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 1st and 3rd 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/ft2

• 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