The Blue Machine

The Fram’s occupants had no shortage of drinkable water because they could melt the sea ice and snow at the surface, benefiting from the low density of ice which forces it to float at the top. Most of the Arctic Ocean has a very cold and relatively fresh layer at the top (brine formation happens only at certain times of year and only in certain places), and the lack of salt outweighs the cold to make this float on top of what’s below. The middle layers of the Arctic Ocean are taken up with salty and relatively dense water, 39 which is slightly warmer than the surface layer (at around 1 ° C instead of–1.7 ° C). The additional density due to the salt outweighs the buoyancy due to the warmth, keeping the warmer waters counter-intuitively trapped in the depths, away from the surface. Below that are the densest waters in the world ocean, the result of the seasonal ice formation above, which creates an annual dose of water that’s just as salty but even colder. And even though this cold salty dense water may form in the Arctic, it doesn’t have to stay there. The density itself can force water to move.