aba64100-c150-4de3-e044-0003ba6f30bd English dataset Mary Mowat British Geological Survey (BGS) +44 (0)131 667 1000 +44 (0)131 668 4140 offshoredata@bgs.ac.uk pointOfContact 2011-08-30 MEDIN Discovery Metadata Standard Version 2.3.5 urn:ogc:def:crs:EPSG::4326 OGP 2005 Strategic Environmental Assessment SEA6 Technical Report - The Distribution and extent of methane-derived authigenic carbonate (Irish Sea) 2005-03-01 publication BGS_SEA_92 British Geological Survey This report is a contribution to the Strategic Environmental Assessment (SEA6) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). Methane-derived authigenic carbonate (MDAC) is formed as a consequence of the anaerobic oxidation of methane by consortia of bacteria. MDAC develops as a rock-like concretion when a carbonate precipitate cements normal seabed sediment; the carbon of this carbonate is derived from methane. It occurs as crusts or slabs at the seabed, or as exposed lumps. The occurrence of MDAC is evidence of methane seepage, although the seepage is not necessarily going on at the present time. Large quantities of MDAC indicate that methane seepage has occurred over a prolonged period of time. 'Submarine structures formed by leaking gas' have been identified by the European Commission's Habitats Directive as habitats worthy of protection. The distribution of MDAC in UK waters is poorly known. This report summarises the available information relevant to MDAC in the SEA6 area, including data acquired by surveys specifically conducted in support of this SEA in 2004. Carbon isotope data for samples recovered in 2004 have confirmed that the cemented hard grounds from two of the areas studied, Texel 11 and Holden's Reef, are composed of MDAC. Paul Henni British Geological Survey (BGS) +44 (0)131 667 1000 Murchison House, West Mains Road Edinburgh EH9 3LA UK offshoredata@bgs.ac.uk custodian Department for Energy and Climate Change (DECC) +44 0300 060 4000 +44 (0) 1823 284077 Admiralty Way London SW1A 2HD UK enquiries@decc.gsi.gov.uk originator notPlanned Documents NDGO0001 Bathymetry and Elevation Concentration of alkanes in sediment samples Sediment acoustics Seismic reflection Side-scan sonar SeaDataNet Parameter Discovery Vocabulary 2011-03-25 revision Geology GEMET - INSPIRE themes, version 1.0 2008-06-01 publication crust sediment SeaVoX Vertical Co-ordinate Coverages 2008-06-01 publication The SEAs data were produced as part of the UK Department of Energy and Climate Change's Offshore Energy Strategic Environmental Assessment programme; Crown Copyright, all rights reserved. The DECC SEA must be acknowledged in any maps or publications that make use of the data. All the data files are freely available to the public. The Strategic Environmental Assessment (SEA) data portal provides free access to available data and reports which have been produced through the SEA process. The site is run and managed by BGS on behalf of the Department of Energy and Climate Change (DECC). Many files can be downloaded directly from this website. Those that are too large to download can be ordered via the website for postal delivery from BGS. BGS (NERC) has been contracted by DECC to publish SEA datasets on its behalf. All intellectual property rights (including , without limitation, copyrights, database rights and all other rights which subsist or may at any time in the future subsist in the Dataset(s)) in the Dataset(s) ('Intellectual Property Rights') are owned by DECC (formerly the Department of Trade and Industry, and the Department for Business, Enterprise and Regulatory Reform). BGS has been authorised by DECC to use SEA datasets for all purposes but on a 'not-for-profit basis'. BGS has been authorised by DECC to pass on SEA datasets to third parties so that they can use them for all purposes but on a 'not-for-profit' basis. intellectualPropertyRights 5 English environment geoscientificInformation oceans SeaVoX salt and fresh water body gazetteer 2006-01-01 revision Irish Sea -6 -4 51.7 55.3 2005-01-01 2005-01-01 http://www.offshore-sea.org.uk/site/index.php http://www.bgs.ac.uk/data/sea/home.html Strategic Environmental Assessment (SEA) data portal The Strategic Environmental Assessment (SEA) data portal provides free access to available data and reports which have been produced through the UK Department of Energy and Climate Change SEA process. The site is run and managed by BGS on behalf of the Department of Energy and Climate Change (DECC). Many files can be downloaded directly from this website. Those that are too large to download can be ordered via the website for postal delivery from BGS. download dataset The report was prepared by Dr A. G. Judd as part of the UK Department of Energy and Climate Change's Offshore Energy Strategic Environmental Assessment programme. There are no published reports of methane-derived authigenic carbonate (MDAC) in the SEA6 area, but carbon isotope data have confirmed that the cemented hard grounds of two areas studied for the SEA6 project, Texel 11, and Holden's Reef, are composed of MDAC. Geophysical surveys, sampling and photographic surveys of other parts of the SEA6 area have confirmed that indicators of gas seepage (seep plumes, and pockmarks) are present in several other areas, and that acoustic turbidity (shallow gas) is widespread. A specific objective of the SEA6 surveys was to investigate possible occurrences of MDAC in examples of a range of the geological contexts present in the SEA6 area. To that end 12 study areas were identified. Two surveys were undertaken during the period 24th August to 31st October 2004 geophysical surveys (S/V Meridian): single-beam echo sounder (SBES), multi-beam echo sounder (MBES), side-scan sonar (SSS), and chirp sub-bottom profiler (SBP); photography, seabed sediment sampling, and water sampling (S/V Kommandor Jack).