Riikka Alvik rests her chin in her palm as she imagines the last terrifying moments of the life of a 13-year-old girl trapped in a cabin on the St Mikael as it mysteriously sank in the icy Baltic.

“We found her skeleton,” says Ms Alvik, a marine archaeologist and curator with Finland’s National Board of Antiquities.

“She never got out. Think of the panic she felt as the cabin filled with icy water – it was November, after all... November 1747, that is.

It is Ms Alvik’s life’s work to piece together the histories of shipwrecks, stories she finds more meaningful and valuable than any sunken treasure.

Finland’s coastline is so treacherous that even modern-day sailors must strictly adhere to maps to navigate the labyrinth of islands, shallow water, skerries and rocks that have doomed countless boats over the centuries.

And yet the waters have low levels of corrosive salt, a unique absence of ship-eating worms and very little sunlight, all of which create ideal conditions for preserving sunken wrecks.

There are 1,500 confirmed wrecks in Finnish waters and nearly half of them are more than a century old, according to the Board of Antiquities, but most experts believe the actual number to be much higher.

Ms Alvik says new sightings are reported every year.

“Seeing an intact ship on the bottom of the sea is heart-stopping,” says Rami Kokko, a marine archaeologist who has made countless dives to the bottom of the ocean.

“But the wrecks from the Middle Ages are also intriguing, because even though they are in worse shape, they still hold the pottery and cargo from the era,” he says.

Painstaking research into the ships, their cargo and sometimes the remains of those still trapped inside reveal not only moving personal stories but clues to the life of that era.

For example the St Nikolai, a Russian war frigate which sank in the battle of Svenskung in 1790, shows that around 400 men were packed into a ship that was only around 40 metres (around 130 feet) long.

“Most people then didn’t know how to swim, and with all that gunpowder, some of them caught fire,” remarked Ms Alvik.

But it is the Vrow Maria, a Dutch vessel jammed on the seabed 41 metres below the surface, that captivated Ms Alvik from the first moment she dove to it.

“I’ve never seen anything so beautiful under water in my life. It was like falling into a fairy tale,” she says.

The Vrow Maria was bound for the court of Catherine the Great in 1771, heavy with goods for trade, priceless paintings, porcelain and personal mementos, when it hit a shoal and sank three days later.

In another remarkable find, just this past July divers discovered bottles of pristine champagne and beer, believed to be the world’s oldest, in a ship that sank in the region of Aaland nearly two centuries ago.

But hundreds of other sunken ships have yet to give up their secrets from the seabed.

And while diving in Finland can be dark, dangerous and cold compared to diving elsewhere in the world, the wrecks are attracting growing numbers of curious divers.

The number of thefts or accidents is small considering how many divers frequent the wrecks, Mr Kokko says.

And, “Of course you have to be even more careful when there’s been a dramatic wreck that may have resulted in a loss of life... You have to think about it as a grave, and respect it as one,” he says.

Wrecks less than a century old are generally considered to belong to the defence forces since many, like those from the Baltic Sea battles of World War II, can conceal toxic or explosive dangers.

But anything more than 100 years falls under the purview of the Board of Antiquities, which is faced with the difficult task of deciding what – if anything – can be raised from the depths and restored.

Very old shipwrecks have settled into the conditions at the bottom of the sea and moving them disturbs the delicate balance of salt, light and bacterial conditions that keep them intact.

And yet leaving them where they are condemns them to a slow deterioration.

“The destruction process under water is slow. But the conservation process accelerates their destruction... when they come to the surface, it’s like a disaster for the wreck,” says Ms Alvik.

Conservation is also expensive and can take years, with every piece of the ship and its cargo having to be de-salted, dried and then bathed in a liquid plastic to fill the collapsing cell structures.

Finland’s maritime museum in Kotka contains many successful and unsuccessful attempts at such conservation.

Great iron canons corrode in the air and little wooden spoons taken from a sunken dining table have warped and twisted into gnarled spiral forms.

Ms Alvik says she could learn much more about her beloved Vrow Maria if she started bringing up and conserving its bits and pieces, but she might also end up destroying what she loves.

“Do we risk excavating the wreck entirely, to learn so many secrets... or let it slowly disintegrate as we wait for better technology to conserve it?” she asks.

But waiting risks losing forever the stories resting on the seabed.

“Do we accept the fact that we may never know the full story of the Vrow Maria?” Ms Alvik ponders. It’s not a question she is able to answer.