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Iron oxide reduction in methane-rich deep Baltic Sea sediments

Profile image of Mathilde HagensMathilde Hagens

2017, Geochimica et Cosmochimica Acta

https://doi.org/10.1016/J.GCA.2017.03.019
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Abstract

Methane is a powerful greenhouse gas and its emission from marine sediments to the atmosphere is largely controlled by anaerobic oxidation of methane (AOM). Traditionally, sulfate is considered to be the most important electron acceptor for AOM in marine sediments. Recent evidence suggests, however, that AOM may also be coupled to the reduction of iron (Fe) oxides. In the Baltic Sea, the post-glacial transition from the Ancylus freshwater phase to the Littorina brackish/marine phase (A/L-transition) around 9-7 kyr BP (before present), resulted in the accumulation of organic-rich brackish/marine sediments overlying organic-poor limnic deposits rich in Fe oxides. Methane produced in the organic-rich layer diffuses into the lake sediments, thus allowing for the possible coupling between Fe oxide reduction and methane oxidation. Here, we combine detailed geochemical analyses of the sediment and pore water retrieved from three sites that were drilled during the IODP Baltic Sea Paleoenvironment Expedition 347 with multicomponent diagenetic modeling to study the possible role of Fe-mediated AOM as a mechanism for the apparent Fe oxide reduction in the methane-bearing lake deposits below the A/L transition. Our results reveal a complex interplay between production, oxidation and transport of methane showing that besides organoclastic Fe reduction, oxidation of downward migrating methane with Fe oxides may also explain the elevated concentrations of dissolved ferrous Fe in deep Baltic Sea sediments. Our findings imply that the transition of a lake toward a marine system could lead to reactivation of deeply buried, mostly crystalline Fe oxides in organic-poor lake deposits through reactions with downward diffusing methane from the overlying organic-rich marine sediments. Based on the geochemical profiles and numerical modeling, we propose that a potential coupling between Fe oxide reduction and methane oxidation likely affects deep Fe cycling and related biogeochemical processes, such as burial of phosphorus, in systems subject to changes in organic matter loading or bottom water salinity.

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References (120)

  1. Achtnich C., Bak F. and Conrad R. (1995) Competition for electron donors among nitrate reducers, ferric iron reducers, sulfate reducers, and methanogens in anoxic paddy soil. Biol. Fertil. Soils 19, 65-72.
  2. Aller R. C. and Rude P. D. (1988) Complete oxidation of solid phase sulfides by manganese and bacteria in anoxic marine sediments. Geochim. Cosmochim. Acta 52, 751-765.
  3. Alperin M. J., Reeburgh W. S. and Whiticar M. J. (1988) Carbon and hydrogen isotope fractionation resulting from anaerobic methane oxidation. Glob. Biogeochem. Cycl. 2, 279-288.
  4. Amos R. T., Bekins B. A., Cozzarelli I. M., Voytek M. A., Kirshtein J. D., Jones E. J. P. and Blowes D. W. (2012) Evidence for iron-mediated anaerobic methane oxidation in a crude oil-contaminated aquifer. Geobiology 10, 506-517.
  5. Andre ´n E., Andre ´n T. and Sohlenius G. (2000) The Holocene history of the southwestern Baltic Sea as reflected in a sediment core from the Bornholm Basin. Boreas 29, 233-250.
  6. Andre ´n T., Jørgensen B. B., Cotterill C., G S., and the Expedition 347 Scientists (2015). Integrated ocean drilling program. In: Proceedings of IODP, College Station, TX, p. 347.
  7. Arndt S., Brumsack H.-J. and Wirtz K. W. (2006) Cretaceous black shales as active bioreactors: a biogeochemical model for the deep biosphere encountered during ODP Leg 207 (Demerara Rise). Geochim. Cosmochim. Acta 70, 408-425.
  8. Beal E. J., House C. H. and Orphan V. J. (2009). Manganese-and iron-dependent marine methane oxidation. Science 325(80-.), 184-187.
  9. Berg P., Rysgaard S. and Thamdrup B. (2003) Dynamic modeling of early diagenesis and nutrient cycling. A case study in an Arctic marine sediment. Am. J. Sci. 303, 905-955.
  10. Berner R. A. and Westrich J. T. (1985) Bioturbation and the early diagenesis of carbon and sulfur. Am. J. Sci. 285, 193-206.
  11. Bethke C. M., Sanford R. A., Kirk M. F., Jin Q. and Flynn T. M. (2011) The thermodynamic ladder in geomicrobiology. Am. J. Sci. 311, 183-210.
  12. Bjo ¨rck S. (1995) A review of the history of the Baltic Sea, 13.0- 8.0 ka BP. Quat. Int. 27, 19-40.
  13. Bodegom P. M., Scholten J. C. M. and Stams A. J. M. (2004) Direct inhibition of methanogenesis by ferric iron. FEMS Microbiol. Ecol. 49, 261-268.
  14. Boesen C. and Postma D. (1988) Pyrite formation in anoxic environments of the Baltic. Am. J. Sci. 288, 575-603.
  15. Boetius A., Ravenschlag K., Schubert C. J., Rickert D., Widdel F., Gieseke A., Amann R., Jørgensen B. B., Witte U. and Pfannkuche O. (2000) A marine microbial consortium appar- ently mediating anaerobic oxidation of methane. Nature 407, 623-626.
  16. Bond D. R. and Lovley D. R. (2002) Reduction of Fe(III) oxide by methanogens in the presence and absence of extracellular quinones. Environ. Microbiol. 4, 115-124.
  17. Borowski W. S., Paull C. K. and Ussier W. (1997) Carbon cycling within the upper methanogenic zone of continental rise sediments: an example from the methane-rich sediments over- lying the blake ridge gas hydrate deposits. Mar. Chem. 57, 299- 311. Bo ¨ttcher M. E. and Lepland A. (2000) Biogeochemistry of sulfur in a sediment core from the west-central Baltic Sea: evidence from stable isotopes and pyrite textures. J. Mar. Syst. 25, 299-312.
  18. Boudreau B. P. (1996) The diffusive tortuosity of fine-grained unlithified sediments. Geochim. Cosmochim. Acta 60, 3139- 3142.
  19. Boudreau B. P. (1997) Diagenetic Models and Their Implementa- tion. Modelling Transport and Reactions in Aquatic Sediments. Springer.
  20. Brass M. and Ro ¨ckmann T. (2010) Continuous-flow isotope ratio mass spectrometry method for carbon and hydrogen isotope measurements on atmospheric methane. Atmos. Meas. Tech. 3, 1707-1721.
  21. Brunner B., Arnold G. L., Røy H., Mu ¨ller I. A. and Jørgensen B. B. (2016) Off limits: sulfate below the sulfate-methane transi- tion. Front. Earth Sci. 4, 1-16.
  22. Burdige D. J. and Nealson K. H. (1986) Chemical and microbi- ological studies of sulfide-mediated manganese reduction. Geomicrobiol. J. 4, 361-387.
  23. Burton E. D., Sullivan L. A., Bush R. T., Johnston S. G. and Keene A. F. (2008) A simple and inexpensive chromium- reducible sulfur method for acid-sulfate soils. Appl. Geochem. 23, 2759-2766.
  24. Chanton J. P. (2005) The effect of gas transport on the isotope signature of methane in wetlands. Org. Geochem. 36, 753-768.
  25. Coplen T. B., Brand W. A., Gehre M., Gro ¨ning M., Meijer H. A. J., Toman B. and Verkouteren R. M. (2006) New guidelines for d13C measurements. Anal. Chem. 78, 2439-2441.
  26. Crowe S. A., Katsev S., Leslie K., Sturm A., Magen C., Nomosatryo S., Pack M. A., Kessler J. D., Reeburgh W. S., Roberts J. A., Gonza ´lez L., Douglas Haffner G., Mucci A., Sundby B. and Fowle D. A. (2011) The methane cycle in ferruginous Lake Matano. Geobiology 9, 61-78.
  27. Cruz Viggi C., Rossetti S., Fazi S., Paiano P., Majone M. and Aulenta F. (2014) Magnetite particles triggering a faster and more robust syntrophic pathway of methanogenic propionate degradation. Environ. Sci. Technol. 48, 7536-7543.
  28. Daniels L., Fulton G., Spencer R. W. and Orme-Johnson W. H. (1980) Origin of hydrogen in methane produced by Methanobacterium thermoautotrophicum. J. Bacteriol. 141, 694-698.
  29. Dijkstra N., Slomp C. P. and Behrends T.Expedition 347 Scientists (2016) Vivianite is a key sink for phosphorus in sediments of the Landsort Deep, an intermittently anoxic deep basin in the Baltic Sea. Chem. Geol. 438, 58-72.
  30. Egger M., Jilbert T., Behrends T., Rivard C. and Slomp C. P. (2015a) Vivianite is a major sink for phosphorus in methano- genic coastal surface sediments. Geochim. Cosmochim. Acta 169, 217-235.
  31. Egger M., Kraal P., Jilbert T., Sulu-Gambari F., Sapart C. J., Ro ¨ckmann T. and Slomp C. P. (2016a) Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea. Biogeosciences 13, 5333-5355.
  32. Egger M., Lenstra W., Jong D., Meysman F. J. R., Sapart C. J., van der Veen C., Ro ¨ckmann T., Gonzalez S. and Slomp C. P. (2016b) Rapid sediment accumulation results in high methane effluxes from coastal sediments. PLoS One 11, e0161609.
  33. Egger M., Rasigraf O., Sapart C. J., Jilbert T., Jetten M. S. M., Ro ¨ckmann T., van der Veen C., Ba ˆnda ˘N., Kartal B., Ettwig K. F. and Slomp C. P. (2015b) Iron-mediated anaerobic oxidation of methane in brackish coastal sediments. Environ. Sci. Technol. 49, 277-283.
  34. Ettwig K. F., Zhu B., Speth D., Keltjens J. T., Jetten M. S. M. and Kartal B. (2016) Archaea catalyze iron-dependent anaerobic oxidation of methane. Proc. Natl. Acad. Sci. 113, 12792-12796.
  35. Froelich P. N., Klinkhammer G. P., Bender M. L., Luedtke N. A., Heath G. R., Cullen D., Dauphin P., Hammond D., Hartman B. and Maynard V. (1979) Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis. Geochim. Cosmochim. Acta 43, 1075-1090.
  36. Happell J. J. D., Chanton J. P. J. and Showers W. W. J. (1995) Methane transfer across the water-air interface in stagnant wooded swamps of Florida: evaluation of mass-transfer coef- ficients and isotopic fractionation. Limnol. Oceanogr. 40, 290- 298.
  37. Henkel S., Mogollo ´n J. M., No ¨then K., Franke C., Bogus K., Robin E., Bahr A., Blumenberg M., Pape T., Seifert R., Ma ¨rz C., de Lange G. J. and Kasten S. (2012) Diagenetic barium cycling in Black Sea sediments -a case study for anoxic marine environments. Geochim. Cosmochim. Acta 88, 88-105.
  38. Hindmarsh A. C. (1983). ODEPACK, a systematized collection of ODE solvers. In: Stepleman R. S., et al. (Eds.), IMACS Transactions on Scientific Computation, vol. 1. North-Holland, Amsterdam, pp. 55-64.
  39. Hinrichs K. U., Hayes J. M., Sylva S. P., Brewer P. G. and DeLong E. F. (1999) Methane-consuming archaebacteria in marine sediments. Nature 398, 802-805.
  40. Hoehler T. M., Alperin M. J., Albert D. B. and Martens C. S. (1994) Field and laboratory studies of methane oxidation in an anoxic marine sediment: Evidence for a methanogen-sulfate reducer consortium. Global Biogeochem. Cycles 8, 451-463.
  41. Holler T., Wegener G., Niemann H., Ferdelman T. G., Boetius A., Kristiansen T. Z., Molina H., Pandey A., Werner J. K., Juluri K. R., Xu Y., Glenn D., Parang K. and Snyder S. H. (2012) Carbon and sulfur back flux during anaerobic microbial oxidation of methane and coupled sulfate reduction. Proc. Natl. Acad. Sci. 109, 21170-21170.
  42. Holmkvist L., Ferdelman T. G. and Jørgensen B. B. (2011) A cryptic sulfur cycle driven by iron in the methane zone of marine sediment (Aarhus Bay, Denmark). Geochim. Cos- mochim. Acta 75, 3581-3599.
  43. Holmkvist L., Kamyshny A., Bru ¨chert V., Ferdelman T. G. and Jørgensen B. B. (2014) Sulfidization of lacustrine glacial clay upon Holocene marine transgression (Arkona Basin, Baltic Sea). Geochim. Cosmochim. Acta 142, 75-94.
  44. Holmkvist L., Kamyshny A., Vogt C., Vamvakopoulos K., Ferdelman T. G. and Jørgensen B. B. (2011) Sulfate reduction below the sulfate-methane transition in Black Sea sediments. Deep Sea Res. Part I Oceanogr. Res. Pap. 58, 493-504.
  45. Hsu T.-W., Jiang W.-T. and Wang Y. (2014) Authigenesis of vivianite as influenced by methane-induced sulfidization in cold- seep sediments off southwestern Taiwan. J. Asian Earth Sci. 89, 88-97.
  46. Jilbert T. and Slomp C. P. (2013) Rapid high-amplitude variability in Baltic Sea hypoxia during the Holocene. Geology 41, 1183- 1186.
  47. Jørgensen B. B., Bo ¨ttcher M. E., Lu ¨schen H., Neretin L. N. and Volkov I. I. (2004) Anaerobic methane oxidation and a deep H2S sink generate isotopically heavy sulfides in Black Sea sediments. Geochim. Cosmochim. Acta 68, 2095-2118.
  48. Karnachuk O., Kurochkina S. and Tuovinen O. (2002) Growth of sulfate-reducing bacteria with solid-phase electron acceptors. Appl. Microbiol. Biotechnol. 58, 482-486.
  49. Kasten S., Freudenthal T., Gingele F. X. and Schulz H. D. (1998) Simultaneous formation of iron-rich layers at different redox boundaries in sediments of the Amazon deep-sea fan. Geochim. Cosmochim. Acta 62, 2253-2264.
  50. Kato S., Hashimoto K. and Watanabe K. (2012) Methanogenesis facilitated by electric syntrophy via (semi)conductive iron-oxide minerals. Environ. Microbiol. 14, 1646-1654.
  51. Knab N. J., Cragg B. A., Hornibrook E. R. C., Holmkvist L., Pancost R. D., Borowski C., Parkes R. J. and Jørgensen B. B. (2009) Regulation of anaerobic methane oxidation in sediments of the Black Sea. Biogeosciences, 1505-1518.
  52. Knittel K. and Boetius A. (2009) Anaerobic oxidation of methane: progress with an unknown process. Annu. Rev. Microbiol. 63, 311-334.
  53. Leloup J., Fossing H., Kohls K., Holmkvist L., Borowski C. and Jørgensen B. B. (2009) Sulfate-reducing bacteria in marine sediment (Aarhus Bay, Denmark): abundance and diversity related to geochemical zonation. Environ. Microbiol. 11, 1278- 1291.
  54. Leloup J., Loy A., Knab N. J., Borowski C., Wagner M. and Jørgensen B. B. (2007) Diversity and abundance of sulfate- reducing microorganisms in the sulfate and methane zones of a marine sediment, Black Sea. Environ. Microbiol. 9, 131-142.
  55. Lenz C., Jilbert T., Conley D. J. and Slomp C. P. (2015) Hypoxia- driven variations in iron and manganese shuttling in the Baltic Sea over the past 8 kyr. Geochem. Geophys. Geosyst. 16, 3754- 3766.
  56. Li H., Chang J., Liu P., Fu L., Ding D. and Lu Y. (2014) Direct interspecies electron transfer accelerates syntrophic oxidation of butyrate in paddy soil enrichments. Environ. Microbiol. 17, 1- 45.
  57. Liu D., Wang H., Dong H., Qiu X., Dong X. and Cravotta C. A. (2011) Mineral transformations associated with goethite reduc- tion by Methanosarcina barkeri. Chem. Geol. 288, 53-60.
  58. Lovley D. R. (1991) Dissimilatory Fe(III) and Mn(IV) reduction. Microbiol. Rev. 55, 259-287.
  59. Lovley D. R. and Phillips E. J. P. (1987) Competitive mechanisms for inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments. Appl. Environ. Microbiol. 53.
  60. Lovley D. R., Phillips E. J. P. and Lonergan D. J. (1989) Hydrogen and formate oxidation coupled to dissimilatory reduction of iron or manganese by Alteromonas putrefaciens. Appl. Environ. Microbiol. 55, 700-706.
  61. Mackin J. E. and Aller R. C. (1984) Ammonium adsorption in marine sediments. Limnol. Oceanogr. 29, 250-257.
  62. Martens C. S., Albert D. B. and Alperin M. J. (1999) Stable isotope tracing of anaerobic methane oxidation in the gassy sediments of Eckernforde Bay, German Baltic Sea. Am. J. Sci. 299, 589- 610. Ma ¨rz C., Hoffmann J., Bleil U., de Lange G. J. and Kasten S. (2008) Diagenetic changes of magnetic and geochemical signals by anaerobic methane oxidation in sediments of the Zambezi deep-sea fan (SW Indian Ocean). Mar. Geol. 255, 118-130.
  63. McGlynn S. E., Chadwick G. L., Kempes C. P. and Orphan V. J. (2015) Single cell activity reveals direct electron transfer in methanotrophic consortia. Nature 526, 531-535.
  64. Meyerdierks A., Kube M., Kostadinov I., Teeling H., Glo ¨ckner F. O., Reinhardt R. and Amann R. (2010) Metagenome and mRNA expression analyses of anaerobic methanotrophic archaea of the ANME-1 group. Environ. Microbiol. 12, 422- 439.
  65. Meysman F. J. R., Boudreau B. P. and Middelburg J. J. (2005) Modeling reactive transport in sediments subject to bioturba- tion and compaction. Geochim. Cosmochim. Acta 69, 3601- 3617.
  66. Middelburg J. J. (1991) Organic carbon, sulphur, and iron in recent semi-euxinic sediments of Kau Bay, Indonesia. Geochim. Cosmochim. Acta 55, 815-828.
  67. Milucka J., Ferdelman T. G., Polerecky L., Franzke D., Wegener G., Schmid M., Lieberwirth I., Wagner M., Widdel F. and Kuypers M. M. M. (2012) Zero-valent sulphur is a key intermediate in marine methane oxidation. Nature 491, 541- 546. Mogollo ´n J. M., Dale aW., Fossing H. and Regnier P. (2012) Timescales for the development of methanogenesis and free gas layers in recently-deposited sediments of Arkona Basin (Baltic Sea). Biogeosciences 9, 1915-1933.
  68. Moodley L., Middelburg J. J., Herman P. M. J., Soetaert K. and de Lange G. J. (2005) Oxygenation and organic-matter preserva- tion in marine sediments: direct experimental evidence from ancient organic carbon-rich deposits. Geology 33, 889.
  69. Moran J. J., Beal E. J., Vrentas J. M., Orphan V. J., Freeman K. H. and House C. H. (2008) Methyl sulfides as intermediates in the anaerobic oxidation of methane. Environ. Microbiol. 10, 162- 173.
  70. Myhre G., Schindell D., Bre ´on F. M., Collins W., Fuglestvedt J., Huang J., Koch D., Lamarque J. F., Lee D., Mendoza B., Nakajima T., Robock A., Stephens G., Takemura T. and Zhang H. (2013) Anthropogenic and natural radiative forcing. In Climate Change 2013: The physical science basis (eds. T. F. Stocker, D. Qin, G. K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
  71. Neretin L. N., Bo ¨ttcher M. E., Jørgensen B. B., Volkov I. I., Lu ¨schen H. and Hilgenfeldt K. (2004) Pyritization processes and greigite formation in the advancing sulfidization front in the Upper Pleistocene sediments of the Black Sea. Geochim. Cosmochim. Acta 68, 2081-2093.
  72. Niewo ¨hner C., Hensen C., Kasten S., Zabel M. and Schulz H. (1998) Deep sulfate reduction completely mediated by anaer- obic methane oxidation in sediments of the upwelling area off Namibia. Geochim. Cosmochim. Acta 62, 455-464.
  73. Oni O., Miyatake T., Kasten S., Richter-Heitmann T., Fischer D., Wagenknecht L., Kulkarni A., Blumers M., Shylin S. I., Ksenofontov V., Costa B. F. O., Klingelho ¨fer G. and Friedrich M. W. (2015) Distinct microbial populations are tightly linked to the profile of dissolved iron in the methanic sediments of the Helgoland mud area, North Sea. Front. Microbiol. 6, 1-15.
  74. Petzoldt L. R. (1983) Automatic selection of methods for solving stiff and nonstiff systems of ordinary differential equations. SIAM J. Sci. Stat. Comput. 4, 136-148.
  75. Postma D. and Jakobsen R. (1996) Redox zonation: Equilibrium constraints on the Fe(III)/SO4-reduction interface. Geochim. Cosmochim. Acta 60, 3169-3175.
  76. Poulton S. and Canfield D. (2005) Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates. Chem. Geol. 214, 209-221.
  77. Pyzik A. J. and Sommer S. E. (1981) Sedimentary iron monosul- fides: kinetics and mechanism of formation. Geochim. Cos- mochim. Acta 45, 687-698.
  78. Qu D., Ratering S. and Schnell S. (2004) Microbial reduction of weakly crystalline iron (III) oxides and suppression of methano- genesis in paddy soil. Bull. Environ. Contam. Toxicol. 72, 1172- 1181.
  79. Rayleigh J. W. S. (1896) Theoretical considerations respecting the separation of gases by diffusion and similar processes. Philos. Mag., 493-499.
  80. Reeburgh W. (2007) Oceanic methane biogeochemistry. Am. Chem. Soc. 107, 486-513.
  81. Reed D. C., Gustafsson B. G. and Slomp C. P. (2016) Shelf-to- basin iron shuttling enhances vivianite formation in deep Baltic Sea sediments. Earth Planet. Sci. Lett. 434, 241-251.
  82. Reed D. C., Slomp C. P. and Gustafsson B. G. (2011a) Sedimen- tary phosphorus dynamics and the evolution of bottom-water hypoxia: A coupled benthic-pelagic model of a coastal system. Limnol. Oceanogr. 56, 1075-1092.
  83. Reed D. C., Slomp C. P. and de Lange G. J. (2011b) A quantitative reconstruction of organic matter and nutrient diagenesis in Mediterranean Sea sediments over the Holocene. Geochim. Cosmochim. Acta 75, 5540-5558.
  84. Reiche M., Torburg G. and Ku ¨sel K. (2008) Competition of Fe(III) reduction and methanogenesis in an acidic fen. FEMS Micro- biol. Ecol. 65, 88-101.
  85. Rice A. L., Gotoh A. A., Ajie H. O. and Tyler S. C. (2001) High- precision continuous-flow measurement of d13C and dD of atmospheric CH 4 . Anal. Chem. 73, 4104-4110.
  86. Rickard D. and Luther, III, G. W. (1997) Kinetics of pyrite formation by the H2S oxidation of iron (II) monosulfide in aqueous solutions between 25 and 125°C: the mechanism. Geochim. Cosmochim. Acta 61, 135-147.
  87. Rickard D. and Luther, III, G. W. (2007) Chemistry of iron sulfides. Chem. Rev. 107, 514-562.
  88. Riedinger N., Formolo M. J., Lyons T. W., Henkel S., Beck A. and Kasten S. (2014) An inorganic geochemical argument for coupled anaerobic oxidation of methane and iron reduction in marine sediments. Geobiology 12, 172-181.
  89. Riedinger N., Kasten S., Gro ¨ger J., Franke C. and Pfeifer K. (2006) Active and buried authigenic barite fronts in sediments from the Eastern Cape Basin. Earth Planet. Sci. Lett. 241, 876-887.
  90. Riedinger N., Pfeifer K., Kasten S., Garming J. F. L., Vogt C. and Hensen C. (2005) Diagenetic alteration of magnetic signals by anaerobic oxidation of methane related to a change in sedimentation rate. Geochim. Cosmochim. Acta 69, 4117-4126.
  91. Rooze J., Egger M., Tsandev I. and Slomp C. P. (2016) Iron- dependent anaerobic oxidation of methane in coastal surface sediments: potential controls and impact. Limnol. Oceanogr. 61, S267-S282.
  92. Van Santvoort P. J. M., De Lange G. J., Thomson J., Colley S., Meysman F. J. R. and Slomp C. P. (2002) Oxidation and origin of organic matter in surficial Eastern Mediterranean hemi- pelagic sediments. Aquat. Geochem. 8, 153-175.
  93. Sapart C. J., van der Veen C., Vigano I., Brass M., van de Wal R. S. W., Bock M., Fischer H., Sowers T., Buizert C., Sperlich P., Blunier T., Behrens M., Schmitt J., Seth B. and Ro ¨ckmann T. () Simultaneous stable isotope analysis of methane and nitrous oxide on ice core samples. Atmos. Meas. Tech. 4, 2607-2618.
  94. Scheller S., Yu H., Chadwick G. L., McGlynn S. E. and Orphan V. J. (2016). Artificial electron acceptors decouple archaeal methane oxidation from sulfate reduction. Science 351(80-.), 703-707.
  95. Schippers A. and Jørgensen B. B. (2002) Biogeochemistry of pyrite and iron sulfide oxidation in marine sediments. Geochim. Cosmochim. Acta 66, 85-92.
  96. Segarra K. E. A., Comerford C., Slaughter J. and Joye S. B. (2013) Impact of electron acceptor availability on the anaerobic oxidation of methane in coastal freshwater and brackish wetland sediments. Geochim. Cosmochim. Acta 115, 15-30.
  97. Seifert R., Nauhaus K., Blumenberg M., Kru ¨ger M. and Michaelis W. (2006) Methane dynamics in a microbial community of the Black Sea traced by stable carbon isotopes in vitro. Org. Geochem. 37, 1411-1419.
  98. Sivan O., Adler M., Pearson A., Gelman F., Bar-Or I., John S. G. and Eckert W. (2011) Geochemical evidence for iron-mediated anaerobic oxidation of methane. Limnol. Oceanogr. 56, 1536- 1544.
  99. Sivan O., Antler G., Turchyn A. V., Marlow J. J. and Orphan V. J. (2014) Iron oxides stimulate sulfate-driven anaerobic methane oxidation in seeps. Proc. Natl. Acad. Sci. 111, 4139-4147.
  100. Sivan O., Shusta S. and Valentine D. L. (2016) Methanogens rapidly transition from methane production to iron reduction. Geobiology 14, 190-203.
  101. Slomp C. P., Mort H. P., Jilbert T., Reed D. C., Gustafsson B. G. and Wolthers M. (2013) Coupled dynamics of iron and phosphorus in sediments of an oligotrophic coastal basin and the impact of anaerobic oxidation of methane. PLoS One 8, e62386.
  102. Soetaert K. and Herman P. M. J. (2009) A Practical Guide to Ecological Modelling: Using R as a Simulation Platform. Springer.
  103. Soetaert K. and Meysman F. (2012) Reactive transport in aquatic ecosystems: rapid model prototyping in the open source software R. Environ. Model. Softw. 32, 49-60.
  104. Soetaert K., Petzoldt T. and Meysman F. J. R. (2010) marelac: Tools for Aquatic Sciences. R Package Version 2.1.3.
  105. Sohlenius G., Emeis K.-C., Andre ´n E., Andre ´n T. and Kohly A. (2001) Development of anoxia during the Holocene fresh- brackish water transition in the Baltic Sea. Mar. Geol. 177, 221- 242. Torres M. E., Brumsack H. J., Bohrmann G. and Emeis K. C. (1996) Barite fronts in continental margin sediments: a new look at barium remobilization in the zone of sulfate reduction and formation of heavy barites in diagenetic fronts. Chem. Geol. 127, 125-139.
  106. Torres M. E., Mix A. C. and Rugh W. D. (2005) Precise d13C analysis of dissolved inorganic carbon in natural waters using automated headspace sampling and continuous-flow mass spectrometry. Limnol. Oceanogr. Meth. 3, 349-360.
  107. Treude T., Krause S., Maltby J., Dale A. W., Coffin R. and Hamdan L. J. (2014) Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: implications for deep sulfur cycling. Geochim. Cosmochim. Acta 144, 217-237.
  108. Vargas M., Kashefi K., Blunt-Harris E. L. and Lovley D. R. (1998) Microbial evidence for Fe(III) reduction on early Earth. Nature 395, 65-67.
  109. Wallace P. J., Dickens G. R., Paull C. K. and Ussler, III, W. (2000) Effects of core retrieval and degassing on the carbon isotope composition of methane in gas hydrate-and free gas-bearing sediments from the Blake Ridge. Proc. Ocean Drill. Program. Sci. Results 164, 101-112.
  110. Wang Y. and Van Cappellen P. (1996) A multicomponent reactive transport model of early diagenesis : Application to redox cycling in coastal marine sediments. Geochim. Cosmochim. Acta 60, 2993-3014.
  111. Wankel S. D., Adams M. M., Johnston D. T., Hansel C. M., Joye S. B. and Girguis P. R. (2012) Anaerobic methane oxidation in metalliferous hydrothermal sediments: influence on carbon flux and decoupling from sulfate reduction. Environ. Microbiol. 14, 2726-2740.
  112. Wegener G., Krukenberg V., Riedel D., Tegetmeyer H. E. and Boetius A. (2015) Intercellular wiring enables electron transfer between methanotrophic archaea and bacteria. Nature 526, 587-590.
  113. Westrich J. T. and Berner R. A. (1984) The role of sedimentary organic matter in bacterial sulfate reduction: The G model tested. Limnol. Oceanogr. 29, 236-249.
  114. Whiticar M. J. (1999) Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane. Chem. Geol. 161, 291-314.
  115. Xia X. and Tang Y. (2012) Isotope fractionation of methane during natural gas flow with coupled diffusion and adsorption/ desorption. Geochim. Cosmochim. Acta 77, 489-503.
  116. Yoshinaga M. Y., Holler T., Goldhammer T., Wegener G., Pohlman J. W., Brunner B., Kuypers M. M. M., Hinrichs K. and Elvert M. (2014) Carbon isotope equilibration during sulphate-limited anaerobic oxidation of methane. Nat. Geosci. 7, 190-194.
  117. Zhou S., Xu J., Yang G. and Zhuang L. (2014) Methanogenesis affected by the co-occurrence of iron(III) oxides and humic substances. FEMS Microbiol. Ecol. 88, 107-120.
  118. Zhuang L., Xu J., Tang J. and Zhou S. (2015) Effect of ferrihydrite biomineralization on methanogenesis in an anaerobic incuba- tion from paddy soil. J. Geophys. Res. Biogeosci. 120, 876-886.
  119. Zille ´n L., Conley D. J., Andre ´n T., Andre ´n E. and Bjo ¨rck S. (2008) Past occurrences of hypoxia in the Baltic Sea and the role of climate variability, environmental change and human impact. Earth-Sci. Rev. 91, 77-92.
  120. Associate Editor: Orit Sivan

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    Dan Palcu

    Scientific Drilling

    The MagellanPlus workshop "BlackGate" addressed fundamental questions concerning the dynamic evolution of the Mediterranean-Black Sea (MBS) gateway and its palaeoenvironmental consequences. This gateway drives the Miocene-Quaternary circulation patterns in the Black Sea and governs its present status as the world's largest example of marine anoxia. The exchange history of the MBS gateway is poorly constrained because continuous Pliocene-Quaternary deposits are not exposed on land adjacent to the Black Sea or northern Aegean. Gateway exchange is controlled by climatic (glacio-eustatic-driven sea-level fluctuations) and tectonic processes in the catchment as well as tectonic propagation of the North Anatolian Fault Zone (NAFZ) in the gateway area itself. Changes in connectivity trigger dramatic palaeoenvironmental and biotic turnovers in both the Black Sea and Mediterranean domains. Drilling a Messinian to Holocene transect across the MBS gateway will recover high-amplitude records of continent-scale hydrological changes during glacial-interglacial cycles and allow us to reconstruct marine and freshwater fluxes, biological turnover events, deep biospheric Published by Copernicus Publications on behalf of the IODP and the ICDP. 94 W. Krijgsman et al.: Mediterranean-Black Sea gateway exchange processes, subsurface gradients in primary sedimentary properties, patterns and processes controlling anoxia, chemical perturbations and carbon cycling, growth and propagation of the NAFZ, the timing of land bridges for Africa and/or Asia-Europe mammal migration, and the presence or absence of water exchange during the Messinian salinity crisis. During thorough discussions at the workshop, three key sites were selected for potential drilling using a mission-specific platform (MSP): one on the Turkish margin of the Black Sea (Arkhangelsky Ridge, 400 m b.s.f., metres below the seafloor), one on the southern margin of the Sea of Marmara (Northİmrali Basin, 750 m b.s.f.), and one in the Aegean (North Aegean Trough, 650 m b.s.f.). All sites target Quaternary oxic-anoxic marl-sapropel cycles. Plans include recovery of Pliocene lacustrine sediments and mixed marinebrackish Miocene sediments from the Black Sea and the Aegean. MSP drilling is required because the JOIDES Resolution cannot pass under the Bosporus bridges. The wider goals are in line with the aims and scope of the International Ocean Discovery Program (IODP) "2050 Science Framework: Exploring Earth by Scientific Ocean Drilling" and relate specifically to the strategic objectives "Earth's climate system", "Tipping points in Earth's history", and "Natural hazards impacting society". Code and data availability. No codes or data sets were used in this article.

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