Recycle the Atmosphere
Jump to the wall seen on the first screen and then near the generator switch. Turn it off to remove the electric obstacle.
Jump to the next wall and then over the generator.
You should now be able to get back to the entrance to the zero g area. You can use the Stasis recharger on your way out.
You shouldn't have problems getting to Atmosphere Control from here. When you get there activate the filters. Before moving on be sure to check the Store, and the Save station.
Poison the Leviathan(2)
Leave through the large round gate picking up the Audio log and checking the containers on your way. Activate the terminal.
Kill the Leviathan
Time for a boss fight... conducted in zero g. There are quite a few ways to dispatch the Leviathan. Knowing its weaknesses is the main point here. One of them are the yellow bumps on its limbs. After some time it will reveal a mouth that spits out something of a fireball You need to keep moving not to get hit be either of his attacks. If you're playing on low difficulty you'll only need a weapon with improved damage rate to deal with him effectively. The higher difficulties require a bit more cunning and reflex. You'll need to toss the exploding barrels at him as well as the balls he shoots at you - just throw them back into its maw. This way allows you to conserve a lot of ammo.
Go to the mining deck
Jump in front of the gate and back to the Atmosphere control, then head to the tram station.