Methane in shallow cold seeps at Mocha Island off central Chile

Jessen, Gerdhard L; Pantoja, Silvio; Gutiérrez, Marcelo A.; Quiñones, Renato A.; González, Rodrigo R.; Sellanes, Javier; Kellermann, Matthias Y.; Hinrichs, Kai‐Uwe

doi:10.1016/j.csr.2010.12.012

Cited by 26 publications

(18 citation statements)

References 33 publications

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“…The Central Chilean continental margin is known for widespread marine gas hydrates and gas-bearing sediments [e.g., Bangs et al, 1993;Grevemeyer et al, 2006] and for some locations, methane seeps at the seafloor have been reported [Sellanes et al, 2004;Coffin et al, 2007;Jessen et al, 2011;Scholz et al, 2013]. The best studied seep area is the Concepci on Methane Seep Area (CMSA in the following) at about 368S (Figure 1) where methane seepage has been proposed based on dredged fragments of chemosymbiotic clams and carbonate blocks [Sellanes et al, 2004], sediment pore water data [Scholz et al, 2013], and acoustic and visual observation of seep communities [Klaucke et al, 2012;Zapata-Hern andez et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile

Geersen

Scholz

Линке

et al. 2016

Geochem Geophys Geosyst

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Seafloor seepage of hydrocarbon-bearing fluids has been identified in a number of marine fore arcs. However, temporal variations in seep activity and the structural and tectonic parameters that control the seepage often remain poorly constrained. Subduction zone earthquakes, for example, are often discussed to trigger seafloor seepage but causal links that go beyond theoretical considerations have not yet been fully established. This is mainly due to the inaccessibility of offshore epicentral areas, the infrequent occurrence of large earthquakes, and challenges associated with offshore monitoring of seepage over large areas and sufficient time periods. Here we report visual, geochemical, geophysical, and modeling results and observations from the Concepcion Methane Seep Area (offshore Central Chile) located in the rupture area of the 2010 Mw. 8.8 Maule earthquake. High methane concentrations in the oceanic water column and a shallow subbottom depth of sulfate penetration indicate active methane seepage. The stable carbon isotope signature of the methane and hydrocarbon composition of the released gas indicate a mixture of shallow-sourced biogenic gas and a deeper sourced thermogenic component. Pristine fissures and fractures observed at the seafloor together with seismically imaged large faults in the marine fore arc may represent effective pathways for methane migration. Upper plate fault activity with hydraulic fracturing and dilation is in line with increased normal Coulomb stress during large plate-boundary earthquakes, as exemplarily modeled for the 2010 earthquake. On a global perspective our results point out the possible role of recurring large subduction zone earthquakes in driving hydrocarbon seepage from marine fore arcs over long timescales.

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Section: Introductionmentioning

confidence: 99%

Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile

Geersen

Scholz

Линке

et al. 2016

Geochem Geophys Geosyst

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“…Mocha Island is characterised by active seismicity and constitutes an emerged block uplifted during the Quaternary in the Arauco peninsula [37,38]. Further, Mocha Island is known for intertidal and subtidal gas seepage system [39,40] and deeper seeps at 1400 water depth [41], whose presence probably is related to gas hydrates dissociation. In this context, gas-phase estimates contribute to map and understand its role in fluid escapes supply.…”

mentioning

confidence: 99%

High Gas Hydrate and Free Gas Concentrations: An Explanation for Seeps Offshore South Mocha Island

et al. 2018

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Recent studies have reported cold seeps offshore of Mocha Island. Gas hydrate occurrences along the Chilean margin could explain seeps presence. Gas-phase (gas hydrate and free gas) and geothermal gradients were estimated analysing two seismic sections. Close to Mocha Island (up to 20 km) were detected high (up to 1900 m/s) and low (1260 m/s) velocities associated with high gas hydrate (up to 20% of total volume) and free gas (up to 1.1% of total volume) concentrations, respectively. A variable and high geothermal gradient (65-110 • C/km) was obtained. These results are related to high supply of deep fluids canalised by faults and fractures. Faraway from Mocha Island (>60 km), free gas concentrations decrease to 0.3% of total volume and low geothermal gradient (from 35 to 60 • C/km) are associated with low fluids supply. Finally, we propose gas hydrate dissociation processes as the main supply source for seeps in the vicinity of Mocha Island. These processes can be caused by: (a) active faults and seismic activity; and (b) warm fluid expulsion from deeper zones altering hydrate stability conditions. In both cases, gas hydrate dissociation could generate slope instability and landslides, as occurred in the past in this region and reported in the literature.Energies 2018, 11, 3062 2 of 13 close to 3000 km (from 33 • S until 56 • S). In the second case, some authors have modelled possible scenarios for gas hydrate dissociation in shallow water (from 150 to 600 m water depth) considering the increasing temperature due to the global warming and the consequent potential methane release into the atmosphere. They concluded that the gas hydrate dissociation processes are induced just by a slight increment of temperature [25][26][27][28][29][30][31]. In this context, gas hydrate estimates contribute to evaluate submarine geohazards, global warming contribution related to gas hydrate dissociation and the potential methane reservoir. Moreover, estimates of methane stored in marine sediments as gas hydrate and free gas phases can be used to model more realistic scenarios associated with gas hydrates dissociation and its effects as a greenhouse gas.Relationships between gas hydrates and cold seeps have been documented in active and passive margins [5,[31][32][33][34][35][36], in which chemosynthetic communities, authigenic carbonate nodules, enrichment stable isotopes in pore water, and faults and fractures, connected with BSR and detected in seismic profiles, can be related to gas hydrate presence.The present study adds new information regarding gas-phase concentrations of the southern Chilean margin by using seismic and theoretical velocity models (Figure 1). Mocha Island is characterised by active seismicity and constitutes an emerged block uplifted during the Quaternary in the Arauco peninsula [37,38]. Further, Mocha Island is known for intertidal and subtidal gas seepage system [39,40] and deeper seeps at 1400 water depth [41], whose presence probably is related to gas hydrates dissociation. In this context, gas-phase est...

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“…Estos sitios constituyen hábitats para las comunidades bentónicas, caracterizadas con altas dominancias ecológicas de invertebrados tales como: poliquetos, braquiópodos, escafópodos, crustáceos y particularmente conchas de bivalvos de las familias Vesicomyidae, Solemyidae y Lucinidae (Sellanes et al, 2004(Sellanes et al, , 2007(Sellanes et al, , 2008Quiroga y Levin, 2010). A la fecha, solo se ha documentado un sumidero de hidrocarburo en aguas someras de isla Mocha (38°20' S, 73°55' W), en el margen centro-sur de Chile Jessen et al, 2011). Sin embargo, en este sitio no se han desarrollado costras de carbonato autigénico, ya que en presencia de oxígeno, la oxidación aeróbica de metano origina la producción de H 2 CO 3, un ácido débil que genera disolución del carbonato (Levin, 2005).…”

Section: Ch 4 + So 4 2-→ Hco 3 -+ Hs -+ H 2 O (1)unclassified

“…Por lo anterior, su identificación en otras unidades neógenas de similares características y edad, con presencia de estructuras de deslizamiento, diques de arena o volcanes de barro, representan potenciales indicios de flujos de hidrocarburos desde el subsuelo marino. Esto debe ser corroborado mediante isotopía, con la determinación de los típicos valores negativos de δ 13 C en las conchas de lucinomas Jessen et al, 2011). El desarrollo o no de acumulaciones carbonatadas, dependerá de la profundidad y condiciones fisicoquímicas del medio al momento de las emisiones.…”

Section: Temprano a Mediounclassified

Finding of the first fossil seep in the emerged coast of Central Chile (33°56’ S). Characterization and implications.

Contardo-Berrios¹,

Mena-Hodges²,

Quiroga³

2017

andgeo

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Methane in shallow cold seeps at Mocha Island off central Chile

Cited by 26 publications

References 33 publications

Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile

Fault zone controlled seafloor methane seepage in the rupture area of the 2010 Maule earthquake, Central Chile

High Gas Hydrate and Free Gas Concentrations: An Explanation for Seeps Offshore South Mocha Island

Finding of the first fossil seep in the emerged coast of Central Chile (33°56’ S). Characterization and implications.

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