Disputas: Karen Elizabeth Webb

Prøveforelesning

Bedømmelseskomité

D. Sc David J. Wildish, Fisheries & Oceans Canada, St. Andrews, Canada
Ph.D Sabine Cochrane, Akvaplan-niva, Tromsø
Førsteamanuensis Torgeir Bakke, Biologisk institutt, Universitetet i Oslo

Leder av disputas:  Professor Trond Schumacher

Veileder:  Dr Øyvind Hammer and Professor Ketil Hylland (Main supervisor was Professor John S. Gray who is deceased)

Sammendrag

Pockmarks are large craters in the seabed and one of the most obvious and abundant structural features of the seafloor in many areas, including the Oslofjord. Yet there is still little knowledge of how old they are, how they are formed and which consequences they have for organisms living on the seafloor. A Ph.D. carried out jointly at the Physics of Geological Processes (PGP) and the Department of Biology at the University of Oslo has investigated these questions.

In 2005 a survey revealed over 500 pockmarks in the Inner Oslofjord. The pockmarks are up to 50 meters in diameter and up to 10 meters deep. Core records and microfossil dating showed that they were probably created just after the ice age, ten thousand years ago and likely formed by groundwater seeping up through the seafloor.

Seafloor organisms in the Oslofjord and North Sea are affected by the pockmark structures. Faunal communities were studied inside pockmarks in the Oslofjord and North Sea using grab samples and underwater video observations. The findings suggest that different communities of sediment living animals occur inside pockmarks compared to outside in the Oslofjord. This will have a large overall effect on the fauna present in the fjord due to the sheer number of pockmarks present.

The most important observation was the high numbers of animals, including corals, living inside pockmarks in the North Sea. The seabed in this area is heavily trawled and finding such high numbers and diversity of animals here is rare. These pockmarks are up to 250 meters in diameter and 10 meters deep and it appears that fishing nets will not the bottom of these craters so that animals within them are protected. These pockmarks are therefore important refuges for marine life.

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