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〉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〉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.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〉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〉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〉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〉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., 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〉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〉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〉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〉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〉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.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.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., 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〉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.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., 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〉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〉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〉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〉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: 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.

Description: C 5 glycolipids of heterocystous cyanobacteria track symbiont abundance in the diatom Hemiaulus hauckii across the tropical North Atlantic Nicole J. Bale, Tracy A. Villareal, Ellen C. Hopmans, Corina P. D. Brussaard, Marc Besseling, Denise Dorhout, Jaap S. Sinninghe Damsté, and Stefan Schouten Biogeosciences, 15, 1229-1241, https://doi.org/10.5194/bg-15-1229-2018, 2018 Associations between diatoms and N-fixing cyanobacteria (diatom–diazotroph associations, DDAs) play an important role in the N cycle of the tropical North Atlantic. Heterocysts are the site of N fixation and contain unique glycolipids. We measured these glycolipids in the water column and surface sediment from the tropical North Atlantic. We found a significant correlation between the concentration of glycolipid and of DDAs, strengthening their application as biomarkers.

Description: Technical Note: Rapid image-based field methods improve the quantification of termite mound structures and greenhouse-gas fluxes Philipp A. Nauer, Eleonora Chiri, David de Souza, Lindsay B. Hutley, and Stefan K. Arndt Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-43,2018 Manuscript under review for BG (discussion: open, 0 comments) Termites provide important functions in tropical ecosystems, but the complex structure of their mounds impede an accurate quantitative description. We present two novel field methods, based on photogrammetry and image analysis, to quantify the volume, surface area and porosities of termite mounds. The methods are accurate, rapid to apply and superior to established methods, therefore greatly improve biogeochemical rate estimates such as greenhouse-gas fluxes from termite mounds.

Description: Fire intensity impacts on post-fire temperate coniferous forest net primary productivity Aaron M. Sparks, Crystal A. Kolden, Alistair M. S. Smith, Luigi Boschetti, Daniel M. Johnson, and Mark A. Cochrane Biogeosciences, 15, 1173-1183, https://doi.org/10.5194/bg-15-1173-2018, 2018 Through landscape-scale satellite observations we demonstrate that fire intensity has a dose–response relationship with temperate forest net primary productivity. Increasing fire intensity resulted in persisting step-wise reductions in post-fire net primary productivity. Forests with higher proportions of fire-resistant species generally had lower reductions in post-fire net primary productivity. A conceptual framework for assessing spatiotemporal post-fire effects is presented.

Description: Coral reef carbonate budgets and ecological drivers in the naturally high temperature and high total alkalinity environment of the Red Sea Anna Roik, Till Roethig, Claudia Pogoreutz, Vincent Saderne, and Christian R. Voolstra Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-57,2018 Manuscript under review for BG (discussion: open, 0 comments) In this study we collected in situ accretion/erosion rates and abiotic/biotic variables to estimate carbonate budgets and ecological drivers of coral reef growth in the central Red Sea. Our data suggest that reef growth is comparable to estimates of other regions, but the erosive forces in the Red Sea are not as pronounced. Comparison with recent data suggest that Red Sea reef growth might not have decreased over the past decades, despite warming, calling for more detailed investigations.

Description: 〈b〉Silicon cycled by tropical forest trees: effects of species, elevation and bedrock on Mount Kinabalu, Malaysia〈/b〉〈br〉 Ryosuke Nakamura, Hidehiro Ishizawa, Rota Wagai, Shizuo Suzuki, Kanehiro Kitayama, and Kaoru Kitajima〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-447,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Silicon (Si) accumulation by plants should affect biogeochemical cycling of Si, but its geographical patterns are unknown for tropical forests. Comparing forests from 700–3100 m a.s.l. on Mt. Kinabalu, we demonstrate for the first time that lowland forests include more trees with high Si concentrations and have greater annual Si flux via leaf litter, regardless of the bedrock types. Our data of 71 tree species strongly suggest the importance of plant traits in modulating ecosystem Si cycling.

Description: 〈b〉Export flux of unprocessed atmospheric nitrate from temperate forested catchments: a possible new index for nitrogen saturation〈/b〉〈br〉 Fumiko Nakagawa, Urumu Tsunogai, Yusuke Obata, Kenta Ando, Naoyuki Yamashita, Tatsuyoshi Saito, Shigeki Uchiyama, Masayuki Morohashi, and Hiroyuki Sase〈br〉 Biogeosciences, 15, 7025-7042, https://doi.org/10.5194/bg-15-7025-2018, 2018〈br〉 To clarify the biological processing of nitrate within temperate forested catchments using unprocessed atmospheric nitrate exported from each catchment as a tracer, we continuously monitored stream nitrate concentrations and stable isotopic compositions in three forested catchments for more than 2 years. We concluded that the export flux of unprocessed atmospheric nitrate relative to the deposition flux in each forest ecosystem is applicable as an index for nitrogen saturation.

Description: 〈b〉Factors controlling coccolithophore biogeography in the Southern Ocean〈/b〉〈br〉 Cara Nissen, Meike Vogt, Matthias Münnich, Nicolas Gruber, and F. Alexander Haumann〈br〉 Biogeosciences, 15, 6997-7024, https://doi.org/10.5194/bg-15-6997-2018, 2018〈br〉 Using a regional ocean model, we find that coccolithophore biomass in the Southern Ocean is highest in the subantarctic in late summer when diatom growth becomes limited by silicate. We show that zooplankton grazing is crucial to explain phytoplankton biomass distributions in this area and conclude that assessments of future distributions should not only consider physical and chemical factors (temperature, light, nutrients, pH), but also interactions with other phytoplankton or zooplankton.

Description: 〈b〉A trait-based modelling approach to planktonic foraminifera ecology〈/b〉〈br〉 Maria Grigoratou, Fanny M. Monteiro, Daniela N. Schmidt, Jamie D. Wilson, Ben A. Ward, and Andy Ridgwell〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-483,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 The manuscript presents a novel study based on the traits of shell size, calcification and feeding behaviour of two planktonic foraminifera life stages using modelling simulations. With the model, we tested the cost and benefit of calcification and explored how the interactions of planktonic foraminifera among other plankton groups influence their biomass under different environmental conditions. Our results provide new insights into environmental controls in planktonic foraminifera ecology.

Description: 〈b〉Multi-trace element sea surface temperature coral reconstruction for the southern Mozambique Channel reveals teleconnections with the tropical Atlantic〈/b〉〈br〉 Jens Zinke, Juan-Pablo D'Olivo, Johannes C. Gey, Malcolm T. McCulloch, J. Henrich Bruggemann, Janice M. Lough, and Mireille M. M. Guillaume〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-441,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Here we report seasonally resolved sea surface temperature (SST) reconstructions for the southern Mozambique Channel in the SW Indian Ocean, a region located along the thermohaline ocean surface circulation route, based on multi-trace element temperatures proxy records preserved in two Porites sp. coral cores for the past 42 years. Particularly, we show the suitability of both separate and combined Sr / Ca and Li / Mg proxies for improved multi-element SST reconstructions.

Description: 〈b〉Mechanisms of northern North Atlantic biomass variability〈/b〉〈br〉 Galen A. McKinley, Alexis L. Ritzer, and Nicole S. Lovenduski〈br〉 Biogeosciences, 15, 6049-6066, https://doi.org/10.5194/bg-15-6049-2018, 2018〈br〉 Phytoplankton biomass changed significantly in the North Atlantic north of 40° N over 1998–2007. With a physical-ecosystem model, we show that biomass increases in the northwest are due to reduced vertical mixing that partially relieves light limitation of phytoplankton. To the east, these circulation changes lead to fewer nutrients being supplied horizontally from the west. Relationships between these biomass variations and atmosphere and ocean physics are not straightforward.

Description: 〈b〉Surface transport of DOC acts as a trophic link among Mediterranean sub-basins〈/b〉〈br〉 Chiara Santinelli, Roberto Iacono, Ernesto Napolitano, and Maurizio Ribera d'Alcalá〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-418,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Part of the energy in the ocean is stored as dissolved organic carbon. Water moves around, bringing this energy from one place to another, down to the deep layers and up again. Here, we show that horizontal currents can have a strong impact on the carbon cycle, because they can transport chemical energy far away, establishing links between distant areas of the ocean and feeding regions in which the local accumulation of chemical energy is low.

Description: 〈b〉Contrasting biosphere responses to hydrometeorological extremes: revisiting the 2010 western Russian heatwave〈/b〉〈br〉 Milan Flach, Sebastian Sippel, Fabian Gans, Ana Bastos, Alexander Brenning, Markus Reichstein, and Miguel D. Mahecha〈br〉 Biogeosciences, 15, 6067-6085, https://doi.org/10.5194/bg-15-6067-2018, 2018〈br〉 Northern forests enhanced their productivity during and before the 2010 Russian mega heatwave. We scrutinize this issue with a novel type of multivariate extreme event detection approach. Forests compensate for 54 % of the carbon losses in agricultural ecosystems due to vulnerable conditions in spring and better water management in summer. The findings highlight the importance of forests in mitigating climate change, while not alleviating the consequences of extreme events for food security.

Description: 〈b〉Baseline for ostracod-based northwestern Pacific and Indo-Pacific shallow-marine paleoenvironmental reconstructions: ecological modeling of species distributions〈/b〉〈br〉 Yuanyuan Hong, Moriaki Yasuhara, Hokuto Iwatani, and Briony Mamo〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-405,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 This study analyzed microfaunal assemblages in surface sediments from 52 sites in Hong Kong marine waters. We selected 18 species for linear regression modeling, to reveal the relationship between species distribution and environmental factors statistically. These results show environmental preferences of commonly distributed species in Asian coasts, providing robust baseline for past environmental reconstruction of broad Asian region using microfossils in sediment cores.

Description: 〈b〉Assessment of paleo-ocean pH records from boron isotope ratio in the Pacific and Atlantic ocean corals: Role of anthropogenic CO〈sub〉2〈/sub〉 forcing and oceanographic factors to pH variability〈/b〉〈br〉 Mohd Tarique and Waliur Rahaman〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-438,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Boron isotopes (δ〈sup〉11〈/sup〉B) records from tropical ocean corals have been used to reconstruct paleo-pH of ocean for the past several decades to few centuries which are comparable to the resolution of instrumental records. In most of the studies, attempts have been made to decipher the role of anthropogenic CO〈sub〉2〈/sub〉 forcing to recent trend of ocean acidification based on δ〈sup〉11〈/sup〉B derived paleo-pH records. However, such attempts in past were often hindered by limited knowledge of oceanographic factors that contributed to past pH variability and changes. In this study, we have evaluated pH records reconstructed using δ〈sup〉11〈/sup〉B records from the Pacific and the Atlantic Oceans corals and investigated major forcing factors that contributed to sub annual-decadal scale pH variability and changes since the industrial era ~ 1850 AD.〈/p〉 〈p〉To the best of our knowledge, total eight δ〈sup〉11〈/sup〉B records from the Pacific and two from the Atlantic Oceans are available in published literatures. The compilations of these records show large variability; range between 26.27–20.82 ‰ which corresponds to pH range 8.40–7.63 respectively. Our investigation of pH records from the Pacific ocean based on principal component analysis (PCA) reveals that atmospheric CO〈sub〉2〈/sub〉 can explains maximum up to ~ 26 % of the total pH variability during 1950–2004 AD, followed by the ocean-climate oscillations (i.e. ENSO and PDO) driven oceanographic factors up to ~ 17 %. The remaining large variability (~ 57 %) could not be explained by above forcing factors and hence we invoke possible influence of metabolic processes of corals and/or changes in micro-environments within the reefs which are often neglected in interpreting paleo-pH records. Therefore, we highlight the need for detailed investigation in future studies to understand about the exact mechanism, processes/factors that controlled boron isotope fractionations in coral reef environments. Further, our investigation reveals that amplitude of the ENSO driven pH variability shows fivefold increase during 1980–2000 AD compared to the previous three decades (1950–1980 AD). This observation is consistent with the historical records of global coral bleaching events and therefore underscores role of ENSO driven environmental stress responsible for coral bleaching events. Considering model based projections of increasing frequency and amplitude of extreme ENSO events in the backdrop of recent global warming, bleaching events are likely to increase in the next decades/centuries.〈/p〉

Description: 〈b〉Salinity control on Na incorporation into calcite tests of the planktonic foraminifera 〈i〉Trilobatus sacculifer〈/i〉 – evidence from culture experiments and surface sediments〈/b〉〈br〉 Jacqueline Bertlich, Dirk Nürnberg, Ed C. Hathorne, Lennart J. de Nooijer, Eveline M. Mezger, Markus Kienast, Steffanie Nordhausen, Gert-Jan Reichart, Joachim Schönfeld, and Jelle Bijma〈br〉 Biogeosciences, 15, 5991-6018, https://doi.org/10.5194/bg-15-5991-2018, 2018〈br〉 〈p〉The quantitative reconstruction of past seawater salinity has yet to be achieved, and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na∕Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na∕Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na∕Ca data measured on cultured specimens of 〈i〉Trilobatus sacculifer.〈/i〉 The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5 to 29.5 °C under constant salinity conditions. Foraminiferal Na∕Ca values positively correlate with seawater salinity (Na∕Ca〈sub〉T. sacculifer〈/sub〉 = 0.97+0.115 ⋅ salinity, 〈i〉R〈/i〉 = 0.97, 〈i〉p〈/i〉 〈 0.005). Temperature, on the other hand, exhibits no statistically significant relationship with Na∕Ca values, indicating salinity to be one of the dominant factors controlling Na incorporation. The culturing results are corroborated by measurements on 〈i〉T. sacculifer〈/i〉 from Caribbean and Gulf of Guinea surface sediments, indicating no dissolution effect on Na∕Ca in foraminiferal calcite with increasing water depth up to  〉 4 km. In conclusion, planktonic foraminiferal Na∕Ca can be applied as a potential proxy for reconstructing sea surface salinities, although species-specific calibrations might be necessary.〈/p〉

Description: 〈b〉A quest for the biological sources of long chain alkyl diols in the western tropical North Atlantic Ocean〈/b〉〈br〉 Sergio Balzano, Julie Lattaud, Laura Villanueva, Sebastiaan W. Rampen, Corina P. D. Brussaard, Judith van Bleijswijk, Nicole Bale, Jaap S. Sinninghe Damsté, and Stefan Schouten〈br〉 Biogeosciences, 15, 5951-5968, https://doi.org/10.5194/bg-15-5951-2018, 2018〈br〉 We tried to identify the microbes which biosynthesize a class of lipids widespread in seawater, the long chain alkyl diols (LCDs). We could not find any microorganism likely involved in the production of LCDs. The amounts of LCDs found are too high to be produced by living organisms and are likely to be part of the refractory organic matter persisting for long periods in the water column.

Description: 〈b〉Coastal primary productivity changes over the last millennium: a case study from the Skagerrak (North Sea)〈/b〉〈br〉 Anna Binczewska, Bjørg Risebrobakken, Irina Polovodova Asteman, Matthias Moros, Amandine Tisserand, Eystein Jansen, and Andrzej Witkowski〈br〉 Biogeosciences, 15, 5909-5928, https://doi.org/10.5194/bg-15-5909-2018, 2018〈br〉 Primary productivity is an important factor in the 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 palaeothermometers.

Description: 〈b〉Trend analysis of the airborne fraction and sink rate of anthropogenically released CO〈sub〉2〈/sub〉〈/b〉〈br〉 Mikkel Bennedsen, Eric Hillebrand, and Siem Jan Koopman〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-402,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Is the fraction of anthropogenically released CO〈sub〉2〈/sub〉 that remains in the atmosphere increasing? Is the rate at which the ocean and land sinks take up CO〈sub〉2〈/sub〉 from the atmosphere decreasing? We analyze these questions by means of a statistical dynamic multivariate model from which we estimate the unobserved trend processes together with the parameters that govern them. We find no statistical evidence of an increasing airborne fraction but we do find statistical evidence of a decreasing sink rate.

Description: 〈b〉Reviews and syntheses: Influences of landscape structure and land uses on local to regional climate and air quality〈/b〉〈br〉 Raia Silvia Massad, Juliette Lathiére, Mathieu Perrin, Erwan Personne, Marc Stefanon, Patrick Stella, Susanna Strada, Sophie Szopa, and Nathalie de Noblet-Ducoudré〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-419,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Human activities strongly interfere in the land-atmosphere interactions through changes in land-use and land-cover changes and land management. The objectives of this review is to synthesize the existing experimental and modelling works that investigate physical, chemical and biogeochemical interactions between land surface and the atmosphere. Greater consideration to atmospheric chemistry, through land-atmosphere interactions, as a decision parameter for land-management is essential.

Description: 〈b〉The role of light as vital effect on coral skeleton oxygen isotopic ratio〈/b〉〈br〉 Anne Juillet-Leclerc〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-433,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 My manuscript is the result of a reflexion process about the meaning of coral skeleton tracers. I realized that in contrast to biologists, geochemists always neglect the light role on proxies. Light influence is difficult to separate from temperature. Thus, I used coral culture in controlled conditions. Once the process identified, I read differently the literature dedicated to the coral skeleton δ〈sup〉18〈/sup〉 and found several evidences demonstrating that light could explain the vital effect.

Description: 〈b〉Unifying soil organic matter formation and persistence frameworks: the MEMS model〈/b〉〈br〉 Andy D. Robertson, Keith Paustian, Stephen Ogle, Matthew D. Wallenstein, Emanuele Lugato, and M. Francesca Cotrufo〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-430,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Predicting how soils respond to varying environmental conditions or land-use change is essential if we aim to promote sustainable management practices and help mitigate climate change. Here, we present a new ecosystem-scale soil model (MEMS v1) that is built upon recent, novel findings and can be run using very few inputs. The model accurately predicted soil carbon stocks for more than 8000 sites across Europe, ranging from cold, wet forests in sandy soils to hot, dry grasslands in clays.

Description: 〈b〉Nitrogen and phosphorus recycling mediated by copepods and response of bacterioplankton community from three contrasting areas in the western tropical South Pacific (20° S)〈/b〉〈br〉 Valentina Valdés, François Carlotti, Ruben Escribano, Katty Donoso, Marc Pagano, Verónica Molina, and Camila Fernandez〈br〉 Biogeosciences, 15, 6019-6032, https://doi.org/10.5194/bg-15-6019-2018, 2018〈br〉 The role of N and P released by copepods on biogeochemical cycles and the microbial community during the OUTPACE cruise was studied. In the presence of copepods, NH4+ and DON increase, and an enhanced remineralization was observed. A shift in active bacterial composition was observed, linked with changes in nutrient concentrations. Copepods can be a source of (in)organic compounds for bacterial communities that contribute to nutrient recycling and regenerated production in the photic zone.

Description: 〈b〉Organic matter characteristics in yedoma and thermokarst deposits on Baldwin Peninsula, west Alaska〈/b〉〈br〉 Loeka L. Jongejans, Jens Strauss, Josefine Lenz, Francien Peterse, Kai Mangelsdorf, Matthias Fuchs, and Guido Grosse〈br〉 Biogeosciences, 15, 6033-6048, https://doi.org/10.5194/bg-15-6033-2018, 2018〈br〉 Arctic warming mobilizes belowground organic matter in northern high latitudes. This study focused on the size of organic carbon pools and organic matter quality in ice-rich permafrost on the Baldwin Peninsula, West Alaska. We analyzed biogeochemistry and found that three-quarters of the carbon is stored in degraded permafrost deposits. Nonetheless, using biomarker analyses, we showed that the organic matter in undisturbed yedoma permafrost has a higher potential for decomposition.

Description: 〈b〉Evaluation of atmospheric nitrogen inputs into marine ecosystems of the North Sea and Baltic Sea – part A: validation and time scales of nutrient accumulation〈/b〉〈br〉 Daniel Neumann, Matthias Karl, Hagen Radtke, and Thomas Neumann〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-364,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Atmospheric nitrogen deposition contributes 20 % to 40 % to bioavailable nitrogen inputs into the North Sea and Baltic Sea. Excessive bioavailable nitrogen may lead to intensified algal blooms in these water bodies resulting in several negative consequences for the marine ecosystem. We traced atmospheric nitrogen in the marine ecosystem via an ecosystem model and estimated the contribution of atmospheric nitrogen to plankton biomass in different regions of the North and Baltic Sea over five years.

Description: 〈b〉Shifting Mineral and Redox Controls on Carbon Cycling in Seasonally Flooded Soils〈/b〉〈br〉 Rachelle LaCroix, Malak Tfaily, Menli McCreight, Morris E. Jones, Lesley Spokas, and Marco Keiluweit〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-432,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Soils contain three times the amount of carbon (C) than the atmosphere, with C turnover times ranging from centuries to millennia. Although wetland soils represent a relatively small portion of the terrestrial landscape, they account for an estimated 20–30 % of the global C reservoir. Among wetlands, seasonally flooded soils are likely the most vulnerable to increased severity and duration of droughts in response to climate change. Yet, the relative influence of associated changes in oxygen limitations, root dynamics, and mineral protection on C cycling in seasonally flooded mineral soils is largely unknown. To address this knowledge gap, we combined seasonal monitoring of soil moisture, redox potential, and CO〈sub〉2〈/sub〉 efflux with a characterization of root biomass, mineralogy, C quantity and organic matter composition along upland-to-lowland transects of both top- and subsoils in temperate forested wetlands. We found that lower CO〈sub〉2〈/sub〉 effluxes in lowland than upland topsoils coincided with greater total C concentrations as well as a greater abundance of high molecular weight and chemically reduced organic compounds, indicating that selective preservation of organic compounds during anaerobic periods caused C accumulation in seasonally flooded surface soils. In subsoils, however, seasonal flooding and associated anaerobic conditions did not result in soil C accumulation. Instead, total C concentrations were significantly lower in lowland than in upland subsoils. Lower soil C accumulation in seasonally flooded subsoils coincided with lower abundance of root biomass and reducible Fe phases, and relied primarily on non-reducible Al phases rather than anaerobic conditions. Combined, our results demonstrate that seasonal flooding and associated anaerobic conditions accumulate C in topsoils, but limit C accumulation in subsoils by restricting root C inputs and removing of protective Fe phases through reductive dissolution. Our findings indicate that C accrual in seasonally flooded soil is due primarily to oxygen limitations in the surface soil, and that the overall lack of mineral protection leaves these C stocks highly vulnerable to climate change.〈/p〉

Description: 〈b〉Patterns and drivers of dimethylsulfide concentration in the northeast Subarctic Pacific across multiple spatial and temporal scales〈/b〉〈br〉 Alysia E. Herr, Ronald P. Kiene, John W. H. Dacey, and Philippe D. Tortell〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-411,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Dimethylsulfide (DMS) is an essential component of the global sulfur cycle and a major source of climate-influencing aerosols. We examine the drivers of DMS concentration gradients along the British Columbia shelf by comparing DMS measurements to environmental variables and biological rates. We further combine new and existing data sets to provide a new summertime DMS climatology for the northeast Subarctic Pacific. Our results highlight the importance of phytoplankton taxonomy to DMS cycling.

Description: 〈b〉Tropical climate–vegetation–fire relationships: multivariate evaluation of the land surface model JSBACH〈/b〉〈br〉 Gitta Lasslop, Thomas Moeller, Donatella D'Onofrio, Stijn Hantson, and Silvia Kloster〈br〉 Biogeosciences, 15, 5969-5989, https://doi.org/10.5194/bg-15-5969-2018, 2018〈br〉 We apply a multivariate model evaluation to the relationship between climate, vegetation and fire in the tropics using the JSBACH land surface model and two remote-sensing data sets, with the aim to identify the potential for model improvement. The overestimation of tree cover for low precipitation and a very strong relationship between tree cover and burned area indicates opportunities in the improvement of drought effects and the impact of fire on tree cover or the adaptation of trees to fire.

Description: 〈b〉Seasonal Net Ecosystem Metabolism of the Near-Shore Reef System in La Parguera, Puerto Rico〈/b〉〈br〉 Melissa Meléndez, Joseph Salisbury, Dwight Gledhill, Chris Langdon, Julio M. Morell, Derek Manzello, Sylvia Musielewicz, and Adrienne Sutton〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-408,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 Using observations from the NOAA CO〈sub〉2〈/sub〉 buoy in La Parguera, Puerto Rico along with modeling approaches yield useful indices of biological processes affecting the water column over the reef. This study provided the first long-term monitoring of coral reef biological processes. Results show that processes that produce CO〈sub〉2〈/sub〉 dominated over most of the year leading to high dissolution rates. This can have implications on the reef system's ability to recover to other climate-scale stressors (warming).

Description: 〈b〉Reviews and syntheses: Carbon use efficiency from organisms to ecosystems – definitions, theories, and empirical evidence〈/b〉〈br〉 Stefano Manzoni, Petr Čapek, Philipp Porada, Martin Thurner, Mattias Winterdahl, Christian Beer, Volker Brüchert, Jan Frouz, Anke M. Herrmann, Björn D. Lindahl, Steve W. Lyon, Hana Šantrůčková, Giulia Vico, and Danielle Way〈br〉 Biogeosciences, 15, 5929-5949, https://doi.org/10.5194/bg-15-5929-2018, 2018〈br〉 Carbon fixed by plants and phytoplankton through photosynthesis is ultimately stored in soils and sediments or released to the atmosphere during decomposition of dead biomass. Carbon-use efficiency is a useful metric to quantify the fate of carbon – higher efficiency means higher storage and lower release to the atmosphere. Here we summarize many definitions of carbon-use efficiency and study how this metric changes from organisms to ecosystems and from terrestrial to aquatic environments.

Description: 〈b〉Ideas and perspectives: Tracing terrestrial ecosystem water fluxes using hydrogen and oxygen stable isotopes – challenges and opportunities from an interdisciplinary perspective〈/b〉〈br〉 Daniele Penna, Luisa Hopp, Francesca Scandellari, Scott T. Allen, Paolo Benettin, Matthias Beyer, Josie Geris, Julian Klaus, John D. Marshall, Luitgard Schwendenmann, Till H. M. Volkmann, Jana von Freyberg, Anam Amin, Natalie Ceperley, Michael Engel, Jay Frentress, Yamuna Giambastiani, Jeff J. McDonnell, Giulia Zuecco, Pilar Llorens, Rolf T. W. Siegwolf, Todd E. Dawson, and James W. Kirchner〈br〉 Biogeosciences, 15, 6399-6415, https://doi.org/10.5194/bg-15-6399-2018, 2018〈br〉 Understanding how water flows through ecosystems is needed to provide society and policymakers with the scientific background to manage water resources sustainably. Stable isotopes of hydrogen and oxygen in water are a powerful tool for tracking water fluxes, although the heterogeneity of natural systems and practical methodological issues still limit their full application. Here, we examine the challenges in this research field and highlight new perspectives based on interdisciplinary research.

Description: 〈b〉Limited impact of El Niño–Southern Oscillation on variability and growth rate of atmospheric methane〈/b〉〈br〉 Hinrich Schaefer, Dan Smale, Sylvia E. Nichol, Tony M. Bromley, Gordon W. Brailsford, Ross J. Martin, Rowena Moss, Sylvia Englund Michel, and James W. C. White〈br〉 Biogeosciences, 15, 6371-6386, https://doi.org/10.5194/bg-15-6371-2018, 2018〈br〉 To quantify the impact of El Nino–Southern Oscillation (ENSO) climate events on the methane budget, we studied the correlation between CH〈sub〉4〈/sub〉 time series and ENSO indices. We find that ENSO explains less than one-third of the variability in CH〈sub〉4〈/sub〉 levels and their stable carbon isotopes, which constrain the source processes of emissions. ENSO forcing of the CH〈sub〉4〈/sub〉 cycle is too small, episodic, and regional to force atmospheric trends, which are more likely caused by agricultural or industrial emissions.

Description: 〈b〉Macrofaunal burrowing enhances deep-sea carbonate lithification on the Southwest Indian Ridge〈/b〉〈br〉 Hengchao Xu, Xiaotong Peng, Shun Chen, Jiwei Li, Shamik Dasgupta, Kaiwen Ta, and Mengran Du〈br〉 Biogeosciences, 15, 6387-6397, https://doi.org/10.5194/bg-15-6387-2018, 2018〈br〉 Processes involved in the formation of deep-sea carbonate rocks remain controversial. It is reported in present study that macrofaunal burrowing may trigger the dissolution of the original calcite above the saturation horizon and thus drive deep-sea carbonate lithification on mid-ocean ridges. The novel mechanism proposed here for nonburial carbonate lithification at the deep-sea seafloor sheds light on the potential interactions between deep-sea biota and sedimentary rocks.

Description: 〈b〉Assessing shadow effects on Photochemical Reflectance Index (PRI) for the water stress detection in winter wheat〈/b〉〈br〉 Xin Yang, Shishi Liu, Yinuo Liu, Xifeng Ren, and Hang Su〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-452,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉The photochemical reflectance index (PRI) has emerged to be a pre-visual indicator of water stress. However, whether the varying shadow fraction, which may be caused by multiple view angles or the changing crop density in the field, affects the performance of PRI in detecting water stress of crops is still uncertain. This study evaluated the impact of the varying shadow fraction on estimating relative water content (RWC) across growth stages of winter wheat using different formulations of PRI. Results demonstrated that PRI570, PRI1, and PRI2 of shadow were higher than those of sunlit leaves for unstressed plants, but the contrary results were achieved for stressed plants. Despite the difference between PRI_shadow and PRI_leaf, the significance of the linear relationship between RWC and PRI did not change with the different ratio of sunlit leaves and shadow. For most studied PRI formulations, the slope and intercept of the linear regression model between PRI and RWC changed proportionally with the shadow fractions. We applied a uniform RWC prediction model to the data of varying shadow fractions and found that the accuracy of RWC predictions was not significantly affected, indicating that the effect of varying shadow fractions was minimal to the seasonal water stress detection in winter wheat using PRI.〈/p〉

Description: 〈b〉A perturbed biogeochemistry model ensemble evaluated against in situ and satellite observations〈/b〉〈br〉 Prima Anugerahanti, Shovonlal Roy, and Keith Haines〈br〉 Biogeosciences, 15, 6685-6711, https://doi.org/10.5194/bg-15-6685-2018, 2018〈br〉 Minor changes in the biogeochemical model equations lead to major dynamical changes. We assessed this structural sensitivity for the MEDUSA biogeochemical model on chlorophyll and nitrogen concentrations at five oceanographic stations over 10 years, using 1-D ensembles generated by combining different process equations. The ensemble performed better than the default model in most of the stations, suggesting that our approach is useful for generating a probabilistic biogeochemical ensemble model.

Description: 〈b〉Assessing biotic contributions to CO〈sub〉2〈/sub〉 fluxes in northern China using the Vegetation, Photosynthesis and Respiration Model (VPRM-CHINA) and observations from 2005 to 2009〈/b〉〈br〉 Archana Dayalu, J. William Munger, Steven C. Wofsy, Yuxuan Wang, Thomas Nehrkorn, Yu Zhao, Michael B. McElroy, Chris P. Nielsen, and Kristina Luus〈br〉 Biogeosciences, 15, 6713-6729, https://doi.org/10.5194/bg-15-6713-2018, 2018〈br〉 Accounting for the vegetation signal is critical for comprehensive CO〈sub〉2〈/sub〉 budget assessment in China. We model and evaluate hourly vegetation carbon dioxide (CO〈sub〉2〈/sub〉) exchange (mass per unit area per unit time) in northern China from 2005 to 2009. The model is driven by satellite and meteorological data, is linked to ground-level ecosystem observations, and is applicable to other time periods. We find vegetation uptake of CO〈sub〉2〈/sub〉 in summer is comparable to emissions from fossil fuels in northern China.

Description: 〈b〉Effect of elevated 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 on trace gas production during an ocean acidification mesocosm experiment〈/b〉〈br〉 Sheng-Hui Zhang, Juan Yu, Qiong-Yao Ding, Gui-Peng Yang, Kun-Shan Gao, Hong-Hai Zhang, and Da-Wei Pan〈br〉 Biogeosciences, 15, 6649-6658, https://doi.org/10.5194/bg-15-6649-2018, 2018〈br〉 Environmental effects of ocean acidification and trace gases have drawn much attention in recent years and existing studies reveal that the response of communities and trace gases to ocean acidification is still not predictable and requires further study. The present study examined the effect of elevated 〈i〉p〈/i〉CO〈sub〉2〈/sub〉 on trace gas production and phytoplankton during an ocean acidification mesocosm experiment.

Description: 〈b〉Impacts of temperature and soil characteristics on methane production and oxidation in Arctic tundra〈/b〉〈br〉 Jianqiu Zheng, Taniya RoyChowdhury, Ziming Yang, Baohua Gu, Stan D. Wullschleger, and David E. Graham〈br〉 Biogeosciences, 15, 6621-6635, https://doi.org/10.5194/bg-15-6621-2018, 2018〈br〉 Arctic soils store vast amounts of frozen carbon that will thaw, fueling microbes that produce carbon dioxide and methane greenhouse gases. We compared methane producing and oxidizing activities in incubated soils and permafrost of Arctic tundra to improve estimates of net emissions. The methane oxidation profile in these soils differs from temperate ecosystems: maximum methane oxidation potential occurs in suboxic soils and permafrost layers, close to the methanogens that produce methane.

Description: 〈b〉Spatiotemporal transformation of dissolved organic matter along an alpine stream flow path on the Qinghai–Tibet Plateau: importance of source and permafrost degradation〈/b〉〈br〉 Yinghui Wang, Robert G. M. Spencer, David C. Podgorski, Anne M. Kellerman, Harunur Rashid, Phoebe Zito, Wenjie Xiao, Dandan Wei, Yuanhe Yang, and Yunping Xu〈br〉 Biogeosciences, 15, 6637-6648, https://doi.org/10.5194/bg-15-6637-2018, 2018〈br〉 With global warming, thawing of permafrost releases dissolved organic matter (DOM) into streams. By analyzing DOM along an alpine stream on the Qinghai–Tibet Plateau, we found DOM was mainly from the active layer, but with deepening of the active layer, the contribution of the deep permafrost layer increased, causing a change in the chemical composition of DOM. From the head- to downstream, DOM is undergoing rapid degradation, but some components are persistent and can be transported downstream.

Description: 〈b〉Ecosystem carbon transit versus turnover times in response to climate warming and rising atmospheric CO〈sub〉2〈/sub〉 concentration〈/b〉〈br〉 Xingjie Lu, Ying-Ping Wang, Yiqi Luo, and Lifen Jiang〈br〉 Biogeosciences, 15, 6559-6572, https://doi.org/10.5194/bg-15-6559-2018, 2018〈br〉 How long does C cycle through terrestrial ecosystems is a critical question for understanding land C sequestration capacity under future rising atmosphere [CO〈sub〉2〈/sub〉] and climate warming. Under climate change, previous conventional concepts with a steady-state assumption will no longer be suitable for a non-steady state. Our results using the new concept, C transit time, suggest more significant responses in terrestrial C cycle under rising [CO〈sub〉2〈/sub〉] and climate warming.

Description: 〈b〉Weaving of biomineralization framework in rotaliid foraminifera: implications for paleoceanographic proxies〈/b〉〈br〉 Yukiko Nagai, Katsuyuki Uematsu, Chong Chen, Ryoji Wani, Jarosław Tyszka, and Takashi Toyofuku〈br〉 Biogeosciences, 15, 6773-6789, https://doi.org/10.5194/bg-15-6773-2018, 2018〈br〉 We interpret detailed SEM and time-lapse observations of the calcification process in living foraminifera, which we reveal to be directly linked to the construction mechanism of organic membranes where the calcium carbonate precipitation takes place. We show that these membranes are a highly perforated outline is first woven by skeletal pseudopodia and then later overlaid by a layer of membranous pseudopodia to close the gaps. The chemical composition is related to these structures.

Description: 〈b〉The effect of salinity on the biogeochemistry of the coccolithophores with implications for coccolith-based isotopic proxies〈/b〉〈br〉 Michaël Hermoso and Marceau Lecasble〈br〉 Biogeosciences, 15, 6761-6772, https://doi.org/10.5194/bg-15-6761-2018, 2018〈br〉 This work examines the effect of salinity changes on the biogeochemistry of the coccolithophores with a palaeoproxy perspective. Although substantial changes in growth rate are observed between cells grown under various salinities, these physiological changes have no significant impact on the oxygen isotope composition of their biominerals. Thus, established coccolith δ〈sup〉18〈/sup〉O / temperature calibrations are not complicated by salinity. By contrast, it does influence coccolith δ〈sup〉13〈/sup〉C values.

Description: 〈b〉The origin and role of biological rock crusts in rocky desert weathering〈/b〉〈br〉 Nimrod Wieler, Hanan Ginat, Osnat Gillor, and Roey Angel〈br〉 Biogeosciences Discuss., https//doi.org/10.5194/bg-2018-442,2018〈br〉 〈b〉Manuscript under review for BG〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉In drylands, microbes that colonise rock surfaces were linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies though originating from arid and hyperarid environments, respectively. We hypothesised that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterise rocks morphologies and the origin and diversity of their biofilm. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla formed laminar biofilms only on rock surfaces that were exposed to the atmosphere and burrowed up to 6 mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances that form an evaporation barrier, reducing water loss rates by 65–75 %. The reduced water transport rates through the rock also limit salt transport and its crystallisation in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilises the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms as weathering-promoting agents. In contrast, we propose the microbial colonisation of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.〈/p〉