RIASSUNTO
Abstract
The Ormen Lange field is located at water depths of 800 to 1100 m, within the scar of the gigantic prehistoric Storegga Slide. The seabed in the area very rugged, with small softbottom troughs between peaks and ridges formed by slide blocks. The baseline survey and biodiversity mapping of the field therefore utilized both ROV survey with video transects, and traditional sediment sampling for macrofauna investigation. These complement each other, and were necessary in order to get a full overview of the benthic communities in the area.
Introduction
When petroleum activities move into new areas where the knowledge of biological processes and biodiversity is insufficient, there is a need for baseline survey to map the pre-activity situation. An equally important objective is to understand the environment in order to plan activities such that impacts are minimised. For petroleum activities on the Norwegian Continental Shelf (NCS) there is today a well-established procedure for how marine baseline and monitoring surveys should be carried out. This is part of the Activities Regulations1, which are part of the joint regulations relating to HSE on the NCS. It states that the operator shall carry out an environmental baseline survey to map the environmental status:
a) prior to exploration drilling in deep waters,
b) prior to exploration drilling in areas where the presence of particularly vulnerable environmental resources has been established or where the presence of such resources is likely,
c) prior to production drilling.
The Activities regulations focus on sediment surveys, with investigation of macrofauna communities, sediment characteristics and concentration levels of hydrocarbons and metals. The methods prescribed are mainly directed towards monitoring of a homogenous and soft seabed where impacts may be traced as gradients from a point source. Sampling equipments are box corers and grabs.
The Ormen Lange gas field is an example of an area where these methods are insufficient for establishment of an environmental baseline and insufficient for gaining information and understanding of the biodiversity of seabed communities. Ormen Lange is located in the Norwegian Sea, 100 km off the North West coast of Norway. The water depth is 800-1100 m, which makes this the deepest Norwegian offshore development project to date. Other technical challenges in the Ormen Lange field development are low temperature (average temperature at seabed - 0.9oC, minimum -1.0oC) and a very rugged topography. The field is situated in the scar from the Storegga slide that took place 8200 years ago and is one of the world's largest known landslides2 (Figure 1). The seabed consists of troughs with soft sediments, extending a few hundred metres, divided by peaks and ridges of hard clay slide blocks that jut up 30 to 60 m (Figure 2).
The main objective of this study is to demonstrate a strategy for deep-sea biodiversity mapping in a very heterogeneous area.