Warm on top, salty below

The idea

Warm equatorial water flows poleward at the surface while colder, denser water returns towards the equator at depth; less saline, less dense water stays near the surface and more saline, denser water sinks.

Layers in the sea

Ocean water is not the same everywhere. It differs in warmth and in saltiness (salinity).

Which water would sink: the denser water or the less dense water?

• The denser water
• The less dense water
• Neither can sink

Near the top or deep down

Put each kind of water where it flows.

Density decides

Warm water travels at the top toward the poles, and cold, dense water comes back deep down. Water with less salt is lighter and stays on top. Water with more salt is heavier and sinks.

Warm equatorial water flows poleward at the surface while colder, denser water returns towards the equator at depth. Less saline, less dense water stays near the surface and more saline, denser water sinks.

Notes

Warm water flows poleward at the surface, colder, denser water returns at depth; less saline, less dense water stays near the top and more saline, denser water sinks.

Check yourself

Where does warm equatorial water travel towards the poles?

What happens to water with higher salinity?

Which water tends to remain near the surface?

How does colder, denser water return towards the equator?

• Over the surface — correct. Yes!
• Through deeper ocean levels. Colder and denser waters flow back towards the equator through deeper ocean levels.
• Along the sea floor. The chapter says warm equatorial waters travel over the surface.
• It is less dense, so it stays near the surface. That is true of water with lower salinity.
• It is denser, so it sinks and moves at deeper levels — correct. Yes!
• It evaporates first. The chapter says higher salinity water is denser and sinks.
• Colder, denser water. Colder and denser water flows back towards the equator at deeper levels.
• Water with higher salinity. Higher salinity water is denser and sinks to deeper levels.
• Water with lower salinity, being less dense — correct. Yes!
• Slowly, through deeper ocean levels — correct. Yes!
• Quickly, over the surface. Warm water travels over the surface toward the poles. The colder, denser water returns slowly through deeper levels.
• It does not return. The chapter says colder, denser waters slowly flow back towards the equator.