[dentstudent (OP)]

If you brought up a cubic metre of sea water from the bottom of the Mariana Trench, by how much would it expand at the surface?

[daveshorts]

About 3-4% according to a rough extrapolation from compressibility figures in Wikipedia

[dentstudent (OP)]

Thanks! It's not much is it, considering the hundreds of atmospheres of pressure at that depth.

[Batroost]

Thanks! It's not much is it, considering the hundreds of atmospheres of pressure at that depth.

No it isn't. But water responds far more to temperature. Even under 155 atmospheres of pressure water at 300 degrees C (~45 degrees from boiling) has a relative density of only about 75% of that of water at room temperature and pressure.