16.1: Ocean Circulation
I. Surface Circulation
•
Ocean currents: masses of ocean water that flow from one place to another
– Vary in size and depth location
•
Surface currents: flow horizontally in the upper part of the ocean’s surface
– Develop from friction between the ocean and wind that blows across the surface
– Lifetime & areas affected vary from temporary to almost permanent
•
Gyres: huge circular moving currents that dominate the ocean surface
– Five main ocean gyres: North Pacific, South Pacific, North Atlantic, South Atlantic, & Indian
Ocean
– The Coriolis Effect determines direction of spin (Northern Hemisphere opposite of Southern)
– Within each gyre are usually four main currents
•
Ocean Currents & Climate:
– Ocean currents from low latitudes transfer heat from warmer to cooler areas.
• EX: The Gulf Stream brings warm water to the North Atlantic, warming Europe during the
winter.
– Cold currents travel toward the equator and moderate the water temperatures of adjacent land areas.
– Ocean currents play a major role in maintaining Earth’s heat balance.
• Ocean currents account for ¼ of Earth’s heat transfer.
• Winds transport the other ¾.
•
Upwelling: the rising of cold water from deeper layers to replace warmer surface water
– Occurs when surface waters are pulled away from the shore.
– Upwelling brings greater concentrations of dissolved nutrients to the ocean surface.
• This is important to fishing industries worldwide.
II. Deep-Ocean Circulation
•
Deep-ocean currents are largely vertical (versus horizontal surface currents).
•
Density currents: vertical currents resulting from density differences among water masses
– Denser water sinks and spreads out slowly.
•
•
•
– Density can increase by a decrease in temperature or an increase in salinity.
High Latitudes:
– Dense water masses form at high latitudes and initiate deep-ocean density currents when they sink.
– The dense water masses remain largely unchanged as they travel, making tracking possible.
Evaporation:
– When sea water evaporates, the salt is left behind increasing salinity and density.
• Happens specifically in the Mediterranean Sea; water mass then flows out to the Atlantic
Ocean and travels toward Antarctica.
A Conveyor Belt:
– A simple model of ocean circulation looks like a conveyor belt.
– Warm waters flow near the surface; cooler water has a subsurface flow.