Describe the general atmospheric and oceanic circulation patterns that characterize La Nina and El Nino Describe the effects of La Nina and El Nino Explain some of the related ecological effects of El Nino Explain coral bleaching and how it relates to El Nino and La Nina Explain how hurricanes are impacted by El Nino/La Nina Explain how we know that ENSO is natural Describe the relationship between ENSO and global warming Describe the current ENSO conditions

The Southern Oscillation Naturally occurring cyclical change in Pacific ocean and wind circulation patterns Paleorecord indicates it has been occurring for 50 million years ago Has global teleconnections Occurs every 2-7 years, a temporal scale larger than seasons Global warming does not cause El Nino, but there may be interactions between the two. Two endpoints of oscillation, La Nina and El Nino Also referred to as ENSO

The Southern Oscillation

Walker circulation: normal or average conditions West Pacific Warm ocean water Low pressure Unstable atmospheric conditions East Pacific Cold water upwelling High pressure Stable atmospheric conditions

El Nino Tradewinds slow and reverse direction Eastern Pacific Upwelling ceases Warmer surface water STHP weakens Wet and unstable conditions Western Pacific Cooler surface water Low pressure weakens Drier and stable conditions

El Nino Drawing/animation

El Nino: Flooding and mudslides in California and South American coast

El Nino: Drought and fire in western Pacific

El Nino: Loss of cold water upwelling and diminished phyoplankton blooms in E. Pacific Animation

Phytoplankton: primary producers Serve as food for zooplankton and higher trophic levels Diatoms Coccolithophorids Cyanobacteria Dinoflagellates

El Nino: Collapse of fisheries along South American coasts due to loss of cold water upwelling

Increased rainfall and vegetation cover in arid regions of western US

El Nino: Hanta virus outbreaks in Western US http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/elnino.htm

La Nina Amplification of normal Walker circulation Easterly tradewinds grow stronger (E to W) More warm water piles up in western Pacific Lower pressure, more wet and unstable in western Pacific STHP in eastern Pacific grows stronger, cooler and drier conditions Greater upwelling Drawing

La Nina Drawing

Hurricanes and the Southern Oscillation Hurricane tracks for La Nina (left) and El Nino years (right) 1950-2001

Hurricanes and the Southern Oscillation Fewer hurricanes in Atlantic/Caribbean with El Nino Reversal of tradewinds and strong more southerly subtropical jet weaken hurricanes through increased wind shear More hurricanes in Atlantic/Caribbean with La Nina Tradewinds blowing from east to west favor hurricane development. Subtropical jet stream further north

bleaching

Coral bleaching and the Southern Oscillation Caused by prolonged high sea surface temperatures. At high temps: Zooxanthellae (photosynthetic algae) in coral decrease production of photosynthate for coral animal These changes result in the expulsion of zooxanthellae from coral polyps Corals deprived of color and food, decline and death Coral already tolerate a narrow temperature range, 77 - 84.2 F. Corals bleach when they reach a constant 89.6 F.

El Nino brings coral bleaching to central-eastern Pacific and Caribbean. La Nina brings bleaching events to Australia and the western Pacific

ENSO and global warming models ENSO not caused by global warming ENSO is natural cycle but influenced by global warming More El Nino conditions under global warming? Greatest variability in ENSO over past century than the preceding 7000 years

Normal ENSO fluctuations during Eocene (50 mya) PETM: average global temperature exceeded today's by at least 10°C But what will things be like in the future? How will the worldwide temperature rise influence ENSO? Will there perhaps be a permanent El Niño? To answer this important question, scientists are looking at the past – particularly at the Eocene period 60 to 37 million years ago. "The Eocene is considered to be the last real prolonged warm period. At that time the Antarctic was ice-free and green. Even trees grew and we know about the water temperature of the ocean that it fluctuated between 10 and 16 degrees Celsius over the year”. He and colleagues from the USA and Germany have now succeeded for the first time in verifying a rhythm according to the pattern of the ENSO phenomenon in the growth patterns of fossil clams and wood from the early Eocene. Their results will soon appear in the journal Geophysical Research Letters and are already available on its website in a text entitled "El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica". Brey and his colleagues investigated shells of the bivalve species Cucullaea raea and Eurhomalea antarctica that are 50 million years old as well as a piece of wood from Seymour Island in the Antarctic. "Like trees, clams form growth rings. We measured their width and examined them for growth rhythms," states Brey. Whether clams grow depends on the availability of food and heat. "That means the change from "good" and "poor" environmental conditions at that time is still reflected in the width of the growth rings we find today. And as we were able to show, this change took place in the same three to six year rhythm we are familiar with in connection with ENSO today," says Brey. The shells are a real piece of luck for him. "To verify ENSO, we need climate archives that cover the largest possible period year by year. Back then clams lived for up to 100 years. This is a good basis for our work.“ To examine the significance of the growth rings of clams and wood, the researchers compared their measurement results with current ENSO data as well as with the ENSO-like fluctuations produced by a climate model of the Eocene. The result: all patterns correspond. "Our results are a strong indication that an ENSO phenomenon which fluctuated between warm and cold phases also existed in the warm Eocene," says Brey.

Normal ENSO fluctuations during Eocene warm period (50 mya) But what will things be like in the future? How will the worldwide temperature rise influence ENSO? Will there perhaps be a permanent El Niño? To answer this important question, scientists are looking at the past – particularly at the Eocene period 60 to 37 million years ago. "The Eocene is considered to be the last real prolonged warm period. At that time the Antarctic was ice-free and green. Even trees grew and we know about the water temperature of the ocean that it fluctuated between 10 and 16 degrees Celsius over the year”. He and colleagues from the USA and Germany have now succeeded for the first time in verifying a rhythm according to the pattern of the ENSO phenomenon in the growth patterns of fossil clams and wood from the early Eocene. Their results will soon appear in the journal Geophysical Research Letters and are already available on its website in a text entitled "El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica". Brey and his colleagues investigated shells of the bivalve species Cucullaea raea and Eurhomalea antarctica that are 50 million years old as well as a piece of wood from Seymour Island in the Antarctic. "Like trees, clams form growth rings. We measured their width and examined them for growth rhythms," states Brey. Whether clams grow depends on the availability of food and heat. "That means the change from "good" and "poor" environmental conditions at that time is still reflected in the width of the growth rings we find today. And as we were able to show, this change took place in the same three to six year rhythm we are familiar with in connection with ENSO today," says Brey. The shells are a real piece of luck for him. "To verify ENSO, we need climate archives that cover the largest possible period year by year. Back then clams lived for up to 100 years. This is a good basis for our work.“ To examine the significance of the growth rings of clams and wood, the researchers compared their measurement results with current ENSO data as well as with the ENSO-like fluctuations produced by a climate model of the Eocene. The result: all patterns correspond. "Our results are a strong indication that an ENSO phenomenon which fluctuated between warm and cold phases also existed in the warm Eocene," says Brey.

Current Southern Oscillation conditions Synopsis: The chance of El Niño is at 60-65% during the Northern Hemisphere fall and winter. http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.pdf

Other ENSO states and oscillations Modokai El Nino North Atlantic Oscillation Arctic Oscillation Pacific Decadal Oscillation