Diving is used to map marine nature and perform marine archaeological inventories and inspections. These surveys are particularly important when planning construction or other seabed intervention works in the area. Marine archaeological inspections are also often carried out due to new shipwreck or artefact finds.
Much of the results of the VELMU Programme (Underwater Marine Biodiversity Mapping Programme) are based on dive observations, as well as plant and algae samples collected by diving.
A diver prepares to chart the underwater vegetation.
Research diving requires careful preparation
Each dive assignment is carefully prepared to provide the most useful and varied data. Attention is also given to the diver’s safety. A blue and white flag, i.e. a so-called “A-flag” is used to warn other nearby boaters that there is a diver in the water and so that they know to stay out of the dive area.
Marine archaeological inspection dives are usually conducted in pairs. When diving alone, the diver has an assistant in the boat to monitor the diver's movements and air bubbles rising to the surface, as well as the surrounding boat traffic. The diver is fitted with a brightly coloured and floating safety rope to communicate with their surface assistant.
If the main purpose of diving is to survey and collect samples from marine nature, a graduated rope line is lowered along the seabed to guide the diver. This rope is extended from the water's edge up to 100 metres from the shore.
Both ends of the line are marked with buoys and their coordinates recorded. These coordinates make it easy to find the location again if it is necessary to revisit at a later date.
Data is recorded in the forms, samples are stored in jars
When everything is ready, the diver descends to the deeper end of the line. From there, he begins to advance towards the shoreline, guided by the rope. Along the way, he takes notes about the bottom area, which extends one metre to each side of the rope.
To take notes, the diver carries a writing pad, upon which is records the bottom type, vegetation, benthic fauna, and other specific observations at regular intervals. For each entry, data about its location and depth is added. This information is obtained from the diver’s depth gauge and the line-markings. Samples of alien or difficult-to-identify species are collected in small plastic jars.
The information is collected on a diving form.
When diving, it is also possible to take larger samples of bottom sediments or communities living on rocky surfaces. Sediment samples are taken with a tube-like corer equipped with removable plugs at both ends. On rocky surfaces, divers use a small metal frame which has mesh collection bag attached. The frame is placed on the rock surface and the biota, i.e. algae and other fauna, are scraped off with a metal scraper into the mesh bag. After the dive, the line rope and buoys are retrieved to the boat.
Marine archaeological sites are documented by diving
Scuba diving is a must when exploring marine archaeological sites. By diving, the underwater remains are inspected and documented. Documentation includes measurement, drawing, photography and video recording of the subject and its details.
Nowadays, video is the most commonly used documentation method. Good quality footage and sophisticated computer programmes make it possible to produce 3D models from shipwrecks, for example. At their best, such models can be very accurate and informative.
Samples taken from a wreck reveal the ship's age and history
Wooden shipwrecks are also often sampled to find the date of the wreck. The annual growth rings can be examined from a sample of wood material. It is usual for a diver to saw off a wood sample and bring it to the surface. Occasionally a part of the wreck is brought up whole and a sample core can be drilled from it.
With the help of a microscope, the annual growth rings in a sample can be counted and compared to a reference set of annual rings collected from samples of different ages. If it is a good sample, it can show where the tree grew, the time it was felled, and the tree species.
Samples may also be taken from the wreck’s artefacts, from the cargo or the ballast for other scientific purposes. Such samples can be used to determine, for example, the sailing route of the ship, the quality of the cargo and the living conditions of the crew.
Underwater excavation reveals archaeological sites
Diving is also used for archaeological excavations when the remains are partially or completely covered by sediments. If there is a risk that an underwater relic may be destroyed, experimental excavations are usually carried out before new building projects, such as fairway construction begins. In the case of experimental excavations, the ancient remains are only partly excavated such that the find can be identified, and the extent of the discovery determined.
During excavation, the object or its part is systematically studied and documented using archaeological methods. The equipment and methods used for excavation vary according to the situation. For example, masses of sediment are transferred using a water jet or pump. The diver conducting the excavation holds the pump with one hand and guides the sediment gradually to the mouth of the suction hose. In this way, objects and parts of the wreck buried in the sand and clay slowly emerge.
To ensure the retrieval of minor finds, a mesh basket is placed at the end of the suction hose through which the bottom sediments are screened. The artefacts are first documented and only then brought to the surface in lifting baskets. On the surface, archaeologists must still ensure that the finds are properly packaged, kept moist, protected from the light, and submitted for conservation as soon as possible.