Marine geological mapping
The sea is a resource that is used for many different purposes. For example, there are building activities in and near the sea, ports are dredged and enlarged, cables are laid on the bottom of the sea, offshore wind farms and fish farms are built etc. Human impact on the marine environment also occur in other ways, e.g. most of the man made substances that are released into the environment eventually are deposited in the seabed sediments.
We must possess knowledge about the marine environment in order to understand the impact of human activities on the sea and to ensure that various human projects are implemented in a sustainable way. This knowledge is also essential for environmental monitoring and environmental protection.
We need to know, among other things, what the sea bottom is made of, what it looks like, what substances are accumulated in the sediments and where sedimentation and erosion take place, i.e. where sediment builds up and where material is carried away.
In order to meet the need for marine geological information, SGU is surveying and mapping the seabed in Sweden’s territorial waters and exclusive economic zone (EEZ). The information thus produced is used in local and regional spatial planning etc., in the planning of marine construction projects, as data for the fishing industry, for military surveillance, and environmental monitoring. The users include individual fishermen, local, regional and national authorities, industry, and the Armed Forces.
To map the seabed, SGU uses a specially equipped survey vessel, Ocean Surveyor, and a small boat for use in shallow waters. To obtain data concerning seabed composition and appearance, various hydroacoustic systems are used, e.g. echo sounders, seismics and side scan sonar. Gravity corers and piston corers are used to take sediment samples. Underwater video cameras are also used.
After the data is collected it is interpreted and added to databases that can be used to access various kinds of data. The information can be presented in different forms, such as plotted maps of the distribution of soils and rocks in the sea bottom surface and of the content of pollutants such as cadmium, mercury and PCB in deposition areas and bottom sediments. It is also possible to obtain cross-sections of geological conditions down to 100 metres under the sea bottom surface.
The sediment samples provide information, inter alia, about the distribution of pollutants. They may also be regarded as historical records that tell us what types of substances, including toxins, have been deposited on the sea bed at various times and about changes in the climate. The samples taken so far provide information that dates back more than 100 years.