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Transient paleo simulations and what we can learn from them

Transient paleo simulations and what we can learn from them. Part I: Understanding deglacial temperature rise in the tropical Pacific?. Axel Timmermann, IPRC, University of Hawai’i Oliver Timm, IPRC, University of Hawai’i. “correlation” Analysis D (G(F)) ne aF. Orbital forcing F

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Transient paleo simulations and what we can learn from them

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  1. Transient paleo simulations and what we can learn from them

  2. Part I: Understanding deglacial temperature rise in the tropical Pacific? Axel Timmermann, IPRC, University of Hawai’i Oliver Timm, IPRC, University of Hawai’i

  3. “correlation” Analysis D(G(F)) ne aF Orbital forcing F Complex spatio-temporal signature Climate resonse R: Seasonal sensitivities (sea ice, westerlies, MLD) G(F) Climate proxy response Seasonal sensitivities D(R)

  4. Alkenone versus Mg/Ca SST in eastern equatorial Pacific • Difference in timing • Difference in magnitude • millennial-scale changes in Uk38 • Possibilities: • Seasonal effects • Physiological effects • Preservational effects This is not dilemma, but a challenge!

  5. Heinrich I Termination I in Uk38 EOF analysis of alkenone-based temperature reconstructions In eastern equatorial Pacific PC1 PC2 (-1)*EOF2 and GFDL_CM2.1 SSTA Timmermann, CLIVAR Exchanges (2008)

  6. Seasonal window for Atlantic-Pacific connection 1x1 degree resol. Xie et al. J. Climate 2008

  7. LOVECLIM (3D) AGISM ICIeS (ice sheets) ECBilt (atmosphere) CLIO (sea ice-ocean) VECODE (terr. biosphere) LOCH (oceaniccarbon cycle) 21ka transient simulations with LOVECLIM

  8. Seasonality and Forcing 4 experiments: ALL forcings GHG only TOPO only ORB only Orbital forcing controls timing

  9. Seasonality of Uk38 • Uk38 exhibits clear millennial-scale signal • Seasonal window: winter to spring • Steinke et al. 2008: • “In South China Sea • Alkenone-producing coccolithophores are • predominant in cold months” • In EEP: • shallow thermocline during spring • but warmer SST • In EEP: two chlorophyll maxima conincide • With thermocline shoaling • Seasonal window: late winter to early spring Kienast et al. 2006

  10. Winter temperature and alkenone data Model simulations suggest that Orbital forcing plays a key role In delaying the onset of deglacial warming CO2 forcing and remote effects of Ice-sheet are responsible for the Warming trend from 21-10 ka B.P. PC1 alkenone

  11. Seasonality of Mg/Ca EEP • Mg/Ca does not show a pronounced millennial • scale signal • Could be suggestive of summer signal • Steinke et al. 2008: • “G. Ruber most abundant in stratified oligotrophic waters” • Seasonal window: early summer and winter • Mg/Ca records in EEP highly correlated with • summer insolation, anti-correlated with • obliquity forcing during termination I • summer signal

  12. Implications & Conclusions Deglacial temperature rise in equatorial Pacific is more than “just” CO2 Forcing; remote effects of ice-sheets play an important role and for the Seasonal temperature evolution the corresponding orbital forcing Estimates of climate sensitivity from tropical SST reconstructions are meaningless without considering seasonality and orbital forcing and dynamical effects due to ice-sheets Average of Mg/Ca (boreal summer bias) and alkenone (boreal winter bias) might be a better proxy for annual mean temperature evolution Sediment trap data are crucial to get a better understanding of what SST paleo-proxy data actually mean Different transient model simulations needed to further evaluate robustness of orbital, GHG and icesheet response in the EEP

  13. Part II: Orbital-scale climate variations in the Southern Hemisphere Axel Timmermann, IPRC, University of Hawai’i Oliver Timm, IPRC, University of Hawai’i Laurie Menviel, University of Hawai’i Lowell Stott, USC Ayako Abe Ouchi, CCSR

  14. Antarctic temperature variations forced locally or remotely? myth

  15. The role of austral spring time insolation

  16. The role of austral spring time insolation Timmermann et al. (2008) Why are glacial variations in North and South almost synchronous? What drives glacial temperature variability in the Southern Hemisphere? What role does sea-ice play and what processes modulate sea-ice variations?

  17. The role of austral spring time insolation Less sea ice More sea ice

  18. The role of austral spring time insolation:LOVECLIM 130ka versus EDML

  19. Austral spring insolation increase In combination with maximum sea-ice Extent during spring and large changes of ice-extent lead to net shortwave forcing of 12 W/m2

  20. Orbital-scale wind, precipitation and dust changes

  21. Deglaciation with H1, YD and MWP Ia (Southern source)

  22. Anderson’s hypothesis: reduced winds trigger weakened upwelling of nutrients Our hypothesis: Reduction of opal production Due to sea-ice expansion in response to MWP-1A

  23. Multiple Sahara Greenings ?

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