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The air and the sea exchange gases. Ocean currents are caused by tides, winds and changes in water temperature and salinity.
The sea is the salty water that includes the Arctic, Atlantic, Indian, Pacific and Southern Oceans. The sea covers 70% of planet Earth.
Gases move backwards and forwards between the sea surface and the air.
How easily gases are able to move between water and air depends on the sea conditions:
The sea is always moving. When huge masses of sea water move they cause currents. Here are the main reasons for why there are currents in the oceans.
The surface can be very different from the rest of the ocean below. Colder water and salty water are both more dense and sink causing ocean currents. Winds stir up the surface water.
Sea ice forms on top of sea water. Salt is squeezed out of the ice as it freezes and collects under the ice. This makes the sea water more dense. Image LEARNZ