1. Ca Isotopes Cheryl Zurbrick 1/29/2010

2. Background

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

4. Background Methodology ProsCons TIMS (single collector) Reproducible precision between runs Requires far less calibration Can only accurately measure 40 Ca, 42 Ca, 44 Ca Long analysis times (hours per sample) MC-ICP-MS Better precision of individual measurements Larger instrument fractionation Unaccountable drift; worsens reproducibility (requires bracketing) Commonly measure 44 Ca/ 40 Ca or 42 Ca/ 40 Ca 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 42 Ca- 48 Ca 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) δ 44/40 Ca 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 Mystery source??? δ 44 Ca decreases with increasing trophic levels

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 V d = flux from diet V ex = flux excreted V b = flux into bones V l = flux leaving bones Δ b = fractionation between bone and soft tissue Skulan & DePaolo PNAS (1999)

11. Bone Growth During bone growth V l << V b : Most Ca diet into bones: 40 Ca is taken up by bones δ 44 Ca soft tissue > δ 44 Ca diet Skulan & DePaolo PNAS (1999)

12. Bone Remodeling Bones are gaining and losing Ca; net [Ca] is zero δ 44 Ca soft tissue reflects δ 44 Ca diet bones differ from diet by Δ b : Skulan & DePaolo PNAS (1999)

13. During bone loss V l /V d is important: CUI = isotopic Ca use index = 0 during bone remodeling > 0 during bone growth < 0 during bone loss 40 Ca is being lost from the bones δ 44 Ca soft tissue < diet Bone Loss Skulan & DePaolo PNAS (1999)

14. Urine: a human biomarker of δ 44 Ca? 2 fractionations: bone/soft-tissue & blood-urine Heuser & Eisenhauer Bone (2010) Observed: δ 44 Ca urine > δ 44 Ca diet

15. Bone Growth vs. Loss Visibility Young, healthy boy: bone growth Elder woman, confirmed osteoporosis: bone loss [Ca] urine twice as large for woman; δ 44 Ca urine, woman < δ 44 Ca urine, boy Heuser & Eisenhauer Bone (2010)

16. Biomedical Application Pitfall δ 44 Ca diet dependent (+ 0.2‰) As bone loss increases, urine becomes lighter

17. δ 44 Ca indicates plant productivity and soil fertility Monitoring forested ecosystems in Hawaii

18. Sr and Ca in soil, plants Wiegand Geophysical Research Letters (2005) 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…

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. δ 44 Ca in Plant Tissues

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

22. Conclusions δ 44 Ca fractionates as a result of bone formation (mineralization) δ 44 Ca fractionates as it is converted from blood to urine δ 44 Ca can be developed as a medical tool* δ 44 Ca 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