Goldschmidt 2012 - Earth in Evolution, June 24-29, Montreal, Canada. Earthworm secreted calcium carbonate - a new palaeothermometer?

1. Geography and Environmental Science
Earthworm secreted
calcium carbonate: A
new palaeothermometer
Emma Versteegh, Stuart Black and Mark Hodson
02 August 2012 © University of Reading 2012 www.reading.ac.uk

2. ?
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3. Earthworm secreted
calcite (CaCO3) granules
Canti (2007)
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4. How are the granules produced?
• Calciferous glands;
• Milky fluid;
• → CaCO3 concretions;
• → granules.
Darwin (1881) / Canti (1998)
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5. Why do they produce them?
• “It is probable that they primarily
serve as organs of excretion, and
secondarily as an aid to digestion”
(Darwin, 1881);
• Egg formation?
• Triturate food in gizzard?
• Absorption of food products?
• Water regulation → evolutionary
adaptation to terrestrial habitat?
• Respiratory organ / eliminate
excess CO2?
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6. Aim
To construct a new terrestrial isotope–temperature
curve for application to earthworm secreted
calcium carbonate granules.
→ Potential for granules in dating and
palaeoenvironmental interpretation.
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7. Oxygen isotopes (δ18O values)
as palaeothermometer
Equilibrium (synthetic calcite):
1000 ln αc-w = 18.03 (103T-1) - 32.42
δ18Owater & temperature → δ18Ocalcite
Standards: VSMOW (H2O) & VPDB (CaCO3)
Goldschmidt 2012 Kim & O’Neil (1997) 7

8. Experiment
• Species: Lumbricus terrestris
• 2 soils
• 3 types of water (England,
Fiji, Norway)
• 3 temperatures (10, 16, 20
°C)
• 3 weeks acclimatisation
• 1 month
• 6 replicates
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9. Experiment
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10. Isotope analyses
Delta V advantage IRMS
& GasBench:
δ18Ocalcite values
Picarro L2120-I:
δ18Owater values
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11. Granule δ13C and δ18O values
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12. Influence of δ18Owater values
Increasing δ18Owater
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13. Influence of temperature
Decreasing T
???
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14. Predicted and measured δ18Ocalcite
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15. Palaeotemperature relationships
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16. Palaeotemperature equation
T(°C) = 19.22 - 3.77 · (δ18OcVPDB - δ18OwVSMOW) - 0.03 ·
(δ18OcVPDB - δ18OwVSMOW)2
R² = 0.95
=
T(°C) = 19.24 - 3.85 · (δ18OcVPDB - δ18OwVSMOW)
R² = 0.95
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17. Fractionation curves CaCO3-H2O
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18. Fractionation factor
1000 ln α = 18.47 (103 T-1) – 32.46
α = (1000 + δ18OcVSMOW) / (1000 + δ18OwVSMOW)
(Equilibrium: 1000 ln αc-w = 18.03 (103T-1) - 32.42)
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19. Conclusions
• Lumbricus terrestris produce calcite granules;
• These are enriched in 18O by 1.5 ‰ compared to
equilibrium;
• δ18Ocalcite values depend on temperature and
δ18Owater values following:
1000 ln α = 18.47 (103 T-1) – 32.46
• Well-preserved archaeological granules can be
used as palaeothermometers.
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20. Future work
• Influence of evaporation with depth?
• Changes of temperature with depth?
→ Analyse recent granules along soil profiles
Canti (2007)
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21. Future work
• Analyse more replicates
• δ13C values: soil organic matter, DOC, earthworm tissues,
milky fluid;
• The influence of [CO2] on granule production;
• δ18O internal structure heterogeneity: ion probe;
• Application to soil archaeological and geological
samples:
– Reconstruction of past temperatures;
– Dating of samples by U/Th;
– Comparison with pedogenic carbonate concretions and Bithynia
tentaculata opercula.
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22. Thank you!
Questions?
Acknowledgements:
• NERC
• Yan Gao
• Matt Canti (English Heritage)
God makes the earthworm
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23. Earthworm granules
vs. Arion slug granules
Canti (1998)
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24. Different species – different granules
Goldschmidt 2012 Canti & Piearce (2003)
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25. δ13C values & temperature
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26. Archaeological and geological samples
Canti (2007)
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27. Goldschmidt 2012 IAEA (2001)
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28. Goldschmidt 2012 28

29. EBSD crystallographic orientation
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30. EBSD composition
Silicon
Magnesium
Calcium
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