Answers for HW 10, Chapter 11

1. What types of geologic evidence are diagnostic of glaciation?

            Terrestrial: glacial striations, moraines, till, and loess.
            Marine: the oxygen isotope record––higher ¹⁸O/¹⁶O in marine sediments means lower temperature (more water tied up in ice sheets).

2. What causes changes in the oxygen isotopic composition of seawater?

Water molecules containing ¹⁸O tend to evaporate more slowly than do those containing ¹⁶O. Thus as the snow enriched in ¹⁶O falls onto the ice caps, the oceans are left enriched in ¹⁸O.

3. Which three characteristics of Earth’s orbit around the Sun vary on the timescale of Pleistocene glaciations? How does each of these affect the amount of energy received from the Sun?

They are eccentricity, tilt, and precession. The greater the eccentricity is, the more total sunlight the earth gets from the Sun. But the difference is small. Tilt and precession do not affect the amount of insolation.

5. How is the oxygen isotopic record of marine limestones used to test Milankovitch’s theory of the ice ages?

The record is separated into its component periodic waves to see whether they match the precession, tilt, and eccentricity bands. They appear to match fairly well except that the direct forcing in the eccentricity band is very small, yet the climate response is the largest of the three bands. There must be positive feedbacks that amplify the eccentricity forcing.

7. What factors might have caused atmospheric CO₂ variations that kept pace with glacial climate fluctuations?

The variations in the biological pump and the growth and weathering of coral reefs might have worked together to keep the atmospheric CO₂ concentration varying with the glacial climate fluctuations.