bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in mobility and solubility of the redox sensitive metals Fe, Mn and Co at the seawater-sediment interface following CO2 seepage
Authors: Ardelan M. V. , Steinnes E.
Published: April 2010

Abstract. The impact of CO2 seepage on the solubility and distribution of the redox-sensitive metals iron, manganese, and cobalt in seawater and sediment pore water has been studied in experiments in laboratory-scale 0.6 m3 chambers. The mobility and solubility of Fe, Mn and Co were investigated in seawater, membrane filtered seawater, and DGT samplers deployed in water and sediment during a 26 day CO2 seepage study. During the first phase of the experiment of CO2 seepage (0–16 days), total acid-leachable (pH 1) and "dissolved" (<0.2 μm) concentrations of Fe, Mn and Co (DFe, DMn and DCo) in the seawater increased significantly; the ratios of concentrations of DFe, DMn and DCo in the CO2 chamber to the corresponding values in the control chamber (RDFe, RDMn and RDCo) were as high as 6, 65 and 58, respectively. The second phase of experiment consisted of an additional 10 days of incubation, where the concentrations of all the metals studied still increased but at reduced rates for DMn and DCo. The highest values of RDFe, RDMn and RDCo were about 3 for all metals during this part of the experiment. DGT (diffusive gradients in thin film) labile fractions denoted FeDGT, MnDGT and CoDGT were, respectively 50, 25 and 22 times higher in the CO2 seepage chamber than in the control chamber in the first phase of the experiment. During the second phase, all DGT labile metal concentrations still increased considerably, most notably for Fe. The ratio of FeDGT in the CO2 chamber to that in the control (RDGT-Fe) was still high, about 5, in the second phase of the experiment, whereas the increase in MnDGT and CoDGT slowed down. Our results indicate that acidification following CO2 seepage enhances the mobility and solubility of Fe Mn and Co in sediment and overlying water with contribution of changing in redox conditions and seepage related re-suspension.
Impact of meteorological anomalies in the 2003 summer on Gross Primary Productivity in East Asia
Authors: Saigusa N. , Ichii K. , Murakami H. , Hirata R. , Asanuma J. , Den H. , Han S.-J. , Ide R. , Li S.-G. , Ohta T. , Sasai T. , Wang S.-Q. , Yu G.-R.
Published: April 2010

Abstract. Northern Eurasia experienced anomalous weather conditions in the 2003 summer. We examined how forest ecosystems responded to the meteorological anomalies during the period using the dataset collected at flux monitoring sites in Asia, including a boreal forest in Mongolia, temperate forests in China and Japan, and a sub-tropical forest in China, as well as the dataset from satellite remote sensing. From July to August 2003, an active rain band stayed in the mid-latitude in East Asia for an unusually long period. Under the influence of the rain band, the Gross Primary Production (GPP), of temperate forests was 20–30% lower in the 2003 summer than in other years due to significant reduction in the Photosynthetic Photon Flux Density (PPFD). The GPP of a cool-temperate forest in the north of the rain band was slightly enhanced by the higher PPFD; however, the GPP of a sub-tropical forest located in the south of the rain band was reduced by drought stress due to extremely hot and dry conditions. The correlation coefficients for the year-to-year changes in the PPFD and GPP during mid-summer were calculated, and the spatial distribution was examined. The spatial pattern of the PPFD was calculated by satellite data, and that of the GPP was estimated by a regression-type model, which was trained and tested by ground observation data. The correlation was positive in the mid- and high-latitudes since light was an essential factor of the summer GPP. On the other hand, a negative correlation appeared in the lower latitudes, suggesting that the water limitation was much more important than the PPFD in the region. Our study illustrated that the integration of flux data from wide areas by combining satellite remote sensing data can help us gain an understanding of the ecosystem responses to large-scale meteorological phenomena.
Effects of an iron-light co-limitation on the elemental composition (Si, C, N) of the marine diatoms Thalassiosira oceanica and Ditylum brightwellii
Authors: Bucciarelli E. , Pondaven P. , Sarthou G.
Published: April 2010

Abstract. We examined the effect of iron (Fe) and Fe-light (Fe-L) co-limitation on cellular silica (BSi), carbon (C) and nitrogen (N) in two marine diatoms, the small oceanic diatom Thalassiosira oceanica and the large coastal species Ditylum brightwellii. We showed that C and N per cell tend to decrease with increasing Fe limitation (i.e. decreasing growth rate), both under high light (HL) and low light (LL). We observed an increase (T. oceanica, LL), no change (T. oceanica, HL) and a decrease (D. brightwellii, HL and LL) in BSi per cell with increasing degree of limitation. The comparison with literature data showed that the trend in C and N per cell for other Fe limited diatoms was similar to ours. Interspecific differences in C and N quotas of Fe limited diatoms observed in the literature seem thus to be mostly due to variations in cell volume. On the contrary, there was no global trend in BSi per cell or per cell volume, which suggests that other interspecific differences than Fe-induced variations in cell volume influence the degree of silicification. The relative variations in C:N, Si:C and Si:N versus the relative variation in specific growth rate (i.e. μ:μmax) followed the same patterns for T. oceanica and D. brightwellii, whatever the irradiance level. However, the variations of C:N under Fe limitation reported in the literature for other diatoms are contrasted, which may thus be more related to growth conditions than to interspecific differences. As observed in other studies, Si:C and Si:N ratios increased by more than 2-fold between 100% and 40% of μmax. Under more severe limitation (HL and LL), we observed for the first time a decrease in these ratios. These results may have important biogeochemical implications on the understanding and the modelling of the oceanic biogeochemical cycles, e.g. carbon and silica export.
Short term changes of microbial processes in Icelandic soils to increasing temperatures
Authors: Guicharnaud R. , Arnalds O. , Paton G. I.
Published: April 2010

Abstract. Temperature change is acknowledged to have a significant effect on soil biological processes and the corresponding sequestration of carbon and cycling of nutrients. Soils at high latitudes are likely to be particularly impacted by increases in temperature. Icelandic soils experience unusually frequent freeze and thaw cycles compare to other Arctic regions, which are increasing due to a warming climate. As a consequence these soils are frequently affected by short term temperature fluctuations. In this study, the short term response of a range of soil microbial parameters (respiration, nutrient availability, microbial biomass carbon, arylphosphatase and dehydrogenase activity) to temperature changes was measured in sub-arctic soils collected from across Iceland. Sample sites reflected two soil temperature regimes (cryic and frigid) and two land uses (pasture and arable). The soils were sampled from the field frozen, equilibrated at −20 °C and then incubated for two weeks at −10 °C, −2 °C, +2 °C and +10 °. Respiration and enzymatic activity were temperature dependent. The soil temperature regime affected the soil microbial biomass carbon sensitivity to temperatures. When soils where sampled from the cryic temperature regime a decreasing soil microbial biomass was detected when temperatures rose above the freezing point. Frigid soils, sampled from milder climatic conditions, where unaffected by difference in temperatures. Nitrogen mineralisation did not change with temperature. At −10 °C, dissolved organic carbon accounted for 88% of the fraction of labile carbon which was significantly greater than that recorded at +10 °C when dissolved organic carbon accounted for as low as 42% of the labile carbon fraction.
Sargasso Sea phosphorus biogeochemistry: an important role for dissolved organic phosphorus (DOP)
Authors: Lomas M. W. , Burke A. L. , Lomas D. A. , Bell D. W. , Shen C. , Dyhrman S. T. , Ammerman J. W.
Published: April 2010

Abstract. Inorganic phosphorus (SRP) concentrations in the subtropical North Atlantic are some of the lowest in the global ocean and have been hypothesized to constrain primary production. Based upon data from several transect cruises in this region, it has been hypothesized that dissolved organic phosphorus (DOP) supports a significant fraction of primary production in the subtropical North Atlantic. In this study, a time-series of phosphorus biogeochemistry is presented for the Bermuda Atlantic Time-series Study site, including rates of phosphorus export. Most parameters have a seasonal pattern, although year-over-year variability in the seasonal pattern is substantial, likely due to differences in external forcing. Suspended particulate phosphorus exhibits a seasonal maximum during the spring bloom, despite the absence of a seasonal peak in SRP. However, DOP concentrations are at an annual maximum prior to the winter/spring bloom and decline over the course of the spring bloom while whole community alkaline phosphatase activities are highest. As a result of DOP bioavailability, the growth of particles during the spring bloom occurs in Redfield proportions, though particles exported from the euphotic zone show rapid and significant remineralization of phosphorus within the first 50 m below the euphotic zone. Based upon DOP data from transect cruises in this region, the southward cross gyral flux of DOP is estimated to support ~25% of annual primary production and ~100% of phosphorus export. These estimates are consistent with other research in the subtropical North Atlantic and reinforce the hypothesis that while the subtropics may be phosphorus stressed (a physiological response to low inorganic phosphorus), utilization of the DOP pool allows production and accumulation of microbial biomass at Redfield proportions.
A spatial resolution threshold of land cover in estimating terrestrial carbon sequestration in four counties in Georgia and Alabama, USA
Authors: Zhao S. Q. , Liu S. , Li Z. , Sohl T. L.
Published: April 2010

Abstract. Changes in carbon density (i.e., carbon stock per unit area) and land cover greatly affect carbon sequestration. Previous studies have shown that land cover change detection strongly depends on spatial scale. However, the influence of the spatial resolution of land cover change information on the estimated terrestrial carbon sequestration is not known. Here, we quantified and evaluated the impact of land cover change databases at various spatial resolutions (250 m, 500 m, 1 km, 2 km, and 4 km) on the magnitude and spatial patterns of regional carbon sequestration in four counties in Georgia and Alabama using the General Ensemble biogeochemical Modeling System (GEMS). Results indicated a threshold of 1 km in the land cover change databases and in the estimated regional terrestrial carbon sequestration. Beyond this threshold, significant biases occurred in the estimation of terrestrial carbon sequestration, its interannual variability, and spatial patterns. In addition, the overriding impact of interannual climate variability on the temporal change of regional carbon sequestration was unrealistically overshadowed by the impact of land cover change beyond the threshold. The implications of these findings directly challenge current continental- to global-scale carbon modeling efforts relying on information at coarse spatial resolution without incorporating fine-scale land cover dynamics.
Impact of cloudiness on net ecosystem exchange of carbon dioxide in different types of forest ecosystems in China
Authors: Zhang M. , Yu G.-R. , Zhang L.-M. , Sun X.-M. , Wen X.-F. , Han S.-J. , Yan J.-H.
Published: April 2010

Abstract. Clouds can significantly affect carbon exchange process between forest ecosystems and the atmosphere by influencing the quantity and quality of solar radiation received by ecosystem's surface and other environmental factors. In this study, we analyzed the effects of cloudiness on net ecosystem exchange of carbon dioxide (NEE) in a temperate broad-leaved Korean pine mixed forest at Changbaishan (CBS) and a subtropical evergreen broad-leaved forest at Dinghushan (DHS), based on the flux data obtained during June–August from 2003 to 2006. The results showed that the response of NEE of forest ecosystems to photosynthetically active radiation (PAR) differed under clear skies and cloudy skies. Compared with clear skies, the light-saturated maximum photosynthetic rate (Pec,max) at CBS under cloudy skies during mid-growing season (from June to August) increased by 34%, 25%, 4% and 11% in 2003, 2004, 2005 and 2006, respectively. In contrast, Pec,max of the forest ecosystem at DHS was higher under clear skies than under cloudy skies from 2004 to 2006. When the clearness index (kt) ranged between 0.4 and 0.6, the NEE reached its maximum at both CBS and DHS. However, the NEE decreased more dramatically at CBS than at DHS when kt exceeded 0.6. The results indicate that cloudy sky conditions are beneficial to net carbon uptake in the temperate forest ecosystem and the subtropical forest ecosystem. Under clear skies, vapor pressure deficit (VPD) and air temperature increased due to strong light. These environmental conditions led to greater decrease in gross ecosystem photosynthesis (GEP) and greater increase in ecosystem respiration (Re) at CBS than at DHS. As a result, clear sky conditions caused more reduction of NEE in the temperate forest ecosystem than in the subtropical forest ecosystem. The response of NEE of different forest ecosystems to the changes in cloudiness is an important factor that should be included in evaluating regional carbon budgets under climate change conditions.
Impact of seawater pCO2 on calcification and Mg/Ca and Sr/Ca ratios in benthic foraminifera calcite: results from culturing experiments with Ammonia tepida
Authors: Dissard D. , Nehrke G. , Reichart G. J. , Bijma J.
Published: April 2010

Abstract. Evidence of increasing concentrations of dissolved carbon dioxide, especially in the surface ocean and its associated impacts on calcifying organisms, is accumulating. Among these organisms, benthic and planktonic foraminifera are responsible for a large amount of the globally precipitated calcium carbonate. Hence, their response to an acidifying ocean may have important consequences for future inorganic carbon cycling. To assess the sensitivity of benthic foraminifera to changing carbon dioxide levels and subsequent alteration in seawater carbonate chemistry, we cultured specimens of the shallow water species Ammonia tepida at two concentrations of atmospheric CO2 (230 and 1900 ppmv) and two temperatures (10 °C and 15 °C). Shell weights and elemental compositions were determined. Impact of high and low pCO2 on elemental composition are compared with results of a previous experiment were specimens were grown under ambient conditions (380 ppvm, no shell weight measurements of specimen grown under ambient conditions are, however, available). Results indicate that shell weights decrease with decreasing [CO32−], although calcification was observed even in the presence of calcium carbonate under-saturation, and also decrease with increasing temperature. Thus both warming and ocean acidification may act to decrease shell weights in the future. Changes in [CO32−] or total dissolved inorganic carbon do not affect the Mg distribution coefficient. On the contrary, Sr incorporation is enhanced under increasing [CO32−]. Implications of these results for the paleoceanographic application of foraminifera are discussed.
The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review
Authors: Duggen S. , Olgun N. , Croot P. , Hoffmann L. , Dietze H. , Delmelle P. , Teschner C.
Published: April 2010

Abstract. Iron is a key micronutrient for phytoplankton growth in the surface ocean. Yet the significance of volcanism for the marine biogeochemical iron-cycle is poorly constrained. Recent studies, however, suggest that offshore deposition of airborne ash from volcanic eruptions is a way to inject significant amounts of bio-available iron into the surface ocean. Volcanic ash may be transported up to several tens of kilometers high into the atmosphere during large-scale eruptions and fine ash may stay aloft for days to weeks, thereby reaching even the remotest and most iron-starved oceanic regions. Scientific ocean drilling demonstrates that volcanic ash layers and dispersed ash particles are frequently found in marine sediments and that therefore volcanic ash deposition and iron-injection into the oceans took place throughout much of the Earth's history. Natural evidence and the data now available from geochemical and biological experiments and satellite techniques suggest that volcanic ash is a so far underestimated source for iron in the surface ocean, possibly of similar importance as aeolian dust. Here we summarise the development of and the knowledge in this fairly young research field. The paper covers a wide range of chemical and biological issues and we make recommendations for future directions in these areas. The review paper may thus be helpful to improve our understanding of the role of volcanic ash for the marine biogeochemical iron-cycle, marine primary productivity and the ocean-atmosphere exchange of CO2 and other gases relevant for climate in the Earth's history.
Modeling the impact of drought on canopy carbon and water fluxes for a subtropical evergreen coniferous plantation in southern China through parameter optimization using an ensemble Kalman filter
Authors: Ju W. , Wang S. , Yu G. , Zhou Y. , Wang H.
Published: April 2010

Abstract. Soil and atmospheric water deficits have significant influences on CO2 and energy exchanges between the atmosphere and terrestrial ecosystems. Model parameterization significantly affects the ability of a model to simulate carbon, water, and energy fluxes. In this study, an ensemble Kalman filter (EnKF) and observations of gross primary productivity (GPP) and latent heat (LE) fluxes were used to optimize model parameters significantly affecting the calculation of these fluxes for a subtropical coniferous plantation in southeastern China. The optimized parameters include the maximum carboxylation rate (Vcmax), the slope in the modified Ball-Berry model (M) and the coefficient determining the sensitivity of stomatal conductance to atmospheric water vapor deficit (D0). Optimized Vcmax and M showed larger variations than D0. Seasonal variations of Vcmax and M were more pronounced than the variations between the two years. Vcmax and M were associated with soil water content (SWC). During dry periods, SWC at the 20 cm depth explained 61% and 64% of variations of Vcmax and M, respectively. EnKF parameter optimization improved the simulations of GPP, LE and SH, mainly during dry periods. After parameter optimization using EnKF, the variations of GPP, LE and SH explained by the model increased by 1% to 4% at half-hourly steps and by 3% to 5% at daily time steps. Further efforts are needed to differentiate the real causes of parameter variations and improve the ability of models to describe the change of stomatal conductance with net photosynthesis rate and the sensitivity of photosynthesis capacity to soil water stress under different environmental conditions.
The carbon budget of terrestrial ecosystems at country-scale – a European case study
Authors: Janssens I. A. , Freibauer A. , Schlamadinger B. , Ceulemans R. , Ciais P. , Dolman A. J. , Heimann M. , Nabuurs G.-J. , Smith P. , Valentini R.
Published: April 2010

Abstract. We summed estimates of the carbon balance of forests, grasslands, arable lands and peatlands to obtain country-specific estimates of the terrestrial carbon balance during the 1990s. Forests and grasslands were sinking carbon consistently, whereas arable soils were carbon sources in all European countries. Hence, countries dominated by arable lands tended to be losing carbon from their terrestrial ecosystems, whereas forest-dominated countries tended to be sinking carbon. In countries where peatlands are still being drained or extracted, net carbon balances were much lower than expected from land use. Net terrestrial carbon fluxes were typically small relative to fossil fuel-related carbon emissions. Only where fossil fluxes were small and net terrestrial fluxes were large did terrestrial carbon fluxes matter (ranged between uptake of 70% of fossil fluxes and increase of emissions with 25%). Nonetheless, at the European scale, the small net balance is composed of two very large but opposing fluxes: uptake by forests and grasslands and losses from arable lands and peatlands. Thus, relatively minor changes in either or both of these large component fluxes could strongly affect the net total, indicating that mitigation schemes should not be discarded a priori. In the absence of carbon-oriented land management, the current net carbon balance is bound to decline soon. Protecting it will require actions at three levels. Firstly, maintaining the current sink activity of forests. Secondly, altered agricultural management practices to turn arable soils into carbon sinks. Lastly, because carbon is lost more rapidly than sequestered, the current large reservoirs (wetlands and old forests) need extra protection.
Carbon sources supporting benthic mineralization in mangrove and adjacent seagrass sediments (Gazi Bay, Kenya)
Authors: Bouillon S. , Moens T. , Dehairs F.
Published: April 2010

Abstract. The origin of carbon substrates used by in situ sedimentary bacterial communities was investigated in an intertidal mangrove ecosystem and in adjacent seagrass beds in Gazi bay (Kenya) by δ13C analysis of bacteria-specific PLFA (phospholipid fatty acids) and bulk organic carbon. Export of mangrove-derived organic matter to the adjacent seagrass-covered bay was evident from sedimentary total organic carbon (TOC) and δ13CTOC data. PLFA δ13C data indicate that the substrate used by bacterial communities varied strongly and that exported mangrove carbon was a significant source for bacteria in the adjacent seagrass beds. Within the intertidal mangrove forest, bacterial PLFA at the surface layer (0-1 cm) typically showed more enriched δ13C values than deeper (up to 10 cm) sediment layers, suggesting a contribution from microphytobenthos and/or inwelled seagrass material. Under the assumption that seagrasses and mangroves are the dominant potential end-members, the estimated contribution of mangrove-derived carbon to benthic mineralization in the seagrass beds (16-74%) corresponds fairly well to the estimated contribution of mangrove C to the sedimentary organic matter pool (21-71%) across different seagrass sites. Based on these results and a compilation of literature data, we suggest that allochtonous carbon trapped in seagrass beds may often represent a significant fraction of the substrate for benthic mineralization - both in cases where seagrass C dominates the sediment TOC pool and in cases where external inputs are significant. Hence, it is likely that community respiration data systematically overestimate the role of mineralization in the overall seagrass C budget.
Coastal upwelling fluxes of O2, N2O, and CO2 assessed from continuous atmospheric observations at Trinidad,California
Authors: Lueker T. J.
Published: April 2010

Abstract. Continuous atmospheric records of O2/N2, CO2 and N2O obtained at Trinidad, California document the effects of air-sea exchange during coastal upwelling and plankton bloom events. The atmospheric records provide continuous observations of air-sea fluxes related to synoptic scale upwelling events over several upwelling seasons. Combined with satellite, buoy and local meteorology data, calculated anomalies in O2/N2 and N2O were utilized in a simple atmospheric transport model to compute air-sea fluxes during coastal upwelling. CO2 fluxes were linked to the oceanic component of the O2 fluxes through local hydrographic data and estimated as a function of upwelling intensity (surface ocean temperature and wind speed). Regional air-sea fluxes of O2/N2O, and CO2 during coastal upwelling were estimated with the aid of satellite wind and SST data. Upwelling CO2 fluxes were found to represent ~10% of export production along the northwest coast of North America. Synoptic scale upwelling events impact the net exchange of atmospheric CO2 along the coastal margin, and will vary in response to the frequency and duration of alongshore winds that are subject to climate change.
The carbon budget of the North Sea
Authors: Thomas H. , Bozec Y. , de Baar H. J. W. , Elkalay K. , Frankignoulle M. , Schiettecatte L.-S. , Vieira Borges A.
Published: April 2010

Abstract. A carbon budget has been established for the North Sea, a shelf sea of the NW European continental shelf. The air-sea exchange of CO2 has been assessed as closing term of the budget. The carbon exchange fluxes with the North Atlantic Ocean dominate the gross carbon budget. The net carbon budget – more relevant to the issue of the contribution of the coastal ocean to the marine carbon cycle – is dominated by the carbon inputs from rivers, the Baltic Sea and the atmosphere. The dominant carbon sink is the final export to the North Atlantic Ocean. The North Sea acts as a sink for organic carbon. More than 90% of the CO2 taken up from the atmosphere is exported to the North Atlantic Ocean making the North Sea a highly efficient continental shelf pump for carbon.
Carbon isotope anomaly in the major plant C1 pool and its global biogeochemical implications
Authors: Keppler F. , Kalin R. M. , Harper D. B. , McRoberts W. C. , Hamilton J. T. G.
Published: April 2010

Abstract. We report that the most abundant C1 units of terrestrial plants, the methoxyl groups of pectin and lignin, have a unique carbon isotope signature exceptionally depleted in 13C. Plant-derived C1 volatile organic compounds (VOCs) are also anomalously depleted in 13C compared with Cn+1 VOCs. The results confirm that the plant methoxyl pool is the predominant source of biospheric C1 compounds of plant origin such as methanol, chloromethane and bromomethane. Furthermore this pool, comprising ca. 2.5% of carbon in plant biomass, represents an important substrate for methanogenesis and could be a significant source of isotopically light methane entering the atmosphere. Our findings have significant implications for the use of carbon isotope ratios in elucidation of global carbon cycling. Moreover methoxyl groups could act as markers for biological activity in organic matter of terrestrial and extraterrestrial origin.
Geodynamic and metabolic cycles in the Hadean
Authors: Russell M. J. , Arndt N. T.
Published: April 2010

Abstract. High-degree melting of hot dry Hadean mantle at ocean ridges and plumes resulted in a crust about 30km thick, overlain in places by extensive and thick mafic volcanic plateaus. Continental crust, by contrast, was relatively thin and mostly submarine. At constructive and destructive plate boundaries, and above the many mantle plumes, acidic hydrothermal springs at ~400°C contributed Fe and other transition elements as well as P and H2 to the deep ocean made acidulous by dissolved CO2 and minor HCl derived from volcanoes. Away from ocean ridges, submarine hydrothermal fluids were cool (≤100°C), alkaline (pH ~10), highly reduced and also H2-rich. Reaction of solvents in this fluid with those in ocean water was catalyzed in a hydrothermal mound, a natural self-restoring flow reactor and fractionation column made up of carbonates and freshly precipitated Fe-Ni sulfide and greenrust pores and bubbles, developed above the alkaline spring. Acetate and the amino acetate glycine were the main products, much of which was eluted to the ocean. Other organic byproducts were retained, concentrated and reacted within the compartments. These compartments comprising the natural hydrothermal reactor consisted partly of greigite (Fe5NiS8). It was from reactions between organic modules confined within these inorganic compartments that the first prokaryotic organism evolved. These acetogenic precursors to the Bacteria diversified and migrated down the mound and into the ocean floor to inaugurate the "deep biosphere". Once there the Bacteria, and the recently differentiated Archaea, were protected from cataclysmic heating events caused by large bolide impacts. Geodynamic forces led to the eventual obduction of the deep biosphere into the photic zone where, initially protected by a thin veneer of sediment, the use of solar energy was mastered and photosynthesis emerged. The further evolution to oxygenic photosynthesis was effected as catalytic [CaMn4+] bearing molecules that otherwise would have been interred in the mineral ranciéite in the shallow marine manganiferous sediments, were sequestered and invaginated within the cyanobacterial precursor where, energized by light, they could oxidize water with greater efficiency. Thus, chemical sediments were required both for the emergence of chemosynthesis and of oxygenic photosynthesis, the two innovations that did most to change the nature of our planet.
The environment recording unit in coral skeletons: structural and chemical evidences of a biochemically driven stepping-growth process in coral fibres
Authors: Cuif J. P. , Dauphin Y.
Published: April 2010

Abstract. To improve our understanding of the environment recording by scleractinian corals, a detailed study of the skeleton microstructure has been carried out. A series of physico-chemical in situ characterizations was made, an approach that provides us with structural and biochemical information at the micrometric and nanometric scales. Gathering of these data results in a significant change in our concept of the growth of coral skeletons. In contrast to the usual view of an aggregate of purely mineral units (the coral fibres) independently growing by a simple chemical precipitation, coral skeletons appear to be biochemically controlled structures. Both structural and biochemical data reveal the micron-scaled stepping growth-mode of fibres, and its global coordination. In this process, sulfated acidic proteoglycans probably play a major role, due to their ability to create polymeric frameworks. Atomic force microscopy confirms the close relationship of organic and mineral phases at the nanometric scale. A new microstructural model of coral skeleton formation is proposed, that places coral skeletons among the typical "matrix mediated structures". From a practical standpoint, these results may contribute to develop a new high resolution approach in the study of paleoenvironments.
Whole-system metabolism and CO2 fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean)
Authors: Gazeau F. , Duarte C. M. , Gattuso J.-P. , Barrón C. , Navarro N. , Ruíz S. , Prairie Y. T. , Calleja M. , Delille B. , Frankignoulle M. , Borges A. V.
Published: April 2010

Abstract. The relationship between whole-system metabolism estimates based on planktonic and benthic incubations (bare sediments and seagrass, Posidonia oceanica meadows), and CO2 fluxes across the air-sea interface were examined in the Bay of Palma (Mallorca, Spain) during two cruises in March and June 2002. Moreover, planktonic and benthic incubations were performed at monthly intervals from March 2001 to October 2002 in a seagrass vegetated area of the bay. From the annual study, results showed a contrast between the planktonic compartment, which was heterotrophic during most of the year, except for occasional bloom episodes, and the benthic compartment, which was slightly autotrophic. Whereas the seagrass community was autotrophic, the excess organic carbon production therein could only balance the excess respiration of the planktonic compartment in shallow waters (<10 m) relative to the maximum depth of the bay (55 m). This generated a horizontal gradient from autotrophic or balanced communities in the shallow, seagrass-covered areas of the bay, to strongly heterotrophic communities in deeper areas, consistent with the patterns of CO2 fields and fluxes across the bay observed during the two extensive cruises in 2002. Finally, dissolved inorganic carbon and oxygen budgets provided NEP estimates in fair agreement with those derived from direct metabolic estimates based on incubated samples over the Posidonia oceanica meadow.
Diatoms and their influence on the biologically mediated uptake of atmospheric CO2 in the Arabian Sea upwelling system
Authors: Rixen T. , Goyet C. , Ittekkot V.
Published: April 2010

Abstract. Model experiments have shown that diatoms can lower the atmospheric CO2-concentration when they grow at the expense of coccolithophorids, since this reduces the precipitation of calcium carbonate, which acts as an oceanic CO2 source. In the Arabian Sea we conducted long-term sediment trap experiments (water depth >1000 m) in order to study processes controlling shifts from diatom to non-diatom dominated systems. One of our major problems was to link sediment trap records to surface ocean processes. Satellite-derived observations on upper ocean parameters were helpful to reduce this problem in the past and gain a new quality by combining it with results obtained during the Joint Global Ocean Flux Study in the Arabian Sea. The new results imply that a deficiency of silicon (Si) in the euphotic zone terminates diatom blooms. Enhanced eolian iron inputs raise the availability of silicon in the surface water by decreasing the Si/N uptake ratios of diatoms. An enhanced abundance of diatoms within the plankton community seems to increase the biologically mediated uptake of atmospheric CO2 by suppressing blooms of calcium carbonate producing organisms and by elevating the carbon to nutrient uptake (Redfield) ratio. These results agree in principle with assumptions made in models but indicate also that enhanced iron concentrations hinder the development of diatom blooms. The latter could be responsible for the amplitude of derived changes in the Redfield ratio and in the ratio between organic carbon and calcium carbonate carbon production which fall below assumptions made in some model experiments.
Sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut, French Guiana): a multi-tracers analysis using δ13C, C/N ratio and pigments
Authors: de Junet A. , Abril G. , Guérin F. , Billy I. , de Wit R.
Published: April 2010

Abstract. Carbon cycling and organic matter transfers in the tropical Sinnamary river system (French Guiana), including a mid-stream reservoir (Petit Saut) and its estuary on the Atlantic coast, were studied during the dry season by analyzing the organic carbon isotopic ratios (δ13C-OC), C/N ratios and pigments contents of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms. In the River upstream as well as in surface sediments at the entrance of the reservoir and at the littoral zone of the reservoir, particulate organic matter (POM) was in majority of terrestrial origin, with a δ13C-C/N signature close to the one of soil and litter collected in the surrounding forest and with high OC/total pigments ratios. High concentrations of Pheopigments a and b in these surface sediments showed that this terrestrial POM, either carried by the river and eolian transport or present in the soil before flooding, undergoes intense degradation. Deeper in the sediment, the δ13C profile showed a decreasing trend with depth typical of what is found in soils, showing that the flooded soil still remains present at the reservoir bottom 10 years after flooding. At the center of the reservoir, POM in the water column, in sediment traps and in surface sediments was in majority of aquatic origin with low C/N and OC/total pigments ratios. In the oxic epilimnion at 3 m depth, Chl a, Chl b and Lutein showed the predominance of Chlorophyceae to the phytoplankton community. At this depth, a C/N ratio of 21 suggests a large contribution of transparent exopolymeric particles to the bulk POM, which, in addition, was 13C-depleted due to a significant contribution of methanotrophic bacteria. At 7 m depth, below the oxicline, high concentrations of BChl d and occasionally BChl c revealed the presence of anoxygenic phototrophic bacteria, namely Chlorobiaceae. In the sediment traps, Chl a, Chl b, Lutein and BChl c and BChl d confirmed the contribution of plankton to the sedimentary POM. This material was undergoing intense degradation as revealed by high concentration of pheopigments and by an increase in C/N ratio and an increase in δ13C-OC with trap depth. Scytonemin was found in a biofilm developed on tree trunks at the reservoir surface and in all sediment traps. Other tracers showed however that the contribution of the biofilm to the sedimentary POM was minor compared to the planktonic source. In the Sinnamary downstream of the dam, POM became more 13C-depleted showing a larger contribution of methanotrophic bacteria. Chl b, Lutein and BChl c + BChl d originating from the reservoir progressively decreased downstream as the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the δ13C-C/N signature matched the one of POM carried by the Amazonian coastal mobile mud belt.
Effect of incubation time and substrate concentration on N-uptake rates by phytoplankton in the Bay of Bengal
Authors: Kumar S. , Ramesh R. , Sardesai S. , Sheshshayee M. S.
Published: April 2010

Abstract. We report here the results of three experiments, which are slight variations of the 15N method (JGOFS protocol) for determination of new production. The first two test the effect of (i) duration of incubation time and (ii) concentration of tracer added on the uptake rates of various N-species (nitrate, ammonium and urea) by marine phytoplankton; while the third compares in situ and deck incubations from dawn to dusk. Results indicate that nitrate uptake can be underestimated by experiments where incubation times shorter than 4h or when more than 10% of the ambient concentration of nitrate is added prior to incubation. The f-ratio increases from 0.28 to 0.42 when the incubation time increases from two to four hours. This may be due to the observed increase in the uptake rate of nitrate and decrease in the urea uptake rate. Unlike ammonium [y{=}2.07x{-}0.002\\, (r2=0.55)] and urea uptakes [y{=}1.88x{+}0.004 (r2=0.88)], the nitrate uptake decreases as the concentration of the substrate (x) increases, showing a negative correlation [y{=}-0.76x+0.05 (r2=0.86)], possibly due to production of glutamine, which might suppress nitrate uptake. This leads to decline in the f-ratio from 0.47 to 0.10, when concentration of tracer varies from 0.01 to 0.04μ M. The column integrated total productions are 519 mg C m-2 d-1 and 251 mg C m-2 d-1 for in situ and deck incubations, respectively. The 14C based production at the same location is ~200 mg C m-2 d-1, which is in closer agreement to the 15N based total production measured by deck incubation.
Controls over N2O, NOx and CO2 fluxes in a calcareous mountain forest soil
Authors: Kitzler B. , Zechmeister-Boltenstern S. , Holtermann C. , Skiba U. , Butterbach-Bahl K.
Published: April 2010

Abstract. We measured nitrogen oxides (N2O and NOx), dinitrogen (N2) and carbon dioxide (CO2) emissions from a spruce-fir-beech forest soil in the North Tyrolean limestone Alps in Austria. The site received 12.1 kg nitrogen via wet and dry deposition. Fluxes of nitric oxide (NO) were measured by an automatic dynamic chamber system on an hourly basis over a two year period. Daily N2O emissions were obtained by a semi-automatic gas measuring system. In order to cover spatial variability biweekly manual measurements of N2O and CO2 emissions were carried out, additionally. For acquiring information on the effects of soil and meteorological conditions and of N-deposition on N-emissions we chose the autoregression procedure (time-series analysis) as our means of investigation. Hence, we could exclude the data's autocorrelation in the course of the time. We found that soil temperature, soil moisture and wet N-deposition followed by air temperature and precipitation were the most powerful influencing parameters effecting N-emissions. With these variables up to 89% of observed temporal variations of N-emissions could be explained. During the two-year investigation period between 2.5 and 3.5% of deposited N was reemitted in form of N2O whereas only 0.2% were emitted as NO. At our mountain forest site the main end-product of microbial activity processes was N2 and trace gases (N2O and NO) were only of minor importance.
Halogens in porewater of peat bogs – the role of peat decomposition and dissolved organic matter
Authors: Biester H. , Selimović D. , Hemmerich S. , Petri M.
Published: April 2010

Abstract. Peatlands are one of the largest active terrestrial reservoirs of halogens. Formation of organo-halogens is a key process for the retention of halogens by organic matter and halogen enrichment in peat is strongly influenced by climatically controlled humification processes. However, little is known about release and transport of halogens in peat bogs. In this study we investigated the release of halogens from peat in three peat bogs located in the Magellanic Moorlands, southern Chile. Peat porewaters were collected using a sipping technique, which allows in situ sampling down to a depth of more than 6 m. Halogens and halogen species in porewater were determined by ion-chromatography (IC) (chlorine) and IC-ICP-MS (bromine and iodine). Results show that halogen concentrations in porewater are 15–30 times higher than in rainwater suggesting that their release from peat during diagenesis is the major source of halogens in porewater. Mean concentrations of chlorine, bromine and iodine in porewater were 7–15 mg l−1, 56–123μg l−1, and 10–20μg l−1, which correspond to mean proportions of 10–15%, 1–2.3% and 0.5–2.2% of total concentrations in peat, respectively. Organo-bromine and organoiodine were predominant in porewaters, whereas the release of organo-chlorine compounds from peat appears to be of minor importance. Results show that the release of bromine and iodine from peat depend on the degree of peat degradation, whereas this relationship is weak for chlorine. Relatively higher release of bromine and iodine was observed in less degraded peat sections, where the release of dissolved organic carbon (DOC) was also the most intensive. Here, proportions of released iodine and bromine follow proportions of released dissolved organic matter (DOM) indicating that the release of halogenated DOM is the predominant process of iodine and bromine release from peat.
Towards an unbiased estimate of fluctuations in reef abundance and volume during the Phanerozoic
Authors: Kiessling W.
Published: April 2010

Abstract. The globally preserved number and volume of ancient biogenic reefs is strongly biased by two factors: geological history and research intensity. These biases are sufficiently strong to cast doubts on the biological meaning of the recorded raw pattern. Without adjustment it is hard or impossible to identify factors potentially controlling the waxing and waning of this important ecosystem through time. Although it is impossible to completely compensate for the biases, I demonstrate herein that spatiotemporal heterogeneities of the biases can largely be evened out by: (1) omitting oceanic reef sites and reef sites only known from subsurface exploration; (2) standardizing for economic factors known to affect research intensity; and (3) adjusting for sedimentary cycling processes. The resulting curves of fossil reef abundance and volume appear quite different from the original ones but neither is the overall volatility reduced, nor are patterns of waxing and waning of the time series significantly altered. Thus, although the differences are sufficiently strong to call for new tests of potential extrinsic controls on Phanerozoic reef proliferation, the raw curves correctly reflect the basic timing of major reef blooms and declines.
Bacterial carbon sources in coastal sediments: a review based on stable isotope data of biomarkers
Authors: Bouillon S. , Boschker H. T. S.
Published: April 2010

Abstract. Coastal ecosystems are typically highly productive, and recieve organic matter from a variety of local and imported sources. To assess if general patterns are present in the origin of carbon sources for sedimentary bacteria and their relation to the origin of the sediment organic carbon pool, we compiled both literature and new data on δ13C of bacterial biomarker PLFA (the phospholipid derived fatty acids i+a15:0) along with δ13C data on sediment organic carbon δ13CTOC and macrophyte biomass. Such data were collected from a variety of typical near-coastal systems, including mangroves, salt marshes (both C3 and C4-dominated sites), seagrass beds, and macroalgae-based systems, as well as unvegetated sediments. First, our δ13Ci+a15:0 data showed a large variability over the entire range of δ13CTOC, indicating that in many settings, bacteria may depend on carbon derived from various origins. Secondly, systems where local macrophyte production is the major supplier of organic carbon for in situ decomposition are generally limited to organic carbon-rich, peaty sites (TOC>10 wt%) which are likely to make up only a small part of the global area of vegetated coastal systems. These carbon-rich sediments also provided a field based estimate of isotopic fractionation in bacterial lipid synthesis (-3.7±2.1), that is similar to the expected value. Thirdly, only in systems with low TOC (below ~1 wt%), we consistently found that bacteria were on average selectively utilizing an isotopically enriched carbon source, which may be root exudates but more likely is derived from microphytobenthos. In other systems with between ~1 and 10 wt% TOC, bacteria appear to show on average little selectivity and δ13Ci+a15:0 data generally follow the δ13CTOC, even in systems where the TOC is a mixture of algal and macrophyte sources that generally are believed to have a very different degradability.
Measurements of hydrocarbon emissions from a boreal fen using the REA technique
Authors: Haapanala S. , Rinne J. , Pystynen K.-H. , Hellén H. , Hakola H.
Published: April 2010

Abstract. Fluxes of biogenic volatile organic compounds (VOC) and methane were measured above a boreal fen. Vegetation on the fen is dominated by Sphagnum mosses and sedges. A relaxed eddy accumulation (REA) system with dynamic deadband was designed and constructed for the measurements. Methane, C2-C6 hydrocarbons and some halogenated hydrocarbons were analysed from the samples by gas chromatographs equipped with FID and ECD. A significant flux of isoprene and methane was detected during the growing seasons. Isoprene emission was found to follow the common isoprene emission algorithm. Average standard emission potential of isoprene was 680 μ g m-2h-1. Fluxes of other non-methane hydrocarbons were below detection limit.
Global uptake of carbonyl sulfide (COS) by terrestrial vegetation: Estimates corrected by deposition velocities normalized to the uptake of carbon dioxide (CO2)
Authors: Sandoval-Soto L. , Stanimirov M. , von Hobe M. , Schmitt V. , Valdes J. , Wild A. , Kesselmeier J.
Published: April 2010

Abstract. COS uptake by trees, as observed under dark/light changes and under application of the plant hormone abscisic acid, exhibited a strong correlation with the CO2 assimilation rate and the stomatal conductance. As the uptake of COS occurred exclusively through the stomata we compared experimentally derived and re-evaluated deposition velocities (Vd for COS and CO2). We show that Vd of COS is generally significantly larger than that of CO2. We therefore introduced this attribute into a new global estimate of COS fluxes into vegetation. The global COS uptake by vegetation as estimated by the new model ranges between 0.69-1.40 Tg a-1, based on the Net Primary Productivity (NPP). Taking into account Gross Primary Productivity (GPP) the deposition estimate ranges between 1.37-2.81 Tg a-1 (0.73-1.50 Tg S a-1). We believe that in order to obtain accurate and reliable global NPP-based estimates for the COS flux into vegetation, the different deposition velocities of COS and CO2 must be taken into account.