O. Elison Timm 1 A. Timmermann 1,4 T. Friedrich 1 A. Abe-Ouchi 2,3 J. Knies 5 Forced response of a Northern Hemisphere ice-sheet model to climate changes

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


atm. forcingObtain atmospheric response patterns to

CO2 and orbital forcing with GCM model

Obtain atmospheric response patterns to


Proxy records with time series of

atmospheric CO2 and orbital forcing

(130,000 BP – 0 BP)



(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



and atm. CO2

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?


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?


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


• 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)


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*


atm. forcing


atm. forcingObtain atmospheric response patterns to


Obtain atmospheric response patterns to




(130,000 BP – 0 BP)



(130,000 BP – 0 BP) NH ice thickness, orography.

(130,000 BP – 0 BP)

NH ice thickness, orography.

(130,000 BP – 0 BP)



and atm. CO2



and atm. CO2





(Abe-Ouchi et al, Clim. Past., 2007)


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.

Documents

O. Elison Timm 1 A. Timmermann 1,4 T. Friedrich 1 A. Abe-Ouchi 2,3 J. Knies 5 Forced response of a Northern Hemisphere ice-sheet model to climate changes