Oxygen

Oxygen  (O2) is a gas that is needed by the player to survive. When diving the player uses a reserve of Oxygen that diminishes over time. The Oxygen reserve automatically replenishes whenever the player comes back to the surface or enters a powered submarine or Seabase. Oxygen can also be replenished by swimming through bubbles produced by Purple Brain Coral.

The HUD indicator for the player's Oxygen supply is located on the bottom left of the screen. The player has a base reserve of 45 units of Oxygen but this can be expanded by using an O2 Tank which allow an additional 60 units. Having multiple tanks in your Inventory will increase the total amount of Oxygen.

Hardcore Game Modes, there are alerts for when the player has 30 seconds and 10 seconds of Oxygen remaining. However, the 30 seconds alert doesn't play unless the player has a tank equipped.

If the player is depleted of Oxygen, and gets to the surface when the screen is fading, different breathing responses will occur coming from the player.

Depth is a factor that effects Oxygen consumption. When diving less than 200m the player will consume one unit per second however when diving 200m or deeper the consumption is two units per second. While the depth effect is supposed to be counteracted by equipping a Rebreather. However, as of 07/05/15 the Rebreather does not affect Oxygen consumption.

The player can use the Console Command OXYGEN to have unlimited Oxygen.

Oxygen is produced in the Seabase, Seamoth, and Cyclops naturally. However, if they run out of power, no Oxygen will be produced, and the player has a limited time before it is completely gone.

Future Plans
In the future, indoor Flora will be able to produce Oxygen within a Seabase, allowing the player to still survive even if the power is depleted.