1. El Niño, La Niña and Thermohaline Circulation

2. El Niño

3. Normal conditions in the tropical Pacific Ocean
Surface winds move from east to west
From high pressure in S. America to low pressure in Australia
Drags water westward
Warm water pools in the western Pacific

4. Normal (Non-El Niño) conditions
Trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador.
The sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, due to an upwelling of cold water from deeper levels. This cold water is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Rainfall is found in rising air over the warmest water, and the east Pacific is relatively dry. The observations at 110 W (left diagram of 110 W conditions) show that the cool water (below about 17 degrees C, the black band in these plots) is within 50m of the surface.

5. Every 3 – 8 years, system reverses
Called the Southern Oscillation
Trade winds weaken or reverse
Warm water migrates from Australia to S. America
Arrives in time for Christmas – Corriente del Niño

6. During El Niño, the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. The observations at 110W show, for example, that during , the 17-degree isotherm dropped to about 150m depth. This reduced the efficiency of upwelling to cool the surface and cut off the supply of nutrient rich thermocline water to the euphotic zone. The result was a rise in sea surface temperature and a drastic decline in primary productivity, the latter of which adversely affected higher trophic levels of the food chain, including commercial fisheries in this region. The weakening of easterly tradewinds during El Niño is evident in this figure as well. Rainfall follows the warm water eastward, with associated flooding in Peru and drought in Indonesia and Australia. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific.

7. What is El Niño?
Basically, it's a giant puddle (or pod) of heated water that sloshes across the Pacific Ocean
Similar to an iceberg
Bulge on the surface
Most of “pod” beneath the surface
Due to difference in density
National Geographic’s Model

8. ENSO - El Niño-Southern Oscillation
Typically lasts 1 year
May last up to 3
In multi-year events, first year not as affected
Affects both hemispheres

9. Effects of El Niño - Biology
Upwelling typical off western S. America
Responsible for great biologic productivity in the area
Reverses to downwelling during El Niño years
Fish, birds, etc. die or migrate away from area
Loss of revenue from fishing, tourism, etc.

10. Effects of El Niño - Oceans
Sea level rises as much as 20 cm (8 in)
Water temp increases up to 7º C
> temperature, > evaporation, > intensity of low pressure system
Increased rainfall amounts in normally dry areas
Intensifies coastal storms

12. Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Ventura - 10/97

13. Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Ventura - 4/98

14. Leo Carrillo State Beach - 10/97
Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Leo Carrillo State Beach - 10/97

15. Leo Carrillo State Beach - 4/98
Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Leo Carrillo State Beach - 4/98

16. Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Pacific Palisades - 10/97

17. Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Pacific Palisades - 10/97

18. Palos Verdes Peninsula - 10/97
Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Palos Verdes Peninsula - 10/97

19. Palos Verdes Peninsula - 4/98
Coastal Erosion from El-Niño Winter Storms - October, 1997 & April, 1998
Palos Verdes Peninsula - 4/98

21. http://www. jason. oceanobs. com/html/applications/enso/nino1997-98_uk
Drought over Indonesia and Papua New Guinea caused the destruction of 2.1 million hectares of trees, through forest fires. Total damage was estimated at $US 4.4 billion, with hundreds of casualties through famine and disease.

22. http://www. jason. oceanobs. com/html/applications/enso/nino1997-98_uk
With sea-surface temperature exceeding 28°C off the coast of Ecuador and
northern Peru, rainfall in December 1997 and January 1998 reached 350 to
775 mm, 15 times the average. This resulted in flooding and landslides, and
the destruction of roads, houses and crops. In Peru alone, the damage was
estimated at $US 3.6 billion. Hundreds of people disappeared, cholera and
malaria broke out.

23. While anchovy fisheries were being disrupted across South America’s
While anchovy fisheries were being disrupted across South America’s
western seaboard, sardine and tuna were thriving in the warmer waters off
Santiago, Chile, producing a bumper year for fishermen.

24. With storms shifting to the central Pacific, the Caribbean was calmer
With storms shifting to the central Pacific, the Caribbean was calmer. And
parts of North America and Japan enjoyed milder winters.

25. Recognizing an El Niño Sea Surface Temperatures (SST)
Normal: 6-8° C warmer in the western tropical Pacific than in the eastern tropical Pacific
Check SST to see if in “normal” range

27. La Niña Return to “normal” conditions from an El Niño strong Produces:
Strong currents
Powerful upwelling
Chilly and stormy conditions along S. American coast

28. La Niña Eastern Pacific cools rapidly, Western Pacific warms rapidly
Renewed Trade Wind activity spreads the cooler eastern Pacific waters westward

29. Thermohaline Circulation

30. Deep ocean currents Very slow moving
Driven by changes in density/temperature/salinity
Therme = heat + halos = salt

31. Water Masses Five water masses Each has different properties
Don’t mix well

32. Water Masses Include: Surface water (0-200 m)
Central water (to bottom of main thermocline)
Intermediate water (to ~1500 m)
Deep water (between Intermediate water and 4000 m)
Bottom water (at the sea floor)

33. Formation and Downwelling of Deep Water
Antarctic Bottom Water
Characteristics:
Salinity = /00
Temperature = -0.5ºC
Density = g/cc

34. Formation and Downwelling of Deep Water
Antarctic Bottom Water
Forms in the Weddell Sea during winter
Sea ice holds 15% of salt
Remainder forms a frigid brine beneath
Brine sinks towards the continental shelf
Mixes with the Circumpolar Current

35. Formation and Downwelling of Deep Water
Arctic Bottom Water
Mostly a closes system
Some “escapes” into the North Atlantic
Becomes a part of the North Atlantic Deep Water
Very little enters the Pacific

37. Circulation Patterns Amount sinking = amount rising
Sinks rapidly in cold regions
Rises rapidly in warm regions
Thermocline “held up” by slowly rising cold water

38. Circulation Patterns Bottom currents also called contour currents
Generally moves around features rather than over them
Typically move 1-2 m/day
Locally can move 60 cm/s

39. Thermocline Circulation Patterns
A model of thermocline circulation caused by heating in lower latitudes and cooling in higher latitudes.
© 2002 Brooks/Cole, a division of Thomson Learning, Inc.

41. The Global Heat Connection
Thermohaline currents moderate Earth’s temperature
Brings cold water to the equators
Brings warm water to the poles
Distributes between ocean basins:
Dissolved gasses
Dissolved solids
Nutrients
Organisms

43. Global Warming Earth heats up Ice at polar caps melt
Increases amount of fresh water in oceans
Decreases density of sea water
Thermohaline /deep ocean currents can’t form
Thermohaline circulation belt slows, stops, or moves towards the equator
Climate not moderated
Poles freeze, start of new ice age?