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Marine cold seeps and their manifestations: geological control, biogeochemical criteria and environmental conditions

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  • Seep characteristics at different geologic settings are the subject of this review primarily based on results of the Research Consortium SFB 574. Criteria are drawn from examples on the erosive convergent margin off Costa Rica, the accretionary margin off Chile supplemented by examples from the transform margin of the Golf of Cadiz and the Hikurangi margin off New Zealand. Others are from well-studied passive margins of the Black Sea, the Golf of Mexico, the eastern Mediterranean Sea and the South China Sea. Seeps at all settings transport water and dissolved compounds into the ocean by different forcing mechanism and from different depths of the submerged geosphere (10s of meters to 10s of km). The compounds sustain oasis-type ecosystems by providing bioactive reductants sulfide, methane and hydrogen. Hereby the interaction between fluid composition, flux rates and biota results in a diagnostic hydrocarbon-metazoan-microbe-carbonate association; currently well over 100 active sites are known. The single most important reaction is microbially mediated anaerobic oxidation of methane (AOM) with secondary reactions involving S-biogeochemistry and carbonate mineral precipitation. Seep fluids and their seafloor manifestations provide clues as to source depth, fluid sediment/rock interaction during ascent, lifetime and cyclicity of seepage events but less so on the magnitude of return flow. At erosive margins Cl-depleted and B-enriched fluids from clay dehydration provide criteria for source depth and temperature. The upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth. At accretionary margins fluid are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate; they are emitted through thrust faults. At highly sedimented margins organic-rich and evaporite-containing strata (when present) determine the final fluid composition, by emitting characteristically gas hydrate-derived methane, brine associated non-methane hydrocarbons or leached elements and their isotopes (Li/δ⁷Li; Ba) from host-sediments. Smectite-illite transformation and associated Cl-depletion from release of interlayer water is a pervasive process at these margins. Rare earth element pattern (REEs) in conjunction with redox-sensitive metals retained in seep carbonates may indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids; clear environmental characterization, though, currently remains inconclusive. More deeply-sourced fluids as in transform margins may be characterized by their ⁸⁷Sr/⁸⁶Sr ratios from interaction with oceanic crustal rocks below. Quantification of flow and reliable estimates of total volatile output from fore-arcs remain a challenge to seep research as does the role of the geologically derived methane in the global methane cycle.
  • Keywords: Global seeps, Active margin fluids, Passive margin seeps, Fore-arc fluids, Biota–carbonate association, Seep carbonates, Continental margin fluids
  • This article is a much expanded version of a review entitled: Marine cold seeps; Suess (2010) in: Handbook of Hydrocarbon and Lipid Microbiology, edited by Kenneth N. Timmis and published by Springer, Heidelberg. The editor and the publication staff of Springer graciously gave permission to build on this previously published material, including the use of several illustrations. This publication is Contribution No. 265 of the Sonderforschungsbereich 574 Volatiles and Fluids in Subduction Zones at Kiel University.
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  • Suess, E. 2014. Marine cold seeps and their manifestations: geological control, biogeo-chemical criteria and environmental conditions. Int J Earth Sci (Geol Rundsch) (2014) 103:1889–1916; DOI 10.1007/s00531-014-1010-0
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  • 103
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  • 7
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  • I wish to acknowledge the College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, for the Courtesy-Appointment extended to me and the associated use of online facilities.
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