ALBERT

Beschreibung: Linking diverse nutrient patterns to different water masses within anticyclonic eddies in the upwelling system off Peru Yonss Saranga José, Heiner Dietze, and Andreas Oschlies Biogeosciences, 14, 1349-1364, doi:10.5194/bg-14-1349-2017, 2017 This study aims to investigate the diverse subsurface nutrient patterns observed within anticyclonic eddies in the upwelling system off Peru. Two simulated anticyclonic eddies with opposing subsurface nitrate concentrations were analysed. The results show that diverse nutrient patterns within anticyclonic eddies are related to the presence of water mass from different origins at different depths, responding to variations in depth of the circulation strength at the edge of the eddy.

Beschreibung: Gas chromatography vs. quantum cascade laser-based N 2 O flux measurements using a novel chamber design Christian Brümmer, Bjarne Lyshede, Dirk Lempio, Jean-Pierre Delorme, Jeremy J. Rüffer, Roland Fuß, Antje M. Moffat, Miriam Hurkuck, Andreas Ibrom, Per Ambus, Heinz Flessa, and Werner L. Kutsch Biogeosciences, 14, 1365-1381, doi:10.5194/bg-14-1365-2017, 2017 We present a novel chamber design for measuring soil–atmosphere N 2 O fluxes and compare the performance of a commonly applied gas chromatography (GC) setup with laser-based (QCL) concentration detection. While GC was still a useful method for longer-term investigations, we found that closure times of 10 min and sampling every 5 s is sufficient when using a QCL system. Further, extremely low standard errors (

Beschreibung: Drivers of multi-century trends in the atmospheric CO 2 mean annual cycle in a prognostic ESM Jessica Liptak, Gretchen Keppel-Aleks, and Keith Lindsay Biogeosciences, 14, 1383-1401, doi:10.5194/bg-14-1383-2017, 2017 We analyzed the evolution of the atmospheric CO 2 mean annual cycle simulated during 1950–2300 under three scenarios designed to separate the effects of climate change, CO 2 fertilization, and land use change. CO 2 fertilization in boreal and temperate ecosystems drove mean annual cycle amplification over the NH midlatitudes during 1950–2300. Boreal and Arctic climate change drove high-latitude amplification before 2200, after which CO 2 fertilization contributed nearly equally to amplification.

Beschreibung: Viable cold-tolerant iron-reducing microorganisms in geographically diverse subglacial environments Sophie L. Nixon, Jon P. Telling, Jemma L. Wadham, and Charles S. Cockell Biogeosciences, 14, 1445-1455, doi:10.5194/bg-14-1445-2017, 2017 Despite their permanently cold and dark characteristics, subglacial environments (glacier ice–sediment interface) are known to harbour active microbial communities. However, the role of microbial iron cycling in these environments is poorly understood. Here we show that subglacial sediments harbour active iron-reducing microorganisms, and they appear to be cold-adapted. These results may have important implications for global biogeochemical iron cycling and export to marine ecosystems.

Beschreibung: Can land degradation drive differences in the C exchange of two similar semiarid ecosystems? Ana López-Ballesteros, Cecilio Oyonarte, Andrew S. Kowalski, Penélope Serrano-Ortiz, Enrique P. Sánchez-Cañete, M. Rosario Moya, and Francisco Domingo Biogeosciences Discuss., doi:10.5194/bg-2017-77,2017 Manuscript under review for BG (discussion: open, 0 comments) The concept of land degradation stems from the loss of an ecosystem's biological productivity, which in turn relies on several degradation processes, such as long-term loss of natural vegetation, depletion of soil nutrients, soil compaction or water and wind erosion, to which drylands are especially vulnerable. Currently, drylands occupy more than one third of the global terrestrial surface and will probably expand under future climate change scenarios. Drylands' key role in the global C balance has been recently demonstrated, but the effects of land degradation on C sequestration by these ecosystems needs further research. In the present study, we compare net carbon exchange, together with satellite data and meteorological, ambient and vadose zone (CO 2 , water content and temperature) variables, between two nearby (~23 km) experimental sites representing natural (i.e. site of reference) and degraded grazed semiarid grasslands located in SE Spain, via eddy covariance measurements over 6 years, with highly variable precipitation magnitude and distribution. Results show a striking difference in the annual C balances with an average release of 196 ± 40 and −23 ± 20 g C m −2 yr −1 for the degraded and natural sites, respectively. At the seasonal scale, differing patterns in net CO 2 fluxes were detected over both growing and dry seasons. As expected, during the growing seasons, greater net C uptake over longer periods was observed in the natural site, however, much greater net C release was measured in the degraded site during drought periods. We tested differences in all monitored meteorological and soil variables and found it most relevant that CO 2 at 1.50 m belowground was around 1000 ppm higher in the degraded site. Thus, we believe that subterranean ventilation of this vadose zone CO 2 , previously observed at both sites, largely drives the differences in C dynamics between them, especially during the dry season maybe due to enhanced subsoil-atmosphere interconnectivity in the degraded site. Overall, the 12 site-years of data allow direct exploration of the roles of climate and land degradation in the biological and non-biological processes that ultimately control the C sequestration capacity of semiarid ecosystems.

Beschreibung: Quantifying nutrient fluxes with a new hyporheic passive flux meter (HPFM) Julia Vanessa Kunz, Michael D. Annable, Jaehyun Cho, Wolf von Tümpling, Kirk Hatfield, Suresh Rao, Dietrich Borchardt, and Michael Rode Biogeosciences, 14, 631-649, doi:10.5194/bg-14-631-2017, 2017 The hyporheic zone, the subsurface region of streams, is a key compartment for in-stream nutrient retention. Knowledge on actual hyporheic processing rates is still limited due to methodological restrictions which are mainly related to the high local and temporal variability of subsurface flow patterns and nutrient transformation processes. We present a new device which allows quantitative assessment of hyporheic nutrient fluxes and demonstrate its advantages in an exemplary field testing.

Beschreibung: Simulating precipitation decline under a Mediterranean deciduous Oak forest: effects on isoprene seasonal emissions and predictions under climatic scenarios Anne-Cyrielle Genard-Zielinski, Christophe Boissard, Elena Ormeño, Juliette Lathière, Ilja M. Reiter, Henri Wortham, Jean-Philippe Orts, Brice Temine-Roussel, Bertrand Guenet, Svenja Bartsch, Thierry Gauquelin, and Catherine Fernandez Biogeosciences Discuss., doi:10.5194/bg-2017-17,2017 Manuscript under review for BG (discussion: open, 0 comments) From seasonal in situ observations on how a Mediterranean ecosystem responds to drought, a specific isoprene emission (ER) algorithm was developed, upon which 2100 projections (IPCC RCP2.6 and RCP8.5 scenarios) were made. ER were found to be mainly sensitive to soil water content, and poorly represented by current empirical emission model. Drought was found to aggravate thermal stress on ER, increase ER intensity and their frequency response to environmental conditions (present and future).

Beschreibung: Evaluating environmental drivers of spatial variability in free-living nematode assemblages along the Portuguese margin Lidia Lins, Frederik Leliaert, Torben Riehl, Sofia Pinto Ramalho, Eliana Alfaro Cordova, André Morgado Esteves, and Ann Vanreusel Biogeosciences, 14, 651-669, doi:10.5194/bg-14-651-2017, 2017 Anthropogenic impacts in the deep sea are regarded as high disturbers of the deep-sea bottom. This study focus in trying to understand the impact of disturbance in the ecosystem and how important functions, such as hydrodynamics and surface primary productivity, affect benthic organisms. Our results showed that high sediment variability due to hydrodynamics, and consequently disturbance, combined with high resource availability are probably the main factors promoting deep-sea species coexistence

Beschreibung: Small-scale variability in geomorphological settings influences mangrove-derived organic matter export in a tropical bay Geraldina Signa, Antonio Mazzola, James Kairo, and Salvatrice Vizzini Biogeosciences, 14, 617-629, doi:10.5194/bg-14-617-2017, 2017 Using a combined analytical approach (fatty acid and isotopic markers), we found that the different settings of the creeks flowing into Gazi Bay influenced the mangrove export to the adjacent seagrasses and coral reef. Given the major influence that organic matter exchange between habitats has on organic matter availability and consumption by fauna, the small-scale variability in mangrove export may have far-reaching consequences for local food webs and for the functioning of the whole ecosystem.

Beschreibung: Amplification of global warming through pH-dependence of DMS-production simulated with a fully coupled Earth system model Jörg Schwinger, Jerry Tjiputra, Nadine Goris, Katharina Six, Alf Kirkevåg, Øyvind Seland, Christoph Heinze, and Tatiana Ilyina Biogeosciences Discuss., doi:10.5194/bg-2017-33,2017 Manuscript under review for BG (discussion: open, 0 comments) Transient global warming under the high emission scenario RCP8.5 is amplified by up to 6 % if a pH-dependency of marine DMS-production is assumed. Importantly, this additional warming is not spatially homogeneous but shows a pronounced north-south gradient. Over the Antarctic continent, the additional warming is almost twice the global average. In the Southern Ocean we find a small DMS-climate feedback that counteracts the original reduction of DMS-production due to ocean acidification.

Beschreibung: Isoprene emission and photosynthesis during heat waves and drought in black locust Ines Bamberger, Nadine K. Ruehr, Michael Schmitt, Andreas Gast, Georg Wohlfahrt, and Almut Arneth Biogeosciences Discuss., doi:10.5194/bg-2017-32,2017 Manuscript under review for BG (discussion: open, 0 comments) We studied the effects of two weeks long summer heat waves and drought on photosynthesis and isoprene emissions in black locust trees. While photosynthesis decreased, isoprene emission increased sharply in response to heat and heat-drought stress. Comparing isoprene emissions at the same temperature, however, demonstrated that stressed trees emitted less isoprene than expected. This reveals that in order to predict isoprene emissions during heat waves, model parameters need to be re-evaluated.

Beschreibung: An assessment of geographical distribution of different plant functional types over North America simulated using the CLASS-CTEM modelling framework Rudra K. Shrestha, Vivek K. Arora, Joe R. Melton, and Laxmi Sushama Biogeosciences Discuss., doi:10.5194/bg-2017-35,2017 Manuscript under review for BG (discussion: open, 0 comments) Computer models of vegetation provide a tool to assess how future changes in climate may affect geographical distribution of vegetation. However, such models must first be assessed for their ability to reproduce present day geographical distribution of vegetation. Here, we assess the ability of one such dynamic vegetation model. We find that while the model is broadly successful in reproducing the geographical distribution of trees and grasses in North America some limitations remain.

Beschreibung: Implications of sea-ice biogeochemistry for oceanic production and emissions of dimethyl sulfide in the Arctic Hakase Hayashida, Nadja Steiner, Adam Monahan, Virginie Galindo, Martine Lizotte, and Maurice Levasseur Biogeosciences, 14, 3129-3155, https://doi.org/10.5194/bg-14-3129-2017, 2017 In remote regions, cloud conditions may be strongly influenced by oceanic source of dimethylsulfide (DMS) produced by plankton and bacteria. In the Arctic, sea ice provides an additional source of these aerosols. The results of this study highlight the importance of taking into account both the sea-ice sulfur cycle and ecosystem in the flux estimates of oceanic DMS near the ice margins and identify key uncertainties in processes and rates that would be better constrained by new observations.

Beschreibung: Leveraging 35 years of forest research in the southeastern U.S. to constrain carbon cycle predictions: regional data assimilation using ecosystem experiment R. Quinn Thomas, Evan Brooks, Annika Jersild, Eric Ward, Randolph Wynne, Timothy J. Albaugh, Heather Dinon Aldridge, Harold E. Burkhart, Jean-Christophe Domec, Thomas R. Fox, Carlos A. Gonzalez-Benecke, Timothy A. Martin, Asko Noormets, David A. Sampson, and Robert O. Teskey Biogeosciences Discuss., doi:10.5194/bg-2017-46,2017 Manuscript under review for BG (discussion: open, 0 comments) Quantitative predictions of forest productivity in a changing world were improved when ecosystem manipulation experiments, including experiments that altered water and nutrient availability, were used to calibrate a mathematical forest model. When ecosystem experiments were not included in calibration, the predictions were overly sensitive to nutrient fertilization but not sensitive enough to drought in the Southeastern U.S., a region that supplies a large fraction of wood products to the world.

Beschreibung: Modelling past, present and future peatland carbon accumulation across the pan-Arctic Nitin Chaudhary, Paul A. Miller, and Benjamin Smith Biogeosciences Discuss., doi:10.5194/bg-2017-34,2017 Manuscript under review for BG (discussion: open, 0 comments) We employed an individual- and patch-based dynamic global ecosystem model to quantify long-term C accumulation rates and to assess the effects of historical and projected climate change on peatland C balances across the pan-Arctic. We found peatlands in Scandinavia, Europe, Russia and C. & E. Canada will become C source while Siberia, Far East Russia, Alaska and W. & N. Canada increase their sink capacity by the end of 21st century.

Beschreibung: Response of export production and dissolved oxygen concentrations in oxygen minimum zones to p CO 2 and temperature stabilization scenarios in the biogeochemical model HAMOCC 2.0 Teresa Beaty, Christoph Heinze, Taylor Hughlett, and Arne M. E. Winguth Biogeosciences, 14, 781-797, doi:10.5194/bg-14-781-2017, 2017 In this study HAMOCC2.0 is used to address how mechanisms of oxygen minimum zone (OMZ) expansion respond to changes in CO 2 radiative forcing within the model. Atmospheric p CO 2 is increased at a rate of 1 % annually until stabilized. Our study suggests that expansion in the Pacific Ocean within the model is controlled largely by changes in particulate organic carbon export (POC). The vertical expansion of the OMZs in the Atlantic and Indian oceans is linked to reduced oxygen solubility.

Beschreibung: Bayesian calibration of terrestrial ecosystem models: A study of advanced Markov chain Monte Carlo methods Dan Lu, Daniel Ricciuto, Anthony Walker, Cosmin Safta, and William Munger Biogeosciences Discuss., doi:10.5194/bg-2017-41,2017 Manuscript under review for BG (discussion: open, 0 comments) Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this study, a Differential Evolution Adaptive Metropolis (DREAM) algorithm was used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The DREAM is a multi-chain method and uses differential evolution technique for chain movement, allowing it to be efficiently applied to high-dimensional problems, and can reliably estimate heavy-tailed and multimodal distributions that are difficult for single-chain schemes using a Gaussian proposal distribution. The results were evaluated against the popular Adaptive Metropolis (AM) scheme. DREAM indicated that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identified one mode. The calibration of DREAM resulted in a better model fit and predictive performance compared to the AM. DREAM provides means for a good exploration of the posterior distributions of model parameters. It reduces the risk of false convergence to a local optimum and potentially improves the predictive performance of the calibrated model.

Beschreibung: Multi-frequency electrical impedance tomography as a non-invasive tool to characterize and monitor crop root systems Maximilian Weigand and Andreas Kemna Biogeosciences, 14, 921-939, doi:10.5194/bg-14-921-2017, 2017 Root systems are essential in nutrient uptake and translocation, but are difficult to characterize non-invasively with existing methods. We propose electrical impedance tomography (EIT) as a new tool for the imaging and monitoring of crop root systems. In a laboratory experiment we demonstrate the capability of the method to capture physiological responses of root systems with high spatial and temporal resolution. We conclude that EIT is a promising functional imaging technique for crop roots.

Beschreibung: The Oligotrophy to the UlTra-oligotrophy PACific Experiment (OUTPACE cruise, Feb. 18 to Apr. 3, 2015) Thierry Moutin, Andrea Doglioli, Alain De Verneil, and Sophie Bonnet Biogeosciences Discuss., doi:10.5194/bg-2017-50,2017 Manuscript under review for BG (discussion: open, 0 comments) The overall goal of OUTPACE was to obtain a successful representation of the interactions between planktonic organisms and the cycle of biogenic elements in the western tropical South Pacific Ocean across trophic and N 2 fixation gradients. The international OUTPACE cruise took place between 18 February and 3 April 2015 aboard the RV L'Atalante and involved 60 scientists. The transect covered ~ 4 000 km from the western part of the Melanesian Archipelago to the western boundary of the gyre.

Beschreibung: Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO 2 Steeve Comeau, Peter J. Edmunds, Coulson A. Lantz, and Robert C. Carpenter Biogeosciences Discuss., doi:10.5194/bg-2017-58,2017 Manuscript under review for BG (discussion: open, 0 comments) Here we investigate how CO 2 enrichment affects in coral reef communities the relationships light–production and light–calcification. For the three communities tested, CO 2 did not affect the light–production, while calcification was lower at elevated CO 2 for all light levels. Our result indicates that CO 2 can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.

Beschreibung: Modeling the effects of tree species and temperature on soil's extracellular enzyme activity in 78-year-old tree plantations Xiaoqi Zhou, Shen S. J. Wang, and Chengrong Chen Biogeosciences Discuss., doi:10.5194/bg-2017-144,2017 Manuscript under review for BG (discussion: open, 0 comments) Here, we measured the responses of soil's extracellular enzyme activity to a gradient of temperatures using incubation methods in 78-year-old tree plantations. We established a new soil–enzyme–C/N model without considering plant C inputs. The modeling results help explain why exotic slash pine can grow faster, as it has longer residual soil N residence time than native hoop pine and kauri pine. This is helpful for understanding the mechanisms of soil C and N cycling by different tree species.

Beschreibung: Effects of long-term mowing on the fractions and chemical composition of soil organic matter in a semiarid grassland Jiangye Li, Qichun Zhang, Yong Li, Yimeng Liu, Jianming Xu, and Hongjie Di Biogeosciences, 14, 2685-2696, doi:10.5194/bg-14-2685-2017, 2017 (1) Solid state 13 C-NMR is a powerful tool to study the nature of soil organic carbon. (2) Moderate mowing improved the stability of the grassland soil organic carbon pool. (3) Heavy mowing decreased the stability of the grassland soil organic carbon pool. (4) Mowing once a year is the most recommended practice in the semiarid grassland. (5) Mowing twice a year should be avoided for the long term in the semiarid grassland.

Beschreibung: Carbon stocks and fluxes in the high latitudes: Using site-level data to evaluate Earth system models Sarah Chadburn, Gerhard Krinner, Philipp Porada, Annett Bartsch, Christian Beer, Luca Belelli Marchesini, Julia Boike, Bo Elberling, Thomas Friborg, Gustaf Hugelius, Margareta Johansson, Peter Kuhry, Lars Kutzbach, Moritz Langer, Magnus Lund, Frans-Jan Parmentier, Shushi Peng, Ko Van Huissteden, Tao Wang, Sebastian Westermann, Dan Zhu, and Eleanor Burke Biogeosciences Discuss., doi:10.5194/bg-2017-197,2017 Manuscript under review for BG (discussion: open, 0 comments) Earth System Models (ESMs) are our main tools to understand future climate. The Arctic is important for the future carbon cycle, particularly due to the large carbon stocks in permafrost. We evaluated the performance of the land component of three major ESMs at Arctic tundra sites, focussing on the fluxes and stocks of carbon. We show that the next steps for model improvement are to better represent the quantity of vegetation, to include mosses and to improve below-ground carbon processes.

Beschreibung: Functional diversity of microbial communities in pristine aquifers inferred by PLFA- and sequencing-based approaches Valérie F. Schwab, Martina Herrmann, Vanessa-Nina Roth, Gerd Gleixner, Robert Lehmann, Georg Pohnert, Susan Trumbore, Kirsten Küsel, and Kai U. Totsche Biogeosciences, 14, 2697-2714, https://doi.org/10.5194/bg-14-2697-2017, 2017 We used phospholipid fatty acids (PLFAs) to link specific microbial markers to the spatio-temporal changes of groundwater physico-chemistry. PLFA-based functional groups were directly supported by DNA/RNA results. O 2 resulted in increased eukaryotic biomass and abundance of nitrite-oxidizing bacteria but impeded anammox, sulphate-reducing and iron-reducing bacteria. Our study demonstrates the power of PLFA-based approaches to study the nature and activity of microorganisms in pristine aquifers.

Beschreibung: Estimating total alkalinity for coastal ocean acidification monitoring at regional to continental scales in Australian coastal waters Kimberlee Baldry, Nick Hardman-Mountford, and Jim Greenwood Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-221,2017 Manuscript under review for BG (discussion: open, 0 comments) Total alkalinity (TA) is a measure of the oceans ability to resist changes in pH. In the face of ocean acidification, having the ability to predict the distribution of TA in coastal waters may provide insight into which regions might be prone to larger pH changes. Here we test a number of commonly used models for reconstructing TA. We find that within Australian coastal waters, using salinity alone is not the best choice in this region and that models are regionally dependent.

Beschreibung: Effects of long-term mowing on the fractions and chemical composition of soil organic matter in a semiarid grassland Jiangye Li, Qichun Zhang, Yong Li, Yimeng Liu, Jianming Xu, and Hongjie Di Biogeosciences, 14, 2685-2696, https://doi.org/10.5194/bg-14-2685-2017, 2017 (1) Solid state 13 C-NMR is a powerful tool to study the nature of soil organic carbon. (2) Moderate mowing improved the stability of the grassland soil organic carbon pool. (3) Heavy mowing decreased the stability of the grassland soil organic carbon pool. (4) Mowing once a year is the most recommended practice in the semiarid grassland. (5) Mowing twice a year should be avoided for the long term in the semiarid grassland.

Beschreibung: Plant n-alkane production from litterfall altered the diversity and community structure of alkane degrading bacteria in litter layer in lowland subtropical rainforest in Taiwan Tung-Yi Huang, Bing-Mu Hsu, Wei-Chun Chao, and Cheng-Wei Fan Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-161,2017 Manuscript under review for BG (discussion: open, 0 comments) The n-alkane in litterfall and the microbial community in litter layer in different habitats of lowland subtropical rainforest were studied. We revealed that the plant vegetation of forest not only dominated the n-alkane input of habitats but also governed the diversity of microbial community of litter layer. In this study, we found that the habitat which had high n-alkane input induced a shift of relative abundance toward phylum of Actinobacteria and the growth of alkB gene contained bacteria.

Beschreibung: Modeling the effects of tree species and temperature on soil's extracellular enzyme activity in 78-year-old tree plantations Xiaoqi Zhou, Shen S. J. Wang, and Chengrong Chen Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-144,2017 Manuscript under review for BG (discussion: open, 0 comments) Here, we measured the responses of soil's extracellular enzyme activity to a gradient of temperatures using incubation methods in 78-year-old tree plantations. We established a new soil–enzyme–C/N model without considering plant C inputs. The modeling results help explain why exotic slash pine can grow faster, as it has longer residual soil N residence time than native hoop pine and kauri pine. This is helpful for understanding the mechanisms of soil C and N cycling by different tree species.

Beschreibung: Carbon stocks and fluxes in the high latitudes: Using site-level data to evaluate Earth system models Sarah Chadburn, Gerhard Krinner, Philipp Porada, Annett Bartsch, Christian Beer, Luca Belelli Marchesini, Julia Boike, Bo Elberling, Thomas Friborg, Gustaf Hugelius, Margareta Johansson, Peter Kuhry, Lars Kutzbach, Moritz Langer, Magnus Lund, Frans-Jan Parmentier, Shushi Peng, Ko Van Huissteden, Tao Wang, Sebastian Westermann, Dan Zhu, and Eleanor Burke Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-197,2017 Manuscript under review for BG (discussion: open, 0 comments) Earth System Models (ESMs) are our main tools to understand future climate. The Arctic is important for the future carbon cycle, particularly due to the large carbon stocks in permafrost. We evaluated the performance of the land component of three major ESMs at Arctic tundra sites, focussing on the fluxes and stocks of carbon. We show that the next steps for model improvement are to better represent the quantity of vegetation, to include mosses and to improve below-ground carbon processes.

Beschreibung: Technical Note: A minimally invasive experimental system for p CO 2 manipulation in plankton cultures using passive gas exchange (atmospheric carbon control simulator) Brooke A. Love, M. Brady Olson, and Tristen Wuori Biogeosciences, 14, 2675-2684, https://doi.org/10.5194/bg-14-2675-2017, 2017 This experimental system simulates future CO 2 conditions in the ocean. It mimics natural processes by allowing the CO 2 to move gently and across the surface of the water though gas exchange, making it well suited for delicate plankton. Researchers can use many small vessels, which allows tracking of the eggs from individual females, for instance. Multiple types of organisms can be grown at once, which facilitates feeding studies and other similar studies of species interactions.

Beschreibung: Assisting the Evolution of the Observing System for the Carbon Cycle through Quantitative Network Design Thomas Kaminski and Peter Julian Rayner Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-168,2017 Manuscript under review for BG (discussion: open, 0 comments) Quantitative Network Design (QND) assesses the impact of a given set of existing or hypothetical observations in a modelling framework. QND has been used to optimise in situ networks and assess the benefit from planned space missions. This paper describes recent progress and points at aspects that are not yet sufficiently addressed. It demonstrates the advantage of an integrated QND system that can simultaneously evaluate a multitude of observational data streams.

Beschreibung: The effects of carbon turnover time on terrestrial ecosystem carbon storage Yaner Yan, Xuhui Zhou, Lifeng Jiang, and Yiqi Luo Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-183,2017 Manuscript under review for BG (discussion: open, 0 comments) The effects of C turnover time on C storage have not been well quantified for previous researches, so we decomposed ecosystem C storage capacity into C turnover time and C fluxes for quantifying it. Our result showed that the resultant terrestrial C release driven by C turnover time decrease only accounted for about 13.5 % of than driven by NPP increase and the larger uncertainties in spatial variation of C turnover time than temporal changes would lead in a greater impact on ecosystem C storage.

Beschreibung: Expansion of oil palm and other cash crops causes an increase of land surface temperature in Indonesia Clifton R. Sabajo, Guerric le Maire, Tania June, Ana Meijide, Olivier Roupsard, and Alexander Knohl Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-203,2017 Manuscript under review for BG (discussion: open, 1 comment) From the analysis of MODIS and Landsat satellite data of the Jambi province in Indonesia, this first study on the effects of oil palm expansion on the surface temperature in Indonesia shows shows a local and regional warming effect caused by the expansion of oil palm plantations and other cash or tree crops between 2000 and 2015. The observed warming effects may affect ecosystem services, reduce water availabilty in the dry period and increase the vulnerability to fires in the province.

Beschreibung: Explaining CO 2 fluctuations observed in snowpacks Laura Graham and David Risk Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-172,2017 Manuscript under review for BG (discussion: open, 0 comments) Winter carbon dioxide (CO 2 ) respiration from soils is a significant and understudied component of the global carbon (C) cycle. In this study, we were able to show with a field campaign and a model how windy (advective) conditions can affect the usually slow (diffusive) transport of CO 2 from soils and out of snowpacks. This research is important to help with understanding winter CO 2 dynamics, especially for continued accurate accounting of the annual global C cycle.

Beschreibung: Optical properties of size and chemical fractions of suspended particulate matter in littoral waters of Quebec Gholamreza Mohammadpour, Jean-Pierre Gagné, Pierre Larouche, and Martin Montes Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-159,2017 Manuscript under review for BG (discussion: open, 0 comments) High mass-specific absorption coefficients of suspended particulate matter (SPM) were measured in waters having iron-enriched particles Particle chemical composition has a major influence on variability of mass-specific absorption coefficients of SPM. Conversely, size distribution mainly rules spatial changes of mass-specific scattering coefficients of SPM. Multiple optical proxies can be combined in optically complex waters for estimating changes on particle size fractions.

Beschreibung: A biophysical approach using drought stress factor for daily estimations of evapotranspiration and CO 2 uptake in high-energy water-limited environments David Helman, Itamar M. Lensky, Yagil Osem, Shani Rohatyn, Eyal Rotenberg, and Dan Yakir Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-204,2017 Manuscript under review for BG (discussion: open, 0 comments) A biophysical approach for estimating daily evapotranspiration and CO 2 uptake was tested in high-energy water-limited forest and non-forest sites in Israel after accounting for drought stress. A newly developed mobile lab system and an active Fluxnet station were used for validation. Models successfully tracked observed seasonal changes showing promise for reliable ecosystem-level flux estimations. Models were used to assess changes in water-use-efficiency due to afforestation in this region.

Beschreibung: Spatial variations in snowpack chemistry and isotopic composition of NO 3 − along a nitrogen deposition gradient in West Greenland Chris J. Curtis, Jan Kaiser, Alina Marca, N. John Anderson, Gavin Simpson, Vivienne Jones, and Erika Whiteford Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-140,2017 Manuscript under review for BG (discussion: open, 0 comments) Few studies have investigated the atmospheric deposition of nitrate in the Arctic or its impacts on Arctic ecosystems. We collected late season snowpack from 3 regions of W Greenland from the coast to the edge of the ice sheet. We found major differences in nitrate concentrations (lower at the coast) and deposition load (higher at the coast). Nitrate in snowpack undergoes losses and isotopic enrichment which are greatest in inland areas, hence deposition impacts may be greatest at the coast.

Beschreibung: The influence of episodic flooding on a pelagic ecosystem in the East China Sea Chung-Chi Chen, Gwo-Ching Gong, Wen-Chen Chou, Chih-Ching Chung, Chih-Hao Hsieh, Fuh-Kwo Shiah, and Kuo-Ping Chiang Biogeosciences, 14, 2597-2609, https://doi.org/10.5194/bg-14-2597-2017, 2017 To understand the flooding effects on a pelagic ecosystem in the East China Sea (ECS), a variety of variables were measured in 2009 (non-flood) and 2010 (flood). In 2010, the organic carbon consumption was higher than in 2009; this could be attributed to the vigorous plankton activities observed in low-salinity areas. A huge amount of f  CO 2 was also drawn down in the flood. This flood effect might become more pronounced as extreme rainfall events increase dramatically throughout the world.

Beschreibung: Limited protection of macro-aggregate-occluded organic carbon in Siberian steppe soils Norbert Bischoff, Robert Mikutta, Olga Shibistova, Alexander Puzanov, Marina Silanteva, Anna Grebennikova, Roland Fuß, and Georg Guggenberger Biogeosciences, 14, 2627-2640, https://doi.org/10.5194/bg-14-2627-2017, 2017 This study set out to determine the quantity of organic carbon (OC) which is protected from microbial decomposition in macro-aggregates of Siberian steppe soils under different land use. Our results imply that the quantity of macro-aggregate protected OC is smaller than in similar steppe ecosystems like the North American prairies. We conclude that the tillage-induced breakdown of macro-aggregates after grassland to arable land conversion has not reduced the OC contents in the studied soils.

Beschreibung: Anatomical structure overrides temperature controls on magnesium uptake -- calcification in the Arctic/subarctic coralline algae Leptophytum laeve and Kvaleya epilaeve (Rhodophyta; Corallinales) Merinda C. Nash and Walter Adey Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-180,2017 Manuscript under review for BG (discussion: open, 0 comments) Past seawater temperatures can be reconstructed using magnesium / calcium ratios of biogenic carbonates. As temperature increases, so does magnesium. Here we show that for these arctic/subarctic coralline algae, anatomy is the first control on Mg / Ca, not temperature. When using coralline algae for temperature reconstruction, it is first necessary to check for anatomical influences on Mg / Ca.

Beschreibung: Flooding-related increases in CO 2 and N 2 O emissions from a temperate coastal grassland ecosystem Amanuel W. Gebremichael, Bruce Osborne, and Patrick Orr Biogeosciences, 14, 2611-2626, https://doi.org/10.5194/bg-14-2611-2017, 2017 Given their increasing trend in Europe, an understanding of the role that flooding events play in carbon (C) and nitrogen (N) cycling and greenhouse gas (GHG) emissions will be important for improved assessments of local and regional GHG budgets. This study presents the results of an analysis of the CO 2 and N 2 O fluxes from a coastal grassland ecosystem affected by episodic flooding that was of either a relatively short (SFS) or long (LFS) duration. Compared to the SFS, the annual CO 2 and N 2 O emissions were 1.4 and 1.3 times higher at the LFS, respectively. Mean CO 2 emissions during the period of standing water were 144 ± 18.18 and 111 ± 9.51 mg CO 2 –C m −2  h −1 , respectively, for the LFS and SFS sites. During the growing season, when there was no standing water, the CO 2 emissions were significantly larger from the LFS (244 ± 24.88 mg CO 2 –C m −2  h −1 ) than the SFS (183 ± 14.90 mg CO 2 –C m −2  h −1 ). Fluxes of N 2 O ranged from −0.37 to 0.65 mg N 2 O–N m −2  h −1 at the LFS and from −0.50 to 0.55 mg N 2 O–N m −2  h −1 at the SFS, with the larger emissions associated with the presence of standing water at the LFS but during the growing season at the SFS. Overall, soil temperature and moisture were identified as the main drivers of the seasonal changes in CO 2 fluxes, but neither adequately explained the variations in N 2 O fluxes. Analysis of total C, N, microbial biomass and Q 10 values indicated that the higher CO 2 emissions from the LFS were linked to the flooding-associated influx of nutrients and alterations in soil microbial populations. These results demonstrate that annual CO 2 and N 2 O emissions can be higher in longer-term flooded sites that receive significant amounts of nutrients, although this may depend on the restriction of diffusional limitations due to the presence of standing water to periods of the year when the potential for gaseous emissions are low.

Beschreibung: 20th century changes in carbon isotopes and water-use efficiency: tree-ring-based evaluation of the CLM4.5 and LPX-Bern models Kathrin M. Keller, Sebastian Lienert, Anil Bozbiyik, Thomas F. Stocker, Olga V. Churakova (Sidorova), David C. Frank, Stefan Klesse, Charles D. Koven, Markus Leuenberger, William J. Riley, Matthias Saurer, Rolf Siegwolf, Rosemarie B. Weigt, and Fortunat Joos Biogeosciences, 14, 2641-2673, https://doi.org/10.5194/bg-14-2641-2017, 2017 Measurements of the stable carbon isotope ratio ( δ 13 C) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO 2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the ratio between the CO 2 partial pressure in the intercellular cavities and the atmosphere ( c i ∕ c a ) and of the ratio of assimilation to stomatal conductance, termed intrinsic water-use efficiency (iWUE). We performed isotope-enabled simulations over the industrial period with the land biosphere module (CLM4.5) of the Community Earth System Model and the Land Surface Processes and Exchanges (LPX-Bern) dynamic global vegetation model. Results for C3 tree species show good agreement with a global compilation of δ 13 C measurements on leaves, though modeled 13 C discrimination by C3 trees is smaller in arid regions than measured. A compilation of 76 tree-ring records, mainly from Europe, boreal Asia, and western North America, suggests on average small 20th century changes in isotopic discrimination and in c i ∕ c a and an increase in iWUE of about 27 % since 1900. LPX-Bern results match these century-scale reconstructions, supporting the idea that the physiology of stomata has evolved to optimize trade-offs between carbon gain by assimilation and water loss by transpiration. In contrast, CLM4.5 simulates an increase in discrimination and in turn a change in iWUE that is almost twice as large as that revealed by the tree-ring data. Factorial simulations show that these changes are mainly in response to rising atmospheric CO 2 . The results suggest that the downregulation of c i ∕ c a and of photosynthesis by nitrogen limitation is possibly too strong in the standard setup of CLM4.5 or that there may be problems associated with the implementation of conductance, assimilation, and related adjustment processes on long-term environmental changes.

Beschreibung: Land-use and land-cover change carbon emissions between 1901 and 2012 constrained by biomass observations Wei Li, Philippe Ciais, Shushi Peng, Chao Yue, Yilong Wang, Martin Thurner, Sassan S. Saatchi, Almut Arneth, Valerio Avitabile, Nuno Carvalhais, Anna B. Harper, Etsushi Kato, Charles Koven, Yi Y. Liu, Julia E. M. S. Nabel, Yude Pan, Julia Pongratz, Benjamin Poulter, Thomas A. M. Pugh, Maurizio Santoro, Stephen Sitch, Benjamin D. Stocker, Nicolas Viovy, Andy Wiltshire, Rasoul Yousefpour, and Sönke Zaehle Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-186,2017 Manuscript under review for BG (discussion: open, 0 comments) We used several observation-based biomass datasets to constrain the historical land use change carbon emissions simulated by models. Compared to the large range of the original modelled emissions (from 94 to 273 Pg C), the observationally constrained global cumulative emission estimate is of 155 ± 50 (1-σ Gaussian error) Pg C from 1901 to 2012. Our approach reduces the uncertainty and can be also applied to evaluate the LULCC impact of land-based climate mitigation policies.

Beschreibung: A zero power warming chamber for investigating plant responses to rising temperature Keith F. Lewin, Andrew McMahon, Kim S. Ely, Shawn P. Serbin, and Alistair Rogers Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-208,2017 Manuscript under review for BG (discussion: open, 0 comments) Experiments that manipulate the temperature of plants and ecosystems are used to improve understanding of how they will respond to climate change. In logistically challenging locations passive warming using solar energy is the the only viable option for warming experiments. Unfortunately current passive warming approaches can only raise air temperature by about 1.5 °C. We have developed a novel approach that doubles the warming possible using solar energy and requires no power.

Beschreibung: Temporal variability of chlorophyll distribution in the Gulf of Mexico: bio-optical data from profiling floats Orens Pasqueron de Fommervault, Paula Perez-Brunius, Pierre Damien, and Julio Sheinbaum Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-201,2017 Manuscript under review for BG (discussion: open, 0 comments) Chlorophyll concentration is a key oceanic biogeochemical variable. In the Gulf of Mexico (GOM), its distribution, which is mainly obtained from satellite surface observations and scarce in situ experiments, is still poorly understood. In 2011–2012, eight profiling floats equipped with biogeochemical sensors were deployed for the first time in the GOM and generated an unprecedented dataset that significantly increased the number of chlorophyll vertical distribution measurements in the region. The analysis of these data, once calibrated, permits us to reconsider the spatial and temporal variability of the chlorophyll concentration in the water column. At a seasonal scale, results confirm the surface signal seen by satellites, presenting maximum concentrations in winter and low values in summer. It is shown that the deepening of the mixed layer depth is the primary factor triggering the chlorophyll surface increase in winter. In the GOM, current belief is that this surface increase corresponds to a biomass increase. However, the present dataset reveals a vertically integrated content of chlorophyll which remains constant throughout the year, suggesting that the surface increase results from a vertical redistribution of subsurface chlorophyll or photoacclimation processes, rather than a net increase of primary productivity. One plausible explanation for this is the decoupling between the mixed layer depth and the deep nutrient reservoir since mixed layer depth only reaches the nitracline in sporadic events in the observations. Float measurements also provide evidence that the depth and the magnitude of the deep chlorophyll maximum is strongly controlled by the mesoscale variability, with higher chlorophyll biomass generally observed in cyclones rather than anticyclones.

Beschreibung: Modelling biogeochemical processes in sediments from the north western Adriatic Sea: response to enhanced POC fluxes Daniele Brigolin, Christophe Rabouille, Bruno Bombled, Silvia Colla, Salvatrice Vizzini, Roberto Pastres, and Fabio Pranovi Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-206,2017 Manuscript under review for BG (discussion: open, 0 comments) This work presents the result of a study carried out in the north-western Adriatic Sea, by combining two different types of biogeochemical models with field sampling efforts. A longline mussel farm was taken as a local source of perturbation to the natural POC downward flux. This flux was first quantified by means of a pelagic model of POC deposition coupled to sediment traps data, and its effects on sediment bioirrigation capacity and OM degradation pathways were investigated by constraining an early diagenesis model, linked to new data in sediment porewaters. The measurements were performed at stations located inside and outside the area affected by mussel farm deposition. Model-predicted POC fluxes showed marked spatial and temporal variability, which were mostly associated with the dynamics of the farming cycle. Sediment traps data at the two sampled stations (in and out of the mussel farm) showed average POC background flux of 20.0–24.2 mmol C m −2  d −1 . The difference of OC fluxes between the two stations was in agreement with model results, ranging between 3.3 and 14.2 mmol C m −2  d −1 , and primarily associated with mussel physiological conditions. Although restricted, these changes in POC fluxes induced visible effects on sediment biogeochemistry. Observed oxygen microprofiles presented a 50 % decrease in oxygen penetration depth (from 2.3 to 1.4 mm), accompanied by an increase in the O 2 influx at the station below the mussel farm (19–31 versus 10–12 mmol O 2  m −2  d −1 ) characterized by higher POC flux. DIC and NH 4 + concentrations had similar behavior, with a more evident effect of bioirrigation underneath the farm. This was confirmed through constraining the early diagenesis model, which calibration leads to an estimation of enhanced and shallower bioirrigation underneath the farm: bioirrigation rates of 40 y −1 and irrigation depth of 15 cm were estimated inside the shellfish deposition footprint versus 20 y −1 and 20 cm outside. These findings were confirmed by independent data on macrofauna composition collected at the study site. Early diagenesis model results indicated a larger organic matter mineralization below the mussel farm (11.1 versus 18.7 mmol m −2  d −1 ), characterized by similar proportions between oxic and anoxic degradation pathways at the two stations, with an increase in the absolute values of oxygen consumed by OM degradation and reduced substances re-oxidation underneath the mussel farm.

Beschreibung: Ocean acidification changes the structure of an Antarctic coastal protistan community Alyce M. Hancock, Andrew T. Davidson, John McKinlay, Andrew McMinn, Kai Schulz, and Rick L. van den Enden Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-224,2017 Manuscript under review for BG (discussion: open, 0 comments) Absorption of carbon dioxide (CO 2 ) realised by humans is decreasing the ocean pH (ocean acidification). Single celled organisms (microbes) support the Antarctic ecosystem, yet little is known about their sensitivity to ocean acidification. This study shows a shift in a natural Antarctic microbial community, with CO 2 levels exceeding 634 μatm changing the community composition and favouring small cells. This would have significant flow-effects for Antarctic food webs and elemental cycles.

Beschreibung: Soil nitrogen oxide fluxes from lowland forests converted to smallholder rubber and oil palm plantations in Sumatra, Indonesia Evelyn Hassler, Marife D. Corre, Syahrul Kurniawan, and Edzo Veldkamp Biogeosciences, 14, 2781-2798, https://doi.org/10.5194/bg-14-2781-2017, 2017 We measured the soil N-oxide gases, N 2 O and NO in four land uses of Jambi, Sumatra, Indonesia. We aimed to assess the impact of forest conversion to rubber and oil palm plantations on these N-oxide gases. We found that there were no differences in soil N-oxide fluxes among land uses. However, soil N-oxide fluxes increased following N-fertilizer application in oil palm plantations. We estimated an annual soil N-oxide emission of 361 t N yr −1 from N fertilization for the Jambi province.

Beschreibung: Continuous fluorescence-based monitoring of seawater pH in a temperate estuary John W. Runcie, Christian Krause, Sergio A. Torres Gabarda, and Maria Byrne Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-222,2017 Manuscript under review for BG (discussion: open, 0 comments) pH in coastal waters can be highly variable. A means to measure this variation is needed. A fully autonomous submersible fluorescence-based pH monitoring device incorporating additional sensors for temperature and salinity was deployed in or adjacent to a shallow estuary for week-long intervals. Results and calculated aragonite/calcite saturation values are presented. The device is well suited to continuous flow-through or standalone measurements with a precision of at least 0.022 pH units.

Beschreibung: Soil microbial biomass, activity and community composition along altitudinal gradients in the High Arctic (Billefjorden, Svalbard) Petr Kotas, Hana Šantrůčková, Josef Elster, and Eva Kaštovská Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-184,2017 Manuscript under review for BG (discussion: open, 0 comments) The soil microbial properties were investigated along altitudinal gradients in the Arctic. The significant shifts in composition, size and activity of microbial communities were mainly controlled by vegetation distribution (through its effect on edaphic conditions) and by bedrock chemistry. The upward migration of vegetation due to global warming will diminish the variability of microbial properties along the altitudinal gradients and could have negative implications for microbial diversity.

Beschreibung: Influence of infrastructure on water quality and greenhouse gas dynamics in urban streams Rose M. Smith, Sujay S. Kaushal, Jake J. Beaulieu, Michael J. Pennino, and Claire Welty Biogeosciences, 14, 2831-2849, https://doi.org/10.5194/bg-14-2831-2017, 2017 Urban streams receive excess nitrogen from numerous sources. We hypothesized that variations in carbon availability and subsurface infrastructure influence emissions of N 2 O and other greenhouse gases (CH 4 and CO 2 ) as excess N is utilized by microbes. We sampled eight streams draining four categories of stormwater and sanitary infrastructure. Dissolved nitrogen concentration was the strongest predictor of CO 2 and N 2 O concentrations, while C : N ratio was the strongest predictor of CH 4 in streams.

Beschreibung: Cyanobacterial carbon concentrating mechanisms facilitate sustained CO 2 depletion in eutrophic lakes Ana M. Morales-Williams, Alan D. Wanamaker Jr., and John A. Downing Biogeosciences, 14, 2865-2875, https://doi.org/10.5194/bg-14-2865-2017, 2017 Our study investigated the mechanisms sustaining cyanobacteria blooms when CO 2 is depleted in lake surface waters. We found that when lake CO 2 concentrations drop below those of the atmosphere, cyanobacteria switch on carbon concentrating mechanisms (CCMs), allowing them to actively take up bicarbonate. This may provide bloom-forming cyanobacteria with a competitive advantage over other algae. These results provide insight into the timing and duration of blooms in high-nutrient lakes.

Beschreibung: Biogeochemical versus ecological consequences of modeled ocean physics Sophie Clayton, Stephanie Dutkiewicz, Oliver Jahn, Christopher Hill, Patrick Heimbach, and Michael J. Follows Biogeosciences, 14, 2877-2889, https://doi.org/10.5194/bg-14-2877-2017, 2017 We present a systematic study of the differences generated by coupling the same ecological–biogeochemical model to a 1°, coarse-resolution, and 1∕6°, eddy-permitting, global ocean circulation model to (a) biogeochemistry (e.g., primary production) and (b) phytoplankton community structure. Surprisingly, we find that the modeled phytoplankton community is largely unchanged, with the same phenotypes dominating in both cases. Conversely, there are large regional and seasonal variations in primary production, phytoplankton and zooplankton biomass. In the subtropics, mixed layer depths (MLDs) are, on average, deeper in the eddy-permitting model, resulting in higher nutrient supply driving increases in primary production and phytoplankton biomass. In the higher latitudes, differences in winter mixed layer depths, the timing of the onset of the spring bloom and vertical nutrient supply result in lower primary production in the eddy-permitting model. Counterintuitively, this does not drive a decrease in phytoplankton biomass but results in lower zooplankton biomass. We explain these similarities and differences in the model using the framework of resource competition theory, and find that they are the consequence of changes in the regional and seasonal nutrient supply and light environment, mediated by differences in the modeled mixed layer depths. Although previous work has suggested that complex models may respond chaotically and unpredictably to changes in forcing, we find that our model responds in a predictable way to different ocean circulation forcing, despite its complexity. The use of frameworks, such as resource competition theory, provides a tractable way to explore the differences and similarities that occur. As this model has many similarities to other widely used biogeochemical models that also resolve multiple phytoplankton phenotypes, this study provides important insights into how the results of running these models under different physical conditions might be more easily understood.

Beschreibung: Spatial variations in snowpack chemistry and isotopic composition of NO 3 − along a nitrogen deposition gradient in West Greenland Chris J. Curtis, Jan Kaiser, Alina Marca, N. John Anderson, Gavin Simpson, Vivienne Jones, and Erika Whiteford Biogeosciences Discuss., doi:10.5194/bg-2017-140,2017 Manuscript under review for BG (discussion: open, 0 comments) Few studies have investigated the atmospheric deposition of nitrate in the Arctic or its impacts on Arctic ecosystems. We collected late season snowpack from 3 regions of W Greenland from the coast to the edge of the ice sheet. We found major differences in nitrate concentrations (lower at the coast) and deposition load (higher at the coast). Nitrate in snowpack undergoes losses and isotopic enrichment which are greatest in inland areas, hence deposition impacts may be greatest at the coast.

Beschreibung: Plant functional types, nutrients and hydrology drive carbon cycling along a transect in an anthropogenically altered Canadian peatland complex Sina Berger, Leandra Praetzel, Marie Goebel, Christian Blodau, and Klaus-Holger Knorr Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-191,2017 Manuscript under review for BG (discussion: open, 0 comments) Peatlands play an important role in global carbon cycling, however, the response of peatland carbon fluxes to anthropogenically changed hydrologic conditions and long-term infiltration of nutrients is still understudied. Along a transect of 4 study sites, spanning from largely pristine to strongly altered conditions within the Wylde Lake peatland complex in Ontario (Canada), we monitored carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes at the soil/atmosphere interface and DIC and CH 4 concentrations in the peat profiles from April 2014 through September 2015. Moreover, we applied δ 13 C-CH 4 and δ 13 C-CO 2 stable isotope abundance analyses to examine CH 4 and CO 2 production and consumption as well as the dominant CH 4 emission pathways during the growing season of 2015. We found that a graminoid-moss dominated site, which was exposed to wet conditions and long-term infiltration of nutrients, was a great sink of CO 2 (2260 ± 480 g CO 2  m −2 ) but a great source of CH 4 (61.4 ± 32 g CH 4  m −2 ). Comparably low δ 13 C-CH 4 signatures (−62.30 ± 5.54 ‰) indicated only low mitigation of CH 4 emission by methanotrophic activity here. On the contrary, a shrub dominated site, which has been subjected to similarly high moisture conditions and loads of nutrients, was a much weaker sink of CO 2 (1093 ± 794 g CO 2  m −2 ) as compared with all other sites. The shrub dominated site featured notably low DIC concentrations in the peat as well as comparably 13 C enriched CH 4 (δ 13 C-CH 4 : −57.81 ± 7.03 ‰) and depleted CO 2 (δ 13 C-CO 2 : −15.85 ± 3.61 ‰) in a more decomposed and surficial aerated peat, suggesting a higher share of CH 4 oxidation. Plant mediated transport was the prevailing methane emission pathway throughout the summer of 2015 among all sites, even where graminoids covered only 10 % of the area. Our study provides insight into the accelerated carbon cycling of a strongly altered peatland and our results supported earlier findings, that strongly altered, shrub dominated peatlands may turn into weak carbon sinks or even sources, while a graminoid-moss dominance may maintain the peatland's carbon storage function.

Beschreibung: Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03 Abigail E. Noble, Daniel C. Ohnemus, Nicholas J. Hawco, Phoebe J. Lam, and Mak A. Saito Biogeosciences, 14, 2715-2739, https://doi.org/10.5194/bg-14-2715-2017, 2017 This study examines sources and sinks of dissolved and labile cobalt in the North Atlantic Ocean. The North and South Atlantic are influenced differently by dust, coastal margin sources, biota, and suspended particles. Dissolved cobalt in both basins is driven by a coastal margin source, leading to large plumes emanating from the north and south African coasts. These plumes are comparable in size despite the high dust flux observed in the North Atlantic that is absent in the South Atlantic.

Beschreibung: Planktonic foraminifera-derived environmental DNA extracted from abyssal sediments preserves patterns of plankton macroecology Raphaël Morard, Franck Lejzerowicz, Kate F. Darling, Béatrice Lecroq-Bennet, Mikkel Winther Pedersen, Ludovic Orlando, Jan Pawlowski, Stefan Mulitza, Colomban de Vargas, and Michal Kucera Biogeosciences, 14, 2741-2754, https://doi.org/10.5194/bg-14-2741-2017, 2017 The exploitation of deep-sea sedimentary archive relies on the recovery of mineralized skeletons of pelagic organisms. Planktonic groups leaving preserved remains represent only a fraction of the total marine diversity. Environmental DNA left by non-fossil organisms is a promising source of information for paleo-reconstructions. Here we show how planktonic-derived environmental DNA preserves ecological structure of planktonic communities. We use planktonic foraminifera as a case study.

Beschreibung: Changing patterns of fire occurrence in proximity to forest edges, roads and rivers between NW Amazonian countries Dolors Armenteras, Joan Sebastian Barreto, Karyn Tabor, Roberto Molowny-Horas, and Javier Retana Biogeosciences, 14, 2755-2765, https://doi.org/10.5194/bg-14-2755-2017, 2017 Tropical forests are highly threatened by the expansion of the agricultural frontier, use of fire and subsequent deforestation. NW Amazonia is the wettest part of the basin and the role of fire is still largely unknown in this subregion. In this study, we compared fire regimes in five countries sharing this tropical biome (Venezuela, Colombia, Ecuador, Peru and Brazil). We studied fire activity in relation to proximity to roads and rivers and how fire occurs in relation to forest fragmentation.

Beschreibung: Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania Paula C. Pardo, Bronte Tilbrook, Clothilde Langlais, Tom W. Trull, and Steve R. Rintoul Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-213,2017 Manuscript under review for BG (discussion: open, 0 comments) The carbon content of the water masses of the Southern Ocean, South of Tasmania has increased over the period 1995–2011, leading to a general decrease of pH. The long-term change in the carbon system is mainly affected by the ocean circulation and atmospheric features. The winds play an important role in the biogeochemical changes of upper to intermediate layers of the ocean while the ocean circulation conditions the long-term changes in deep waters.

Beschreibung: Increased temperature causes different carbon and nitrogen processing patterns in two common intertidal foraminifera ( Ammonia tepida and Haynesina germanica ) Julia Wukovits, Annekatrin Julie Enge, Wolfgang Wanek, Margarete Watzka, and Petra Heinz Biogeosciences, 14, 2815-2829, https://doi.org/10.5194/bg-14-2815-2017, 2017 This study reports the response of two intertidal foraminifera to increased temperatures on the level of carbon and nitrogen uptake. Interspecific variations in the ability to cope with shifting environmental variables within the two commonly associated species show that temperature and food source might be critical factors that control their abundances. This should support the interpretation of sediment samples and increase knowledge about nutrient fluxes through foraminiferal communities.

Beschreibung: An Orphan Problem Looking for Adoption: Responding to Ocean Acidification Utilising Existing International Institutions Ellycia R. Harrould-Kolieb Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-230,2017 Manuscript under review for BG (discussion: open, 0 comments) This research finds that there is a dearth of policy making pertaining to ocean acidification at the international level. Indeed, only three institutions are found to have initiated rue-making or implementation activities with the goal of either preventing worsening acidification or responding to its impacts. In light of this, this paper proposes that there are a variety of institutions that could be utilized to enhance the international response to ocean acidification.

Beschreibung: Seasonal variability of the inorganic carbon system in a large coastal plain estuary Andrew Joesoef, David L. Kirchman, Christopher K. Sommerfield, and Wei-Jun Cai Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-233,2017 Manuscript under review for BG (discussion: open, 0 comments) In this paper, we focus on key, poorly understood properties of carbonate geochemistry in one of the largest estuaries in North America. We explore how varying environmental factors impact total input and export inorganic carbon fluxes to the estuary and overall internal net ecosystem production within the system. In turn, recent and ongoing conclusions gained over this study provide broad implications to the inorganic carbon behavior and budget of present and future coastal ecosystems.

Beschreibung: 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 Discuss., https//doi.org/10.5194/bg-2017-166,2017 Manuscript under review for BG (discussion: open, 0 comments) During the four most recent glacial cycles, atmospheric CO 2 during glacial maxima has been lowered by about 90–100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is however still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to constrain the range in ocean carbon storage for an ensemble of ocean circulation equilibrium states. We do a set of simulations where we run the model to pre-industrial equilibrium, but where we achieve different ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air-sea CO 2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO 2 disequilibrium component. We also relate these contributions to differences in strength of ocean overturning circulation. In cases with weaker circulation, we see that the ocean's capacity for carbon storage is larger. Depending on which ocean forcing parameter that is tuned, the origin of the change in carbon storage is different. When wind stress or ocean vertical diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean horizontal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Finally, we do a drawdown experiment, where we investigate the capacity for increased carbon storage by maximising the efficiency of the biological pump in our ensemble members. 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. This could explain why it is difficult to achieve comparable responses of the ocean carbon pumps in model intercomparison studies, where the initial states vary between models. The drawdown experiment highlights the importance of the strength of the biological pump in the control state for model studies of increased biological efficiency.

Beschreibung: Evidence for microbial mediated nitrate cycling within floodplain sediments during groundwater fluctuations Nicholas J. Bouskill, Mark E. Conrad, Markus Bill, Eoin L. Brodie, Yiwei Cheng, Chad Hobson, Matthew Forbes, Karen L. Casciotti, and Kenneth H. Williams Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-212,2017 Manuscript under review for BG (discussion: open, 0 comments) This work couples isotope geochemical techniques with mechanistic microbial modeling in an attempt to further unravel the major factors responsible for an observed reduction in nitrate concomitant with a rising water table within floodplain sediments. We focus on 3 depths below ground surface with different periods of saturation and varying degrees of microbial nitrate loss. Using a microbial model we identify the controlling factors on denitrification responsible for these differences.

Beschreibung: Biochar reduces yield-scaled emissions of reactive nitrogen gases from vegetable soils across China Changhua Fan, Hao Chen, Bo Li, and Zhengqin Xiong Biogeosciences, 14, 2851-2863, https://doi.org/10.5194/bg-14-2851-2017, 2017 Intensive vegetable fields suffered very low N use efficiency and very high N 2 O emissions as compared to other ecosystems. We have demonstrated that two contrasting biochars affected gaseous reactive nitrogen intensity (N 2 O, NO, NH 3 , yield) across four major vegetable soils in China. Biochar affects gaseous Nr or yield largely depending on soil types. Both wheat straw biochar ( B w ) and swine manure biochar ( B m ) decreased GNI with Bw mitigated gaseous Nr, whereas Bm improved yield.

Beschreibung: Climate engineering and the ocean: effects on biogeochemistry and primary production Siv K. Lauvset, Jerry Tjiputra, and Helene Muri Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-235,2017 Manuscript under review for BG (discussion: open, 0 comments) Solar radiation management (SRM) is suggested as a method to offset global warming and to buy time to reduce emissions. Here we use an Earth System Model to project the impact of SRM on future ocean biogeochemistry. This work underscores the complexity of climate impacts on ocean primary production, and highlights that changes are driven by an integrated effect of many environmental drivers, which all change in different ways.

Beschreibung: Ammonium and nitrate additions differentially affect soil microbial biomass of different communities and enzyme activities in slash pine plantation in subtropical China Chuang Zhang, Xin-Yu Zhang, Hong-Tao Zou, Liang Kou, Yang Yang, Xue-Fa Wen, Sheng-Gong Li, Hui-Min Wang, and Xiao-Min Sun Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-179,2017 Manuscript under review for BG (discussion: open, 0 comments) Ammonium additions had a stronger inhibition effects on soil microbial biomass of different community than nitrate addition. However, the inhibition effects of nitrate additions on P-hydrolase were stronger than ammonium additions, but not on C,N-hydrolase and oxidase. Ammonium additions decreased N-acquisition specific enzyme activities normalized by total microbial biomass, but increased P-acquisition specific enzyme activities. Different effects on soil pH may explained the different effects.

Beschreibung: Peat decomposability in managed organic soils in relation to land-use, organic matter composition and temperature Cédric Bader, Moritz Müller, Rainer Schulin, and Jens Leifeld Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-187,2017 Manuscript under review for BG (discussion: open, 0 comments) Organic soils comprise a large yet fragile carbon (C) store in the global C cycle. Drainage, necessary for agriculture and forestry, triggers rapid decomposition of soil organic matter (SOM), typically increasing in the order forest 

Beschreibung: Coccolithophore fluxes in the open tropical North Atlantic: influence of the Amazon river and of Saharan dust deposition Catarina V. Guerreiro, Karl-Heinz Baumann, Geert-Jan A. Brummer, Gerhard Fischer, Laura F. Korte, Ute Merkel, Carolina Sá, Henko de Stigter, and Jan-Berend W. Stuut Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-216,2017 Manuscript under review for BG (discussion: open, 0 comments) Our study provides insights into the factors governing the spatiotemporal variability of coccolithophores in the equatorial North Atlantic, and illustrates how this supposedly oligotrophic and stable open-ocean region actually reveals significant ecological variability. We provide evidence for Saharan dust and the Amazon River acting as fertilizers for phytoplankton, and highlight the importance of coccolithophore productivity in the lower photic zone for the global oceanic carbonate budget.

Beschreibung: Modelling potential production and environmental effects of macroalgae farms in UK and Dutch coastal waters Johan van der Molen, Piet Ruardij, Karen Mooney, Philip Kerrison, Nessa E. O'Connor, Emma Gorman, Klaas Timmermans, Serena Wright, Maeve Kelly, Adam D. Hughes, and Elisa Capuzzo Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-195,2017 Manuscript under review for BG (discussion: open, 0 comments) Macroalgae farming may provide biofuel. Modelled macroalgae production is given for four sites in UK and Dutch waters. No environmental effects were detected. Macroalgae growth depended on nutrient concentrations and light levels. Macroalgae carbohydrate content, important for biofuel use, was lower for high nutrient concentrations. The hypothetical large-scale farm off the UK north Norfolk coast gave high, stable yields of macroalgae from year to year with substantial carbohydrate content.

Beschreibung: The effect of drought on dissolved organic carbon (DOC) release from peatland soil and vegetation sources Jonathan P. Ritson, Richard E. Brazier, Nigel J. D. Graham, Chris Freeman, Michael R. Templeton, and Joanna M. Clark Biogeosciences, 14, 2891-2902, https://doi.org/10.5194/bg-14-2891-2017, 2017 Peatlands are a globally important store of carbon; however increased droughts in the future may affect their ability to sequester carbon. Using laboratory simulations we show that droughts, through exposure to oxygen, greatly increase the quantity and alter the quality of dissolved organic carbon (DOC) released from peat. Catchment management which keeps water tables high to limit oxygen exposure is therefore likely to deliver positive water quality outcomes.

Beschreibung: Sensitivity of Future Ocean Acidification to Carbon Climate Feedbacks Richard J. Matear and Andrew Lenton Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-225,2017 Manuscript under review for BG (discussion: open, 0 comments) We show climate-carbon feedbacks accelerate and enhance ocean acidification. Such an acceleration of ocean acidification may further undermine the ability of marine biota to adapt to the changing environment. Our study also identifies the need to use Earth System Models to make future ocean acidification projections (relevance to AR6) and the need to reduce the uncertainty in the climate-carbon feedbacks.

Beschreibung: Geological nature of mineral licks and the reasons for geophagy among animals Alexander M. Panichev, Vladimir K. Popov, Igor Yu. Chekryzhov, Ivan V. Seryodkin, Alexander A. Sergievich, and Kirill S. Golokhvast Biogeosciences, 14, 2767-2779, https://doi.org/10.5194/bg-14-2767-2017, 2017 We considers the reasons for geophagy in two regions of the eastern Sikhote-Alin volcanic belt and show that one of the types of rock consumed is kudur, a natural landscape complex. Through comparative analysis of the composition of the rocks and of animal excrement, we establish that the rocks are hydrothermally altered rhyolitic tuffs. The data suggest that the main reason for geophagy may be connected with the animals' urge to discard excessive and toxic concentrations of certain elements.

Beschreibung: Annual greenhouse gas budget for a bog ecosystem undergoing restoration by rewetting Sung-Ching Lee, Andreas Christen, Andrew T. Black, Mark S. Johnson, Rachhpal S. Jassal, Rick Ketler, Zoran Nesic, and Markus Merkens Biogeosciences, 14, 2799-2814, https://doi.org/10.5194/bg-14-2799-2017, 2017 Burns Bog in Vancouver is the largest peatland on North America's west coast. It is undergoing rewetting as a restoration management after peat harvesting. Rewetting of disturbed areas facilitates their ecological recovery but has an immediate impact on carbon dioxide and methane exchange. On the floating flux tower, we quantified annual carbon dioxide and methane exchange to inform future management. Our results suggested that the study area was a net carbon sink after 7-year rewetting.

Beschreibung: Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment Thomas W. Trull, Abraham Passmore, Diana M. Davies, Tim Smit, Kate Berry, and Bronte Tilbrook Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-219,2017 Manuscript under review for BG (discussion: open, 0 comments) We present the first large scale survey of planktonic biogenic carbonate concentrations south of Australia, accompanied by biogenic silica and particulate organic carbon. These suggest that coccolithophores are largely restricted to Subantarctic waters and are present in much lower abundance than in northern hemisphere polar waters. Comparison to upper ocean properties suggests that thermal tolerance and competition with diatoms for limiting iron may be as influential as ocean acidification.

Beschreibung: Empirical methods for the estimation of Southern Ocean CO 2 : Support Vector and Random Forest Regression Luke Gregor, Schalk Kok, and Pedro M. S. Monteiro Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-215,2017 Manuscript under review for BG (discussion: open, 0 comments) We use machine learning to extrapolate ship measurements of CO 2 using satellite data. We present two ML methods new to this field. These methods perform well in context of previous work and reproduce the decadal trends of previous estimates. To test the methods, we simulate the exact observed setup in biogeochemical ocean model output. We show that there are not yet enough measurements of CO 2 in the SO for the community to resolve CO 2 to the point where non-linear ML methods agree.

Beschreibung: New techniques for gap-filling and partitioning of H 2 O and CO 2 eddy fluxes measured over forests in complex mountainous terrain Minseok Kang, Joon Kim, Bindu Malla Thakuri, Junghwa Chun, and Chunho Cho Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-247,2017 Manuscript under review for BG (discussion: open, 0 comments) We proposed two new data processing techniques to reduce uncertainty of H 2 O/CO 2 fluxes measured by eddy covariance method which is widely used to observe mass/energy fluxes between biosphere and atmosphere. There is a common characteristic between the proposed techniques: two existing methods were merged into a new method. Such a strategy strengthens the strength and makes up for the weakness of the original methods. It will contribute to the standardization of eddy covariance data processing.

Beschreibung: Quantifying nutrient uptake as driver of rock weathering in forest ecosystems by magnesium stable isotopes David Uhlig, Jan A. Schuessler, Julien Bouchez, Jean L. Dixon, and Friedhelm von Blanckenburg Biogeosciences, 14, 3111-3128, https://doi.org/10.5194/bg-14-3111-2017, 2017 Plants and soil microbiota play an active role in rock weathering. Here we show that the coupling between erosion and weathering might be established by nutrients that are taken up by trees, are not recycled from plant litter and are missing in the dissolved river flux due to forest re-growth after clear cutting or due to erosion as coarse woody debris. To track this nutrient pathway we used magnesium stable isotopes in combination with innovative metrics over annual and millennial timescales.

Beschreibung: A mechanistic model of an upper bound on oceanic carbon export as a function of mixed layer depth and temperature Zuchuan Li and Nicolas Cassar Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-259,2017 Manuscript under review for BG (discussion: open, 0 comments) Export production reflects the amount of organic matter transferred from the surface ocean to depth through biological processes. This export is in great part controlled by nutrient and light availability, which are conditioned by mixed layer depth (MLD). In this study, building on Sverdrup’s critical depth hypothesis, we derive a mechanistic model of an upper bound on carbon export based on the metabolic balance between photosynthesis and respiration as a function of MLD and temperature. We find that the upper bound is a positively skewed bell-shaped function of MLD. Specifically, the upper bound increases with deepening mixed layers down to a critical depth, beyond which a long tail of decreasing carbon export is associated with increasing heterotrophic activity and decreasing light availability. We also show that in cold regions the upper bound on carbon export decreases with increasing temperature when mixed layers are deep, but increases with temperature when mixed layers are shallow. A metaanalysis shows that our model envelopes field estimates of carbon export from the mixed layer. When compared to satellite export production estimates, our model indicates that export production in some regions of the Southern Ocean, most particularly the Subantarctic Zone, is likely limited by light for a significant portion of the growing season.

Beschreibung: Phosphorus addition mitigates N 2 O and CH 4 emissions in N-saturated subtropical forest, SW China Longfei Yu, Yihao Wang, Xiaoshan Zhang, Peter Dörsch, and Jan Mulder Biogeosciences, 14, 3097-3109, https://doi.org/10.5194/bg-14-3097-2017, 2017 In this study, we applied phosphorus (P) to a nitrogen (N)-saturated forest in the Chinese subtropics and observed significant decreases in both N 2 O and CH 4 emission from soil within 1.5 years. This was associated with a strong decrease of mineral N in soil water, likely due to stimulated N uptake. Our findings suggest that P limitation could be one important reason for large greenhouse gas emissions reported in the subtropical forests receiving excessive N input.

Beschreibung: Tree growth and its climate signal along latitudinal and altitudinal gradients: comparison of tree rings between Finland and the Tibetan Plateau Lixin Lyu, Susanne Suvanto, Pekka Nöjd, Helena M. Henttonen, Harri Mäkinen, and Qi-Bin Zhang Biogeosciences, 14, 3083-3095, https://doi.org/10.5194/bg-14-3083-2017, 2017 Our results reveal that the change in the tree growth–climate relationship is similar along latitudinal and altitudinal gradients, especially during growing seasons. Moreover, the critical periods for climatic effects on tree radial growth occurred earlier at lower latitudes and altitudes than at the cold ends of the gradients. We further demonstrate the use of daily climate data, as they may disclose more precise gradient patterns that could not be detected if monthly climate data were used.

Beschreibung: Spatial variability of CO 2 uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates Norbert Pirk, Jakob Sievers, Jordan Mertes, Frans-Jan W. Parmentier, Mikhail Mastepanov, and Torben R. Christensen Biogeosciences, 14, 3157-3169, https://doi.org/10.5194/bg-14-3157-2017, 2017 The large spatial variability in Arctic tundra complicates the representative assessment of CO 2 budgets. Accurate measurements of these heterogeneous landscapes are, however, essential to understanding their vulnerability to climate change. We surveyed a polygonal tundra lowland on Svalbard with an unmanned aerial vehicle (UAV) that mapped ice-wedge morphology to complement eddy covariance (EC) flux measurements of CO 2 . The analysis of spectral distributions showed that conventional EC methods do not accurately capture the turbulent CO 2 exchange with a spatially heterogeneous surface that typically features small flux magnitudes. Nonlocal (low-frequency) flux contributions were especially pronounced during snowmelt and introduced a large bias of −46 gC m −2 to the annual CO 2 budget in conventional methods (the minus sign indicates a higher uptake by the ecosystem). Our improved flux calculations with the ogive optimization method indicated that the site was a strong sink for CO 2 in 2015 (−82 gC m −2 ). Due to differences in light-use efficiency, wetter areas with low-centered polygons sequestered 47 % more CO 2 than drier areas with flat-centered polygons. While Svalbard has experienced a strong increase in mean annual air temperature of more than 2 K in the last few decades, historical aerial photographs from the site indicated stable ice-wedge morphology over the last 7 decades. Apparently, warming has thus far not been sufficient to initiate strong ice-wedge degradation, possibly due to the absence of extreme heat episodes in the maritime climate on Svalbard. However, in Arctic regions where ice-wedge degradation has already initiated the associated drying of landscapes, our results suggest a weakening of the CO 2 sink in polygonal tundra.

Beschreibung: Species interactions can shift the response of a maerl bed community to ocean acidification and warming Erwann Legrand, Pascal Riera, Mathieu Lutier, Jérôme Coudret, Jacques Grall, and Sophie Martin Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-255,2017 Manuscript under review for BG (discussion: open, 0 comments) In relation to ocean acidification and warming, most studies are focused on specific responses but do not consider species interactions. This study examined experimentally the response of a maerl bed community, composed of calcareous and fleshy algae and grazers, to ocean acidification and warming. Our results indicate that the response of marine communities to climate change will depend on the direct effects on species physiology and the indirect effects due to shifts in species interactions.

Beschreibung: Physiological and biochemical responses of Emiliania huxleyi to ocean acidification and warming are modulated by UV radiation Shanying Tong, David A. Hutchins, and Kunshan Gao Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-269,2017 Manuscript under review for BG (discussion: open, 0 comments) In previous studies, most studies concerning the effects of environmental changes on marine organisms have been carried out under PAR only, without UVR being considered. In this study We found that UVR can counteract the negative effects of the greenhouse treatment on the calcification rate to photosynthesis rate ratio, and may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi .

Beschreibung: Marine isoprene production and consumption in the mixed layer of the surface ocean – A field study over 2 oceanic regions Dennis Booge, Cathleen Schlundt, Astrid Bracher, Sonja Endres, Birthe Zäncker, and Christa A. Marandino Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-257,2017 Manuscript under review for BG (discussion: open, 0 comments) Our isoprene data from field measurements in the mixed layer from the Indian Ocean and the East Pacific Ocean show, that the ability of different phytoplankton functional types to produce isoprene, seems to be mainly influenced by light, ocean temperature, salinity and nutrients. By calculating in-field isoprene production rates we demonstrate that an additional loss is needed to explain the measured isoprene concentration, which is attributed to heterotrophic respiration mainly due to bacteria.

Beschreibung: Regional detection of canopy nitrogen in Mediterranean forests using the spaceborne MERIS Terrestrial Chlorophyll Index Yasmina Loozen, Karin T. Rebel, Derek Karssenberg, Martin J. Wassen, Jordi Sardans, Josep Peñuelas, and Steven M. de Jong Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-228,2017 Manuscript under review for BG (discussion: open, 0 comments) The objective of this study was to investigate the relationship between a vegetation index called the Meris Terretrials Chlorophyll Index (MTCI) calculated from satellite reflectance data and the nitrogen concentration and content of the trees canopy. This was done at the regional scale in Mediterranean forests located in Catalonia, north-eastern Spain. This relationship was studied at several spatial resolutions (20 km, 15 km, 10 km, 5 km and 1 km) and was investigated per type of trees.

Beschreibung: Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO 2 tolerance in phytoplankton productivity Stacy Deppeler, Katherina Petrou, Kai G. Schulz, Karen Westwood, Imojen Pearce, John McKinlay, and Andrew Davidson Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-226,2017 Manuscript under review for BG (discussion: open, 0 comments) We combined productivity and photophysiology measurements to investigate the effects of ocean acidification on a natural Antarctic marine microbial community. Our study identifies a threshold for CO 2 tolerance in the phytoplankton community between 953 and 1140 uatm CO 2 , above which productivity declines. Bacteria were tolerant to CO 2 up to 1641 uatm. We identify physiological changes in the phytoplankton community at high CO 2 that allowed them to acclimate to the high CO 2 treatment.

Beschreibung: Coral calcifying fluid aragonite saturation states derived from Raman spectroscopy Thomas M. DeCarlo, Juan P. D'Olivo, Taryn Foster, Michael Holcomb, Thomas Becker, and Malcolm T. McCulloch Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-194,2017 Manuscript under review for BG (discussion: open, 0 comments) We present a new technique to quantify the chemical conditions under which corals build their skeletons by analysing them with lasers at a very fine resolution, down to 1/100th the width of a human hair. Our first applications to laboratory-cultured and wild corals demonstrates the complex interplay among seawater conditions (temperature and acidity), calcifying fluid chemistry, and bulk skeleton accretion, that will define the sensitivity of coral calcification to 21st century climate change.

Beschreibung: Retrogressive thaw slumps temper dissolved organic carbon delivery to streams of the Peel Plateau, NWT, Canada Cara A. Bulger, Suzanne E. Tank, and Steven V. Kokelj Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-217,2017 Manuscript under review for BG (discussion: open, 0 comments) This study is the first to investigate how permafrost slumping affects dissolved organic carbon (DOC) mobilization in landscapes that are dominated by glacial tills. Unlike previous studies, we find that slumping is associated with DOC decreases downstream of slumps – an effect that appears to be caused by adsorption to fine-grained glacial tills. This work adds significantly to our understanding of how the effects of permafrost thaw on organic carbon mobilization may vary across the Arctic.

Beschreibung: Phytoplankton growth responses to Asian dust additions in the Northwest Pacific Ocean versus the Yellow Sea Chao Zhang, Huiwang Gao, Xiaohong Yao, Zongbo Shi, Jinhui Shi, Yang Yu, Ling Meng, and Xinyu Guo Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-176,2017 Manuscript under review for BG (discussion: open, 0 comments) This study compares the responses of phytoplankton growth in the northwest Pacific to those in the Yellow Sea. In general, larger positive responses of phytoplankton induced by combined nutrients (in the subtropical gyre of the northwest Pacific) than by single nutrient (in the Kuroshio Extension and Yellow Sea) from the AM-dust are observed. We also emphasizes the importance of increase in bioavailable P stock for phytoplankton growth following AM-dust addition.

Beschreibung: Assimilating bio-optical glider data during a phytoplankton bloom in the southern Ross Sea Daniel E. Kaufman, Marjorie A. M. Friedrichs, John C. P. Hemmings, and Walker O. Smith Jr. Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-258,2017 Manuscript under review for BG (discussion: open, 0 comments) Computer simulations of the highly variable phytoplankton in the Ross Sea demonstrated how incorporating data from different sources (satellite, ship or glider) results in different system interpretations. For example, simulations assimilating satellite-based data produced lower estimates of carbon export. Combining observations with models in this remote, harsh, and biologically variable environment should include consideration of the potential impacts of data frequency, duration, and coverage.

Beschreibung: Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system Blanca Ausín, Diana Zúñiga, Jose Abel Flores, Catarina Cavaleiro, María Froján, Nicolás Villacieros-Robineau, Fernando Alonso Pérez, Belén Arbones, Celia Santos, Franciso de la Granda, Carmen G. Castro, Fátima Abrantes, Timothy I. Eglinton, and Emilia Salgueiro Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-236,2017 Manuscript under review for BG (discussion: open, 0 comments) A systematic investigation of the coccolithophore ecology was performed for the first time in the NW Iberian margin to broaden our knowledge on the use of fossil coccoliths in marine sediment records to infer environmental conditions in the past. Coccolithophore proved to be significant primary producers and their abundance and distribution was favored by warmer and nutrient–depleted waters during the upwelling regime, seasonally controlled offshore and influenced by coastal processes onshore.

Beschreibung: Winter phytoplankton blooms in the offshore south Adriatic waters (1995–2012) regulated by hydroclimatic events: Special emphasis on the exceptional bloom of 1995 Mirna Batistić, Damir Viličić, Vedrana Kovačević, Nenad Jasprica, Héloise Lavigne, Marina Carić, Rade Garić, and Ana Car Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-205,2017 Manuscript under review for BG (discussion: open, 0 comments) Contrary to earlier statements winter bloom is typical of the open South Adriatic. Its intensity depends on different water masses that enter the Adriatic, synergy of regional meteorology and mixing processes that affect these water masses. More intense blooms have occurred under certain hydroclimatic conditions: the East Mediterranean Transient (EMT), extreme winters, and reversal years that switch between anticyclonic and ciclonic circulation in the Ionian Sea.

Beschreibung: New molecular evidence for surface and sub-surface soil erosion controls on the composition of stream DOM during storm events Marie Denis, Laurent Jeanneau, Patrice Petitjean, Anaëlle Murzeau, Marine Liotaud, Louison Yonnet, and Gérard Gruau Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-252,2017 Manuscript under review for BG (discussion: open, 0 comments) The results of this study highlight the changes of DOM composition in soil solutions and surface runoff, probably controlled by water-table dynamic and pre-event hydrological conditions. These changes should be taken into account for a better understanding of micropollutant mobility. Moreover, this work has implications for modeling DOM export in headwater catchments, as many studies assume that DOM transfer during storm events consist of the flushing of preexisting soil solution DOM.

Beschreibung: Improving the inverse modeling of a trace isotope: how precisely can radium-228 fluxes toward the ocean and submarine groundwater discharge be estimated? Guillaume Le Gland, Laurent Mémery, Olivier Aumont, and Laure Resplandy Biogeosciences, 14, 3171-3189, https://doi.org/10.5194/bg-14-3171-2017, 2017 In this study, we computed the fluxes of radium-228 from the continental shelf to the open ocean by fitting a numerical model to observations. After determining appropriate model parameters (cost function and number of source regions), we found a lower and more precise global flux than previous estimates: 8.01–8.49×10 23  atoms yr −1 . This result can be used to assess nutrient and trace element fluxes to the open ocean, but we cannot identify specific pathways like submarine groundwater discharge.

Beschreibung: 13 C labelling study of constitutive and stress-induced terpenoide missions from Norway spruce and Scots pine Cheng Wu, Iida Pullinen, Stefanie Andres, Astrid Kiendler-Scharr, Einhard Kleist, Andreas Wahner, Jürgen Wildt, and Thomas F. Mentel Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-260,2017 Manuscript under review for BG (discussion: open, 0 comments) Biogenic volatile organic compounds are important for atmospheric chemistry. We showed by 13 CO 2 labelling experiments that biosynthesis is not restricted to the presence of light. In particular sesquiterpenes exhibit substantial de novo emissions in darkness with the carbon being delivered from alternative carbon sources. Our findings are of importance for future emissions under conditions of climate change as the response of de novo emissions to stresses differs from that of pool emissions.

Beschreibung: Ferrihydrite associated organic matter (OM) stimulates reduction by Shewanella oneidensis MR-1 and a complex microbial consortia Rebecca E. Cooper, Karin Eusterhues, Carl-Eric Wegner, Kai Uwe Totsche, and Kirsten Küsel Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-270,2017 Manuscript under review for BG (discussion: open, 0 comments) In this study we show increasing organic matter (OM) content on ferrihydrite surfaces enhances Fe reduction by the model Fe-reducer S. oneidensis and a microbial consortia extracted from peat. Similarities in reduction rates between S. oneidensis and the consortia suggest electron shuttling dominates in OM-rich soils. Community profile analyses showed enrichment of fermenters with pure ferrihydrite, whereas OM-mineral complexes favored enrichment of Fe-reducing Desulfobacteria and Pelosinus sp.

Beschreibung: Effect of ocean acidification and elevated temperature on growth of calcifying tubeworm shells ( Spirorbis spirorbis ): An in-situ benthocosm approach Sha Ni, Isabelle Taubner, Florian Böhm, Vera Winde, and Michael E. Böttcher Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-185,2017 Manuscript under review for BG (discussion: open, 0 comments) The calcareous tubeworm Spirorbis spirorbis is a wide-spread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus ). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO 2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO 2 may influence S. spirorbis shell growth we carried out four seasonal experiments in the 'Kiel Outdoor Benthocosms' at elevated pCO 2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO 2 conditions. No influence of daily average CaCO 3 saturation state on the growth rates of S. spirorbis was observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favored selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO 2 , the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.

Beschreibung: Nitrogen transformations along a shallow subterranean estuary Mathilde Couturier, Gwendoline Tommi-Morin, Maude Sirois, Alexandra Rao, Christian Nozais, and Gwénaëlle Chaillou Biogeosciences, 14, 3321-3336, https://doi.org/10.5194/bg-14-3321-2017, 2017 At the land–ocean interface, subterranean estuaries (STEs) are a critical transition pathway of nitrogen. Environmental conditions in the groundwater lead to nitrogen transformation, altering the nitrogen species and concentrations exported to the coastal ocean. This study highlights the role of a STE in processing groundwater-derived N in a shallow boreal STE, far from anthropogenic pressures. Biogeochemical transformations provide new N species from terrestrial origin to the coastal ocean.

Beschreibung: 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 Discuss., https//doi.org/10.5194/bg-2017-286,2017 Manuscript under review for BG (discussion: open, 0 comments) Future climate warming of the Arctic could potentially enhance the load of riverine dissolved organic carbon (RDOC) of Arctic rivers due to increased carbon mobilization within watersheds. A greater flux of RDOC might thus impact the biogeochemical processes of the coastal Arctic Ocean (AO). In this study, we show that estimates of RDOC concentrations in the surface waters of the Canadian Beaufort Sea computed for 2003–2011 by both optical remote sensing and a physical-biogeochemical coupled model compare favorably. Our results suggest that, over spring-summer, RDOC contributes to 35 % of primary production and that an equivalent of ~ 10 % of the riverine RDOC is exported westwards with a potential for fueling the biological production of the eastern Alaskan nearshore waters. The combination of model and satellite data can be extended to the entire AO to quantify the expected changes in RDOC fluxes and their potential impact on AO biogeochemistry. This is left for future work.