Active mud volcanoes on the upper slope of the western Nile deep-sea fan—first results from the P362/2 cruise of R/V Poseidon

Feseker, Tomas; Brown, Kevin; Blanchet, Cécile; Scholz, Florian; Nuzzo, Marianne; Reitz, Anja; Schmidt, Mark; Hensen, Christian

doi:10.1007/s00367-010-0192-0

Cited by 32 publications

(31 citation statements)

References 42 publications

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“…This latter effect may be due to vertical upward movement of warm saline pore water. Based on the evidence, we believe that if similar warm water movement occurs at North Alex (and indeed, Feseker et al [2010] observe high surface temperatures at the center of the mud volcano), the fluid must be very fresh (in contrast to the pore water in the surrounding sediments), and/or it must contain significant quantities of free gas to produce the increased resistivities that we observe; in support of this conclusion, Feseker et al (2010) also show evidence of desalinization in the pore water from geochemical data. It is interesting to note that no increased apparent resistivities are observed for short offsets, as would be expected if the gas cap (only a few tens of meters beneath the seafloor) was highly saturated.…”

Section: Discussionsupporting

confidence: 83%

“…Kopf (2002) provides a good general review of the literature on mud volcanoes in the marine environment, whereas Dupre et al (2007), Hensen et al (2007), and Feseker et al (2009) describe previous work on mud volcanoes in the Mediterranean region. In 2007, the Helmholtz Centre for Ocean Research Kiel (GEOMAR), began a project to study the mud volcanoes in the West Nile Delta (WND); Feseker et al (2010) give an overview of some early results of the WND project, which are mainly geochemical and geothermometric in nature. In Feseker et al (2010), fluids rich in hydrocarbons and highly depleted of chloride were recovered at two mud volcanoes: Giza and North Alex.…”

Section: Introductionmentioning

confidence: 99%

“…In 2007, the Helmholtz Centre for Ocean Research Kiel (GEOMAR), began a project to study the mud volcanoes in the West Nile Delta (WND); Feseker et al (2010) give an overview of some early results of the WND project, which are mainly geochemical and geothermometric in nature. In Feseker et al (2010), fluids rich in hydrocarbons and highly depleted of chloride were recovered at two mud volcanoes: Giza and North Alex. Elevated temperature measurements (in some cases, as high as 70°C at North Alex, 6 m beneath the seafloor) indicate significant activity at both sites; indeed, venting was observed during the GEOMAR research cruises, although the time scale is unknown.…”

Section: Introductionmentioning

confidence: 99%

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Rapid resistivity imaging for marine controlled-source electromagnetic surveys with two transmitter polarizations: An application to the North Alex mud volcano, West Nile Delta

2015

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To image the internal resistivity structure of the North Alex mud volcano offshore Egypt, the marine electromagnetics group at the Helmholtz Centre for Ocean Research Kiel (GEOMAR) developed and conducted a novel transient marine controlled-source electromagnetic experiment. The system, which was specifically developed to image the mud volcano, is also generally suitable for surveys of other small seafloor targets, such as gas-hydrate reservoirs, fluid-flow features, and submarine massive-sulfide deposits. An electric bipole antenna is set down by a remotely operated vehicle on the seafloor sequentially in two perpendicular polarizations at each transmission station. Two orthogonal horizontal electric field components are recorded on the seabed by an array of independently deployed nodal receivers (RXs). With two transmitter polarizations, the unique acquisition geometry of the system provides a very rich data set. However, for this geometric setup, conventional marine electromagnetic interpretation schemes (such as normalized magnitude variation with offset plots) have been difficult to implement. We have developed a simple imaging technique, which can be used for a first-step mapping of seafloor apparent resistivity with the GEOMAR system. Images can be produced in just a few minutes on a regular laptop computer, and the robustness of the approach was demonstrated using two synthetic data sets from simple seafloor models. The method was then applied to the real data acquired at the North Alex mud volcano in 2008. Results found increased apparent sediment resistivities of up to 4 Ωm near the center of the mud volcano occurring at source-RX offsets greater than 500 m, which mapped to apparent depths of greater than 150 m. This may be caused by large quantities of free gas or freshwater in the sediment pore space.

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Section: Discussionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Rapid resistivity imaging for marine controlled-source electromagnetic surveys with two transmitter polarizations: An application to the North Alex mud volcano, West Nile Delta

2015

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“…While vents and seep organisms share carbon fixation pathways, vent and seep invertebrate assemblages exhibit distinct average Elevated temperatures associated with methane seepage have been reported previously (electronic supplemental material, table S7). Fluids in brine pools and mud volcanoes in the Gulf of Mexico [62], the SW Barents Sea [63] and the eastern Mediterranean Sea [64] all exhibit temperatures elevated above ambient, but the sediments are typically hypersaline, anoxic and/or physically disrupted, and are marked by an absence of metazoan fauna. Fluids advected at Extrovert Cliff (950 m) in Monterey Bay have temperatures up to 98C in contrast with an ambient 4.18C temperature, and elevated He concentrations and 3 He/ 4 He ratios associated with a deep aquifer and several fault zones [12,65].…”

Section: Resultsmentioning

confidence: 99%

A hydrothermal seep on the Costa Rica margin: middle ground in a continuum of reducing ecosystems

et al. 2012

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Upon their initial discovery, hydrothermal vents and methane seeps were considered to be related but distinct ecosystems, with different distributions, geomorphology, temperatures, geochemical properties and mostly different species. However, subsequently discovered vents and seep systems have blurred this distinction. Here, we report on a composite, hydrothermal seep ecosystem at a subducting seamount on the convergent Costa Rica margin that represents an intermediate between vent and seep ecosystems. Diffuse flow of shimmering, warm fluids with high methane concentrations supports a mixture of microbes, animal species, assemblages and trophic pathways with vent and seep affinities. Their coexistence reinforces the continuity of reducing environments and exemplifies a setting conducive to interactive evolution of vent and seep biota.

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“…• C at shallow depth of about 6 m were observed in 2008 (Feseker et al 2010) during research cruise 64PE298 (R/V PELAGIA). During this research cruise, geophysical investigations (seismics and CSEM) were carried out to further investigate the internal structure of the mud volcano.…”

Section: Geological Setting Of the North Alex Mud Volcanomentioning

confidence: 99%

The use of rotational invariants for the interpretation of marine CSEM data with a case study from the North Alex mud volcano, West Nile Delta

Hölz¹,

Swidinsky²,

Sommer³

et al. 2015

Geophysical Journal International

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S U M M A R YSubmarine mud volcanos at the seafloor are surface expressions of fluid flow systems within the seafloor. Since the electrical resistivity of the seafloor is mainly determined by the amount and characteristics of fluids contained within the sediment's pore space, electromagnetic methods offer a promising approach to gain insight into a mud volcano's internal resistivity structure. To investigate this structure, we conducted a controlled source electromagnetic experiment, which was novel in the sense that the source was deployed and operated with a remotely operated vehicle, which allowed for a flexible placement of the transmitter dipole with two polarization directions at each transmitter location. For the interpretation of the experiment, we have adapted the concept of rotational invariants from land-based electromagnetics to the marine case by considering the source normalized tensor of horizontal electric field components. We analyse the sensitivity of these rotational invariants in terms of 1-D models and measurement geometries and associated measurement errors, which resemble the experiment at the mud volcano. The analysis shows that any combination of rotational invariants has an improved parameter resolution as compared to the sensitivity of the pure radial or azimuthal component alone. For the data set, which was acquired at the 'North Alex' mud volcano, we interpret rotational invariants in terms of 1-D inversions on a common midpoint grid. The resulting resistivity models show a general increase of resistivities with depth. The most prominent feature in the stitched 1-D sections is a lens-shaped interface, which can similarly be found in a section from seismic reflection data. Beneath this interface bulk resistivities frequently fall in a range between 2.0 and 2.5 m towards the maximum penetration depths. We interpret the lens-shaped interface as the surface of a collapse structure, which was formed at the end of a phase of activity of an older mud volcano generation and subsequently refilled with new mud volcano sediments during a later stage of activity. Increased resistivities at depth cannot be explained by compaction alone, but instead require a combination of compaction and increased cementation of the older sediments, possibly in connection to trapped, cooled down mud volcano fluids, which have a depleted chlorinity. At shallow depths (≤50 m) bulk resistivities generally decrease and for locations around the mud volcano's centre 1-D models show bulk resistivities in a range between 0.5 and 0.7 m, which we interpret in terms of gas saturation levels by means of Archie's Law. After a detailed analysis of the material parameters contained in Archie's Law we derive saturation levels between 0 and 25 per cent, which is in accordance with observations of active degassing and a reflector with negative polarity in the seismics section just beneath the seafloor, which is indicative of free gas.

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Active mud volcanoes on the upper slope of the western Nile deep-sea fan—first results from the P362/2 cruise of R/V Poseidon

Cited by 32 publications

References 42 publications

Rapid resistivity imaging for marine controlled-source electromagnetic surveys with two transmitter polarizations: An application to the North Alex mud volcano, West Nile Delta

Rapid resistivity imaging for marine controlled-source electromagnetic surveys with two transmitter polarizations: An application to the North Alex mud volcano, West Nile Delta

A hydrothermal seep on the Costa Rica margin: middle ground in a continuum of reducing ecosystems

The use of rotational invariants for the interpretation of marine CSEM data with a case study from the North Alex mud volcano, West Nile Delta

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