Page 214 - Earth's Climate Past and Future

190 PART III • Orbital-Scale Climate Change

CO 2 (ppm ) CH 4 (ppb ) Review Questions
200 240 280 400 600
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Isotopic stage 1 1. How are ice cores dated?
2. Why are air bubbles in ice cores younger than the
Stage 2 ice in which they are sealed?
3. What features of the ice core CH signal suggest a
4
link to tropical monsoons?
3
50,000 4. To what extent does a cooler glacial ocean explain
lower CO levels in the glacial atmosphere?
2
Years ago 5. Where did the carbon (CO ) removed from the
Stage 4
2
atmosphere go during glaciations?
5.1
6. What effect does fractionation have on carbon
5.2
isotope values?
100,000 5.3
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7. Explain how carbon isotopes (δ C) trace shifts of
5.4
carbon from the land to the ocean.
5.5 8. How does the oceanic carbon pump reduce CO 2
levels in the atmosphere?
Isotopic stage 6 9. What evidence indicates a different glacial
150,000 deep-water flow pattern in the North Atlantic?
δ 18 O/Ice volume ( )
Max Min 10. How could a change in deep circulation in the
Atlantic Ocean alter atmospheric CO ?
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FIGURE 10-18 Ice/Gas Phasing The phasing of the green-
house gases relative to ice volume at the three orbital periods
is evident in the changes of the last 150,000 years. (Adapted Additional Resources
from W. F. Ruddiman, “Ice-Driven CO Feedback on Ice Volume,”
2 Basic Reading
Climate of the Past 2 [2006]: 43–66.)
Ruddiman, W. F. 2005. Plows, Plagues and Petroleum,
Chapter 5. Princeton, NJ: Princeton University
Press.
IN SUMMARY, the greenhouse gases act as a forcing of
the ice sheets at the 23,000-year period, but they act Advanced Reading
as an ice-driven feedback at the 41,000-year period.
The reason why the gases have these completely Broecker, W. S., and T.-H. Peng. 1989. “The Cause of
different roles at the two periods is not known. The the Glacial to Interglacial Atmospheric CO 2
role of the greenhouse gases in the major oscillations Change: A Polar Alkalinity Hypothesis.” Global
near ~100,000 years appears to be a combination of a Biogeochemical Cycles 3: 215–39.
large feedback role and a smaller forcing role. Kohfeld, K., C. Le Quere, S. P. Harrison, and R. F.
Anderson. 2005. “Role of Marine Biology in
Glacial-Interglacial Cycles.” Science 308: 74–78.
Martin, J. H. 1990. “Glacial-Interglacial CO Change:
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Key Terms The Iron Hypothesis.” Paleoceanography 5: 1–13.
Petit, J. R., et al. 1999. “Climate and Atmospheric
ice flow model (p. 177) iron fertilization History of the Past 420,000 Years from the Vostok
sintering (p. 177) hypothesis (p. 184) Ice Core, Antarctica.” Nature 399: 429–37.
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carbon isotopes (p. 178) δ C aging (p. 186) Sigman, D. M., and E. A. Boyle. 2000. “Glacial/
phytoplankton (p. 178) polar alkalinity Interglacial Variations in Atmospheric Carbon
hypotheseis (p. 187)
carbon pump (p. 183) Dioxide.” Nature 407: 859–68.