Tectonic Plates - again The mantle is made up of liquid rock that is constantly moving. The tectonic plates float on top of the mantle. They too are constantly moving.

This map shows the topography of the ocean’s floor

There are three basic motions of ocean water Currents Waves Tide

There are masses of water that are always drifting about in the sea There are masses of water that are always drifting about in the sea. The circulation is very complicated because many things help to push water about. One of these is the tendency of dense water to sink and lighter water to rise. The densest water in the ocean is both cold and salty. It is made this way when sea water freezes in the Arctic or Antarctic oceans. There is very little salt in the ice that is formed by this freezing. The cold, salty water left behind when the ice is formed sinks right to the bottom of the sea. The saltiest water in the ocean is found in the tropics. The water is very warm and therefore not so dense as the cold, less salty water underneath it. It stays at the surface of the ocean. The salty water is pushed about by the winds. Sometimes the winds and the shape of the coastline push the circulating water together. Then the water has to flow much faster and becomes a current. Currents are like rivers in the sea.

The Gulf Stream

The sun and moon affect our tides

Winds affect the waves

The deeper you go in the ocean, the more things change Less sunlight can be seen the deeper you go Water pressure becomes much greater as you go deeper The water temperature becomes colder as you go deeper

Light in the ocean

Phytoplankton Phytoplankton needs two things for photosynthesis – and thus, their survival and growth – energy from the sun and nutrients from the water. In the process of converting these growth resources into more cells, they release oxygen. Half the world’s oxygen!

The Ocean’s Food Chain