APES Chapter 4 Module 11

Gyres

*Redistribute heat near the ocean **Cold water from the polar regionsmoves along the west coasts of continents, and the cooler air above these waters brings cooler temps to the adjacent continents. **That's why coastal areas of California have cooler temps than cities along the same latitude in the Eastern United States. ***Warm water from the tropics moves along the east coasts of continents, the warm air immediately above it brings warmer temps.

Thermohaline Circulation

Drives the mixing of surface water and deep water. **This process Is crucial for moving heat and nutrients around the globe. ***Thermohaline circulation appears to be driven by surface waters that contain unusually large amounts of salt. ****Warm currents flow from warm waters, like the Gulf of Mexico to the colder waters of North Atlantic. Some of this water freezes or evaporates. The salt left behind increases the salt content of water. ***This salty water is dense and sinks, mixing with deeper ocean waters. ****The sinking of cold, salty waters and the rising of warm water near the equator create movement that drive a deep, cold current that moves past Antarctica and northward to the Pacific Ocean. ***It surfaces and returns to the Gulf of Mexico. ***This journey of water can take hundreds of year. But this is the circulation that helps mix the water of all of the oceans. ****The ocean currents associated with thermohaline circulation affect nearby landmasses (as much as those affected by gyres). Movement of warmer tropical waters warm latitudes that would otherwise be much colder. **ex- England's average winter temp. is 20 degress C. warmer than that of Newfoundland, Canada which is located at a similar latitude but receives cold ocean currents from the North Atlantic.

Upwelling

Highly productive ocean ecosystems- Ocean currents separate from one another (diverge) causing deeper waters to rise and replace water that has moved away. This upward movement is called UPWELLING. The deep waters bring nutrients from the ocean bottom that have large populations of producers. These producers, in turn, support populations of fish.

Global Warming and Thermohaline Circulation

If increased air temps. accelerate the melting of glaciers in the Northern Hemisphere, the water will become less salty and less likely to sink. This will upset the cycle. **If this happens it will shut down the transport of warmer water to western Europe and England- and other locations will become much colder places.

How the water moves:

Northern Hemisphere: trade winds push water from northeast to southwest- but Coriolis Effect makes it move purely from east to west at the Equator. **In Northern mid-latitudes when the winds in the Northern mid-latitudes push water from southwest to northeast- the Coriolis Effect deflects it so it moves pure west to pure east.

El Nino

Remember- the cold, waters with lots of fish occur along South America's west coast. **every 3-7 years, the tropical current moves in the opposite direction. ***This occurs around December 25, so it is called "baby boy"- El Nino. This is named El Nino- Southern Oscillation (ENSO). It refers to a reversal of wind. SEE FIGURE 11.3- Ocean currents are important to global climates- but ENSO reduces upwelling off the coast of south America, which reduces fish populations. **El Nino- produces colder, wetter climates along southeastern United States and dry weather in Southern Africa and Asia.

What Drives Ocean Currents?

Temperature, gravity, prevailing winds, the Coriolis Effect, salinity, and the locations of the continents.

Flow of Ocean Water

The flow of ocean water is an important factor for global climates because it moves warm and cold waters to different parts of the globe. ***As a result, the ocean currents affect primary productivity found in different ocean regions as well as the climate of the adjacent continents.

Gyres

The large-scale patterns of water circulation that move clockwise in the northern hemisphere and counterclockwise in the southern hemisphere.

Movement From the Equator

Warm water, like warm air, expands and rises. So- tropical waters are about 8 cm higher than mid-latitude waters. **The force of gravity makes this higher-level water flow away from the Equator. **This is part of what makes surface waters circulate.

Clockwise vs. Counterclockwise

ocean currents between the equator and mid-latitudes rotate in a clockwise direction in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.