Abrupt changes in atmospheric circulation from Greenland Ice Cores

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Abrupt changes in atmospheric circulation from
Greenland Ice Cores
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Greenland Summit Location
NSF Site Summit Camp GISP2 core European
Site True Summit GRIP core
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Summit is very FLAT
Elevation 3200 meters Annual Mean Temperature
about -30 C
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Evidence of Abrupt Climate Change- DO Events from
GISP 2
Warmer
(Stuiver and Grooves, 2000)
(Stuiver and Grooves, 2001)
TIME

• At least 20 DO (Dansgaard-Oeschger) events
  recorded in the last 120 Kyears (Rahmstorf, 2003)
  
• Rapid warming followed by slow cooling then rapid
  cooling

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Composite of 13 DO events
Stuvier, 2000
Composite annual mean warming of 12 C Half point
of transition reached in 2 years
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Spatial Extent of DO Events-Non Atlantic

• coincident changes in monsoon strength observed
  half way around the world
• other proxy records indicate coincident climate
  changes
• Santa Barbara- oxygen 18 in n pachyderma

THIS COULD BE CRAP!
INCREASING MONSOON
Time
Peterson, 2000
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Other things in the snow

• Calcium Dust in air
  (insoluble suspended solids)
  
  
• Sodium Sea Salts in air

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Calcium (Insoluble dust concentration) Record
Fuhrer, 1999
Clear- abrupt changes in dust concentration
across DO events -as temperatures warm,
atmospheric dust load goes down
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Scatter Plot of ice core oxygen isotope and
calcium concentration
Stadial (Cold) Data Points
Interstadial (Warm) Data
Fuhrer,1999

• Temperature (oxygen isotopes) overlap between
  regimes but calcium does not
• CLIMATE REGIME IS BEST CHARACTERIZED BY
  ATMOSPHERC DUST LOAD FACTOR OF 10 change

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The dust burden could change by

• Change in source area
• Change in size of source area
• Change in atmospheric transport time
• Change in atmospheric residence time
• Change in magnitude of flux from source to
  atmosphere- WINDS OVER SOURCE

-------------------------------------------------
Svenson, 2000
--------------------------------------------------
------------- Fuhrer, 1999
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Dust Diameter across DO events
Modal Dust Diameter
Interstadial (warm)
Staidal (cold)
Ruth, 2003
Dust concentration
More Dust Larger Dust BUT Changes in dust
diameter are not nearly as big stadials and
interstadials overlap DIFFERENT PHYSICAL
MECHANISMS IN CLIMATE SYSTEM ARE AT PLAY
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What changes diameter of dust

• Winds over source region
• Change in residence time
• Change in transport time from source to deposition

• ------------------------------------
  affects
  concentration but not size distribution

-----------------------------------------
doesnt change dry deposition
Suggests transport was 1.5 times faster during
cold stadials
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Sea Salt concentration change
Mogenson, 2002
Sea salts were 2x greater during cold stadials
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What could change sea salts

• Storms in the Atlantic
  

Likely up during cold stadials

• Residence time (strength of wet deposition)

Change in sea salt concentration (2X) give upper
bound on the change in residence time between
stadial and interstadial
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The dust burden could change by

• Change in source area
• Change in size of source area
• Change in atmospheric transport time
  
• Change in atmospheric residence time
• Change in magnitude of flux from source to
  atmosphere- WINDS OVER SOURCE

-------------------------------------------------
Svenson, 2000
--------------------------------------------------
------------- Fuhrer, 1999
X 1.5 (size)
X 2 (salts)
Must have changed by factor of 3-4 to explain
X10 change in total dust
(30-40 change in spring time winds over Asia)
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Conclusions

• Ice cores show rapid, concurrent changes in
  temperature, dust load, dust grain size and sea
  salts
• Dust load changes can only be explained by
  changes in atmospheric circulation which are
  hemispheric in extent
• Any proposed mechanism should explain the dust
  data

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