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  • 11
    Publication Date: 2012-12-13
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 12
    Publication Date: 2012-12-13
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 13
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    In:  [Talk] In: Uncertainties of scenario simulations, 14.10.2010, Norrköping, Sweden .
    Publication Date: 2013-05-22
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 14
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    In:  [Talk] In: AGU Fall Meeting 2010, 13.-17.12.2010, San Franciso, USA .
    Publication Date: 2013-05-22
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 15
    Publication Date: 2017-01-30
    Description: A simplified version of a kinetic–bioenergetic reaction model for anaerobic oxidation of methane (AOM) in marine sediments [Dale, A.W., Regnier, P., Van Cappellen, P., 2006. Bioenergetic controls on anaerobic oxidation of methane (AOM) in coastal marine sediments: a theoretical analysis. Am. J. Sci. 306, 246–294.] is used to assess the impact of transport processes on biomass distributions, AOM rates and methane release fluxes from the sea floor. The model explicitly represents the functional microbial groups and the kinetic and bioenergetic limitations of the microbial metabolic pathways involved in AOM. Model simulations illustrate the dominant control exerted by the transport regime on the activity and abundance of AOM communities. Upward fluid flow at active seep systems restricts AOM to a narrow subsurface reaction zone and sustains high rates of methane oxidation. In contrast, pore-water transport dominated by molecular diffusion leads to deeper and broader zones of AOM, characterized by much lower rates and biomasses. Under steady-state conditions, less than 1% of the upward dissolved methane flux reaches the water column, irrespective of the transport regime. However, a sudden increase in the advective flux of dissolved methane, for example as a result of the destabilization of methane hydrates, causes a transient efflux of methane from the sediment. The benthic efflux of dissolved methane is due to the slow growth kinetics of the AOM community and lasts on the order of 60 years. This time window is likely too short to allow for a significant escape of pore-water methane following a large scale gas hydrate dissolution event such as the one that may have accompanied the Paleocene/Eocene Thermal Maximum (PETM).
    Type: Article , PeerReviewed
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  • 16
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    Kline Geology Laboratory
    In:  American Journal of Science, 309 (3). pp. 189-220.
    Publication Date: 2019-01-21
    Description: A one-dimensional reactive transport model including mass, momentum and volume conservation for the solid, aqueous, and gaseous phases is developed to explore the fate of free methane gas in marine sediments. The model assumes steady–state compaction for the solid phase in addition to decoupled gas and aqueous phase transport, instigated by processes such as buoyancy, externally impressed flows and compaction. Chemical species distributions are governed by gas advection, dissolved advection and diffusion as well as by reaction processes, which include organoclastic sulfate reduction, methanogenesis and anaerobic oxidation of methane (AOM). The model is applied to Eckernförde Bay, a shallow-water environment where acoustic profiles confirm a widespread occurrence of year-round biogenic free methane gas within the muddy regions of the sediment, and where subsurface methanogenesis, overlaid by a zone of AOM has been reported. The model results reveal that, under steady-state conditions, upward gas migration is an effective methane transport mechanism from oversaturated to undersaturated intervals of the sediment. Furthermore, sensitivity tests show that when methanogenesis rates increase, the gas flux to the AOM zone becomes progressively more important and may reach values comparable to those of the aqueous methane diffusive flux. Nevertheless, the model also proves that the gas transport rates always remain smaller than the removal rates by combined gaseous methane dissolution and oxidation. Consequently, for the range of environmental conditions investigated here, the AOM zone acts as an efficient subsurface barrier for both aqueous and gaseous methane, preventing methane escape from the sediments to the water column.
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  • 17
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    In:  [Talk] In: 10th International Conference on Gas in Marine Sediments, 09.09.2010, Listvaynka, Irkutsk (Lake Baikal), Russia .
    Publication Date: 2012-02-23
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  • 18
    Publication Date: 2016-08-09
    Description: A kinetic-bioenergetic reaction model for the anaerobic oxidation of methane (AOM) in coastal marine sediments is presented. The model considers a fixed depth interval of sediments below the zone of bioturbation (the window-of-observation), subject to seasonal variations of temperature and inputs of organic substrates and sulfate. It includes (1) nine microbially-mediated reaction pathways involved in CH4 production/consumption; (2) an explicit representation of five functional microbial groups; and (3) bioenergetic limitations of the microbial metabolic pathways. Fermentation of organic substrates is assumed to produce hydrogen (H2) and acetate (Ac) as key reactive intermediates. Competition among the metabolic pathways is controlled by the relative kinetic efficiencies of the various microbial processes and by bioenergetic constraints. Model results imply that the functional microbial biomasses within the window-of-observation undergo little variation over the year, as a result of kinetic and thermodynamic buffering of the seasonal forcings. Furthermore, the microbial processes proceed at only small fractions of their maximum potential rates. These findings provide a theoretical justification for the approximation of steady-state microbial biomasses, which is frequently used in diagenetic modeling. In contrast, AOM rates show a strong seasonal evolution: AOM only becomes spontaneous in winter, when hydrogenotrophic sulfate reduction (hySR) sufficiently reduces the local H2 concentration. The bioenergetic limitation of AOM is thus a critical factor modulating this process in seasonally-forced nearshore marine sediments. A global sensitivity analysis based on a 2-level factorial design reveals that AOM rates are most sensitive to the kinetic parameters describing hySR and acetotrophic methanogenesis (acME). The growth and substrate uptake kinetics of AOM are unimportant, whereas the threshold value of ATP energy conservation for AOM is the most sensitive thermodynamic parameter. These results confirm that anaerobic methane oxidizing microorganisms are metabolizing close to their thermodynamic limit, with the energetic balance being controlled by the relative rates of hySR and acME. The removal of Ac by acME primarily allows more sulfate (SO42−) to be utilized for H2 oxidation, thereby promoting AOM.
    Type: Article , PeerReviewed
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  • 19
    Publication Date: 2018-02-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 20
    Publication Date: 2018-03-29
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth System Science Data 6 (2014): 235-263, doi:10.5194/essd-6-235-2014.
    Description: Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil-fuel combustion and cement production (EFF) are based on energy statistics, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated for the first time in this budget with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2 and land cover change (some including nitrogen–carbon interactions). All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2003–2012), EFF was 8.6 ± 0.4 GtC yr−1, ELUC 0.9 ± 0.5 GtC yr−1, GATM 4.3 ± 0.1 GtC yr−1, SOCEAN 2.5 ± 0.5 GtC yr−1, and SLAND 2.8 ± 0.8 GtC yr−1. For year 2012 alone, EFF grew to 9.7 ± 0.5 GtC yr−1, 2.2% above 2011, reflecting a continued growing trend in these emissions, GATM was 5.1 ± 0.2 GtC yr−1, SOCEAN was 2.9 ± 0.5 GtC yr−1, and assuming an ELUC of 1.0 ± 0.5 GtC yr−1 (based on the 2001–2010 average), SLAND was 2.7 ± 0.9 GtC yr−1. GATM was high in 2012 compared to the 2003–2012 average, almost entirely reflecting the high EFF. The global atmospheric CO2 concentration reached 392.52 ± 0.10 ppm averaged over 2012. We estimate that EFF will increase by 2.1% (1.1–3.1%) to 9.9 ± 0.5 GtC in 2013, 61% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the economy. With this projection, cumulative emissions of CO2 will reach about 535 ± 55 GtC for 1870–2013, about 70% from EFF (390 ± 20 GtC) and 30% from ELUC (145 ± 50 GtC).
    Description: We thank the many researchers and funding agencies responsible for the collection and quality control of the data included in SOCAT, and the support of the International Ocean Carbon Coordination Project (IOCCP), the Surface Ocean Lower Atmosphere Study (SOLAS), and the Integrated Marine Biogeochemistry and Ecosystem Research program (IMBER). The UK Natural Environment Research Council (NERC) provided funding to C. Le Quéré, R. Moriarty and the GCP though their International Opportunities Fund specifically to support this publication (project NE/103002X/1). R. J. Andres and T. A. Boden were supported by the US Department of Energy, Office of Science, Biological and Environmental Research (BER) programs under US Department of Energy contract DE-AC05- 00OR22725. G. P. Peters and R. M. Andrews were supported by the Norwegian Research Council (221355). A. Arneth, A. Omar, C. Le Quéré, J. Schwinger, P. Ciais, P. Friedlingstein, P. Regnier, J. Segschneider, S. Sitch and S. Zaehle were supported by the EU FP7 for funding through projects GEOCarbon (283080), COMBINE (226520), CARBOCHANGE (264879), EMBRACE (GA282672), and LUC4C (GA603542). A. Harper was supported by the NERC Joint Weather and Climate Research Programme. A. K. Jain was supported by the US National Science Foundation (NSF AGS 12-43071) the US Department of Energy, Office of Science and BER programs (DOE DE-SC0006706) and NASA LCLUC program (NASA NNX14AD94G). B. D. Stocker was supported by the Swiss National Science Foundation. A. Wiltshire was supported by the Joint UK DECC/Defra Met Office Hadley Centre Climate Programme (GA01101). E. Kato was supported by the Environment Research and Technology Development Fund (S-10) of the Ministry of Environment of Japan. J. G. Canadell and M. R. Raupach were supported by the Australian Climate Change Science Program. J. I. House was supported by a Leverhulme Research Fellowship. S. C. Doney was supported by the US National Science Foundation (NSF AGS-1048827).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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