High-resolution seismic studies of gas hydrates west of Svalbard

Posewang, Jörg; Mienert, Jürgen

doi:10.1007/s003670050102

Cited by 43 publications

(39 citation statements)

References 7 publications

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“…Generally, onshore seismic data within the Van Mijenfjorden is characterised by strong amplitude reverberations, most likely due to shortwavelength water column multiples on a glacial compacted seafloor (Figures 2a and b). Noise is further expected from strong side-reflections within the fjord and peg-leg type travelpaths within the sedimentary section (Posewang and Mienert, 1999). Along profile 9 signal enhancement by predictive deconvolution of ocean bottom seismometer (OBS)-data was performed.…”

Section: Seismic Refraction Data -Processing and Characteristicsmentioning

confidence: 99%

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

Ritzmann¹,

Jokat

Mjelde³

et al. 2002

Marine Geophysical Researches

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The Alfred Wegener Institute of Polar and Marine Research, the University of Bergen and Hokkaido University acquired new seismic refraction data along a transect from the Knipovich Ridge to the inner Van Mijenfjorden in southern Svalbard. A close spacing of on-and offshore receivers and a dense marine shot pattern provide the data for a high resolution p-wave velocity model for geological interpretation. Additional Zone from more distant sources, or originate in the magmatic interaction between the northern Knipovich Ridge and the neighbouring young rifted crust. Oceanic crust each side of the Knipovich Ridge is thin (∼3.5 km) and is characterised by the absence of oceanic layer 3 (3.5/4.1 to 4.7 km s −1 ). The oceanic section exhibits zones of very thin crust (∼1 km) that are interpreted as fracture zones. Beneath these we observed decreased mantle velocities (∼7.3 km s −1 ) indicating probable serpentinization of peridotites along these fracture zones. Thickness variations further provide information about the segmentation and magma supply along the northern Knipovich Ridge.

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Section: Seismic Refraction Data -Processing and Characteristicsmentioning

confidence: 99%

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

Ritzmann¹,

Jokat

Mjelde³

et al. 2002

Marine Geophysical Researches

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“…Of these, only two core sites are reported from a terrestrial Arctic gas hydrate occurrence Collett 1999, Mt. Elbert Science Team 2007) and one from an Arctic marine gas hydrate occurrence from west of Svalbard (Posewang and Mienert 1999). While significantly more field research has been undertaken since the compilation by Kvenvolden and Lorenson (2001), clearly any global estimate requires significant extension of a limited data set.…”

Section: Terrestrial and Marine Gas Hydratesmentioning

confidence: 99%

Sensitivity of the carbon cycle in the Arctic to climate change

McGuire

Anderson

Christensen

et al. 2009

Ecological Monographs

902

784

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Abstract. The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO 2 and CH 4 . Studies suggest that the Arctic has been a sink for atmospheric CO 2 of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH 4 to the atmosphere (between 32 and 112 Tg CH 4 /yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts.

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“…Predictions from these methods were calibrated against published experimental and closely-controlled field data and the results of laboratory experiments by partners in the consortium (Priest et al, 2005a;Priest et al, 2005b;Chand et al, 2006). The project investigated three separate sites where at one, NW Svalbard, a clear and near-continuous BSR was present (Posewang and Mienert, 1999), at another, SW Svalbard, the presence of hydrate was suspected from velocity anomalies near to the predicted base of the hydrate stability zone, although a prominent BSR was not present , and at the third, Storegga, a BSR was discontinuously present (Bünz et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Estimation of gas hydrate concentration from multi-component seismic data at sites on the continental margins of NW Svalbard and the Storegga region of Norway

Westbrook

Chand

Rossi

et al. 2008

Marine and Petroleum Geology

120

135

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High-resolution seismic experiments, employing arrays of closely spaced, four-component ocean-bottom seismic recorders, were conducted at a site off western Svalbard and a site on the northern margin of the Storegga slide, off Norway to investigate how well seismic data can be used to determine the concentration of methane hydrate beneath the seabed. Data from P-waves and from S-waves generated by P-S conversion on reflection were inverted for P-and S-wave velocity (Vp and Vs), using 3D travel-time tomography, 2D ray-tracing inversion and 1D waveform inversion. At the NW Svalbard site, positive Vp anomalies above a sea-bottomsimulating reflector (BSR) indicate the presence of gas hydrate. A zone containing free gas up to 150-m thick, lying immediately beneath the BSR, is indicated by a large reduction in Vp without significant reduction in Vs. At the Storegga site, the lateral and vertical variation in Vp and Vs and the variation in amplitude and polarity of reflectors indicate a heterogeneous distribution of hydrate that is related to a stratigraphically mediated distribution of free gas beneath the BSR. Derivation of hydrate content from Vp and Vs was evaluated, using different models for how hydrate affects the seismic properties of the sediment host and different approaches for estimating the background velocity of the sediment host. The error in the average Vp of an interval of 20-m thickness is about 2.5%, at 95% confidence, and yields a resolution of hydrate concentration of about 3%, if hydrate forms a connected framework, or about 7%, if it is both pore-filling and framework-forming. At NW Svalbard, in a zone about 90-m thick above the BSR, a Biot-theory-based method predicts hydrate concentrations of up to 11% of pore space, and an effective-medium-based method predicts concentrations of up to 6%, if hydrate forms a connected framework, or 12%, if hydrate is both pore-filling and frameworkforming. At Storegga, hydrate concentrations of up to 10% or 20% were predicted, depending on the hydrate model, in a zone about 120-m thick above a BSR. With seismic techniques alone, we can only estimate with any confidence the average hydrate content of broad intervals containing more than one layer, not only because of the uncertainty in the layer-by-layer variation in lithology, but also because of the negative correlation in the errors of estimation of velocity between adjacent layers. In this investigation, an interval of about 20-m thickness (equivalent to between 2 and 5 layers in the model used for waveform inversion) was the smallest within which one could sensibly estimate the hydrate content. If lithological layering much thinner than 20-m thickness controls hydrate content, then hydrate concentrations within layers could significantly exceed or fall below the average values derived from seismic data.

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High-resolution seismic studies of gas hydrates west of Svalbard

Cited by 43 publications

References 7 publications

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

Sensitivity of the carbon cycle in the Arctic to climate change

Estimation of gas hydrate concentration from multi-component seismic data at sites on the continental margins of NW Svalbard and the Storegga region of Norway

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