ALBERT

Description: 〈b〉High variability of particulate organic carbon export along the North Atlantic GEOTRACES section GA01 as deduced from 〈sup〉234〈/sup〉Th fluxes〈/b〉〈br〉 Nolwenn Lemaitre, Frédéric Planchon, Hélène Planquette, Frank Dehairs, Debany Fonseca-Batista, Arnout Roukaerts, Florian Deman, Yi Tang, Clarisse Mariez, and Géraldine Sarthou〈br〉 Biogeosciences, 15, 6417-6437, https://doi.org/10.5194/bg-15-6417-2018, 2018〈br〉 We investigated the surface particulate organic carbon export fluxes in the North Atlantic with the objective of better understanding the biological carbon pump. Our results highlighted that exports depended on the intensity and stage of the bloom, the phytoplankton size and community structures. After comparing with primary production, we concluded that, during our study, the North Atlantic behaves like most of the highly productive areas in the world's ocean, with a low export efficiency.

Description: 〈b〉Nitric oxide (NO) in the Bohai and Yellow Seas〈/b〉〈br〉 Ye Tian, Chao Xue, Chun-Ying Liu, Gui-Peng Yang, Pei-Feng Li, Wei-Hua Feng, and Hermann W. Bange〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-446,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Nitric oxide (NO) seems to be widespread with different functions in marine ecosystem but know little about it. Concentrations of NO were in the range of from below the detection limit to 616 pmol L〈sup〉−1〈/sup〉 in the surface and to 482 pmol L〈sup〉−1〈/sup〉 in the bottom of the Bohai and Yellow Seas. The study region was a source of the atmospheric NO. NO sea-to-air fluxes were much lower than NO photoproduction rates, implying that the NO produced in the mixed layer was rapidly consumed before enter the atmosphere.

Description: 〈b〉Ideas and perspectives: Tree–atmosphere interaction responds to water-related stem variations〈/b〉〈br〉 Tim van Emmerik, Susan Steele-Dunne, Pierre Gentine, Rafael S. Oliveira, Paulo Bittencourt, Fernanda Barros, and Nick van de Giesen〈br〉 Biogeosciences, 15, 6439-6449, https://doi.org10.5194/bg-15-6439-2018, 2018〈br〉 Trees are very important for the water and carbon cycles. Climate and weather models often assume constant vegetation parameters because good measurements are missing. We used affordable accelerometers to measure tree sway of 19 trees in the Amazon rainforest. We show that trees respond very differently to the same weather conditions, which means that vegetation parameters are dynamic. With our measurements trees can be accounted for more realistically, improving climate and weather models.

Description: 〈b〉Constraints on Enhanced Weathering and related carbon sequestration – a cropland mesocosm approach〈/b〉〈br〉 Thorben Amann, Jens Hartmann, Eric Struyf, Wagner de Oliveira Garcia, Elke K. Fischer, Ivan Janssens, Patrick Meire, and Jonas Schoelynck〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-398,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Weathering is a major control on atmospheric CO〈sub〉2〈/sub〉 at geologic time scales. Enhancement of this process can be used to actively remove CO〈sub〉2〈/sub〉 from the atmosphere. Field results are still scarce and with this experiment we try to add some near natural insights into dissolution processes. Results show CO〈sub〉2〈/sub〉 sequestration potentials but also highlight the strong variability of outcomes that can be expected in natural environments. Such experiments are of utmost importance to identify key processes.

Description: 〈b〉Evaluation of atmospheric nitrogen inputs into marine ecosystems of the North Sea and Baltic Sea – part B: contribution by shipping and agricultural emissions〈/b〉〈br〉 Daniel Neumann, Hagen Radtke, Matthias Karl, and Thomas Neumann〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-365,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The contribution of atmospheric nitrogen deposition to the marine dissolved inorganic nitrogen (DIN) pool of the North and Baltic Sea was assessed for the year 2012. Atmospheric deposition accounted for approximately 10 % to 15 % of the DIN but its residence time differed between both water bodies. The nitrogen contributions of atmospheric shipping and agricultural imissions also were assessed. Particularly the latter source had a large impact in coastal regions.

Description: 〈b〉Evaluation of the seasonal formation of subsurface negative preformed nitrate anomalies in the subtropical North Pacific and North Atlantic〈/b〉〈br〉 Robert T. Letscher and Tracy A. Villareal〈br〉 Biogeosciences, 15, 6461-6480, https://doi.org10.5194/bg-15-6461-2018, 2018〈br〉 The formation rates of oxygen to nitrogen anomalies in the subtropical North Pacific and North Atlantic were estimated from time series data. We find that vertically migrating phytoplankton, which traverse ~ 100–150 m in the upper ocean over days to acquire nutrients from waters at depth and return to the surface for photosynthesis, likely explain the observed anomalies and help sustain surface ocean productivity and the biological pump throughout the annual cycle in the subtropical ocean.

Description: 〈b〉Nitric oxide (NO) in the Bohai and Yellow Seas〈/b〉〈br〉 Ye Tian, Chao Xue, Chun-Ying Liu, Gui-Peng Yang, Pei-Feng Li, Wei-Hua Feng, and Hermann W. Bange〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-446,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Nitric oxide (NO) seems to be widespread with different functions in marine ecosystem but know little about it. Concentrations of NO were in the range of from below the detection limit to 616 pmol L〈sup〉−1〈/sup〉 in the surface and to 482 pmol L〈sup〉−1〈/sup〉 in the bottom of the Bohai and Yellow Seas. The study region was a source of the atmospheric NO. NO sea-to-air fluxes were much lower than NO photoproduction rates, implying that the NO produced in the mixed layer was rapidly consumed before enter the atmosphere.

Description: 〈b〉Towards a more complete quantification of the global carbon cycle〈/b〉〈br〉 Miko U. F. Kirschbaum, Guang Zeng, Fabiano Ximenes, Donna L. Giltrap, and John R. Zeldis〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-436,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Globally, we add carbon to the atmosphere from fossil fuels and deforestation, balanced by ocean uptake and atmospheric increase. The difference is a residual sink equated to plant uptake. But this omits cement carbonation and pools of plastic, bitumen, wood, landfills and lakes, and transport by wind erosion, volatile C compounds and river transport. This reduces the residual sink from 3.6 to 2.1 GtC yr〈sup〉−1〈/sup〉 with important implications for natural feedbacks to amplify or negate human C emissions.

Description: 〈b〉Evaluation of the seasonal formation of subsurface negative preformed nitrate anomalies in the subtropical North Pacific and North Atlantic〈/b〉〈br〉 Robert T. Letscher and Tracy A. Villareal〈br〉 Biogeosciences, 15, 6461-6480, https://doi.org/10.5194/bg-15-6461-2018, 2018〈br〉 The formation rates of oxygen to nitrogen anomalies in the subtropical North Pacific and North Atlantic were estimated from time series data. We find that vertically migrating phytoplankton, which traverse ~ 100–150 m in the upper ocean over days to acquire nutrients from waters at depth and return to the surface for photosynthesis, likely explain the observed anomalies and help sustain surface ocean productivity and the biological pump throughout the annual cycle in the subtropical ocean.

Description: 〈b〉Dynamic mercury methylation and demethylation in oligotrophic marine water〈/b〉〈br〉 Kathleen M. Munson, Carl H. Lamborg, Rene M. Boiteau, and Mak A. Saito〈br〉 Biogeosciences, 15, 6451-6460, https://doi.org10.5194/bg-15-6451-2018, 2018〈br〉 Methylmercury accumulates in marine organisms and is produced by bacterial processes in sediment systems. To date, the contribution of these processes to the marine water column is poorly understood. We measured noncellular production and breakdown of methylmercury in equatorial Pacific waters. We observed enhanced production in filtered waters that suggests noncellular processes result in rapid mercury transformations and, in turn, control methylmercury concentrations in the open ocean.

Description: 〈b〉Dynamic mercury methylation and demethylation in oligotrophic marine water〈/b〉〈br〉 Kathleen M. Munson, Carl H. Lamborg, Rene M. Boiteau, and Mak A. Saito〈br〉 Biogeosciences, 15, 6451-6460, https://doi.org/10.5194/bg-15-6451-2018, 2018〈br〉 Methylmercury accumulates in marine organisms and is produced by bacterial processes in sediment systems. To date, the contribution of these processes to the marine water column is poorly understood. We measured noncellular production and breakdown of methylmercury in equatorial Pacific waters. We observed enhanced production in filtered waters that suggests noncellular processes result in rapid mercury transformations and, in turn, control methylmercury concentrations in the open ocean.

Description: 〈b〉Evaluation of atmospheric nitrogen inputs into marine ecosystems of the North Sea and Baltic Sea – part B: contribution by shipping and agricultural emissions〈/b〉〈br〉 Daniel Neumann, Hagen Radtke, Matthias Karl, and Thomas Neumann〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-365,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The contribution of atmospheric nitrogen deposition to the marine dissolved inorganic nitrogen (DIN) pool of the North and Baltic Sea was assessed for the year 2012. Atmospheric deposition accounted for approximately 10 % to 15 % of the DIN but its residence time differed between both water bodies. The nitrogen contributions of atmospheric shipping and agricultural imissions also were assessed. Particularly the latter source had a large impact in coastal regions.

Description: 〈b〉Constraints on Enhanced Weathering and related carbon sequestration – a cropland mesocosm approach〈/b〉〈br〉 Thorben Amann, Jens Hartmann, Eric Struyf, Wagner de Oliveira Garcia, Elke K. Fischer, Ivan Janssens, Patrick Meire, and Jonas Schoelynck〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-398,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Weathering is a major control on atmospheric CO〈sub〉2〈/sub〉 at geologic time scales. Enhancement of this process can be used to actively remove CO〈sub〉2〈/sub〉 from the atmosphere. Field results are still scarce and with this experiment we try to add some near natural insights into dissolution processes. Results show CO〈sub〉2〈/sub〉 sequestration potentials but also highlight the strong variability of outcomes that can be expected in natural environments. Such experiments are of utmost importance to identify key processes.

Description: 〈b〉High variability of particulate organic carbon export along the North Atlantic GEOTRACES section GA01 as deduced from 〈sup〉234〈/sup〉Th fluxes〈/b〉〈br〉 Nolwenn Lemaitre, Frédéric Planchon, Hélène Planquette, Frank Dehairs, Debany Fonseca-Batista, Arnout Roukaerts, Florian Deman, Yi Tang, Clarisse Mariez, and Géraldine Sarthou〈br〉 Biogeosciences, 15, 6417-6437, https://doi.org10.5194/bg-15-6417-2018, 2018〈br〉 We investigated the surface particulate organic carbon export fluxes in the North Atlantic with the objective of better understanding the biological carbon pump. Our results highlighted that exports depended on the intensity and stage of the bloom, the phytoplankton size and community structures. After comparing with primary production, we concluded that, during our study, the North Atlantic behaves like most of the highly productive areas in the world's ocean, with a low export efficiency.

Description: 〈b〉Isotopic fractionation corrections for the radiocarbon composition of CO〈sub〉2〈/sub〉 in the soil gas environment must include diffusion and mixing〈/b〉〈br〉 Jocelyn E. Egan, David R. Bowling, and David A. Risk〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-451,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Traditionally a mass-dependent correction is made when measuring the radiocarbon composition in organic samples. This correction has not been evaluated for the soil gas environment where gas transport processes are important. Here, we show using theory, analytical models and field data that this traditional correction is not appropriate for estimating the radiocarbon composition of soil biological production. We also propose a new solution that accounts for soil gas transport processes.

Description: 〈b〉Ideas and perspectives: Tree–atmosphere interaction responds to water-related stem variations〈/b〉〈br〉 Tim van Emmerik, Susan Steele-Dunne, Pierre Gentine, Rafael S. Oliveira, Paulo Bittencourt, Fernanda Barros, and Nick van de Giesen〈br〉 Biogeosciences, 15, 6439-6449, https://doi.org/10.5194/bg-15-6439-2018, 2018〈br〉 Trees are very important for the water and carbon cycles. Climate and weather models often assume constant vegetation parameters because good measurements are missing. We used affordable accelerometers to measure tree sway of 19 trees in the Amazon rainforest. We show that trees respond very differently to the same weather conditions, which means that vegetation parameters are dynamic. With our measurements trees can be accounted for more realistically, improving climate and weather models.

Description: 〈b〉Global, Satellite-Driven Estimates of Heterotrophic Respiration〈/b〉〈br〉 Alexandra G. Konings, A. Anthony Bloom, Junjie Liu, Nicholas C. Parazoo, David S. Schimel, and Kevin W. Bowman〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-466,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We estimate heterotrophic respiration (Rh) – the respiration from microbes in the soil – using satellite estimates of the net carbon flux and other quantities. Rh is an important carbon flux but is rarely studied by itself. Our method is the first to estimate how Rh varies in both space and time. The resulting new estimate of Rh is compared to the best currently available alternative – which is based on interpolating field measurements globally. The two estimates disagree and are both uncertain.

Description: 〈b〉Variation of key elements in soils and plant tissues in subalpine forests of the northern Rocky Mountains, USA〈/b〉〈br〉 David P. Pompeani, Kendra K. McLauchlan, Barrie V. Chileen, Kyra D. Wolf, and Philip E. Higuera〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-443,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉The essential elements for the structure and function of forest ecosystems are found in relatively predictable proportions in living tissues and soils; however, both the degree of spatial variability in elemental concentrations and their relationship with wildfire history are unclear. Quantifying the association between nutrient concentrations in living plant tissue and surface soils within fire-affected forests can help determine how these elements contribute to biogeochemical resilience. Here, we present elemental concentration data (C, N, P, K, Ca, Mg, S, Fe, Mn, Zn) from 72 foliar and 44 soil samples from a network of 15 sites located in the fire-prone subalpine forests of the northern Rocky Mountains, USA Plant functional type is strongly correlated with carbon (C) and nitrogen (N) – C concentrations are highest in coniferous needles, and N concentrations are highest in broadleaved plant species. The average N / P ratio of foliage among samples is 9.8 ± 0.6 (μ ± 95 % confidence). This suggests that N is the limiting nutrient for these plants, however several factors can complicate the use of N / P ratios to evaluate nutrient status. Average C concentrations in organic soil horizons that were burned in regionally extensive fires in 1910 or 1918 CE are lower than those from sites that burned prior to 1901 CE (p 〈/p〉

Description: 〈b〉Model-based analysis of latent factors〈/b〉〈br〉 Hans-Rolf Gregorius〈br〉 Web Ecol., 18, 153-162, https://doi.org/10.5194/we-18-153-2018, 2018〈br〉 〈p〉The detection of community or population structure through analysis of explicit cause–effect modeling of given observations has received considerable attention. The complexity of the task is mirrored by the large number of existing approaches and methods, the applicability of which heavily depends on the design of efficient algorithms of data analysis. It is occasionally even difficult to disentangle concepts and algorithms. To add more clarity to this situation, the present paper focuses on elaborating the system analytic framework that probably encompasses most of the common concepts and approaches by classifying them as model-based analyses of latent factors. Problems concerning the efficiency of algorithms are not of primary concern here. In essence, the framework suggests an input–output model system in which the inputs are provided as latent model parameters and the output is specified by the observations. There are two types of model involved, one of which organizes the inputs by assigning combinations of potentially interacting factor levels to each observed object, while the other specifies the mechanisms by which these combinations are processed to yield the observations. It is demonstrated briefly how some of the most popular methods (Structure, BAPS, Geneland) fit into the framework and how they differ conceptually from each other. Attention is drawn to the need to formulate and assess qualification criteria by which the validity of the model can be judged. One probably indispensable criterion concerns the cause–effect character of the model-based approach and suggests that measures of association between assignments of factor levels and observations be considered together with maximization of their likelihoods (or posterior probabilities). In particular the likelihood criterion is difficult to realize with commonly used estimates based on Markov chain Monte Carlo (MCMC) algorithms. Generally applicable MCMC-based alternatives that allow for approximate employment of the primary qualification criterion and the implied model validation including further descriptors of model characteristics are suggested.〈/p〉

Description: 〈b〉Global, Satellite-Driven Estimates of Heterotrophic Respiration〈/b〉〈br〉 Alexandra G. Konings, A. Anthony Bloom, Junjie Liu, Nicholas C. Parazoo, David S. Schimel, and Kevin W. Bowman〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-466,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 We estimate heterotrophic respiration (Rh) – the respiration from microbes in the soil – using satellite estimates of the net carbon flux and other quantities. Rh is an important carbon flux but is rarely studied by itself. Our method is the first to estimate how Rh varies in both space and time. The resulting new estimate of Rh is compared to the best currently available alternative – which is based on interpolating field measurements globally. The two estimates disagree and are both uncertain.

Description: 〈b〉Reviews and syntheses: 〈sup〉210〈/sup〉Pb-derived sediment and carbon accumulation rates in vegetated coastal ecosystems – setting the record straight〈/b〉〈br〉 Ariane Arias-Ortiz, Pere Masqué, Jordi Garcia-Orellana, Oscar Serrano, Inés Mazarrasa, Núria Marbà, Catherine E. Lovelock, Paul S. Lavery, and Carlos M. Duarte〈br〉 Biogeosciences, 15, 6791-6818, https://doi.org/10.5194/bg-15-6791-2018, 2018〈br〉 Efforts to include tidal marsh, mangrove and seagrass ecosystems in existing carbon mitigation strategies are limited by a lack of estimates of carbon accumulation rates (CARs). We discuss the use of 〈sup〉210〈/sup〉Pb dating to determine CARs in these habitats, which are often composed of heterogeneous sediments and affected by sedimentary processes. Results show that obtaining reliable geochronologies in these systems is ambitious, but estimates of mean 100-year CARs are mostly secure within 20 % error.

Description: 〈b〉Reviews and syntheses: 〈sup〉210〈/sup〉Pb-derived sediment and carbon accumulation rates in vegetated coastal ecosystems – setting the record straight〈/b〉〈br〉 Ariane Arias-Ortiz, Pere Masqué, Jordi Garcia-Orellana, Oscar Serrano, Inés Mazarrasa, Núria Marbà, Catherine E. Lovelock, Paul S. Lavery, and Carlos M. Duarte〈br〉 Biogeosciences, 15, 6791-6818, https://doi.org10.5194/bg-15-6791-2018, 2018〈br〉 Efforts to include tidal marsh, mangrove and seagrass ecosystems in existing carbon mitigation strategies are limited by a lack of estimates of carbon accumulation rates (CARs). We discuss the use of 〈sup〉210〈/sup〉Pb dating to determine CARs in these habitats, which are often composed of heterogeneous sediments and affected by sedimentary processes. Results show that obtaining reliable geochronologies in these systems is ambitious, but estimates of mean 100-year CARs are mostly secure within 20 % error.

Description: 〈b〉Quantitative mapping and predictive modeling of Mn nodules' distribution from hydroacoustic and optical AUV data linked by random forests machine learning〈/b〉〈br〉 Iason-Zois Gazis, Timm Schoening, Evangelos Alevizos, and Jens Greinert〈br〉 Biogeosciences, 15, 7347-7377, https://doi.org/10.5194/bg-15-7347-2018, 2018〈br〉 The use of high-resolution hydroacoustic and optic data acquired by an autonomous underwater vehicle can give us detailed sea bottom topography and valuable information regarding manganese nodules' spatial distribution. Moreover, the combined use of these data sets with a random forest machine learning model can extend this spatial prediction beyond the areas with available photos, providing researchers with a new mapping tool for further investigation and links with other data.

Description: 〈b〉Insights from year-long measurements of air-water CH〈sub〉4〈/sub〉 and CO〈sub〉2〈/sub〉 exchange in a coastal environment〈/b〉〈br〉 Mingxi Yang, Thomas G. Bell, Ian J. Brown, James R. Fishwick, Vassilis Kitidis, Philip D. Nightingale, Andrew P. Rees, and Timothy J. Smyth〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-503,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 We quantify the emissions and uptake of greenhouse gases carbon dioxide and methane from the coastal seas of the UK over 1 year using the state-of-the-art eddy covariance technique. Our measurements show how these air-sea fluxes vary twice a day (tidal), diurnally (circadian), and seasonally. We also estimate the air-sea gas transfer velocity, which is essential for modeling and predicting coastal air-sea exchange.

Description: 〈b〉Insights from year-long measurements of air-water CH〈sub〉4〈/sub〉 and CO〈sub〉2〈/sub〉 exchange in a coastal environment〈/b〉〈br〉 Mingxi Yang, Thomas G. Bell, Ian J. Brown, James R. Fishwick, Vassilis Kitidis, Philip D. Nightingale, Andrew P. Rees, and Timothy J. Smyth〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-503,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 We quantify the emissions and uptake of greenhouse gases carbon dioxide and methane from the coastal seas of the UK over 1 year using the state-of-the-art eddy covariance technique. Our measurements show how these air-sea fluxes vary twice a day (tidal), diurnally (circadian), and seasonally. We also estimate the air-sea gas transfer velocity, which is essential for modeling and predicting coastal air-sea exchange.

Description: 〈b〉Underestimation of denitrification rates from field application of the 〈sup〉15〈/sup〉N gas flux method and its correction by gas diffusion modelling〈/b〉〈br〉 Reinhard Well, Martin Maier, Dominika Lewicka-Szczebak, Jan-Reent Köster, and Nicolas Ruoss〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-495,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 〈p〉Common methods for measuring soil denitrification in situ include monitoring the accumulation of 〈sup〉15〈/sup〉N-labelled N〈sub〉2〈/sub〉 and N〈sub〉2〈/sub〉O evolved from 〈sup〉15〈/sup〉N-labelled soil nitrate pool in closed chambers that are placed on the soil surface. Gas diffusion is considered to be the main transport process in the soil. Because accumulation of gases within the chamber decreases concentration gradients between soil and chamber over time, the surface efflux of gases decreases as well and gas production rates are underestimated if calculated from chamber concentrations without consideration of this mechanism. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of 〈sup〉15〈/sup〉N labelled denitrification products. A numerical 3-D model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of 〈sup〉15〈/sup〉N-labelled N〈sub〉2〈/sub〉 and N〈sub〉2〈/sub〉O – and thus potential underestimation of denitrification derived from chamber fluxes – increases with chamber deployment time as well as with increasing soil gas diffusivity. Simulations based on the range of typical soil gas diffusivities of unsaturated soils showed that the fraction of N〈sub〉2〈/sub〉 and N〈sub〉2〈/sub〉O evolved from 〈sup〉15〈/sup〉N-labelled NO〈sub〉3〈/sub〉 that is not emitted at the soil surface during one hour chamber closing is always significant with values up to 〉 50 % of total production due to accumulation in the pore space of the 〈sup〉15〈/sup〉N-labelled soil and diffusive flux to the unlabelled subsoil. Empirical coefficients to calculate denitrification from surface fluxes were derived by modelling multiple scenarios with varying soil water content.〈/p〉 〈p〉Field experiments with arable silt loam soil for measuring denitrification with the 〈sup〉15〈/sup〉N gas flux method were conducted to obtain direct evidence for the incomplete surface emission of gaseous denitrification products. We compared surface fluxes of 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉 and 〈sup〉15〈/sup〉N〈sub〉2〈/sub〉O from 〈sup〉15〈/sup〉N–labelled micro-plots confined by cylinders using the closed chamber method with cylinders open or closed at the bottom, finding 37 % higher surface fluxes with bottom closed. Modeling fluxes of this experiment confirmed this effect, however with a higher increase in surface flux of 89 %.〈/p〉 〈p〉From our model and experimental results we conclude that field surface fluxes of 〈sup〉15〈/sup〉N-labelled N〈sub〉2〈/sub〉 and N〈sub〉2〈/sub〉O severely underestimate denitrification rates if calculated from chamber accumulation only. The extent of this underestimation increases with closure time. Underestimation also occurs during laboratory incubations in closed systems due to pore space accumulation of 〈sup〉15〈/sup〉N-labelled N〈sub〉2〈/sub〉 and N〈sub〉2〈/sub〉O. Due to this bias in past denitrification measurements, denitrification in soils might be more relevant than assumed to date. Corrected denitrification rates can be obtained by estimating subsurface flux and storage with our model. The observed deviation between experimental and modeled subsurface flux revealed the need for refined model evaluation which must include assessment of the spatial variability in diffusivity and production and the spatial dimension of the chamber.〈/p〉

Description: 〈b〉Ideas and perspectives: Synergies from co-deployment of negative emission technologies〈/b〉〈br〉 Thorben Amann and Jens Hartmann〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-500,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 With the recent publication of the IPCC special report on the 1.5° target and increased attention on carbon dioxide removal (CDR) technologies, we think it is time to advance from the current way to look at specific strategies forward to a more holistic CDR perspective, since multiple 〈q〉side effects〈/q〉 may lead to additional CO〈sub〉2〈/sub〉 uptake into different carbon pools. This paper explores potential co-benefits between terrestrial CDR strategies to facilitate a maximum CO〈sub〉2〈/sub〉 sequestration effect.

Description: 〈b〉Ideas and perspectives: Synergies from co-deployment of negative emission technologies〈/b〉〈br〉 Thorben Amann and Jens Hartmann〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-500,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 With the recent publication of the IPCC special report on the 1.5° target and increased attention on carbon dioxide removal (CDR) technologies, we think it is time to advance from the current way to look at specific strategies forward to a more holistic CDR perspective, since multiple 〈q〉side effects〈/q〉 may lead to additional CO〈sub〉2〈/sub〉 uptake into different carbon pools. This paper explores potential co-benefits between terrestrial CDR strategies to facilitate a maximum CO〈sub〉2〈/sub〉 sequestration effect.

Description: 〈b〉Coupled Ca and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite〈/b〉〈br〉 Inge van Dijk, Christine Barras, Lennart Jan de Nooijer, Aurélia Mouret, Esmee Geerken, Shai Oron, and Gert-Jan Reichart〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-481,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Systematics in the incorporation of different elements in shells of marine organisms can be used to test calcification models and hence processes involved in precipitation of calcium carbonates. The observed link between sulfur and magnesium incorporation in shells of foraminifera, unicellar protists, provides insights into the mechanics behind shell formation. The observed patterns imply all species of foraminifera actively take up calcium and carbon in a coupled process.

Description: 〈b〉Geographic distribution of free-living marine nematodes in the Clarion–Clipperton Zone: implications for future deep-sea mining scenarios〈/b〉〈br〉 Freija Hauquier, Lara Macheriotou, Tania N. Bezerra, Great Egho, Pedro Martínez Arbizu, and Ann Vanreusel〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-492,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Future mining operations in the deep sea provide a source of scientific uncertainty and call for detailed study of the ecosystem. We investigated one of the most diverse and abundant taxa present in deep-sea sediments, nematodes, and demonstrate the importance of sediment attributes for their communities. Especially species that are less common and have a limited spatial distribution will be vulnerable to mining-induced changes. Our findings can serve as a reference for future impact studies.

Description: 〈b〉Coupled Ca and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite〈/b〉〈br〉 Inge van Dijk, Christine Barras, Lennart Jan de Nooijer, Aurélia Mouret, Esmee Geerken, Shai Oron, and Gert-Jan Reichart〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-481,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Systematics in the incorporation of different elements in shells of marine organisms can be used to test calcification models and hence processes involved in precipitation of calcium carbonates. The observed link between sulfur and magnesium incorporation in shells of foraminifera, unicellar protists, provides insights into the mechanics behind shell formation. The observed patterns imply all species of foraminifera actively take up calcium and carbon in a coupled process.

Description: 〈b〉From substrate to soil in a pristine environment – pedochemical, micromorphological and microbiological properties from soils on James Ross Island, Antarctica〈/b〉〈br〉 Lars A. Meier, Patryk Krauze, Isabel Prater, Fabian Horn, Carlos E. G. R. Schaefer, Thomas Scholten, Dirk Wagner, Carsten W. Mueller, and Peter Kühn〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-488,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 James Ross Island offers the opportunity to study the undisturbed interplay of microbial activity and pedogenesis. Soils from two sites representing coastal and inland conditions were chosen and analysed with a wide range of techniques to describe soil properties. We are able to show that coastal conditions go along with more intense weathering and therefore favor soil formation and that microbial communities are initially more affected by weathering and structure than by chemical parameters.

Description: 〈b〉Evolution of 〈sup〉231〈/sup〉Pa and 〈sup〉230〈/sup〉Th in overflow waters of the North Atlantic〈/b〉〈br〉 Feifei Deng, Gideon M. Henderson, Maxi Castrillejo, Fiz F. Perez, and Reiner Steinfeldt〈br〉 Biogeosciences, 15, 7299-7313, https://doi.org10.5194/bg-15-7299-2018, 2018〈br〉 To better use Pa / Th to reconstruct deep water ventilation rate, we assessed controls on 〈sup〉230〈/sup〉Th and 〈sup〉231〈/sup〉Pa in the northern North Atlantic. With extended optimum multi-parameter analysis and CFC-based water-mass age, we found the imprint of young overflow water on Th and Pa and enhanced scavenging near the seafloor. A significantly higher advective loss of Pa to the south relative to Th in the Atlantic was estimated, supporting the use of Pa / Th for assessing basin-scale meridional transport.

Description: 〈b〉Commercial traceability of 〈i〉Arapaima spp.〈/i〉 fisheries in the Amazon Basin: can biogeochemical tags be useful?〈/b〉〈br〉 Luciana A. Pereira, Roberto V. Santos, Marília Hauser, Fabrice Duponchelle, Fernando Carvajal, Christophe Pecheyran, Sylvain Bérail, and Marc Pouilly〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-471,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 This study developed the first step for a chemical origin certification of Pirarucu fishery in the Amazon using isotopic tracers and resulted in a preliminary forensic tool. The geographic origin certification of farmed and wild endangered fishes contributes to secure the food and income to communities, the permanent management of fisheries stocks, the continuous advance of aquaculture, the consumer support to legal fisheries and the national and international regulation of natural resources.

Description: 〈b〉Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer〈/b〉〈br〉 Jørgen Bendtsen and Katherine Richardson〈br〉 Biogeosciences, 15, 7315-7332, https://doi.org10.5194/bg-15-7315-2018, 2018〈br〉 New production based on nutrients entering the well-lit surface layer is important for understanding marine ecosystems. Measurements of primary production and turbulence across the shelf edge in the northeastern portion of the North Sea show that new production is concentrated around the shelf-edge zone. The shelf-edge zone is, therefore, a major nutrient supplier to the productive surface layer and makes this area important for higher trophic levels such as zooplankton and fish.

Description: 〈b〉The role of hydrodynamic and biogeochemistry on CO〈sub〉2〈/sub〉 flux and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 at the Amazon River mouth〈/b〉〈br〉 Diani F. S. Less, Alan C. Cunha, Henrique O. Sawakuchi, Vania Neu, Aline M. Valério, Nicholas D. Ward, Daimio C. Brito, Joel E. M. Diniz, William Gagne-Maynard, Carlos M. Abreu, Milton Kampel, Alex V. Krusche, and Jeffrey E. Richey〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-465,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Biogeochemistry studies focused in carbon cycle in the Amazon River mouth are scarce. Our study provided a long-term quantification of CO〈sub〉2〈/sub〉 fluxes and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 and evaluation of the most important hydrodynamic, biogeochemical and meteorological parameters related to them. The highest FCO〈sub〉2〈/sub〉 and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 was obtained at high discharge season, water and air temperatures, dissolved oxygen, dissolved organic carbon, nitrate, dissolved inorganic nitrogen and pH could be considered predictors for 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 and FCO〈sub〉2〈/sub〉.

Description: 〈b〉The role of hydrodynamic and biogeochemistry on CO〈sub〉2〈/sub〉 flux and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 at the Amazon River mouth〈/b〉〈br〉 Diani F. S. Less, Alan C. Cunha, Henrique O. Sawakuchi, Vania Neu, Aline M. Valério, Nicholas D. Ward, Daimio C. Brito, Joel E. M. Diniz, William Gagne-Maynard, Carlos M. Abreu, Milton Kampel, Alex V. Krusche, and Jeffrey E. Richey〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-465,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Biogeochemistry studies focused in carbon cycle in the Amazon River mouth are scarce. Our study provided a long-term quantification of CO〈sub〉2〈/sub〉 fluxes and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 and evaluation of the most important hydrodynamic, biogeochemical and meteorological parameters related to them. The highest FCO〈sub〉2〈/sub〉 and 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 was obtained at high discharge season, water and air temperatures, dissolved oxygen, dissolved organic carbon, nitrate, dissolved inorganic nitrogen and pH could be considered predictors for 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 and FCO〈sub〉2〈/sub〉.

Description: 〈b〉Meso-zooplankton structure and functioning in the western tropical South Pacific along the 20th parallel south during the OUTPACE survey (February–April 2015)〈/b〉〈br〉 François Carlotti, Marc Pagano, Loïc Guilloux, Katty Donoso, Valentina Valdés, Olivier Grosso, and Brian P. V. Hunt〈br〉 Biogeosciences, 15, 7273-7297, https://doi.org/10.5194/bg-15-7273-2018, 2018〈br〉 The paper characterizes the zooplankton community and plankton food web processes between New Caledonia and Tahiti (tropical South Pacific) during the austral summer 2015. In this region, the pelagic production depends on N〈sub〉2〈/sub〉 fixation by diazotroph microorganisms on which the zooplankton community feeds, supporting a pelagic food chain ending with valuable tuna fisheries. We estimated a contribution of up to 75 % of diazotroph‐derived nitrogen to zooplankton biomass in the Melanesian archipelago.

Description: 〈b〉Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the South-East Pacific〈/b〉〈br〉 Lisa Mevenkamp, Katja Guilini, Antje Boetius, Johan De Grave, Brecht Laforce, Dimitri Vandenberghe, Laszlo Vincze, and Ann Vanreusel〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-489,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 To elucidate potential effects of crushed nodule particle deposition on abyssal meiobenthos, we covered soft sediment in the Peru Basin (4200 m depth) with approx. 2 cm of this substrate for 11 days. About half of the meiobenthos migrated into the added crushed nodule layer and nematode feeding type proportions in the added layer were altered. The results indicate that substrate burial has a strong impact abyssal meiobenthos community structure and vertical distribution on the short term.

Description: 〈b〉Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the South-East Pacific〈/b〉〈br〉 Lisa Mevenkamp, Katja Guilini, Antje Boetius, Johan De Grave, Brecht Laforce, Dimitri Vandenberghe, Laszlo Vincze, and Ann Vanreusel〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-489,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 To elucidate potential effects of crushed nodule particle deposition on abyssal meiobenthos, we covered soft sediment in the Peru Basin (4200 m depth) with approx. 2 cm of this substrate for 11 days. About half of the meiobenthos migrated into the added crushed nodule layer and nematode feeding type proportions in the added layer were altered. The results indicate that substrate burial has a strong impact abyssal meiobenthos community structure and vertical distribution on the short term.

Description: 〈b〉Estimation of emissions from biomass burning in China (2003–2017) based on MODIS fire radiative energy data〈/b〉〈br〉 Lifei Yin, Pin Du, Mingxu Liu, Tingting Xu, and Yu Song〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-468,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Biomass burning is an important source of trace gases and aerosols in China, with a significant contribution from small-sized crop residue burning. Compared with conventional methods for emission estimation, the approach based on fire radiative energy (FRE) provides a more reasonable estimate for small fire emissions. By using FRE data derived from satellite, we developed a long-term biomass burning emission inventory for China with a higher resolution (daily, 1 km) than previous studies.

Description: 〈b〉Filtration artefacts in bacterial community composition can affect the outcome of dissolved organic matter biolability assays〈/b〉〈br〉 Joshua F. Dean, Jurgen R. van Hal, A. Johannes Dolman, Rien Aerts, and James T. Weedon〈br〉 Biogeosciences, 15, 7141-7154, https://doi.org/10.5194/bg-15-7141-2018, 2018〈br〉 Lakes, rivers, ponds and streams are significant contributors of the greenhouse gas carbon dioxide to the atmosphere. This is partly due to the decomposition of plant and soil organic matter transported through these aquatic systems by microbial communities. In determining how vulnerable this organic material is to decomposition during aquatic transport, we show that standardized treatments in experiments can affect the way microbial communities behave and potentially the experimental outcome.

Description: 〈b〉Bipolar carbon and hydrogen isotope constraints on the Holocene methane budget〈/b〉〈br〉 Jonas Beck, Michael Bock, Jochen Schmitt, Barbara Seth, Thomas Blunier, and Hubertus Fischer〈br〉 Biogeosciences, 15, 7155-7175, https://doi.org/10.5194/bg-15-7155-2018, 2018〈br〉 Ice core concentration and stable isotope measurements of atmospheric CH〈sub〉4〈/sub〉 give valuable insights into the CH〈sub〉4〈/sub〉 cycle of the past. New carbon and hydrogen stable isotope CH〈sub〉4〈/sub〉 data measured on ice from both Greenland and Antarctica over the Holocene allow us to draw conclusions on the methane emission processes. In particular, our results cast doubt on a hypothesis proposing early human land use to be responsible for the atmospheric methane concentration increase in the second half of the Holocene.

Description: 〈b〉Bipolar carbon and hydrogen isotope constraints on the Holocene methane budget〈/b〉〈br〉 Jonas Beck, Michael Bock, Jochen Schmitt, Barbara Seth, Thomas Blunier, and Hubertus Fischer〈br〉 Biogeosciences, 15, 7155-7175, https://doi.org10.5194/bg-15-7155-2018, 2018〈br〉 Ice core concentration and stable isotope measurements of atmospheric CH〈sub〉4〈/sub〉 give valuable insights into the CH〈sub〉4〈/sub〉 cycle of the past. New carbon and hydrogen stable isotope CH〈sub〉4〈/sub〉 data measured on ice from both Greenland and Antarctica over the Holocene allow us to draw conclusions on the methane emission processes. In particular, our results cast doubt on a hypothesis proposing early human land use to be responsible for the atmospheric methane concentration increase in the second half of the Holocene.

Description: 〈b〉Ecosystem fluxes of carbonyl sulfide in an old-growth forest: temporal dynamics and responses to diffuse radiation and heat waves〈/b〉〈br〉 Bharat Rastogi, Max Berkelhammer, Sonia Wharton, Mary E. Whelan, Frederick C. Meinzer, David Noone, and Christopher J. Still〈br〉 Biogeosciences, 15, 7127-7139, https://doi.org/10.5194/bg-15-7127-2018, 2018〈br〉 Carbonyl sulfide (OCS) has gained prominence as an independent tracer for gross primary productivity, which is usually modelled by partitioning net CO〈sub〉2〈/sub〉 fluxes. Here, we present a simple empirical model for estimating ecosystem-scale OCS fluxes for a temperate old-growth forest and find that OCS sink strength scales with independently estimated CO〈sub〉2〈/sub〉 uptake and is sensitive to the the fraction of downwelling diffuse light. We also examine the response of OCS and CO〈sub〉2〈/sub〉 fluxes to sequential heat waves.

Description: 〈b〉Pacific Decadal Oscillation and recent oxygen decline in the eastern tropical Pacific Ocean〈/b〉〈br〉 Olaf Duteil, Andreas Oschlies, and Claus W. Böning〈br〉 Biogeosciences, 15, 7111-7126, https://doi.org10.5194/bg-15-7111-2018, 2018〈br〉 Oxygen-depleted regions of the Pacific Ocean are currently expanding, which is threatening marine habitats. Based on numerical simulations, we show that the decrease in the intensity of the trade winds and the subsequent slowdown of the oceanic currents lead to a reduction in oxygen supply. Our study suggests that the prevailing positive conditions of the Pacific Decadal Oscillation since 1975, a major source of natural variability, may explain a significant part of the current deoxygenation.

Description: 〈b〉Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise〈/b〉〈br〉 Géraldine Sarthou, Pascale Lherminier, Eric P. Achterberg, Fernando Alonso-Pérez, Eva Bucciarelli, Julia Boutorh, Vincent Bouvier, Edward A. Boyle, Pierre Branellec, Lidia I. Carracedo, Nuria Casacuberta, Maxi Castrillejo, Marie Cheize, Leonardo Contreira Pereira, Daniel Cossa, Nathalie Daniault, Emmanuel De Saint-Léger, Frank Dehairs, Feifei Deng, Floriane Desprez de Gésincourt, Jérémy Devesa, Lorna Foliot, Debany Fonseca-Batista, Morgane Gallinari, Maribel I. García-Ibáñez, Arthur Gourain, Emilie Grossteffan, Michel Hamon, Lars Eric Heimbürger, Gideon M. Henderson, Catherine Jeandel, Catherine Kermabon, François Lacan, Philippe Le Bot, Manon Le Goff, Emilie Le Roy, Alison Lefèbvre, Stéphane Leizour, Nolwenn Lemaitre, Pere Masqué, Olivier Ménage, Jan-Lukas Menzel Barraqueta, Herlé Mercier, Fabien Perault, Fiz F. Pérez, Hélène F. Planquette, Frédéric Planchon, Arnout Roukaerts, Virginie Sanial, Raphaëlle Sauzède, Catherine Schmechtig, Rachel U. Shelley, Gillian Stewart, Jill N. Sutton, Yi Tang, Nadine Tisnérat-Laborde, Manon Tonnard, Paul Tréguer, Pieter van Beek, Cheryl M. Zurbrick, and Patricia Zunino〈br〉 Biogeosciences, 15, 7097-7109, https://doi.org10.5194/bg-15-7097-2018, 2018〈br〉 The GEOVIDE cruise (GEOTRACES Section GA01) was conducted in the North Atlantic Ocean and Labrador Sea in May–June 2014. In this special issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 17 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

Description: 〈b〉Pacific Decadal Oscillation and recent oxygen decline in the eastern tropical Pacific Ocean〈/b〉〈br〉 Olaf Duteil, Andreas Oschlies, and Claus W. Böning〈br〉 Biogeosciences, 15, 7111-7126, https://doi.org/10.5194/bg-15-7111-2018, 2018〈br〉 Oxygen-depleted regions of the Pacific Ocean are currently expanding, which is threatening marine habitats. Based on numerical simulations, we show that the decrease in the intensity of the trade winds and the subsequent slowdown of the oceanic currents lead to a reduction in oxygen supply. Our study suggests that the prevailing positive conditions of the Pacific Decadal Oscillation since 1975, a major source of natural variability, may explain a significant part of the current deoxygenation.

Description: 〈b〉Integrating multimedia models to assess nitrogen losses from the Mississippi River basin to the Gulf of Mexico〈/b〉〈br〉 Yongping Yuan, Ruoyu Wang, Ellen Cooter, Limei Ran, Prasad Daggupati, Dongmei Yang, Raghavan Srinivasan, and Anna Jalowska〈br〉 Biogeosciences, 15, 7059-7076, https://doi.org10.5194/bg-15-7059-2018, 2018〈br〉 Elevated levels of nutrients in surface water, which originate from deposition of atmospheric N, drainage from agricultural fields, and discharges from sewage treatment plants, cause explosive algal blooms that impair water quality. The complex cycling of nutrients through the land, air, and water requires an integrated multimedia modeling system linking air, land surface, and stream processes to assess their sources, transport, and transformation in large river basins for decision making.

Description: 〈b〉Integrating multimedia models to assess nitrogen losses from the Mississippi River basin to the Gulf of Mexico〈/b〉〈br〉 Yongping Yuan, Ruoyu Wang, Ellen Cooter, Limei Ran, Prasad Daggupati, Dongmei Yang, Raghavan Srinivasan, and Anna Jalowska〈br〉 Biogeosciences, 15, 7059-7076, https://doi.org/10.5194/bg-15-7059-2018, 2018〈br〉 Elevated levels of nutrients in surface water, which originate from deposition of atmospheric N, drainage from agricultural fields, and discharges from sewage treatment plants, cause explosive algal blooms that impair water quality. The complex cycling of nutrients through the land, air, and water requires an integrated multimedia modeling system linking air, land surface, and stream processes to assess their sources, transport, and transformation in large river basins for decision making.

Description: 〈b〉Mg ∕ Ca and 〈strong〉〈i xmlns=""〉δ〈/i〉〈/strong〉〈sup〉18〈/sup〉O in living planktic foraminifers from the Caribbean, Gulf of Mexico and Florida Straits〈/b〉〈br〉 Anna Jentzen, Dirk Nürnberg, Ed C. Hathorne, and Joachim Schönfeld〈br〉 Biogeosciences, 15, 7077-7095, https://doi.org/10.5194/bg-15-7077-2018, 2018〈br〉 〈p〉Past ocean temperatures and salinities can be approximated from combined stable oxygen isotopes (〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉) and 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉 measurements in fossil foraminiferal tests with varying success. To further refine this approach, we collected living planktic foraminifers by net sampling and pumping of sea surface water from the Caribbean Sea, the eastern Gulf of Mexico and the Florida Straits. Analyses of 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉 and 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉 in eight living planktic species (〈i〉Globigerinoides sacculifer〈/i〉, 〈i〉Orbulina universa〈/i〉, 〈i〉Neogloboquadrina dutertrei〈/i〉, 〈i〉Pulleniatina obliquiloculata〈/i〉, 〈i〉Globorotalia menardii〈/i〉, 〈i〉Globorotalia ungulata〈/i〉, 〈i〉Globorotalia truncatulinoides〈/i〉 and 〈i〉Globorotalia tumida〈/i〉) were compared to measured in situ properties of the ambient seawater (temperature, salinity and 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉〈span〉〈sub〉seawater〈/sub〉〈/span〉) and fossil tests of underlying surface sediments. “Vital effects” such as symbiont activity and test growth cause 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉 disequilibria with respect to the ambient seawater and a large scatter in foraminiferal 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉. Overall, ocean temperature is the most prominent environmental influence on 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉〈span〉〈sub〉calcite〈/sub〉〈/span〉 and 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉. Enrichment of the heavier 〈span〉〈sup〉18〈/sup〉O〈/span〉 isotope in living specimens below the mixed layer and in fossil tests is clearly related to lowered in situ temperatures and gametogenic calcification. 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉-based temperature estimates of 〈i〉G. sacculifer〈/i〉 indicate seasonal maximum accumulation rates on the seafloor in early spring (March) at Caribbean stations and later in the year (May) in the Florida Straits, related to the respective mixed layer temperatures of 〈span〉∼26〈/span〉 〈span〉〈sup〉∘〈/sup〉〈/span〉C. Notably, 〈i〉G. sacculifer〈/i〉 reveals a weak positive linear relationship between foraminiferal derived 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉〈span〉〈sub〉seawater〈/sub〉〈/span〉 estimates and both measured in situ 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉〈span〉〈sub〉seawater〈/sub〉〈/span〉 and salinity. Our results affirm the applicability of existing 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉 and 〈span〉Mg〈/span〉 〈span〉∕〈/span〉 〈span〉Ca〈/span〉 calibrations for the reconstruction of past ocean temperatures and 〈span〉〈i〉δ〈/i〉〈sup〉18〈/sup〉O〈/span〉〈span〉〈sub〉seawater〈/sub〉〈/span〉 reflecting salinity due to the convincing accordance of proxy data in both living and fossil foraminifers, and in situ environmental parameters. Large vital effects and seasonally varying proxy signals, however, need to be taken into account.〈/p〉

Description: 〈b〉Introduction to the French GEOTRACES North Atlantic Transect (GA01): GEOVIDE cruise〈/b〉〈br〉 Géraldine Sarthou, Pascale Lherminier, Eric P. Achterberg, Fernando Alonso-Pérez, Eva Bucciarelli, Julia Boutorh, Vincent Bouvier, Edward A. Boyle, Pierre Branellec, Lidia I. Carracedo, Nuria Casacuberta, Maxi Castrillejo, Marie Cheize, Leonardo Contreira Pereira, Daniel Cossa, Nathalie Daniault, Emmanuel De Saint-Léger, Frank Dehairs, Feifei Deng, Floriane Desprez de Gésincourt, Jérémy Devesa, Lorna Foliot, Debany Fonseca-Batista, Morgane Gallinari, Maribel I. García-Ibáñez, Arthur Gourain, Emilie Grossteffan, Michel Hamon, Lars Eric Heimbürger, Gideon M. Henderson, Catherine Jeandel, Catherine Kermabon, François Lacan, Philippe Le Bot, Manon Le Goff, Emilie Le Roy, Alison Lefèbvre, Stéphane Leizour, Nolwenn Lemaitre, Pere Masqué, Olivier Ménage, Jan-Lukas Menzel Barraqueta, Herlé Mercier, Fabien Perault, Fiz F. Pérez, Hélène F. Planquette, Frédéric Planchon, Arnout Roukaerts, Virginie Sanial, Raphaëlle Sauzède, Catherine Schmechtig, Rachel U. Shelley, Gillian Stewart, Jill N. Sutton, Yi Tang, Nadine Tisnérat-Laborde, Manon Tonnard, Paul Tréguer, Pieter van Beek, Cheryl M. Zurbrick, and Patricia Zunino〈br〉 Biogeosciences, 15, 7097-7109, https://doi.org/10.5194/bg-15-7097-2018, 2018〈br〉 The GEOVIDE cruise (GEOTRACES Section GA01) was conducted in the North Atlantic Ocean and Labrador Sea in May–June 2014. In this special issue, results from GEOVIDE, including physical oceanography and trace element and isotope cyclings, are presented among 17 articles. Here, the scientific context, project objectives, and scientific strategy of GEOVIDE are provided, along with an overview of the main results from the articles published in the special issue.

Description: 〈b〉How representative are FLUXNET measurements of surface fluxes during temperature extremes?〈/b〉〈br〉 Sophie V. J. van der Horst, Andrew J. Pitman, Martin G. De Kauwe, Anna Ukkola, Gab Abramowitz, and Peter Isaac〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-502,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Measurements of surface fluxes are taken around the world and are extremely valuable for understanding how the land and atmopshere interact, and how the land can amplify temerature extremes. However, do these measurements sample extreme temperatures, or are they biased to the average? We examine this question and highlight data that do measure surface fluxes under extreme conditions. This provides a way forward to help model developers improve their models.

Description: 〈b〉Biogeochemical evidence of anaerobic methane oxidation on active submarine mud volcanoes on the continental slope of the Canadian Beaufort Sea〈/b〉〈br〉 Dong-Hun Lee, Jung-Hyun Kim, Yung Mi Lee, Alina Stadnitskaia, Young Keun Jin, Helge Niemann, Young-Gyun Kim, and Kyung-Hoon Shin〈br〉 Biogeosciences, 15, 7419-7433, https://doi.org/10.5194/bg-15-7419-2018, 2018〈br〉 In this study, we provide first evidence of lipid biomarker patterns and phylogenetic identities of key microbes mediating anaerobic oxidation of methane (AOM) communities in active mud volcanoes (MVs) on the continental slope of the Canadian Beaufort Sea. Our lipid and 16S rRNA results indicate that archaea of the ANME-2c and ANME-3 clades are involved in AOM in the MVs investigated.

Description: 〈b〉Composition and cycling of dissolved organic matter from tropical peatlands of coastal Sarawak, Borneo, revealed by fluorescence spectroscopy and PARAFAC analysis〈/b〉〈br〉 Yongli Zhou, Patrick Martin, and Moritz Müller〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-508,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 We found that peatlands in coastal Sarawak, Borneo are exporting extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photo-lability, still account for 20 % of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in coastal carbon cycle.

Description: 〈b〉Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing〈/b〉〈br〉 Ulrike Löptien and Heiner Dietze〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-491,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth System Models provide a base for related political decision making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls where flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.

Description: 〈b〉Composition and cycling of dissolved organic matter from tropical peatlands of coastal Sarawak, Borneo, revealed by fluorescence spectroscopy and PARAFAC analysis〈/b〉〈br〉 Yongli Zhou, Patrick Martin, and Moritz Müller〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-508,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 We found that peatlands in coastal Sarawak, Borneo are exporting extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photo-lability, still account for 20 % of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in coastal carbon cycle.

Description: 〈b〉Sensitivity of atmospheric CO〈sub〉2〈/sub〉 to regional variability in particulate organic matter remineralization depths〈/b〉〈br〉 Jamie D. Wilson, Stephen Barker, Neil R. Edwards, Philip B. Holden, and Andy Ridgwell〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-509,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The remains of plankton rain down from the surface ocean to the deep ocean acting to store CO〈sub〉2〈/sub〉 in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. We found that the amount of CO〈sub〉2〈/sub〉 stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean may be most impacted by climate change, the amount of CO〈sub〉2〈/sub〉 they store in the deep ocean could also be affected.

Description: 〈b〉Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate 〈i〉Alexandrium minutum〈/i〉 during a simulated marine heat wave〈/b〉〈br〉 Elisabeth Deschaseaux, James O'Brien, Nachshon Siboni, Katherina Petrou, and Justin R. Seymour〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-497,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Here we report that abrupt increases in temperature simulating marine heatwaves might have the potential to shape the physiological state and biogenic sulfur production in microalgae involved in harmful algal blooms. Changing physiology and biochemistry seem to trigger a shift in the bacteria community associated with these microalgae. Since microalgae and associated bacteria play an important role in climate regulation, this could have serious consequences for our future ocean and climate.

Description: 〈b〉Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis〈/b〉〈br〉 Laura A. Casella, Sixin He, Erika Griesshaber, Lourdes Fernández-Díaz, Martina Greiner, Elizabeth M. Harper, Daniel J. Jackson, Andreas Ziegler, Vasileios Mavromatis, Martin Dietzel, Anton Eisenhauer, Sabino Veintemillas-Verdaguer, Uwe Brand, and Wolfgang W. Schmahl〈br〉 Biogeosciences, 15, 7451-7484, https://doi.org/10.5194/bg-15-7451-2018, 2018〈br〉 Biogenic carbonates record past environmental conditions. Fossil shell chemistry and microstructure change as metastable biogenic carbonates are replaced by inorganic calcite. Simulated diagenetic alteration at 175 °C of different shell microstructures showed that (nacreous) shell aragonite and calcite were partially replaced by coarse inorganic calcite crystals due to dissolution–reprecipitation reactions. EBSD maps allowed for qualitative assessment of the degree of diagenetic overprint.

Description: 〈b〉Longitudinal contrast in turbulence along a  ∼ 19° S section in the Pacific and its consequences for biogeochemical fluxes〈/b〉〈br〉 Pascale Bouruet-Aubertot, Yannis Cuypers, Andrea Doglioli, Mathieu Caffin, Christophe Yohia, Alain de Verneil, Anne Petrenko, Dominique Lefèvre, Hervé Le Goff, Gilles Rougier, Marc Picheral, and Thierry Moutin〈br〉 Biogeosciences, 15, 7485-7504, https://doi.org10.5194/bg-15-7485-2018, 2018〈br〉 The OUTPACE cruise took place between New Caledonia and French Polynesia. The main purpose was to understand how micro-organisms can survive in a very poor environment. One main source of nutrients is at depth, below the euphotic layer where micro-organisms live. The purpose of the turbulence measurements was to determine to which extent turbulence may 〈q〉uplift〈/q〉 nutrients into the euphotic layer. The origin of the turbulence that was found contrasted along the transect was also determined.

Description: 〈b〉Longitudinal contrast in turbulence along a  ∼ 19° S section in the Pacific and its consequences for biogeochemical fluxes〈/b〉〈br〉 Pascale Bouruet-Aubertot, Yannis Cuypers, Andrea Doglioli, Mathieu Caffin, Christophe Yohia, Alain de Verneil, Anne Petrenko, Dominique Lefèvre, Hervé Le Goff, Gilles Rougier, Marc Picheral, and Thierry Moutin〈br〉 Biogeosciences, 15, 7485-7504, https://doi.org/10.5194/bg-15-7485-2018, 2018〈br〉 The OUTPACE cruise took place between New Caledonia and French Polynesia. The main purpose was to understand how micro-organisms can survive in a very poor environment. One main source of nutrients is at depth, below the euphotic layer where micro-organisms live. The purpose of the turbulence measurements was to determine to which extent turbulence may 〈q〉uplift〈/q〉 nutrients into the euphotic layer. The origin of the turbulence that was found contrasted along the transect was also determined.

Description: 〈b〉Decadal impacts of nitrogen additions on temperate forest carbon sinks: A data-model comparison〈/b〉〈br〉 Susan J. Cheng, Peter G. Hess, William R. Wieder, R. Quinn Thomas, Knute J. Nadelhoffer, Julius Vira, Danica L. Lombardozzi, Per Gundersen, Ivan J. Fernandez, Patrick Schleppi, Marie-Cécile Gruselle, Filip Moldan, and Christine L. Goodale〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-505,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Nitrogen pollution and fertilizer can change how much carbon is stored in plant and soil stocks. Understanding how much added nitrogen is recovered in plants or soils is critical to estimating the size of the future land carbon sink. We compared how nitrogen additions are recovered in modeled soil and plant stocks against data from long-term nitrogen addition experiments. We found that the model simulates recovery of added nitrogen into soils through a different process than found in the field.

Description: 〈b〉Decadal impacts of nitrogen additions on temperate forest carbon sinks: A data-model comparison〈/b〉〈br〉 Susan J. Cheng, Peter G. Hess, William R. Wieder, R. Quinn Thomas, Knute J. Nadelhoffer, Julius Vira, Danica L. Lombardozzi, Per Gundersen, Ivan J. Fernandez, Patrick Schleppi, Marie-Cécile Gruselle, Filip Moldan, and Christine L. Goodale〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-505,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Nitrogen pollution and fertilizer can change how much carbon is stored in plant and soil stocks. Understanding how much added nitrogen is recovered in plants or soils is critical to estimating the size of the future land carbon sink. We compared how nitrogen additions are recovered in modeled soil and plant stocks against data from long-term nitrogen addition experiments. We found that the model simulates recovery of added nitrogen into soils through a different process than found in the field.

Description: 〈b〉Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate 〈i〉Alexandrium minutum〈/i〉 during a simulated marine heat wave〈/b〉〈br〉 Elisabeth Deschaseaux, James O'Brien, Nachshon Siboni, Katherina Petrou, and Justin R. Seymour〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-497,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Here we report that abrupt increases in temperature simulating marine heatwaves might have the potential to shape the physiological state and biogenic sulfur production in microalgae involved in harmful algal blooms. Changing physiology and biochemistry seem to trigger a shift in the bacteria community associated with these microalgae. Since microalgae and associated bacteria play an important role in climate regulation, this could have serious consequences for our future ocean and climate.

Description: 〈b〉Hydrothermal alteration of aragonitic biocarbonates: assessment of micro- and nanostructural dissolution–reprecipitation and constraints of diagenetic overprint from quantitative statistical grain-area analysis〈/b〉〈br〉 Laura A. Casella, Sixin He, Erika Griesshaber, Lourdes Fernández-Díaz, Martina Greiner, Elizabeth M. Harper, Daniel J. Jackson, Andreas Ziegler, Vasileios Mavromatis, Martin Dietzel, Anton Eisenhauer, Sabino Veintemillas-Verdaguer, Uwe Brand, and Wolfgang W. Schmahl〈br〉 Biogeosciences, 15, 7451-7484, https://doi.org10.5194/bg-15-7451-2018, 2018〈br〉 Biogenic carbonates record past environmental conditions. Fossil shell chemistry and microstructure change as metastable biogenic carbonates are replaced by inorganic calcite. Simulated diagenetic alteration at 175 °C of different shell microstructures showed that (nacreous) shell aragonite and calcite were partially replaced by coarse inorganic calcite crystals due to dissolution–reprecipitation reactions. EBSD maps allowed for qualitative assessment of the degree of diagenetic overprint.

Description: 〈b〉Fluvial organic carbon fluxes from oil palm plantations on tropical peatland〈/b〉〈br〉 Sarah Cook, Mick J. Whelan, Chris D. Evans, Vincent Gauci, Mike Peacock, Mark H. Garnett, Lip Khoon Kho, Yit Arn Teh, and Susan E. Page〈br〉 Biogeosciences, 15, 7435-7450, https://doi.org10.5194/bg-15-7435-2018, 2018〈br〉 This paper presents the first comprehensive assessment of fluvial organic carbon loss from oil palm plantations on tropical peat: a carbon loss pathway previously unaccounted for from carbon budgets. Carbon in the water draining four plantations in Sarawak was monitored across a 1-year period. Greater fluvial carbon losses were linked to sites with lower water tables. These data will be used to complete the carbon budget from these ecosystems and assess the full impact of this land conversion.

Description: 〈b〉Fluvial organic carbon fluxes from oil palm plantations on tropical peatland〈/b〉〈br〉 Sarah Cook, Mick J. Whelan, Chris D. Evans, Vincent Gauci, Mike Peacock, Mark H. Garnett, Lip Khoon Kho, Yit Arn Teh, and Susan E. Page〈br〉 Biogeosciences, 15, 7435-7450, https://doi.org/10.5194/bg-15-7435-2018, 2018〈br〉 This paper presents the first comprehensive assessment of fluvial organic carbon loss from oil palm plantations on tropical peat: a carbon loss pathway previously unaccounted for from carbon budgets. Carbon in the water draining four plantations in Sarawak was monitored across a 1-year period. Greater fluvial carbon losses were linked to sites with lower water tables. These data will be used to complete the carbon budget from these ecosystems and assess the full impact of this land conversion.

Description: 〈b〉How representative are FLUXNET measurements of surface fluxes during temperature extremes?〈/b〉〈br〉 Sophie V. J. van der Horst, Andrew J. Pitman, Martin G. De Kauwe, Anna Ukkola, Gab Abramowitz, and Peter Isaac〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-502,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Measurements of surface fluxes are taken around the world and are extremely valuable for understanding how the land and atmopshere interact, and how the land can amplify temerature extremes. However, do these measurements sample extreme temperatures, or are they biased to the average? We examine this question and highlight data that do measure surface fluxes under extreme conditions. This provides a way forward to help model developers improve their models.

Description: 〈b〉Reciprocal bias compensation and ensuing uncertainties in model-based climate projections: pelagic biogeochemistry versus ocean mixing〈/b〉〈br〉 Ulrike Löptien and Heiner Dietze〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-491,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth System Models provide a base for related political decision making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls where flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.

Description: 〈b〉Sensitivity of atmospheric CO〈sub〉2〈/sub〉 to regional variability in particulate organic matter remineralization depths〈/b〉〈br〉 Jamie D. Wilson, Stephen Barker, Neil R. Edwards, Philip B. Holden, and Andy Ridgwell〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-509,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The remains of plankton rain down from the surface ocean to the deep ocean acting to store CO〈sub〉2〈/sub〉 in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. We found that the amount of CO〈sub〉2〈/sub〉 stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean may be most impacted by climate change, the amount of CO〈sub〉2〈/sub〉 they store in the deep ocean could also be affected.

Description: 〈b〉Quantitative mapping and predictive modeling of Mn nodules' distribution from hydroacoustic and optical AUV data linked by random forests machine learning〈/b〉〈br〉 Iason-Zois Gazis, Timm Schoening, Evangelos Alevizos, and Jens Greinert〈br〉 Biogeosciences, 15, 7347-7377, https://doi.org10.5194/bg-15-7347-2018, 2018〈br〉 The use of high-resolution hydroacoustic and optic data acquired by an autonomous underwater vehicle can give us detailed sea bottom topography and valuable information regarding manganese nodules' spatial distribution. Moreover, the combined use of these data sets with a random forest machine learning model can extend this spatial prediction beyond the areas with available photos, providing researchers with a new mapping tool for further investigation and links with other data.

Description: 〈b〉Geographic distribution of free-living marine nematodes in the Clarion–Clipperton Zone: implications for future deep-sea mining scenarios〈/b〉〈br〉 Freija Hauquier, Lara Macheriotou, Tania N. Bezerra, Great Egho, Pedro Martínez Arbizu, and Ann Vanreusel〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-492,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Future mining operations in the deep sea provide a source of scientific uncertainty and call for detailed study of the ecosystem. We investigated one of the most diverse and abundant taxa present in deep-sea sediments, nematodes, and demonstrate the importance of sediment attributes for their communities. Especially species that are less common and have a limited spatial distribution will be vulnerable to mining-induced changes. Our findings can serve as a reference for future impact studies.

Description: 〈b〉Ecosystem responses to elevated CO〈sub〉2〈/sub〉 using airborne remote sensing at Mammoth Mountain, California〈/b〉〈br〉 Kerry Cawse-Nicholson, Joshua B. Fisher, Caroline A. Famiglietti, Amy Braverman, Florian M. Schwandner, Jennifer L. Lewicki, Philip A. Townsend, David S. Schimel, Ryan Pavlick, Kathryn J. Bormann, Antonio Ferraz, Emily L. Kang, Pulong Ma, Robert R. Bogue, Thomas Youmans, and David C. Pieri〈br〉 Biogeosciences, 15, 7403-7418, https://doi.org10.5194/bg-15-7403-2018, 2018〈br〉 Carbon dioxide levels are rising globally, and it is important to understand how this rise will affect plants over long time periods. Volcanoes such as Mammoth Mountain, California, have been releasing CO〈sub〉2〈/sub〉 from their flanks for decades, and this provides a test environment in order to study the way plants respond to long-term CO〈sub〉2〈/sub〉 exposure. We combined several airborne measurements to show that plants may have fewer, more productive leaves in areas with increasing CO〈sub〉2〈/sub〉.

Description: 〈b〉Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer〈/b〉〈br〉 Jørgen Bendtsen and Katherine Richardson〈br〉 Biogeosciences, 15, 7315-7332, https://doi.org/10.5194/bg-15-7315-2018, 2018〈br〉 New production based on nutrients entering the well-lit surface layer is important for understanding marine ecosystems. Measurements of primary production and turbulence across the shelf edge in the northeastern portion of the North Sea show that new production is concentrated around the shelf-edge zone. The shelf-edge zone is, therefore, a major nutrient supplier to the productive surface layer and makes this area important for higher trophic levels such as zooplankton and fish.

Description: 〈b〉Commercial traceability of 〈i〉Arapaima spp.〈/i〉 fisheries in the Amazon Basin: can biogeochemical tags be useful?〈/b〉〈br〉 Luciana A. Pereira, Roberto V. Santos, Marília Hauser, Fabrice Duponchelle, Fernando Carvajal, Christophe Pecheyran, Sylvain Bérail, and Marc Pouilly〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-471,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 1 comment)〈br〉 This study developed the first step for a chemical origin certification of Pirarucu fishery in the Amazon using isotopic tracers and resulted in a preliminary forensic tool. The geographic origin certification of farmed and wild endangered fishes contributes to secure the food and income to communities, the permanent management of fisheries stocks, the continuous advance of aquaculture, the consumer support to legal fisheries and the national and international regulation of natural resources.

Description: 〈b〉From substrate to soil in a pristine environment – pedochemical, micromorphological and microbiological properties from soils on James Ross Island, Antarctica〈/b〉〈br〉 Lars A. Meier, Patryk Krauze, Isabel Prater, Fabian Horn, Carlos E. G. R. Schaefer, Thomas Scholten, Dirk Wagner, Carsten W. Mueller, and Peter Kühn〈br〉 Biogeosciences Discuss., doi:10.5194/bg-2018-488,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 James Ross Island offers the opportunity to study the undisturbed interplay of microbial activity and pedogenesis. Soils from two sites representing coastal and inland conditions were chosen and analysed with a wide range of techniques to describe soil properties. We are able to show that coastal conditions go along with more intense weathering and therefore favor soil formation and that microbial communities are initially more affected by weathering and structure than by chemical parameters.

Description: 〈b〉Effects of dry and wet Saharan dust deposition in the tropical North Atlantic Ocean〈/b〉〈br〉 Laura F. Korte, Franziska Pausch, Scarlett Trimborn, Corina P. D. Brussaard, Geert-Jan A. Brummer, Michèlle van der Does, Catarina V. Guerreiro, Laura T. Schreuder, Chris I. Munday, and Jan-Berend W. Stuut〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-484,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 This paper shows the differences of nutrient release after dry and wet Saharan dust deposition in the tropical North Atlantic Ocean at 12° N. Incubation experiments were conducted along an east-west transect. Large differences were observed between both deposition types with wet deposition being the dominant source of phosphate, silicate, and iron. Both deposition types suggest that Saharan dust particles might be incorporated into marine snow aggregates and act as ballast mineral.

Description: 〈b〉The number of past and future regenerations of iron in the ocean〈br〉and its intrinsic fertilization efficiency〈/b〉〈br〉 Benoît Pasquier and Mark Holzer〈br〉 Biogeosciences, 15, 7177-7203, https://doi.org10.5194/bg-15-7177-2018, 2018〈br〉 We analyze data-constrained state estimates of the global marine iron cycle, a key control on the ocean's biological carbon pump. We develop new techniques for counting the iron's number of passages through the biological pump and link this number to the ocean's natural iron fertilization efficiency. We find that the majority of iron is not biologically utilized before being scavenged, and we identify the central equatorial Pacific as having the highest iron fertilization efficiency.

Description: Use of argon to measure gas exchange in turbulent mountain streams Robert O. Hall Jr. and Hilary L. Madinger Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-108,2018 Manuscript under review for BG (discussion: open, 0 comments) Streams exchange oxygen with the atmosphere, but this rate is difficult to measure. We added argon to small mountain streams to estimate gas exchange. We compared these rates with sulfur hexafluoride, an intense greenhouse gas. Argon worked well to measure gas exchange, but had higher than predicted rates than sulfur hexafluoride. Argon exchange is more likely to represent that for oxygen because they share similar physical properties. We suggest argon to measure gas exchange in small streams.

Description: Leaf phenology as one important driver of seasonal changes in isoprene emission in central Amazonia Eliane G. Alves, Julio Tóta, Andrew Turnipseed, Alex B. Guenther, José Oscar W. Vega Bustillos, Raoni A. Santana, Glauber G. Cirino, Julia V. Tavares, Aline Lopes, Bruce W. Nelson, Rodrigo A. de Souza, Dasa Gu, Trissevgeni Stavrakou, David K. Adams, Jin Wu, Scott Saleska, and Antonio O. Manzi Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-26,2018 Manuscript under review for BG (discussion: open, 0 comments) Isoprene fluxes vary seasonally with changes in environmental factors (e.g., solar radiation and temperature) and biological factors (e.g., leaf phenology). However, our understanding of seasonal patterns of isoprene fluxes and associated mechanistic controls are still limited, especially in Amazonian evergreen forests. In this paper, we aim to connect intensive, field-based measurements of canopy isoprene flux over a central Amazonian evergreen forest with meteorological observations and with tower-camera leaf phenology to improve understanding of patterns and causes of isoprene flux seasonality. Our results demonstrate that the highest isoprene emissions are observed during the dry and dry-to-wet transition seasons, whereas the lowest emissions were found during the wet-to-dry transition season. Our results also indicate that light and temperature can not totally explain the isoprene flux seasonality. Instead, the camera-derived leaf area index (LAI) of recently mature leaf-age class (e.g. leaf ages of 3–5 months) exhibits the highest correlation with observed isoprene flux seasonality ( R 2  = 0.59, p  

Description: The influence of the ocean circulation state on ocean carbon storage and CO 2 drawdown potential in an Earth system model Malin Ödalen, Jonas Nycander, Kevin I. C. Oliver, Laurent Brodeau, and Andy Ridgwell Biogeosciences, 15, 1367-1393, https://doi.org/10.5194/bg-15-1367-2018, 2018 We conclude that different initial states for an ocean model result in different capacities for ocean carbon storage due to differences in the ocean circulation state and the origin of the carbon in the initial ocean carbon reservoir. This could explain why it is difficult to achieve comparable responses of the ocean carbon system in model inter-comparison studies in which the initial states vary between models. We show that this effect of the initial state is quantifiable.

Description: Climate effects on vegetation vitality at the treeline of boreal forests of Mongolia Michael Klinge, Choimaa Dulamsuren, Stefan Erasmi, Dirk Nikolaus Karger, and Markus Hauck Biogeosciences, 15, 1319-1333, https://doi.org/10.5194/bg-15-1319-2018, 2018 Treelines are one of the most obvious borders between vegetation units and can easily be detected by remote sensing. They provide information on climate conditions and human impact on forest distribution. Performing a GIS analysis by combining different datasets leads to detection of the major determining factors for current forest distribution and helps to evaluate past and future conditions for tree growth. This is especially feasible for regions without extensive forest management.

Description: The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model Emeline Chaste, Martin P. Girardin, Jed O. Kaplan, Jeanne Portier, Yves Bergeron, and Christelle Hély Biogeosciences, 15, 1273-1292, https://doi.org/10.5194/bg-15-1273-2018, 2018 A vegetation model was used to reconstruct fire activity from 1901 to 2012 in relation to changes in lightning ignition, climate, and vegetation in eastern Canada's boreal forest. The model correctly simulated the history of fire activity. The results showed that fire activity is ignition limited but is also greatly affected by both climate and vegetation. This research aims to develop a vegetation model that could be used to predict the future impacts of climate changes on fire activity.

Description: Towards an assessment of riverine dissolved organic carbon in surface waters of the western Arctic Ocean based on remote sensing and biogeochemical modeling Vincent Le Fouest, Atsushi Matsuoka, Manfredi Manizza, Mona Shernetsky, Bruno Tremblay, and Marcel Babin Biogeosciences, 15, 1335-1346, https://doi.org/10.5194/bg-15-1335-2018, 2018 Climate warming could enhance the load of terrigenous dissolved organic carbon (tDOC) of Arctic rivers. We show that tDOC concentrations simulated by an ocean–biogeochemical model in the Canadian Beaufort Sea compare favorably with their satellite counterparts. Over spring–summer, riverine tDOC contributes to 35 % of primary production and an equivalent of ~ 10 % of tDOC is exported westwards with the potential for fueling the biological production of the eastern Alaskan nearshore waters.

Description: Patterns and controls of soil respiration and its temperature sensitivity in grassland ecosystems across China Jiguang Feng, Jingsheng Wang, Yanjun Song, and Biao Zhu Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-83,2018 Manuscript under review for BG (discussion: open, 0 comments) Soil respiration (Rs), a key process in the terrestrial carbon cycle, is very sensitive to climate change. In this study, we synthesized 54 measurements of annual Rs and 171 estimates of Q 10 value (the temperature sensitivity of soil respiration) in grasslands across China. We quantitatively analyzed their spatial patterns and controlling factors in five grassland types, including temperate typical steppe, temperate meadow steppe, temperate desert steppe, alpine grassland, and warm-tropical grassland. Results showed that the mean (± SE) annual Rs was 582.0 ± 57.9 g C m −2  yr −1 across Chinese grasslands. Annual Rs significantly differed among grassland types, and positively correlated with mean annual temperature, mean annual precipitation, soil organic carbon content and aboveground biomass, but negatively correlated with latitude and soil pH ( P 〈 0.05). Among these factors, mean annual precipitation was the primary factor controlling the spatial variation of annual Rs in Chinese grasslands. The mean contributions of growing season Rs and heterotrophic respiration to annual Rs were 78.7 % and 72.8 %, respectively. Moreover, the mean (± SE) of Q 10 across Chinese grasslands was 2.60 ± 0.08, ranging from 1.03 to 8.13, and varied largely within and among grassland types, and among soil temperature measurement depths. Generally, the seasonal variation of soil respiration in Chinese grasslands cannot be well explained by soil temperature using the van't Hoff equation. Longitude and altitude were the dominant driving factors and accounted for 26.0 % of the variation in Q 10 derived by soil temperature at the depth of 5 cm. Overall, our findings advance our understanding of the spatial variation and environmental control of soil respiration and Q 10 across Chinese grasslands, and also improve our ability to predict soil carbon efflux under climate change on the regional scale.

Description: Manganese incorporation in living (stained) benthic foraminiferal shells: A bathymetric and in-sediment study in the Gulf of Lions (NW Mediterranean) Shauna Ní Fhlaithearta, Christophe Fontanier, Frans Jorissen, Aurélia Mouret, Adriana Dueñas-Bohórquez, Pierre Anschutz, Mattias B. Fricker, Detlef Günther, Gert J. de Lange, and Gert-Jan Reichart Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-42,2018 Manuscript under review for BG (discussion: open, 0 comments) This study looks to how foraminifera interact with their geochemical environment in the seabed. We focus on the incorporation of the trace metal manganese (Mn), with the aim of developing a tool to reconstruct past pore water profiles. Manganese concentrations in foraminifera are investigated relative to their ecological preferences and geochemical environment. This study demonstrates that Mn in foraminiferal tests is a promising tool to reconstruct oxygen conditions in the seabed.

Description: Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea) Anna Binczewska, Bjørg Risebrobakken, Irina Polovodova Asteman, Matthias Moros, Amandine Tisserand, Eystein Jansen, and Andrzej Witkowski Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-94,2018 Manuscript under review for BG (discussion: open, 0 comments) Primary productivity is an important factor in functioning and structuring of the coastal ecosystem. Thus, two sediment cores from the Skagerrak (North Sea) were investigated in order to obtain a comprehensive picture of primary productivity changes during the last millennium and identify associated forcing factors (e.g. anthropogenic, climate). The cores were dated, and analysed for palaeoproductivity proxies and paleothermometers.

Description: Impacts of droughts and extreme-temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones Jannis von Buttlar, Jakob Zscheischler, Anja Rammig, Sebastian Sippel, Markus Reichstein, Alexander Knohl, Martin Jung, Olaf Menzer, M. Altaf Arain, Nina Buchmann, Alessandro Cescatti, Damiano Gianelle, Gerard Kiely, Beverly E. Law, Vincenzo Magliulo, Hank Margolis, Harry McCaughey, Lutz Merbold, Mirco Migliavacca, Leonardo Montagnani, Walter Oechel, Marian Pavelka, Matthias Peichl, Serge Rambal, Antonio Raschi, Russell L. Scott, Francesco P. Vaccari, Eva van Gorsel, Andrej Varlagin, Georg Wohlfahrt, and Miguel D. Mahecha Biogeosciences, 15, 1293-1318, https://doi.org/10.5194/bg-15-1293-2018, 2018 Our work systematically quantifies extreme heat and drought event impacts on gross primary productivity (GPP) and ecosystem respiration globally across a wide range of ecosystems. We show that heat extremes typically increased mainly respiration whereas drought decreased both fluxes. Combined heat and drought extremes had opposing effects offsetting each other for respiration, but there were also strong reductions in GPP and hence the strongest reductions in the ecosystems carbon sink capacity.

Description: Divergence of dominant factors in soil microbial communities and functions in forest ecosystems along a climatic gradient Zhiwei Xu, Guirui Yu, Xinyu Zhang, Nianpeng He, Qiufeng Wang, Shengzhong Wang, Xiaofeng Xu, Ruili Wang, and Ning Zhao Biogeosciences, 15, 1217-1228, https://doi.org/10.5194/bg-15-1217-2018, 2018 Forest types with specific soil conditions supported the development of distinct soil microbial communities with variable functions. Our results indicate that the main controls on soil microbes and functions vary across forest ecosystems in different climatic zones. This information will add value to the modeling of microbial processes and will contribute to carbon cycling on a large scale.

Description: Modelling biogeochemical processes in sediments from the north-western Adriatic Sea: response to enhanced particulate organic carbon fluxes Daniele Brigolin, Christophe Rabouille, Bruno Bombled, Silvia Colla, Salvatrice Vizzini, Roberto Pastres, and Fabio Pranovi Biogeosciences, 15, 1347-1366, https://doi.org/10.5194/bg-15-1347-2018, 2018 We present the result of a study carried out in the north-western Adriatic Sea by combining two different types of models with field sampling. A mussel farm was taken as a local source of perturbation to the natural flux of particulate organic carbon to the sediment. Differences in fluxes were primarily associated with mussel physiological conditions. Although restricted, these changes in particulate organic carbon fluxes induced visible effects on sediment biogeochemistry.

Description: Impacts of flocculation on the distribution and diagenesis of iron in boreal estuarine sediments Tom Jilbert, Eero Asmala, Christian Schröder, Rosa Tiihonen, Jukka-Pekka Myllykangas, Joonas J. Virtasalo, Aarno Kotilainen, Pasi Peltola, Päivi Ekholm, and Susanna Hietanen Biogeosciences, 15, 1243-1271, https://doi.org/10.5194/bg-15-1243-2018, 2018 Iron is a common dissolved element in river water, recognizable by its orange-brown colour. Here we show that when rivers reach the ocean much of this iron settles to the sediments by a process known as flocculation. The iron is then used by microbes in coastal sediments, which are important hotspots in the global carbon cycle.

Description: Plant responses to volcanically-elevated CO 2 in two Costa Rican forests Robert R. Bogue, Florian M. Schwandner, Joshua B. Fisher, Ryan Pavlick, Troy S. Magney, Caroline A. Famiglietti, Kerry Cawse-Nicholson, Vineet Yadav, Justin P. Linick, Gretchen B. North, and Eliecer Duarte Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-100,2018 Manuscript under review for BG (discussion: open, 0 comments) We studied trees growing on the outer areas of two volcanoes in Costa Rica to examine the effects of volcanic CO 2 emissions on tree characteristics. We measured two tree species and found that they were comprised of carbon from the volcanic CO 2 . Volcanic CO 2 emissions may also have measurable impacts on leaf function measurements. Our results have implications for reconstructing volcanic degassing histories at previously unmonitored volcanoes and studying biological impacts of elevated CO 2 .

Description: A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change Natasha A. Gafar and Kai G. Schulz Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-88,2018 Manuscript under review for BG (discussion: open, 1 comment) Emiliania huxleyi and Gephyrocapsa oceanica are the most prolific calcifying phytoplankton in todays oceans. Here we compare their sensitivity to combined anthropogenic stressors of temperature, light and CO 2 . For the future we project a niche contraction for G. oceanica . Furthermore, there was good correlation of our new metric, the CaCO 3 production potential, with satellite derived concentrations in the modern ocean, indicating means of assessing overall coccolithophorid success in the future.

Description: Catchment tracers reveal discharge, recharge and sources of groundwater-borne pollutants in a novel lake modelling approach Emil Kristensen, Mikkel Madsen-Østerbye, Philippe Massicotte, Ole Pedersen, Stiig Markager, and Theis Kragh Biogeosciences, 15, 1203-1216, https://doi.org/10.5194/bg-15-1203-2018, 2018 We propose a novel modelling approach enabling swift hydrological surveys based on multiple conservative and non-conservative tracers to estimate water retention time, groundwater discharge sites, fractions of water originating from the discharge sites, groundwater recharge sites and sites that are especially important in regard to groundwater recharge. Thus we provide a whole lake hydrological survey while pinpointing sources of pollutants like colored dissolved organic matter and nutrients.