JOURNEY TO MIDDLE EARTH:

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JOURNEY TO MIDDLE EARTH OPPORTUNITIES AND
CHALLENGES AT THE CENTER OF THE PERIODIC TABLE
Thomas Bullen Water Resources Discipline U.S.
Geological Survey Menlo Park, CA
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Cover of book released at 2-day MSA short course
on non-traditional stable isotopes held May
15-16, 2004 in Montreal, Canada
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OPPORTUNITIES GALORE

• Until only a few years ago, I would never have
  imagined that a volume on the stable isotope
  geochemistry of elements such as Mg, Fe or Cu
  would be written. I am about ready to eat those
  words (Jim ONeil)

• It appears that Mg in waters is related to
  mantle and crustal reservoirs by kinetic
  fractionation while Mg in carbonates is related
  to the waters by equilibrium processes (Ed Young)

• Very little is known about the isotopic
  composition of Cu and Zn in biological material
  (Francis Albarede)

• There is a major gap in our ability to measure
  stable isotope fractionations and our
  understanding of the processes that cause
  fractionations to occur (Ed Schauble)

• Fractionation factors for Ca isotopes, their
  causes, magnitude, temperature dependence and
  ubiquity in metabolic processes are still poorly
  understood (Don DePaolo)

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WHY WE ARE HERE
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THE MAJOR PLAYERS AT A GLANCE

• Li isotopes fractionated during weathering
  highly fractionated anthropogenic pool out in
  environment

• Mg fractionated by equilibrium processes during
  carbonate formation central component of
  chlorophyll molecule

• Ca fractionated by plants and bone
  fractionation in carbonates may depend on
  temperature, growth rate, nutrient supply,

• Cr fractionated during reduction of toxic Cr(VI)
  to Cr(III)

• Fe significant equilibrium fractionation between
  Fe(II) and Fe(III) abiotic and biotic
  fractionations indistinguishable

• Cu and Zn fractionations observed in ore
  deposits and sediments important enzymatic
  functions

• Se fractionated during reduction of toxic Se(VI)
  to Se(0)

• Mo fractionated during sorption of Mo(VI)
  important paleo-redox applications as indicator
  of euxinic conditions

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SOME OTHER DENIZENS OF MIDDLE EARTH
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NEW UNDERSTANDING AT THE PROCESS-LEVEL
Sorption on d-MnO2
Barling and Anbar, 2004
Ellis et al., 2002
Cr reduction kinetic fractionation e
(CrO42- - Cr(III)) 1.0034
Mo sorption equilibrium fractionation a
(MoO42-aq - xMoxsorb ) 1.0018
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DISTINGUIISHING KINETIC AND EQUILIBRIUM PROCESSES
What about Si??
Or Ca??
Young and Galy, 2004
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ANALYTICAL CHALLENGES
With the Neptune, it is possible to obtain a lot
of very precise stable isotope data very quickly

• But is the data accurate?

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JUST ANOTHER DAY FOR THE NEPTUNE

• Based on repeated TIMS double spike analysis
• d56Fe of ICP-Fe solution -0.19 relative to
  BIR-1 basalt

• Column-processed ICP-Fe and BIR-1, measured using
  standard-sample-standard approach
• d56Fe of ICP-Fe solution 0.24 relative to
  BIR-1 basalt

• Column-processed ICP-Fe and BIR-1 with Cu
  internal standard, measured using
  standard-sample-standard approach
• d56Fe of ICP-Fe solution -0.63 relative to
  BIR-1 basalt

• Column-processed ICP-Fe and BIR-1, with Fe double
  spike
• d56Fe of ICP-Fe solution -0.19 relative to
  BIR-1 basalt

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SAMPLE-RELATED SOURCES OF BIAS
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TOMS TOP 10 CHALLENGES
1. Challenge everything you read
2. More women in the field!
3. Use appropriate internal standardization
4. Duplicates Duplicates Duplicates
5. Design experiments that answer the question
6. Consider your element in major- and trace
element settings
7. Beware of standard-sample-standard
bracketing
8. Keep the chemistry clean and sample
preparation constant
9. Dont forget TIMS
10. Challenge everything you read