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On the Origin of Antarctic Warming Events: A Modeling Study of Causes and Effects

On the Origin of Antarctic Warming Events: A Modeling Study of Causes and Effects. AGU Chapman Conference on Abrupt Climate Change Columbus Ohio, 15-19 June, 2009. Oliver Timm, Laurie Menviel, Axel Timmermann International Pacific Research Center, University of Hawaii at Manoa.

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On the Origin of Antarctic Warming Events: A Modeling Study of Causes and Effects

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  1. On the Origin of Antarctic Warming Events: A Modeling Study of Causes and Effects AGU Chapman Conference on Abrupt Climate Change Columbus Ohio, 15-19 June, 2009 Oliver Timm, Laurie Menviel, Axel Timmermann International Pacific Research Center, University of Hawaii at Manoa

  2. What are the “patterns” of millennial-scale climate variability in the Southern Hemisphere? What are the primary forcing factors? How important are remote, local forcing and feedbacks? Can tropical oceans affect Antarctic climate? What terminates A-events? Can Antarctic warming events trigger an Antarctic cold reversal? On the Origin of Antarctic Warming Events: A Modeling Study of Causes and Effects AGU Chapman Conference on Abrupt Climate Change Columbus Ohio, 15-19 June, 2009

  3. What are the “patterns” of millennial-scale climate variability in the Southern Hemisphere? Signatures of non-uniform warming pattern EPICA Dome C Siple Dome Taylor Dome Vostok Oxygen/Deuterium Isotopes from Antarctic ice cores 1 3 2 4 1 3 2 4 Timmermann et al. QSR, accepted, 2009

  4. Signatures of non-uniform warming pattern in “waterhosing” model simulations Wind and SST anomalies during shutdown of the Atlantic Meridional Overturning Circulation SST anomaly [K] Timmermann et al. QSR, accepted, 2009

  5. tropical Atlantic forcing only What are the primary forcing factors? Negative SST anomalies in tropical Atlantic and tropical Pacific lead to SH circulation anomalies Atmosphere only experiments: SST anomalies from preindustrial waterhosing experiments green (orange) contours: positive (negative) rainfall anomalies (interval 1mm/day) contours: sea level pressure anomaly surface temp. anomalies [K] Timmermann et al. QSR, accepted, 2009

  6. What are the primary forcing factors today? Tropical forcing projects onto Pacific South America (PSA) pattern contours: sea level pressure anomaly associated with second EOF surface temperature anomaly [K] Timmermann et al. QSR, accepted, 2009

  7. Conceptual model: ocean seesaw and atmospheric bridge Heinrich event northern hemisphere cooling atmospheric connection via tropics bi-polar seesaw non-uniform warming pattern southern hemisphere warming + albedo feedback reduced sea-ice

  8. Causes of Antarctic Warming: Oceanic seesaw accompanied by atmospheric CO2 increase Causes of Antarctic Warming: Oceanic seesaw accompanied by atmospheric CO2 increase Figure 1 from Jinho Ahn and Edward Brook, Science, 322,83-85,2008

  9. Causes of Antarctic Warming: Model* experiments show importance of CO2 increase for warming Figure 2 from Timmermann et al. QSR, accepted, 2009 Atmospheric CO2 increase can account for 25-30% of Antarctic warming during A-events Source of atm. CO2 increase in this model: Northern Hemisphere terrestrial vegetation *Model LOVECLIM forced with ice core reconstructed CO2 time series Orbital parameters, albedo, forest fraction and topography were fixed at LGM values

  10. Pre-industrial meltwater pulse Freshwater input area 600 yrs Maximum overturning circulation, Sv What are the primary forcing factors? Remote freshwater input into North Atlantic Ocean Freshwater flux in the North Atlantic starting from a pre-industrial and a glacial climate state

  11. Carbon reservoir anomalies (GtC)‏ Atmospheric CO2 (ppm)‏ Ocean +100 GtC -120 GtC +15 ppm Vegetation Time (yrs)‏ Causes of Antarctic Warming: Sources and sinks of atmospheric CO2 Terrestrial carbon release outweighs ocean carbon uptake Menviel et al., Paleoceanography (2007)

  12. Enhanced southern hemispheric warming due to CO2 increase during Heinrich events Air temperature anomalies during AMOC collapse CO2 = 300 ppmv (CO2 = 300 ppmv) – (CO2= 280 ppmv)‏ CO2 contributes to an additional warming of ~1ºC at high southern latitudes

  13. Conceptual model: ocean seesaw and atmospheric bridge and CO2 Heinrich event Heinrich event marine carbon cycle reduced terrestrial vegetation northern hemisphere cooling northern hemisphere cooling ? atmospheric connection via tropics bi-polar seesaw southern hemisphere warming southern hemisphere warming + albedo feedback + albedo feedback reduced sea-ice reduced sea-ice atmospheric CO2 increase reduction (in LOVECLIM model)‏

  14. Revisiting the Antarctic Cold Reversal ACR ACR Kanfoush et al. 2000, Science During the last deglaciation South Atlantic IRD peak SA0 (14.2 to 13.5 ka) coincides with the Antarctic Cold Reversal and global meltwater pulse 1a and may point to an influx of icebergs from the AIS as the cause of these events. ACR Anderson et al. 2009, Science

  15. Causes of Antarctic Cold Reversal: Meltwater pulse from West Antarctic Ice Sheet Freshening of the Southern Ocean “Waterhosing” model simulation with LOVECLIM: Meltwater pulse in Ross Sea area (158°E-60°W, 70°S-80°S)‏ Maximum overturning circulation in the Southern Ocean (Sv)‏

  16. Climate response to Meltdown of the Westantarctic Ice-sheet • Cooling of Southern Ocean • Annual mean sea-ice area doubles • Ekman transport intensifies • Westerly winds intensify by 50% • Export production in SO decreases by 30% • Global opal production decrease by 10%

  17. Alternative explanation to Anderson et al. (Science, 2009) Antarctic Ice-sheet instability • Meltwater pulse Increased Stratification Reduced light ACR Reduced opal flux Reduced CO2 flux Cooling of ACC area • Sea ice increases • Westerlies increase Productivity decreases AABW formation decreases

  18. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth 20-50m

  19. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth 50-100m

  20. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth 100-140m

  21. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth 140-250m

  22. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth 250-500m

  23. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? Ocean Layer depth Ocean Layer depth 500-1000m

  24. Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet? subsurface warming

  25. reduction of AABW formation freshwater forcing destabilization of marine-based ice-sheets subsurface warming Antarctic Subsurface Warming: Further Destabilization of West Antarctic Ice Sheet?

  26. Conceptual model for Heinrich 1, A(0)-event and Antarctic Cold Reversal: Heinrich event sea level rise marine carbon cycle reduced terrestrial vegetation northern hemisphere cooling - feedback atmospheric connection via tropics bi-polar seesaw southern hemisphere warming - feedback + albedo feedback Cooler SST Southern Ocean (Antarctic Cold Reversal)‏ reduced sea-ice delayed trigger ? Meltwater pulse into Southern Ocean Meltwater pulse into Southern Ocean ? trigger ? Subsurface warming atmospheric CO2 increase increase increase/reduction (?)‏

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