The Younger DryasThe Younger Dryasandand

Rapid Climate ChangeRapid Climate Change

Bruno TremblayBruno TremblayMcGill UniversityMcGill Universitybruno.tremblay@mcgill.ca

DyasOctopetalaDyasOctopetala

Last seen in the pollen record of Northern Europe between 11,600 and 12,800 BP

Central Greenland Central Greenland ClimateClimate

Tem

pera

ture

(C)

Acc

umul

atio

n (c

m/y

ear)

Age (Kyr BP)

Abrupt change

Proxy Evidence Proxy Evidence NHNH

Global THCGlobal THC

EvidenceEvidence 10-15 C cooling at Greenland Summit. Other 10-15 C cooling at Greenland Summit. Other

ocean sediment proxi confirms this with ocean sediment proxi confirms this with several degrees of ocean cooling in the N. several degrees of ocean cooling in the N. Atl.Atl.

Cooling observed off the coast of Portugal Cooling observed off the coast of Portugal and as far south as the Cariaco Basin off the and as far south as the Cariaco Basin off the coast of Venezuela, off the coast of Santa coast of Venezuela, off the coast of Santa Barbara CA, and in cave records from China.Barbara CA, and in cave records from China.

Slow down of the thermohaline circulation, Slow down of the thermohaline circulation, and perhaps even a complete shut off.and perhaps even a complete shut off.

Sea Level Rise Time Sea Level Rise Time SeriesSeries

Parenthesis

Carbon Dating

But how Global is this But how Global is this signal?signal?

Problematic Problematic Signal is Global - Signal is Global - Synchroneous!Synchroneous!

Dating of Antarctica ice core is not very Dating of Antarctica ice core is not very good. Northern Hemisphere signal and good. Northern Hemisphere signal and Antarctic cooling could be one and the Antarctic cooling could be one and the same.same.

New Zealand ice advance was dated at New Zealand ice advance was dated at around the same time as the YD.around the same time as the YD.

Global signal – Our previous Global signal – Our previous mechanism no longer match the data.mechanism no longer match the data.

New Technique to New Technique to synchronize synchronize Greenland - Greenland -

Antarctica Ice CoreAntarctica Ice Core

Use Use methane methane data in data in both both cores.cores.

Ice Core Locations

Antarctica

GISP2 GISP2 and and

Dome Dome C Ice C Ice Core Core datadata

Bipolar Sea-Saw in the Ocean

Recent FindingsRecent FindingsBarrow et al, Nature, 2007.Barrow et al, Nature, 2007.

New Dating of the New Zealand glacial New Dating of the New Zealand glacial advance is much more recent than the advance is much more recent than the YD. YD.

Confirmed by nearby ocean sediment that Confirmed by nearby ocean sediment that show continued warming during the YDshow continued warming during the YD

So now we have data from both Northern So now we have data from both Northern and Southern Hemisphere in line with the and Southern Hemisphere in line with the modelmodel

Do we have a complete Do we have a complete understanding of the understanding of the

event?event? Not quite!Not quite! We still don’t know what triggered We still don’t know what triggered

the eventthe event A shift in the drainage pathways of lake A shift in the drainage pathways of lake

AgasizAgasiz A solar trigger or a Pacific trigger (Clement A solar trigger or a Pacific trigger (Clement

et al, 2001)et al, 2001) A cometary impact?A cometary impact?

Drainage PathwaysDrainage PathwaysLake AgassizLake Agassiz

Lake Agassiz ShorelineLake Agassiz Shoreline

EvidenceEvidenceDigital Elevation Model – Southern Digital Elevation Model – Southern

OutletOutlet

Evidence – Comet ImpactEvidence – Comet Impact12,900 BP12,900 BP

Glass like carbon

Carbon Spherule

Magnetic grain rich in Ir

More...More... http://www.realclimate.org/http://www.realclimate.org/

index.php/archives/2007/10/index.php/archives/2007/10/younger-dry-as-dust/younger-dry-as-dust/

Sea Level Rise StorySea Level Rise Story Difficulty in measuring sea levelDifficulty in measuring sea level Ice flow on glacierIce flow on glacier Region of uplift-downlift. See Region of uplift-downlift. See

Ruddiman discussion.Ruddiman discussion. GRACEGRACE Antarctica without ice!Antarctica without ice!