Ca Isotopes

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Ca Isotopes. Cheryl Zurbrick 1/29/2010. Background. Background. 40 Ca produced by β -decay of 40 K Most Ca from primordial earth. DePaolo Reviews in Mineral Geology (2004). Background. Methodology. Commonly measure 44 Ca/ 40 Ca or 42 Ca/ 40 Ca ratio. Background. Double Spikes - PowerPoint PPT Presentation

Transcript of Ca Isotopes

  • Ca IsotopesCheryl Zurbrick1/29/2010

  • Background

  • BackgroundDePaolo Reviews in Mineral Geology (2004)40Ca produced by -decay of 40KMost Ca from primordial earth

  • BackgroundMethodologyCommonly measure 44Ca/40Ca or 42Ca/40Ca ratio

    ProsConsTIMS (single collector)Reproducible precision between runsRequires far less calibrationCan only accurately measure 40Ca, 42Ca, 44CaLong analysis times (hours per sample)MC-ICP-MSBetter precision of individual measurementsLarger instrument fractionationUnaccountable drift; worsens reproducibility (requires bracketing)

  • BackgroundDouble Spikes

    Separate natural fractionation (+0.1% per mass unit) vs. instrumental fractionation (+0.5% per mass unit)

    e.g. spike with 42Ca-48CaAnalyze 42/40, 44/40, and 48/40Solve equations iteratively for:-spike/sample ratio-mass discrimination-sample 44/40 ratio

    DePaolo Reviews in Mineral Geology (2004)

  • BackgroundStandards

    Established in 2008Before 2008, labs used varying in-house standards (seawater, terrestrial igneous rocks, and fluorite)44/40Ca NIST SRM 915b and NIST SRM 1486

  • BackgroundFractionation as a result of:Igneous and metamorphic rocks, & petrogenetic processesWeathering cycleBiology

  • The Biological Observation Mystery source???44Ca decreases with increasing trophic levels

  • Soft vs. Mineralized TissueSoft tissues heavier than bones by ~1.3 Mineralization responsible for fractionationSkulan & DePaoloPNAS (1999)

  • Calcium Transport ModelVd = flux from dietVex = flux excretedVb = flux into bonesVl = flux leaving bonesb = fractionation between bone and soft tissueSkulan & DePaoloPNAS (1999)

  • Bone GrowthDuring bone growth Vl 44Cadiet

    Skulan & DePaoloPNAS (1999)

  • Bone RemodelingBones are gaining and losing Ca; net [Ca] is zero44Casoft tissue reflects 44Cadiet bones differ from diet by b:Skulan & DePaoloPNAS (1999)

  • During bone loss Vl/Vd is important:

    CUI = isotopic Ca use index = 0 during bone remodeling > 0 during bone growth < 0 during bone loss

    40Ca is being lost from the bones 44Ca soft tissue < diet

    Bone LossSkulan & DePaoloPNAS (1999)

  • Urine: a human biomarker of 44Ca?2 fractionations: bone/soft-tissue & blood-urineHeuser & EisenhauerBone (2010)Observed: 44Ca urine > 44Ca diet

  • Bone Growth vs. Loss VisibilityYoung, healthy boy: bone growthElder woman, confirmed osteoporosis: bone loss[Ca]urine twice as large for woman; 44Ca urine, woman < 44Ca urine, boy Heuser & EisenhauerBone (2010)

  • Biomedical Application Pitfall44Cadiet dependent (+ 0.2)As bone loss increases, urine becomes lighter

  • 44Ca indicates plant productivity and soil fertilityMonitoring forested ecosystems in Hawaii

  • Sr and Ca in soil, plantsWiegand Geophysical Research Letters (2005)Leaves & soil have isotopically similar Sr values; over time the source of plant available Sr is more marine aerosols than lavaCa leaves & soil also see a source-dependent shift with time, but

  • Ca in Soil, LeavesSr and Ca deviate from each other with timeCa is leached from soil whereas Sr isntSr/Ca lower in leaves than in soil

  • 44Ca in Plant Tissues

  • Sr vs. Ca uptakeFrom ocean (0.7092)Wiegand Geophysical Research Letters (2005)From basalt (0.704)Marine aerosols 44Ca = 0.00 +0.2 Volcanic rocks 44Ca = -1.1 +0.3

  • Conclusions44Ca fractionates as a result of bone formation (mineralization)44Ca fractionates as it is converted from blood to urine44Ca can be developed as a medical tool*44Ca can be used to better understand the biogeochemical cycle of terrestrial Ca which Sr alone cannot

  • Background painting Cows in field, courtesy of Peter Allsop