Ocean Currents, Waves, and Tides

Major Ocean Currents An Ocean Current is a large volume of water flowing in a certain direction. Wind-driven currents are called surface currents. Surface currents carry warm or cold water horizontally across the ocean’s surface

Major Ocean Currents Surface currents extend to about 400 m below the surface, and they move as fast as 100 km/day. Earth’s major wind belts, called prevailing winds, influence the formation of ocean currents and the direction they move.

Rip Currents A rip current is a narrow, powerful surface current which flows away from the shore. It is caused by pressure building up from uneven buildup of water from waves. They can flow very quickly and can be difficult to detect until you are in one.

Rip Currents are Dangerous! Rip currents are responsible for about 150 deaths every year in the United States. About 80 percent of all beach rescues are related to rip currents. Rip currents don’t pull swimmers under, they flow out for several miles. If you get caught in a rip current, swim parallel to the shore until you are out of the current.

Coriolis Effect The Coriolis Effect is the movement of wind and water to the right or left that is caused by Earth’s rotation. It causes fluids such as air and water to curve to the right in the Northern hemisphere, in a clockwise direction. cases fluids to curve to the left in the southern hemisphere, in a counterclockwise direction.

Coriolis Effect The shapes of continents and other land masses affect the flow and speed of currents. Currents form small or large loops and move at different speeds, depending on the land masses they contact.

Upwelling Upwelling is the vertical movement of water toward the ocean’s surface. Upwelling occurs when wind blows across the ocean’s surface and pushes water away from an area. Deeper colder water then rises to replace it. Upwelling often occurs along coastlines. Upwelling brings cold, nutrient-rich water from deep in the ocean to the ocean’s surface.

Density Currents Density Currents are a type of vertical current that carries water from the surface to deeper parts of the ocean. Density Currents are caused by changes in density rather than wind. Cold water is more dense than warm water Density currents circulate thermal energy, nutrients and gases.

Impacts of Weather and Climate Warm-water currents and cold-water currents affect weather and climate in different ways Regions near warm-water currents are often warmer and wetter than regions near cold-water currents

Impacts on Weather and Climate The Gulf Stream is a warm-water current that affects coastal areas of the southwestern United States by transferring lots of thermal energy and moisture to the surrounding air. The cold California Current affects coastal areas of the southwestern United States.

Great Ocean Conveyor Belt The Great Ocean conveyor Belt is the name for a model of the large system of ocean currents that affects weather and climate by circulating thermal energy around Earth. In this model, high salinity water cools and sinks in the North Atlantic, and deep water returns to the surface in the Indian and Pacific Oceans through upwelling

Great Ocean Conveyor Belt Scientists estimate that the Great Ocean Conveyor Belt model takes about 1,000 years to complete a cycle.

Tides The rhythmic rise and fall of the ocean’s water High tide = rising, incoming tide, flow Low tide = receding, outgoing tide, ebb Slack tide = vertical movement stops

Tides are very long, slow waves They have a wave period of 12 hours 25 min Tidal day is 24 hours 50 min

What Causes Tides? 1. Gravitational pull of sun & moon on Earth Moon closer, therefore > effect Like magnet, pulls water away from surface = TIDAL BULGE

2. Centrifugal Forces Bulge on opposite side because centr. force > pull of moon Produced by motions of Earth, sun, & moon

Types of Tides Spring Tide - Moon and sun are in direct line with one another - Results in unusually high tidal range Tidal Range = vertical distance between high & low tides 2x’s/month

Neap Tide sun and moon are at right angles Pulls cancel each other out – causes a weak pull unusually low tidal range 2 x’s / month

Spring vs. Neap Tides

Distance bet. Moon & Earth Perigee Tides Moon closest to earth, very high tides (causes flooding) Apogee Tides Moon farthest away from earth, very low tides

Types of Tides Continued Diurnal Tides 1 high & 1 low / day Parts of Gulf of Mexico and Asia Semi-Diurnal Tides 2 high & 2 low / day Atlantic coasts of North America and Europe Mixed 2 high & 2 low / day (height varies) Pacific coast

Importance of Tides Expose & submerge orgs Circulate water in bays & estuaries Circulates food, wastes, etc Trigger spawning (grunion, horseshoe crab)

Waves A disturbance which moves through or over the surface of a fluid Mostly caused by winds (Also earthquakes, volcanoes, grav. pull) Form of great energy

Wave Characteristics Parts of a Wave Crest = high point Trough = low point Height = vertical distance from crest to trough Wavelength = Horizontal distance between crest to crest or trough to trough

Wave period : time for 2 crests to pass fixed point (T) sec Wave speed (C) : C = wavelength / T (m/s) Wave steepness : H / wavelength When H / wavelength = 1/7 or angle at crest 120 or less = Breaker

Size of Wind Generated Waves Depends on 3 things: Wind Speed Wind Duration (length of time wind blows) “Fetch” Extent of open water across which the wind can blow

Water Motion in Waves Water travels in vertical circular orbits Wave moves, particles don’t!

Importance of Waves Shaping Coastlines Ecology Erode cliffs Grind rock into sand Ecology Returns O2 to water Stir up food for filter feeders

Types of Waves CHOP – Short period (back bays) SWELL – Long period (boat rolls; seasickness) SWASH – water up beach BACKWASH – back down

TSUNAMI “TIDAL WAVE” Caused by undersea quake or volcano Wavelength = ~150 mi. Wave height = 6” – 1’ Can NOT perceive in boat Speed > 500 mph Slows down to ~25 mph at shore; water builds up to ~65+ ft

Tsunami Waves

Creation of a Tsunami