Amazing Accuracy of Medieval Sea Chart

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Medieval Sea Chart In Line

With Current Thinking

16th-Century Carta Marina Gives Accurate

Location For Dangerous Eddies

By Roger Highfield

The Telegraph - UK

5-4-4

 

A satellite image of the north-east Atlantic has revealed that

medieval cartographers knew much more about ocean currents than was

thought.

 

The ornate Carta Marina, published in 1539, appears crude by today's

standards, depicting sea monsters off the coast of Scotland, sinking

galleons, sea snakes, and wolves urinating against trees.

 

But when oceanographers examined a large group of swirls and whorls

drawn off the south-east of Iceland, complete with ships, a giant

fish and red sea serpent, they found it corresponded with the

Iceland-Faroes Front - where the Gulf Stream meets cold Arctic

waters, causing huge swirling eddy currents that could sweep a ship

off course.

 

The earliest known reference of its kind, which suggests generations

of seafarers including the Vikings were aware of ocean eddies, is

reported in the journal Oceanography by a team from the Plymouth

Marine Laboratory and the University of Rhode Island.

 

The cartographer, Olaus Magnus, an exiled Swedish priest living in

Italy, covered the map with ink. But Prof Tom Rossby, from Rhode

Island, believes that not every elaborate quill stroke was artistic

licence.

 

"Their location, size and spacing seem too deliberate to be purely

artistic expression. Nowhere else on the chart do these whorls

appear in such a systematic fashion," he said.

 

"They are the earliest known description of large scale eddies in

the ocean - these are huge bodies of water, 100 kilometres in

diameter, that turn slowly. It seems the lines were deliberately

drawn to aid navigation.

 

"We know mariners were aware of these fronts but they would not have

the tools to quantify them nor the means to express them," he said.

 

The discovery, from research part-funded by the Natural Environment

Research Council, followed a discussion of the Iceland-Faroes Front

at a workshop in Bergen, Norway. Shortly after the meeting Prof

Rossby read Cod, the international bestseller by Mark Kurlansky,

which contains an illustration of the Carta Marina.

 

"When I turned the page and saw the map I said, 'holy s**t! These

are identical to our satellite images'. I don't think I would ever

have registered this had I not been in Bergen."

 

Dr Peter Miller from the Remote Sensing Group at Plymouth Marine

Laboratory provided more accurate satellite information on water

temperatures. "Things got exciting when I was able to provide Tom

with an image of the eddy field. The data confirmed Tom's theory

that the swirls on the map were not artistic licence," he said.

 

The satellite image shows how waters from the south, shown in orange

and red, can be as much as five degrees warmer than the cold

currents from the north, marked in purple.

 

At the point they meet, these huge eddies form, revealed as a blue

border. "Sailors would have been aware of these large rotations of

water as they affected navigation," he said. "They would notice a

change in colour of the water too. The cold currents to the north

are generally greener than the Atlantic water to the south due to a

greater abundance of plankton."

 

At the front, deep nutrient-rich waters move up to the surface

supporting phytoplankton and grazing zooplankton. "This ready food

supply brings pilot whales and other marine creatures to the front

to feed," said Dr Miller.

 

The Carta Marina took 12 years to complete and contains an

extraordinary amount of information. The list of towns, lakes and

regions is far more comprehensive than any map before well into the

17th century.

 

It is one of the first maps to give Finland and parts of Russia

roughly correct proportions and it is the first map to fully portray

the Baltic Sea, the Finnish Gulf and the Gulf of Bothnia in the

north.

 

Northern Scotland, the Hebrides, Orkneys, Faroes and Greenland are

described in detail but so, oddly, is a non-existent island, Tile.

This island may be related to the mythical northern community Thule.

To the ancient Greeks, Thule was the northernmost habitable region

of the world. Curiously, its location on the map puts it near St

Kilda in the Hebrides.

 

The map reveals details of shipping routes at the time and warns

sailors of drift ice in the north - illustrated by a stranded polar

bear on a floe. Whales, sea lions, walruses, crabs and lobsters are

also depicted.

 

© Copyright of Telegraph Group Limited 2004.

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