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

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Transcript of Ca Isotopes Cheryl Zurbrick 1/29/2010. Background.

  • Slide 1
  • Ca Isotopes Cheryl Zurbrick 1/29/2010
  • Slide 2
  • Background
  • Slide 3
  • DePaolo Reviews in Mineral Geology (2004) 40 Ca produced by -decay of 40 K Most Ca from primordial earth
  • Slide 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
  • Slide 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)
  • Slide 6
  • Background Standards Established in 2008 Before 2008, labs used varying in-house standards (seawater, terrestrial igneous rocks, and fluorite) 44/40 Ca NIST SRM 915b and NIST SRM 1486
  • Slide 7
  • Background Fractionation as a result of: Igneous and metamorphic rocks, & petrogenetic processes Weathering cycle Biology
  • Slide 8
  • The Biological Observation Mystery source??? 44 Ca decreases with increasing trophic levels
  • Slide 9
  • Soft vs. Mineralized Tissue Soft tissues heavier than bones by ~1.3 Mineralization responsible for fractionation Skulan & DePaolo PNAS (1999)
  • Slide 10
  • Calcium Transport Model V d = flux from diet V ex = flux excreted V b = flux into bones V l = flux leaving bones b = fractionation between bone and soft tissue Skulan & DePaolo PNAS (1999)
  • Slide 11
  • Bone Growth During bone growth V l 44 Ca diet Skulan & DePaolo PNAS (1999)
  • Slide 12
  • Bone Remodeling Bones are gaining and losing Ca; net [Ca] is zero 44 Ca soft tissue reflects 44 Ca diet bones differ from diet by b : Skulan & DePaolo PNAS (1999)
  • Slide 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 44 Ca soft tissue < diet Bone Loss Skulan & DePaolo PNAS (1999)
  • Slide 14
  • Urine: a human biomarker of 44 Ca? 2 fractionations: bone/soft-tissue & blood-urine Heuser & Eisenhauer Bone (2010) Observed: 44 Ca urine > 44 Ca diet
  • Slide 15
  • Bone Growth vs. Loss Visibility Young, healthy boy: bone growth Elder woman, confirmed osteoporosis: bone loss [Ca] urine twice as large for woman; 44 Ca urine, woman < 44 Ca urine, boy Heuser & Eisenhauer Bone (2010)
  • Slide 16
  • Biomedical Application Pitfall 44 Ca diet dependent (+ 0.2) As bone loss increases, urine becomes lighter
  • Slide 17
  • 44 Ca indicates plant productivity and soil fertility Monitoring forested ecosystems in Hawaii
  • Slide 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
  • Slide 19
  • Ca in Soil, Leaves Sr and Ca deviate from each other with time Ca is leached from soil whereas Sr isnt Sr/Ca lower in leaves than in soil
  • Slide 20
  • 44 Ca in Plant Tissues
  • Slide 21
  • Sr vs. Ca uptake From ocean (0.7092) Wiegand Geophysical Research Letters (2005) From basalt (0.704) Marine aerosols 44 Ca = 0.00 +0.2 Volcanic rocks 44 Ca = -1.1 +0.3
  • Slide 22
  • Conclusions 44 Ca fractionates as a result of bone formation (mineralization) 44 Ca fractionates as it is converted from blood to urine 44 Ca can be developed as a medical tool* 44 Ca can be used to better understand the biogeochemical cycle of terrestrial Ca which Sr alone cannot
  • Slide 23
  • Background painting Cows in field, courtesy of Peter Allsop