APES Video Notes 4.9 - El Nino & La Nina

Ocean Circulation and Upwelling

• Ocean gyres are large surface-current circulation patterns driven by prevailing winds and shaped by continents:
  • They rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
  • Trade winds generally move equatorial surface water from east to west, while westerlies move it from west to east.
• Upwelling occurs when warm surface water moves away from a coast and colder, deeper water rises to replace it.
  • Deep water brings oxygen and nutrient-rich sediments to the surface.
  • This supports productive fisheries, including along the coast of South America during normal conditions.
• Thermohaline circulation is the global movement and mixing of ocean water. Temperature and salinity affect water density: cold, salty water becomes dense and sinks, helping move water and nutrients through the oceans.
  • This circulation also transfers heat. For example, the Gulf Stream carries heat toward Europe, helping make some regional climates warmer and more moderate.

ENSO and Normal Conditions

ENSO (El Niño–Southern Oscillation) is a recurring pattern of changes in Pacific Ocean surface temperatures, winds, and currents. It fluctuates between El Niño and La Niña conditions, with neutral conditions in between. These events may build and weaken over several years rather than occurring only within one calendar year.

In neutral conditions, easterly trade winds push warm surface water west toward Australia and Southeast Asia. This contributes to greater rainfall in those regions. Near the Americas, colder water rises to the surface, supporting nutrient-rich, productive fisheries. The pressure and air-circulation pattern helps maintain the east-to-west trade winds.

El Niño

During El Niño, trade winds weaken and may reverse, shifting warm surface water east toward the Americas. Likely regional effects described in the video include:

• The Americas: Warmer, rainier conditions can bring flooding. Suppressed upwelling off South America can damage fisheries, affecting the livelihoods and food supplies of people who depend on fishing. Flooding may also harm farmers.
• Australia and Southeast Asia: Reduced rainfall can bring drought, affecting farmers.
• North America: Winters are often milder.
• The Atlantic and South/Southeast Asia: Atlantic hurricane activity and monsoon activity in India and Southeast Asia typically weaken.

La Niña

During La Niña, trade winds become stronger than normal, pushing warm surface water west toward Australia and Southeast Asia. Likely regional effects described in the video include:

• Australia and Southeast Asia: Warmer, rainier conditions can bring flooding and stronger monsoon activity, though the rainfall may benefit agriculture.
• The Americas: Conditions are cooler and drier than average. Stronger upwelling off South America can support especially productive fisheries.
• The United States and Atlantic: The video notes the potential for more severe tornadoes in the United States and greater Atlantic hurricane activity.

Describing an El Niño Environmental Problem

For the video’s practice question—describe two environmental problems related to El Niño—trace the cause-and-effect chain:

• Reduced fishery productivity: Weakened or reversed trade winds shift warm water toward the Americas. Upwelling off South America is suppressed, so fewer nutrients reach surface waters. Fisheries become less productive, harming fishing-based food supplies and incomes.
• Flooding: Warm water and associated rainfall shift toward the Americas. Unusually rainy conditions can cause flooding and damage crops and farms.
• Drought: Rainfall decreases in Australia or Southeast Asia as warm Pacific surface water shifts toward the Americas.

Speakers and Sources

Jordan Dischinger-Smedes is the video’s instructor and narrator. The subtitles introduce him as “Mr. Speeds,” likely an auto-captioning error. No other speakers or sources are identified.