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,
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