Abstract
The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates “from above”. As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years.
Similar content being viewed by others
References
Aloisi G, Pierre C, Rouchy J, Foucher J, Woodside J, MEDINAUT Scientific Party (2000) Methane-related authigenic carbonates of eastern Mediterranean Sea mud volcanoes and their possible relation to gas hydrate destabilization. Earth Planet Sci Lett 184:321–338
Aloisi G, Wallmann K, Bollwerk SM, Derkachev A, Bohrmann G, Suess E (2004) The effect of dissolved barium on biogeochemical processes at cold seeps. Geochim Cosmochim Acta 68:1735–1748
Andresen KJ, Huuse M (2011) ‘Bulls-eye’ pockmarks and polygonal faulting in the Lower Congo Basin: relative timing and implications for fluid expulsion during shallow burial. Mar Geol 279:111–127
Archer D, Buffett B, Brovkin V (2009) Ocean methane hydrate as a slow tipping point in the global carbon cycle. Proc Natl Acad Sci 106:20596–20601
Arndt S, Hetzel A, Brumsack H-J (2009) Evolution of organic matter degradation in Cretaceous black shales inferred from authigenic barite: a reaction-transport model. Geochim Cosmochim Acta 73:2000–2022
Bigalke NK, Rehder G, Gust G (2009) Methane hydrate dissolution rates in undersaturated seawater under controlled hydrodynamic forcing. Mar Chem 115:226–234
Boetius A, Ravenschlag K, Schubert CJ, Rickert D, Widdel F, Gieseke A, Amann R, Jørgensen BB, Witte U, Pfannkuche O (2000) A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407:623–626
Bohrmann G, Greinert J, Suess E, Torres M (1998) Authigenic carbonates from the Cascadia subduction zone and their relation to gas hydrate stability. Geology 26:647–650
Borowski WS, Paull CK, Ussler W III (1996) Marine pore-water sulfate profiles indicate in situ methane flux from underlying gas hydrate. Geology 24:655–658
Borowski WS, Paull CK, Ussler W III (1999) Global and local variations of interstitial sulfate gradients in deep-water, continental margin sediments: sensitivity to underlying methane and gas hydrates. Mar Geol 159:131–154
Boudreau BP (1997) Diagenetic models and their implementation – Modelling transport and reactions in aquatic sediments. Springer, Berlin
Brewer PG, Paull C, Peltzer ET, Ussler W, Rehder G, Friederich G (2002) Measurements of the fate of gas hydrates during transit through the ocean water column. Geophys Res Lett 29(22):2081. doi:10.1029/2002GL014727
Brice SE, Cochran MD, Pardo G, Edwards AD (1982) Tectonics and sedimentation of the South Atlantic rift sequence: Cabinda, Angola. In: Watkins JS, Drake CL (eds) Studies in continental margin geology. Am Assoc Petrol Geol Memoir 34:5–18
Castellini DG, Dickens GR, Snyder GT, Ruppel CD (2006) Barium cycling in shallow sediment above active mud volcanoes in the Gulf of Mexico. Chem Geol 226:1–30
Charlou JL, Donval JP, Fouquet Y, Ondréas H, Knoery J, Cochonat P, Levaché D, Poirier Y, Jean-Baptiste P, Fourré E, Chazallon B, The ZAIROV Leg 2 Scientific Party (2004) Physical and chemical characterization of gas hydrates and associated methane plumes in the Congo-Angola Basin. Chem Geol 205:405–425
Clifford AC (1986) African oil – past, present, and future. In: Halbouty MT (ed) Future petroleum provinces of the world. Am Assoc Petrol Geol Memoir 40:339–372
Dickens GR (2001a) The potential volume of oceanic methane hydrates with variable external conditions. Org Geochem 32:1179–1193
Dickens GR (2001b) Sulfate profiles and barium fronts in sediment on the Blake Ridge: present and past methane fluxes through a large gas hydrate reservoir. Geochim Cosmochim Acta 65:529–543
Dickens G (2003) Rethinking the global carbon cycle with a large, dynamic and microbially mediated gas hydrate capacitor. Earth Planet Sci Lett 213:169–183
Dickens G (2011) Down the rabbit hole: toward appropriate discussion of methane release from gas hydrate systems during the Paleocene-Eocene thermal maximum and other past hyperthermal events. Clim Past 7:831–846
Egorov AV, Crane K, Vogt PR, Rozhkov AN, Shirshov PP (1999) Gas hydrates that outcrop on the sea floor: stability models. Geo-Mar Lett 19(1/2):68–75. doi:10.1007/s003670050094
Emery KO, Uchupi E (1984) The geology of the Atlantic Ocean. Springer, New York
Gay A, Lopez M, Cochonat P, Levaché D, Sermondadaz G, Seranne M (2006a) Evidences of early to late fluid migration from an upper Miocene turbiditic channel revealed by 3D seismic coupled to geochemical sampling within seafloor pockmarks, Lower Congo Basin. Mar Petrol Geol 23:387–399
Gay A, Lopez M, Cochonat P, Seranne M, Levaché D, Sermondadaz G (2006b) Isolated seafloor pockmarks linked to BSRs, fluid chimneys, polygonal faults and stacked Oligocene-Miocene turbiditic palaeochannels in the Lower Congo Basin. Mar Geol 226:25–40
Gay A, Lopez M, Ondréas H, Charlou JL, Sermondadaz G, Cochonat P (2006c) Seafloor facies related to upward methane flux within a Giant Pockmark of the Lower Congo Basin. Mar Geol 226:81–95
Gay A, Lopez M, Berndt C, Seranne M (2007) Geological controls on focused fluid flow associated with seafloor seeps in the Lower Congo Basin. Mar Geol 244:68–92
Greinert J, Bohrmann G, Suess E (2001) Gas hydrate-associated carbonates and methane-venting at Hydrate Ridge: classification, distribution, and origin of authigenic lithologies. In: Paull CK, Dillon WP (eds) Natural gas hydrates: occurrence, distribution, and detection. Geophys Monogr 124:99–113
Haas A, Peckmann J, Elvert M, Sahling H, Bohrmann G (2010) Patterns of carbonate authigenesis at the Kouilou pockmarks on the Congo deep-sea fan. Mar Geol 268:129–136
Henderson GM, Bayon G, Pierre C, Caprais JC, Voisset M (2006) Constraints on the dynamics of gas hydrates in Niger Delta sediments from U/Th dating of cold-seep carbonates. Goldschmidt Conf Abstr A25. doi:10.1016/j.gca2006.06.494
Hoehler T, Alperin MJ, Albert DB, Martens C (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
Holtvoeth J, Wagner T, Horsfield B, Schubert CJ, Wand U (2001) Late-Quaternary supply of terrigenous organic matter to the Congo deep-sea fan (ODP site 1075): implications for equatorial African paleoclimate. Geo-Mar Lett 21(1):23–33. doi:10.1007/s003670100060
Holtvoeth J, Wagner T, Schubert CJ (2003) Organic matter in river-influenced continental margin sediments: the land-ocean and climate linkage at the Late Quaternary Congo fan (ODP Site 1075). Geochem Geophys Geosys 4:1109. doi:10.1029/2003GC000590
Hovland M, Judd AG (1988) Seabed pockmarks and seepage. Impact on geology, biology and the marine environment. Graham & Trotman, London
Iversen N, Jørgensen BB (1985) Anaerobic methane oxidation rates at the sulfate-methane transition in marine sediments from Kattegat and Skagerrak (Denmark). Limnol Oceanogr 30:944–955
Kvenvolden KA (1993) Gas hydrates: geological perspective and global change. Rev Geophys 31:173–187
Lapham L, Chanton JP, Chapman R, Martens CS (2010) Methane under-saturated fluids in deep-sea sediments: implications for gas hydrate stability and rates of dissolution. Earth Planet Sci Lett 298:275–285
Meister P, Gutjahr M, Frank M, Bernasconi SM, Vasconcelos C, McKenzie JA (2011) Dolomite formation within the methanogenic zone induced by tectonically driven fluids in the Peru accretionary prism. Geology 39:563–566
Nähr TH, Birgel D, Bohrmann G, MacDonald IR, Kasten S (2009) Biogeochemical controls on authigenic carbonate formation at the Chapopote “asphalt volcano”, Bay of Campeche. Chem Geol 266:390–402
Niewöhner C, Hensen C, Kasten S, Zabel M, Schulz HD (1998) Deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off Namibia. Geochim Cosmochim Acta 62:455–464
Nöthen K, Kasten S (2011) Reconstructing changes in seep activity by means of pore water and solid phase Sr/Ca and Mg/Ca ratios in pockmark sediments of the Northern Congo Fan. Mar Geol 287:1–13
Ondréas H, Olu K, Fouquet Y, Charlou JL, Gay A, Dennielou B, Donval JP, Fifis A, Nadalig T, Cochonat P, Cauquil E, Bourillet JF, Le Moigne M, Sibuet M (2005) ROV study of a giant pockmark on the Gabon continental margin. Geo-Mar Lett 25(5):281–292. doi:10.1007/s00367-005-0213-6
Orcutt BN, Boetius A, Lugo SK, MacDonald IR, Samarkin VA, Joye SB (2004) Life at the edge of methane ice: microbial cycling of carbon and sulfur in Gulf of Mexico gas hydrates. Chem Geol 205:239–251
Peckmann J, Thiel V (2004) Carbon cycling at ancient methane-seeps. Chem Geol 205:443–467
Peckmann J, Reimer A, Luth U, Luth C, Hansen BT, Heinicke C, Hoefs J, Reitner J (2001) Methane-derived carbonates and authigenic pyrite from the northwestern Black Sea. Mar Geol 177:129–150
Pierre C, Fouquet Y (2007) Authigenic carbonates from methane seeps of the Congo deep-sea fan. Geo-Mar Lett 27(2/4):249–257. doi:10.1007/s00367-007-0081-3
Reeburgh WS (1976) Methane consumption in Cariaco trench waters and sediments. Earth Planet Sci Lett 28:337–344
Rehder G, Kirby SH, Durham WB, Stern LA, Peltzer ET, Pinkston J, Brewer PG (2004) Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 100-m depth. Geochim Cosmochim Acta 68:285–292
Riedinger N, Kasten S, Gröger J, Franke C, Pfeifer K (2006) Active and buried authigenic barite fronts in sediments from the Eastern Cape Basin. Earth Planet Sci Lett 241:876–887
Ritger S, Carson B, Suess E (1987) Methane-derived authigenic carbonates formed by subduction-induced pore-water expulsion along the Oregon/Washington margin. Geol Soc Am Bull 98:147–156
Sahling H, Bohrmann G, Spiess V, Bialas J, Breitzke M, Ivanov M, Kasten S, Krastel S, Schneider R (2008) Pockmarks in the Northern Congo Fan area, SW Africa: complex seafloor features shaped by fluid flow. Mar Geol 249:206–225
Savoye B, Babonneau N, Dennielou B, Bez M (2009) Geological overview of the Angola-Congo margin, the Congo deep-sea fan and its submarine valleys. Deep-Sea Res I 56:2169–2182
Schneider RR, Price B, Müller PJ, Kroon D, Alexander I (1997) Monsoon related variations in Zaire (Congo) sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial Atlantic during the last 200,000 years. Paleoceanography 12:463–481
Snyder GT, Dickens GR, Castellini DG (2007a) Labile barite contents and dissolved barium concentrations on Blake Ridge: new perspectives on barium cycling above gas hydrate systems. J Geochem Explor 95:48–65
Snyder GT, Hiruta A, Matsumoto R, Dickens GR, Tomaru H, Takeuchi R, Komatsubara J, Ishida Y, Yu H (2007b) Pore water profiles and authigenic mineralization in shallow marine sediments above the methane-charged system on Umitaka Spur, Japan Sea. Deep-Sea Res II 54:1216–1239
Spieß V, cruise participants (2002) Report and preliminary results of METEOR-Cruise M 47/3, Libreville – Walvis Bay, 01.06. – 03.07.2000. Berichte Reports, Fachbereich Geowissenschaften, Universität Bremen, no 202
Suess E, Torres ME, Bohrmann G, Collier J, Greinert J, Linke P, Rehder G, Tréhu A, Wallmann K, Winckler G, Zuleger E (1999) Gas hydrate destabilization: enhanced dewatering, benthic material turnover and large methane plumes at the Cascadia margin. Earth Planet Sci Lett 170:1–15
Sultan N, Cochonat P, Foucher J-P, Mienert J (2004) Effect of gas hydrates melting on seafloor slope instability. Mar Geol 213:379–401
Torres ME, Brumsack HJ, Bohrmann G, Emeis KC (1996a) 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
Torres ME, Bohrmann G, Suess E (1996b) Authigenic barites and fluxes of barium associated with fluid seeps in the Peru subduction zone. Earth Planet Sci Lett 144:469–481
Torres M, McManus J, Hammond DE, de Angelis MA, Heeschen KU, Colbert SL, Tryon MD, Brown KM, Suess E (2002) Fluid and chemical fluxes in and out of sediments hosting methane hydrate deposits on Hydrate Ridge, OR, I: Hydrological provinces. Earth Planet Sci Lett 201:525–540
Treude T, Boetius A, Knittel K, Wallmann K, Jørgensen BB (2003) Anaerobic oxidation of methane above gas hydrates at Hydrate Ridge, NE Pacific Ocean. Mar Ecol Prog Ser 264:1–14
Uenzelmann-Neben G (1998) Neogene sedimentation history of the Congo Fan. Mar Petrol Geol 15:635–650
Uenzelmann-Neben G, Spieß V, Bleil U (1997) A seismic reconnaissance survey of the northern Congo Fan. Mar Geol 140:283–306
Wefer G, Berger WH, Richter C et al (1998) Proc ODP, initial reports, vol 175. Ocean Drilling Program, College Station
Acknowledgments
We thank the master and crew of RV Meteor during cruise M47/3. For technical assistance on board ship and in the home laboratory, we are indebted to Anja Reitz, Karsten Enneking, Silvana Pape, and Susanne Siemer. We thank Michael Schweizer for performing the solid-phase analyses, and Volker Thiel for numerous fruitful discussions. The manuscript benefitted from very constructive and insightful reviews by G. Dickens and one anonymous referee, as well as comments by the editors M.T. Delafontaine and B.W. Flemming. This research was funded by the Deutsche Forschungsgemeinschaft DFG (RV Meteor cruise M47/3). We acknowledge further financial support from the Helmholtz Association (Alfred Wegener Institute, Bremerhaven). The full set of pore-water and solid-phase data is available via the geological data network PANGAEA (http://www.pangaea.de).
Author information
Authors and Affiliations
Corresponding author
Additional information
Responsible guest editors: M. De Batist and O. Khlystov
Rights and permissions
About this article
Cite this article
Kasten, S., Nöthen, K., Hensen, C. et al. Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan. Geo-Mar Lett 32, 515–524 (2012). https://doi.org/10.1007/s00367-012-0288-9
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00367-012-0288-9