ERTH 535: Planetary Climate Change (Spring 2018) Pre-class Quiz #4: Pleistocene Glaciations Dr. Dave Dempsey Dept. of Earth & Climate Sci., SFSU

This is a "preview" version of Pre-class Quiz #6. The preview version is suitable for printing and leisurely inspection before you submit your answers to the interactive or "live" version—that is, the real thing. When you feel ready to submit your answers, go to iLearn's ERTH 535 "Pre-class Quiz" section, select the interactive version, and follow its instructions.

(Responses must be submitted via iLearn by 12:00 p.m. on Friday, May 4.)

Description: The questions below pertain to glacial/interglacial intervals in the last several million years and Milankovitch cycles. They are based on Reading Assignment #8.

Questions:

(1) Multiple Answer. Controls on oxygen isotope ratios in sea water. 18O to 16O are two isotopes of oxygen (the former heavier than the latter). Which of the following processes affect the ratio of of these two oxygen isotopes present in sea water and thereby tells us something about past climate? (Select all answers that are reasonably correct; there might be none, one, or more than one.)

1. formation of ozone from atmospheric oxygen
2. dissolving of iron in dust deposited by winds in sea water
3. evaporation of water from the sea surface
4. falling of rain back into the sea and accumulation of snowfall on land farther from the oceanic source of the water

(2) Multiple Choice. Orbital and rotational variations and solar insolation. Two parameters (rotational parameters) characterize the orientation of the earth's axis of rotation in three-dimensional space:

1. Azimuth angle. This angle is measured in, or parallel to, the plane of the earth's orbit around the sun. You can think of this angle as measured "horizontally", if you think of the plane of the earth's orbit around the sun as a "horizontal" plane. The azimuth angle is measured relative to a reference direction based on distant stars. (The axis currently is oriented toward Polaris, the North Star.) The systematic, periodic change that an azimuth angle undergoes is called precession.
2. Tilt angle, or obliquity. This angle is measured between the earth's axis of rotation and the plane of the earth's orbit around the sun. You can think of this angle as measured "vertically", in a direction perpendicular to the plane of the earth's orbe and hence to the azimuth angle. (The earth's obliquity is currently 23.5°.) The systematic, periodic change that an obliquity angle undergoes is called nutation.

A third parameter (an orbital parameter) characterizes the extent to which the earth's elliptical orbit around the sun departs from a perfect circle:

1. Eccentricity. (The eccentricity of a perfect circle is zero. The eccentricity of the earth's orbit is currently 0.017.)
For the earth, all three—azimuth angle, obliquity, and eccentricity—vary over time. Which of these changes affects the annual average amount of sunlight striking the earth as a whole? (Pick the one best answer.)
1. azimuth angle
2. obliquity
3. eccentricity
4. a combination of obliquity and azimuth angle (which together define the orientation of the earth's axis of rotation in 3-D space)
5. all three (azimuth angle, obliquity, and eccentricity)

(3) Multiple Choice. Low CO2 levels during glacial periods. Geologic evidence from the last several million years indicates that during glacial intervals, carbon dioxide (CO2) levels are lower than they are during interglacial intervals. Which one of the following could NOT help explain this observation, at least in principle? (Pick the one best answer.)

1. As a liquid (such as water near the ocean surface) cools, it is able to dissolve more gas (such as CO2 from the atmosphere) before becoming saturated with that gas
2. Weathering and erosion of continental shelves exposed by low sea levels increases nutrients available to photosynthetic marine organisms and spurs their growth
3. Greater deposition of iron in wind-blown dust under drier conditions spurs the growth of photosynthetic marine organisms
4. Forest cover decreases as ice covers more land, thereby decreasing terrestrial biomass and adding the carbon it contains back to the atmosphere as CO2
5. Corals exposed by low sea levels die and weather, removing CO2 from the atmosphere

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