(Thank you to Dr. Wolfgang Rack for authoring this article, which originally appeared on the Weddell Sea Expedition 2019 website. Dr. Rack is a glaciologist at Gateway Antarctica, a center for Antarctic studies and research at the University of Canterbury in New Zealand. His research focuses on the use of advanced technology to measure ice thickness over time.)
The world's oceans are the plumbing system of our planet. Cold water is transported from the poles to the equator, where cold water warms before it is sent back to the poles. Without that mechanism, the poles would be much colder, and the equator regions even warmer. But how is that circulation driven? It cannot be the sun, as warming the oceans from above stabilizes the water column. To understand this process better, just imagine a pot filled with water on a heating element. Heating from below makes the water circulate, while heating from above makes the surface water light and stable.
Here is what mother nature does: it makes polar surface water heavy. As sea water freezes, the salt isn't built into the crystal structure of ice, but is, instead, rejected as brine (high concentration of salt in water) into the cold ocean below.
