Ocean Currents

Surface Currents

Water is in constant motion due to tides, winds and currents

· Surface currents are caused by wind in the atmosphere

· Winds blow in a curved path because of the Coriolis Effect

o Caused by the Earth’s rotation

Surface Currents and Wind Patterns

Earth rotates in an easterly direction

· Makes winds blowing toward the equator curve westward and winds blowing towards the poles curve eastward

· Surface currents in ocean form similar patterns

o Change direction if winds change

Surface Currents in World Oceans

Surface currents form a circular pattern called a GYRE

· In Northern Hemisphere gyres flow clockwise and in Southern Hemisphere gyres flow counterclockwise

· See figure 15.9 pg. 347 for world ocean currents

Deep Currents

· Deep currents are kept in motion by density differences

o Densest water in poles- surface water is very cold with high salinity

o This water sinks and flows as a deep current towards the equator

· Coriolis Effect also affects deep currents

· Upwelling: deep cold water moves upward to take place of surface water

o Brings up nutrient rich water

Shoreline Currents

· Short currents that form near shore

o Longshore current: form when waves approach the shore at an angle; forms a zigzag current parallel to the shore

o Rip Current: formed by longshore currents getting trapped by sand or rocks. Creates a powerful stream of water that flows away at a right angle to the shore

§ Dangerous to swimmers: to escape swim parallel to the shore

o Undertow: water carried to the shore in waves pulls back to ocean; usually not very strong