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Understanding Oxygen and Hydrogen Isotopes in Animal Systems

Explore the correlations between isotopic values and local precipitation, as well as the impact of aridity on water isotopic values in animals. Learn about the major oxygen fluxes in animals, bioapatite analysis, and models for oxygen in body water. Discover the geographic patterns of isotopes in human hair and the role of hydrogen isotopes in animal systems.

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Understanding Oxygen and Hydrogen Isotopes in Animal Systems

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  1. Systematics of O and H isotopes in Animals Presentation modified by Nadine Quintana Krupinski

  2. Background • 18O and D values correlate strongly with local precipitation isotopic value • Precip isotopic value varies w/ latitude and elevation • Local water isotopic value also affected by aridity (evaporation effect)

  3. Oxygen in animals • 18O measured in tissues (body water, hair) and tooth enamel (bone not generally used) • Hair is isotopically offset from body water 18O (hair is more positive) • Food effect • Enamel and bone have a constant offset from body water 18O

  4. Major O Fluxes IN • Drinking and food water (not fractionated during uptake) • Atmosphere O2 • Food solids OUT • Respired CO2 (fractionated) • Water in urine and feces • Water lost in exhalation, sweat, evaporation (fractionated)

  5. 18O in bioapatite • Measured from PO4 and CO3 in bioapatite and CO3 in carbonate (bone) • Apatite: Ca5(PO4)3(OH, F, Cl) • CO3 can substitute for PO4 or for OH (also in other places) • O in PO4 and CO3 rapidly equilibrates with body water O • Either PO4 or CO3 is selected for analysis, depending on the diagenetic history of the bioapatite

  6. Apatite 18O “vital” effects • 18OApatite depends on the temperature and fluid composition (in 18O) at which the biomineral precipitates. • For homeotherms (mammals, birds), assume constant body temp. and derive info about the animal’s environment. • For heterotherms, as temp. , bioapatite 18O  and carbonate 18O values . • In mammal apatite, constant offset btw. 18O of body water and PO4 (~18‰), btw. PO4 and CO3 (~8‰)

  7. Box model for animals

  8. Mass balance model 0.25 * [18OBW + 38.65] + 0.4 * [18OBW + 0] + 0.25 * [18OBW - 8.5] + 0.1 * [18OBW - 18] = 0.25 * 15 + 0.45 * [18OLW + 26.2 * (1 - h)] + 0.3 * 18OLW ) BW = body water LW = local water output input

  9. Models for O in body water • Portion of O from food, air (Ehleringer): • Isotopic ratio of body water (same eqn. for O&H, Podlesak): r = molar quantity of the input or output, R = ratio of the heavy isotope to the light isotope A = fractionation between body water and the output Alternatively, in  notation (Ehleringer)

  10. 18O in hair • Hair (keratin) 18O is related to gut water 18O (Ehleringer): OR, in R notation (same eqn. for O&H; Podlesak): Rfw = isotopic ratio of follicle water Rbw = isotopic ratio of body water Rfd = isotopic ratio of food

  11. 18O in tooth enamel • Tooth isotopic composition is derived from body water composition • Equilibrium fractionation yields a constant, temperature-dependent offset from body water • Podlesak use a model for continually growing teeth (e.g. rats) - large time-averaging of tooth isotopic signal • General tooth model using known input and output 18O values (Kohn & Cerling):

  12. Rats with a change in drinking water 18O Enamel Body water Hair

  13. Geographic patterns in human hair 18O • Tap water 18O varies • Diet constant: ‘‘continental supermarket’’ diet w/ 18O 26‰ Above: Geographic Information System-generated maps of the predicted average 18O of human scalp hair across the continental United States. Ehleringer et al. 2008

  14. Hydrogen in animals • D measured in tissues (hair, feathers, chitin), body water, breath, tooth enamel or bone collagen • Hair is isotopically offset from body water D • Food effect “removed” in these studies

  15. H sources and sinks • IN • Drinking water • Food water • Food (important! But may be controlled) • Small portion (10-15%) of H in synthesized hair exchanges w/ water • OUT • Urine and feces • Water lost in exhalation, sweat, evaporation (fractionated)

  16. D in tissues and body water • Hair follicle D is a mix of blood water and food water D: • Fraction of H atoms from food: • Body water D: Equations from Ehleringer et al. 2008

  17. Rats with a change in drinking water D Body water Hair

  18. Geographic patterns in human hair D • Tap water D varies • Diet constant: ‘‘continental supermarket’’ diet w/ Dd 115‰ Above: Geographic Information System-generated maps of the predicted average D of human scalp hair across the continental United States. Ehleringer et al. 2008

  19. Extra slides

  20. Changes in hair 18O, D with “migration” Ehleringer et al. 2008

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