This victory objective represents the Soviet desire for a port that was ice free in the winter, allowing year round trade. If you look at the map, Sea Zones are numbered from east to west, starting in the North. This means that any sea zone with a number higher than “8” was liable to be frozen part of the year. None of this has any importance to the game, but gives historical context.
The objective itself is rather straightforward. At the end of the game, look at the map. For all the Soviet major naval bases, look at the number of the sea zone they border. If at least one of those sea zones has a number greater than 8, the Soviets get a victory point. For instance, at the start of the game, the soviets would get this objective or controlling the major port in Primorsky Krai bordering Sea Zone 38. Or for the major shipyard in Leningrad that borders sea zone 16.
Hope that helps!