Currents, Waves, & TidesHighways in the Sea

What forces are responsible for currents? Wind: transfers energy through friction on

surface; causes currents and waves Sea level: steeper slope=greater pressure

gradient=drives a larger, faster current Water density: greater density in one area

causes pressure gradient to drive a current below the surface

Causes of Currents

What influences the direction and nature of these currents?- Ocean boundaries force currents in various

directions; - Trade winds and the westerlies account

for most of the wind’s energy that drives currents

Causes of Currents

How do Western Boundary Currents differ from Eastern Boundary Currents?- Eastern Currents: carry cool water towards

equator; tend to be wide and shallow; not common to have eddies spin off these currents

- Western Currents: much stronger; western intensification: Coriolis effect is a major contributor; Trade winds also contribute to the strong western currents

Western VS Eastern

Wind-driven currents that flow vertically Upwelling: upward vertical current that

brings deep water to the surface Downwelling: downward vertical current

that pushes surface water deep into the ocean

What kind of biological effect does this have?-nutrients to shallow waters and to deeper waters-weather patterns

Upwellings & Downwellings

Buildup of warm water in the Central and Eastern Equatorial Pacific

Tremendously affects world weather patterns

El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime

El Nino

Powerful upwellings bring deep cooler waters to the surface

This colder than normal condition is called La Nina (opposite of El Nino)

Scientists still trying to determine what exactly causes these warm and cold phases

La Nina

The interconnected flow of currents that redistribute heat

Earth’s “air conditioner” Moderates the world’s climateOcean Conveyor Belt Animation:http://bcs.whfreeman.com/thelifewire/content/chp58/5802003.html

Ocean Conveyor Belt

1. Drogue: float that determines the drift of currents2. Argo Float: float that transmits data to satellites 3. Various Flow Meters: measure and record current

speed and direction (Eulerian study method)4. Doppler Acoustic Current Meter: determines

current direction and speed5. Flotsam method: accidental opportunities to study

currents; ships losing cargo that wash up on beaches and can improve computer models of currents

How do we study currents?

Waves & Tides

What is a wave?-Transmission of energy through matter; matter moves back and forth or rotates, but then returns to its original position Three types of progressive waves:1) Longitudinal: when matter moves back and forth in same

direction energy travels2) Transverse: motion of matter is perpendicular to the

direction in which the whole wave is moving3) Orbital: transmit through fluids only; main waves that

concern us with respect to the ocean; energy moves fluid in a circular motion

Anatomy of a Wave

Wavelength: measured as horizontal distance between identical points on two waves; crest to crest

Crest: highest point above the avg water level Trough: lowest point Height: vertical distance from the trough to the crest Period: time it takes for the same spot on two waves

to pass a single point Frequency: number of waves that pass a fixed point

in one second

Wave Terms:

Disturbing forces (cause waves):1. Winds (most common)2. Changes in gravity3. Seismic activity: eartquakes and volcanic eruptions

(tsunamis) Restoring forces (resist waves):1. Gravity (main force here for large waves)2. Coriolis Effect: good for resisting tides3. Surface tension: resists surface distrubances in

tiny waves

Forces that Cause Waves

Deepwater Waves:- Occur in water that is deeper than half their wavelength- No interaction with the bottom floor can change any

wave characteristics- The orbital motion progression is also unaffected Shallow-water Waves:- Occur in water that is shallower than one-fourth the

wavelength- Bottom creates a drag that affects the orbital motion- Flattens the circular motion Both can exist at the same time!

Deep Waves VS Shallow Waves

Refraction: bending of light rays; bend the ocean waves as well when waves begin to approach the ocean shore at an angle

Diffraction: occurs when waves pass an obstacle, like a jetty; energy shift within a wave, allowing a new wave pattern to form

Reflection: occurs when waves hit an abrupt obstacle that is nearly perpendicular in the water, like a sea wall; in this case, the wave retains much of its energy and bounces back towards open waters

Refraction, Diffraction, Deflection

What causes a storm surge?- This is a destructive wave that forms when high

winds push water against the shore, where it piles up What causes seiches?- This is a form of standing wave that can be destructive;

result from a strong wind that pushes the water level up on one side of a lake or basin

What causes tsunamis? -results from sudden water displacement caused by a landslide, an iceberg falling into sea from a glacier, a volcanic eruption, or an earthquake (most common)

Destructive Waves

TIDES

Tides: variations in the ocean’s level Result from the gravitational pull of the moon and

(to a lesser degree) the sun They pull the ocean into a huge wave with a wave

length the size of an ocean basin Sun and moon create two bulges on opposite sides

of the Earth; position of the sun and moon change slowly, causing the bulge to rotate around the Earth

As a coastline rotates into the bulge, the tide rises; as it rotates out, the tide falls

What causes Tides?

The imperfect sphere of the Earth The season Time of the month The shape of the ocean basin Coriolis effect

What influences besides lunar and solar gravity affect the tides?

Diurnal: single high and low tide that occurs daily in certain locations; Gulf of Mexico

Semidiurnal: have two roughly equal high and low tides daily; happens on east coast of US

Mixed: consists of two unequal high and low tides daily; happens in Pacific coast of the US

Types of tides: vary with location

The influence of the moon on the tides is about twice the influence of the sun

1) Spring Tides: when the sun and the moon are aligned on the same side of Earth (new moon) AND when the sun and moon are aligned on opposite sides of Earth (full moon)

2) Neap Tides: when the sun’s gravitation pulls to the side of the moon’s tidal bulge and tends to raise low tides and lower the high tide

Sun, Moon, and Types of Tides