Over the past 50 years, we see a dramatic freshening of seawater in some parts of the North Atlantic. We also see salinity increasing, or getting saltier, in other regions. So global warming will have a signature in ocean salinity, that is why we want to measure it from space.

At the moment, it's just being used by salinity scientists trying to understand the measurement itself. It's not quite ready for prime time yet but the reason it's flying is to understand the water cycle on the planet, among other things. In this warming world that we have, the oceans are warming, the atmosphere's warming, there's the idea that the water cycle on the planet will accelerate, there'll be more moisture in the atmosphere, more precipitation, more cycling of water through the system. And the ocean can be kind of integrated gauge for that - changes in salinity can indicate changes in evaporation and precipitation over the ocean.

In fact, if you look back over all the measurements that have been made from ships over the last 50 years and you map the changes in salinity you actually find that most of the saltier places in the ocean surface have gotten saltier and the fresher places have gotten fresher, which is exactly the fingerprint that you would think to see in an acceleration of the water cycle. So as Aquarius is coming along ocean scientists are trying to diagnose if this is really true, that there is an acceleration. We have to act like a doctor doing diagnostics on a human, we have to rule out other diseases so what we're trying to do with salinity here is rule out that it's not ocean processes fooling us to make it look like an acceleration of the water cycle. Want to read more from Eric's interview? Click here.