1. Carbon System Controls on CO 2 Increase biologic carbon pump in coastal and tropical ocean Increase carbon pump in Antarctic Change chemistry of Antarctic surface water Change chemistry of shallow Southern Ocean subsurface water

2. High Latitude Stratification Sigman et al. (2004; Nature 428, 59-63) Sigman et al. (2004; Nature 428, 59-63)  Cold climates promote polar ocean stratification Opal MAR decreased at ~2.7 mya Opal MAR decreased at ~2.7 mya  Fewer diatoms  15 N OM increased or did not change  15 N OM increased or did not change  Greater NO 3 2- utilization or no change in NO 3 2- utilization Indicates stratification Indicates stratification

3. Density at Cold Temperatures Variation in seawater density as a function of temperature, with salinity at 35‰ Variation in seawater density as a function of temperature, with salinity at 35‰ Density of sea water increases less rapidly as the temperature drops towards freezing point Density of sea water increases less rapidly as the temperature drops towards freezing point High latitude SST cold enough so winter cooling did not have enough of an effect to overcome salinity gradients High latitude SST cold enough so winter cooling did not have enough of an effect to overcome salinity gradients From Francois (2004; Nature 428 31-32)

4. Salinity Variations Today

5. Density  (cooling) Density as a function of depth in the modern wintertime Antarctic and changes in this density structure for uniform changes in seawater temperature. Cooling entire water column nearly doubles the vertical density difference.

6. Effect of Stratification on PCO 2 Global cooling an important factor promoting high- latitude stratification Global cooling an important factor promoting high- latitude stratification Polar ocean stratification prevents deep ocean ventilation Polar ocean stratification prevents deep ocean ventilation  Traps more carbon in the deep sea During Quaternary climatic cycles During Quaternary climatic cycles  Interglacial periods sufficiently warm to allow deep water convection in Antarctic  Not the North Pacific During glacial periods During glacial periods  Stratification in Antarctica and North Pacific  Contribute to lower atmospheric CO 2

7. Six factors may contribute to glacial atmospheric CO 2 change Six factors may contribute to glacial atmospheric CO 2 change  Four factors tied to carbon cycle through changes in  Nutrient upwelling  Antarctic surface water chemistry Factors contributing most to drop in CO 2 Factors contributing most to drop in CO 2  Lower SST  Stronger biological carbon pump  Increased CO 3 2- linked to changes in deep ocean circulation

8. Ice-Driven Climate Responses Ice sheets can become drivers of climate within the system because Ice sheets can become drivers of climate within the system because  Large height  Influences wind direction and temperature  Bright surface  Major albedo contrast  Calve icebergs  Deliver cold fresh water to oceans

9. Glacier Climate Interactions Regions in close geographic proximity to ice sheet Regions in close geographic proximity to ice sheet  The tempo of climate change is set by the change in ice sheet  Ice sheet has highest thermal inertia

10. Ice-Driven Responses Orbital scale ice sheet rhythms Orbital scale ice sheet rhythms  Quickly transferred to other parts of the climate system  Atmosphere  Oceans  Ice sheets respond to solar insolation  Other systems respond quickly to change in ice sheets

11. Ocean Surface Temperature N. Atlantic SST should respond to change in N. Hemisphere glaciations N. Atlantic SST should respond to change in N. Hemisphere glaciations  SST track ice volume with no lag  SST reconstruction from faunal assemblages  Ice volume and SST follow 41,000 year cycles  Similar relationships found in younger cores  Correlate with 100,000 year cycles

12. Mechanisms for Ocean Cooling Calving icebergs undoubtedly important Calving icebergs undoubtedly important Changes in winds Changes in winds  GCM sensitivity tests  Clockwise flow of winds initiated over ice sheets Cold winds blown over N. AtlanticCold winds blown over N. Atlantic Replaced warm flow from southwestReplaced warm flow from southwest  Simulations predict 5-10°C drop in SST Similar to documented SST changeSimilar to documented SST change

13. Cold Winds Affect Climate Pollen changes in France Pollen changes in France  N. Europe’s climate changed  Warm and moist (trees)  Cold and dry (herbs)  Changes correlate with ice volume  Cold winds from Scandinavian ice sheets  N. Atlantic ocean colder than today  Relative warm N. Atlantic moderates Europe’s winter weather

14. GCM Test of N. Atlantic SST Boundary condition Boundary condition  N. Atlantic glacial SST  Output indicated cooling over N. Atlantic, European maritime regions and central Eurasia  Produced lower rainfall  N. Hemisphere ice sheet growth  Cooled N. Atlantic  Cooled Europe and Asia Cooling occurred without lagCooling occurred without lag

15. Loess Plateaus Evidence of ice-driven response found in China Evidence of ice-driven response found in China  Plateaus of wind-blown silt  Deposited by strong winds and dry conditions Loess deposition post-date weathered soil at 2.75 mya Loess deposition post-date weathered soil at 2.75 mya  Onset of dry conditions at glacial inception  100,000 year cycle over last 0.5 my

16. Onset of Loess Deposition Loss of N. Atlantic moisture Loss of N. Atlantic moisture  Cold and ice-covered N. Atlantic  Stop moisture flow to Europe and Asia Siberian high-pressure center Siberian high-pressure center  Today source of strong winter winds  Could have strengthen during glaciers Windy and dry conditions deposited loess Windy and dry conditions deposited loess  Western N. Pacific  Greenland ice sheet

17. Summary Ice volume signal can be transferred far from ice sheets Ice volume signal can be transferred far from ice sheets  Altered wind patterns  Changes in air and sea surface temperature  Changes in rainfall over land Northern Hemisphere ice sheet growth Northern Hemisphere ice sheet growth  Drives the climate signal on orbital time scales  Ice sheets respond to orbital forcing  Changes in ice sheets drive other climate responses in northern latitudes

18. Other Effects of N. Ice Sheets Aeolian deposition in western Indian Ocean Aeolian deposition in western Indian Ocean  Follows timing of ice sheet growth and melting More dust deposited from Arabian desert More dust deposited from Arabian desert  During glacial intervals defined by  18 O maxima  Less dust deposited during interglacial periods

19. Effects in South America Long cores from eastern Columbian lakes Long cores from eastern Columbian lakes  Pollen records that alternate between grass and trees  100,000 year cycles  Trees grew during rapid warming  Grassland dominated during slow cooling intervals

20. Effects in New Zealand Marine sediment core east of New Zealand Marine sediment core east of New Zealand  Cyclic variations in tree and grass pollen  100,000 year dominant cycle

21. Effects in Southern Ocean Marine sediment cores in Southern Ocean Marine sediment cores in Southern Ocean  Assemblages of radiolarians  Indicative of ice cover and cold SST  Match well colder temperatures in glacial Appears that only summer monsoon signal not affected by N. Hemisphere ice volume Appears that only summer monsoon signal not affected by N. Hemisphere ice volume  Not expected due to summer forcing of monsoon

22. Southern Hemisphere Surprises Large Antarctic ice sheets do not appear to force S. Hemisphere glacial/interglacial changes Large Antarctic ice sheets do not appear to force S. Hemisphere glacial/interglacial changes  Most land mass of Antarctica now covered  Not much room to grow so no major expansion of ice volume In contrast, N. Hemisphere ice sheets fluctuated enormously In contrast, N. Hemisphere ice sheets fluctuated enormously  If climate signals forced by ice sheets  Probably forced by changes in N. Hemisphere ice sheets

23. Seasonal Changes in Precession Although insolation changes due to axial tilt in N and S Hemispheres in phase Although insolation changes due to axial tilt in N and S Hemispheres in phase  Precession changes are out of phase  When one hemisphere is warm (close to Sun)  Other Hemisphere is cold Patterns of insolation changes look different Patterns of insolation changes look different  Phase of the precession cycle is reversed between hemispheres

24. Phasing of Insolation and Ice Volume 41,000 and 23,000 year components of ice volume 41,000 and 23,000 year components of ice volume  Lag behind N. Hemisphere insolation by physically reasonable amount 41,000 year S. Hemisphere cycles has same lag 41,000 year S. Hemisphere cycles has same lag  23,000 year ice volume leads S. Hemisphere summer insolation forcing  Unreasonable relationship

25. Global Transfer of Signals Changes in sea level Changes in sea level  Creating more temperate maritime or harsh continental climate regions Change in deep water circulation Change in deep water circulation  Relatively warm and salty water directed away from Southern Hemisphere in Atlantic Atmospheric CO 2 levels Atmospheric CO 2 levels  Lower glacial CO 2 levels can cool entire planet  Reduce the amount of water vapor in atmosphere  Most reasonable explanation for widespread changes Which came first CO 2 change or glaciations?Which came first CO 2 change or glaciations?

26. CO 2 and Ice Volume Records of CO 2 and ice volume well correlated Records of CO 2 and ice volume well correlated  Both must be related ultimately to orbital changes  Strong correlation also indicates  Two records are linked

27. CO 2 Drives Ice Sheets Sensible conclusion since CO 2 affects temperature Sensible conclusion since CO 2 affects temperature  Therefore ice sheet mass balance However, CO 2 should lead ice volume However, CO 2 should lead ice volume  Pattern in records are not consistent with premise  No persistent lag in signals  Correlation between CO 2 and temperature excellent  CO 2 does not lead ice volume

28. Ice Sheets Drive CO 2 CO 2 signal tracks closely ice volume CO 2 signal tracks closely ice volume  Similar to other ice-driven climate signals  CO 2 record connected to changes in ocean circulation and carbon storage  Ocean circulation responds quickly to changes in climate forcing  Timing of changes in CO 2 and ice volume match this expectation

29. CO 2 Feedbacks CO 2 levels provide positive feedbacks to climate system CO 2 levels provide positive feedbacks to climate system  Ice sheet growth caused CO 2 decrease  Lower CO 2 levels further cool climate Increase ice sheet growthIncrease ice sheet growth  CO 2 levels should also carry ice volume signal  Other parts of climate system Changes in temperature or moistureChanges in temperature or moisture

30. Complete Story Unknown Text points to mismatches in CO 2 and ice volume/temperature records Text points to mismatches in CO 2 and ice volume/temperature records  Mismatch with temperature is not as great as believed only 2-3 years ago  Mismatch with ice volume real?  However, records still insufficiently refined To answer clearly chicken and egg dilemmaTo answer clearly chicken and egg dilemma  Part of the uncertainty lies in poorly dated ice cores