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Origin of the 100,000-yr Glacial-Interglacial CO 2 Cycle in the Southern Ocean

Origin of the 100,000-yr Glacial-Interglacial CO 2 Cycle in the Southern Ocean. J. R. Toggweiler GFDL/NOAA Princeton, NJ USA. Outline. Problems with the Astronomical Theory Internal Cycle in the Climate System Components of the Internal Cycle Origin of the Long Time Scale

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Origin of the 100,000-yr Glacial-Interglacial CO 2 Cycle in the Southern Ocean

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  1. Origin of the 100,000-yr Glacial-Interglacial CO2 Cycle in the Southern Ocean J. R. Toggweiler GFDL/NOAA Princeton, NJ USA

  2. Outline • Problems with the Astronomical Theory • Internal Cycle in the Climate System • Components of the Internal Cycle • Origin of the Long Time Scale • Box Model / Results • What is Really Driving the System?

  3. Problems with the Astronomical Theory

  4. Hypothesis • The Earth’s climate system contains a threshold that is capable of pushing the atmospheric pCO2 away from its long-term mean. • Crossing the threshold brings on a crisis in ocean chemistry that holds the pCO2 above or below the long-term mean for 40-50,000 years. • Short-term climate excursions, like those that lead to Heinrich Events, bring the system back to the threshold.

  5. Evidence for a Threshold

  6. δ13C in the deep South Atlantic

  7. ThresholdSchematic

  8. Threshold Feedback • Warmer climates have stronger, poleward-shifted westerlies. • Stronger westerlies over the ACC increase Southern Ocean ventilation. • Southern ocean ventilation increases the atmospheric pCO2

  9. Chemistry Crisis I pCO2 atm = f(CO2 deep− CO2 surf) Broecker (1982)

  10. Chemistry Crisis II But, pCO2 atm, CO3=deep are constrained. Something has to give.

  11. Chemistry Crisis III

  12. Short-Term Excursions

  13. Short-Term Excursions, Detail

  14. Weathering Cycle

  15. CaCO3Overproduction

  16. Build-Up of Respired CO2 in the Deep Ocean

  17. Seven-Box Model

  18. External Components

  19. Synthetic CO2 Cycles

  20. Detail of 100,000-yr Cycle

  21. Detail of 100,000-yr Cycle

  22. Sawtooth-Shaped Cycles

  23. Conclusions I • The 100,000-yr cycle in atmospheric CO2 is an internally generated cycle that is independent of the 100,000-yr cycle in orbital eccentricity. • Its first component is a threshold and a feedback mechanism that knocks the pCO2 away from its long-term mean. Threshold-crossing events produce a crisis in ocean chemistry that holds the pCO2 away from the long-term mean for the next 40-50,000 years.

  24. Conclusions II • Short-term climate excursions of unknown origin bring the pCO2 back to the threshold. They are the real drivers of the 100,000-yr ice age cycles. Successful excursions are spaced out by the chemistry crisis. Only those that occur after the chemistry crisis has run its course can bring the pCO2 back to the threshold. • The threshold is a particular strength of position of the Southern Hemisphere westerlies in relation to the ACC. Warmer climates produce stronger westerlies that draw more deep water to the surface and extract more CO2 from the deep ocean. Stronger winds associated with warmer tropical temperatures could be the driving agent behind the short-term excursions as well.

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