During an El Niño event, the southeast trade winds weaken and so does the amount upwelling in the eastern Pacific. The deeper thermocline means that any upwelling that does occur is unable to tap into the rich nutrients found in deeper waters. Consequently, warm nutrient-poor water predominates the region and a decrease in the fish population is observed. During non-El Niño years, the southeast trade winds, drag surface water westward away from shore. As surface water moves away, upwelling brings up colder waters from depths of 40-80 meters or more. This deep sea water is rich in nutrients which can sustain large fish populations.
El nino and La nina
El Nino La Nina
Normal Conditions Sea Surface Temperature (SST)
Normal Conditions Green = cold Red = warm Sea Surface Temperature (SST)Garrison 8-15b
HOTPOOL COLD TONGUE NORMAL UPWELLING“NORMAL” CONDITIONS
Normal ConditionsGarrison’s Oceanography text, 8-15a
Surface winds blow westwardEQUATOR AUSTRALIA Warm waters SOUTH pushed westward AMERICA Warm water Cold water Normal Conditions
Causes coldtongue to extend west Deep, cold & nutrient rich waters NORMAL CONDITIONS SUPPORT COASTAL UPWELLING.
SUNLIGHT ONLY UPWELLING CANRETURN THE FERTILIZINGNUTRIENTS TO THE PHOTIC ZONE NORMAL CONDITIONS SUPPORT COASTAL UPWELLING.
El nino conditions Normally, temperatures of surface waters in the western Pacific are 6 to 8 degrees Celsius (10 to 15 degrees Fahrenheit) warmer than in the east. But during an El Niño, the temperature differential reverses. The nutrient-poor warm water forces the fish that normally thrive off the west coast of South America to go elsewhere to find food. Birds that would feed on the fish die off, and the local fishing economy suffers. El Niño causes far-reaching weather events as well, including drought and heatwaves across Australia, torrential rainfall in Central and South America, and heavy winter snows and floods in the southern United States -- all of which affect water resources and food supply.
HOT POOL SHIFTS EAST NO COLD TONGUE NO UPWELLINGEL NINO CONDITIONS
El Niño Conditions • Weakening of Walker • Decreased pressure gradient • Weaken Trade winds • Stronger Eq Counter Current • Migration of warm pool • Reduced upwelling (east) • Shallower thermocline (west) • Shift in rainfall to the east
Winds weaken, causing updrafts and storms Drought in Australia and Southeast AsiaEQUATOR Warm water AUSTRALIA flow stopped SOUTH or reversed AMERICA Warm water deepens off Warm water South America Cold water El Niño Conditions
EL NINO SUPRESSES COASTALUPWELLING, REDUCES NUTRIENTS& CAUSES SURFACE POPULATIONS TO DISAPPEAR.
El Niño plays havoc with world weather Fires in the Amazon Worsening drought in Sahel • Weakens Indian Monsoon. • Causes drought in central North America.
1983 El Niño caused severe drought, heat waves and Bushfires in Australia.Flames devour farmland in Victoria,Australia.El Niño triggered prolonged droughtof 1983 made fire a constant hazard.In 1983, winds whipped fires fromAdelaide to Melbourne, destroyingseven towns and several thousandhomes.
ENEN Approximately 25% of the 23,000 pups born in June 1997 at San Miguel Island died.
El Niño• During an El Niño year – normally strong trade winds weaken, and sometimes even reverse direction – warm water of the western Pacific Ocean moves eastward, keeping deep cold water from rising to the surface off the west coast of South America. – Jet stream brings warm, moist air to the US – causes • Storms in California • Heavier than normal precipitation in much of the US • Droughts in Africa and Australia • Monsoon rains in Indonesia
La Niña• During a La Niña year – Trade winds increase in strength and blow even stronger than normal from east to west • water in the western Pacific Ocean becomes warmer • water in the Eastern Pacific near the coast of South America becomes colder • Warm ocean waters, clouds and moisture are pushed away from North America – Causes: • Hot, dry weather with droughts in the southern US • Cool weather and excess rainfall in the northeastern US
El Niño / La Niña• El Niño and La Niña change worldwide weather patterns in complex ways.• Scientists do not yet understand what triggers these events.• An El Niño or La Niña event lasts 1 to 2 years, and occurs every 3 to 6 years, but some events are mild while others are severe.• The most severe recent El Niño events occurred in 1982-83 and 1998.• An El Niño generally causes more disruption in global weather patterns than La Niña, but severe drought occurs in the southern U.S. during a La Niña.