by kristen luebbert and tiffany roberts geological oceanography dr. gray 11/20/02

By Kristen Luebbert and Tiffany Roberts

Geological Oceanography

Dr. Gray 11/20/02

Outline of Today’s Presentation

I. IntroductionII. Relative AbundancesIII. Vibrational energyIV. FractionationV. Rayleigh DistillationVI. Mass SpectrometryVII. Del ValuesVIII. StandardsIX. Applications

Why are stable isotopes Why are stable isotopes important?important?

Ratios used to trace many processes in Ratios used to trace many processes in various fields of sciencevarious fields of science

Geological OceanographyGeological Oceanography

Reconstruct past ocean temps, Reconstruct past ocean temps, ocean circulation, ice volumes, etc.ocean circulation, ice volumes, etc.

• Isotopes - atoms of elements which Isotopes - atoms of elements which contain a different number of neutrons, contain a different number of neutrons, but chemically act the same. but chemically act the same.

• Stable isotopes - isotope that does not Stable isotopes - isotope that does not decay radioactively.decay radioactively.

http://van.hep.uiuc.edu/van/qa/section/everything_else/atoms/920424670.htmhttp://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/

nucnot.html#c2

Relative AbundancesRelative Abundances

11H: H: 99.99%99.99%

1212C: C: 98.9%98.9%

1414N: N: 99.6%99.6%

1616O: O: 99.8%99.8%

3232S: S: 95%95%

22H: H: 0.01%0.01%

1313C: C: 1.1%1.1%

1515N: N: 0.4%0.4%

1717O: O: 0.04%0.04%

3333S: S: 0.8%0.8%

33H: RareH: Rare 1414C: C: 1010^-10^-10 % %

1818O: O: 0.2%0.2%

3434S: S: 4.2%4.2%3636S: S: 0.2%0.2%

Heat increases vibrational energyHeat increases vibrational energy

-A greater amount of heat is -A greater amount of heat is need to need to evaporate heavier isotopesevaporate heavier isotopes

FractionationFractionation

• Fractionation – process by which Fractionation – process by which certain isotopes are selected certain isotopes are selected preferentially over otherspreferentially over others

•Chemical ReactionsChemical Reactions

•Phase ChangesPhase Changes

•Molecular DiffusionMolecular Diffusion

Ex. Freezing or boiling waterEx. Freezing or boiling water

Evaporation 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 How are StableStable Isotopes Isotopes Measured?Measured?

• Mass SpectrometryMass Spectrometry

http://minyos.its.rmit.edu.au/~rcmfa/mstheory.html

So What is Mass Spectrometry?So What is Mass Spectrometry?•separates atoms based separates atoms based on masson mass

•Ion beam shot; deflection Ion beam shot; deflection of ionsof ions

•Heavier isotopes are Heavier isotopes are deflected less; separates deflected less; separates heavy and lightheavy and light

•Mass analysis obtained.Mass analysis obtained.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/krypton.html#c1

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

StandardsStandards

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

SMOW – Standard Mean Ocean WaterSMOW – Standard Mean Ocean Water-isotopes of water-isotopes of water

PDB – Peedee BelemitePDB – Peedee Belemite-isotopes of solid carbonates-isotopes of solid carbonates

Timing of glacial and Timing of glacial and interglacial cyclesinterglacial cycles

Timing of Glacial and Interglacial Timing of Glacial and Interglacial CyclesCycles

• Obtain coreObtain core

• Pick foraminifera noting depth pickedPick foraminifera noting depth picked

• Measure Measure 18O of foraminifera of foraminifera

• Plot depth vs Plot depth vs 18O

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

In Conclusion…In Conclusion…

• Isotopes are important in geological Isotopes are important in geological oceanography.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/interglacial cycles.cycles.