Alan Judd

John Lewis Partnership (United Kingdom)

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Martin Hovland

University of Bergen

Soledad García‐Gil

Universidade de Vigo

Jorge Iglesias

Universidade de Vigo

Ira Leifer

SRI International

Natalia Martínez‐Carreño

Instituto Español de Oceanografía

Briony Silburn

Centre for Environment, Fisheries and Aquaculture Science

Jason Wilson

Markus Diesing

Norwegian Geological Survey

Gordon Baron

Heriot-Watt University

Andrew Jones

University of Missouri

Cooperative Institutions

Universidade de Vigo

Geoscience Australia

Newcastle University

Aarhus University

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Universidade de Santiago de Compostela

Centre for Environment, Fisheries and Aquaculture Science

Max Planck Society

Max Planck Institute for Marine Microbiology

Plymouth Marine Laboratory

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Characterisation and preliminary quantification of the methane reservoir in a coastal sedimentary source: San Simón Bay, Ría de Vigo, NW Spain

Estuarine Coastal and Shelf Science (2010)

Soledad García‐Gil E. de Blas Natalia Martínez‐Carreño Jorge Iglesias R. Rial‐Otero

Marine transgression

10.1016/j.ecss.2010.10.038

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Citations (28)

Contributions to atmospheric methane by natural seepages on the U.K. continental shelf

Marine Geology (1997)

Alan Judd Gareth M. Davies Jason Wilson R. Holmes Gordon Baron

Seabed

Atmospheric methane

10.1016/s0025-3227(97)00067-4

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Citations (43)

The Croker Carbonate Slabs: extensive methane-derived authigenic carbonate in the Irish Sea—nature, origin, longevity and environmental significance

Geo-Marine Letters (2019)

Alan Judd Tamsyn Noble‐James Neil Golding Andrew Eggett Markus Diesing

Abstract The Croker Carbonate Slabs, in the UK sector of the Irish Sea, has shallow (70 to 100 m) water, strong (> 2 knot) tidal currents, coarse mobile surficial sediments and the most extensive methane-derived authigenic carbonate (MDAC) known in European waters. Multi-disciplinary studies (2004 to 2015) were commissioned specifically to document the benthic habitat, and have resulted in the designation of this site as a Marine Protected Area (MPA) under the European Commission’s Habitats Directive as an example of “ Submarine structures formed by leaking gases ”. However, this paper is focussed on the geoscience aspects of the site: the mineralogy and isotopic composition of the MDAC, its formation and age. It considers the implications of these findings with respect to the timing of the deglaciation of the area since the Last Glacial Maximum (LGM), and the environmental implications of the seepage of methane from the site over a period of at least 17,000 years. Carbon isotope ratios (δ 13 C − 34 to − 54‰) confirm that the carbonate minerals (high-Mg calcite and aragonite) result from the anaerobic oxidation of methane. Widespread shallow gas within post-glacial sediments is sourced from underlying coal-bearing Carboniferous strata. Geophysical (side-scan sonar and multi-beam echo sounder) and visual surveys show that the MDAC occurs as isolated lumps, continuous pavements, and cliffs < 6 m tall, which post-date the post-glacial sediments, but are in places covered by a veneer of coarse mobile surficial sediments. U-Th dates (17,000 ± 5500 to 4000 ± 200 BP) suggest continual MDAC formation since the last glacial maximum, and constrain the postglacial sea level rise in this part of the Irish Sea; the site must have been submarine before MDAC formation started, whether or not methane was escaping. Visual and acoustic evidence of gas seepage is limited, but methane concentrations in the water are high (< 21.4 nmol l −1 ) and suggest present-day export to the atmosphere. It is also implied that significant methane release to the atmosphere occurred immediately after the retreat of the ice that covered the site during the LGM until 21.9 to 20.7 ka BP.

Authigenic

Deglaciation

Dalradian

10.1007/s00367-019-00584-0

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Citations (20)

Climate and anthropogenic factors influencing an estuarine ecosystem from NW Iberia: new high resolution multiproxy analyses from San Simón Bay (Ría de Vigo)

Quaternary Science Reviews (2014)

Castor Muñoz Sobrino Iria García‐Moreiras Yoel Castro Natalia Martínez‐Carreño E. de Blas

Salt marsh

10.1016/j.quascirev.2014.03.021

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Citations (33)

Environmental change in theRía deVigo,NW Iberia, since the mid‐Holocene: new palaeoecological and seismic evidence

Boreas (2012)

Castor Muñoz Sobrino Soledad García‐Gil Jorge Iglesias Natalia Martínez‐Carreño Javier Ferreiro da Costa

Pollen analyses (pollen, dinocysts and others) were combined with high‐resolution seismic‐stratigraphy sequences to reconstruct environmental dynamics and regional sea‐level ( RSL ) changes in a ria in NW Iberia. The chronological framework was established using radiocarbon dating and pollen markers that are related to a number of historical events. Major intensifications of the regional upwelling regime occurred during predominant NAO positive stages, dated to c . 4600–4300, 3800–3600, 3200–2700 and 2600–2400 cal. a BP . The regional E arly H ighstand S ystem T ract spans from before 4500 to c. 3200 cal. a BP . During this period RSL was still rising, but several short episodes of higher terrestrial influence were detected between c. 4300–3800 and 3600–3200 cal. a BP . A readjustment occurred between 3200 and 2300 cal. a BP , including the first stage of relative sea‐level drop (2.8 ka event) dated to 3200–2800 cal. a BP , with the RSL recovering between 2800 and 2300 cal. a BP . The subsequent L ater H ighstand S ystem T ract, after 2300 cal. a BP , corresponds to a final period of rising sea level that caused the final inundation of S an S imón B ay. Since then, only minor changes in relative sea level can be postulated (e.g. towards the end of the R oman P eriod, in the M iddle A ges and during the L ittle I ce A ge). This new evidence is consistent with most of the available palaeoecological and historical information, but it provides a more detailed, near‐complete succession of simultaneous changes occurring in both the terrestrial and the marine ecosystems.

10.1111/j.1502-3885.2012.00255.x

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Citations (26)

Shallow gas and fluid migration in the northern Arafura Sea (offshore Northern Australia)

Marine and Petroleum Geology (2007)

Nadège Rollet Graham A. Logan Georgina Ryan Alan Judd Jennifer Totterdell

Shoal

Hydrocarbon exploration

Mud volcano

Seabed

Clathrate hydrate

10.1016/j.marpetgeo.2007.07.010

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Citations (22)

Gas seepage on an intertidal site: Torry Bay, Firth of Forth, Scotland

Continental Shelf Research (2002)

Alan Judd R. G. Sim P. F. Kingston J. McNally

Petroleum seep

Cold seep

Coal measures

10.1016/s0278-4343(02)00058-4

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Citations (39)

The biogeochemical cycling of methane in Ria de Vigo, NW Spain: Sediment processing and sea–air exchange

Journal of Marine Systems (2006)

Vassilis Kitidis Louise Tizzard Günther Uher Alan Judd Robert C. Upstill‐Goddard

Biogeochemical Cycle

Sediment–water interface

Sediment trap

10.1016/j.jmarsys.2006.03.022

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Citations (23)

Methane emission and consumption at a North Sea gas seep (Tommeliten area)

Biogeosciences (2005)

Helge Niemann Marcus Elvert Martin Hovland Beth N. Orcutt Alan Judd

Abstract. The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea (56°29.90' N, 2°59.80' E, Norwegian Block 1/9, 75 m water depth). Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments as well as carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the AOM zone. This zone is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses of this horizon give evidence that AOM is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw−1 biphythanes, 140 ng g-dw−1 fatty acid ai-C15:0), cell numbers (1.5×108 cells cm−3), AOM and SR rates (3 nmol cm−3 d−1) in the Tommeliten AOM zone are 2–3 orders of magnitude lower compared to AOM zones of highly active deep water cold seeps such as Hydrate Ridge or the Gulf of Mexico.

Authigenic

Cold seep

Marl

10.5194/bg-2-335-2005

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Citations (158)

The geological methane budget at Continental Margins and its influence on climate change

Geofluids (2002)

Alan Judd Martin Hovland Lyubomir Dimitrov Soledad García‐Gil V. Jukes

Abstract Geological methane, generated by microbial decay and the thermogenic breakdown of organic matter, migrates towards the surface (seabed) to be trapped in reservoirs, sequestered by gas hydrates or escape through natural gas seeps or mud volcanoes (via ebullition). The total annual geological contribution to the atmosphere is estimated as 16–40 Terragrammes (Tg) methane; much of this natural flux is ‘fossil’ in origin. Emissions are affected by surface conditions (particularly the extent of ice sheets and permafrost), eustatic sea‐level and ocean bottom‐water temperatures. However, the different reservoirs and pathways are affected in different ways. Consequently, geological sources provide both positive and negative feedback to global warming and global cooling. Gas hydrates are not the only geological contributors to feedback. It is suggested that, together, these geological sources and reservoirs influence the direction and speed of global climate change, and constrain the extremes of climate.

Seabed

Clathrate hydrate

Atmospheric methane

10.1046/j.1468-8123.2002.00027.x

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Citations (328)