Review sheet – Chapter 8
• Know that a current is a moving mass of water driven by wind, or by differences in water density
• Know that surface currents are wind-driven and involve ~10% of the world’s ocean water
• Know that thermohaline currents are slow-deep currents that originate from density differences
caused by variations in water’s temperature and salinity
• Understand that surface currents move water horizontally, while thermohaline currents move
water vertically
• Know that ~2% of the wind speed is transferred to ocean current (the current’s speed is 2% of
wind speed)
• Understand that when currents occur in a circular pattern, they are called gyres
• Know that the North Atlantic gyre includes four currents: Gulf Stream, North Atlantic Current,
Canary Current, and North Equatorial Current
• Know that the Gulf Stream is an example of a western boundary current
• Understand that western boundary currents are the fast, narrow and deep surface currents that
bring warm water from the equator to the poles
• Understand that Coriolis has an impact on water currents; in the Northern Hemisphere, currents
move to the right of the wind direction
• Understand that the Ekman spiral results from subsequent layers of water exerting a frictional
drag on molecules immediately below them, with Coriolis effect acting upon each layer,
deflecting each layer to the right (in the Northern Hemisphere) of the direction of flow
• Understand that the net transport over the Ekman spiral is 90 degrees to the right of the wind
direction in the Northern Hemisphere
• Understand that because of Ekman transport, water in the center of gyres is piled up, creating a
hill of elevated water
• Understand that the North Atlantic Current transports warm water to Great Britain and the west
coast of Europe
• Understand that upwelling is the vertical upward movement of cold, nutrient-rich water to the
surface, while downwelling is the vertical downward movement of surface water (usually
nutrient-poor) to the depths of the ocean
• Know that upwelling commonly occurs along the equator and the west coast of the United
States, creating regions of high productivity
• Understand that El Niño is a phenomenon whereby warm water from the western Pacific (the
Pacific Warm Pool) travels eastward off the coast of Peru and creates a band of warm water
(and low pressure) across the equatorial Pacific
• Understand that sea surface temperature off the coast of Peru can increase by as much as 10°C
(18°F) causing sea level to rise by as much as 8 inches during an El Niño event
• Understand that during a La Niña event, the opposite occurs, where stronger trade winds
promote increased upwelling (and enhanced productivity) and results in a band of cooler water
stretching across the equatorial Pacific
• Understand that La Niña events usually occur after an El Niño event
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