Class Business

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Class Business

• February 15th, first in class exam

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Isotopic ratios

• Evaporation of vapor depletes the vapor of about
  10 of Oxygen 18 (similarly for Deutorium).
  
• Of the remaining vapor, once it forms
  precipitation (either snow or rain) it is further
  depleted in Oxygen 18 (and Deuterium).
  
• In Summary, water vapor has a greater proportion
  of the LIGHT element (Oxygen 16 and Hydrogen)
  relative to the Heavy elements (Oxygen 18 and
  Deuterium). And Snow is lighter than regular
  water vapor.

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• The coldest snow is the lightest because as air
  cools down, it loses moisture, in essence, the
  heavier isotopes drop out earlier so what is left
  when snow is finally formed is the lighter
  elements.

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• Scientists measure the temperature of an ice
  sheet directly by lowering a thermometer into the
  borehole that was drilled to retrieve the ice
  core. Like an insulated thermos, snow and ice
  preserve the temperature of each successive layer
  of snow, which reflects general atmospheric
  temperatures when the layer accumulated. Close to
  the surface of the bedrock, the lowest layers of
  the ice are warmed by the heat of the Earth.
  These physical temperature measurements help
  calibrate the temperature record scientists
  obtain from oxygen isotopes.

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Vostok Ice Core
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Review
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Proxy data Tree rings

• Dendroclimatology - the study of the
  relationships between climate and tree-growth
  parameters and their use in the reconstruction of
  past climates.

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In parts of the world with four seasons, trees
usually grow best in the spring because of higher
rainfall. The cells produced are larger. As the
season progresses the cells get smaller and
smaller and then eventually as winter comes,
growth stops. Thus, trees growing in seasonal
climates exhibit growth rings. These annual
growth rings allow us to age the tree. However,
they also provide a record of what kind of year
was present during that years growth.
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How is it done?
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Tree core
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Many factors can influence the width of tree rings

• Soil and air temperatures,
• Soil moisture conditions,
• Sunshine
• Wind

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Older trees work best
Bristle cone pine tree in the Great Basin region
of western North America. These are the oldest kn
own living trees, and can live up to 5,000 years.
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• 400 year old Scots pine

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Sometimes can core fossil trees

• Fossilized tree from a lake in Scotland

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How to analyze

• Compare current tree cores with recent climate
  records to establish the relationship between
  climate and tree ring growth
  
• Then analyze the tree rings of either older trees
  (100-400 years old) or fossilized trees

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• By carefully comparing, aligning and averaging
  yearly growth rings from many trees in an area,
  you can create a chronology.
  
• Sometimes you can measure tree rings taken from
  old buildings, in peat bogs or lakes to extend
  the chronology backwards.

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How is it done?
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• Scientists from 15 institutions in Europe and 9
  countries are working on reconstructing climate
  from trees in northern Eurasia going back several
  recent centuries
• In some locations (N. Sweden), fossil trees are
  allowing records to go back for 7000 years

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Other proxy measures

• In the Ocean sediments core the ooze
• Ooze (which is in fact the technical term)
• Ooze contains fossil remains of living creatures
• Types of creatures and relative abundance
• Oxygen ratio of the calcium carbonate in the
  skeletons

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Pollen records

• Record of species living in different areas from
  pollen cores
  

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Pollen coring
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Pollen core

• Species composition and relative abundance
• Can infer climate based on species distributions

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El Nino Southern Oscillation (ENSO)

• Example of interaction between ocean and
  atmosphere
  
• Disruption of ocean-atmosphere system in tropical
  Pacific
  
• Results in redistribution of rains with flooding
  and droughts

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How it works? (ENSO)

• Along the equator, western Pacific has very warm
  water, but the eastern Pacific has cool water
  which wells up carrying nutrients that support
  large fish populations
• Every 2-7 years, trade-winds subside, warm water
  moves eastward across the Pacific
  
• Interrupts the upwelling of cool nutrient rich
  water

Easterncold
Western warm
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El Nino Southern Oscillation
NORMAL
During a normal year, trade winds push warm water
west (towards Australia), cool water rises in its
wake
Trade winds push warm water west
West
East
El Nino
During El Nino year, trade winds weak and switch
direction, push warm water east and prevent cold
water from upwelling
The upwelling brings nutrients to the surface.
Trade winds weak, push warm water east
West
East
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El Nino effect on ocean temperature
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El Nino facts

• El Nino is Spanish for the Christ Child.
• First used by fisherman in Ecuador and Peru to
  refer to the warm, nutrient poor ocean currents
  appear around Christmas time
  
• El Nino event can last 2-3 years
• Following El Nino can get La Nina (colder than
  average temperatures in the Eastern Pacific)

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El Nino in Words (from NASA)

• Stretching across nearly a third of the Earths
  surface, the tropical Pacific Ocean soaks up more
  sunlight than any other single system on Earth.
  
• Most of the sunlight is stored in the ocean as
  heat, but the heat isn't distributed evenly.
  Winds stir the surface of the ocean, creating
  pools of warm water and stretches of cool water.
  
• In the tropical Pacific, the section of the ocean
  between 23 degrees North and 23 degrees South,
  trade winds blow from east to west. The winds
  push the sun-warmed surface water west, away from
  the South American coast, to a deep pool of warm
  water east of Indonesia.
• Along the South American coast, deep, cold water
  rises to the surface to replace the warm water
  being pushed west. As a result, waters in the
  eastern tropical Pacific are typically cool,
  while the western tropical Pacific is warm.
• Periodically the trade winds will slow or even
  reverse directions so that warm water is no
  longer pushed west. The western Pacific cools,
  while the eastern Pacific warms. This distinctive
  reversal in the Pacifics temperature pattern is
  called El Niño. (The name, Spanish for boy
  child, arose because the pattern often becomes
  obvious around Christmas.)

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This year

• Satellite measurements of sea surface
  temperatures in the tropical Pacific revealed a
  clear El Niño pattern in November 2006.
  

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What to expect with El Nino

• .

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Warmer-than-average sea surface temperatures
stretch away from the South American coast, while
cooler-than-average temperatures (blue) pool
around Indonesia and Australia
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Effects of El Nino

• Though El Niño is a normal climate pattern that
  develops every 3-7 years, it can cause unusual
  weather patterns around the globe.
  
• Heavy rains, flooding result in South America and
  part of North America. parts of North and South
  America.
  
• Loss of fish and birds around South American
  coast because there is no food supply.
  
• Drought in western Pacific nations such as
  Australia and Indonesia.
  

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A typical El Nino year can lead to warmer winters
in North America but warmer and drier in
Southern hemisphere
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Biological Impacts of an El Nino Year (from NASA)

• During normal years, when there is a steep
  thermocline tilt, the cold, deep currents flowing
  from Antarctica up the west coast of South
  America are allowed to upwell, bringing essential
  nutrients that would otherwise lie at the bottom.
  Phytoplankton living near the surface depend upon
  these nutrients for survival. In turn, fish and
  mammals depend upon phytoplankton as the very
  foundation of the marine food chain. As
  previously explained, the warm surface waters of
  an El Niño prevent this upwelling, effectively
  starving the phytoplankton population there and
  those animals higher up the food chain that
  depend upon it. Fishermen in Peru and Ecuador
  generally suffer heavy losses in their anchovy
  and sardine industries.
• At Christmas Island, as a result of the sea level
  rise during the 1982-83 El Niño, sea birds
  abandoned their young and flew out over a wide
  expanse of ocean in a desperate search for food.
  Along the coast of Peru during that same time
  period, 25 percent of the adult fur seal and sea
  lion populations starved to death, and all of the
  pups in both populations died. Similar losses
  were experienced in many fish populations.
• Meanwhile, over a six-month period about 100
  inches of rainfall fell in Ecuador and northern
  Peru--ordinarily a desert region. Vegetation
  thrived and the region grew lush with grasslands
  and lakes, attracting swarms of grasshoppers and,
  subsequently, birds and frogs that fed on the
  grasshoppers. Many fish that had migrated
  upstream during the coastal flooding became
  trapped in the drying lakes and were harvested by
  local residents. Shrimp harvests were also very
  high in some of the coastal flood regions, but so
  too was the incidence of malaria cases due to
  thriving mosquito populations

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From Australian climate website

• A regular commentary on the El Nino-Southern
  Oscillation
  
• CURRENT STATUS as at 31st January 2007
• Equatorial Pacific SSTs have cooled and are close
  to or below El Niño thresholds.
  
• Negative subsurface anomalies have strengthened
  and spread further east along the thermocline and
  have nearly reached the surface in the eastern
  Pacific.
• Trade Winds have generally been somewhat stronger
  than average apart from a weakening in the
  central-west Pacific in the middle of the month.
  
• Cloudiness near the date-line has recently been
  above average.
  
• Most computer models predict the decay of El Niño
  conditions in the first half of 2007.
  

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El Nino events
1998 strongest on record. In general, they are th
ought to be intensifying
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Bottom Line

• ENSO is the largest single cause of inter-annual
  climate variability