Currents • Giant streams of water that flow in the ocean • 2 major types • Surface: caused by wind • Deep: caused by density/gravity
Surface Currents • This results in giant circular patterns called gyres • Gyres rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere • Created and maintained by wind • Generally move from east to west near the equator • Move west to east nearer to the poles
Surface Currents • The Kuroshio Current • Carries water out of the South China Sea north along the shore of Asia and then east across the far N. Pacific • The Gulf Stream • Carries water out of the Gulf of Mexico north along the shore of N. America and then east across the far N. Atlantic
Surface Currents • North Pacific Drift • Very slow current that carries water across the northern part of the Pacific Ocean, from west to east. • West Wind Drift • Very slow current that carries water around the world in the far southern hemisphere, from west to east
Surface Currents • North Pacific Gyre • General clockwise rotation of the Pacific Ocean, north of the equator. Near the center is relatively calm, current free water • There is NOT a giant garbage island in the middle of this Gyre, BUT there is a lot of microscopic plastic pollutants in the water.
Surface Currents • North Atlantic Gyre • General clockwise rotation of the Atlantic Ocean, north of the equator. Near the center is calm current free water called the Sargasso Sea • The Sargasso Sea is NOT a solid mass of seaweed that mysteriously clears ships of their crews.
Deep Currents • Very slow moving currents that are caused by differences in density • The deepest is the Antarctic Bottom Water • Very cold water = very dense water • Freezing water off the surface leaves very saline water behind = very dense water • This super-dense water sinks to fill the deepest parts of the ocean • This current is very slow
Deep Currents • North Atlantic Deep Water • Similar to the Antarctic Bottom water, but slightly less dense • Floats on top of the Bottom water and the current carries it down almost to Antarctica • The deep currents provide a foundation of water for the surface currents to ride over. • Movement of the surface water causes upwelling, which brings the deep water up to the surface.