Ocean Currents and Climate: Surface Currents A current is a large stream of moving water that flows through the oceans. Surface currents, which affect water to a depth of several hundred meters, are driven mainly by winds. Climate is the pattern of temperature and precipitation typical of an area over a long period of time. Currents affect climate by moving cold and warm water around the globe. In general, currents carry warm water from the tropics toward the poles and bring cold water back toward the equator. A surface current warms or cools the air above it, influencing the climate of the land near the coast. Deep Currents* Deep currents are caused by differences in the density of ocean water. Currents move water from the equator to the poles. As water temperatures begin to decrease and salinity increase, the water becomes denser and sinks. Then, the cold water flows back along the ocean floor as a deep current. Deep currents move and mix water around the world. They carry cold water from the poles toward the equator. *Upwelling Upwelling is the movement of cold water upward from the deep ocean Upwelling brings up tiny ocean organisms, minerals, and other nutrients from the deeper layers of the water. Without this motion, the surface waters of the open ocean would be very scarce in nutrients. Review Questions: 1. What is a current? - A large stream of water moving through the ocean. 2. Explain how deep currents form and move in the ocean. - Deep currents form when dense ocean water that is near the poles is cold and sinks and slowly, flowing along the ocean floor towards the equator. 3. What causes upwelling? - Upwelling occurs when wind blows surface water away from a coast and cold water rises from the ocean depths.