Methane fluxes and carbonate deposits at a cold seep area of the Central Nile Deep Sea Fan, Eastern Mediterranean Sea

Römer, Miriam; Sahling, Heiko; Pape, Thomas; Ferreira, Christian dos Santos; Wenzhöfer, Frank; Boetius, Antje; Bohrmann, Gerhard

doi:10.1016/j.margeo.2013.10.011

Cited by 72 publications

(62 citation statements)

References 78 publications

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“…According to Table 2, the measured gas fluxes vary from 35 to 368 mLn⋅min −1 . These values are in the range of volumetric fluxes measured in the Central Nile Deep-Sea Fan in the Eastern Mediterranean Sea [76], the Kerch seep area in the northeastern Black Sea [79], and the convergent Makran continental margin [78]. However, these settings are located at much deeper depth than the Aquitaine Shelf.…”

Section: Local Methane Flux From the Nine Gas Streamsmentioning

confidence: 56%

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

et al. 2017

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During the scientific expedition GAZCOGNE2 at the Bay of Biscay nine gas seeps were sampled for the first time and their flux was measured using an in situ pressure-preservation sampler (PEGAZ, © IFREMER). Overall, three sites were investigated to determine the nature and the origin of the gases bubbling at the seafloor and forming acoustic plumes into the water column, as this was the question raised from the first geologic study of the area. This has guided our study and accordingly corresponds to the main purpose of the present article. Thus, the molecular and isotopic ( D and 13 C) analyses revealed that the gas seeps were primarily composed of methane. Both methane and ethane are of microbial origin, and the former has been generated by microbial reduction of carbon dioxide. Heavier hydrocarbons accounted for less than 0.06% mol of the total amount. Despite the microbial origin of methane, the samples exhibit subtle differences with respect to the 13 C CH 4 values, which varied between −72.7 and −66.1‰. It has been suggested that such a discrepancy was predominantly governed by the occurrence of anaerobic methane oxidation. The PEGAZ sampler also enabled us to estimate the local gas fluxes from the sampled streams. The resulting values are extremely heterogeneous between seeps, ranging from 35 to 368 mLn⋅min −1 . Assuming a steady discharge, the mean calculated methane emission for the nine seeps is of 38 kmol⋅yr −1 . Considering the extent of the seep area, this very local estimate suggests that the Aquitaine Shelf is a very appropriate place to study methane discharge and its fate on continental shelves.

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Section: Local Methane Flux From the Nine Gas Streamsmentioning

confidence: 56%

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

et al. 2017

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“…Geochemistry, Geophysics, Geosystems 10.1002/2017GC007166 as crusts of authigenic carbonate, to clast content (grain size) as well as the presence of gas bubbles or gas hydrate in shallow sediments (Ceramicola et al, 2018;Klaucke et al, 2006;Paull et al, 2015;R€ omer et al, 2014;Sahling et al, 2009;Volgin & Woodside, 1996). At Venere MV, authigenic carbonates occur at several cold seep sites along the periphery of the MV (Bohrmann et al, 2015) and are found to coincide with subcircular patches of very high backscatter intensity (Figure 3b).…”

Section: Discussionmentioning

confidence: 99%

Mud Volcanism in a Canyon: Morphodynamic Evolution of the Active Venere Mud Volcano and Its Interplay With Squillace Canyon, Central Mediterranean

Loher

Ceramicola

Wintersteller

et al. 2018

Geochem Geophys Geosyst

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Submarine mud volcanoes develop through the extrusion of methane‐rich fluids and sediments onto the seafloor. The morphology of a mud volcano can record its extrusive history and processes of erosion and deformation affecting it. The study of offshore mud volcano dynamics is limited because only few have been mapped at resolutions that reveal their detailed surface structures. More importantly, rates and volumes of extruded sediment and methane are poorly constrained. The 100 m high twin cones of Venere mud volcano are situated at ∼1,600 m water depth within Squillace Canyon along the Ionian Calabrian margin, Mediterranean Sea. Seafloor bathymetry and backscatter data obtained by a ship‐based system and an autonomous underwater vehicle (AUV) allow mapping of mudflow deposits of the mud volcano and bedforms in the surrounding canyon. Repeated surveying by AUV document active mud movement at the western summit in between 2014 and 2016. Through sediment coring and tephrochronology, ages of buried mudflow deposits are determined based on the sedimentation rate and the thickness of overlying hemipelagic sediments. An average extrusion rate of 27,000 m3/yr over the last ∼882 years is estimated. These results support a three‐stage evolutionary model of Venere mud volcano since ∼4,000 years ago. It includes the onset of quiescence at the eastern cone (after ∼2,200 years ago), erosive events in Squillace Canyon (prior to ∼882 years ago), and mudflows from the eastern cone (since ∼882 years). This study reveals new interactions between a mud volcano and a canyon in the deep sea.

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“…These organic-rich layers could originate from high OC accumulation during deglaciation. The anaerobic oxidation of methane by sulfate produces bicarbonate and induces the formation of authigenic minerals [Bohrmann et al, 1998;N€ othen and Kasten, 2011;R€ omer et al, 2014b]. These peats can be eroded and transported by glacio-fluvial processes and deposited offshore during deglaciation.…”

Section: Methane Sourcementioning

confidence: 99%

Carbon cycling fed by methane seepage at the shallow Cumberland Bay, South Georgia, sub‐Antarctic

Geprägs

Torres

Mau

et al. 2016

Geochem Geophys Geosyst

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Recent studies have suggested that the marine contribution of methane from shallow regions and melting marine‐terminating glaciers may have been underestimated. Here we report on methane sources and potential sinks associated with methane seeps in Cumberland Bay, South Georgia's largest fjord system. The average organic carbon content in the upper 8 m of the sediment is around 0.65 wt %; this observation combined with Parasound data suggest that the methane gas accumulations probably originate from peat‐bearing sediments currently located several tens of meters below the seafloor. Only one of our cores indicates upward advection; instead most of the methane is transported via diffusion. Sulfate and methane flux estimates indicate that a large fraction of methane is consumed by anaerobic oxidation of methane (AOM). Carbon cycling at the sulfate‐methane transition (SMT) results in a marked fractionation of the δ13C‐CH4 from an estimated source value of −65‰ to a value as low as −96‰ just below the SMT. Methane concentrations in sediments are high, especially close to the seepage sites (∼40 mM); however, concentrations in the water column are relatively low (max. 58 nM) and can be observed only close to the seafloor. Methane is trapped in the lowermost water mass; however, measured microbial oxidation rates reveal very low activity with an average turnover of 3.1 years. We therefore infer that methane must be transported out of the bay in the bottom water layer. A mean sea‐air flux of only 0.005 nM/m2 s confirms that almost no methane reaches the atmosphere.

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Methane fluxes and carbonate deposits at a cold seep area of the Central Nile Deep Sea Fan, Eastern Mediterranean Sea

Cited by 72 publications

References 78 publications

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

Mud Volcanism in a Canyon: Morphodynamic Evolution of the Active Venere Mud Volcano and Its Interplay With Squillace Canyon, Central Mediterranean

Carbon cycling fed by methane seepage at the shallow Cumberland Bay, South Georgia, sub‐Antarctic

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