Down the tunnel, through the flood area up the ramp, an audio diary (Meeting Fontaine) is on the far right side of the room, leaning up against some crates. Head down the ramp that's right next to the one that you walked up to enter this area. Following the arrow at the top of the screen leads you to the Control Panel. Approach the Control Panel and activate it.
After the short event has played out, proceed through the door opposite the one you used to enter the control room. Travel down the wooden walkway. The walkway is littered with Leadhead and Spider Splicers, remember to take pictures of them to further your research. As you travel down the walkway, you'll eventually reach a padlocked door on your right. Break the lock, there is an audio diary (Kraut Scientist) within.
Continue moving towards the submarine. After the event, turn left and head in this direction, towards the walkway. Pick up the audio diary (Offered A Deal) next to the box at the base of the walkway. Travel down the walkway and enter the next level, Arcadia.