By Kristen Luebbert and Tiffany Roberts Geological Oceanography Dr. Gray 11/20/02

Outline of Today’s Presentation I. Introduction II. Relative Abundances III. Vibrational energy IV. Fractionation V. Rayleigh Distillation VI. Mass Spectrometry VII. Del Values VIII. Standards IX. Applications

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.

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

Relative Abundances 1 H: 99.99% 12 C: 98.9% 14 N: 99.6% 16 O: 99.8% 32 S: 95% 2 H: 0.01% 13 C: 1.1% 15 N: 0.4% 17 O: 0.04% 33 S: 0.8% 3 H: Rare 14 C: 10 ^-10 % 18 O: 0.2% 34 S: 4.2% 36 S: 0.2%

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

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

Evaporation

http ://blueox.uoregon.edu/~courses/dlivelyb/ph161/L14.html Rayleigh Distillation isotopic concentration of product differs from original material

Example: The isotopic concentration of the lightest isotope will be lowest at a mountain peak, than in the surrounding valley.

How are Stable Isotopes Measured? Mass Spectrometry Mass Spectrometry

So What is Mass Spectrometry? separates atoms based on massseparates atoms based on mass Ion beam shot; deflection of ionsIon beam shot; deflection of ions Heavier isotopes are deflected less; separates heavy and lightHeavier isotopes are deflected less; separates heavy and light Mass analysis obtained.Mass analysis obtained.

Del Value… relative difference measured between the isotope ratio and the relative standard Del value = [(R sample – R standard )/R standard ] x 1000 measured in ‰ (permil) R = isotope ratio with most abundant isotope in the denominator. Ex. High  18 O – more rare relative to abundant Less  18 O – more of most abundant *reminder – values compared to standard

Standards Standard value to which the isotopic ratio can be compared to. 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

Timing of glacial and interglacial cycles

Timing of Glacial and Interglacial Cycles Obtain core Obtain core Pick foraminifera noting depth picked Pick foraminifera noting depth picked Measure of foraminifera Measure  18 O of foraminifera Plot depth vs Plot depth vs  18 O

Glacial/Interglacial Periods vs. Age Determined by radiocarbon dating the collected foraminifera. MAthesis/MAthesis.html glacial/glacial2.html

In Conclusion… Isotopes are important in geological oceanography. Isotopes are important in geological oceanography. Isotope fractionate during phase changes. Isotope fractionate during phase changes. Measured by mass spectrometer. Measured by mass spectrometer. Determine timing of past glacial/interglacial Determine timing of past glacial/interglacialcycles.