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Re: isotopic analysis of fossils
Mike Muller (muller@flmhh.ufl.edu)
Sat, 13 Jul 1996 10:38:14 -0400
Dan Evens wrote:
There are two major isotopes used in research today carbon and oxygen.
In regards to the oxygen isotopes only this is a long and fairly involved
subject but I will try to simplify...
Precipitation has a ratio of oxygen isotopes present. 18O is
heavier and 16O is lighter. If the rain is c old it will have a higher
ratio of 18O to 16O and if it is warm the amount of 16O increases in the
ratio. This is due to many mechanisms Look for papers by Daansgard 1964
to elaborate on this. When the rain falls it is stored in lakes, rivers
etc. Still maintaing the oxygen isotope ratios. When an animal drinks
this water the body fractionates these isotopes in equilibrium with its
body water. Read articles by J.D. Bryant or of you are truly interested I
can send you copies of these. These isotopes then appear in the
carbonate and phosphate of the enamel apatite of the teeth and the
apatite of the bones and still retain the same ratios of 18O to 16O.
Although, usually in enriched amounts due to the metabolic processes and
other sources of water in the animals diet such as plant water. When
these samples are reacted with certain acids etc... and run through a
mass spectometer the isotopes are released and measured.
It is this data that allow us to determine the
seasonality...highs and lows...and general paleoclimate of a geographic
region. Many articles have been published on this Quade et al....Fricke
and O'Neil....Koch et al...Bryant et al...are some of the best.
Using my research for an example I am sampling Equus teeth and
Mercinaria shells from Leisey Shell Pit in Florida. I will drill samples
of their enamel/shells, react them to release the 18O from the carbonate
and put them in the Isocarb. My results should show the seasonal
fluctuations that occurred over the animals life by showing high and low
peaks in the ratios of 18O. High peaks indicate cold temperature and low
peaks indicate warm ones. With a paleotemperature equation I will be
able to determine how high the highs and low the lows in regards to
degrees Celcius. I can then draw a firm conclusion regarding the
seasonality of Florida between 1.2 and 1.8 million years ago.
I have left out many of the finer details etc for the sake of simplicity
and brevity...I have listed articles that can be found to read further
but I doubt that a public library would have the journal you will need to
go to a university science library. Happy Hunting!
Holly reeser@flmnh.ufl.edu
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