Most of the oceans are kilometres deep, with some trenches in the Pacific plunging to depths in excess of ten thousand metres. The Baltic, by contrast, has an average depth of only 55 metres. In fact, it is one of the smallest, shallowest, most island-dotted and shoaliest seas in the world.
For as long as the seas have been sailed, hundreds of vessels that have strayed off course or lost their battles with storms have ended up at the bottom of the Baltic, especially in its countless bays and inlets. Floor plates believed to have belonged to a Viking ship have been found in the Gulf of Finland. As research methods become more systematic, much more is likely to be uncovered.
The Baltic is the world's biggest body of brackish water; its salinity varies from almost nothing to 1.5 per cent, compared with an average of 3.4 per cent in the oceans. Maija Fast of the Finnish Maritime Museum sees the Baltic as a paradise for marine archaeologists: "It's really an exceptional inland sea. The low salinity means that the wood-eating shipworms common in the oceans do not thrive here. Wooden wrecks are very well-preserved. It is different elsewhere; for example, we are collaborating with Australian scientists to study the wreck of a Finnish ship that went down north of Kangaroo Island in 1860 and is now a protected archaeological site. All that remains of it is a collection of glass, pottery and metal objects; the worms have completely devoured the wooden hull. That would not happen in the Baltic. One of the most interesting research sites off the Finnish coast is 40 metres below the waves. It is the Russian merchant ship St. Michael, which foundered near Börstö off south-west Finland in autumn 1747 while en route from Amsterdam to St. Petersburg. Some of the cargo was washed up on the shore and auctioned in Turku the following year. Divers have been studying the wreck, under the supervision of the Maritime Museum, for the past nearly forty summers. Among the objects that they have found are a rococo carriage made for the Czarina Elisabeth Petrovna, extraordinarily beautiful tableware and other valuables. Several other important, if lesser-known, wrecks are likewise being studied on a continuing basis. Experts expect that side-scanning sonar will enable new completely preserved wrecks to be found at depths of 40 - 50 metres over the next few years.
There are about 20,000 amateur divers in Finland and foreign guests are welcome to join them in the depths. Clubs organise diving trips for visitors, and permits to visit wrecks can be obtained. Visitors should, however, bear in mind that the water in this part of the world is a good deal colder than in the tropics and visibility can be poor. By law, wrecks over 100 years old - counted from the date of sinking - are preserved sites that may not be interfered with without official permission.
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