1. Past ENSO : observations and simulations with the IPSL model for the Holocene and the last Millennium P. Braconnot, Laboratoire des Sciences du climat et de l’envrionnement, Gif-sur-Yvette, France With input from different collegues

2. High resolution proxy records to infer ENSO variability From T. Correge, G. Cabioche, C. E. Lazareth, M. Carré S. Tudhope, M. Helliot

3. Massive corals Chemical analyses of massive corals: A window on tropical climate S. Thudope T. Correge ~8000 yr old porites coral

4. Tracers in corals: Sr/Ca Calibration of Sr/Ca vs SST in a live coral from New Caledonia Sr/Ca appears to be a robust SST tracer ("proxy") from Correge

5. (Tudhope et al., unpublished) r 2 = 0.62 for monthly data Jarvis coral  18 O and NINO3.4 SST

6. Marine bivalves

7. ENSO strength from corals and bivalves (Tudhope et al, 2001) From Living and fossil corals Comparison with bivalves Cabioche and Correge

8. Paleo-ENSO from mollusk shells Ex East Pacific R=0.74  TCallao Annual Niño1+2 index 50-70% reduction of ENSO activity M. Carré

9. Multi proxy reconstruction for the early to mid Holocene Need to combine different proxy to reconstruct mean-state, seasonality and variability Variability reduced in Early to mid-Holocene Link with the insolation forcing through Bjerknes feedback (Clement et al. 1999, 2000, etc…) or monsoon activity (Liu et al. 2003) La Niña type mean state ? From literature : Braconnot et al. subm

10. ENSO in PMIP 6ka simulations  Almost all simulations show reduced ENSO  The increased monsoon counteracts the development of ENSO  Case where the change in large scale dynamics dominate the signal different from future or LGM where thermodynamics seems more important. Zheng et al 2008 Niño 3 ENSO reduction underestimated? Pb model? Pb proxy interpretation?

11. Mid and Early Holocene Response to insolation forcing and fresh water fluxes Results from Yihu Luan’s PhD Collaboration S. Brewer, W. Zheng Braconnot et al. Subm.

12. Early vs mid-Holocene? Differences in the response depending on precession? Insolation 6ka-0kaInsolation 9.5ka-0ka Latitude > 20 W/m2> 25 W/m2 From Berger 1978 Summer solstice

13. Simulations with IPSLCM4 OAGCM Ocean-atmosphere-sea-ice- land surface Same version as in AR4 and PMIP2 Resolution atm : 96x72xL19 Ocean : 2° (refined at eq) xL31 SimulationCTRL6ka9.5ka Length (yrs)1000650300 Test to insolation forcing only Marzin and Braconnot 2009

14. Role of fresh water in the North Atlantic? Fresh water flux on present day mean state enhances ENSO in a multimodel ensemble simulations (Timmermann et al. 2007) Test for 9.5ka and 6ka using IPSL-CM4 and a crude representation of interactive ice-sheet melting with climate Following Swingedouw et al. 2006 Simulation6kawF9kawF Length (yrs)800280 Test to insolation forcing and fresh water forcing Ice-sheet Fresh water interactive with climate, uniformly distributed over the ocean > 40°N in Atlantic and Arctic

15. Change in DJF interannual variability SST : standard deviation 0k 6k 9.5k Insolation Insolation +wF Variability larger in model than in observations Variability increases from 9.5k to 0k Fresh water flux in NA enhances variability

16. Change in seasonality Niño 3 box : annual mean cycle Wind and precipitation changes in July-August mm/d Insolation Fresh water Braconnot et al. Subm. Luan et al. In prep

17. ENSO composites Typical evolution in Niño3 box Rms computed over this period SST isolines Pr : color Months Yr previousYr after Ex: role of EH insolation Niño Niña Normal= seasonal cycle mm/d

18. Relative changes induced by changes in seasonality, El-Niño and La Niña on SST Braconnot et al. Subm.

19. The last millenium: ENSO response to volcanic forcing From M. Khodri

20. IPSL-CM4 Model Calendar time Gao et al. 2008 Khodri et al. In prep Influence of external (volcanic and solar) forcing on SST? Warm Medieval Period (≈ 950-1250 Year A.D.) simulated cooling in Niño 3 in respone to volcanic forcing Persistant cooling in data (multi- year La Niña or La Niña like state? Transition to LIA (≈1400-1700?) Higher Low Frequency (decadal) Variability Modulation of El Niño events? Volcanic Forcing Mann et al 2009

21. SST (ENSO) response to Volcanic Forcing SST Anomaly (°C) Niño 4 Index Control Run Millennium Run Volcanic Forcing (W/m 2 ) SST Anomaly (°C) Niño 3 Index Control Run Millennium Run Volcanic Forcing (W/m 2 ) Selected Eruption (max >2.5 W/m2) Random SST with same variance (  ) as in CTRL Simulated SST SST >  for at least 9 months

22. Conclusion Insolation and fresh water flux damp the SST seasonal cycle in the east Pacific (link with large scale dynamics) Increase ENSO magnitude from 9.5 ka to 0k in response to insolation Early and mid-Holocene ENSO development is damped in Autumn Fresh water flux enhances ENSO magnitude Volcanic eruptions favors increased decadal variability at the MWP/LIA transition in last millennium simulation with insolation and volcanic forcing Colder SST (more La Niña? ) after volcanic eruption? What about the hypothesis of El-Niño 1 year after? Need to better understand relative impact of seasonality and variability on relationship between proxy records and ENSO variability to produce reliable model-data comparisons.