I'll second Judy's reply on working with the Swedish language, it's not that difficult. You don't need to be fluent, just aware of some basic words for vital records, etc. And it shows respect for the Swedish people & culture. The native Swedes on this board make a big effort, it's nice to meet them at least half way. On the other hand, if you are in the US, many of us are having tough economic problems and spending time & money on a CD may seem like a luxury.
The reason I asked about the merchant marine connection is that the island was totally reliant on shipping and of the dozen or so churches I've been to on the island, they all had a model sailing ship hanging over the pews. Joining the merchant marine was a great way for a dirt poor person to see the world and find greener pastures. My gg grandfather signed up for the Swedish merchant marine as a teenager, sailed the world a couple of times, got thrown off ship for theft and jumped at least once in France.
Your family's lore about Carl signing up with a British ship makes perfect sense. I've read that the British & American ships paid better than the Scandinavians, so that's one reason sailors jumped ship. I suspect that Carl originally signed up in the Swedish merchant marine as a teenager. The closest seaman's house (hiring hall, dispute resolution & retirement programs) would have been the Kalmar Sjömanshus, in the city of Kalmar on the mainland, directly across from Öland. The seaman's houses kept excellent records and the records for Kalmar are located at the Vadstena Regional Archives in the city of Vadstena. You can contact the archives and hire a researcher for 400 SEK an hour, I believe, and it should only take 1 hour of research. It was common for merchant marine sailors to use their patronymic names, having a name like Törnqvist, if Carl used that surname, would make it easy to find his record. Records of the 1850's yield birth year, birth parish & parish of residence of the sailor. I suppose records of ~1800 would yield the same information, althought I've never seen one of that period.
If you don't want to do your own research, I'll broaden the search for Carl's birth from 1770-80 on the PLF CD.
Another thing that came to mind: there's a Finnish island named Åland between Sweden & Finland. Which might explain your DNA tests. Are you sure that Carl was from Öland & not Åland?