Seed: 490798691970183764
Coordinates: Imprinted on the screenshot below

Tl;DR Its not possible to activate the portal with a flint and steel in the ocean. (Tried removing the crying obsidian and replacing it with normal obsidian)

Update: There's no proper way to activate the ruined portal in the oceanfloor. You have to block the portal, clear the inside of the portal with water and then it can be activated BUT, this creates a problem you cannot break the blocks while inside of the portal in Survival Mode. This means that there is no proper way out as you cannot destroy the obsidian blocks. The only way out is either by getting a friend in your location and for them to break it or  initiating the /kill command.