Basically it means something is under consideration or something is being thought about. As the future of the Weddell Sea is under consideration. As the future of the Weddell Sea is being considered. As the future of the Weddell Sea is thought about. As people think about the future of the Weddell Sea... It just means to think about something. I deliberated between the ham or the chicken sandwich. I hope that helps.

"Deliberation" means an long, serious, careful, thoughtful discussion, taken by a group of people, before making a decision. "This is an important decision. We should not make it hastily, but only after careful deliberation."

like a mix between debated and discussed, I would say..

A more technical explanation: Notice the word contains "liberated" meaning "free". So, logically, "de-liberated" means "not free". In this case they are talking about the future of something, of which there are currently many possibilities (the outcome is free to change). They want to reduce all these possibilities to a single definite outcome, so that everyone agrees what will happen: to de-liberate this subject's future.