bluuebunny/crossref_metadata_2025 huggingface dataset:
Biotic stoichiometric controls on the deep ocean N:P ratio
Authors: Lenton T. M. , Klausmeier C. A.
Published: April 2010

Abstract. We re-examine what controls the deep ocean N:P ratio in the light of recent findings that the C:N:P stoichiometry of phytoplankton varies with growth rate, nutrient and light limitation, species and phylum, and that N2-fixation may be limited by Fe, temperature and/or light in large parts of the world ocean. In particular, we assess whether a systematic change in phytoplankton stoichiometry can alter the deep ocean N:P ratio. To do this we adapt recent models to include non-Redfieldian stoichiometry of phytoplankton and restriction of N2-fixers to a fraction of the surface ocean. We show that a systematic change in phytoplankton C:N:P can alter the concentrations of NO3 and PO4 in the deep ocean but cannot greatly alter their ratio, unless it also alters the N:P threshold for N2-fixation. This occurs if competitive dynamics set the N:P threshold for N2-fixation, in which case it remains close to the N:P requirement of non-fixers (rather than that of N2-fixers) and consequently so does the deep ocean N:P ratio. Then, even if N2-fixers are restricted to a fraction of the surface ocean, they reach higher densities there, minimising variations in deep ocean N:P. Theoretical limits on the N:P requirements of phytoplankton suggest that whilst the deep ocean has been well oxygenated (i.e. since the Neoproterozoic, with the possible exception of Oceanic Anoxic Events), its N:P ratio is unlikely to have varied by more than a factor of two in either direction. Within these bounds, evolutionary changes in phytoplankton composition, and increased phosphorus weathering due to the biological colonisation of the land surface, are predicted to have driven long-term changes in ocean composition.
Spatial variation in N2-fixation rate and diazotroph activity in the Tropical Atlantic
Authors: Montoya J. P. , Voss M. , Capone D. G.
Published: April 2010

Abstract. A variety of N2-fixers occur in oligotrophic waters and these diazotrophs make a substantial contribution to the nitrogen budget of the upper water column. A synthesis of previously published and new rate measurements for the North Atlantic provides insight into the role of two different groups of N2-fixers (Trichodesmium and small diazotrophs) in supporting N2 fixation in the tropical Atlantic. The highest rates of N2 fixation occurred in the western part of the basin, but the full data set showed no significant difference between the eastern and western parts of the basin in overall rates of N2-fixation by the two groups of diazotrophs. N2-fixation by Trichodesmium was strongly dominant in the western part of the basin while small diazotrophs played a much larger role to the east of 40° W. The reasons for this shift in dominance are unclear, as is the identity of the small organisms fixing N2 in the water column.
Minor changes in soil organic carbon and charcoal concentrations detected in a temperate deciduous forest a year after an experimental slash-and-burn
Authors: Eckmeier E. , Gerlach R. , Skjemstad J. O. , Ehrmann O. , Schmidt M. W. I.
Published: April 2010

Abstract. Anthropogenic fires affected the temperate deciduous forests of Central Europe over millennia. Biomass burning releases carbon to the atmosphere and produces charcoal, which potentially contributes to the stable soil carbon pools and is an important archive of environmental history. The fate of charcoal in soils of temperate deciduous forests, i.e. the processes of charcoal incorporation and transportation and the effects on soil organic matter are still not clear. We investigated the effects of slash-and-burn at a long-term experimental burning site and determined soil organic carbon and charcoal carbon concentrations as well as the soil lightness of colour (L*) in the topmost soil material (0–1, 1–2.5 and 2.5–5 cm depths) before, immediately after the fire and one year later. The main results are that (i) only a few of the charcoal particles from the forest floor were incorporated into the soil matrix, presumably by soil mixing animals. In the 0–1 cm layer, during one year, the charcoal C concentration increased only by 0.4 g kg−1 and the proportion of charcoal C to SOC concentration increased from 2.8 to 3.4%; (ii) the SOC concentrations did not show any significant differences; (iii) soil lightness decreased significantly in the topmost soil layer and correlated well with the concentrations of charcoal C (r=−0.87**) and SOC (r=−0.94**) in the samples from the 0–5 cm layer. We concluded that Holocene biomass burning could have influenced soil charcoal concentrations and soil colour.
The full greenhouse gas balance of an abandoned peat meadow
Authors: Hendriks D. M. D. , van Huissteden J. , Dolman A. J. , van der Molen M. K.
Published: April 2010

Abstract. Globally, peat lands are considered to be a sink of CO2, but a source when drained. Additionally, wet peat lands are thought to emit considerable amounts of CH4 and N2O. Hitherto, reliable and integrated estimates of emissions and emission factors for this type of land cover have been lacking and the effects of wetland restoration on methane emissions have been poorly quantified. In this paper we estimate the full greenhouse gas (GHG) balance of a restored natural peat land by determining the fluxes of CO2, CH4 and N2O through atmosphere and water, while accounting for the different Global Warming Potentials (GWP's). The site is an abandoned agricultural peat meadow, which has been converted into a wetland nature reserve ten years ago, after which the water level was raised. GHG fluxes were measured continuously with an eddy covariance system (CO2) and flux chamber measurements (CH4 and N2O). Meteorological and hydrological measurements were collected as well. With growing seasons of respectively 192, 168 and 129 days, the annual net ecosystem exchange of CO2 (NEE) was −446+±83 g C m−2 yr−1 for 2004, −311±58 g C m−2 yr−1 for 2005 and −232±57 g m−2 yr−1 for 2006. Ecosystem respiration (Reco) was estimated as 869±668 g C m−2 yr−1 for 2004, 866±666 g C m−2 yr−1 for 2005 and 924±711 g C m−2 yr−1 for 2006. CH4 emissions from the saturated land and water surfaces were high compared to the relatively dry land. Annual weighted CH4 emissions were 31.27±20.40 g C m−2 yr−1 for 2005 and 32.27±21.08 g C m−2 yr−1 for 2006. N2O fluxes were too low to be of significance. The water balance of the area was dominated by precipitation and evapotranspiration and therefore fluxes of carbon and CH4 through seepage, infiltration and drainage were relatively small (17.25 g C m−2 yr−1). The carbon-balance consisted for the largest part of CO2 uptake, CO2 respiration and CH4 emission from water saturated land and water. CO2 emission has decreased significantly as result of the raised water table, while CH4 fluxes have increased. In GWP's the area was a small net GHG sink given as CO2-equiv. of −86 g m−2 yr−1 (over a 100-year period).
Scaling net ecosystem production and net biome production over a heterogeneous region in the western United States
Authors: Turner D. P. , Ritts W. D. , Law B. E. , Cohen W. B. , Yang Z. , Hudiburg T. , Campbell J. L. , Duane M.
Published: April 2010

Abstract. Bottom-up scaling of net ecosystem production (NEP) and net biome production (NBP) was used to generate a carbon budget for a large heterogeneous region (the state of Oregon, 2.5×105 km2) in the western United States. Landsat resolution (30 m) remote sensing provided the basis for mapping land cover and disturbance history, thus allowing us to account for all major fire and logging events over the last 30 years. For NEP, a 23-year record (1980–2002) of distributed meteorology (1 km resolution) at the daily time step was used to drive a process-based carbon cycle model (Biome-BGC). For NBP, fire emissions were computed from remote sensing based estimates of area burned and our mapped biomass estimates. Our estimates for the contribution of logging and crop harvest removals to NBP were from the model simulations and were checked against public records of forest and crop harvesting. The predominately forested ecoregions within our study region had the highest NEP sinks, with ecoregion averages up to 197 gC m−2 yr−1. Agricultural ecoregions were also NEP sinks, reflecting the imbalance of NPP and decomposition of crop residues. For the period 1996–2000, mean NEP for the study area was 17.0 TgC yr−1, with strong interannual variation (SD of 10.6). The sum of forest harvest removals, crop removals, and direct fire emissions amounted to 63% of NEP, leaving a mean NBP of 6.1 TgC yr−1. Carbon sequestration was predominantly on public forestland, where the harvest rate has fallen dramatically in the recent years. Comparison of simulation results with estimates of carbon stocks, and changes in carbon stocks, based on forest inventory data showed generally good agreement. The carbon sequestered as NBP, plus accumulation of forest products in slow turnover pools, offset 51% of the annual emissions of fossil fuel CO2 for the state. State-level NBP dropped below zero in 2002 because of the combination of a dry climate year and a large (200 000 ha) fire. These results highlight the strong influence of land management and interannual variation in climate on the terrestrial carbon flux in the temperate zone.
Suitability of quantum cascade laser spectroscopy for CH4 and N2O eddy covariance flux measurements
Authors: Kroon P. S. , Hensen A. , Jonker H. J. J. , Zahniser M. S. , van 't Veen W. H. , Vermeulen A. T.
Published: April 2010

Abstract. A quantum cascade laser spectrometer was evaluated for eddy covariance flux measurements of CH4 and N2O using three months of continuous measurements at a field site. The required criteria for eddy covariance flux measurements including continuity, sampling frequency, precision and stationarity were examined. The system operated continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system for the infrared detector was employed to provide unattended operation of the system. The electronic sampling frequency was 10 Hz, however, the flow response time was 0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of 2.9 and 0.5 ppb Hz−1/2 was obtained for CH4 and N2O, respectively. Accuracy was assured by frequent calibrations using low and high standard additions. Drifts in the system were compensated by using a 120 s running mean filter. The average CH4 and N2O exchange was 512 ngC m−2 s−1 (2.46 mg m−2 hr−1) and 52 ngN m−2 s−1 (0.29 mg m−2 hr−1). Given that 40% of the total N2O emission was due to a fertilizing event.
Variability of annual CO2 exchange from Dutch grasslands
Authors: Jacobs C. M. J. , Jacobs A. F. G. , Bosveld F. C. , Hendriks D. M. D. , Hensen A. , Kroon P. S. , Moors E. J. , Nol L. , Schrier-Uijl A. , Veenendaal E. M.
Published: April 2010

Abstract. An intercomparison is made of the Net Ecosystem Exchange of CO2, NEE, for eight Dutch grassland sites: four natural grasslands, two production grasslands and two meteorological stations within a rotational grassland region. At all sites the NEE was determined during at least 10 months per site, using the eddy-covariance (EC) technique, but in different years. The NEE does not include any import or export other than CO2. The photosynthesis-light response analysis technique is used along with the respiration-temperature response technique to partition NEE into Gross Primary Production (GPP) and Ecosystem Respiration (Re) and to obtain the eco-physiological characteristics of the sites at the field scale. Annual sums of NEE, GPP and Re are then estimated using the fitted response curves with observed radiation and air temperature from a meteorological site in the centre of The Netherlands as drivers. These calculations are carried out for four years (2002–2005). Land use and management histories are not considered. The estimated annual Re for all individual sites is more or less constant per site and the average for all sites amounts to 1390±30 gC m−2 a−1. The narrow uncertainty band (±2%) reflects the small differences in the mean annual air temperature. The mean annual GPP was estimated to be 1325 g C m−2 a−1, and displays a much higher standard deviation, of ±110 gC m−2 a−1 (8%), which reflects the relatively large variation in annual solar radiation. The mean annual NEE amounts to –65±85 gC m−2 a−1. From two sites, four-year records of CO2 flux were available and analyzed (2002–2005). Using the weather record of 2005 with optimizations from the other years, the standard deviation of annual GPP was estimated to be 171–206 gC m−2 a−1 (8–14%), of annual Re 227–247 gC m−2 a−1 (14–16%) and of annual NEE 176–276 gC m−2 a−1. The inter-site standard deviation was higher for GPP and Re, 534 gC m−2 a−1 (37.3%) and 486 gC m−2 a−1 (34.8%), respectively. However, the inter-site standard deviation of NEE was similar to the interannual one, amounting to 207 gC m−2 a−1. Large differences occur due to soil type. The grasslands on organic (peat) soils show a mean net release of CO2 of 220±90 g C m−2 a−1 while the grasslands on mineral (clay and sand) soils show a mean net uptake of CO2 of 90±90 g C m−2 a−1. If a weighing with the fraction of grassland on organic (20%) and mineral soils (80%) is applied, an average NEE of 28 ±90 g C m−2 a−1 is found. The results from the analysis illustrate the need for regionally specific and spatially explicit CO2 emission estimates from grassland.
The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia
Authors: van der Molen M. K. , van Huissteden J. , Parmentier F. J. W. , Petrescu A. M. R. , Dolman A. J. , Maximov T. C. , Kononov A. V. , Karsanaev S. V. , Suzdalov D. A.
Published: April 2010

Abstract. Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, Reco and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m−2 yr−1, which is composed of an Reco=+141 g C m−2 yr−1 and GPP=−232 g C m−2 yr−1. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (Rg<200 W m−2), whereas Reco depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO2e m−2 yr−1, so that the greenhouse gas balance was −64 g C-CO2e m−2 yr−1. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition.
Inter- and intra-specimen variability masks reliable temperature control on shell Mg/Ca ratios in laboratory- and field-cultured Mytilus edulis and Pecten maximus (bivalvia)
Authors: Freitas P. S. , Clarke L. J. , Kennedy H. A. , Richardson C. A.
Published: April 2010

Abstract. The Mg/Ca ratios of biogenic calcite is commonly seen as a valuable palaeo-proxy for reconstructing past ocean temperatures. The temperature dependence of Mg/Ca ratios in bivalve calcite has been the subject of contradictory observations. The palaeoceanographic use of a geochemical proxy is dependent on initial, rigorous calibration and validation of relationships between the proxy and the ambient environmental variable to be reconstructed. Shell Mg/Ca ratio data are reported for the calcite of two bivalve species, Mytilus edulis (common mussel) and Pecten maximus (king scallop), which were grown in laboratory culturing experiments at controlled and constant aquarium seawater temperatures over a range from ~10 to ~20°C. Furthermore, Mg/Ca ratio data of laboratory- and field-grown M. edulis specimens were compared. Only a weak, albeit significant, shell Mg/Ca ratio–temperature relationship was observed in the two bivalve species: M. edulis (r2=0.37, p
Wetland succession in a permafrost collapse: interactions between fire and thermokarst
Authors: Myers-Smith I. H. , Harden J. W. , Wilmking M. , Fuller C. C. , McGuire A. D. , Chapin F. S.
Published: April 2010

Abstract. To determine the influence of fire and thermokarst in a boreal landscape, we investigated peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate ~600 years of vegetation succession with a transition from a terrestrial forest to a sedge-dominated wetland over 100 years ago, and to a Sphagnum-dominated peatland in approximately 1970. The shift from sedge to Sphagnum, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature record from Fairbanks. This concurrent wetland succession and reduced growth of black spruce trees indicates a step-wise ecosystem-level response to a change in regional climate. In 2001, fire was observed coincident with permafrost collapse and resulted in lateral expansion of the peatland. These observations and the peat profile suggest that future warming and/or increased fire disturbance could promote permafrost degradation, peatland expansion, and increase carbon storage across this landscape; however, the development of drought conditions could reduce the success of both black spruce and Sphagnum, and potentially decrease the long-term ecosystem carbon storage.
Paleovegetation reconstruction using δ13C of Soil Organic Matter
Authors: Wang G. , Feng X. , Han J. , Zhou L. , Tan W. , Su F.
Published: April 2010

Abstract. The relative contributions of C3 and C4 plants to vegetation at a given locality may be estimated by means of δ13C of soil organic matter. This approach holds a great potential for paleoecological reconstruction using paleosols. However, two main uncertainties exist, which limits the accuracy of this application. One is δ13C-enrichment as the plant carbon becomes incorporated into soil organic matter. The other is due to environmental influences on δ13C of plants. Two types of data were collected and analyzed with an objective of narrowing the error of paleovegetation reconstruction. First, we investigated δ13C variations of 557 C3 and 136 C4 plants along a precipitation gradient in North China. A strong negative correlation is found between the δ13C value of C3 plants averaged for each site and the annual precipitation with a coefficient of −0.40‰/100mm, while no significant coefficients were found for C4 plants. Second, we measured δ13C of soil organic matters for 14 soil profiles at three sites. The isotopic difference between vegetation and soil organic matter are evaluated to be 1.8‰ for the surface soil and 2.8‰ for the soil at the bottom of soil profiles. We conducted a sample reconstruction of paleovegetation at the central Chinese Loess Plateau during the Holocene and the Last Glacial (LG), and conclude that, without corrections for δ13C-enrichment by decomposition, the C4 abundance would be overestimated. The importance and uncertainties of other corrections are also discussed.
Distribution and fluxes of aggregates >100 μm in the upper kilometer of the South-Eastern Pacific
Authors: Guidi L. , Gorsky G. , Claustre H. , Miquel J. C. , Picheral M. , Stemmann L.
Published: April 2010

Abstract. Large sinking particles transport organic and inorganic matter into the deeper layers of the oceans. Between 70 and 90% of the aggregates exported from the surface mixed layer are disaggregated within the upper 1000 m. This decrease with depth indicates that fragmentation and remineralization processes are intense during sedimentation. Generally, the estimates of vertical flux rely on sediment trap data but difficulties inherent in their design limit the reliability of this information. During the BIOSOPE study in the south-eastern Pacific, 76 vertical casts using the Underwater Video Profiler (UVP) and deployments of drifting sediment traps provided an opportunity to fit the UVP data to sediment trap flux measurements. We applied the calculated UVP flux in the upper 1000 m to the whole 8000 km BIOSOPE transect. Comparison between the large particulate material (LPM) abundance and the estimated fluxes from both UVP and sediment traps showed different patterns in different regions. On the western end of the BIOSOPE section the standing stock of particles in the surface layer was high but the export between 150 and 250 m was low. Below this layer the flux values increased. High values of about 30% of the calculated UVP maximum surface zone flux were observed below 900 m at the HNLC station. The South Pacific Gyre exported about 2 mg m−2 d−1. While off Chilean coast 95% of the surface mixed layer matter was disaggregated, remineralized or advected in the upper kilometer, 20% of the surface zone flux was observed below 900 m near the Chilean coast. These results suggest that the export to deep waters is spatially heterogeneous and related to the different biotic and abiotic factors.
Do we miss the hot spots? – The use of very high resolution aerial photographs to quantify carbon fluxes in peatlands
Authors: Becker T. , Kutzbach L. , Forbrich I. , Schneider J. , Jager D. , Thees B. , Wilmking M.
Published: April 2010

Abstract. Accurate determination of carbon balances in heterogeneous ecosystems often requires the extrapolation of point based measurements. The ground resolution (pixel size) of the extrapolation base, e.g. a land-cover map, might thus influence the calculated carbon balance, in particular if biogeochemical hot spots are small in size. In this paper, we test the effects of varying ground resolution on the calculated carbon balance of a boreal peatland consisting of hummocks (dry), lawns (intermediate) and flarks (wet surfaces). The generalizations in lower resolution imagery led to biased area estimates for individual micro-site types. While areas of lawns and hummocks were stable below a threshold resolution of ~60 cm, the maximum of the flark area was located at resolutions below 25 cm and was then decreasing with coarsening resolution. Using a resolution of 100 cm instead of 6 cm led to an overestimation of total CO2 uptake of the studied peatland area (approximately 14 600 m2) of ~5% and an underestimation of total CH4 emission of ~6%. To accurately determine the surface area of scattered and small-sized micro-site types in heterogeneous ecosystems (e.g. flarks in peatlands), a minimum ground resolution appears necessary. In our case this leads to a recommended resolution of 25 cm, which can be derived by conventional airborne imagery. The usage of high resolution imagery from commercial satellites, e.g. Quickbird, however, is likely to underestimate the surface area of biogeochemical hot spots. It is important to note that the observed resolution effect on the carbon balance estimates can be much stronger for other ecosystems than for the investigated peatland. In the investigated peatland the relative hot spot area of the flarks is very small and their hot spot characteristics with respect to CH4 and CO2 fluxes is rather modest.
Fluxes and 13C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought
Authors: Knorr K.-H. , Glaser B. , Blodau C.
Published: April 2010

Abstract. Peatlands contain a carbon stock of global concern and significantly contribute to the global methane burden. The impact of drought and rewetting on carbon cycling in peatland ecosystems is thus currently debated. We studied the impact of experimental drought and rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing drought for 50 days. In one of the mesocosms, vegetation had been removed. Net production of CH4 was calculated from mass balances in the peat and emission using static chamber measurements. Results were compared to 13C isotope budgets of CO2 and CH4 and energy yields of acetoclastic and hydrogenotrophic methanogenesis. Drought retarded methane production after rewetting for days to weeks and promoted methanotrophic activity. Based on isotope and flux budgets, aerobic soil respiration contributed 32–96% in the wet treatment and 86–99% in the other treatments. Drying and rewetting did not shift methanogenic pathways according to δ13C ratios of CH4 and CO2. Although δ13C ratios indicated a prevalence of hydrogenotrophic methanogenesis, free energies of this process were small and often positive on the horizon scale. This suggests that methane was produced very locally. Fresh plant-derived carbon input apparently supported respiration in the rhizosphere and sustained methanogenesis in the unsaturated zone, according to a 13C-CO2 labelling experiment. The study documents that drying and rewetting in a rich fen soil may have little effect on methanogenic pathways, but result in rapid shifts between methanogenesis and methanotrophy. Such shifts may be promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis occurred locally even when conditions were not conducive for this process in the bulk peat.
Changes of the potential distribution area of French Mediterranean forests under global warming
Authors: Gaucherel C. , Guiot J. , Misson L.
Published: April 2010

Abstract. This work aims at understanding future spatial and temporal distributions of tree species in the Mediterranean region of France under various climates. We focused on two different species (Pinus Halepensis and Quercus Ilex) and compared their growth under the IPCC-B2 climate scenario in order to quantify significant changes between present and future. The influence of environmental factors such as atmospheric CO2 increase and topography on the tree growth has also been quantified. We modeled species growth with the help of a process-based model (MAIDEN), previously calibrated over measured ecophysiological and dendrochronological series with a Bayesian scheme. The model was fed with the ARPEGE – MeteoFrance climate model, combined with an explicit increase in CO2 atmospheric concentration. The main output of the model gives the carbon allocation in boles and thus tree production. Our results show that the MAIDEN model is correctly able to simulate pine and oak production in space and time, after detailed calibration and validation stages. Yet, these simulations, mainly based on climate, are indicative and not predictive. The comparison of simulated growth at end of 20th and 21st centuries, show a shift of the pine production optimum from about 650 to 950 m due to 2.5 K temperature increase, while no optimum has been found for oak. With the direct effect of CO2 increase taken into account, both species show a significant increase in productivity (+26 and +43% for pine and oak respectively) at the end of the 21st century. While both species have different growth mechanisms, they have a good chance to extend their spatial distribution and their elevation in the Alps during the 21st century under the IPCC-B2 climate scenario. This extension is mainly due to the CO2 fertilization effect.
Marine ecosystem community carbon and nutrient uptake stoichiometry under varying ocean acidification during the PeECE III experiment
Authors: Bellerby R. G. J. , Schulz K. G. , Riebesell U. , Neill C. , Nondal G. , Heegaard E. , Johannessen T. , Brown K. R.
Published: April 2010

Abstract. Changes to seawater inorganic carbon and nutrient concentrations in response to the deliberate CO2 perturbation of natural plankton assemblages were studied during the 2005 Pelagic Ecosystem CO2 Enrichment (PeECE III) experiment. Inverse analysis of the temporal inorganic carbon dioxide system and nutrient variations was used to determine the net community stoichiometric uptake characteristics of a natural pelagic ecosystem perturbed over a range of pCO2 scenarios (350, 700 and 1050 μatm). Nutrient uptake showed no sensitivity to CO2 treatment. There was enhanced carbon production relative to nutrient consumption in the higher CO2 treatments which was positively correlated with the initial CO2 concentration. There was no significant calcification response to changing CO2 in Emiliania huxleyi by the peak of the bloom and all treatments exhibited low particulate inorganic carbon production (~15 μmol kg−1). With insignificant air-sea CO2 exchange across the treatments, the enhanced carbon uptake was due to increase organic carbon production. The inferred cumulative C:N:P stoichiometry of organic production increased with CO2 treatment from 1:6.3:121 to 1:7.1:144 to 1:8.25:168 at the height of the bloom. This study discusses how ocean acidification may incur modification to the stoichiometry of pelagic production and have consequences for ocean biogeochemical cycling.
CO2 enrichment increases nutrient leaching from model forest ecosystems in subtropical China
Authors: Liu J. X. , Zhang D. Q. , Zhou G. Y. , Faivre-Vuillin B. , Deng Q. , Wang C. L.
Published: April 2010

Abstract. The effect of high atmospheric CO2 concentrations on the dynamics of mineral nutrient is not well documented, especially for subtropical China. We used model forest ecosystems in open-top chambers to study the effects of CO2 enrichment alone and together with N addition on the dynamics of soil cations and anions. Two years of exposure to a 700 ppm CO2 atmospheric concentration resulted in increased annual nutrient losses by leaching below 70 cm soil profile. Compared to the control, net Mg2+ losses increased by 385%, K+ by 223%, Ca2+ by 167% and NO3−-N by 108%, respectively. Increased losses following exposure to elevated CO2 were related to both faster weathering of minerals/organic matter decomposition and greater amounts of leaching water. Net annual nutrient losses in the high CO2 concentration chambers reached 22.2 kg ha−1 year−1 for K+, 171.3 kg ha−1 year−1 for Ca2+, 8.2 kg ha−1 year−1 for Mg2+ and about 2 kg ha−1 year−1 for NO3−-N. The N addition alone had no significant effect on the mineral nutrient leaching losses. However, addition of N together with the high CO2 treatment significantly reduced mineral nutrient losses.We hypothesize that forests in subtropical China might suffer from nutrient limitation and reduction in plant biomass under elevated CO2 concentration due to mineral leaching losses in the future.
Meeting the challenge of mapping peatlands with remotely sensed data
Authors: Krankina O. N. , Pflugmacher D. , Friedl M. , Cohen W. B. , Nelson P. , Baccini A.
Published: April 2010

Abstract. Boreal peatlands play a major role in carbon and water cycling and other global environmental processes but understanding this role is constrained by inconsistent representation of peatlands on, or omission from, many global land cover maps. The comparison of several widely used global and continental-scale databases on peatland distribution with a detailed map for the St. Petersburg region of Russia showed significant under-reporting of peatland area, or even total omission. Analysis of the spatial agreement and disagreement with the detailed regional map indicated that the error of comission (overestimation) was significantly lower than the error of omission (underestimation) which means, that overall, peatlands were correctly classified as such in coarse resolution datasets but a large proportion (74–99%) was overlooked. The coarse map resolution alone caused significant omission of peatlands in the study region. In comparison to categorical maps, continuous field mapping approach utilizing MODIS sensor data showed potential for a greatly improved representation of peatlands on coarse resolution maps. Analysis of spectral signatures of peatlands with different types of surface vegetation suggested that improved mapping of boreal peatlands on categorical maps is feasible. The lower reflectance of treeless peatlands in the near- and shortwave-infrared parts of the electromagnetic spectrum is consistent with the spectral signature of sphagnum mosses. However, when trees are present, the canopy architecture appears to be more important in defining the overall spectral reflectance of peatlands. A research focus on developing remote sensing methods for boreal peatlands is needed for adequate characterization of their global distribution.
Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)
Authors: Hippler D. , Kozdon R. , Darling K. F. , Eisenhauer A. , Nägler T. F.
Published: April 2010

Abstract. The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability.
The ACCENT-VOCBAS field campaign on biosphere-atmosphere interactions in a Mediterranean ecosystem of Castelporziano (Rome): site characteristics, climatic and meteorological conditions, and eco-physiology of vegetation
Authors: Fares S. , Mereu S. , Scarascia Mugnozza G. , Vitale M. , Manes F. , Frattoni M. , Ciccioli P. , Gerosa G. , Loreto F.
Published: April 2010

Abstract. Biosphere-atmosphere interactions were investigated on a sandy dune Mediterranean ecosystem in a field campaign held in 2007 within the frame of the European Projects ACCENT and VOCBAS. The campaign was carried out in the Presidential estate of Castelporziano, a peri-urban park close to Rome. Former campaigns (e.g. BEMA) performed in Castelporziano investigated the emission of biogenic volatile organic compounds (BVOC). These campaigns focused on pseudosteppe and evergreen oak groves whereas the contribution of the largely biodiverse dune vegetation, a prominent component of the Mediterranean ecosystem, was overlooked. While specific aspects of the campaign will be discussed in companion papers, the general climatic and physiological aspects are presented here, together with information regarding BVOC emission from the most common plant species of the dune ecosystem. During the campaign regular air movements were observed, dominated by moderate nocturnal land breeze and diurnal sea breeze. A regular daily increase of ozone concentration in the air was also observed, but daily peaks of ozone were lower than those measured in summer on the same site. The site was ideal as a natural photochemical reactor to observe reaction, transport and deposition processes occurring in the Mediterranean basin, since the sea-land breeze circulation allowed a strong mixing between biogenic and anthropogenic emissions and secondary pollutants. Measurements were run in May, when plant physiological conditions were optimal, in absence of severe drought and heat stress. Foliar rates of photosynthesis and transpiration were as high as generally recorded in unstressed Mediterranean sclerophyllous plants. Most of the plant species emitted high level of monoterpenes, despite measurements being made in a period in which emissions of volatile isoprenoids could be restrained by developmental and environmental factors, such as leaf age and relatively low air temperature. Emission of isoprene was generally low. Accounting for the high monoterpene spring emission of the dune ecosystem may be important to correct algorithms at regional and ecosystem levels, and to interpret measurements of fluxes of volatile isoprenoids and secondary pollutants.
A new European plant-specific emission inventory of biogenic volatile organic compounds for use in atmospheric transport models
Authors: Karl M. , Guenther A. , Köble R. , Leip A. , Seufert G.
Published: April 2010

Abstract. We present a new European plant-specific emission inventory for isoprene, monoterpenes, sesquiterpenes and oxygenated VOC (OVOC), on a spatial resolution of 0.089×0.089 degrees, for implementation in atmospheric transport models. The inventory incorporates more accurate data on foliar biomass densities from several litterfall databases that became available in the last years for the main tree species in Europe. A bioclimatic correction factor was introduced to correct the foliar biomass densities of trees and crops for the different plant growth conditions that can be found in Pan-Europe. Long-term seasonal variability of agriculture and forest emissions was taken into account by implementing a new growing season concept. The 2004–2005 averaged annual total biogenic volatile organic compound (BVOC) emissions for the Pan-European domain are estimated to be about 12 Tg with a large contribution from the OVOC class of about 4.5 Tg and from monoterpenes of about 4 Tg. Annual isoprene emissions are found to be about 3.5 Tg, insensitive to the chosen emission algorithm. Emissions of OVOC were found to originate to a large extent from agriculture. Further experiments on crop emissions should be carried out to check the validity of the applied standard emission factors. The new inventory aims at a fully transparent and verifiable aggregation of detailed land use information and at the inclusion of plant-specific emission data. Though plant-specific land use data is available with relatively high accuracy, a lack of experimental biomass densities and emission data on terpenes, sesquiterpenes and oxygenated VOC, in particular for agricultural plants, currently limits the setup of a highly accurate plant-specific emission inventory.
Contrasting carbon dioxide fluxes between a drying shrub wetland in Northern Wisconsin, USA, and nearby forests
Authors: Sulman B. N. , Desai A. R. , Cook B. D. , Saliendra N. , Mackay D. S.
Published: April 2010

Abstract. Wetland biogeochemistry is strongly influenced by water and temperature dynamics, and these interactions are currently poorly represented in ecosystem and climate models. A decline in water table of approximately 30 cm was observed at a wetland in Northern Wisconsin, USA over a period from 2001–2007, which was highly correlated with an increase in daily soil temperature variability. Eddy covariance measurements of carbon dioxide exchange were compared with measured CO2 fluxes at two nearby forests in order to distinguish wetland effects from regional trends. As wetland water table declined, both ecosystem respiration and ecosystem production increased by over 20% at the wetland, while forest CO2 fluxes had no significant trends. Net ecosystem exchange of carbon dioxide at the wetland was not correlated with water table, but wetland evapotranspiration decreased substantially as the water table declined. These results suggest that changes in hydrology may not have a large impact on shrub wetland carbon balance over inter-annual time scales due to opposing responses in both ecosystem respiration and productivity.
Short term summer to autumn variability of dissolved lipid classes in the Ligurian sea (NW Mediterranean)
Authors: Goutx M. , Guigue C. ,   D. Aritio D., Ghiglione J. F. , Pujo-Pay M. , Raybaud V. , Duflos M. , Prieur L.
Published: April 2010

Abstract. Changes in concentration and composition of Iatroscan-measured dissolved lipids were examined at a daily to month scale, in relation to the hydrological and biological context at a central site of the Ligurian sea, NW Mediterranean during the PECHE-DYNAPROC 2 experiment (14 September to 17 October 2004). Lipid concentrations (excluding hydrocarbons) (TLd-HC) and TLd-HC to DOC ratios in the 0–1000 m water column, varied from 5.3 to 48.5 μg l−1 and 0.01 to 0.09, respectively. The highest TLd-HC concentration values were found in the 0–50 m surface layer, coinciding with phytoplankton biomass. Significant correlations (p<0.01, n=87) between glycolipids from chloroplast membranes, namely the monogalactosyldiacylglycerols, a major component of dissolved lipids (25.1±10.8% of TLd-HC, n=166), and various phytoplankton pigments (chlorophyll cs-170, violaxanthin, diadinoxanthin, zeaxanthin, and lutein), suggested that picoeucaryote phytoplankton were a major source of dissolved lipids. Lipid metabolites (free fatty acids, alcohols, diacylglycerols and monoacylglycerols), an other important component of TLd-HC (37.6±11.1%, n=166), showed a greater degree of degradation of lipids in this transitional period than previously observed earlier in the year. Zooplankton wax and steryl ester biomarkers (WSE) and triacylglycerols showed a distinct periodicity in the mesopelagic layer throughout the period investigated. Concentrations of WSE (5.5–13.6 μg/l) increased in the 0–150 m surface layer, mid-way through the cruise (4–6 October), before the winter mixing. WSE were observed later and deeper in the mesopelagic layer (6–11 October), accompanied by rebounds in hydrocarbons (6–8 October) and phospholipid concentrations (12 October) in the 400–1000 m depth layer. Zooplankton migration and/or fecal pellet egestion, followed by DOM release from POM, were likely responsible for the appearance of these lipid signatures in the mesopelagic layer. Because we observed these signatures during low wind period only (<15 knots: 28 September–12 October), it may indicate that this organic matter transfer to depth was related to undisturbed trophic web in the water column above. The low salinity water lenses that appeared twice during the cruise in the 40–80 m surface layer had little effect on dissolved lipid concentrations. Lower concentrations in phosphoglycerides and hydrocarbons (HC) than in nearby sea water suggested different microbial assemblages and different level of HC contamination in this low salinity water.
Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France
Authors: Brut A. , Rüdiger C. , Lafont S. , Roujean J.-L. , Calvet J.-C. , Jarlan L. , Gibelin A.-L. , Albergel C. , Le Moigne P. , Soussana J.-F. , Klumpp K. , Guyon D. , Wigneron J.-P. , Ceschia E.
Published: April 2010

Abstract. A CO2-responsive land surface model (the ISBA-A-gs model of Météo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the interannual variability of LAI at a regional scale, is assessed with satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and two products are based on MODIS data. The comparison reveals discrepancies between the satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops than the satellite observations, which may be due to a saturation effect within the satellite signal or to uncertainties in model parameters. The simulated leaf onset presents a significant delay for C3 crops and mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale.
Anthropogenic carbon distribution in the eastern South Pacific Ocean
Authors: Goyet C. , Ito Gonçalves R. , Touratier F.
Published: April 2010

Abstract. We present results of the CO2/carbonate system from the BIOSOPE cruise in the Eastern South Pacific Ocean, in an area not sampled previously. In particular, we present estimates of the anthropogenic carbon (C>TrOCAant) distribution in the upper 1000 m of this region using the TrOCA method. The highest concentrations of CTrOCAant found around 13° S, 132° W and 32° S, 91° W, are higher than 80 μmol.kg−1 and 70 μmol.kg−1, respectively. The lowest concentrations are observed below 800 m depth (≤2 μmol.kg−1) and within the Oxygen Minimum Zone (OMZ), mainly around 140° W (<11 μmol.kg−1). As a result of the anthropogenic carbon penetration there has been decrease in pH by over 0.1 on an average in the upper 200 m. This work further improves our understanding on the penetration of anthropogenic carbon in the Eastern Pacific Ocean.
Methanotrophy potential versus methane supply by pore water diffusion in peatlands
Authors: Hornibrook E. R. C. , Bowes H. L. , Culbert A. , Gallego-Sala A. V.
Published: April 2010

Abstract. Low affinity methanotrophic bacteria consume a significant quantity of methane in wetland soils in the vicinity of plant roots and at the oxic-anoxic interface. Estimates of the efficiency of methanotrophy in peat soils vary widely in part because of differences in approaches employed to quantify methane cycling. High resolution profiles of dissolved methane abundance measured during the summer of 2003 were used to quantity rates of upward methane flux in four peatlands situated in Wales, UK. Aerobic incubations of peat from a minerotrophic and an ombrotrophic mire were used to determine depth distributions of kinetic parameters associated with methane oxidation. The capacity for methanotrophy in a 3 cm thick zone immediately beneath the depth of nil methane abundance in pore water was significantly greater than the rate of upward diffusion of methane in all four peatlands. Rates of methane diffusion in pore water at the minerotrophic peatlands were small (<10%) compared to surface emissions during June to August. The proportions were notably greater in the ombrotrophic bogs because of their typically low methane emission rates. Methanotrophy appears to consume entirely methane transported by pore water diffusion in the four peatlands with the exception of 4 of the 33 gas profiles sampled. Flux rates to the atmosphere regardless are high because of gas transport through vascular plants, in particular, at the minerotrophic sites. Cumulative rainfall amount 3-days prior to sampling correlated well with the distance between the water table level and the depth of 0 μmol l−1 methane, indicating that precipitation events can impact methane distributions in pore water. Further work is needed to characterise the kinetics of methane oxidation spatially and temporally in different wetland types in order to determine generalized relationships for methanotrophy in peatlands that can be incorporated into process-based models of methane cycling in peat soils.