Speleothems of South American and Asian Monsoons ...Speleothems of South American and Asian Monsoons...
Transcript of Speleothems of South American and Asian Monsoons ...Speleothems of South American and Asian Monsoons...
Speleothems of South American and Asian Monsoons Influenced
by a Green SaharaClay Tabor1, Bette Otto-Bliesner2, Zhengyu Liu3
1University of Connecticut2National Center for Atmospheric Research3Ohio State University
2020 CESM Workshop
• Warmer than preindustrial• More NH summer insolation
than preindustrial• Green Sahara
Mid-Holocene (6 ka)
2020 CESM Workshop
• iCESM1.2 (Brady et al., 2019)• 3 simulations• Preindustrial control (PI)• 6-ka GHGs and orbital (MHDESERT)• 6-ka + “Green Sahara” (MHVEGE)
Experiment Design
2020 CESM Workshop
δ18O of precipresponses• Isotopic response with 6-ka
GHGs (MHDESERT) and orbit produces little change in monsoon regions• Addition of a Green Sahara
(MHVEGE) amplifies the signals, in better agreement with speleothem records
2020 CESM Workshop
Model-Proxy comparison
δ18O Response: Model vs Data
Mod
el A
nnua
l ∆δ18
O
Speleothem ∆δ18O
MHDESERT
MHVEGE
Asia
South Americar2 = 0.62
r2 = 0.55
• Improved comparison at almost every location• Both δ18O and annual
temperature work to improve comparison
2020 CESM Workshop
Austral Summer Precipitation
• A Green Sahara shifts the Atlantic ITCZ northward• Less efficient
precipitation in Brazil drives δ18O enrichment with a Green Sahara
kg m-1 s-1
2020 CESM Workshop
Boreal Summer Precipitation
• 6-ka orbit leads to more NH summer insolation, which drives the ITCZ north • Intensified Asian
monsoon sources more distant moisture, driving δ18O depletion
kg m-1 s-1
2020 CESM Workshop
Annual Temperature• Lower GHG
concentration at 6-ka results in cooling• Inclusion of a
Green Sahara results in warming• Helps explain
model-proxy disagreement