ALBERT

Beschreibung: Sources and Transformations of Anthropogenic Nitrogen along an Urban River-Estuarine Continuum Michael J. Pennino, Sujay S. Kaushal, Sudhir Murthy, Joel Blomquist, Jeff Cornwell, and Lora Harris Biogeosciences Discuss., doi:10.5194/bg-2016-264,2016 Manuscript under review for BG (discussion: open, 0 comments) The results of this manuscript report the analysis of the fate and transport of wastewater and anthropogenic nitrogen along the Potomac River Estuary, from Washington D.C. to the Chesapeake Bay. In conjunction with a mass balance approach, nitrate isotopes were used to estimate fluxes and trace the sources and transformations N along the estuary. This study shows that estuaries have a large capacity to transform N inputs, but with large seasonal variability due to hydrological extremes.

Beschreibung: Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra Inge Juszak, Werner Eugster, Monique M. P. D. Heijmans, and Gabriela Schaepman-Strub Biogeosciences, 13, 4049-4064, doi:10.1594/PANGAEA.860561, 2016 Changes in Arctic vegetation composition and structure feed back to climate and permafrost. Using field observations at a Siberian tundra site, we find that dwarf shrubs absorb more solar radiation than wet sedges and thus amplify surface warming, especially during snow melt. On the other hand, permafrost thaw was enhanced below sedges as a consequence of high soil moisture. Standing dead sedge leaves affected the radiation budget strongly and deserve more scientific attention.

Beschreibung: Diversity and mineral substrate preference in endolithic microbial communities from marine intertidal outcrops (Isla de Mona, Puerto Rico) Estelle Couradeau, Daniel Roush, Brandon Scott Guida, and Ferran Garcia-Pichel Biogeosciences Discuss., doi:10.5194/bg-2016-254,2016 Manuscript under review for BG (discussion: open, 0 comments) Endolithic (inside rock) microbial communities are dominated by cyanobacteria, among which the true boring cyanobacteria actively perforate the mineral and play a significant role in the erosion of coastal outcrops that may increase with ocean acidification. We interrogated the microbial communities associated with various intertidal substrates of Mona Island (PR) and brought the first evidence that there exists a mineralogical substrate preference among the pioneers true boring cyanobacteria.

Beschreibung: Anaerobic methane oxidation in an East African great lake (Lake Kivu) Fleur A. E. Roland, François Darchambeau, Cédric Morana, Sean A. Crowe, Bo Thamdrup, and Alberto V. Borges Biogeosciences Discuss., doi:10.5194/bg-2016-300,2016 Manuscript under review for BG (discussion: open, 0 comments) We studied methane consumption in a tropical Great Lake (Lake Kivu, East Africa). Lake Kivu has huge methane concentrations in its deep anoxic waters, but is a very poor emitter of methane to the atmosphere, which suppose a strong methane consumption in the water column. During this study, we put in evidence high aerobic and anaerobic consumption rates, whose relative importance varied with the season (higher aerobic rates in dry season, when the oxic compartment is wider).

Beschreibung: Coastal-ocean uptake of anthropogenic carbon Timothée Bourgeois, James C. Orr, Laure Resplandy, Jens Terhaar, Christian Ethé, Marion Gehlen, and Laurent Bopp Biogeosciences, 13, 4167-4185, doi:10.5194/bg-13-4167-2016, 2016 The global coastal ocean took up 0.1 Pg C yr −1 of anthropogenic carbon during 1993–2012 based on new biogeochemical simulations with an eddying 3-D global model. That is about half of the most recent estimate, an extrapolation based on surface areas. It should not be confused with the continental shelf pump, perhaps 10 times larger, which includes natural as well as anthropogenic carbon. Coastal uptake of anthropogenic carbon is limited by its offshore transport.

Beschreibung: Anthropogenically induced environmental changes in the northeastern Adriatic Sea in the last 400 years (Panzano Bay, Gulf of Trieste) Jelena Vidović, Rafał Nawrot, Ivo Gallmetzer, Alexandra Haselmair, Adam Tomašových, Michael Stachowitsch, Vlasta Ćosović, and Martin Zuschin Biogeosciences Discuss., doi:10.5194/bg-2016-273,2016 Manuscript under review for BG (discussion: open, 0 comments) Shallow and sheltered marine embayments in urbanized areas are prone to the accumulation of pollutants, but little is known about the historical baselines of such marine ecosystems. Here we study foraminiferal assemblages, geochemical proxies and sedimentological data from 1.6 m long sediment cores to uncover ~ 400 years of anthropogenic pressure from mining, port and industrial zones in the Gulf of Trieste, Italy. From 1600 to 1900 AD, element concentrations and foraminiferal assemblages point to negligible effects of agricultural activities. The only significant anthropogenic activity during this period is mercury mining in the hinterlands of the gulf, releasing high amounts of mercury into the bay and significantly exceeding today's Italian sediment quality guidelines (SQG) and the standards on the effects of trace elements to benthic organisms (ERL and ERM). Nonetheless, the fluctuations in the concentrations of mercury do not correlate with changes in the composition and diversity of foraminiferal assemblages due to its nonbioavailability. Intensified agricultural and maricultural activities in the first half of the 20th century caused slight nutrient enrichment and a minor increase in foraminiferal diversity. Intensified port and industrial activities in the second half of 20th century increased the normalised trace element concentrations and persistent organic pollutants (PAH, PCB) in the topmost part of the core, with solely Ni exceeding Italian SQG, ERL and ERM. This increase caused only minor changes in the foraminiferal community because foraminifera in Panzano Bay have a long history of adaptation to naturally elevated trace element concentrations. Our study underlines the importance of using an integrated, multidisciplinary approach in reconstructing the history of environmental and anthropogenic changes in marine systems. Given the prolonged human impacts in coastal areas like the Gulf of Trieste, such long term baseline data are crucial for interpreting the present state of marine ecosystems.

Beschreibung: Mechanisms of Trichodesmium demise within the New Caledonian lagoon during the VAHINE mesocosm experiment Dina Spungin, Ulrike Pfreundt, Hugo Berthelot, Sophie Bonnet, Dina AlRoumi, Frank Natale, Wolfgang R. Hess, Kay D. Bidle, and Ilana Berman-Frank Biogeosciences, 13, 4187-4203, doi:10.5194/bg-13-4187-2016, 2016 The marine cyanobacterium Trichodesmium spp. forms massive blooms important to carbon and nitrogen cycling in the oceans that often collapse abruptly. We investigated a Trichodesmium bloom in the lagoon waters of New Caledonia to specifically elucidate the cellular processes mediating the bloom decline. We demonstrate physiological, biochemical, and genetic evidence for nutrient and oxidative stress that induced a genetically controlled programmed cell death (PCD) pathway leading to bloom demise.

Beschreibung: Spring phytoplankton communities of the Labrador Sea (2005–2014): pigment signatures, photophysiology and elemental ratios Glaucia M. Fragoso, Alex J. Poulton, Igor M. Yashayaev, Erica J. H. Head, and Duncan A. Purdie Biogeosciences Discuss., doi:10.5194/bg-2016-295,2016 Manuscript under review for BG (discussion: open, 0 comments) This research describes a detailed analysis of current distributions of spring phytoplankton communities in the Labrador Sea based on ten years of observations. Phytoplankton community composition varied mainly according to the contrasting hydrographical zones of the Labrador Sea. The taxonomic distinctions of these communities influenced the photosynthetic and biochemical signatures of near surface waters, which may have a profound impact on the carbon cycle in high latitude seas.

Beschreibung: Sedimentary response to sea ice and atmospheric variability over the instrumental period off Adélie Land, East Antarctica Philippine Campagne, Xavier Crosta, Sabine Schmidt, Marie Noëlle Houssais, Olivier Ther, and Guillaume Massé Biogeosciences, 13, 4205-4218, doi:10.5194/bg-13-4205-2016, 2016 Diatoms and biomarkers have been recently used for palaeoclimate reconstructions in the Southern Ocean. Few sediment-based ecological studies have investigated their relationships with environmental conditions. Here, we compare high-resolution sedimentary records with meteorological data to study relationships between our proxies and recent atmospheric and sea surface changes. Our results indicate that coupled wind pattern and sea surface variability act as the proximal forcing at that scale.

Beschreibung: Observing and modelling phytoplankton community structure in the North Sea: can ERSEM-type models simulate biodiversity? David A. Ford, Johan van der Molen, Kieran Hyder, John Bacon, Rosa Barciela, Veronique Creach, Robert McEwan, Piet Ruardij, and Rodney Forster Biogeosciences Discuss., doi:10.5194/bg-2016-304,2016 Manuscript under review for BG (discussion: open, 0 comments) This study presents a novel set of in situ observations of phytoplankton community structure for the North Sea. These observations were used to validate two physical-biogeochemical ocean model simulations, each of which used different variants of the widely-used European Regional Seas Ecosystem Model (ERSEM). It was found that the ability of the models to reproduce the observed biodiversity was strongly dependent on the details of the biogeochemical model formulations and parameterisations used.

Beschreibung: Evaluation of 4 years of continuous δ 13 C(CO 2 ) data using a moving Keeling plot method Sanam Noreen Vardag, Samuel Hammer, and Ingeborg Levin Biogeosciences, 13, 4237-4251, doi:10.5194/bg-13-4237-2016, 2016 Using a synthetic dataset, we show how to best determine the mean source signature, δ S , at high temporal resolution using continuous CO 2 and δ 13 C(CO 2 ) data. We apply this method to measured data from Heidelberg and find a distinct seasonal cycle of δ S . Disentangling this record into its source components requires the isotopic end members of CO 2 from the biosphere and those from the fuel mix. They can be estimated from the δ S record, but only when their relative share is close to 100 %.

Beschreibung: Long-term drainage reduces CO 2 uptake and increases CO 2 emission on a Siberian floodplain due to shifts in vegetation community and soil thermal characteristics Min Jung Kwon, Martin Heimann, Olaf Kolle, Kristina A. Luus, Edward A. G. Schuur, Nikita Zimov, Sergey A. Zimov, and Mathias Göckede Biogeosciences, 13, 4219-4235, doi:10.5194/bg-13-4219-2016, 2016 A decade-long drainage on an Arctic floodplain has altered dominant plant species and soil temperature regimes. Consequently, CO 2 exchange rates between the atmosphere and the terrestrial ecosystem were modified: CO 2 uptake rates by the terrestrial ecosystem decreased and CO 2 emission rates to the atmosphere increased. Ongoing global warming may thaw ice-rich permafrost and make some regions drier in the Arctic, and this will reduce carbon accumulation in the terrestrial ecosystem.

Beschreibung: Physiological responses of coastal and oceanic diatoms to diurnal fluctuations in seawater carbonate chemistry under two CO 2 concentrations Futian Li, Yaping Wu, David A. Hutchins, Feixue Fu, and Kunshan Gao Biogeosciences Discuss., doi:10.5194/bg-2016-281,2016 Manuscript under review for BG (discussion: open, 0 comments) Ongoing ocean acidification is being superimposed on the natural carbonate buffer system to influence the physiology of phytoplankton. Here, we show that coastal and oceanic diatoms respond differentially to diurnal fluctuating carbonate chemistry in current and ocean acidification scenarios. We propose that the ability to acclimate to dynamic carbonate chemistry may act as one determinant of the spatial distribution of diatom species.

Beschreibung: Hydrogen dynamics in soil organic matter as determined by 13 C and 2 H labeling experiments Alexia Paul, Christine Hatté, Lucie Pastor, Yves Thiry, Françoise Siclet, and Jérôme Balesdent Biogeosciences Discuss., doi:10.5194/bg-2016-317,2016 Manuscript under review for BG (discussion: open, 0 comments) The terrestrial environment has been affected by tritium contamination. There is a need to assess the residence time and the dynamics of organic hydrogen in soils organic matter in order to predict the fate of tritium. In the present study we traced carbon and hydrogen from plant derived molecule or from water in different soil types. We showed that water is the main donor of hydrogen in soil and it is dependent on carbon biosynthesis and on soil type.

Beschreibung: Ocean acidification over the next three centuries using a simple global climate carbon-cycle model: projections and sensitivities Corinne A. Hartin, Benjamin Bond-Lamberty, Pralit Patel, and Anupriya Mundra Biogeosciences, 13, 4329-4342, doi:10.5194/bg-13-4329-2016, 2016 Continued oceanic uptake of anthropogenic CO 2 is projected to significantly alter the chemistry of the upper oceans over the next three centuries, with potentially serious consequences for marine ecosystems. Relatively few models have the capability to make projections of ocean acidification, limiting our ability to assess the impacts and probabilities of ocean changes. In this study we examine the ability of Hector v1.1, a reduced-form global model, to project changes in the upper ocean carbonate system over the next three centuries, and quantify the model's sensitivity to parametric inputs. Hector is run under prescribed emission pathways from the Representative Concentration Pathways (RCPs) and compared to both observations and a suite of Coupled Model Intercomparison (CMIP5) model outputs. Current observations confirm that ocean acidification is already taking place, and CMIP5 models project significant changes occurring to 2300. Hector is consistent with the observational record within both the high- (〉 55°) and low-latitude oceans (〈 55°). The model projects low-latitude surface ocean pH to decrease from preindustrial levels of 8.17 to 7.77 in 2100, and to 7.50 in 2300; aragonite saturation levels (Ω Ar ) decrease from 4.1 units to 2.2 in 2100 and 1.4 in 2300 under RCP 8.5. These magnitudes and trends of ocean acidification within Hector are largely consistent with the CMIP5 model outputs, although we identify some small biases within Hector's carbonate system. Of the parameters tested, changes in [H + ] are most sensitive to parameters that directly affect atmospheric CO 2 concentrations – Q 10 (terrestrial respiration temperature response) as well as changes in ocean circulation, while changes in Ω Ar saturation levels are sensitive to changes in ocean salinity and Q 10 . We conclude that Hector is a robust tool well suited for rapid ocean acidification projections and sensitivity analyses, and it is capable of emulating both current observations and large-scale climate models under multiple emission pathways.

Beschreibung: Decadal and long-term boreal soil carbon and nitrogen sequestration rates across a variety of ecosystems Kristen L. Manies, Jennifer W. Harden, Christopher C. Fuller, and Merritt R. Turetsky Biogeosciences, 13, 4315-4327, doi:10.5194/bg-13-4315-2016, 2016 Boreal soils are important to the global C cycle. We need to understand what controls how C accumulates and is lost from this soil. To help we examined C & N accumulation rates for five boreal ecosystems. Most ecosystems were similar. But the rich fen had higher long-term C & N accumulation rates, likely due to differences in nutrient cycling & because it burns less. Therefore, shifts among ecosystems will not change regional C & N dynamics much, unless there is a shift to or from a rich fen.

Beschreibung: Exploring the distance between nitrogen and phosphorus limitation in mesotrophic surface waters using a sensitive bioassay Enis Hrustic, Risto Lignell, Ulf Riebesell, and Tron Frede Thingstad Biogeosciences Discuss., doi:10.5194/bg-2016-313,2016 Manuscript under review for BG (discussion: open, 0 comments) In the stratified season, phytoplankton in the ocean's top layer are limited by mineral nutrients, normally nitrogen, phosphorous or iron. It is important to know, not only which element is limiting, but also the surplus of the secondary limiting element, referred to as e.g. N* when N is the secondary limiting element. Determination of *N by chemical methods in surface waters is not straight forward. We here show how one instead can "ask the organisms".

Beschreibung: The importance of an estuarine salinity gradient on soil organic carbon stocks of tidal marshes Marijn Van de Broek, Stijn Temmerman, Roel Merckx, and Gerard Govers Biogeosciences Discuss., doi:10.5194/bg-2016-285,2016 Manuscript under review for BG (discussion: open, 0 comments) The results of this study on the OC stocks of tidal marshes show that variations in OC stocks of tidal marshes along estuaries are important and should be taken into account in order to make of accurate estimates of the total amount of OC stored in these ecosystems. Moreover, our results clearly show that most studies underestimate the variation in OC stocks along estuaries due to a shallow sampling depth, neglecting the variation in OC decomposition after burial along estuaries.

Beschreibung: Ecological response to collapse of the biological pump following the mass extinction at the Cretaceous-Paleogene boundary Johan Vellekoop, Lineke Woelders, Sanem Açikalin, Jan Smit, Bas van de Schootbrugge, Ismail Ö. Yilmaz, Henk Brinkhuis, and Robert P. Speijer Biogeosciences Discuss., doi:10.5194/bg-2016-275,2016 Manuscript under review for BG (discussion: open, 0 comments) The Cretaceous-Paleogene boundary, ~ 66 Ma, is characterized by a mass-extinction. We studied groups of both surface-dwelling and bottom-dwelling organisms to unravel the oceanographic consequences of these extinctions. Our integrated records indicate that a reduction of the transport of organic matter to the sea floor resulted in enhanced recycling of nutrients in the upper water column and decreased food supply at the sea floor, in the first tens of thousands of years after the extinctions.

Beschreibung: The long-solved problem of the best-fit straight line: Application to isotopic mixing lines Richard Wehr and Scott R . Saleska Biogeosciences Discuss., doi:10.5194/bg-2016-315,2016 Manuscript under review for BG (discussion: open, 0 comments) In 1969, Derek York published a highly general solution to the common problem of how to fit a straight line to points measured with error in both x and y . Unfortunately York’s solution is almost unknown outside the geophysical literature, and new studies wrestle with the problem each year. We introduce York’s solution and demonstrate it using an example from biogeochemistry: the isotopic mixing line. By Monte Carlo simulation, we show that York’s solution is superior to all popular fit methods.

Beschreibung: Patterns of carbon processing at the seafloor: the role of faunal and microbial communities in moderating carbon flows Clare Woulds, Steven Bouillon, Gregory L. Cowie, Emily Drake, Jack J. Middelburg, and Ursula Witte Biogeosciences, 13, 4343-4357, doi:10.5194/bg-13-4343-2016, 2016 Estuarine sediments are important locations for carbon cycling and burial. We used tracer experiments to investigate how site conditions affect the way in which seafloor biological communities cycle carbon. We showed that while total respiration rates are primarily determined by temperature, total carbon processing by the biological community is strongly related to its biomass. Further, we saw a distinct pattern of carbon cycling in sandy sediment, in which uptake by bacteria dominates.

Beschreibung: Temporal changes in photoreactivity of dissolved organic carbon and implications for aquatic carbon fluxes from peatlands Amy E. Pickard, Kate V. Heal, Andrew R. McLeod, and Kerry J. Dinsmore Biogeosciences Discuss., doi:10.5194/bg-2016-296,2016 Manuscript under review for BG (discussion: open, 0 comments) Peatland catchments export significant volumes of photoreactive carbon to aquatic systems, particularly headwater streams. Delivery of photoreactive material is subject to seasonal variation, and is also influenced by the timing and magnitude of rainfall events. We suggest that photoprocessing of peatland derived carbon may contribute to carbon dioxide emissions from aquatic systems, although considerable uncertainty remains as to how much material is processed 'in situ' within these systems.

Beschreibung: Species-specific temporal variation in photosynthesis as a moderator of peatland carbon sequestration Aino Korrensalo, Tomáš Hájek, Pavel Alekseychik, Janne Rinne, Timo Vesala, Lauri Mehtätalo, Ivan Mammarella, and Eeva-Stiina Tuittila Biogeosciences Discuss., doi:10.5194/bg-2016-265,2016 Manuscript under review for BG (discussion: open, 0 comments) Photosynthetic parameters of peatland plant species were measured over one growing season in an ombrotrophic bog. Based on these measurements, ecosystem-level photosynthesis was calculated for the whole growing season and compared with an estimate derived from micrometeorological measurements. These two estimates corresponded well. Species with low areal cover at the site but high photosynthetic efficiency appeared to potentially important for the ecosystem-level carbon balance.

Beschreibung: The effect of warm summer 2012 on seasonal and annual methane dynamics in adjacent small lakes on the ice-free margin of Greenland Sarah B. Cadieux, Jeffrey R. White, and Lisa M. Pratt Biogeosciences Discuss., doi:10.5194/bg-2016-293,2016 Manuscript under review for BG (discussion: open, 0 comments) In thermally stratified lakes, the greatest annual methane emissions typically occur during thermal overturn events. In July of 2012, Greenland experienced significant warming that resulted in substantial melting of the Greenland Ice Sheet and enhanced runoff events. This unusual climate phenomenon provided an opportunity to examine the effects of short-term natural heating on lake thermal structure and methane dynamics and compare these observations with those from the following year when temperatures were normal. Here, we focus on methane concentrations within the water column of 5 adjacent small lakes on the ice-free margin of Southwest Greenland under open-water and ice-covered conditions from 2012–2014. Enhanced warming of the epilimnion in the lakes under open-water conditions in 2012 led to strong thermal stability and the development of anoxic hypolimnions in each of the lakes. As a result, during open-water conditions, mean dissolved methane concentrations in the water column were significantly ( p  

Beschreibung: Quantifying the Cenozoic marine diatom deposition history: links to the C and Si cycles Johan Renaudie Biogeosciences Discuss., doi:10.5194/bg-2016-290,2016 Manuscript under review for BG (discussion: open, 0 comments) Marine planktonic diatoms are, today, among the world's main primary producers as well as the main organic carbon exporter to the deep-sea despite the fact that they were a very minor component of the plankton at the beginning of the Cenozoic. They are also the main silica exporter to the deep-sea, thus balancing global chemical weathering. This study reviews their global Cenozoic depositional pattern in order to understand the modality and the context of their rise to dominance, but also to understand how diatom evolution affected the Cenozoic functioning of the ocean's biological pump. After two short-lived major abundance peaks in the late Eocene and the late Oligocene, diatom abundance in sediments shifted in the mid-Miocene to globally higher values which have largely persisted to the modern day. These quantitative findings provide support for the hypothesis according to which diatoms, through their ecological role in the ocean's biological carbon pump, have contributed to the Cenozoic changes in atmospheric carbon dioxide pressure and consequently to changes in the global climate state. Additionally, correlations between diatom abundance peaks and shifts in seawater strontium and osmium isotopic composition hint at a strong control of the silicate weathering on diatom deposition.

Beschreibung: Drivers of atmospheric methane uptake by montane forest soils in the southern Peruvian Andes Sam P. Jones, Torsten Diem, Lidia P. Huaraca Quispe, Adan J. Cahuana, Dave S. Reay, Patrick Meir, and Yit Arn Teh Biogeosciences, 13, 4151-4165, doi:10.5194/bg-13-4151-2016, 2016 Tropical montane forests represent a significant portion of Andean land cover, however, soil-atmosphere methane exchange in these ecosystems is under studied. Here we report on soil methane cycling in montane forests of the southern Peruvian Andes. These soils acted as a net sink for atmospheric methane and variation in uptake across the studied forests was best explained by nitrate inhibition of oxidation and/or limitations on the inward diffusion of methane from the atmosphere into the soil.

Beschreibung: Biochar carrying hydrocarbon decomposers promotes degradation during the early stage of bioremediation P. Galitskaya, L. Akhmetzyanova, and S. Selivanovskaya Biogeosciences Discuss., doi:10.5194/bg-2016-292,2016 Manuscript under review for BG (discussion: open, 0 comments) Biochar carrying hydrocarbon degrading bacterial strains was used as a tool for remediation of oil polluted soil. It was shown, that amendment of oil polluted soil by biochar causes acceleration of hydrocarbon decomposition as compared with mixing and moistening. Inoculation of hydrocarbon degrading bacteria on biochar may be recommended as an additional tool of remediation. New generation sequencing methods were used to analyze how microbial community changes in the process of bioremediation.

Beschreibung: Ideas and Perspectives: Climate-Relevant Marine Biologically-Driven Mechanisms in Earth System Models Inga Hense, Irene Stemmler, and Sebastian Sonntag Biogeosciences Discuss., doi:10.5194/bg-2016-289,2016 Manuscript under review for BG (discussion: open, 0 comments) Marine biota drives a number of climate-relevant mechanisms not all of which are included in current Earth system models (ESMs) used for climate projections. We identify three classes of mechanisms and argue that to adequately resolve these mechanisms and to ensure links to and feedbacks with other Earth system components, ESMs need to account for five marine organism groups.

Beschreibung: CH 4 exchange at the forest floor of a forestry-drained fen: low flux rates but high temporal variation Mika Korkiakoski, Markku Koskinen, Kari Minkkinen, Paavo Ojanen, Timo Penttilä, Juuso Rainne, Tuomas Laurila, and Annalea Lohila Biogeosciences Discuss., doi:10.5194/bg-2016-239,2016 Manuscript under review for BG (discussion: open, 0 comments) We measured methane exchange rates at the forest floor of a nutrient-rich drained peatland in southern Finland. The forest floor acted mainly as a small methane sink, but emission peaks were occasionally observed during spring and rainfall events. The strength of the sink correlated best with groundwater level and soil temperatures at 20 and 30 cm depths. Even thought the exchange rates were often low, observed diurnal variations during warm and dry summer periods were relatively high.

Beschreibung: Uncertainties in the national inventory of methane emissions from rice cultivation: field measurements and modeling approaches Wen Zhang, Tingting Li, and Wenjuan Sun Biogeosciences Discuss., doi:10.5194/bg-2016-250,2016 Manuscript under review for BG (discussion: open, 0 comments) Regional estimated uncertainties originate from methodological failures, errors and supporting data insufficiency. A case study showed that the fallacy of the CH4MOD contributing 56.6 % to the uncertainty of a national inventory, with the remaining 43.4 % attributed to the scarcity of model inputs. We also revealed dilemma between model performance and data availability: a model with better performance may help in reducing uncertainty by model fallacy but increases the uncertainty by data scarcity.

Beschreibung: Technical note: 3-hourly temporal downscaling of monthly global terrestrial biosphere model net ecosystem exchange Joshua B. Fisher, Munish Sikka, Deborah N. Huntzinger, Christopher Schwalm, and Junjie Liu Biogeosciences, 13, 4271-4277, doi:10.5194/bg-13-4271-2016, 2016 Atmospheric models of CO 2 require estimates of land CO 2 fluxes at relatively high temporal resolutions because of the high rate of atmospheric mixing and wind heterogeneity. However, land CO 2 fluxes are often provided at monthly time steps. Here, we describe a new dataset created from 15 global land models and 4 combined products in the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP), which we have converted from monthly to 3-hourly output.

Beschreibung: Hotspots of gross emissions from the land use sector: patterns, uncertainties, and leading emission sources for the period 2000–2005 in the tropics Rosa Maria Roman-Cuesta, Mariana C. Rufino, Martin Herold, Klaus Butterbach-Bahl, Todd S. Rosenstock, Mario Herrero, Stephen Ogle, Changsheng Li, Benjamin Poulter, Louis Verchot, Christopher Martius, John Stuiver, and Sytze de Bruin Biogeosciences, 13, 4253-4269, doi:10.5194/bg-13-4253-2016, 2016 This research provides spatial data on gross emissions from the land use sector for the tropical region for the period 2000–2005. This sector contributes up to 24 % of the global emissions, but there is little understanding of where the hotspots of emissions are, how uncertain they are, and what the human activities behind these emissions are. Data provided here should assist countries to identify priority areas for mitigation action and contrast the effectiveness of their current measures.

Beschreibung: Predicting carbon dioxide and energy fluxes across global FLUXNET sites with regression algorithms Gianluca Tramontana, Martin Jung, Christopher R. Schwalm, Kazuhito Ichii, Gustau Camps-Valls, Botond Ráduly, Markus Reichstein, M. Altaf Arain, Alessandro Cescatti, Gerard Kiely, Lutz Merbold, Penelope Serrano-Ortiz, Sven Sickert, Sebastian Wolf, and Dario Papale Biogeosciences, 13, 4291-4313, doi:10.5194/bg-13-4291-2016, 2016 We have evaluated 11 machine learning (ML) methods and two complementary drivers' setup to estimate the carbon dioxide (CO 2 ) and energy exchanges between land ecosystems and atmosphere. Obtained results have shown high consistency among ML and high capability to estimate the spatial and seasonal variability of the target fluxes. The results were good for all the ecosystems, with limitations to the ones in the extreme environments (cold, hot) or less represented in the training data (tropics).

Beschreibung: Chemodiversity of dissolved organic matter in the Amazon Basin Michael Gonsior, Juliana Valle, Philippe Schmitt-Kopplin, Norbert Hertkorn, David Bastviken, Jenna Luek, Mourad Harir, Wanderley Bastos, and Alex Enrich-Prast Biogeosciences, 13, 4279-4290, doi:10.5194/bg-13-4279-2016, 2016 We present in this study a highly diverse and complex chemodiversity of dissolved organic matter (DOM) in the Amazon Basin analyzed by modern ultrahigh-resolution mass spectrometry and optical property analyses. DOM within the Rio Madeira (white water), Rio Negro (black water) and Rio Tapajós (clear water) area showed a large overlap of thousands of molecular formulae, but also unique signatures were apparent for each region, with significant correlations to colored DOM.

Beschreibung: Changes in soil carbon and nutrients following six years of litter removal and addition in a tropical semi-evergreen rain forest Edmund Vincent John Tanner, Merlin William Alfred Sheldrake, and Benjamin L. Turner Biogeosciences Discuss., doi:10.5194/bg-2016-229,2016 Manuscript under review for BG (discussion: open, 0 comments) Increasing atmospheric CO 2 and temperature may increase forest productivity, including litterfall, but the consequences for soil organic matter remain poorly understood. To address this, we measured soil carbon and nutrient concentrations at nine depths to 2 m after six years of continuous litter removal and litter addition in a semi-evergreen rain forest in Panama. Soils in litter addition plots, compared to litter removal plots, had higher pH and contained greater concentrations of KCl-extractable nitrate (both to 30 cm); Mehlich-III extractable phosphorus and total carbon (both to 20 cm); total nitrogen (to 15 cm); Mehlich-III calcium (to 10 cm); Mehlich-III magnesium and lower bulk density (both to 5 cm). In contrast, litter manipulation did not affect ammonium, manganese, potassium or zinc, and soils deeper than 30 cm did not differ for any nutrient. Comparison with previous analyses in the experiment indicates that overall the effect of litter manipulation on nutrient concentrations and the depth to which the effects are significant are increasing with time. To allow for changes in bulk density in calculation of changes in carbon stocks, we standardized total carbon and nitrogen on the basis of a constant mineral mass. For 200 kg m −2 of mineral soil (approximately the upper 20 cm of the profile) about 0.5 kg C m −2 was 'missing' from the litter removal plots, with a similar amount accumulated in the litter addition plots. There was an additional 0.4 kg C m −2 extra in the litter standing crop of the litter addition plots compared to the control. This increase in carbon in surface soil and the litter standing crop can be interpreted as a potential partial mitigation of the effects of increasing CO 2 concentrations in the atmosphere.

Beschreibung: Quantification of multiple simultaneously occurring nitrogen flows in the euphotic ocean Min Nina Xu, Yanhua Wu, Li Wei Zheng, Zhenzhen Zheng, Huade Zhao, Edward A. Laws, and Shuh-Ji Kao Biogeosciences Discuss., doi:10.5194/bg-2016-298,2016 Manuscript under review for BG (discussion: open, 0 comments) The general features of the N cycle in the sunlit ocean are known, but quantitative information about multiple transformation rates among nitrogen pools, i.e., ammonium (NH 4 + ), nitrite (NO 2 − ), nitrate (NO 3 − ) and particulate/dissolved organic nitrogen (PN/DON), are limited due to methodological difficulties. By adding a single 15 N-labelled NH 4 + tracer into incubators, we monitor ed the changes in concentration and isotopic composition of the total dissolved nitrogen (TDN), PN, NH 4 + , NO 2 − , and NO 3 − pools to trace the 15 N and 14 N flows. Based on mass conservation and isotope mass balance, we formulate d a matrix equation that allow edus to simultaneously derive the rates of multiple transformation processes in the nitrogen reaction web . We abandoned inhibitors and minimized the alteration of the system by adding a limited amount of tracer. In one single incubation, solution of the matrix equation provided the rates of NH 4 + , NO 2 − , and NO 3 − uptake; ammonia oxidation; nitrite oxidation; nitrite excretion; DON release; and potentially, the remineralization rate. To our knowledge, this is the first and most convenient method designed to quantitatively and simultaneously resolve complicated nitrogen transformation rates, albeit with some uncertainties. Field examples are given, and c omparisons with conventional labeling methods are discussed.

Beschreibung: Yedoma Ice Complex of the Buor Khaya Peninsula (southern Laptev Sea) Lutz Schirrmeister, Georg Schwamborn, Pier Paul Overduin, Jens Strauss, Margret C. Fuchs, Mikhail Grigoriev, Irina Yakshina, Janet Rethemeyer, Elisabeth Dietze, and Sebastian Wetterich Biogeosciences Discuss., doi:10.5194/bg-2016-283,2016 Manuscript under review for BG (discussion: open, 0 comments) The composition of permafrost deposits holds information on the paleo-environment during and following deposition. Sampling natural exposures and drilling are two methods used to access permafrost archives. In this study, we combine both approaches at the western coast of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia) to study late Pleistocene permafrost; namely the Yedoma Ice Complex (IC), which is prominent across much of eastern Siberia. Two Yedoma IC exposures and one drill core were studied for cryolithological (i.e. ice and sediment features), geochemical, and geochronological parameters. Borehole temperatures were measured for three years to capture the current thermal state of permafrost. The studied sequences were composed of ice-oversaturated silts and fine-grained sands with considerable amounts of organic matter (0.2 to 24 wt %). Syngenetic ice wedges intersect the frozen deposits. The deposition of the Yedoma IC, as revealed by radiocarbon dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP. Continued Yedoma IC deposition until about 14.7 kyr BP is shown by dates from organic matter preserved in ice-wedge ice. For the lowermost and oldest Yedoma IC part, infrared-stimulated luminescence dates on feldspar show deposition ages between 51.1 ± 4.9 and 44.2 ± 3.6 kyr BP. End-member modelling was applied to grain-size-distribution data to unmix sedimentation processes during Yedoma IC formation. Three to five statistical end-members were detected within Yedoma IC deposits of different ages, which we interpret as signals of alluvial, proluvial, and aeolian transport and redeposition as well as in-situ frost weathering in a polygonal tundra landscape. The study captures the internal variation of Yedoma IC characteristics and puts its local stratigraphy into regional scale. The cryolithological inventory of the Yedoma IC preserved on the Buor Khaya Peninsula is closely related to the results of other IC studies, for example, to the west on the Bykovsky Peninsula, where formation time (mainly during the late Pleistocene MIS 3 interstadial) and conditions were similar. Local freezing conditions on Buor Khaya, however, differed, and created solute-enriched (salty) and isotopically-light porewater pointing to deep active-layer and thaw-bulb freezing after deposition. Due to intense coastal erosion, the biogeochemical signature of the studied Yedoma IC represents the terrestrial end-member for, and is closely related to organic matter currently being deposited in the marine realm of the Laptev Sea shelf.

Beschreibung: Isotopic composition of nitrate and particulate organic matter in a pristine dam-reservoir of western India: Implications for biogeochemical processes Pratirupa Bardhan, S. W. A. Naqvi, Supriya G. Karapurkar, Damodar M. Shenoy, Siby Kurian, and Hema Naik Biogeosciences Discuss., doi:10.5194/bg-2016-270,2016 Manuscript under review for BG (discussion: open, 0 comments) Although India has the 3rd highest number of dams globally, there is a knowledge gap on the cycling of bioessential elements in such systems.This study, first of its kind, investigates the stable isotopes of nitrate and particulate organic matter in a pristine Indian reservoir. Nitrogen transformations in the anaerobic bottom waters were isotopically characterised. Overall, solar intensity, water depth and redox conditions are the major controls on the biogeochemical cycling in this system.

Beschreibung: Photochemical mineralisation in a boreal brown water lake: considerable temporal variability and minor contribution to carbon dioxide production Marloes Groeneveld, Lars Tranvik, Sivakiruthika Natchimuthu, and Birgit Koehler Biogeosciences, 13, 3931-3943, doi:10.5194/bg-13-3931-2016, 2016 Temporal variability in the apparent quantum yield of photochemical CDOM mineralisation in a boreal brown water lake was severalfold smaller than previously reported across different lakes. Simulated DIC photoproduction (2012–2014) averaged 2.0 ± 0.1 to 10.3 ± 0.7 g C m −2 yr −1 using the least and most reactive sample, which represented 1 to 8 % of the total mean CO 2 emissions. Thus, direct CDOM photomineralisation makes only a minor contribution to mean CO 2 emissions from Swedish brown water lakes.

Beschreibung: No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community Allanah J. Paul, Eric P. Achterberg, Lennart T. Bach, Tim Boxhammer, Jan Czerny, Mathias Haunost, Kai-Georg Schulz, Annegret Stuhr, and Ulf Riebesell Biogeosciences, 13, 3901-3913, doi:10.5194/bg-13-3901-2016, 2016 Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox, and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N 2 -fixation rates are sensitive to ocean acidification, with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ∼ 55 m 3 ) and manipulated f CO 2 over a range relevant for projected ocean acidification by the end of this century (average treatment f CO 2 : 365–1231 µatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N 2 -fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15 N-N 2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead, regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO 2 -related differences in neither inorganic nor organic N pool sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO 2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.

Beschreibung: Technical note: Assessing gas equilibration systems for continuous p CO 2 measurements in inland waters Tae Kyung Yoon, Hyojin Jin, Neung-Hwan Oh, and Ji-Hyung Park Biogeosciences, 13, 3915-3930, doi:10.5194/bg-13-3915-2016, 2016 Spray- and marble-type equilibrators and a membrane-enclosed CO 2 sensor were compared to assess their suitability for continuous p CO 2 measurements in inland waters. The results suggest that the fast response of the equilibration systems facilitates capturing large spatial variations in p CO 2 during short underway measurements. The membrane-enclosed sensor would be suitable for long-term continuous measurements if biofouling could be overcome by antifouling measures such as copper mesh coverings.

Beschreibung: New strategies for submicron characterization the carbon binding of reactive minerals in long-term contrasting fertilized soils: implications for soil carbon storage Jian Xiao, Xinhua He, Jialong Hao, Ying Zhou, Lirong Zheng, Wei Ran, Qirong Shen, and Guanghui Yu Biogeosciences, 13, 3607-3618, doi:10.5194/bg-13-3607-2016, 2016 Reactive minerals are ubiquitous in soil and are proposed as a primary driver for carbon (C) retention. However, regulation of soil reactive minerals and direct evidence in sequestrating C by them are scarce. Here we show that, compared with chemical fertilization, inorganic and organic fertilization enhanced the C-binding loadings of Al and Fe minerals in soil colloids, suggesting that reactive mineral species and their associations with C are differentially affected by fertilization practices.

Beschreibung: Shift in the chemical composition of dissolved organic matter in the Congo River network Thibault Lambert, Steven Bouillon, François Darchambeau, Philippe Massicotte, and Alberto V. Borges Biogeosciences Discuss., doi:10.5194/bg-2016-240,2016 Manuscript under review for BG (discussion: open, 0 comments) This paper aims to investigate the spatial variability of dissolved organic matter (DOM) both in terms of concentration and composition in the Congo River network. Stable carbon isotopes and absorption and fluorescent properties of DOM were used as proxies for DOM composition. This study highlights that DOM degradation within the Congo Basin results in the transition from aromatic to aliphatic DOM as well as the role of landscape and water residence time on this transition.

Beschreibung: No-tillage lessens soil CO 2 emissions the most under arid and sandy soil conditions: results from a meta-analysis Khatab Abdalla, Pauline Chivenge, Philippe Ciais, and Vincent Chaplot Biogeosciences, 13, 3619-3633, doi:10.5194/bg-13-3619-2016, 2016 Discrepancies exist on the impact of tillage on soil CO 2 emissions and on the main soil and environmental controls. Results from a meta-analysis using 174 paired observations comparing CO 2 emissions over entire seasons or years from tilled (untilled) soils across different climates, crop types and soil conditions show that on average: (1) tilled soils emit 21 % more CO 2 than untilled soils; (2) the difference increase to 29 % in sandy soils from arid climates with low soil organic carbon content.

Beschreibung: Effect of sporadic destratification, seasonal overturn, and artificial mixing on CH 4 emissions from a subtropical hydroelectric reservoir Frédéric Guérin, Chandrashekhar Deshmukh, David Labat, Sylvie Pighini, Axay Vongkhamsao, Pierre Guédant, Wanidaporn Rode, Arnaud Godon, Vincent Chanudet, Stéphane Descloux, and Dominique Serça Biogeosciences, 13, 3647-3663, doi:10.5194/bg-13-3647-2016, 2016 Methane (CH 4 ) emissions from hydroelectric reservoirs could represent a significant fraction of global CH 4 emissions from inland waters. The monitoring of methane emissions every 2 weeks at nine stations in a subtropical hydroelectric reservoir revealed that emissions could occasionally be 1 to 2 orders of magnitude higher than expected for these man-made ecosystems. Upstream of the water intake, emissions are enhanced by the water column mixing that upwells CH 4 -rich water to the surface.

Beschreibung: Blooms of cyanobacteria in a temperate Australian lagoon system post and prior to European settlement Perran L. M. Cook, Miles Jennings, Daryl P. Holland, John Beardall, Christy Briles, Atun Zawadzki, Phuong Doan, Keely Mills, and Peter Gell Biogeosciences, 13, 3677-3686, doi:10.5194/bg-13-3677-2016, 2016 The Gippsland Lakes, Australia, have suffered from periodic blooms of cyanobacteria (blue green algae) since the mid 1980s. Prior to this, little is known about the history of cyanobacterial blooms in this system. We investigated the history of cyanobacterial blooms using a sediment core taken from the Gippsland Lakes which had each layer dated using lead isotopes. The results showed that surprising blooms of cyanobacteria were also prevalent prior to European settlement

Beschreibung: Carbon and nitrogen contents in particle–size fractions of topsoil along a 3000 km aridity gradient in grasslands of northern China Xiao-Guang Wang, Seeta A. Sistla, Xiao-Bo Wang, Xiao-Tao Lü, and Xing-Guo Han Biogeosciences, 13, 3635-3646, doi:10.5194/bg-13-3635-2016, 2016 With a large-scale survey and sampling, results from this study provides strong evidence that increasing aridity would reduce the soil C and N storage in arid and semi-arid ecosystems due both to the changes of particle-sized fractions in soils (i.e. relatively more sand but less clay and silt in sites with higher aridity) and to the decline of C and N concentrations in each soil fraction.

Beschreibung: Preface: Impacts of extreme climate events and disturbances on carbon dynamics Jingfeng Xiao, Shuguang Liu, and Paul C. Stoy Biogeosciences, 13, 3665-3675, doi:10.5194/bg-13-3665-2016, 2016 This special issue showcases recent advancements on the impacts of disturbances and extreme events on the carbon (C) cycle. Notable advancements include quantifying harvest impacts on forest structure, recovery, and carbon stocks; observed dissolved organic C and methane increases in thermokarst lakes following summer warming; disentangling the roles of herbivores and fire on forest carbon dioxide flux; and improved atmospheric inversion of regional C flux by incorporating disturbances.

Beschreibung: The nitrogen, carbon and greenhouse gas budget of a grazed, cut and fertilised temperate grassland Stephanie K. Jones, Carole Helfter, Margaret Anderson, Mhairi Coyle, Claire Campbell, Daniela Famulari, Chiara Di Marco, Netty van Dijk, Cairistiona F. E. Topp, Ralf Kiese, Reimo Kindler, Jan Siemens, Marion Schrumpf, Klaus Kaiser, Eiko Nemitz, Peter Levy, Robert M. Rees, Mark A. Sutton, and Ute M. Skiba Biogeosciences Discuss., doi:10.5194/bg-2016-221,2016 Manuscript under review for BG (discussion: open, 0 comments) We assessed the nitrogen (N), carbon (C) and greenhouse gas (GHG) budget from an intensively managed grassland in Southern Scotland using flux budget calculations as well as changes in soil N and C pools over time. Estimates from flux budget calculations indicated that N and C were sequestered, whereas soil stock measurements indicated a smaller N storage and a loss of C from the ecosystem. The GHG sink strength of the net CO 2 ecosystem exchange was strongly affected by CH 4 and N 2 O emissions.

Beschreibung: Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific oceans Carolin R. Löscher, Hermann W. Bange, Ruth A. Schmitz, Cameron M. Callbeck, Anja Engel, Helena Hauss, Torsten Kanzow, Rainer Kiko, Gaute Lavik, Alexandra Loginova, Frank Melzner, Judith Meyer, Sven C. Neulinger, Markus Pahlow, Ulf Riebesell, Harald Schunck, Sören Thomsen, and Hannes Wagner Biogeosciences, 13, 3585-3606, doi:10.5194/bg-13-3585-2016, 2016 The ocean loses oxygen due to climate change. Addressing this issue in tropical ocean regions (off Peru and Mauritania), we aimed to understand the effects of oxygen depletion on various aspects of marine biogeochemistry, including primary production and export production, the nitrogen cycle, greenhouse gas production, organic matter fluxes and remineralization, and the role of zooplankton and viruses.

Beschreibung: Feasibility for detection of ecosystem response to disturbance by atmospheric carbon dioxide Bjorn-Gustaf J. Brooks, Ankur R. Desai, Britton B. Stephens, Anna M. Michalak, and Jakob Zscheischler Biogeosciences Discuss., doi:10.5194/bg-2016-223,2016 Manuscript under review for BG (discussion: open, 0 comments) CO 2 is the primary greenhouse gas, and its abundance in the atmosphere tends to increase during disturbances like drought. This paper demonstrates how CO 2 measurements are combined with models to determine not only how strongly different locations influence CO 2 measurement stations, but also the capacity of those measurement stations to detect drought effects. Understanding detection sensitivity will help assess what kinds of changes and turnings points can be monitored using atmospheric CO 2 .

Beschreibung: Reviews and syntheses: Parameter identification in marine planktonic ecosystem modelling Markus Schartau, Philip Wallhead, John Hemmings, Ulrike Loeptin, Iris Kriest, Shubham Krishna, Ben A. Ward, Thomas Slawig, and Andreas Oschlies Biogeosciences Discuss., doi:10.5194/bg-2016-242,2016 Manuscript under review for BG (discussion: open, 0 comments) Plankton ecosystem models have become an integral part in marine ecological and biogeochemical research. These models differ in structural complexity and in their number of parameters. We are concerned with the identification of parameter values that determine a model's solution. We stress that it is important to find careful balances between model complexity, data availability, level of sophistication of the mechanistic modelling approach, and the elaboration of the parameter estimation method.

Beschreibung: Source and flux of POC in a karstic area in the Changjiang River watershed: impacts of reservoirs and extreme drought Hongbing Ji, Cai Li, Huaijian Ding, and Yang Gao Biogeosciences, 13, 3687-3699, doi:10.5194/bg-13-3687-2016, 2016 The mineral composition, C / N ratios as well as 13 C and 15 N, of POC was firstly analyzed in suspended and surface sediments in the Wujiang River after the Three Gorges Dam began impounding sediment in 2004. A comparison of POC yield was made between karstic rivers and non-karstic rivers to evaluate the influence of carbonate distribution on POC transport. Considering the cascade reservoir and climate in the Wujiang River, the impacts of reservoirs and extreme drought were estimated in this study.

Beschreibung: Ocean acidification in the subpolar North Atlantic: rates and mechanisms controlling pH changes Maribel I. García-Ibáñez, Patricia Zunino, Friederike Fröb, Lidia I. Carracedo, Aida F. Ríos, Herlé Mercier, Are Olsen, and Fiz F. Pérez Biogeosciences, 13, 3701-3715, doi:10.5194/bg-13-3701-2016, 2016 We assessed the progressive acidification (pH decrease) of the North Atlantic waters from direct observations between 1991 and 2015. The greatest pH decreases were observed in surface and intermediate waters. We conclude that the observed pH decreases are a consequence of the oceanic uptake of anthropogenic CO 2 . In addition we find that they have been partially offset by alkalinity increases.

Beschreibung: Role of zooplankton in determining the efficiency of the biological carbon pump Emma L. Cavan, Stephanie A. Henson, Anna Belcher, and Richard Sanders Biogeosciences Discuss., doi:10.5194/bg-2016-251,2016 Manuscript under review for BG (discussion: open, 0 comments) The biological carbon pump (BCP) plays a key role in regulating atmospheric CO 2 . Controls on the efficiency at which this occurs are poorly known. Here we combine in situ observations with an ecosystem model to show that zooplankton have an important role in regulating the efficiency of the BCP. Predicted future changes in ocean conditions, such as expansion of oxygen minimum zones, may decrease the role of zooplankton in the BCP globally, increasing its efficiency and altering atmospheric CO 2 .

Beschreibung: Continuous measurements of nitrous oxide isotopomers during incubation experiments Malte Winther, David Balslev-Harder, Søren Christensen, Anders Priemé, Bo Elberling, Eric Crosson, and Thomas Blunier Biogeosciences Discuss., doi:10.5194/bg-2016-258,2016 Manuscript under review for BG (discussion: open, 0 comments) Nitrous oxide (N 2 O) is an important and strong greenhouse gas in the atmosphere and part of climate. N 2 O is produced by microbes in terrestrial and aquatic ecosystems. The properties of each specific molecule can be used to determine the source. We implemented continuous measurements of N 2 O during incubation of denitrifying bacteria and believe that similar experiments will lead to a better understanding of N 2 O turnover and on the biotic mechanisms behind greenhouse gas exchange of the Globe.

Beschreibung: Seasonal variability of dissolved organic matter in the Columbia River: In situ sensors elucidate biogeochemical and molecular analyses Urban Johannes Wünsch, Boris Peter Koch, Matthias Witt, and Joseph Andrew Needoba Biogeosciences Discuss., doi:10.5194/bg-2016-263,2016 Manuscript under review for BG (discussion: open, 0 comments) We used a combination of continuously measuring water chemistry sensors and periodic sampling efforts to assess the seasonal variability of dissolved organic matter (DOM) in the Columbia River in spring and summer 2013. We found that our sensors can provide detailed data on carbon export that far exceed usual monitoring efforts. The detailed data help to understand the impact of short-lived events, such as rainstorms, on the overall terrestrial carbon flux in the Columbia River.

Beschreibung: Are flood-driven turbidity currents hot spots for priming effect in lakes? Damien Bouffard and Marie-Elodie Perga Biogeosciences, 13, 3573-3584, doi:10.5194/bg-13-3573-2016, 2016 This survey of an exceptional flood over Lake Geneva challenges the long-standing hypothesis that dense, particle-loaded and oxygenated rivers plunging into lakes necessarily contribute to deep-oxygen replenishment. We identified some river intrusions as hot spots for oxygen consumption, where inputs of fresh river-borne organic matter reactivate the respiration of more refractory lacustrine organic matter in a process referred to as "priming effect".

Beschreibung: A multi-scale comparison of modeled and observed seasonal methane cycles in northern wetlands Xiyan Xu, William J. Riley, Charles D. Koven, Dave P. Billesbach, Rachel Y.-­W. Chang, Róisín Commane, Eugénie S. Euskirchen, Sean Hartery, Yoshinobu Harazono, Hiroki Iwata, Kyle C. McDonald, Charles E. Miller, Walter C. Oechel, Benjamin Poulter, Naama Raz-Yaseef, Colm Sweeney, Margaret Torn, Steven C. Wofsy, Zhen Zhang, and Donatella Zona Biogeosciences Discuss., doi:10.5194/bg-2016-167,2016 Manuscript under review for BG (discussion: open, 0 comments) Wetlands are the single largest global natural methane source. Peat-rich bogs and fens lying between 50°N and 70°N contribute 10–30% to this source. The predictive capability of seasonal methane cycle can directly affect the estimation of global methane budget. We present multi-scale methane seasonal cycle by observations and modeling and find the greatest uncertainties in predicting the seasonal methane cycle are from the wetland extent, cold season CH 4 production and CH 4 transport processes.

Beschreibung: Processes regulating progressive nitrogen limitation under elevated carbon dioxide: a meta-analysis Junyi Liang, Xuan Qi, Lara Souza, and Yiqi Luo Biogeosciences, 13, 2689-2699, doi:10.5194/bg-13-2689-2016, 2016 It is unclear how the nitrogen (N) cycle regulates climate change through influencing carbon sequestration. By using meta-analysis, we tested a popular hypothesis, progressive N limitation (PNL), which postulates that greater N sequestration in organisms leads to declining N availability for further plant growth under elevated CO 2 . Our analyses suggest that extra nitrogen supply by increased biological N fixation and decreased leaching may potentially alleviate PNL.

Beschreibung: Change in coccolith size and morphology due to response to temperature and salinity in coccolithophore Emiliania huxleyi (Haptophyta) isolated from the Bering and Chukchi seas Kazuko Saruwatari, Manami Satoh, Naomi Harada, Iwane Suzuki, and Yoshihiro Shiraiwa Biogeosciences, 13, 2743-2755, doi:10.5194/bg-13-2743-2016, 2016 Coccolithophore Emiliania huxleyi (Haptophyta) strains collected from the subarctic North Pacific and Arctic oceans during the R/V MIRAI cruise in 2010 (MR10-05) were established as clone cultures. This is the first report of a detailed morphometric and morphological investigation of Arctic Ocean coccolithophore strains. Taken together, our results suggest that calcification productivity can be used to predict future oceanic environmental conditions in the polar regions.

Beschreibung: Sex-associated variations in coral skeletal oxygen and carbon isotopic composition of Porites panamensis in the southern Gulf of California Rafael A. Cabral-Tena, Alberto Sánchez, Héctor Reyes-Bonilla, Angel H. Ruvalcaba-Díaz, and Eduardo F. Balart Biogeosciences, 13, 2675-2687, doi:10.5194/bg-13-2675-2016, 2016 Coral growth rate is known to influence the δ 18 O and δ 13 C isotope record to a lesser extent. Recent published data show differences in growth parameters between female and male coral; thus, skeletal δ 18 O and δ 13 C are hypothesized to be different in each sex. Our results support the hypothesis of a sex-associated difference in skeletal δ 18 O and δ 13 C signal, and suggest that environmental conditions and coral growth parameters affect skeletal isotopic signal differently in each sex.

Beschreibung: Global warming potential and greenhouse gas intensity in rice agriculture driven by high yields and nitrogen use efficiency Xiaoxu Zhang, Xin Xu, Yinglie Liu, Jinyang Wang, and Zhengqin Xiong Biogeosciences, 13, 2701-2714, doi:10.5194/bg-13-2701-2016, 2016 The intensive agriculture is facing environmental problems due to low nitrogen use efficiency (NUE) in China. Integrated soil-crop system management (ISSM) has been developed to increase crop yield and NUE. We investigated greenhouse gas intensity after accounting for CO 2 emissions from all sources, including methane and nitrous oxide emissions, agrochemical inputs and farm operations and sinks. We found that the ISSM strategies are promising for both food security and environmental protection.

Beschreibung: Effect of light on photosynthetic efficiency of sequestered chloroplasts in intertidal benthic foraminifera ( Haynesina germanica and Ammonia tepida ) Thierry Jauffrais, Bruno Jesus, Edouard Metzger, Jean-Luc Mouget, Frans Jorissen, and Emmanuelle Geslin Biogeosciences, 13, 2715-2726, doi:10.5194/bg-13-2715-2016, 2016 Some benthic foraminifera can incorporate chloroplasts from microalgae. We investigated chloroplast functionality of two benthic foraminifera ( Haynesina germanica & Ammonia tepida ) exposed to different light levels. Only H. germanica was capable of using the kleptoplasts, showing net oxygen production. Chloroplast functionality time was longer in darkness (2 weeks) than at high light (1 week). Kleptoplasts are unlikely to be completely functional, thus requiring continuous chloroplast resupply.

Beschreibung: Along-stream transport and transformation of dissolved organic matter in a large tropical river Thibault Lambert, Cristian R. Teodoru, Frank C. Nyoni, Steven Bouillon, François Darchambeau, Philippe Massicotte, and Alberto V. Borges Biogeosciences, 13, 2727-2741, doi:10.5194/bg-13-2727-2016, 2016 This manuscript presents a detailed analysis of transport and transformation of dissolved organic matter along the Zambezi River and its largest tributary. A particular focus is put on the effects of floodplains/wetlands and reservoirs as well as low-flow vs. high-flow conditions on the longitudinal patterns in DOM concentration and composition. It is the first study to present such a detailed analysis for a whole, large river system, and in particular for a tropical river other than the Amazon.

Beschreibung: Australian vegetation phenology: new insights from satellite remote sensing and digital repeat photography Caitlin E. Moore, Tim Brown, Trevor F. Keenan, Remko A. Duursma, Albert I. J. M. van Dijk, Jason Beringer, Darius Culvenor, Bradley Evans, Alfredo Huete, Lindsay B. Hutley, Stefan Maier, Natalia Restrepo-Coupe, Oliver Sonnentag, Alison Specht, Jeffrey R. Taylor, Eva van Gorsel, and Michael J. Liddell Biogeosciences Discuss., doi:10.5194/bg-2016-175,2016 Manuscript under review for BG (discussion: open, 0 comments) Australian vegetation phenology is highly variable due to the diversity of ecosystems on the continent. We explore continental scale variability using satellite remote sensing by broadly classifying areas as seasonal, non-seasonal or irregularly seasonal. We also examine ecosystem scale phenology using phenocams and show that some broadly non-seasonal ecosystems do display phenological variability. Overall, phenocams are useful for understanding ecosystem scale Australian vegetation phenology.

Beschreibung: Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO) Jason Beringer, Ian McHugh, Lindsay B. Hutley, Peter Isaac, and Natascha Kljun Biogeosciences Discuss., doi:10.5194/bg-2016-188,2016 Manuscript under review for BG (discussion: open, 0 comments) Standardised, quality-controlled and robust data from flux networks underpin the understanding of ecosystem processes and tools to manage our natural resources. The Dynamic INtegrated Gap-filling and partitioning for OzFlux (DINGO) system enables gap-filling and partitioning of fluxes and subsequently provides diagnostics and results. Quality data from robust systems like DINGO ensure the utility and uptake of flux data and facilitates synergies between flux, remote sensing and modelling.

Beschreibung: Sediment characteristics as an important factor for revealing carbon storage in Zostera marina meadows: a comparison of four European areas Martin Dahl, Diana Deyanova, Silvia Gütschow, Maria E. Asplund, Liberatus D. Lyimo, Ventzislav Karamfilov, Rui Santos, Mats Björk, and Martin Gullström Biogeosciences Discuss., doi:10.5194/bg-2016-137,2016 Manuscript under review for BG (discussion: open, 0 comments) The seagrass ecosystem is an important natural carbon sink but the efficiency varies greatly depending on species composition and environmental conditions. What causes this variation is not fully known and could have important implications for management and protection of the seagrass habitat to continue to act as a natural carbon sink. Here, we assessed sedimentary organic carbon in Zostera marina meadows (and adjacent unvegetated sediment) in four areas of Europe (Gullmar Fjord on the Swedish west coast, Askö in the Baltic Sea, Sozopol in Black Sea and Ria Formosa in southern Portugal) down to ~ 35 cm depth. We also tested how sedimentary organic carbon in Z. marina meadows relates to different sediment characteristics, a range of seagrass-associated variables and water depth. The carbon storage varied both among and within areas, where the Gullmar Fjord had a 15 times higher carbon storage compared to Askö and Sozopol. We found that high carbon content in Z. marina sediment is strongly related to a high proportion of fine grain size, high porosity and low density of the sediment. We suggest that sediment characteristics should be highlighted as an important factor when evaluating high priority areas in management of Z. marina generated carbon sinks.

Beschreibung: Introduction to the project VAHINE: VAriability of vertical and tropHIc transfer of diazotroph derived N in the south wEst Pacific Sophie Bonnet, Thierry Moutin, Martine Rodier, Jean-Michel Grisoni, Francis Louis, Eric Folcher, Bertrand Bourgeois, Jean-Michel Boré, and Armelle Renaud Biogeosciences, 13, 2803-2814, doi:10.5194/bg-13-2803-2016, 2016 e main goal of the VAHINE project was to study the fate of N 2 fixation in the ocean. Three large-volume (~ 50 m 3 ) mesocosms were deployed in a tropical oligotrophic ecosystem (the New Caledonia lagoon, south-eastern Pacific). This introductory paper describes the scientific objectives of the project in detail as well as the implementation plan: the mesocosm description and deployment, the selection of the study site, and the logistical and sampling strategy.

Beschreibung: Challenges and opportunities in modelling savanna ecosystems Rhys Whitley, Jason Beringer, Lindsay B. Hutley, Gabriel Abramowitz, Martin G. De Kauwe, Bradley Evans, Vanessa Haverd, Longhui Li, Caitlin Moore, Youngryel Ryu, Simon Scheiter, Stanislaus J. Schymanski, Benjamin Smith, Ying-Ping Wang, Mathew Williams, and Qiang Yu Biogeosciences Discuss., doi:10.5194/bg-2016-190,2016 Manuscript under review for BG (discussion: open, 0 comments) This paper attempts to review some of the current challenges faced by the modelling community in simulating the behaviour of savanna ecosystems. We provide a particular focus on three dynamic processes (phenology, root-water access, and fire) that are characteristic of savannas, which we believe are not adequately represented in current-generation terrestrial biosphere models. We highlight reasons for these misrepresentations, possible solutions and a future direction for research in this area.

Beschreibung: Ragweed pollen production and dispersion modelling within a regional climate system, calibration and application over Europe Li Liu, Fabien Solmon, Robert Vautard, Lynda Hamaoui-Laguel, Csaba Zsolt Torma, and Filippo Giorgi Biogeosciences, 13, 2769-2786, doi:10.5194/bg-13-2769-2016, 2016 To study the distribution of airborne ragweed pollen in changing environments and associated health risks over Europe, we introduce an approach with explicit treatment of pollen ripening, release and dispersion due to environmental drivers in an online modelling framework where climate is integrated with dispersion and vegetation production. From a simulated pollen season and concentration pattern health risks are evaluated through calculation of exposure time above health-relevant threshold levels.

Beschreibung: What drives the spatial variability of primary productivity and matter fluxes in the North-West African upwelling system? A modelling approach and box analysis Pierre-Amaël Auger, Thomas Gorgues, Eric Machu, Olivier Aumont, and Patrice Brehmer Biogeosciences Discuss., doi:10.5194/bg-2016-156,2016 Manuscript under review for BG (discussion: open, 0 comments) A box modeling approach reveals that horizontal currents drive the spatial distribution of phytoplankton biomass and primary production in the North-West African upwelling system. Alongshore (cross-shore) currents limit (enhance) cross-shore exchanges north (south) of Cape Blanc. Off Cape Blanc, a meridional convergence makes ambiguous the response of coastal nutrient upwelling to wind forcings, and high production is based upon nutrients and remineralized carbon injected by horizontal currents.

Beschreibung: Dynamics of N 2 fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia) Sophie Bonnet, Hugo Berthelot, Kendra Turk-Kubo, Sarah Fawcett, Eyal Rahav, Stéphane L'Helguen, and Ilana Berman-Frank Biogeosciences, 13, 2653-2673, doi:10.5194/bg-13-2653-2016, 2016 N 2 fixation rates were measured daily in ~ 50 m 3 mesocosms deployed in New Caledonia to investigate the high-frequency dynamics of diazotrophy and the fate of diazotroph-derived nitrogen (DDN) oligotrophic ecosystems. ~ 10 % of UCYN-C from the water column were exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. 16 ± 6 % of the DDN was released to the dissolved pool and 21 ± 4 % was transferred to non-diazotrophic plankton.

Beschreibung: Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil: I. Decomposition and priming effect Zhenke Zhu, Guanjun Zeng, Tida Ge, Yajun Hu, Chengli Tong, Olga Shibistova, Juan Wang, Georg Guggenberger, and Jinshui Wu Biogeosciences Discuss., doi:10.5194/bg-2016-86,2016 Manuscript under review for BG (discussion: open, 0 comments) The main contribution of our study is our finding that rhizodeposits and microbe-assimilated carbon contribute significantly to the sequestration of carbon substrates in rice paddy soils. This contribution is theoretically and practically relevant because few studies have investigated the effects of different carbon substrates on the mineralization of native soil organic carbon and our findings have immediate applications for improving the fertility of paddy soils and mitigating global warming.

Beschreibung: Interannual variability in Australia's terrestrial carbon cycle constrained by multiple observation types Cathy M. Trudinger, Vanessa Haverd, Peter R. Briggs, and Josep G. Canadell Biogeosciences Discuss., doi:10.5194/bg-2016-186,2016 Manuscript under review for BG (discussion: open, 0 comments) Semi-arid ecosystems in Australia are responsible for a significant part of the variability in global atmospheric carbon dioxide. Here we use Australian observations to estimate parameters in a land surface model of carbon and water cycles. We quantify the variability in Australian carbon fluxes between 1982–2013, including the large uptake in 2011 associated with wet conditions following a prolonged drought. We estimate the effect of parameter uncertainty on these estimates.

Beschreibung: Use of remote-sensing reflectance to constrain a data assimilating marine biogeochemical model of the Great Barrier Reef Emlyn M. Jones, Mark E. Baird, Mathieu Mongin, John Parslow, Jenny Skerratt, Nugzar Margvelashvili, Richard J. Matear, Karen Wild-Allen, Barbara Robson, Farhan Rizwi, Peter Oke, Edward King, Thomas Schroeder, Andy Steven, and John Taylor Biogeosciences Discuss., doi:10.5194/bg-2016-168,2016 Manuscript under review for BG (discussion: open, 0 comments) Marine biogeochemical models are often used to understand water quality, nutrient and blue-carbon dynamics at scales that range from rivers through to the global ocean. We introduce a new methodology allowing for the assimilation of observed remote sensing reflectances, avoiding the need to use error prone satellite derived chlorophyll-a concentrations. This method opens up the possibility to assimilate of reflectances from a varety of missions and potentially non-satellite platforms.

Beschreibung: Sensitivity towards elevated p CO 2 in great scallop ( Pecten maximus Lamarck) embryos and fed larvae Sissel Andersen, Ellen S. Grefsrud, and Torstein Harboe Biogeosciences Discuss., doi:10.5194/bg-2016-176,2016 Manuscript under review for BG (discussion: open, 0 comments) Ocean acidification (OA) in the near future is affecting several marine organisms negatively. To increase our knowledge on the effects we studied embryos and larvae of the great scallop. They were exposed to an increasing level of OA, from natural seawater to levels expected in 50–100 years from now. Larvae were negatively affected already after 2 days, and fed larva seemed as sensitive as unfed larvae after 7 days. Adaption and acclimatization may counteract future OA effects on scallops.

Beschreibung: OzFlux Data: Network integration from collection to curation Peter Isaac, James Cleverly, Ian McHugh, Eva van Gorsel, Cacilia Ewenz, and Jason Beringer Biogeosciences Discuss., doi:10.5194/bg-2016-189,2016 Manuscript under review for BG (discussion: open, 0 comments) Networks of flux towers present diverse challenges to data collectors, managers and users. For data collectors, the goal is to minimise the time spent producing usable data sets. For data managers, the challenge is making data available in a timely and broad manner. For data users, the quest is for consistency in data processing across sites and networks. The OzFlux data path was developed to address these disparate needs and serves as an example of intra- and inter-network integration.

Beschreibung: Deep ocean mass fluxes in the coastal upwelling off Mauritania from 1988 to 2012: variability on seasonal to decadal timescales Gerhard Fischer, Oscar Romero, Ute Merkel, Barbara Donner, Morten Iversen, Nico Nowald, Volker Ratmeyer, Götz Ruhland, Marco Klann, and Gerold Wefer Biogeosciences, 13, 3071-3090, doi:10.5194/bg-13-3071-2016, 2016 The studies were initiated to investigate potential changes in the important coastal upwelling system off NW Africa and to evaluate the role of mineral dust for carbon sequestration into the deep ocean. For this purpose, we deployed time series sediment traps in the deep water column off Cape Blanc, Mauritania. A more than two-decadal sediment trap record from this coastal upwelling system is now presented with respect to deep ocean mass fluxes, flux components and their longer term variability.

Beschreibung: An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM 4.5) Brett Raczka, Henrique F. Duarte, Charles D. Koven, Daniel Ricciuto, Peter E. Thornton, John C. Lin, and David R. Bowling Biogeosciences Discuss., doi:10.5194/bg-2016-73,2016 Manuscript under review for BG (discussion: open, 0 comments) We use carbon isotopes of CO 2 to improve the performance of a land surface model, a component with earth system climate models. We found that isotope observations can provide important information related to the exchange of carbon and water from vegetation driven by environmental stress from low atmospheric moisture and nitrogen limitation. It follows that isotopes have a unique potential to improve model performance and provide insight into land surface model development.

Beschreibung: Foraging segregation of two congeneric diving seabird species breeding on St. George Island, Bering Sea Nobuo Kokubun, Takashi Yamamoto, Nobuhiko Sato, Yutaka Watanuki, Alexis Will, Alexander S. Kitaysky, and Akinori Takahashi Biogeosciences, 13, 2579-2591, doi:10.5194/bg-13-2579-2016, 2016 Subarctic climate changes may affect the foraging ecology of top predators. We studied the foraging characteristics of two diving seabirds: common (COMUs) and thick-billed murres (TBMUs). COMUs had smaller wing area, partly used deeper depths with more frequent wing strokes, and used higher trophic prey than TBMUs. The smaller wing of COMUs may facilitate swimming agility so that they can capture more mobile prey. These may lead to their different responses to local marine environmental changes.

Beschreibung: Decoupled carbonate chemistry controls on the incorporation of boron into Orbulina universa . E. L. Howes, K. Kaczmarek, M. Raitzsch, A. Mewes, N. Bijma, I. Horn, S. Misra, J.-P. Gattuso, and J. Bijma Biogeosciences Discuss., doi:10.5194/bg-2016-90,2016 Manuscript under review for BG (discussion: open, 0 comments) In order to fully constrain paleo-carbonate systems, proxies for two out of seven parameters, plus temperature and salinity are required. The boron isotopic composition ( δ 11 B) of planktonic foraminifera shells is a powerful tool to reconstruct changes in past surface ocean pH. As B(OH) 4 − is substituted into the biogenic calcite lattice in place of CO 3 2− , it has been suggested that B/Ca ratios in biogenic calcite are a possible proxy for [CO 3 2− ]. However, differentiating between the effects of pH and [CO 3 2− ] is problematic, as they co-vary closely in natural systems, and so the major control on boron incorporation remains unclear. To deconvolve the effects of pH and [CO 3 2− ] on the B/Ca ratio and to test whether δ 11 B remains constant at constant pH, but under changing [CO 3 2− ] (pH 8.05 with 238, 285 and 532 µmol kg −1 CO 3 2− ) and vice versa, we decoupled pH and [CO 3 2− ] (276 ± 19.5 µmol kg −1 CO 3 2− with pH 7.7, 7.9 and 8.05) and grew the planktonic foraminifer Orbulina universa in these manipulated culture media. Measurements of the isotope composition of boron and the B/Ca ratio were performed simultaneously using a femtosecond laser ablation system coupled to an MC ICP-MS. Results show that δ 11 B is controlled by pH and does not respond to changes in [CO 3 2− ]. On the other hand, the B/Ca ratio is driven by [HCO 3 − ] independently of pH. This suggests that B/Ca ratios in foraminiferal calcite may be used as a second, independent, proxy for paleo-carbonate system reconstructions.

Beschreibung: Manganese in the world ocean: a first global model Marco van Hulten, Jean-Claude Dutay, Rob Middag, Hein de Baar, Matthieu Roy-Barman, Marion Gehlen, Alessandro Tagliabue, and Andreas Sterl Biogeosciences Discuss., doi:10.5194/bg-2016-282,2016 Manuscript under review for BG (discussion: open, 0 comments) We ran a model to understand manganese (Mn) that is a biologically essential element and influences other trace metals. Our ocean circulation model shows: – There is a lot of manganese at the surface of the ocean due to photoreduction and dust and sediments sources to the upper ocean. – There must be a minimal concentration of particulate Mn before settling becomes efficient; this explains the mostly homogeneous background concentration of dissolved Mn in the deep ocean.

Beschreibung: Analysing the uncertainty of estimating forest carbon stocks in China Tian Xiang Yue, Yi Fu Wang, Zheng Ping Du, Ming Wei Zhao, Li Li Zhang, Na Zhao, Ming Lu, Guy R. Larocque, and John P. Wilson Biogeosciences, 13, 3991-4004, doi:10.5194/bg-13-3991-2016, 2016 The fusion of ground-based forest inventory data with satellite observations achieved with HASM-S provided much more accurate estimates of forest carbon stocks, comparing with either the remote sensing descriptions or the forest inventory data. The HASM-S results show that the forest carbon stocks of China have increased by 2.24 Pg during the period 1984–2008 to a new high of 7.08 Pg C in 2008.

Beschreibung: Transfer of diazotroph-derived nitrogen towards non-diazotrophic planktonic communities: a comparative study between Trichodesmium erythraeum , Crocosphaera watsonii and Cyanothece sp. Hugo Berthelot, Sophie Bonnet, Olivier Grosso, Véronique Cornet, and Aude Barani Biogeosciences, 13, 4005-4021, doi:10.5194/bg-13-4005-2016, 2016 Biological dinitrogen (N 2 ) fixation is the major source of new nitrogen (N) for the open ocean, and thus promotes marine productivity, in particular in the vast N-depleted regions of the surface ocean. Yet, the fate of the diazotroph-derived N (DDN) in marine ecosystems is poorly understood, and its transfer to auto- and heterotrophic surrounding plankton communities is rarely measured due to technical limitations. Moreover, the different diazotrophs involved in N 2 fixation ( Trichodesmium spp. vs. UCYN) exhibit distinct patterns of N 2 fixation and inhabit different ecological niches, thus having potentially different fates in the marine food webs that remain to be explored. Here we used nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15 N 2 isotopic labelling and flow cytometry cell sorting to examine the DDN transfer to specific groups of natural phytoplankton and bacteria during artificially induced diazotroph blooms in New Caledonia (southwestern Pacific). The fate of the DDN was compared according to the three diazotrophs: the filamentous and colony-forming Trichodesmium erythraeum (IMS101), and the unicellular strains Crocosphaera watsonii WH8501 and Cyanothece ATCC51142. After 48 h, 7–17 % of the N 2 fixed during the experiment was transferred to the dissolved pool and 6–12 % was transferred to non-diazotrophic plankton. The transfer was twice as high in the T. erythraeum bloom than in the C. watsonii and Cyanothece blooms, which shows that filamentous diazotrophs blooms are more efficient at promoting non-diazotrophic production in N-depleted areas. The amount of DDN released in the dissolved pool did not appear to be a good indicator of the DDN transfer efficiency towards the non-diazotrophic plankton. In contrast, the 15 N-enrichment of the extracellular ammonium (NH 4 + ) pool was a good indicator of the DDN transfer efficiency: it was significantly higher in the T. erythraeum than in unicellular diazotroph blooms, leading to a DDN transfer twice as efficient. This suggests that NH 4 + was the main pathway of the DDN transfer from diazotrophs to non-diazotrophs. The three simulated diazotroph blooms led to significant increases in non-diazotrophic plankton biomass. This increase in biomass was first associated with heterotrophic bacteria followed by phytoplankton, indicating that heterotrophs took the most advantage of the DDN in this oligotrophic ecosystem.

Beschreibung: Annual variability and regulation of methane and sulfate fluxes in Baltic Sea estuarine sediments Joanna E. Sawicka and Volker Brüchert Biogeosciences Discuss., doi:10.5194/bg-2016-272,2016 Manuscript under review for BG (discussion: open, 0 comments) The biogeochemistry of methane was studied in high-latitude fjord-type estuarine sediment in the Baltic Sea from April 2012 to April 2013. A large variability in methane-producing and methane-oxidizing processes was observed over the year. Oxygen was the most important regulator for the methane flux. In addition to eutrophication effects, free gas movement is suggested as a factor controlling methane concentrations.

Beschreibung: Projected decreases in future marine export production: the role of the carbon flux through the upper ocean ecosystem Charlotte Laufkötter, Meike Vogt, Nicolas Gruber, Olivier Aumont, Laurent Bopp, Scott C. Doney, John P. Dunne, Judith Hauck, Jasmin G. John, Ivan D. Lima, Roland Seferian, and Christoph Völker Biogeosciences, 13, 4023-4047, doi:10.5194/bg-13-4023-2016, 2016 We compare future projections in marine export production, generated by four ecosystem models under IPCC's high-emission scenario RCP8.5. While all models project decreases in export, they differ strongly regarding the drivers. The formation of sinking particles of organic matter is the most uncertain process with models not agreeing on either magnitude or the direction of change. Changes in diatom concentration are a strong driver for export in some models but of low significance in others.

Beschreibung: Quantifying Soil Carbon Accumulation in Alaskan Terrestrial Ecosystems during the Last 15,000 Years Sirui Wang, Qianlai Zhuang, and Zicheng Yu Biogeosciences Discuss., doi:10.5194/bg-2016-284,2016 Manuscript under review for BG (discussion: open, 0 comments) We used a model to quantify the carbon stock and its changes in terrestrial ecosystems of Alaska during the last 15,000 years. We found that the changes of vegetation distribution due to climatic were the key factors to the spatial variations of carbon in different time periods. The warming during 11–9k yrs ago characterized by the increased summer temperature and seasonality of radiation, along with the high precipitation might play an important role in causing the high carbon accumulation.

Beschreibung: Low planktic foraminiferal diversity and abundance observed in a 2013 West-East Mediterranean Sea transect Miguel Mallo, Patrizia Ziveri, P. Graham Mortyn, Ralf Schiebel, and Michaël Grelaud Biogeosciences Discuss., doi:10.5194/bg-2016-266,2016 Manuscript under review for BG (discussion: open, 0 comments) Single-celled living calcareous planktic foraminifera data, across the Mediterranean Sea suggest that stratification of the surface water column, nutrient concentration and food availability, and temperature are the main factors controlling their distribution. Increasing temperature, salinity, surface ocean stratification and trophic conditions could be the causes of reduced abundance, diversity and species-specific changes in calcification in planktic foraminifera.

Beschreibung: Diatoms Si uptake capacity drives carbon export in coastal upwelling systems Fatima Abrantes, Pedro Cermeno, Cristina Lopes, Oscar Romero, Lélia Matos, Jolanda Van Iperen, Marta Rufino, and Vitor Magalhães Biogeosciences, 13, 4099-4109, doi:10.5194/bg-13-4099-2016, 2016 Diatoms are the dominant primary producers of the most productive and best fishing areas of the modern ocean, the coastal upwelling systems. This turns them into important contributors to the biological pump and climate change. To help untangle their response to warming climate, we compare the worldwide diatom sedimentary abundance (SDA) to environmental variables and find that the capacity of diatoms to take up silicic acid sets an upper limit on global export production in these ocean regions.

Beschreibung: Nitrogen fixation in sediments along a depth transect through the Peruvian oxygen minimum zone Jessica Gier, Stefan Sommer, Carolin R. Löscher, Andrew W. Dale, Ruth A. Schmitz, and Tina Treude Biogeosciences, 13, 4065-4080, doi:10.5194/bg-13-4065-2016, 2016 Benthic nitrogen fixation and sulfate reduction were investigated in the Peruvian oxygen minimum zone. The data suggest a coupling of both activities to a large extent, but that also sulfide and organic matter availability are controlling the benthic diazotrophy in this area. The molecular analysis confirms the presence of heterotrophic diazotrophs. This work improves our understanding of N cycling in OMZ sediments and the understanding of N sources in the marine environment.

Beschreibung: Air-water CO 2 evasion from U.S. East Coast estuaries Nicolas Goossens, Goulven Gildas Laruelle, Sandra Arndt, Wei - Jun Cai, and Pierre Regnier Biogeosciences Discuss., doi:10.5194/bg-2016-278,2016 Manuscript under review for BG (discussion: open, 0 comments) This study presents the first regional-sca–45° N). The focus is on 43 tidal estuaries, which together drain a catchment of 697 10 3  km 2 or 76 % of the total area within this latitudinal band. The approach is based on the Carbon – Generic Estuarine Model (C-GEM) that allows simulating hydrodynamics, transport and biogeochemistry for a wide range of estuarine systems using readily available geometric parameters and global databases of seasonal climatic, hydraulic, and riverine biogeochemical information. Together, US East coast estuaries emit 1.9 TgC yr −1 , which correspond to about 40 % of the carbon inputs from rivers, marshes and mangroves. Carbon removal within estuaries results from a combination of physical (outgassing of supersaturated riverine waters) and biogeochemical processes (net heterotrophy and nitrification). The CO 2 evasion and its underlying drivers show important variations across individual systems, but reveal a clear latitudinal pattern characterized by a decrease in the relative importance of physical over biogeochemical processes along a North-South gradient. Finally, results reveal that the ratio of estuarine surface area to the river discharge, S/Q (which has a scale of per meter discharged water per year), could be used as a predictor of the estuarine carbon processing in future regional and global scale assessments.

Beschreibung: Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles Corinne Le Quéré, Erik T. Buitenhuis, Róisín Moriarty, Séverine Alvain, Olivier Aumont, Laurent Bopp, Sophie Chollet, Clare Enright, Daniel J. Franklin, Richard J. Geider, Sandy P. Harrison, Andrew G. Hirst, Stuart Larsen, Louis Legendre, Trevor Platt, I. Colin Prentice, Richard B. Rivkin, Sévrine Sailley, Shubha Sathyendranath, Nick Stephens, Meike Vogt, and Sergio M. Vallina Biogeosciences, 13, 4111-4133, doi:10.5194/bg-13-4111-2016, 2016 We present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types, and use the model to assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean. Our results suggest that observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton growth.

Beschreibung: Methods to retrieve the complex refractive index of aquatic suspended particles: going beyond simple shapes Albert-Miquel Sánchez and Jaume Piera Biogeosciences, 13, 4081-4098, doi:10.5194/bg-13-4081-2016, 2016 In this paper, several methods for the retrieval of the refractive indices are used in three different examples modeling different shapes and particle size distributions. The error associated with each method is discussed and analyzed. It is finally demonstrated that those inverse methods using a genetic algorithm provide optimal estimations relative to other techniques that, although faster, are less accurate.

Beschreibung: Archive of bacterial community in anhydrite crystals from a deep-sea basin provides evidence of past oil-spilling in a benthic environment in the Red Sea Yong Wang, Tie Gang Li, Meng Ying Wang, Qi Liang Lai, Jiang Tao Li, Zhao Ming Gao, Zong Ze Shao, and Pei Yuan Qian Biogeosciences Discuss., doi:10.5194/bg-2016-204,2016 Manuscript under review for BG (discussion: open, 0 comments) Mild eruption of hydrothermal solutions on deep-sea benthic floor can produce anhydrite crystal layers, where microbes are trapped and preserved for a long period of time. These original inhabitants will be biomarkers for the environments when the hydrothermal eruption occurred. This study discovered a thick anhydrite layers in a deep-sea brine pool in the Red Sea. Oil-degrading bacteria were revealed in the crystals with genomic and microscopic evidence.

Beschreibung: Linking phosphorus and potassium deficiency to microbial methane cycling in rice paddies Rong Sheng, Anlei Chen, Miaomiao Zhang, Andrew S. Whiteley, Deepak Kumaresan, and Wenxue Wei Biogeosciences Discuss., doi:10.5194/bg-2016-213,2016 Manuscript under review for BG (discussion: open, 0 comments) Whilst previous studies have focused on the impact of nitrogen on microbe-mediated methane flux, little is known about the role of phosphorus and potassium. Here, we report that methane flux was much more affected by P deficiency compared to K deficiency in the paddy soil, which was closely correlated with the abundance and community structures of active methanogens and methanotrophs. These results can benefit the effective nutrient management of paddy fields to reduce methane emission.

Beschreibung: Global analysis of gene expression dynamics within the marine microbial community during the VAHINE mesocosm experiment in the southwest Pacific Ulrike Pfreundt, Dina Spungin, Sophie Bonnet, Ilana Berman-Frank, and Wolfgang R. Hess Biogeosciences, 13, 4135-4149, doi:10.5194/bg-13-4135-2016, 2016 The VAHINE experiment in the New Caledonia lagoon (SW Pacific) targeted the dynamics of nutrient pools and fluxes, N 2 fixation, and the composition and productivity of the microbial communities. To connect this information to the actual activities of diverse microbial taxa, we present the analysis of the community-wide gene expression for 23 days. The results from this experiment provide insight into the microbial activities in a low-nutrient, low-chlorophyll ecosystem and within a mesocosm.

Beschreibung: Food selectivity and processing by the cold-water coral Lophelia pertusa Dick van Oevelen, Christina E. Mueller, Tomas Lundälv, and Jack J. Middelburg Biogeosciences Discuss., doi:10.5194/bg-2016-294,2016 Manuscript under review for BG (discussion: open, 0 comments) Cold-water corals form true hotspots of biodiversity in the dark and cold deep sea, but need to live of only small amounts of food that reaches the deep sea. This study investigated, using chemical tracers, whether cold-water corals are picky eaters. We found that under low food conditions, they do not differentiate between food sources but they become picky at high food concentrations. This adaptation suggests that they are well adapted to exploit short food pulses efficiently.

Beschreibung: Development and evaluation of an ozone deposition scheme for coupling to a terrestrial biosphere model Martina Franz, David Simpson, Almut Arneth, and Sönke Zaehle Biogeosciences Discuss., doi:10.5194/bg-2016-299,2016 Manuscript under review for BG (discussion: open, 0 comments) Ozone is a toxic air pollutant that can damage plant leaves and impact their carbon uptake from the atmosphere. We extend a terrestrial biosphere model to account for ozone damage of plants and investigate the impact on the terrestrial carbon cycle. Our approach accounts for ozone transport from free troposphere to leaf level. We find that this substantially affects simulated ozone uptake into the plants. Simulations indicate that ozone damages plants less than expected from previous studies.

Beschreibung: C / N ratio, stable isotope (δ 13 C, δ 15 N), and n -alkane patterns of bryophytes along hydrological gradients of low-centred polygon of the Siberian Arctic Romy Zibulski, Felix Wesener, Heinz Wilkes, Birgit Plessen, Luidmila A. Pestryakova, and Ulrike Herzschuh Biogeosciences Discuss., doi:10.5194/bg-2016-141,2016 Manuscript under review for BG (discussion: open, 0 comments) We investigated variations of isotopic and biochemical parameters in arctic mosses, which are useful for palaeo-environmental reconstructions. We were able to differentiate habitat groups of mosses (classified by moisture gradient) by elemental content and d15N ratios. Some species showed intraspecific variability in their isotopic signature along the moisture gradient. Furthermore n-alkanes showed interesting patterns for species identification.