Great game mechanics!
I especially loved the idea of having the O2 depletes overtime as you go deeper as well as the need to repair the submarine. Brilliant idea to have the darkness crawls on you as you go deeper where lights were important to see where exactly you're going.
Some possible improvements is maybe having sea monsters or sea quakes where you coukd have the background shaking while going deeper.
I really enjoyed playing your game.
My top score was 923m in around 5 minutes.
Was there a specific distance to win or infinite depth?