speleothems of south american and asian monsoons ...speleothems of south american and asian monsoons...
TRANSCRIPT
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