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Overview on seismic survey activities in the Southern Ocean

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Citation:
Breitzke, M. (2006): Overview on seismic survey activities in the Southern Ocean , International workshop "Impacts of seismic survey activities on whales and other marine biota", 6-7 Sept., Dessau, Germany. .
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Abstract:

The Southern Ocean is the body of water which encircles the Antarctic continent. It extends from 60°S latitude to the Antarctic coastline and encompasses 360° longitude. It covers an area of about 20 million km2, which are about 56 times the size of Germany and slightly more than twice the size of the United States. It mainly includes the Amundsen Sea, Bellingshausen Sea, Wedell Sea, Ross Sea and parts of the Scotia Sea and Drake Passage. The Southern Ocean is rather deep with 4000 - 5000 m water depth over most of is extent and only limited parts of shallow water. Most parts of the continental shelves are ice-covered.Based on the Antarctic Treaty System seismic survey activities in the Southern Ocean are confined to academic research. Due to the environmental conditions they only take place during the austral summer seasons. In order to allow a scientific exchange and provide an open access to all Antarctic multichannel seismic reflection data (MCS) for use in cooperative research projects the Antarctic Seismic Data Library System For Cooperative Research (SDLS) was created in April 1991 to function under the auspices of the Scientific Committee of Antarctic Research (SCAR). According to the regulations described in the SCAR Report No 9, January 2001, all digital MCS data has to be submitted to the SDLS within 4 years of collection, remain there under SDLS guidelines for 4 years and go to World Data Centres or equivalents for general dissemination 8 years after collection. Additionally, the navigation data of all MCS track lines should be made available via the SDLS almost immediately after the end of the cruises. Thus, the SDLS is not only a tool for scientific data exchange and access but is also a tool which provides an overview on all completed MCS survey activities, so that future track lines can be planned, duplication of lines can be avoided and acoustic impacts can be minimized.After a recent update finished 30 June, 2006 the SDLS presently contains data from 121 MCS cruises collected by 15 nations between 1976/77 and 2005/06. The total length of all profiles amounts to 305'111 km. Among the 15 nations USSR/Russia were most active and collected 70'160 km of MCS lines during 24 surveys, followed by Germany with 52'975 km during 16 surveys, Japan with 48'980 km during 21 surveys, Australia with 30'479 km during 5 surveys, Italy with 28'090 km during 11 surveys, USA with 18'780 km during 11 surveys and Norway with 12'771 km during 6 surveys. The contributions of the other 8 nations are less than 10'000 km/nation. Poland, China and New Zealand range at the lower end with only 1 cruise of 1'100, 2'015 and 3'400 km MCS survey line length.Enhanced seismic survey activities occurred during the seasons 1985/86 - 1987/88 with 11'235 - 19'104 profile km/season, from 1989/90 - 1991/92 with 16'623 - 22'281 profile km/season, from 1993/94 - 1996/97 with 10'114 - 14'411 profile km/season and from 2000/01 - 2001/02 with 19'826 - 21'223 profile km/season around the whole Antarctic Continent with a coastline of about 18'000 km length, which is about 30 times the distance between Hamburg and Munich and more than 4 times the distance between New York and San Francisco. Assuming an average survey velocity of 5 kn these enhanced activities are equivalent to 51 - 85 survey days/season between 1985/86 - 1987/88, 75 - 100 survey days/season between 1989/90 - 1991/92, 46 - 65 survey days/season during 1993/94 - 1996/97 and to 90 - 96 survey days/season between 2000/01 - 2001/02 in the whole Southern Ocean.A more detailed examination of the survey activities in five different areas surrounding the Antarctic Continent shows that the greatest portion of all MCS survey lines - 87'409 km totally - were collected around the Antarctic Peninsula and Marie Byrd Land, an area covering ~4.6 million km2 (~13 times the size of Germany or about half the size of the United States). Assuming a survey velocity of 5 kn and 30 seasons between 1976/77 and 2005/06 this is equivalent to an average of 13.1 survey days/season and 2'914 profile km/season. The second most seismic activities occurred in the Wedell Sea and Queen Maud Land with an average of 10.4 survey days/season and 2'322 profile km/season in an area of ~5.4 million km2 (~15 times the size of Germany and slightly more than half the size of the United States). In Wilkes Land (~1.9 million km2), an average of 1'683 profile km was collected during 7.6 days/season. In the Ross Sea (~1.2 million km2) the average profile length was 1'634 km and the average number of survey days/season 7.4. Lowest survey activities occurred in Prydz Bay and Enderby Land (~0.8 million km2) with an average of 1'617 profile km/season collected during 7.3 days/season.All of these MCS surveys were conducted as 2D seismic lines and had often the meaning of reconnaissance surveys. A comparison with marine seismic exploration surveys for example undertaken by the Norwegian Petroleum Department on the continental margins off Norway mainly as 3D- and to a lesser extent as 2D-surveys shows that between 1999 and 2005 the total length of survey lines varied between ~330'000 and ~750'000 km/year in an area which covers less than 2% of the area of the Antarctic Continent or the Southern Ocean.

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