Black Sea Treasure Hunters by Mananuk is an Amstrad CPC which beta version is available if you order the physical version. The game is already available on ZX Spectrum. You can see a video of the game Black Sea by Xenomorph.
The story of the game is the following : submarine Captain Robinson goes deep into the Black Sea to search for treasures and discover all the secrets that those waters hold. The small bathyscaphe has a very limited oxygen deposit, so you will have to go to the nearby ports to recharge the cylinders. You must be careful not to disturb the inhabitants of the sea if you do not want to end up in the depths of the Black Sea.