(c) McGraw Hill Ryerson 2007 Ocean Currents Textbook pages 414-427 (c) McGraw Hill Ryerson 2007

11.2 Ocean Currents What is an ocean current? ocean currents are like huge rivers moving through the ocean There are more than 20 major currents, moving around the Earth.

11.2 Ocean Currents The largest current is the Antarctic Circumpolar Current, which is 24 000 km long

11.2 Ocean Currents There are two types of ocean currents: 1) surface currents (0 - 200 m deep) 2) deep water currents (below 200 m)

11.2 Ocean Currents 1) What Makes Surface Currents Move? a) Wind Becomes less dense and rises

11.2 Ocean Currents The sun warms the air so it rises. Cooler air rushes to replace it This creates a convection current that we call wind. As the wind moves over the surface of the ocean, it pushes the water molecules along in the same direction

11.2 Ocean Currents b) Spin of the Earth

11.2 Ocean Currents The Earth spins from West to East (counter clockwise) dragging the winds and oceans with it Winds and currents are deflected toward the west This is called the Coriolis effect.

11.2 Ocean Currents c) Shape of continents Currents flow around the continents like water moves around rocks in a stream.

11.2 Ocean Currents 2) What Makes Deep Currents Move? Water temperature There are 3 layers in the ocean: Surface: 0 - 200 m - warm Thermocline: 200 m - 1 km - cold Deep water: > 1 km - just above freezing

11.2 Ocean Currents

11.2 Ocean Currents b) Water salinity Fresh water from rivers decreases the salinity of ocean water near continents Fresh water is less dense and rises Evaporation and freezing increases the salinity of ocean water Salty water is more dense and sinks

11.2 Ocean Currents The densest coldest and saltiest ocean waters are at the north and south poles This water sinks, then moves along the ocean floor in a Density current.

11.2 Ocean Currents When cold dense nutrient-rich water is pushed up to the surface from the bottom of the ocean it is called Upwelling. Upwellings bring nutrients to the surface.

11.2 Ocean Currents How do Waves Move Ocean Water? Most waves are created by wind. In open ocean, waves are called swells. When swells approach shallow water, they “break,” showing the characteristic curl.

11.2 Ocean Currents The largest waves are called tsunamis, and are caused by undersea earthquakes, undersea landslides, undersea volcanic eruptions

11.2 Ocean Currents How do Tides Move Ocean Water? Tides are caused by the gravities of the Earth and the Moon. The moon orbits the Earth, pulling all of the water in the oceans along with it.

11.2 Ocean Currents High tides occur on the areas of the Earth closest to the Moon (and the opposite side) Low tides occur at 90º to the high tides.

11.2 Ocean Currents When the Sun, Moon and Earth all line up, their combined gravities can create extreme tides, called spring tides When the Sun, Moon and Earth are not lined up, the tides are called neap tides.

11.3 Oceans and Climate Weather is the state of the atmosphere at any one time. Weather includes features such as: temperature wind air pressure moisture Climate is weather averaged over many years.

11.3 Oceans and Climate How do Oceans Affect Weather and Climate? Water has a high heat capacity. this means ocean water can store large amounts of thermal energy (heat) and takes a long time to heat up or cool down.

11.3 Oceans and Climate because water heats up and cools down slowly, ocean temperatures remain relatively stable. stable ocean temperatures influence weather in nearby areas, keeping temperatures relatively stable

11.3 Oceans and Climate Check Your Understanding: Vancouver and Penticton are at the same latitude, yet have very different climates. The climate of Penticton has much more extreme temperatures than that of Vancouver. Explain why.