Currents, Waves, & Tides Highways 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 surface 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

 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 Christmas time. El Niño

 Powerful upwellings bring deep cooler waters to the surface  This colder than normal condition is called La Niña (opposite of El Niño) La Niña

 The interconnected flow of currents that redistribute heat  Earth’s “air conditioner”  Moderates the world’s climate Ocean Conveyor Belt Animation: html Ocean Conveyor Belt

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  Main type of progressive wave for oceans: 1)Orbital: transmit through fluids only; energy moves fluid in a circular motion Anatomy of a Wave

 Disturbing forces (cause waves): 1.Winds (most common) 2.Seismic activity: earthquakes and volcanic eruptions (tsunamis)  Restoring forces (resist waves): 1.Gravity (main force here for large waves) 2.Coriolis Effect: good for resisting tides 3.Surface tension: resists surface disturbances in tiny waves Forces that Cause Waves

 Refraction: bending of light rays; as will bend the ocean waves 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 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 (first-quarter and third-quarter). Sun, Moon, and Types of Tides

First Quarter Moon Third Quarter Moon