The ocean surface may look turbulent and chaotic but the lower levels can be surprisingly well ordered. Research from the University of Toronto sheds light on the decades-old mystery of thermohaline staircases: the way the ocean in some places is structured into distinct layers, each tens of metres deep, each with sharply defined temperature and salinity.
Oceanographers call these staircases striking and spectacular. The liquid equivalent of towering rock formations, they can be several hundred metres high but nobody could fully explain how they form.
The density of a region of water depends on its temperature (colder is heavier) and salinity (saltier is heavier). A warm, less-salty packet of water will rise, while cold, salty water will sink.
Yuchen Ma, a researcher, says under some circumstances this leads to a feedback process. Dense water gets even denser as it sinks, and rising light water gets lighter. This means even if the water is initially evenly distributed, any perturbation causes it to sort itself into layers.
“A positive feedback loop will try to twist the even gradient into the staircase configuration,” says Ma.
The research shows how this effect dominates in the Arctic Ocean where salinity is the most important factor. In tropical and subtropical oceans temperature is more significant and staircase formation occurs differently.
