Waves, Tides, and Currents MOTION IN THE OCEAN

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

Wave Characteristics  Parts of a Wave Crest = high point Crest = high point Trough = low point Trough = low point Height = vertical distance from crest to trough Height = vertical distance from crest to trough Wavelength = Horizontal distance between crest to crest or trough 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 Speed Wind Duration (length of time wind blows) Wind Duration (length of time wind blows) “Fetch” Extent of open water across which the wind can blow “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 Erode cliffs Erode cliffs Grind rock into sand Grind rock into sand  Ecology Returns O 2 to water Returns O 2 to water Stir up food for filter feeders Stir up food for filter feeders

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 “TIDAL WAVE”

Tsunami Waves

Creation of a Tsunami

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 They have a wave period of 12 hours 25 min Tidal day is 24 hours 50 min Tidal day is 24 hours 50 min NJ has 2 high and 2 low tides daily NJ has 2 high and 2 low tides daily

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

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

Types of Tides 2x’s/month 2x’s/month 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

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

Spring vs. Neap Tides

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

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

Currents What are currents? - “Rivers” of circulating water Causes - Wind - Rotating Earth - Density Changes

Surface Ocean Currents Broad, slow drifts; never cross equator Wind generated; circular gyres

Coriolis Effect - N. Hemis – clockwise; Right - S. Hemis – counterclockwise; Left

Gulf Stream - Brings warm water from equator north along east coast of N. A. - N. Atlantic -Sometimes form eddies – circulating water that pinches off from the current

MIGRATION NAVIGATION WEATHER

Localized Surface Currents Longshore Current. Flows parallel to shore; move sediment Flows parallel to shore; move sediment

RIP CURRENT - Caused by converging longshore currents - Very dangerous ; Red Flag - DO NOT fight rip current; swim parallel to shore to get out of channel

Deep Ocean Currents  Separated from surface currents by boundary called a “Thermohaline” (diff in densities)  Flow beneath surface; cross equator  Move North to South

Importance Of Deep Currents Upwelling Upwelling Brings deep water to surf.Brings deep water to surf. Circulates nutrients upCirculates nutrients up Moves plankton & larvaeMoves plankton & larvae