Abrupt changes in atmospheric circulation from Greenland Ice

Cores

Greenland Summit Location

NSF Site = Summit Camp = GISP2 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

• At least 20 DO (Dansgaard-Oeschger) events recorded in the last 120 Kyears (Rahmstorf, 2003)

• Rapid warming followed by slow cooling then rapid cooling

(Stuiver and Grooves, 2000)(Stuiver and Grooves, 2001)TIME

Warmer

Composite of 13 DO events

Composite annual mean warming of 12 CHalf point of transition reached in 2 years

[Stuvier, 2000]

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

Time

INCREASINGMONSOON

THIS COULD

BE CRAP![Peterson, 2000]

Other things in the snow

• Calcium Dust in air (insoluble suspended solids)

• Sodium Sea Salts in air

Calcium (Insoluble dust concentration) Record

Clear- abrupt changes in dust concentration across DO events-as temperatures warm, atmospheric dust load goes down

[Fuhrer, 1999]

Scatter Plot of ice core oxygen isotope and calcium concentration

Stadial (Cold)Data Points

Interstadial (Warm) Data

Temperature (oxygen isotopes) overlap between regimes but calcium does not

•CLIMATE REGIME IS BEST CHARACTERIZED BY ATMOSPHERC

DUST LOAD – FACTOR OF 10 change

[Fuhrer,1999]

• 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]

The dust burden could change by------------------------------------------------- [Svenson, 2000]

--------------------------------------------------------------- [Fuhrer, 1999]

Dust Diameter across DO events

Interstadial (warm)Staidal (cold)

More Dust = Larger Dust BUTChanges in dust diameter are not nearly as big [stadials and interstadials overlap]DIFFERENT PHYSICAL MECHANISMS IN CLIMATE SYSTEM ARE AT PLAY

[Ruth, 2003]Dust concentration

ModalDust

Diameter

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

Suggests transport was 1.5 times faster during cold stadials

----------------------------------------- doesn’t change dry deposition

Sea Salt concentration change

Sea salts were 2x greater during cold stadials

[Mogenson, 2002]

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

• 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]

The dust burden could change by------------------------------------------------- [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)

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