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Multi-year time scale variations • El Nino and La Nina are important phenomena • Occur every ~2 to 7 years when typical ocean-atmosphere circulation breaks down During normal years, warm surface waters in the Pacific lie in the east off Indonesia When the pattern oscillates to an “El Nino”, the warm water shifts east “La Nina” is characterized by colder sea-surface temperatures and stronger trade winds in the eastern tropical Pacific During “Normal Years” Warm water in the western Pacific causes low pressure and high rainfall; pressure system drives tradewinds from east to west; tradewinds drive warm water to the west; causing cold water to rise off South America and flow west. South America During “El Nino” Warm water shift to the eastern Pacific causes drought in western Pacific; low pressure over the warm eastern Pacific causes heavy rains and inhibits upwellings along the coast of South America. South America During “El Nino” Warm water shift to the eastern Pacific causes drought in western Pacific; low pressure over the warm eastern Pacific causes heavy rains and inhibits upwellings along the coast of South America. South America Strong El Nino year 1982-83: 1982-83 El Nino • Floods in Peru-Ecuador (600 fatalities) • California flooding led to $300 million damages • Hurricanes in Hawaii, Tahiti • Australia: drought and wildfires 1997-1998 El Nino Effects La Nina hazards • Can bring warming and low rainfall to much of U.S. – Can lead to fires • Allows growth of hurricanes in Atlantic Climate Change 2003 1958 Records of Climate Change National Academy of Science Report, 2006 Records of Climate Change • Historical data • Proxy data – – – – – – – – Marine sediment Ice Coral Lake sediment Tree Rings Boreholes Glacial advance/retreat Old glacial deposits, etc. Oxygen isotopes • Same atomic number (8) • Different atomic mass concise.britannica.com 99.63% 0.0375% 0.1995% Delta notation Ice data • Influence of temperature on ice composition • Record of atmospheric composition Composition of precipitation versus temperature earthobservatory.nasa.gov Greenland and Antarctic Ice Sheet Records >700,000 yrs Layers counted like tree rings Photos: NASA Figure 21.5A Interpreted from Greenland ice core O-isotope data Seafloor record • Microfossils of organisms in surface and bottom water • Limited by age of oceanic crust (oldest ~180 my) Source: NOAA Influence of ice volume on Oisotope composition of seawater Influence of ice volume on Oisotope composition of seawater • Ice is depleted in 18O • Residual seawater is enriched in 18O • Positive (18O-enriched) values of organisms indicate larger ice volume Figure 21.4 Temperature effects The ratio of 18O to 16O in foraminifera shells varies slightly depending on the temperature of the surrounding water, as well the water's salinity. Dealing with temperature effect • Use benthic organisms in from deep bottom waters (relatively constant temperature) • Use trace element ratios tied to precipitation temperature (e.g., Sr/Ca) Figure 21.8 Annual growth rings in x-rayed coral (NASA) Chapter 21 Opening Figure Figure 21.6 Ring thickness and density a function of climate (e.g., high latitude and altitude trees sensitive mainly to temperature) Cross dating in dendrochronology Mapping glacial deposits 300 my old glacial deposits on Pangaea Figure 18.32 Long term climate record Climate Variations over Time • Early earth: atmosphere full of CO2 • Surface would have been much hotter because of greenhouse effect • What changed? Much CO2 has gone into rock form (limestones primarily) Figure 21.5B Interpreted from Greenland ice core O-isotope data • Dust can be a large scale process