Hahaha they just revealed the black goo curse to symbolize our very human flesh!

-Capitan, you know the danger.
Don't do it.
-He has no choice.
Jack is on land going for the Trident.
-Capitan, there must be another way.
Once you possess the living,
there's no coming back.
You will be trapped in his body forever.
-The Trident will set me free.

Pay big attention to the words "forever" and "trident" which reveal death is not an escape from this black goo dimension/dreamworld but something else we need to do!

I dont think this movie will show it but that Poseidon's trident is what we need to destroy and it symbolizes the trinity god/three head cerberus/three moon hades!
[link to www.godlikeproductions.com]

So far is shown whoever possesses that trident rules the sea/black goo world and makes sense if we destroy it the one who rules this world and keep us imprisoned loses control and we all are set free.