bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective preservation of organic matter in marine environments; processes and impact on the sedimentary 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 DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the Alfred Wegener Institute for Polar and Marine 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. It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, understood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown. To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation. Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation. Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.
The African contribution to the global climate-carbon cycle feedback of the 21st century
Authors: Friedlingstein P. , Cadule P. , Piao S. L. , Ciais P. , Sitch S.
Published: April 2010

Abstract. Future climate change will have impact on global and regional terrestrial carbon balances. The fate of African tropical forests over the 21st century has been investigated through global coupled climate carbon cycle model simulations. Under the SRES-A2 socio-economic CO2 emission scenario of the IPCC, and using the Institut Pierre Simon Laplace coupled ocean-terrestrial carbon cycle and climate model, IPSL-CM4-LOOP, we found that the warming over African ecosystems induces a reduction of net ecosystem productivity, making a 38% contribution to the global climate-carbon cycle positive feedback. Most of this contribution comes from African grasslands, followed by African savannahs, African tropical forest contributing little to the global climate-carbon feedback. However, the vulnerability of the African rainforest ecosystem is quite large. In contrast, the Amazon forest, despite its lower vulnerability, has a much larger overall contribution due to its 6 times larger extent.
The annual ammonia budget of fertilised cut grassland – Part 2: Seasonal variations and compensation point modeling
Authors: Flechard C. R. , Spirig C. , Neftel A. , Ammann C.
Published: April 2010

Abstract. The net annual NH3 exchange budget of a fertilised, cut grassland in Central Switzerland is presented. The observation-based budget was computed from semi-continuous micrometeorological fluxes over a time period of 16 months and using a process-based gap-filling procedure. The data for emission peak events following the application of cattle slurry and for background exchange were analysed separately to distinguish short-term perturbations from longer-term ecosystem functioning. A canopy compensation point model of background exchange is parameterised on the basis of measured data and applied for the purposes of gap-filling. The data show that, outside fertilisation events, grassland behaves as a net sink for atmospheric NH3 with an annual dry deposition flux of −3.0 kg N ha−1 yr−1, although small NH3 emissions by the canopy were measured in dry daytime conditions. The median Γs ratio in the apoplast (=[NH4+]/[H+]) estimated from micrometeorological measurements was 620, equivalent to a stomatal compensation point of 1.3 μg NH3 m−3 at 15 °C. Non-stomatal resistance to deposition Rw was shown to increase with temperature and decrease with surface relative humidity, and Rw values were among the highest published for European grasslands, consistent with a relatively high ratio of NH3 to acid gases in the boundary layer at this site. Since the gross annual NH3 emission by slurry spreading was of the order of +20 kg N ha−1 yr−1, the fertilised grassland was a net NH3 source of +17 kg N ha−1 yr−1. A comparison with the few other measurement-based budget values from the literature reveals considerable variability, demonstrating both the influence of soil, climate, management and grassland type on the NH3 budget and the difficulty of scaling up to the national level.
Atmospheric deposition of nutrients and excess N formation in the North Atlantic
Authors: Zamora L. M. , Landolfi A. , Oschlies A. , Hansell D. A. , Dietze H. , Dentener F.
Published: April 2010

Abstract. Anthropogenic emissions of nitrogen (N) to the atmosphere have been strongly increasing during the last century, leading to greater atmospheric N deposition to the oceans. The North Atlantic subtropical gyre (NASTG) is particularly impacted. Here, upwind sources of anthropogenic N from North American and European sources have raised atmospheric N deposition to rates comparable with N2 fixation in the gyre. However, the biogeochemical fate of the deposited N is unclear because there is no detectable accumulation in the surface waters. Most likely, deposited N accumulates in the main thermocline instead, where there is a globally unique pool of N in excess of the canonical Redfield ratio of 16N:1 phosphorus (P). To investigate this depth zone as a sink for atmospheric N, we used a biogeochemical ocean transport model and year 2000 nutrient deposition data. We examined the maximum effects of three mechanisms that may transport excess N from the ocean surface to the main thermocline: physical transport, preferential P remineralization of sinking particles, and nutrient uptake and export by phytoplankton at higher than Redfield N:P ratios. Our results indicate that atmospheric deposition may contribute 13–19% of the annual excess N input to the main thermocline. Modeled nutrient distributions in the NASTG were comparable to observations only when non-Redfield dynamics were invoked. Preferential P remineralization could not produce realistic results on its own; if it is an important contributor to ocean biogeochemistry, it must co-occur with N2 fixation. The results suggest that: 1) the main thermocline is an important sink for anthropogenic N deposition, 2) non-Redfield surface dynamics determine the biogeochemical fate of atmospherically deposited nutrients, and 3) atmospheric N accumulation in the main thermocline has long term impacts on surface ocean biology.
The impact of Saharan dust on the particulate export in the water column of the North Western Mediterranean Sea
Authors: Ternon E. , Guieu C. , Loÿe-Pilot M.-D. , Leblond N. , Bosc E. , Gasser B. , Miquel J.-C. , Martín J.
Published: April 2010

Abstract. Simultaneous measurements of atmospheric deposition and of sinking particles at 200 and 1000 m depth, were performed in the Ligurian Sea (North-Western Mediterranean) between 2003 and 2007, along with phytoplanktonic activity derived from satellite images. Atmospheric deposition of Saharan dust particles was very irregular and confirmed the importance of sporadic high magnitude events over the annual average (11.4 g m−2 yr−1 for the 4 years). The average marine total mass flux was 31 g m−2 yr−1, the larger fraction being the lithogenic one (~37%). The marine total mass flux displayed a seasonal pattern with a maximum in winter, occurring before the onset of the spring bloom. The highest POC fluxes did not occur during the spring bloom nor could they be directly related to any noticeable increase in the surface phytoplanktonic biomass. Over the 4 years of the study, the strongest POC fluxes were concomitant with large increases of the lithogenic marine flux, which had originated from either recent Saharan fallout events (February 2004 and August 2005), from "old" Saharan dust "stored" in the upper water column layer (March 2003 and February 2005), or alternatively from lithogenic material originating from Ligurian riverine flooding (December 2003, Arno, Roya and Var rivers). Those associated export fluxes defined as "lithogenic events", are believed to result from a combination of forcing (winter mixing or Saharan events, in particular extreme ones), biological (zooplankton) activity, and also organic-mineral aggregation inducing a ballast effect. By fertilising the surface layer, mixed Saharan dust events were shown to be able to induce "lithogenic events" during the stratification period. These events would be more efficient in transferring POC to the deeper layers than the spring bloom itself. The extreme Saharan event of February 2004 exported ~45% of the total annual POC, compared to an average of ~25% for the bloom period. This emphasises the role played by these "lithogenic events", and in particular those that are induced by the more extreme Saharan events, in the carbon export efficiency in the North-western Mediterranean Sea.
Incorporation of Mg and Sr in calcite of cultured benthic foraminifera: impact of calcium concentration and associated calcite saturation state
Authors: Raitzsch M. , Dueñas-Bohórquez A. , Reichart G.-J. , de Nooijer L. J. , Bickert T.
Published: April 2010

Abstract. We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (Ω) on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing) and Ammonia tepida (low-Mg calcite, symbiont-barren) were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite)/(TE/Caseawater). The culturing study shows that DMg of A. tepida significantly decreases with increasing Ω at a gradient of −4.3×10−5 per Ω unit. The DSr value of A. tepida does not change with Ω, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing Ω, while DSr increases considerably with Ω at a gradient of 0.009 per Ω unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50–100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep-sea benthic foraminifera typically used for paleostudies, the higher Ca concentrations in the past may potentially bias temperature reconstructions to a considerable degree. For instance, 25 Myr ago Mg/Ca ratios in A. tepida would have been 0.2 mmol/mol lower than today, due to the 1.5 times higher [Ca2+] of seawater, which in turn would lead to a temperature underestimation of more than 2 °C.
Annual carbon gas budget for a subarctic peatland, Northern Sweden
Authors: Bäckstrand K. , Crill P. M. , Jackowicz-Korczyñski M. , Mastepanov M. , Christensen T. R. , Bastviken D.
Published: April 2010

Abstract. Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 29.7, −35.3 and −34.9 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m−2 for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO2 sink of 2.6 gC m−2 and a THC source of 6.4 gC m−2 over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m−2 (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.
Projected 21st century decrease in marine productivity: a multi-model analysis
Authors: Steinacher M. , Joos F. , Frölicher T. L. , Bopp L. , Cadule P. , Cocco V. , Doney S. C. , Gehlen M. , Lindsay K. , Moore J. K. , Schneider B. , Segschneider J.
Published: April 2010

Abstract. Changes in marine net primary productivity (PP) and export of particulate organic carbon (EP) are projected over the 21st century with four global coupled carbon cycle-climate models. These include representations of marine ecosystems and the carbon cycle of different structure and complexity. All four models show a decrease in global mean PP and EP between 2 and 20% by 2100 relative to preindustrial conditions, for the SRES A2 emission scenario. Two different regimes for productivity changes are consistently identified in all models. The first chain of mechanisms is dominant in the low- and mid-latitude ocean and in the North Atlantic: reduced input of macro-nutrients into the euphotic zone related to enhanced stratification, reduced mixed layer depth, and slowed circulation causes a decrease in macro-nutrient concentrations and in PP and EP. The second regime is projected for parts of the Southern Ocean: an alleviation of light and/or temperature limitation leads to an increase in PP and EP as productivity is fueled by a sustained nutrient input. A region of disagreement among the models is the Arctic, where three models project an increase in PP while one model projects a decrease. Projected changes in seasonal and interannual variability are modest in most regions. Regional model skill metrics are proposed to generate multi-model mean fields that show an improved skill in representing observation-based estimates compared to a simple multi-model average. Model results are compared to recent productivity projections with three different algorithms, usually applied to infer net primary production from satellite observations.
Modeling the nitrogen fluxes in the Black Sea using a 3D coupled hydrodynamical-biogeochemical model: transport versus biogeochemical processes, exchanges across the shelf break and comparison of the shelf and deep sea ecodynamics
Authors: Grégoire M. , Beckers J. M.
Published: April 2010

Abstract. A 6-compartment biogeochemical model of nitrogen cycling and plankton productivity has been coupled with a 3D general circulation model in an enclosed environment (the Black Sea) so as to quantify and compare, on a seasonal and annual scale, the typical internal biogeochemical functioning of the shelf and of the deep sea as well as to estimate the nitrogen and water exchanges at the shelf break. Model results indicate that the annual nitrogen net export to the deep sea roughly corresponds to the annual load of nitrogen discharged by the rivers on the shelf. The model estimated vertically integrated gross annual primary production is 130 g C m-2yr-1 for the whole basin, 220 g C m-2yr-1 for the shelf and 40 g C m-2yr-1 for the central basin. In agreement with sediment trap observations, model results indicate a rapid and efficient recycling of particulate organic matter in the sub-oxic portion of the water column (60-80m) of the open sea. More than 95% of the PON produced in the euphotic layer is recycled in the upper 100m of the water column, 87% in the upper 80 m and 67% in the euphotic layer. The model estimates the annual export of POC towards the anoxic layer to 4 1010mol yr-1. This POC is definitely lost for the system and represents 2% of the annual primary production of the open sea.
Environmental proteomics – what proteins from soil and surface water can tell us: a perspective
Authors: Schulze W.
Published: April 2010

Abstract. Mass spectrometry based proteomics is widely used to study cellular processes in model organisms. However, it has not much been applied in environmental research because it was thought that free proteins would not be sufficiently stable in the environments. Based on recent observations that protein can readily be detected as a component of dissolve organic carbon, this article gives an overview about the possible use of proteomic methods in ecology and environmental sciences. At this stage, there are two areas of interest: (1) the identification of phylogenetic groups contributing to the DOC pool, and (2) identification of the origin of specific enzymes that are important for ecosystem processes. In this paper methods of mass spectrometry based proteomics were applied to identify proteins from DOC and water samples from different environments. It is demonstrated, that environmental proteomics is capable to distinguish the active set of organisms of different horizons of soils, and from various sources of surface water. Currently the limitation is given by the present knowledge of the genome of soil organisms. In addition, environmental proteomics allows to relate protein presence to biogeochemical processes, and to identify the source organisms for specific enzymes. Taking laccases as an example, it is shown that this enzyme is excreted into soils by a whole range of organisms from different phylogenetic groups. Further applications, such as in pollution reseach are conceivable. In summary, environmental proteomcis opens a new area of research between the fields of microbiology and biogeochemistry.
Link or sink: a modelling interpretation of the open Baltic biogeochemistry
Authors: Vichi M. , Ruardij P. , Baretta J. W.
Published: April 2010

Abstract. A 1-D model system, consisting of the 1-D version of the Princeton Ocean Model (POM) coupled with the European Regional Seas Ecosystem Model (ERSEM) has been applied to a sub-basin of the Baltic Proper, the Bornholm basin. The model has been forced with 3h meteorological data for the period 1979-1990, producing a 12-year hindcast validated with datasets from the Baltic Environmental Database for the same period. The model results demonstrate the model to hindcast the time-evolution of the physical structure very well, confirming the view of the open Baltic water column as a three layer system of surface, intermediate and bottom waters. Comparative analyses of modelled hydrochemical components with respect to the independent data have shown that the long-term system behaviour of the model is within the observed ranges. Also primary production processes, deduced from oxygen (over)saturation are hindcast correctly over the entire period and the annual net primary production is within the observed range. The largest mismatch with observations is found in simulating the biogeochemistry of the Baltic intermediate waters. Modifications in the structure of the model (addition of fast-sinking detritus and polysaccharide dynamics) have shown that the nutrient dynamics is linked to the quality and dimensions of the organic matter produced in the euphotic zone, highlighting the importance of the residence time of the organic matter within the microbial foodweb in the intermediate waters. Experiments with different scenarios of riverine nutrient loads, assessed in the limits of a 1-D setup, have shown that the external input of organic matter makes the open Baltic model more heterotrophic. The characteristics of the inputs also drive the dynamics of nitrogen in the bottom layers leading either to nitrate accumulation (when the external sources are inorganic), or to coupled nitrification-denitrification (under strong organic inputs). The model indicates the permanent stratification to be the main feature of the system as regulator of carbon and nutrient budgets. The model predicts that most of the carbon produced in the euphotic zone is also consumed in the water column and this enhances the importance of heterotrophic benthic processes as final closures of carbon and nutrient cycles in the open Baltic.
Net ecosystem exchange of carbondioxide and water of far eastern Siberian Larch (Larix dahurica) on permafrost
Authors: Dolman A. J. , Maximov T. C. , Moors E. J. , Maximov A. P. , Elbers J. A. , Kononov A. V. , Waterloo M. J. , van der Molen M. K.
Published: April 2010

Abstract. Observations of the net ecosystem exchange of water and CO2were made during two seasons in 2000 and 2001 above a Larch forest in Far East Siberia (Yakutsk). The measurements were obtained by eddy correlation. There is a very sharply pronounced growing season of 100 days when the forest is leaved. Maximum daytime uptake rates are 18 μmol m-2 s-1 maximum respiration rates are 5 μmol m-2 s-1. Net annual sequestration of carbon (C) was estimated at 1.7 (±0.5) ton C ha-1 in 2001. The net carbon exchange of the forest was extremely sensitive to small changes in weather that may switch the forest easily from a sink to a source, even in summer. June was the month with highest uptake in 2001. The average evaporation rate of the forest approached 1.46mm day-1 during the growing season, with peak values of 3mm day-1 with an estimated annual evaporation of 213mm, closely approaching the average annual rainfall amount. 2001 was a drier year than 2000 and this is reflected in the evaporation rates that show lower evaporation rates in 2001 than in 2000. The surface conductance of the forest shows a marked response to increasing atmospheric humidity deficits. This affects the CO2 uptake and evaporation in a different manner, with the CO2 uptake being more affected. There appears to be no change in the relation between surface conductance and normalized net ecosystem uptake at the monthly time scale. The response to atmospheric humidity deficits is an efficient mechanism to prevent severe water loss during the short intense growing season. The associated cost to the sequestration of carbon may be another explanation for the slow growth of these forests in this environment.
Regional hydrology controls stream microbial biofilms: evidence from a glacial catchment
Authors: Battin T. J. , Wille A. , Psenner R. , Richter A.
Published: April 2010

Abstract. Glaciers are highly responsive to global warming and important agents of landscape heterogeneity. While it is well established that glacial ablation and snowmelt regulate stream discharge, linkage among streams and streamwater hydrogeochemistry, the controls of these factors on stream microbial biofilms remain insufficiently understood. We investigated glacial (metakryal, hypokryal), groundwater-fed (krenal) and snow-fed (rhithral) streams – all of them representative for alpine stream networks – and present evidence that these hydrologic and hydrogeochemical factors differentially affect sediment microbial biofilms. Average microbial biomass and bacterial carbon production were low in the glacial streams, whereas bacterial cell size, biomass, and carbon production were higher in the tributaries, most notably in the krenal stream. Whole-cell in situ fluorescence hybridization revealed reduced detection rates of the Eubacteria and higher abundance of α-Proteobacteria in the glacial stream, a pattern that most probably reflects the trophic status of this ecosystem. Our data suggest low flow during the onset of snowmelt and autumn as a short period (hot moment) of favorable environmental conditions with pulsed inputs of allochthonous nitrate and dissolved organic carbon, and with disproportional high microbial growth. Krenal and rhithral streams with more constant and favorable environments serve as possible sources of microbes and organic matter to the main glacial channel during periods (e.g. snowmelt) of elevated hydrologic linkage among streams. Ice and snow dynamics have a crucial impact on microbial biofilms, and we thus need better understanding of the microbial ecology and enhanced consideration of critical hydrological episodes in future models predicting alpine stream communities.
Protein analysis in dissolved organic matter: what free proteins from soil leachate and surface water can tell us – a perspective
Authors: Schulze W.
Published: April 2010

Abstract. Mass spectrometry based analysis of proteins is widely used to study cellular processes in model organisms. However, it has not yet routinely been applied in environmental research. Based on observations that protein can readily be detected as a component of dissolved organic matter (DOM), this article gives an example about the possible use of protein analysis in ecology and environmental sciences focusing on different terrestrial ecosystems. At this stage, there are two areas of interest: (1) the identification of phylogenetic groups contributing to the DOM protein pool, and (2) identification of the organismic origin of specific enzymes that are important for ecosystem processes. In this paper, mass spectrometric protein analysis was applied to identify proteins from DOM and organism-free surface water samples derived from different environments. It is concluded, that mass spectrometric protein analysis is capable of distinguishing phylogenetic origin of proteins from leachates of different soil horizons, and from various sources of terrestrial surface water. Current limitation is imposed by the limited knowledge of complete genomes of soil organisms. The protein analysis allows to relate protein presence to biogeochemical processes, and to identify the source organisms for specific active enzymes. Further applications, such as in pollution research are conceivable. In summary, the analysis of proteins opens a new area of research between the fields of microbiology and biogeochemistry.
DMS cycle in the marine ocean-atmosphere system – a global model study
Authors: Kloster S. , Feichter J. , Maier-Reimer E. , Six K. D. , Stier P. , Wetzel P.
Published: April 2010

Abstract. A global coupled ocean-atmosphere modeling system is established to study the production of Dimethylsulfide (DMS) in the ocean, the DMS flux to the atmosphere, and the resulting sulfur concentrations in the atmosphere. The DMS production and consumption processes in the ocean are simulated in the marine biogeochemistry model HAMOCC5, embedded in a ocean general circulation model (MPI-OM). The atmospheric model ECHAM5 is extended by the microphysical aerosol model HAM, treating the sulfur chemistry in the atmosphere and the evolution of the microphysically interacting internally- and externally mixed aerosol populations. We simulate a global annual mean DMS sea surface concentration of 1.8 nmol/l, a DMS emission of 28 Tg(S)/yr, a DMS burden in the atmosphere of 0.077 Tg(S), and a DMS lifetime of 1.0 days. To quantify the role of DMS in the atmospheric sulfur cycle we simulate the relative contribution of DMS-derived SO2 and SO4-2 to the total atmospheric sulfur concentrations. DMS contributes 25% to the global annually averaged SO2 column burden. For SO4-2 the contribution is 27%. The coupled model setup allows the evaluation of the simulated DMS quantities with measurements taken in the ocean and in the atmosphere. The simulated global distribution of DMS sea surface concentrations compares reasonably well with measurements. The comparison to SO4-2 surface concentration measurements in regions with a high DMS contribution to SO4-2 shows an overestimation by the model. This overestimation is most pronounced in the biologically active season with high DMS emissions and most likely caused by a too high simulated SO4-2 yield from DMS oxidation.
A simple parameterization of nitrogen limitation on primary productivity for global vegetation models
Authors: Krinner G. , Ciais P. , Viovy N. , Friedlingstein P.
Published: April 2010

Abstract. Nitrogen limitation of ecosystem productivity is ubiquitous, and it is thought that it has and will have a significant impact on net ecosystem productivity, and thus carbon sequestration, in the context of ongoing future increase of atmospheric CO2 concentration and climate change. However, many vegetation models do not represent nitrogen limitation, and might thus overestimate future terrestrial C sequestration. This work presents a simple parameterization of nitrogen limitation that can be easily implemented in vegetation models which do not yet include a complete nitrogen cycle. This parameterization is based on the ratio between heterotrophic respiration (considered a "proxy" of net mineralization rate) and net primary productivity of the ecosystem (considered a "proxy" of nitrogen demand). It is implemented in a global vegetation model and tested against site experiments of CO2 fertilization and soil warming. Furthermore, global simulations of past and future CO2 fertilization are carried out and compared to other model results and available estimates of global C sequestration. It is shown that when N limitation is taken into account using the simple parameterization presented here, the model reproduces fairly realistically the carbon dynamics observed under CO2 fertilization and soil warming.
Biological control of the terrestrial carbon sink
Authors: Schulze E.-D.
Published: April 2010

Abstract. This is a summary of the Vernadsky medal lecture given at the Nice EGU meeting in 2004. The lecture reviews the past (since the International Biological Program) and the future of our understanding of terrestrial carbon fluxes with focus on photosynthesis, respiration, primary, ecosystem, and biome productivity. Consideration is given to the interactions between biodiversity and biogeochemical processes.
The effect of temperature and salinity on the stable hydrogen isotopic composition of long chain alkenones produced by Emiliania huxleyi and Gephyrocapsa oceanica
Authors: Schouten S. , Ossebaar J. , Schreiber K. , Kienhuis M. V. M. , Langer G. , Bijma J.
Published: April 2010

Abstract. Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G. oceanica were on average depleted in D by 30 per mil compared to those of E. huxleyi when grown under similar conditions. The fractionation factor, αalkenones-H2O, ranged from 0.760 to 0.815 for E. huxleyi and from 0.741 to 0.788 for G. oceanica. There was no significant correlation of αalkenones-H2O with temperature but a positive linear correlation was observed between αalkenones-H2O and salinity with ~3 per mil change in fractionation per salinity unit. This suggests that salinity can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments and, vice versa, that δD can possibly be used as a proxy to estimate paleosalinity.
Seasonal variation of mono- and sesquiterpene emission rates of Scots pine
Authors: Hakola H. , Tarvainen V. , Bäck J. , Ranta H. , Bonn B. , Rinne J. , Kulmala M.
Published: April 2010

Abstract. The seasonal variation of mono-and sesquiterpene emission rates of Scots pine was measured from April to October in 2004. The emission rates were measured daily in the afternoons with the exception of weekends. Emissions were measured from two branches; one of them was debudded in May (branch A), while the other was allowed to grow new needles (branch B). The monoterpene emission pattern remained almost constant throughout the measurement period, Δ3-carene being the dominant monoterpene (50–70% of the VOC emission). The standard monoterpene emission potential was highest during early summer in June (the average of the two branches 0.55 μg−1(dw) h−1) and lowest during early autumn in September (the average of the two branches 0.12 μg g−1(dw) h−1). The monoterpene emission potential of branch A remained low also during October, whereas the emission potential of branch B was very high in October. The sesquiterpenes were mainly emitted during mid summer, the dominant sesquiterpene being β-caryophyllene. Branch A had a higher sesquiterpene emission potential than branch B and the emission maximum occurred concomitant with the high concentration of airborne pathogen spores indicating the defensive role of the sesquiterpene emissions. The sesquiterpene emissions were well correlated with linalool and 1,8-cineol emissions, but not with monoterpenes. Sesquiterpene and 1,8-cineol emissions were equally well described by the temperature dependent and the temperature and light dependent algorithms. This is due to the saturation of the light algorithm as the measurements were always conducted during high light conditions.
Atmospheric concentrations of carbon dioxide and its isotopic composition in southern Poland: comparison of high-altitude mountain site and a near-by urban environment
Authors: Chmura L. , Rozanski K. , Necki J. M. , Zimnoch M. , Kuc T. , Korus A.
Published: April 2010

Abstract. The results of regular observations of atmospheric CO2 mixing ratios and its carbon isotope composition (δ13C, Δ14C), carried out at two continental sites located in central Europe are presented and discussed. The sites (Kasprowy Wierch, 49°14' N, 19°59' E, 1989 m a.s.l.; Krakow, 50°04' N, 19°55' E, 220 m a.s.l.), are located in two contrasting environments: (i) high-altitude mountaneous area, relatively free of anthropogenic influences, and (ii) typical urban environment with numerous local sources of carbon dioxide. Despite of relative proximity of those sites (ca. 100 km), substantial differences in both the recorded CO2 levels and their isotopic composition were detected. The CO2 mixing ratios measured in the urban atmosphere revealed quasi-permanent excess concentration of this gas when compared with near-by background atmosphere. The annual mean CO2 concentration recorded in Krakow in 2004 was almost 10% higher than that recorded at high-altitude mountain site (Kasprowy Wierch). Such effect is occuring probably in all urban centers. Carbon isotopic composition of atmospheric CO2 proved to be efficient tool for identification the surface CO2 fluxes into the atmosphere related to fossil fuel burning and their influence on the recorded levels of this gas in the local atmosphere. The available records of Δ14C for Krakow and Kasprowy Wierch suggest gradual reduction of 14C-free CO2 fluxes into the urban atmosphere of Krakow in the past several years.
Nitrous oxide fluxes and nitrogen cycling along a pasture chronosequence in Central Amazonia, Brazil
Authors: Wick B. , Veldkamp E. , de Mello W. Z. , Keller M. , Crill P.
Published: April 2010

Abstract. We studied nitrous oxide (N2O) fluxes and soil nitrogen (N) cycling following forest conversion to pasture in the central Amazon near Santarém, Pará, Brazil. Two undisturbed forest sites and 27 pasture sites of 0.5 to 60 years were sampled once each during wet and dry seasons. In addition to soil-atmosphere fluxes of N2O we measured 27 soil chemical, soil microbiological and soil physical variables. Soil N2O fluxes were higher in the wet season than in the dry season. Fluxes of N2O from forest soils always exceeded fluxes from pasture soils and showed no consistent trend with pasture age. At our forest sites, nitrate was the dominant form of inorganic N both during wet and dry season. At our pasture sites nitrate generally dominated the inorganic N pools during the wet season and ammonium dominated during the dry season. Net mineralization and nitrification rates displayed large variations. During the dry season net immobilization of N was observed in some pastures. Compared to forest sites, young pasture sites (≤2 years) had low microbial biomass N and protease activities. Protease activity and microbial biomass N peaked in pastures of intermediate age (4 to 8 years) followed by consistently lower values in older pasture (10 to 60 years). The C/N ratio of litter was low at the forest sites (~25) and rapidly increased with pasture age reaching values of 60–70 at pastures of 15 years and older. Nitrous oxide emissions at our sites were controlled by C and N availability and soil aeration. Fluxes of N2O were negatively correlated to leaf litter C/N ratio, NH4+-N and the ratio of NO3--N to the sum of NO3--N + NH4+-N (indicators of N availability), and methane fluxes and bulk density (indicators of soil aeration status) during the wet season. During the dry season fluxes of N2O were positively correlated to microbial biomass N, β-glucosidase activity, total inorganic N stocks and NH4+-N. In our study region, pastures of all age emitted less N2O than old-growth forests, because of a progressive decline in N availability with pasture age combined with strongly anaerobic conditions in some pastures during the wet season.
N2O, NO and CH4 exchange, and microbial N turnover over a Mediterranean pine forest soil
Authors: Rosenkranz P. , Brüggemann N. , Papen H. , Xu Z. , Seufert G. , Butterbach-Bahl K.
Published: April 2010

Abstract. Trace gas exchange of N2O, NO/NO2 and CH4 between soil and the atmosphere was measured in a typical Mediterranean pine (Pinus pinaster) forest during two intensive field campaigns in spring and autumn 2003. Furthermore, gross and net turnover rates of N mineralization and nitrification as well as soil profiles of N2O and CH4 concentrations were determined. For both seasons a weak but significant N2O uptake from the atmosphere into the soil was observed. During the unusually dry and hot spring mean N2O uptake was -4.32 µg N m-2 h-1, whereas during the wet and mild autumn mean N2O uptake was -7.8 µg N m-2 h-1. The observed N2O uptake into the soil was linked to the very low availability of inorganic nitrogen at the study site. Organic layer gross N mineralization decreased from 5.06 mg N kg-1 SDW d-1 in springtime to 2.68 mg N kg-1 SDW d-1 in autumn. Mean NO emission rates were significantly higher in springtime (9.9 µ N m-2 h-1 than in autumn (1.4 µg N m-2 h-1. A significant positive correlation between NO emission rates and gross N mineralization as well as nitrification rates was found. The negative correlation between NO emissions and soil moisture was explained with a stimulation of aerobic NO uptake under N limiting conditions. Since NO2 deposition was continuously higher than NO emission rates the examined forest soil did function as a net NOx sink. Observed mean net CH4 uptake rates were in spring significantly higher (-73.34 µg C m-2 h-1 than in autumn (-59.67 µg C m-2 h-1. Changes in CH2 uptake rates were strongly negatively correlated with changes in soil moisture. The N2O and CH4 concentrations in different soil depths revealed the organic layer and the upper 10 cm of mineral soil as the most important soil horizons for N2O and CH4 consumption.
Is resistant soil organic matter more sensitive to temperature than the labile organic matter?
Authors: Fang C. , Smith P. , Smith J. U.
Published: April 2010

Abstract. A recent paper by Knorr et al. (2005) suggested that the decomposition of resistant soil organic matter is more temperature sensitive than labile organic matter. In Knorr et al.'s model, the reference decay rate was fixed for all pools of soil carbon. We refit Knorr et al.'s model but allow both the activation energy and the reference decay rate to vary among soil C pools. Under these conditions, a similar fit to measured data can be obtained without invoking the assumption that the resistant C pool is more temperature sensitive than the labile pool. Other published evidence does not unequivocally support Knorr et al.'s hypothesis of increased temperature sensitivity of resistant pools of soil carbon.
Does the temperature sensitivity of decomposition vary with soil organic matter quality?
Authors: Reichstein M. , Kätterer T. , Andrén O. , Ciais P. , Schulze E.-D. , Cramer W. , Papale D. , Valentini R.
Published: April 2010

Abstract. Knorr et al. (2005) concluded that soil organic carbon pools with longer turnover times are more sensitive to temperature. We show that this conclusion is equivocal, largely dependent on their specific selection of data and does not persist when the data set of Kätterer et al. (1998) is analysed in a more appropriate way. Further, we analyse how statistical properties of the model parameters may interfere with correlative analyses that relate the Q10 of soil respiration with the basal rate, where the latter is taken as a proxy for soil organic matter quality. We demonstrate that negative parameter correlations between Q10-values and base respiration rates are statistically expected and not necessarily provide evidence for a higher temperature sensitivity of low quality soil organic matter. Consequently, we reckon it is premature to conclude that stable soil carbon is more sensitive to temperature than labile carbon.
Inventories of N2O and NO emissions from European forest soils
Authors: Kesik M. , Ambus P. , Baritz R. , Brüggemann N. , Butterbach-Bahl K. , Damm M. , Duyzer J. , Horváth L. , Kiese R. , Kitzler B. , Leip A. , Li C. , Pihlatie M. , Pilegaard K. , Seufert G. , Simpson D. , Skiba U. , Smiatek G. , Vesala T. , Zechmeister-Boltenstern S.
Published: April 2010

Abstract. Forest soils are a significant source for the primary and secondary greenhouse gases N2O and NO. However, current estimates are still uncertain due to the still limited number of field measurements and the herein observed pronounced variability of N trace gas fluxes in space and time, which are due to the variation of environmental factors such as soil and vegetation properties or meteorological conditions. To overcome these problems we further developed a process-oriented model, the PnET-N-DNDC model, which simulates the N trace gas exchange on the basis of the processes involved in production, consumption and emission of N trace gases. This model was validated against field observations of N trace gas fluxes from 19 sites obtained within the EU project NOFRETETE, and shown to perform well for N2O (r=0.68, slope=0.76) and NO (r2=0.78, slope=0.73). For the calculation of a European-wide emission inventory we linked the model to a detailed, regionally and temporally resolved database, comprising climatic properties (daily resolution), and soil parameters, and information on forest areas and types for the years 1990, 1995 and 2000. Our calculations show that N trace gas fluxes from forest soils may vary substantial from year to year and that distinct regional patterns can be observed. Our central estimate of NO emissions from forest soils in the EU amounts to 98.4, 84.9 and 99.2 kt N yr-1, using meteorology from 1990, 1995 and year 2000, respectively. This is <1.0% of pyrogenic NOx emissions. For N2O emissions the central estimates were 86.8, 77.6 and 81.6 kt N yr-1, respectively, which is approx. 14.5% of the source strength coming from agricultural soils. An extensive sensitivity analysis was conducted which showed a range in NO emissions from 44.4 to 254.0 kt N yr-1 for NO and 50.7 to 96.9 kt N yr-1 for N2O, for year 2000 meteorology. The results show that process-oriented models coupled to a GIS are useful tools for the calculation of regional, national, or global inventories of biogenic N-trace gas emissions from soils. This work represents the most comprehensive effort to date to simulate NO and N2O emissions from European forest soils.
The relationship between ammonia emissions from a poultry farm and soil NO and N2O fluxes from a downwind source
Authors: Skiba U. , Dick J. , Storeton-West R. , Fernades-Lopez S. , Wood C. , Tang S. , van Dijk N.
Published: April 2010

Abstract. Intensive livestock farms emit large concentrations of NH3, most of which is deposited very close to the source. The presence of trees enhances the deposition. Rates to down wind forests can exceed 40 kg N ha-1. The steep gradient in large NH3 concentration and deposition at the edge of a downwind forest to background concentrations within a few hundred meters provides an ideal site to study the effect of different rates of N deposition on biological and chemical processes under similar environmental conditions. We have investigated the effect of different rates of NH3 deposition (62, 45, 24 and 5 kg NH3-N ha-1 y-1) on the flux of NO and N2O from soil in a mixed woodland downwind of a large poultry farm (160000 birds) in Scotland, which has been operating for about 40 years. Measurements were carried out for a 6 month period, with hourly NO flux measurements, daily N2O fluxes close to the farm and monthly at all sites and monthly cumulative wet and dry N deposition. The increased NH3 and NH4+ deposition to the woodland increased emissions of NO and N2O and soil available NH4+ and NO3- concentrations. Average NO and N2O fluxes measured 15, 25 and 45 m downwind of the farm were 111.2±41.1, 123.3±40.7, 38.3±28.8 µg NO-N m-2 h-1 and 9.9±7.5, 34.3±33.3 and 21.2±6.1 µg NO-N m-2 h-1, respectively. At the background site 270 m downwind the N2O flux was reduced to 1.75±2.1 µg N2O-N m-2 h-1. NO emissions were significantly influenced by seasonal and daily changes in soil temperature and followed a diurnal pattern with maximum emissions approximately 3h after noon. For N2O no consistent diurnal pattern was observed. Changes in soil moisture content had a less clear effect on the NO and N2O flux. On average the NO emissions expressed as a fraction of the elevated N deposited were 7.1% (at 15 m), 6% (at 25 m) and 2.3% (at 45 m) downwind of the farm, whereas for N2O the emissions were only 2.8% (at 15 m), 3% (at 25 m) and 3% (at 45 m) downwind. These emission fractions exceed the emission factor of 1% advised by the IPCC for N2O emissions resulting from atmospheric N deposition.