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9 Cards in this Set
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Oxygen isotopes provide climate information
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Two stable isotopes of oxygen, 18 (heavy) and 16 (light).
Lighter isotope evaporates more easily, heavier isotope precipitates more easily. During cold periods, more water trapped as continental ice sheets. These sheets form from atmospheric water, which has more of the lighter isotope. So in cold periods, ocean water is 16O depleted and 18O enriched. Some marine organisms incorporate oceanic oxygen into their shells, preserving the isotopic signal of the ocean water, which in turn reflects global temperature |
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Long term climatic
trends revealed by oxygen isotopes |
Overall cooling since the
onset of the Eocene 55 mya. Cooling during Eocene coincides with the separation of Antarctica from South America, leading to the establishment of a circum-Antarctic current |
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Continental drift and climate
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Cooling trend in the Plio-Pleistocene coincides with
increased climatic variability Figure 12.1. A benthic foraminiferal oxygen isotope record from the eastern equatorial Pacific (ODP Sites 846 and 849) covering the past several million years. An overall trend to colder more glaciated conditions began approximately 3.5 million years ago. Superimposed on this overall trend is marked variability on 41,000-year timescales in the early Pleistocene followed by dramatically dominant 100,000-year cycles of the Quaternary ice ages (Mix, et al. 1995a,b). |
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Orbital sources of
climatic variability |
Eccentricity.
Tilt. Precession. |
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Eccentricity.
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Orbit around sun
changes from circular to elliptical at 100 kyr intervals. Northern hemisphere is cold during elliptical orbit. |
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Tilt.
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Axis of earth varies from 22
to 25 degrees at 41 kyr intervals. With higher tilt, polar regions receive more direct sunlight during summer. |
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Precession
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Due to “wobble” in
the axial tilt of the earth, and “drift” in the orientation of the earth’s orbit, the season in which the earth is closest to the sun varies at 11 kyr intervals. Warm periods occur when the earth is closest to the sun during winter. |
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Ecomorphology
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Functional relationships
between skeletal elements and environment can be used to reconstruct local habitats. |
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Glaciers and sea
level |
As glaciers advance,
sea levels fall. As glaciers retreat, sea levels rise |