CO2) emission caused by decomposition of drained peatlands was between 355 and 855 Mt y