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Ca Isotopes

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

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Ca Isotopes

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  1. Ca Isotopes Cheryl Zurbrick 1/29/2010

  2. Background

  3. Background 40Ca produced by β-decay of 40K Most Ca from primordial earth DePaolo Reviews in Mineral Geology (2004)

  4. Background Methodology Commonly measure 44Ca/40Ca or 42Ca/40Ca ratio

  5. Background Double Spikes Separate natural fractionation (+0.1% per mass unit) vs. instrumental fractionation (+0.5% per mass unit) e.g. spike with 42Ca-48Ca Analyze 42/40, 44/40, and 48/40 Solve equations iteratively for: -spike/sample ratio -mass discrimination -sample 44/40 ratio DePaolo Reviews in Mineral Geology (2004)

  6. Background Standards • Established in 2008 • Before 2008, labs used varying in-house standards (seawater, terrestrial igneous rocks, and fluorite) • δ44/40Ca NIST SRM 915b and NIST SRM 1486

  7. Background Fractionation as a result of: • Igneous and metamorphic rocks, & petrogenetic processes • Weathering cycle • Biology

  8. The Biological Observation δ44Ca decreases with increasing trophic levels Mystery source???

  9. Soft vs. Mineralized Tissue • Soft tissues heavier than bones by ~1.3‰ • Mineralization responsible for fractionation Skulan & DePaolo PNAS (1999)

  10. Calcium Transport Model Vd = flux from diet Vex = flux excreted Vb = flux into bones Vl = flux leaving bones Δb = fractionation between bone and soft tissue Skulan & DePaolo PNAS (1999)

  11. Bone Growth • During bone growth Vl << Vb: • Most Cadiet into bones: • 40Ca is taken up by bones • δ44Casoft tissue > δ44Cadiet Skulan & DePaolo PNAS (1999)

  12. Bone Remodeling Bones are gaining and losing Ca; net [Ca] is zero • δ44Casoft tissue reflects δ44Cadiet • bones differ from diet by Δb: Skulan & DePaolo PNAS (1999)

  13. Bone Loss 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 • δ44Ca soft tissue < diet Skulan & DePaolo PNAS (1999)

  14. Urine: a human biomarker of δ44Ca? 2 fractionations: bone/soft-tissue & blood-urine Observed: δ44Ca urine > δ44Ca diet Heuser & Eisenhauer Bone (2010)

  15. Bone Growth vs. Loss Visibility Young, healthy boy: bone growth Elder woman, confirmed osteoporosis: bone loss [Ca]urine twice as large for woman; δ44Ca urine, woman < δ44Ca urine, boy Heuser & Eisenhauer Bone (2010)

  16. Biomedical Application Pitfall δ44Cadiet dependent (+ 0.2‰) As bone loss increases, urine becomes lighter

  17. Monitoring forested ecosystems in Hawaii δ44Ca indicates plant productivity and soil fertility

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

  19. Ca in Soil, Leaves • Sr and Ca deviate from each other with time • Ca is leached from soil whereas Sr isn’t • Sr/Ca lower in leaves than in soil

  20. δ44Ca in Plant Tissues

  21. Sr vs. Ca uptake From ocean (0.7092) From basalt (0.704) Marine aerosols δ44Ca = 0.00 +0.2 ‰ Volcanic rocks δ44Ca = -1.1 +0.3 ‰ Wiegand Geophysical Research Letters (2005)

  22. Conclusions • δ44Ca fractionates as a result of bone formation (mineralization) • δ44Ca fractionates as it is converted from blood to urine • δ44Ca can be developed as a medical tool* • δ44Ca can be used to better understand the biogeochemical cycle of terrestrial Ca which Sr alone cannot

  23. Background painting Cows in field, courtesy of Peter Allsop

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