Currents and Waves Surface Currents Ocean Circulation Patterns

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