Question

Why does water sink in polar regions?

A. Evaporation due to strong wind creates gyres.
B. Water gets colder and saltier there, increasing its density.
C. Southern Oscillation currents force water down as they strike land.
D. The Great Ocean Conveyor Belt transports water around the globe over many
years' time.

Answer 1

Because colder water has more density due to state changing, added with saline/salt, making it even more dense, causing it to sink.

B is your answer.