Currents and Waves

Surface Currents Ocean Circulation Patterns –Winds are the primary driving force –Relationship between oceanic circulation and atmospheric circulation

Surface Currents –Coriolis effect Currents are deflected due to the Earth’s rotation To the right in the Northern Hemisphere To the left in the Southern Hemisphere

Surface Currents Ocean Currents and Upwelling –Upwelling Rising of cold water from deeper layers to replace warmer surface water— vertical movement Brings up concentrated nutrients

Surface Currents The Importance of Ocean Currents –Affect time to reach a destination –Affect climates—moderate temperatures –Helps maintain Earth’s heat balance

Deep-Ocean Circulation Gravity and density differences Temperature and salinity create a dense mass of water –Thermohaline circulation –Water is made colder and saltier at the surface, becomes more dense, and sinks –Arctic and Antarctic mainly affected

Tides Causes –Gravity –Bulge toward and away from the moon –Two high tides and two low tides per day –During new and full moons, moon and sun affect tides Spring tide—higher crests and lower troughs –During 1 st and 3 rd quarters of the moon Neap tide—daily tidal range is less

Tides Types of Tides –Semidiurnal Twice daily –Diurnal Single high and low water height each day –Mixed Inequality of tides

Tides Tidal Currents –Horizontal flow of water accompanying the rise and fall of the tide –Flood currents Advance into the coastal zone as the tide rises –Ebb currents Water retreats during low tide –Slack water Between flood and ebb

Tides –Tidal flats Areas affected by flood and ebb currents –Tidal deltas Deposits created by tidal currents

Waves Modify the Shoreline Characteristics of Waves –Crest—top of a wave –Trough—bottom of a wave –Wave height—length between crest and trough –Wavelength—length between two crests –Wave period—time interval between successive crests

Waves Modify the Shoreline Types of Waves –Energy Move through the nearly stationary medium of the water –Oscillation Waves in the open sea –Translation Water advances up the shore because of a break

Wave Erosion Pressure from waves can exceed 2000 lb/ft 2 Causes air in cracks to compress and then expand as the wave recedes Abrasion –Sawing and grinding of water with rock fragments

Wave Refraction Bending of waves Affects distribution of energy Influences erosion, sediment transport, and deposition