Question

Why does pressure decrease exponentially with height in the atmosphere but linearly in the ocean?

Answer 1

I THINK (but you need to check this) -

The density of water does not change significantly with pressure - so each metre of depth contributes the same 'additional pressure' so it increases linearly.
With the gases of the atmosphere - the density decreases with the pressure - so as you rise through the atmosphere the density decreases, and hence the pressure falls more rapidly since there is less 'mass' of air above you as altitude increase.

Not a very lucid explanation - but I hope you can see what I mean.