Chapter 5—Part 1 Ocean Circulation/ Upwelling Zones/ El Niño

Ocean Circulation 1. Eckman spiral 2. Upwelling zones 3. El Niño

Ocean surface currents are driven by atmospheric winds Energy from wind transferred to water by friction

Wind Wind moves surface water (friction) Velocity of water decreases with depth

But Both the wind and the ocean currents are deflected near the atmosphere-ocean interface by a combina- tion of the Coriolis effect, friction, and gravity This gives rise to what is termed the Eckman Spiral - Surface wind rotated 45 o relative to the geostrophic (free troposphere) wind - Surface waters move 45 o relative to the surface wind direction - Net transfer of water 90 o to the surface wind

The Eckman Spiral

Surface waters move 45 o relative to surface wind Net transfer of water 90 o to surface wind direction Eckman Pumping Equator Surface wind Surface current Net ocean transport Surface water is driven offshore by Eckman spiral Replaced by water from below  upwelling! Geostrophic wind (Easterlies)

Consequences of upwelling Deep water is rich in nutrients (P, N, Fe) –These elements are found in critical biological molecules 

Nitrogen in organisms Amino acids (shown at left) are the building blocks of proteins Nitrogen is part of the amino (NH 2 ) group Diagram from Wikipedia

Phosphorus in organisms Phosphorus is a key component of nucleic acids, i.e., DNA and RNA Nucleic acids also contain nitrogen

Iron in organisms Iron is used as part of various catalysts There evidently is some iron in chlorophyll, but not much (main metal atom is Mg) –But, iron is required for the synthesis of chlorophyll

Consequences of upwelling Deep water is rich in nutrients (P, N, Fe) Upwelling brings nutrient-rich water to the surface ocean, fueling biological productivity (phytoplankton) Zooplankton eat the phytoplankton Fish eat both of these  get good fisheries in upwelling zones

El Niño (the Christ child) Every 3-7 years Last 6-18 months Happens near Christmas season

El Niño (the Christ child) Every 3-7 years Last 6-18 months Happens near Christmas season Opposite: La Niña (the girl child)

Normally… Warm waters pushed by trade winds towards Asia and Australia Cold waters upwell near South America

Pacific warm pool

Normal Conditions: This east-west circulation pattern, which is sort of like a Hadley cell, is called the Walker Circulation It reinforces the normal tropical easterlies, thus helping to foster upwelling off the coast of Peru Australia/ Indonesia South America

Normal Conditions: El Niño Condition: Normal Walker Circulation Weakened Walker Circulation South America Australia/ Indonesia Australia/ Indonesia

Atmospheric Pressure: Normal high over Tahiti, low over Darwin, Australia El Nino low over Tahiti, high over Darwin The shift in pressure is called the Southern Oscillation The combined El Niño/Southern Oscillation is referred to as ENSO

Atmospheric Pressure: Normal high over Tahiti, low over Darwin, Australia El Niño low over Tahiti, high over Darwin * Darwin

Southern Oscillation Index [ P diff - P diffav ] SOI = SD(P diff ) where P diff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month), P diffav = long term average of P diff for the month in question, and SD(P diff ) = long term standard deviation of P diff for the month in question.

Strong El Nino

La Niña Is this what is caused the 2011 Texas drought? “ENSO neutral” conditions persisted during most of 2012

The fact that we have been in an extended La Niña may explain why the climate has not warmed as fast as expected over the past 15 years…

Total heat accumulation in sea, land, and air continuation-global-warming.html

El Niño is returning… A strong El Niño has been developing during the past year or so This could mark a swing from cold-phase to warm-phase in the Pacific Decadal Oscillation, a year natural climate cycle  We may well break the global temperature record again this year enso_advisory/ensodisc.html

Results of El Niño In the Pacific Region: weaker trade winds warm waters across the Pacific rain in South America, drought in Australia

Results of El Niño In the Pacific Region: weaker trade winds warm waters across the Pacific rain in South America, drought in Australia Teleconnections--shifting atmospheric patterns (global) high rain in the US midwest more storms in the Pacific, fewer in the Atlantic heavy rains in California cold winters in the Northeastern US