Deep Ocean Currents & Thermohaline Circulation

Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

In this lesson, you will learn how the deep waters beneath the wavy top layers move with a strength that is 16 times stronger than all the rivers in the world combined.

Deep Ocean Currents

When you look at surfers riding the waves, you are looking at the result of surface currents in the top layers of the ocean. Now, picture yourself diving, preferably in a submarine, so you won't succumb to the intense pressure of the deep ocean, and you'll soon see the waters become less wavy. Now, when you first see the waters calm down, you may think that the waters are fairly still. And as you go deeper and deeper, you may even think the water is still like it is in a cup that's sitting on a desk. However, this is not the case. The waters in the deep oceans are, in fact, moving. These deep moving waters, referred to as deep ocean currents, actually moves all the waters in the deep oceans. This movement is global, moving waters all around the globe in what is called a global conveyor belt that connects both the deep ocean currents as well as the surface currents that moves waters on the ocean's surface. This global conveyor belt does move slowly, though. It takes 1,000 years for this conveyor belt to move waters around the globe.

The global conveyor belt moves all the waters down to the bottoms of the oceans
global conveyor belt

Where They Come From

Where does this global conveyor belt start? Do deep ocean currents have a beginning? They actually do. We can say that these currents start in the colder regions of the planet, such as near both the North and South Poles. It is here that ocean waters are cold enough to freeze. Think of all the glaciers that form at the North Pole and the arctic ice sheets in the South Pole.

Thermohaline Circulation

Now, as the surface waters in these locations freeze, it leaves behind salt that makes the immediately surrounding waters saltier, colder, and denser than the rest of the ocean. This colder, denser water begins to sink to the ocean's bottom. As this water sinks, new surface water that's a bit warmer and less salty rushes in to fill the void. As this new surface water comes, it becomes colder, saltier, and denser and also begins to sink. Thus starts the global conveyor belt in a process referred to as thermohaline circulation, water circulation that depends on both temperature (the thermo part) and salinity (the haline part).

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