No, that dark area on the satellite photo is not an ocean. It's North Korea.
One of the easiest ways of seeing the wealth disparity between North and South Korea is by viewing the countries from space. This photo taken by astronauts on the International Space Station shows that North Korea is truly in the dark.
The only bright spot in the country is Pyongyang, which, as of 2008, had a population of 2.26 million people. In a labeled NASA map, you can see that the minor city of Gunsan, South Korea, which has a population of 280,000 people, is lit just as much as the much larger North Korean capital.
According to 2011 World Bank figures, South Korea's per capita power consumption was 10,162 kilowatt hours, while North Korea's was 739 kilowatt hours.
A video of ISS flyover of East Asia can be seen here.