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1998 Seabed Environmental Survey

A second major survey of the seafloor to the west of Britain was carried out during 1998. This followed on from the first AFEN survey in 1996 which covered the area to the west of Shetland licensed for oil and gas exploration before or during 1996 when the 16th licencing awards were made.

The 17th offshore licensing round was held in 1997 and included acreage in deep waters to the west of the Hebrides and to the north of Shetland. This area was mapped and sampled during the early summer of 1998 by the research vessels Charles Darwin and Colonel Templer, using the same techniques as in 1996.

The fieldwork part of the surveys was completed in June 1998 after two months at sea and some exciting findings were immediately apparent. The entire area was heavily influenced by the last Ice Age and iceberg ploughmarks are common in a broad band between 300 and 500m water depth.

Below this are numerous channels and gullies believed to be erosion features, and broad areas of sediment deposited from the melting icesheets and glaciers. The area to the south of the Wyville-Thomson Ridge is more complex and fascinating - there are giant sandwaves up to 30m high apparently made by strong water currents flowing from the northeast. In contrast, the predominant water flow today is weaker and of warm Atlantic water moving in the opposite direction, that is to the northeast. These sandwaves can be thought of as prehistoric features.


The most fascinating discovery made on the 1998 survey was an area on the south flank of the Wyville-Thomson Ridge covered with numerous small carbonate mounds (termed "Darwin Mounds") and an adjacent area of pockmarked seabed. Both features may have formed as a result of fluid escape from the seabed. Dense populations of xenophyophores (giant protozoans) have been photographed on the seafloor in this area - a species first found in the region in the last century but until these observations, believed to be rare.

Click on the image shown to the right to view the full picture.


Darwin Mounds

Darwin Mounds

TOBI 30 kHz sidescan sonar images showing an example of Darwin Mounds with tails found in the northern Rockall Trough.

Please see the map below for the location.

Darwin Mounds Location Map

Click on the image below to view the full map:

Darwin Mounds Map

The 1998 Survey report is:
Bett, B.J. RRS Charles Darwin Cruise 112c, 19th May - 24th June 1998. Atlantic Margin Environmental Survey: Seabed survey of deep water areas (17th Round Tranches) to the north and west of Scotland. Southampton Oceanography Centre Cruise Report No.25 171pp.

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