9.2 Ocean Waves, Tides and Currents

Wave Characteristics Most ocean waves are energy passing through water caused by the wind Crests are the top of the waves Troughs are the bottom of the waves

Wave Characteristics Wave Height is the vertical distance between trough and crest Wavelength is the horizontal distance between two crests or two troughs Wave period is the time one wave takes to pass a fixed position.

Wave Characteristics The height, length, and period of a wave depends of three factors: Wind speed Length of time the wind has blown Fetch, or the distance that the wind has traveled across open water

Wave Motion Waves can travel great distances across ocean basins The energy of the wave, not the water itself, travels across the ocean Circular orbital motion allows energy to move through the water, water particles move in circles Energy is moved across the ocean as well as downward

Breaking Waves In deep water waves are unaffected by depth In shallow water waves speed slows down causing waves farther out to catch up Speed and length decrease, wavelength shortens, the wave grows higher When wave is too high to support itself, it collapses Turbulent water created by breaking waves is called surf

Tides Tides are regular changes in the elevation of the ocean surface The pull of gravity from the moon and, to a lesser extent by the sun, creates tides The pull of gravity of the moon and sun is greater on the Earth that’s nearest the source of gravity

The Cause of Tides The difference in gravitational pull on Earth closest and farthest from the moon stretches the Earth Inertia is the property of an object that is in motion to stay in motion, and an object at rest to stay at rest Due to inertia ocean water flows towards both areas - closest and farthest from the moon - creating a tidal bulge, or high tide Question: What causes the high tides on both sides of the Earth? Answer: Inertia!

Tidal Cycle Spring tides are when the sun and moon are aligned, their forces of gravity creates larger tidal bulges Spring tides happen during new and full moons Neap tides are when the sun and moon are not aligned, their forces off-set each other, creating small tidal bulges Question: Do Spring tides happen only in the Spring? Answer: No they happen twice every month.

Tidal Patterns Many factors effect tides, such as shape of the coastline, the ocean basins, and water depth Three main tidal patters: Diurnal tides – single high tide and single low tide each tidal day Semidiurnal tide – two high tides and two low tides each tidal day Mixed tide – Usually two high and two low tides, however heights are varied. (Our tides here on the Pacific Coast) Question: Name the factors that effect tides. Answer: Moon and sun’s position; day in the tidal cycle; shape of coastline; ocean basin; and water depth.

OCEAN SURFACE CIRCULATION Ocean currents - masses of ocean water that flows from one place to another Surface currents – water that flows horizontally in the upper part of the ocean’s surface Developed from friction between the ocean and wind that blows across its surface

Gyres Gyres – Large circular currents moving water in a circular motion on the ocean’s surface in an ocean basin 5 main ocean gyres: North Pacific Gyre, South Pacific Gyre, North Atlantic Gyre, South Atlantic Gyre, Indian Ocean Gyre Pair Share: What do you think the red and blue lines represent? Answer: Red - warm water, Blue - cold water

Coriolis Effect Coriolis effect – the deflection of currents away from their original course as a result of Earth’s rotation Flow in opposite directions in the two different hemispheres

Ocean Currents and Climate Ocean currents effect climate by transferring heat from one area to another When water flows from the equator to the poles the warm water heats the atmosphere. Some countries such as England have warmer weather because of ocean currents.

DEEP-OCEAN CIRCULATION Deep-Ocean Currents – water that flows vertically mixing deep & surface water caused by differences in density Upwelling – The rising of cold water from deeper layers to replace warmer surface water Important in providing nutrients to sea life

Sources of currents Deep currents are: found primarily in high latitudes (poles) at the surface. created from increased salinity of ocean water due to evaporation. Question: Why is the warm water shallow & the cold water deep? Answer: Colder water is denser and sinks below warm water Conveyor Belt model