Abrupt changes in atmospheric circulation from Greenland Ice

Abrupt changes in atmospheric circulation from Greenland Ice Cores

Greenland Summit Location NSF Site = Summit Camp = GISP 2 core European Site = True Summit = GRIP core

Summit is very FLAT Elevation = 3200 meters Annual Mean Temperature about -30 C

Evidence of Abrupt Climate Change - DO Events from GISP 2 Warmer TIME (Stuiver and Grooves, 2001) (Stuiver and Grooves, 2000) • At least 20 DO (Dansgaard-Oeschger) events recorded in the last 120 Kyears (Rahmstorf, 2003) • Rapid warming followed by slow cooling then rapid cooling

Composite of 13 DO events [Stuvier, 2000] Composite annual mean warming of 12 C Half point of transition reached in 2 years

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 INCREASING THIS COULD BE CRAP! MONSOON Santa Barbara- oxygen 18 in n pachyderma Time [Peterson, 2000]

Other things in the snow • Calcium • Sodium Dust in air (insoluble suspended solids) Sea Salts in air

Calcium (Insoluble dust concentration) Record [Fuhrer, 1999] Clear- abrupt changes in dust concentration across DO events -as temperatures warm, atmospheric dust load goes down

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

The dust burden could change by • • • ------------------------Change in source area [Svenson, 2000] -------------------------------Change in size of source area [Fuhrer, 1999] Change in atmospheric transport time Change in atmospheric residence time Change in magnitude of flux from source to atmosphere- [WINDS OVER SOURCE]

Dust Diameter across DO events Modal Dust Diameter Interstadial (warm) Staidal (cold) Dust concentration [Ruth, 2003] 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

What changes diameter of dust • ------------------Winds over source region affects concentration but not size distribution • • --------------------Change in residence time doesn’t change dry deposition • Change in transport time from source to deposition Suggests transport was 1. 5 times faster during cold stadials

Sea Salt concentration change [Mogenson, 2002] Sea salts were 2 x greater during cold stadials

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 (2 X) give upper bound on the change in residence time between stadial and interstadial

The dust burden could change by • • • ------------------------Change in source area [Svenson, 2000] -------------------------------Change in size of source area [Fuhrer, 1999] Change in atmospheric transport time X 1. 5 (size) Change in atmospheric residence time X 2 (salts) Change in magnitude of flux from source to atmosphere- [WINDS OVER SOURCE] Must have changed by factor of 3 -4 to explain X 10 change in total dust (30%-40% change in spring time winds over Asia)

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