DYNAMIC OCEAN Chapter 16

SURFACE CIRCULATION  Surface currents  Move horizontally on the upper surface of the ocean  Wind blowing across the surface  Usually local and seasonal  Gyres  Large circular movements that dominate the ocean surface  North Pacific Gyre, South Pacific Gyre, North Atlantic Gyre, South Atlantic Gyre, and Indian Ocean Gyre  Clockwise in northern hemisphere and counterclockwise in southern hemisphere

SURFACE CIRCULATION CONT…  Ocean Currents and Climate  The ocean currents bring heat to the land at higher elevations (water changes temperature slower than the air)  Ocean currents also bring colder water to the tropics cooling the neighboring land  Upwelling  Vertical movement of water due to wind  When the colder water from the deeper ocean is lifted up the nutrients come with it  Coastal upwelling happens when wind blowing towards the equator are parallel to the coast which moves the surface layer away from the coast – the surface water is replaced by colder water from deeper in the ocean

DEEP-OCEAN CIRCULATION  Density Currents  Vertical currents due to density differences (remember temperature and salinity)  In high latitudes the water stays cold and as sea ice forms salinity increases so the water gets more dense so it sinks  Once it sinks it slowly moves thanks to under water currents  Evaporation also increases salinity (more likely to happen in the tropics where it is warmer) so the water sinks and again gets moved slowly  The Conveyer Belt  Ocean circulation that moves water from the Atlantic Ocean to the Indian Ocean and then the Pacific Ocean  Cold water from the poles moves to the equator where it gets warmed and goes back to the poles

WAVES  Energy transfer (a way see the energy moving through the water)  Usually due to wind  Crests are the tops of the wave – separated by troughs  Trough to crest is wave height  Distance between two crests is the wavelength  Time it takes for the wave to travel is the wave period  Wind speed  How long has the wind been blowing  Fetch (distance the wind has travelled across open ocean)

WAVES CONT…  Wave Motion  The energy of a wave can travel from one continent to another  Water passes the energy by flowing in circles – called circular orbital motion  This is why a floating object in the ocean bobs up and down as also rocks back and forth  The water molecules move in a circle but the energy moves forward  As the energy moves into the deeper water is does dissipate  Breaking Waves  In deep water wave depth doesn’t matter but in shallow water the base of the wave hits bottom and slows  Waves behind it catch up as it slows so the wavelength decreases  The wave gets higher until it is so steep it breaks – makes surf

TIDES  Daily changes in the level of the ocean surface  Gravity attracts the Earth and Moon to each other  Inertia is an objects tendency to keep moving in a straight line  Gravity is greater on the side of Earth where the moon is located so water is pulled towards the moon (a tidal bulge)  Inertia has the greatest pull on the side of Earth opposite the moon so water moves away from the moon (a tidal bulge)  The Earth rotates through the tidal bulges giving you two high tides and two low tides each day

TIDES CONT…  Sun also pulls on water - most noticeable during full and new moons because the pull of the sun is added to the moon’s pull – makes the tidal bulges larger (higher tides)  Tidal range – difference between high and low tides  Spring tides have the largest tidal range (new and full moons)  Neap tides have the lowest tidal range (moon and sun are at right angles)  Diurnal tides – one high and low tide a day (Gulf of Mexico)  Semidiurnal tides – two high tides and low tides a day (Atlantic US)  Mixed tidal pattern – the heights of the high and low tide differ greatly (usually semidiurnal) (Pacific US)

SHORELINE FORCES  Waves cause erosion, especially during storms  Water enters cracks in rocks which compresses the air – the air expands when the water leaves making the cracks bigger  Abrasion  Rocks in the water scrape rocks on the shore – the broken down rocks makes sand  Wave Refraction  Bending of the waves  Waves are usually almost parallel to the shore because the wave bottom slows and the top stays fast  Wave energy stronger against sides and ends of headlines but weaker in bays

SHORELINE FORCES CONT…  Swash, an uprush of water, as the wave break on shore  Creates a longshore current that pulls sediment along the shore  Usually flows southwards along the Atlantic and pacific coast of the US  Erosional Features  Wave-cut cliffs and platforms  Sea Arches start as sea caves and end as sea stacks  Depositional Features  Spit – deposited ridge of sand projecting from the land into the bay  Sandbars – sand is deposited across the bay separating the bay from the ocean  Tombolo – deposited sand connects an island to the mainland or another island  Barrier Island – sandbars that are parallel but separate from the coast

STABILIZING THE SHORE  Protective Structures  Groins – barrier built at a right angle to the beach designed to trap sand so the beach can be maintained or widened  Breakwater – stops the energy from large waves, generally used to protect boats moored in calm water  Seawall – shields the coast from breaking waves, usually to protect buildings  Beach Nourishment  Adding sand to a beach  Expensive and temporary  The replacement sand at Waikikii Beach caused the water to get murky and killed the offshore coral (lack of sunlight)