23
Ca Isotopes Cheryl Zurbrick 1/29/2010

Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

  • View
    221

  • Download
    2

Embed Size (px)

Citation preview

Page 1: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Ca Isotopes

Cheryl Zurbrick1/29/2010

Page 2: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Background

Page 3: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Background

DePaolo Reviews in Mineral Geology (2004)

40Ca produced by β-decay of 40KMost Ca from primordial earth

Page 4: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

BackgroundMethodology

Pros Cons

TIMS (single collector)

•Reproducible precision between runs•Requires far less calibration

•Can only accurately measure 40Ca, 42Ca, 44Ca•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 44Ca/40Ca or 42Ca/40Ca ratio

Page 5: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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)

Page 6: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

BackgroundStandards

• 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

Page 7: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Background

Fractionation as a result of:– Igneous and metamorphic rocks, &

petrogenetic processes– Weathering cycle– Biology

Page 8: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

The Biological Observation

Mystery source???

δ44Ca decreases with increasing trophic levels

Page 9: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Soft vs. Mineralized Tissue

• Soft tissues heavier than bones by ~1.3‰ • Mineralization responsible for fractionation

Skulan & DePaoloPNAS (1999)

Page 10: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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 & DePaoloPNAS (1999)

Page 11: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Bone Growth

During bone growth Vl << Vb:

Most Cadiet into bones: •40Ca is taken up by bones•δ44Casoft tissue > δ44Cadiet

Skulan & DePaoloPNAS (1999)

Page 12: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Bone RemodelingBones are gaining and losing Ca; net [Ca] is zero• δ44Casoft tissue reflects δ44Cadiet

• bones differ from diet by Δb:

Skulan & DePaoloPNAS (1999)

Page 13: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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

Bone Loss

Skulan & DePaoloPNAS (1999)

Page 14: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Urine: a human biomarker of δ44Ca?

2 fractionations: bone/soft-tissue & blood-urine

Heuser & EisenhauerBone (2010)

Observed: δ44Ca urine > δ44Ca diet

Page 15: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Bone Growth vs. Loss Visibility

Young, healthy boy: bone growthElder woman, confirmed osteoporosis: bone loss

[Ca]urine twice as large for woman; δ44Ca urine, woman < δ44Ca urine, boy Heuser & Eisenhauer

Bone (2010)

Page 16: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Biomedical Application Pitfall

δ44Cadiet dependent (+ 0.2‰)

As bone loss increases, urine becomes lighter

Page 17: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

δ44Ca indicates plant productivity and soil fertility

Monitoring forested ecosystems in Hawaii

Page 18: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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…

Page 19: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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

Page 20: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

δ44Ca in Plant Tissues

Page 21: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Sr vs. Ca uptakeFrom ocean (0.7092)

Wiegand Geophysical Research Letters (2005)

From basalt (0.704)

Marine aerosols δ44Ca = 0.00 +0.2 ‰Volcanic rocks δ44Ca = -1.1 +0.3 ‰

Page 22: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

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

Page 23: Ca Isotopes Cheryl Zurbrick 1/29/2010. Background

Background painting Cows in field, courtesy of Peter Allsop