1. El Niño/La Niña

3. Upwelling
Upward movement of water which brings nutrients from deep in the ocean to the surface. (Nutrient-rich water!)
This stimulates the growth of marine plants (phytoplankton), which supports fisheries (high biological productivity).
This is positive along the whole food chain.

4. Equatorial Upwelling Tradewinds push water away from the equator.
Water from the deep ocean comes up to take the place of the missing water.

5. A normal (non-El Niño) Year
Trade winds blow from the normally high-pressure area over the eastern Pacific (near South America) to the normally stable low-pressure area over the western Pacific (north of Australia)
Upwelling happens along the coast of South America

6. A normal (non-El Niño) Year
Also look at figure 9.19 a
A normal (non-El Niño) Year

7. A normal (non-El Niño) Year
sea surface is about 1/2 meter higher in the west than in the east
sea surface temperature is about 8° C higher in the west, with cool temperatures off South America
Rainfall is found in rising air over the warmest water (western Pacific), and the east Pacific is relatively dry
Strong upwelling = high primary productivity

8. A normal (non-El Niño) Year

9. An El Niño Year – Southern Oscillation
Every 3 to 8 years the pressure areas change places (high pressure builds in western Pacific and low pressure dominates the eastern Pacific)
The trade winds in the central and western Pacific diminish or reverse
This change in atmospheric pressure (and thus wind direction) is called the Southern Oscillation

10. An El Niño Year
Equatorial currents weaken; warm water usually found in western Pacific drifts eastward (rise in sea surface temperature)
reduces the efficiency of upwelling and cuts off the supply of nutrient rich bottom water to the surface
drastic decline in primary productivity (bad for whole food chain)

11. figure 9.19 c
An El Niño Year

12. An El Niño Year Sea level rises in eastern Pacific as much as 8”
Water temp in eastern Pacific rises up to 7°C
increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding
drought in the West Pacific, sometimes associated with devastating brush fires in Australia.
Little to no upwelling = low primary productivity

13. An El Niño Year

14. ENSO
The phenomena of the Southern Oscillation and El Niño are related, so the terms are often combined to form the acronym ENSO (El Niño / Southern Oscillation)
Event usually lasts about a year, but some have lasted much longer

15. La Niña Normal circulation sometimes returns with surprising vigor
Strong tradewinds
strong surface currents
powerful upwelling
chilly/stormy conditions along the South American coast.