The oceans are in motion. Persistent winds at the surface drag the water creating currents.

Winds arise due to differences in pressure that result from differential heating at the earth's surface. The movement of the winds is also affected by the Coriolis Force which refers to the apparent deflection of air at the earth's surface due to the rotation of the earth. The Coriolis Force also affects the movement of water in the oceans.

Differential heating at the earth's surface gives rise to local effects such as sea breezes or land breezes because the land and water have different heat capacities.

Differential heating at the earth's surface also influence wind patterns globally because of the tilt of the earth and the seasonal movement around the sun. These persistent wind patterns in turn give rise to the major surface circulation patterns that are evident in the oceans.

The direction of currents can be determined with various devices. One of these instruments is a drifter. The Global Drifter Center is located in Miami, Florida. The center manages the deployment of drifting buoys around the world. The speed of currents is determined with current meters.