The Movement of Ocean Water Chapter 14 The Movement of Ocean Water

I. Currents Ocean currents are streamlike movements that can be influenced by a number of factors - weather, Earth’s rotation, the position of the continents

A. Surface Currents Horizontal, streamlike movements of water that occur at or near the surface of the ocean Controlled by three factors: global winds, the Coriolis effect, and continental deflections

1. Global Winds - Winds that blow across the Earth’s surface create surface currents in the ocean - Near the equator, the winds blow ocean water east to west - Near the poles, the winds blow ocean water west to east

2. The Coriolis Effect - The apparent curving of moving objects from a straight path due to the Earth’s rotation - Causes surface currents in the Northern hemisphere to turn clockwise - Causes surface currents in the Southern Hemisphere to turn counterclockwise

3. Continental Deflections - Surface currents deflect, or change direction when they meet continents

B. Deep Currents Streamlike movements of ocean water located far below the surface Form in parts of the ocean where water density increases - Density is the amount of matter in a given space, or volume - Density is affected by temperature and salinity - Increases with decreased temperature as water molecules slow down - Increases with increased salinity

II. Currents and Climate A. Surface Currents and Climate 1. Warm-Water Currents and Climate Create warmer climates in coastal areas that would otherwise be much cooler 2. Cold-Water Currents and Climate Keeps the climate near the coast cooler than the inland climate year-round

3. Upwelling Cold, nutrient-rich water from the deep ocean rises to the surface and replaces warm surface water The nutrients that are brought to the surface of the ocean support the growth of phytoplankton and zooplankton that in turn support other organisms

4. El Niño A change in water temperature that produces a warm current Side Note: La Niña is a change in water temperature that produces a cool current

El Niño can create flash floods and mudslides in regions that usually receive little rain Regions that usually get a lot of rain may experience droughts Occurs every 2 to 12 years so predicting it can be difficult

III. Waves A. Anatomy of a Wave Waves are made up of two main parts – crests and troughs - A crest is the highest point of a wave - A trough is the lowest point of a wave The distance between two adjacent crests or troughs is a wavelength The vertical distance between the crest and trough of a wave is called the wave height

B. Wave Formation and Movement Waves form as wind blows across the water’s surface and transfers energy to the water The energy moves through the water, but the water itself stays behind - Water from the middle of the ocean does not “move” to the shore

Wave energy decreases as the water depth increases Wave energy reaches only a certain depth - Water is not affected by wave energy below that depth

C. Specifics of Wave Movement Waves travel at different speeds To calculate wave speeds, scientists must know the wavelength and the wave periods Wave period is the time between the passage of two wave crests (or troughs) at a fixed point

wavelength (m) Wave speed (m/s) = wave period (s) - An increase in the wave period decreases wave speed - A decrease in the wave period increases wave speed

D. Types of Waves Underwater earthquakes and landslides as well as impacts of cosmic bodies can form different types of waves

1. Deep-Water Waves and Shallow-Water Waves Deep-water waves are waves that move in water deeper than one-half their wavelength When deep-water waves reach the shore, the bottom of their waves begin to interact with the ocean floor This interaction creates shallow-water waves

This change increases wave height Gravity pulls the high wave crests down creating breakers Waves that “break” make up the breaker zone The area between the breaker zone and the shore is the surf

2. Shore Currents When waves crash on the beach, or the surf, the water the waves crash into flows back to the ocean underneath new incoming waves This movement of water is called an undertow Undertows carry sand, rock particles, and plankton away from the shore

3. Longshore Currents Occur when waves hit the shore at an angle Produces a current that travels near and parallel to the shoreline

4. Open-Ocean Waves a. Whitecaps - Usually form during stormy weather - Short lived - Very steep crests that break before getting close to the shore

b. Swells - Formed by calmer winds far away from the shore - Travel for thousands of kilometers - Roll gently

5. Tsunamis Form when a large volume of water is suddenly moved up or down - Due to underwater earthquake’s volcanic eruptions, landslides, underwater explosions, or the impact of a meteorite or comet

6. Storm Surges A rise in sea level near the shore caused by strong winds, such as a hurricane Water is blown in a center direction, allowing it to gather at a higher level

IV. Tides Daily changes in the level of ocean water Influenced by the sun and the moon A. The Lure of the Moon The gravity of the moon pulls on every particle of the Earth Its pull on liquids is greater than its pull on solids because liquids move more easily

1. High Tide and Low Tide - The moon’s pull is strongest on the part of the Earth directly facing the moon - When part of the ocean is directly facing the moon, the water there bulges toward the moon creating high tides - The water on the opposite side of the Earth is “left behind” as the moon also pulls on the center of the Earth, creating another high tide - Low tides occur on each side of Earth not in the Earth-Moon line

2. Timing the Tides - Because Earth’s rotation is faster than the moon’s revolution around the Earth, tides occur on different locations on Earth, twice a day - It takes 24 hours and 50 minutes of a spot on Earth and the moon to rotate and face one another again

B. Tidal Variations The sun’s influence on tides is less powerful than the moon’s because it is further away A tidal range is created by the position of the Earth, Sun, and Moon, and the influences of the Sun and Moon on Earth’s tides

1. Spring Tides - Occur when the Sun, Earth, and Moon are aligned - When the moon is full or new; occur every 14 days - Creates the largest daily tidal range, or the difference between high and low tides

2. Neap Tides - Occur when the Sun, Earth, and Moon form a 90° angle - The first and third quarters of the moon - Creates the smallest daily tidal range because the gravitational forces by the sun and moon are working against each other - Occur halfway between the occurrence of spring tides