O. Elison Timm 1 A. Timmermann 1,4 T. Friedrich 1 A. Abe-Ouchi 2,3 J. Knies 5 Forced response of a...
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Transcript of O. Elison Timm 1 A. Timmermann 1,4 T. Friedrich 1 A. Abe-Ouchi 2,3 J. Knies 5 Forced response of a...
O. Elison Timm1
A. Timmermann1,4 T. Friedrich1
A. Abe-Ouchi2,3
J. Knies5
Forced response of a Northern Forced response of a Northern Hemisphere ice-sheet model Hemisphere ice-sheet model
to climate changes during to climate changes during the last 130,000 yearsthe last 130,000 years
1. International Pacific Research Center, University of Hawaii at Manoa, Honolulu, HI, UnitedStates.2. Center for Climate System Research, University of Tokyo, Kashiwa, Japan.3. Research Institute for Global Change, JAMSTEC, Yokohama, Japan.4. Dept. of Oceanography, University of Hawaii at Manoa, Honolulu, HI, United States.5 Geological Survey of Norway, Trondheim, Norway
Introduction • Glacial-Interglacial CyclesGlacial-Interglacial Cycles
Orbital forcing: precession and/or obliquity. (Berger in the 1970s, P. Huybers, 2005, 2006, 2010)Prolonged synchronous increase in NH and SH summer insolation(Schulz and Zeebe (2006))
• What are the driving What are the driving forces?forces?
Changes in land albedo, sea-ice,ocean circulation, vegetation, carbon cycle.
We use LOVECLIM (V1.0) an ’Earth System Model of Intermediate Complexity’ to obtain atmospheric forcing fields for the community Ice-sheet model GLIMMER
• How important are How important are internal feedbacksinternal feedbacks? ?
• Methods:Methods:• Transient paleoclimateTransient paleoclimate
simulationssimulations• Time-slice sensitivity Time-slice sensitivity
experimentsexperiments
Hypothesis:
Increasing summer insolation triggers ice-sheet discharge,reduction in Atlantic Meridional OverturningCirculation, NH cooling, and thus negative, stabilizing feedback.
• IRD events during times of IRD events during times of increasing summer increasing summer insolationinsolation
(Timmermann et al., Paleoceanography, 2010)
timetime
H6C21 C24
LOVECLIM
Ice-sheet forcingfrom IcIES ECBilt – atmosphere
T21, L3t2m
precip
t2m
precip
CLIO – ocean sea-ice
3x3, L20
aia
aia
air-sea fluxes
VECODE –vegetation
t2m,precip
albedo
t2m,precip
albedo
LOCH – Marine carbon cycle
aia
aia
CO2 fluxes
Transientexternal forcing
Freshwater Forcing
albedo +
orography
albedo +
orography
External forcingSources: Daily mean irradiance for true longitude λ=90o (mid-June) were calculated with the routines provided by Dr. Laskar (Laskar 2004).
Atmospheric CO2 derived from Antarctic ice-cores (as described in Timm et al, Paleoceanography, 2008)
time
• Modeling Approach:Modeling Approach:
For our transient simulations and sensitivity studies, we use LOVECLIM (V1.0) an Earth System Model Of Intermediate Complexity
Northern Hemisphere Ice-sheet model (IcIES) with time dependent
atm. forcing
Northern Hemisphere Ice-sheet model (IcIES) with time dependent
atm. forcingObtain atmospheric response patterns to
CO2 and orbital forcing with GCM model
Obtain atmospheric response patterns to
CO2 and orbital forcing with GCM model
Proxy records with time series of
atmospheric CO2 and orbital forcing
(130,000 BP – 0 BP)
Proxy records with time series of
atmospheric CO2 and orbital forcing
(130,000 BP – 0 BP) NH ice thickness, orography.
(130,000 BP – 0 BP)
NH ice thickness, orography.
(130,000 BP – 0 BP)
LOVECLIM:Transient simulation with
forcing from NH ice-sheets, orbital changes,
and atm. CO2
LOVECLIM:Transient simulation with
forcing from NH ice-sheets, orbital changes,
and atm. CO2
Northern Hemisphere Ice-Sheet model
(GLIMMER*) with time dependent atm. forcing.
Northern Hemisphere Ice-Sheet model
(GLIMMER*) with time dependent atm. forcing.
(Abe-Ouchi et al, Clim. Past., 2007)
* Rutt, I. C., M. Hagdorn, N. R. J. Hulton, and A. J. Payne, J. Geophys. Res., 114, F02004, 2009
• Shutdown of the Atlantic Meridional Shutdown of the Atlantic Meridional Overturning Circulation (AMOC)Overturning Circulation (AMOC)
Difference in summer air temperatures 102ka BP minus 114ka BP.(high minuxs low NH summer insolation)
Difference in summer air temperatures at 108ka BP with/ without freshwater input into North Atlantic (AMOC shutdown – active AMOC)
Why does precessional forcing not lead to glacial terminations before 19 ka BP?
• Shutdown of the Atlantic Meridional Shutdown of the Atlantic Meridional Overturning Circulation (AMOC)Overturning Circulation (AMOC)
LOVECLIM simulation:Diagnosed mass balance over the ice-sheets of North America and Greenland
LOVECLIM simulation:Diagnosed mass balance over the ice-sheets of Eurasia
timetime timetime
Why does precessional forcing not lead to glacial terminations before 19 ka BP?
• Shutdown of the Atlantic Meridional Shutdown of the Atlantic Meridional Overturning Circulation (AMOC)Overturning Circulation (AMOC)
Difference in annual mean air temperatures between 18 and 17ka BP
Difference in annual mean air temperatures at 18-17 ka BP with 17ka BP shutdown of AMOC.
Last glacial termination and Heinrich 1 event
GLIMMER* forced withclimatological annual cyclefrom transient simulation with LOVECLIM and freshwater forcing in North Atlantic.Climatology at 18 and 17ka BP(with bias correction)
• Effect of AMOC shutdown Effect of AMOC shutdown onto NH ice-sheonto NH ice-sheetsets
18 ka BP (active AMOC) equilibrium 17 ka BP (AMOC shutdown) equilibrium
* Rutt, I. C., M. Hagdorn, N. R. J. Hulton, and A. J. Payne, J. Geophys. Res., 114, F02004, 2009
• Effect of incremental COEffect of incremental CO22 increase and insolation increase and insolation increase onto NH ice-increase onto NH ice-shesheetsets
18 ka BP (active AMOC) equilibrium 17 ka BP (AMOC active) equilibrium
GLIMMER* forced withclimatological annual cyclefrom transient simulation with LOVECLIM without freshwater input.Climatology at 18 and 17ka BP(with bias correction)
images created with IDV (Integrated Data Viewer)
* Rutt, I. C., M. Hagdorn, N. R. J. Hulton, and A. J. Payne, J. Geophys. Res., 114, F02004, 2009
GLIMMER forced withclimatological annual cyclefrom transient simulation LOVECLIM at 18 an 17ka BP
• Effect of AMOC shutdown Effect of AMOC shutdown onto NH ice-sheetsonto NH ice-sheets
Adjustment to THC shutdown
17 ka AMOC shutdown
17 ka BP active AMOC
Adjustment over 15000 model years Difference after 15000 model years
+2000m
-1000m
time
2 4 6 8 10 12 14
6.3
6.9
7.5
• Transient Ice-Sheet Modeling Transient Ice-Sheet Modeling Approach:Approach:
For our transient simulations and sensitivity studies, we use LOVECLIM (V1.0) an Earth System Model Of Intermediate and the community ice-sheet model GLIMMER*
Northern Hemisphere Ice-sheet model (IcIES) with time dependent
atm. forcing
Northern Hemisphere Ice-sheet model (IcIES) with time dependent
atm. forcingObtain atmospheric response patterns to
CO2 and orbital forcing with GCM model
Obtain atmospheric response patterns to
CO2 and orbital forcing with GCM model
Proxy records with time series of
atmospheric CO2 and orbital forcing
(130,000 BP – 0 BP)
Proxy records with time series of
atmospheric CO2 and orbital forcing
(130,000 BP – 0 BP) NH ice thickness, orography.
(130,000 BP – 0 BP)
NH ice thickness, orography.
(130,000 BP – 0 BP)
LOVECLIM:Transient simulation with
forcing from NH ice-sheets, orbital changes,
and atm. CO2
LOVECLIM:Transient simulation with
forcing from NH ice-sheets, orbital changes,
and atm. CO2
Northern Hemisphere Ice-Sheet model
(GLIMMER*) with time dependent atm. forcing.
Northern Hemisphere Ice-Sheet model
(GLIMMER*) with time dependent atm. forcing.
(Abe-Ouchi et al, Clim. Past., 2007)
* Rutt, I. C., M. Hagdorn, N. R. J. Hulton, and A. J. Payne, J. Geophys. Res., 114, F02004, 2009
Comparison between theice-sheet simulationsobtained with IcIES,LOVECLIM-GLIMMERand ICE5G (Peltier, 2004)
• IcIES, GLIMMER simulationIcIES, GLIMMER simulation
Termination I simulated with IcIES and GLIMMER lags the ICE5G reconstructed timing of the deglaciation.
LOVECLIM-GLIMMER underestimates the early buildup of the Eurasian ice-sheet.
time
Effect of global temperature offset on ice-volume
• GLIMMER simulationGLIMMER simulation
LOVECLIM-GLIMMER: problem with the early buildup of the Eurasian ice-sheet:
Sensitivity runs with temperatureoffsets (-8, -2, -1, 1, 2, 8 K ) suggest negative precipitation bias is the likely cause for the failure in ice-sheet buildup over Eurasia between MIS5a-d (115-80ka B.P.)
With cooler global temperatures(larger ice-volumes) the response to precessional forcing increases.
t2m offset
8 2 1 0-1-2-8
time
SummaryForced response of a global ice-sheet model toForced response of a global ice-sheet model toclimate changes during the last 130,000 yearsclimate changes during the last 130,000 years
• What are the driving forces?What are the driving forces?
• How important are internal feedbacksHow important are internal feedbacks? ?
Ice-sheet simulations indicate strong sensitivity to precessionally driven summer insolation changes.
We discussed an additional feedback: AMOC shutdown provide stabilizing, negative feedback mechanism for ice-sheet growth.
=> The sequence of freshwater input into the North Atlantic between 115ka and 80ka BP could have helped to sustain glacial conditions during periods of high summer insolation.