Distribution and classification of pockmarks on the seabed around western Scotland

Audsley, Allan; Bradwell, Tom; Howe, John; Baxter, John M.

doi:10.1080/17445647.2019.1676320

Cited by 12 publications

(19 citation statements)

References 34 publications

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“…Enhanced OC degradation has been widely observed within estuaries and coastal mud deposits, which are often described as "factories for OC burn off" due to the rate at which fresh OC is remineralized (Aller and Blair 2006;Yao et al, 2014;Zhao et al, 2018). The enhanced degradation of buried OC in these environments may also explain the abundance of gas release features (pockmarks) on the seabed in areas such as the Minch (Audsley et al, 2019). The BGS Quaternary sediment thickness map of the UK EEZ indicates that sediments over much of the UK EEZ extend beyond 50 m in depth.…”

Section: United Kingdom's Exclusive Economic Zone Sedimentary C Stockmentioning

confidence: 99%

Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone

Smeaton¹,

Hunt²,

Turrell³

et al. 2021

Front. Earth Sci.

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Continental shelf sediments are recognized as long-term stores of globally significant quantities of carbon (C) and potentially provide an important, yet largely overlooked climate regulation service via the Earth’s C cycle. Current understanding of the spatial distribution of sedimentary C across continental shelves remains poor, inhibiting the targeted management and potential inclusion of these globally significant C stores into national C budgets. Further understanding of the spatial heterogeneity of continental shelf sediments and associated C provides a foundation to quantify the organic carbon (OC) stock and better understand the role that marine sediments play in regulating the global climate and the potential for CO2 to be released through anthropogenic disturbance of these C stores. Utilizing a spectrum of available marine data, we have created bespoke sediment maps that quantify the surficial (top 10 cm) OC stock and highlight significant spatial heterogeneity in the distribution of sediments and their associated C content across the United Kingdom’s Exclusive Economic Zone (EEZ). The surficial sediments within the UK EEZ are estimated to store 524 ± 68 Mt of organic carbon (OC) and 2,582 ± 168 Mt of inorganic carbon (IC). The spatial mapping of this C highlights well-defined OC accumulation hotspots in fjords, estuaries and coastal muds, while large accumulations of IC are found in the tidally swept areas around Orkney, Shetland and the South West of England. Within the well-defined OC hotspots, muddy sediments store the greatest quantity of OC; the muds offer potentially valuable opportunities for targeted future management and protection of sedimentary C stores within the UK EEZ. In the future, if areas of the seafloor were to be managed to include the protection of these valuable sedimentary C resources, we recommend an initial focus on hotspots of high sedimentary OC density.

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Section: United Kingdom's Exclusive Economic Zone Sedimentary C Stockmentioning

confidence: 99%

Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone

Smeaton¹,

Hunt²,

Turrell³

et al. 2021

Front. Earth Sci.

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“…This is supported by research into the carbon signature of fjordic and offshore/shelf sediments, where the majority of organic carbon is stored within fjordic systems; however, localised hot-spots of organic and inorganic carbon can also be found in sediments of the wider continental shelf [27]. Regional mapping of pockmarks in Scottish west-coast waters has suggested a link between pockmark morphology, hydrographic setting and the activity history of pockmarks [18]. The authors have already mapped pockmarks within Loch Linnhe, part of a wider mapping initiative, and inferred the presence of widespread seabed gas/fluid escape (of unknown age).…”

Section: Introductionmentioning

confidence: 92%

“…An ESRI shapefile containing the position of seismic lines and fixes was obtained from the British Geological Survey (BGS) Offshore GeoIndex (https://www.bgs.ac.uk/mapviewers/geoindex-offshore (accessed on 29 January 2019)). Location data for each pockmark mapped within Loch Linnhe were taken from our existing published dataset [18]. The mapping process used the BGS seabed-mapping toolbox [35].…”

Section: Sub-seabed Geophysical Datamentioning

confidence: 99%

“…Regions of acoustic turbidity are often found to be near pockmarks, where gas has vented into the water column during pockmark formation/activity. Pockmark 2 shown in Figure 4 Line A was identified and described as a 'deep' pockmark [18]; that is a statistically deeper-than-average pockmark depth (based on depth/area ratio) across the studied sites around western Scotland. The L1 reflector is not present within the centre of this pockmark.…”

Section: Seismic Interpretationmentioning

confidence: 99%

“…Seabed pockmarks are relatively widespread across the continental shelf around Scotland, occurring mainly in the North Sea sector, discovered during oil and gas surveys [11,15,16]. More recently, pockmarks have also been discovered further inshore within the fjords and fjord approaches of western Scotland [17,18], similar in size and bathymetric setting to those identified in the western fjords of Arctic Svalbard [19][20][21]. These fjordic environments are shown to be effective stores of organic carbon [22,23].…”

Section: Introductionmentioning

confidence: 99%

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Spatial Relationships between Pockmarks and Sub-Seabed Gas in Fjordic Settings: Evidence from Loch Linnhe, West Scotland

et al. 2021

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Sub-seabed gas is commonly associated with seabed depressions known as pockmarks—the main venting sites for hydrocarbon gases to enter the water column. Sub-seabed gas accumulations are characterized by acoustically turbid or opaque zones in seismic reflection profiles, taking the form of gas blankets, curtains or plumes. How the migration of sub-seabed gas relates to the origin and distribution of pockmarks in nearshore and fjordic settings is not well understood. Using marine geophysical data from Loch Linnhe, a Scottish fjord, we show that shallow sub-seabed gas occurs predominantly within glaciomarine facies either as widespread blankets in basins or as isolated pockets. We use geospatial ‘hot-spot’ analysis conducted in ArcGIS to identify clusters of pockmarks and acoustic (sub-seabed) profile interpretation to identify the depth to gas front across the fjord. By combining these analyses, we find that the gas below most pockmarks in Loch Linnhe is between 1.4 m and 20 m deep. We anticipate that this work will help to understand the fate and mobility of sedimentary carbon in fjordic (marine) settings and advise offshore industry on the potential hazards posed by pockmarked seafloor regions even in nearshore settings.

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Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

Lefebvre

Düring

et al. 2023

Earth Surf Processes Landf

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In deep‐marine environments, the inception of channels can be induced by the interaction between bottom currents and rough topography. However, it is still unclear under which conditions such features can form and what happens in the earliest phase of channel development. In this study, based on the morphological, sedimentary and oceanographic settings of a pockmark field in the NW South China Sea, we reveal the process of channel inception through the erosion of pockmarks by bottom currents. Using numerical simulations, we show that an appropriate current velocity can induce the erosion of pockmark trains in cohesive sediments, leading to the coalescence of discrete pockmarks and the formation of a channel with a rough thalweg. The interaction of bottom currents with the pockmarks induces a significant erosion along the pockmarks axis. Bottom‐current erosion is strongest at the downstream edges of pockmarks, where the horizontal velocity reaches a maximum and an upwelling forms. Erosion increases as the distance between pockmarks reduces. In our simulation results, a channel is only formed by the coalescence of pockmarks if the distance between pockmarks is <6 times the diameter of the pockmark. This study provides evidence of the formation of channels by bottom currents, which helps reconstruct palaeoceanographic conditions based on sediment architecture. It also shows the complex hydrodynamics at these structures that strongly control sedimentary processes and may affect distribution of benthic ecosystems in marine environments.

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Distribution and classification of pockmarks on the seabed around western Scotland

Cited by 12 publications

References 34 publications

Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone

Marine Sedimentary Carbon Stocks of the United Kingdom’s Exclusive Economic Zone

Spatial Relationships between Pockmarks and Sub-Seabed Gas in Fjordic Settings: Evidence from Loch Linnhe, West Scotland

Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

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