Ocean in Motion: Currents - Coastal Current

Sometimes currents occur along the coast and only affect small areas. One current found along the coast is the Longshore Current. This current is caused when waves strike the beach at an angle. The front part of the wave hits the shallow water first and slows down. The rest of the wave bends as it comes onto the shore creating a current that parallels the beach. Larger waves, which strike the beach less often at greater angles, create stronger Longshore currents. In areas where Longshore currents often occur, sandbars form.

Rip currents are a potentially dangerous effect of Longshore currents. Rip currents, sometimes called rip tides, can happen when Longshore currents, which move parallel to the beach, bounce seaward because of a change in the bottom's structure. Breaks in sandbars are also optimal places for rips to happen. Swimmers need to be careful in areas where rips can occur. A swimmer can be carried out to sea with this flow of water. Swimmers caught in this current should swim parallel to the shore until they are out of the rip current. Then, they can swim safely to shore.

One type of vertical current is called a coastal upwelling. Winds blowing offshore (or toward the ocean) push water away from the shore. Deep, colder water rises to replace the water that has been blown out into the ocean. This cold water from deep off the ocean floor brings many nutrients to the surface. Why do you think this water has so many nutrients? Dying organisms and fecal matter fall to the ocean floor. As these decompose (rot), nutrients are released, but few organisms are there to use the nutrients. They remain trapped on the ocean floor until an upwelling pushes them to the surface. Plankton blooms usually follow coastal upwellings because of the abundant nutrients that come with it.

Downwelling is another coastal happening. Onshore winds (or winds blowing toward the shore) push water toward the coast. This drives the nearshore surface water down and away from the coast.