Title: Chapter 14Part 1
1Chapter 14Part 1
- i) Oxygen isotopes and climate
- /Keplers laws
2How do we know how warm it was millions of years
ago?
- Ice cores bubbles contain samples of the
atmosphere that existed when the ice formed.
(ancient pCO2) - Marine isotopes oxygen isotopes in carbonate
sediments from the deep ocean preserve a record
of temperature. - The records indicate that glaciations advanced
and retreated and that they did so frequently and
in regular cycles.
3Oxygen isotopes and paleoclimate
- Oxygen has three stable isotopes 16O, 17O, and
18O. (We only care about 16O and 18O.) - 18O is heavier than 16O.
- The amount of 18O compared to 16O is expressed
using delta notation - Fractionation Natural processes tend to
preferentially take up the lighter isotope, and
preferentially leave behind the heavier isotope.
? 1000
4Oxygen isotopes and paleoclimate
- Oxygen isotopes are fractionated during
evaporation and precipitation of H2O - H216O evaporates more readily than H218O
- H218O precipitates more readily than H216O
- Oxygen isotopes are also fractionated by marine
organisms that secrete CaCO3 shells. The
organisms preferentially take up more 16O as
temperature increases.
18O is heavier than 16O H218O is heavier than
H216O
5Oxygen isotopes and paleoclimate
so cloud water becomes progressively more
depleted in H218O as it moves poleward
Precipitation favors H218O
and snow and ice are depleted in H218O
relative to H216O.
Evaporation favors H216O
H218O
H218O
Ice
Land
H216O, H218O
Ocean
6Oxygen isotopes and paleoclimate
- As climate cools, marine carbonates record an
increase in d18O. - Warming yeilds a decrease in d18O of marine
carbonates.
JOIDES Resolution
Scientists examining core from the ocean floor.
7Long-term oxygen isotope record
From K. K. Turekian, Global Environmental Change,
1996
8Drake passage
- Once the Drake passage had formed, the
- circum-Antarctic current prevented warm ocean
- currents from reaching Antarctica
9O isotopes during the last 3 m.y.
Kump et al., The Earth System, Fig. 14-4
- Climatic cooling accelerated during the last 3
m.y. - Note that the cyclicity changes around 0.8-0.9
Ma - - 41,000 yrs prior to this time
- - 100,000 yrs after this time
10O isotopesthe last 900 k.y.
- Dominant period is 100,000 yrs during this time
- Note the sawtooth pattern..
after Bassinot et al. 1994
11Ice Age Cycles 100,000 years between ice
ages Smaller cycles also recorded
every 41,000 years, 19,000 - 23,000
years This was the dominant period prior to
900 Ma
12Milutin Milankovitch, Serbian mathematician 1924
--he suggested solar energy changes and seasonal
contrasts varied with small variations in Earths
orbit He proposed these energy and seasonal
changes led to climate variations
NOAA
13Before studying Milankovitch cycles, we need to
become familiar with the basic characteristics of
planetary orbits Much of this was worked out in
the 17th century by Johannes Kepler (who observed
the planets using telescopes) and Isaac Newton
(who invented calculas)
14Keplers Laws
First law Planets travel around the sun in
elliptical orbits with the Sun at one focus
r
r
r r 2a a semi-major axis ( 1 AU for
Earth)
a
Major axis
Minor axis
15 Ellipse Combined distances to two fixed points
(foci) is fixed
r
r
r r 2a
a
16Aphelion Point in orbit furthest from the sun
Earth (not to scale!)
ra
ra aphelion distance
17Aphelion Point in orbit furthest from the
sun Perihelion Point in orbit closest to the sun
Earth
rp
rp perihelion distance
18Eccentricity e b/a so b ae a 1/2 major
axis (semi-major axis) b 1/2 distance between
foci
b
a
19Eccentricity e b/a a 1/2 major axis b 1/2
distance between foci Sun-Earth
distances Aphelion a ae a(1
e) Perihelion a ae a(1 e)
b
a
20Eccentricity e b/a a 1/2 major axis b 1/2
distance between foci Sun-Earth
distances Aphelion a(1 e) Perihelion
a(1 e)
Today e 0.017 Range 0 to 0.06 Cycles
100,000 yrs
b
a
21Keplers Second Law
2nd law A line joining the Earth to the Sun
sweeps out equal areas in equal times
Corollary Planets move fastest when they are
closest to the Sun
22Keplers Third Law
- 3rd law The square of a planets period, P, is
proportional to the cube of its semi-major axis,
a - Periodthe time it takes for the planet to go
around the Sun (i.e., the planets year) - If P is in Earth years and a is in A.U., then
- P2 a3
23Other characteristics of Earths orbit vary as
well. The three factors that affect climate are ?
24Eccentricity (orbit shape) 100,000
yrs 400,000 yrs Obliquity (tilt--21.5 to
24.5o) 41,000 yrs Precession (wobble)
19,000 yrs 23,000 yrs
http//www.geo.lsa.umich.edu/crlb/COURSES/205/Lec
20/lec20.html