What process brings the deep cold ocean currents up?

The following choices are given;

Conduction

Convection currents

Global wind patterns

Temperature and salinity

The answer is Convection Currents.

Explanation:

This occurs when the warm less dense ocean currents from the equator meet the cool more dense currents from the poles. The less dense currents move up at the boundary (in  a process called upwelling) while the denser currents sink to the bottom. The upwelling brings with it nutrients from the deep oceans hence these boundaries are great breeding grounds for planktons and the rest of the food chain.