Stable%20Isotopes

1
Stable Isotopes
By Kristen Luebbert and Tiffany Roberts
Geological Oceanography Dr. Gray
11/20/02
2

• Outline of Todays Presentation
• Introduction
• Relative Abundances
• Vibrational energy
• Fractionation
• Rayleigh Distillation
• Mass Spectrometry
• Del Values
• Standards
• Applications

3
Why are stable isotopes important?

• Ratios used to trace many processes in various
  fields of science
• Geological Oceanography
• Reconstruct past ocean temps, ocean circulation,
  ice volumes, etc.

4

• Isotopes - atoms of elements which contain a
  different number of neutrons, but chemically act
  the same.
• Stable isotopes - isotope that does not decay
  radioactively.

http//van.hep.uiuc.edu/van/qa/section/everything_
else/atoms/920424670.htm
http//hyperphysics.phy-astr.gsu.edu/hbase/nuclear
/nucnot.htmlc2
5
Relative Abundances
1H 99.99 12C 98.9 14N 99.6 16O 99.8 32S 95
2H 0.01 13C 1.1 15N 0.4 17O 0.04 33S 0.8
3H Rare 14C 10-10 18O 0.2 34S 4.2
36S 0.2
6

• Heat increases vibrational energy
• -A greater amount of heat is need to evaporate
  heavier isotopes

7
Fractionation

• Fractionation process by which certain isotopes
  are selected preferentially over others
• Chemical Reactions
• Phase Changes
• Molecular Diffusion
• Ex. Freezing or boiling water

8
Evaporation
9
Rayleigh Distillation isotopic concentration of
product differs from original material
http//blueox.uoregon.edu/courses/dlivelyb/ph161/
L14.html
10
Example The isotopic concentration of the
lightest isotope will be lowest at a mountain
peak, than in the surrounding valley.
11
How are Stable Isotopes Measured?

• Mass Spectrometry

http//minyos.its.rmit.edu.au/rcmfa/mstheory.html
12
So What is Mass Spectrometry?

• separates atoms based on mass
• Ion beam shot deflection of ions
• Heavier isotopes are deflected less separates
  heavy and light
• Mass analysis obtained.

http//hyperphysics.phy-astr.gsu.edu/hbase/nuclear
/krypton.htmlc1
13
Del Value relative difference measured between
the isotope ratio and the relative standard Del
value (Rsample Rstandard)/Rstandard x 1000
measured in (permil) R isotope
ratio with most abundant isotope in the
denominator. Ex. High ?18O more rare relative
to abundant Less ?18O more of most
abundant reminder values compared to
standard
14
Standards

• Standard value to which the isotopic ratio can be
  compared to.
• SMOW Standard Mean Ocean Water
• -isotopes of water
• PDB Peedee Belemite
• -isotopes of solid carbonates

15
Timing of glacial and interglacial cycles
16
Timing of Glacial and Interglacial Cycles

• Obtain core
• Pick foraminifera noting depth picked
• Measure ?18O of foraminifera
• Plot depth vs ?18O

17
Glacial/Interglacial Periods vs. Age Determined
by radiocarbon dating the collected foraminifera.
www.ldeo.columbia.edu/christa/
MAthesis/MAthesis.html
www.carleton.ca/.../climatechange/
glacial/glacial2.html
18
In Conclusion

• Isotopes are important in geological
  oceanography.
• Isotope fractionate during phase changes.
• Measured by mass spectrometer.
• Determine timing of past glacial/interglacial
• cycles.