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Life at Cold Seeps: a Synthesis of Biogeochemical and Ecological Data from Kazan Mud Volcano, Eastern Mediterranean Sea

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Life at Cold Seeps: a Synthesis of Biogeochemical and Ecological Data from Kazan Mud Volcano, Eastern Mediterranean Sea Chemical Geology 205 (2004) 367–390 www.elsevier.com/locate/chemgeo Life at cold seeps: a synthesis of biogeochemical and ecological data from Kazan mud volcano, eastern Mediterranean Sea Josef P. Wernea,*, Ralf R. Haeseb,1, Tiphaine Zitterc, Giovanni Aloisid,2, Ioanna Bouloubassie, Sander Heijsf, Aline Fiala-Me´dionig, Richard D. Pancosta,3, Jaap S. Sinninghe Damste´ a, Gert de Langed, Larry J. Forneyf,4, Jan C. Gottschalf, Jean-Paul Foucherh, Jean Masclei, John Woodsideb the MEDINAUT and MEDINETH Shipboard Scientific Parties5 a Department of Marine Biogeochemistry and Toxicology, Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, The Netherlands b Department of Geochemistry, Faculty of Earth Sciences, Utrecht University, Utrecht, The Netherlands c Department of Sedimentology and Marine Geology, Faculty of Earth and Life Sciences, Free University Amsterdam, Amsterdam, The Netherlands d Laboratoire d’Oce´anographie Dynamique et de Climatologie, Universite´ Pierre et Marie Curie, Paris, France e Laboratoire de Chimie et Biogeochimie Marines, Universite´ Pierre et Marie Curie, Paris, France f Department of Microbiology, Center for Ecological and Evolutionary Studies, University of Groningen, Haren, The Netherlands g Observatoire Oce´anologique, Universite´ Pierre et Marie Curie, Banyuls-sur-Mer, France h DRO/Environments Se´dimentaires, IFREMER, Brest, France i Ge´osciences Azur, Observatoire Oce´anologique de Villefranche, Villefranche-sur-Mer, France Received 4 October 2002; received in revised form 30 September 2003; accepted 23 December 2003 Abstract Recent field observations have identified the widespread occurrence of fluid seepage through the eastern Mediterranean Sea floor in association with mud volcanism or along deep faults. Gas hydrates and methane seeps are frequently found in cold seep areas and were anticipated targets of the MEDINAUT/MEDINETH initiatives. The study presented herein has utilized a multi- disciplinary approach incorporating observations and sampling of visually selected sites by the manned submersible Nautile and by ship-based sediment coring and geophysical surveys. The study focuses on the biogeochemical and ecological processes and conditions related to methane seepage, especially the anaerobic oxidation of methane (AOM), associated with ascending fluids on Kazan mud volcano in the eastern Mediterranean. Sampling of adjacent box cores for studies on the microbiology, biomarkers, pore water and solid phase geochemistry allowed us to integrate different biogeochemical data within a spatially * Corresponding author. Current address: Large Lakes Observatory and Department of Chemistry, University of Minnesota Duluth, 10 University Dr. 109 RLB, Duluth, MN 55812, USA. Tel.: +1-218-726-7435; fax: +1-218-726-6979. E-mail addresses: [email protected] (J.P. Werne), [email protected] (R.R. Haese). 1 Address as of October 2003: Geoscience Australia, Canberra. 2 Current address: Department of Marine Environmental Geology, GEOMAR, Kiel, Germany. 3 Current address: Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, UK. 4 Current address: Department of Biological Sciences, University of Idaho, Moscow, ID, USA. 5 S. Asjes, K. Bakker, M. Bakker, J.L. Charlou, J.P. Donval, R. Haanstra, P. Henry, C. Huguen, B. Jelsma, S. de Lint, M. van der Maarel, S. Muzet, G. Nobbe, H. Pelle, C. Pierre, W. Polman, L. de Senerpont, M. Sibuet. 0009-2541/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2003.12.031 368 J.P. Werne et al. / Chemical Geology 205 (2004) 367–390 highly heterogeneous system. Geophysical results clearly indicate the spatial heterogeneity of mud volcano environments. Results from pore water geochemistry and modeling efforts indicate that the rate of AOM is f6 mol mÀ2 yearÀ1, which is lower than at active seep sites associated with conditions of focused flow, but greater than diffusion-dominated sites. Furthermore, under the non-focused flow conditions at Kazan mud volcano advective flow velocities are of the order of a few centimeters per year and gas hydrate formation is predicted to occur at a sediment depth of about 2 m and below. The methane flux through these sediments supports a large and diverse community of micro- and macrobiota, as demonstrated by carbon isotopic measurements on bulk organic matter, authigenic carbonates, specific biomarker compounds, and macrofaunal tissues. Because the AOM community appears to be able to completely oxidize methane at the rate it is seeping through the sediments, ultimate sinks for methane in this environment are authigenic carbonates and biomass. Significant differences in organic geochemical data between this site and those of other cold seep environments, even within the eastern Mediterranean mud volcanoes, indicate that the microbiological communities carrying out AOM varies depending on specific conditions such as methane flux and salinity. D 2004 Elsevier B.V. All rights reserved. Keywords: Anaerobic oxidation of methane; Cold seep fauna; Gas hydrate; Mud volcano; Biogeochemistry; Microbiology 1. Introduction tidisciplinary investigations combined visual observa- tions from dives aboard the manned submersible R/V Methane cold seeps have become environments of Nautile (launched from the support vessel N/O Nadir) intensive study in recent years for several reasons. and geophysical/acoustic surveys with shore-based Among these are: (1) the potential for methane release sedimentological, (bio)geochemical and (micro)bio- from hydrates and the subsequent impact on climate logical investigations on seafloor sediment samples (Dickens et al., 1995), (2) slope destabilization associ- taken from the Nautile and via box core from the R/V ated with gas hydrate dissociation (Henriet and Mie- Professor Logachev (MEDINAUT/MEDINETH Ship- nert, 1998), (3) energy sources for chemosynthetically board Scientific Parties, 2000). based life (Sassen et al., 1993; Sibuet and Olu, 1998), One of the major objectives of the MEDINAUT/ and (4) as a potential energy resource (Hovland, 2000). MEDINETH expeditions was an in depth biogeo- Furthermore, the anaerobic oxidation of methane chemical and (micro)biological investigation of (AOM) has been identified in methane seep environ- AOM. It is now generally accepted that a microbial ments world-wide, and is believed to scavenge signif- consortium consisting at least of methane-oxidizing icant amounts of methane (Reeburgh et al., 1993) archaea and sulfate-reducing bacteria consumes sulfate which could otherwise be released to the atmosphere, and methane in a 1:1 molar ratio during AOM, potentially contributing to global warming (e.g., Dick- producing sulfide and DIC according to the general- ens et al., 1995). ized net reaction Mud volcanoes, which result from the extrusion of 2À À À fluid-rich mudflows (mud breccias), are often associ- SO4 þ CH4 ! HS þ HCO3 þ H2O ð1Þ ated with methane seepage, and, given the appropriate pressure and temperature conditions, with gas hydrates as proposed by Reeburgh (1976). While the consor- (Brown, 1990; Milkov, 2000). Mud volcanoes have tium hypothesis for net AOM has been proven through been identified in the eastern Mediterranean (Cita et al., a number of studies (Boetius et al., 2000; Hinrichs et 1981, 1989; Cronin et al., 1997), and active methane al., 1999; Orphan et al., 2001), the specific pathways seepage has been documented on these mud volcanoes of methane-derived carbon incorporation into micro- (Emeis et al., 1996; Limonov et al., 1996; Woodside et bial biomass remain debated (Valentine and Reeburgh, al., 1998). In 1998 and 1999, the joint French–Dutch 2000; Sørensen et al., 2001). Furthermore, the specific MEDINAUT and the Dutch MEDINETH expeditions organisms remain unknown and uncultured, though were made to investigate eastern Mediterranean mud significant advances have been made in narrowing volcanoes and their associated cold seeps. These mul- down the organisms based in large part on phyloge- J.P. Werne et al. / Chemical Geology 205 (2004) 367–390 369 netic studies (Hinrichs et al., 1999; Boetius et al., bers of the MEDINAUT and MEDINETH expeditions. 2000; Orphan et al., 2001; Aloisi et al., 2002). This The focus is on studies of methane cold-seeps on paper is a synthesis of the geophysical, (bio)geochem- Kazan mud volcano, located in the Anaximander ical and (micro)biological studies carried out by mem- Mountains area (Fig. 1). Fig. 1. (A) Eastern Mediterranean Sea geodynamic map, with location of the main features cited in the text and of the mud diapiric fields within the Mediterranean ridge (triangles)—(1) Prometheus, (2) Pan di Zucchero, (3) Prometheus 2, (4) Olimpi, (5) United Nation. (B) Multibeam bathymetry map of the Anaximander Mountains and location of mud volcanoes (stars). 370 J.P. Werne et al. / Chemical Geology 205 (2004) 367–390 2. Geologic setting and regional tectonics: Mediterranean Sea Ryan et al., 1973) beneath the formation of the cold seep environment Anaximander Mountains. The gravity signature (Woodside, 1977; Woodside et al., 1997), lithological Eastern Mediterranean tectonics record the initial facies (Woodside et al., 1997), and surface deformation stages of collision between Africa and Europe, from (Zitter et al., 2003) vary between the eastern and incipient stages south of Crete to more advanced stages western Anaximander Mountains regions, clearly indi- south of Cyprus (and eastwards into the Zagros area cating differences in the geology of the two regions. where continental
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