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9 Cards in this Set

  • Front
  • Back
Oxygen isotopes provide climate information
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
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
Continental drift and climate
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).
Orbital sources of
climatic variability
Eccentricity.
Tilt.
Precession.
Eccentricity.
Orbit around sun
changes from circular to elliptical
at 100 kyr intervals. Northern
hemisphere is cold during
elliptical orbit.
Tilt.
Axis of earth varies from 22
to 25 degrees at 41 kyr intervals.
With higher tilt, polar regions
receive more direct sunlight
during summer.
Precession
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.
Ecomorphology
Functional relationships
between skeletal elements
and environment can be
used to reconstruct local
habitats.
Glaciers and sea
level
As glaciers advance,
sea levels fall.
As glaciers retreat, sea
levels rise