Transcript Dust Records During Dansgaard

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
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 EventsNon 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 2x 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 (2X) 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
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