Deep-ocean currents are driven by differences in the water’s density, which is controlled by temperature (cold water is denser than warm water) and salinity (salty water is denser than freshwater). The cold water is now denser, due to its lower temperature and the additional salt, so it sinks toward the ocean bottom.

Currents on the surface are determined by three major factors: the major overall global wind patterns, the rotation of the Earth, and the shape of ocean basins. When you blow across a cup of hot chocolate, you create tiny ripples on its surface that continue to move after you’ve stopped blowing.

By moving heat from the equator toward the poles, ocean currents play an important role in controlling the climate. Ocean currents are also critically important to sea life. They carry nutrients and food to organisms that live permanently attached in one place, and carry reproductive cells and ocean life to new places.

Off the Atlantic seaboard of the United States, the Gulf Stream flows at a rate nearly 300 times faster than the typical flow of the Amazon River. The velocity of the current is fastest near the surface, with the maximum speed typically about 5.6 miles per hour (nine kilometers per hour).

It is produced by equatorial trade winds that blow from east to west, piling up warm surface water in the west Pacific, and also pushing surface water away from the equator itself. This makes way for colder waters to well up from the depths, creating the cold tongue.

Toward the middle of a river, water tends to flow fastest; toward the margins of the river it tends to flow slowest. 2. In a meandering river, water will tend to flow fastest along the outside bend of a meander, and slowest on the inside bend.

Waters density is affected by its temperature and salinity, or saltiness. The colder and saltier the water is, the denser and heavier it is. Cold, dense water tends to sink and flow under warmer, lighter water, creating a current.