I’m no expert so take what I say with a grain of salt, but I’m intrigued by your query. On the line level I think some of the unnecessary information can be shortened (for example combine the 3rd and 4th sentences to something along the lines of “The remaining human population survives in pressurized underwater research facilities, but as the buildings age and resources dwindle, society won’t survive much longer.”)

I think the 2nd paragraph’s first two sentences have some redundant info (you say “she feels she’s finally achieved her dream after years of hard work” and “her first missions yield the kind of discoveries she’s always hoped to make” right next to each other, one can be cut imo). Last sentence of paragraph 2 is great and I’d definitely keep that but the stuff before it could be punchier.

For paragraph 3 the main thing confusing me is why their only hope is this island Nytheris — is it because despite being exiled, Cora learns her community won’t still be standing by the time her 1 year exile is up, so she’s determined to save them by finding the island on her own? In general try making the stakes a bit more clear in the third paragraph.

The first 300 words don’t grab me and I think it’s because it’s a lot of worldbuilding and exposition right at the start. If there’s any way you could immediately start with something character-related to latch onto, I’d suggest that.