That really depends on what you're looking to study, specifically. Speaking in generalities, places like Australia and the Pacific coasts and islands such as the Galapagos or New Caledonia; the Pacific Northwest; Cape Horn; the Cape of Good Hope and the Caribbean sea all have very biodiverse marine ecosystems, although many coastlines have interesting creatures important and deserving of research. Were you to work as an aquatic biologist, there are many rivers that would be good to study as well, although since they are not salt water they are not technically considered marine environments.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.