Update 9 July.
http://www.expressen.se/nyheter/roboten-ska-losa-ostersjomysteriet/
(Swedish only, I provide a short summary below)
Translated title: "A robot will solve the Baltic Sea mystery."
It's mostly info about the robot submarine. Some info which might be of interest:
"The diver team will now be working for ten to twelve days. This time they have a robot and a sledgehammer with which they will try to extract a piece of the circle. They hope that analyses of a piece will give them better answers."
[...]
"This is what the circle looks like according to the divers
The circle looks almost like a concrete casting. At one place there is something which looks like a pearl necklace - or like someone have tried to make a fireplace with decimeter-sized rocks on the ocean floor. These rocks lie on top of the big circle.
The pictures taken by the divers show that the circle itself consists of multiple rocks shaped like buns or mushrooms which are connected to each other, forming the big circle.
The diameter of the object is approximately 60 meters.
In one place it looks like someone has pinched the side of the formation, like two shapes have been cast together and there is a rock pushed out between the shapes."
(not very good English, sorry, but it was pretty bad Swedish too

, and I don't want to provide a false translation. Maybe the object in the Baltic Sea emits radiation which severly interferes with the language center in Swedish brains?)