Ch' 11

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Ch. 11 Water in Landscapes (Cont) Paleolimnology
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New lake sediment is created over time
Thousands of years
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(No Transcript)
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In the core, track changes in
Pollen
Inorganic chemistry (N, P)
geography.berkeley.edu/.../ byFamiliesAll-in-1.htm
l
www-personal.umich.edu/ gtamaska/diatom.html
Diatom frustules
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In the core, track changes in
Pigmentsmostly degraded pigments such as
pheophytin
www.acadweb.wwu.edu/.../ 77_spongilla_spicules_40x
.jpg
Animal partssponge spicules, midge head capsules
http//www.biologica.bc.ca/photos/chironomid.jpg
http//www.fw.umn.edu/research/milfoil/images/Cric
otopus.jpeg
www.robresint.co.uk/.../biostrat/
overview/overview.asp
Dormant eggs or cysts
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Dating sediments
Known historical event e.g. volcano
Annual varves alternation of light and dark bands
in the sediment
Isotopes 14C, 210Pb, 137Cs
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Calcium Carbonate Varves
http//earthobservatory.nasa.gov/Newsroom/NewImage
s/Images/seawifs_lake_mich_2001_tn.jpg
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Isotope Analysis
14C is created naturally from cosmic radiation
14N (neutron) gt 14C and 1H
Decays to 14N with the emission of a Beta-
particle (electron) with a half life of 5700
years
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Isotope Analysis
For recent sediments, use 210Pb, which is also
created naturally from cosmic radiation.
Half-life is 22.6 years, can go back about 150
years.
www.geo.umass.edu/climate/ TILPHTML/Pb210.html
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Isotope Analysis
Cesium-137Cs In the atmosphere since 1950s
because of atomic bomb testing
http//water.usgs.gov/pubs/circ/circ1171/images/ce
sium.gif
Some use the Chernobyl spike (1986) to date
recent sediments
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Davis, M. 1969. Ecology
Pollen Analysis
Relatively low pollen deposition rates
14,000-12,000 years ago reflects tundra
vegetation with few trees 11,000 Spruce, pine
dominated, some birch and oak 9,000 spruce
mostly gone pine, birch, some oak 8,000 - pine
declined, deciduous became dominant, immigration
of beech, hickory, chestnut, maple
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Laird et al. 1996, 1998
Sediments from Moon Lake, ND used to reconstruct
regional climate patterns
www.chebucto.ns.ca/Science/ SWCS/PALEO/bc-46.html
Diatoms live in freshwater and salt water, but
each species has a very specific salinity optimum
The depth of lakes in the Great Plains fluctuates
with regional climate patterns
Chaetoceros
In dry years, the lake levels are lower and
salinity is higher. In wet years, more
freshwater input, less saline
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Laird et al. 1996, 1998
www.washington.edu/.../hstaa432/
lesson_19/uwio18381.html
The extreme drought of the Dust Bowl era
(1930s) covered 65 of the continental USA
Results from the sediment record suggest that
historically, droughts were more frequent and
more intense
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REMINDER
Homework Assignment 9
p. 292, Questions 4 6 (10 points) Submit your
answers typed and written in complete sentences.
Explain your answers (i.e. why).
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Practice Question
Explain how diatoms can be used to reconstruct
past climate patterns. A complete answer will
address both the general factors of how
microfossils are used to reconstruct past
patterns, and the specifics of how diatoms are
used to reconstruct past climate patterns.