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Egu2008

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Presentation given at the EGU conference in Vienna April 13-18 2008

Presentation given at the EGU conference in Vienna April 13-18 2008

Published in: Education
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Transcript

  • 1. Stable oxygen isotopes in freshwater mussels (Unionidae) as a proxy for late Holocene floods and droughts of Rhine and Meuse Emma Versteegh Hubert Vonhof Simon Troelstra Dick Kroon
  • 2. Freshwater mussels
    • Common
    • Archaeological finds
    • Museum collections
    • Seasonal growth increments
    • Precipitate  18 O in shell carbonate; shell  18 O depends on:
      • T
      • Water  18 O
    • Species: Unio crassus , U. pictorum , U. tumidus
  • 3. Stable oxygen isotopes
  • 4. Rivers Rhine and Meuse
  • 5. δ 18 O rivers Glacier melting High discharge Flood Dry summer
  • 6. Aim
    • Address the possibilities for shell δ 18 O as a proxy for river discharge and flood and drought frequencies in Meuse and Rhine:
    • Do growth lines in the shells correspond to yearly winter growth cessations?
    • The temperature lower limits below which growth cessation occurs.
    • Do the shells of two species precipitate aragonite in isotopic equilibrium with the ambient water, i. e. predicted values correspond to measured values?
    • Can past river floods and droughts be reconstructed from shell δ 18 O?
  • 7. Methods
    • Microsampling
      • Merchantek Micromill
    • Stable isotopes
      • Finnigan MAT 252
      • Finnigan Delta
    • Water sampling
  • 8. Setup of the project
    • Monitoring experiment
    • 20 th century shells
    • Late Holocene shells
  • 9. Monitoring experiment
    • Cages with living mussels in fish ladders
    • - Hagestein (Lek)
    • - Lith (Meuse)
  • 10. 20 th century shells
    • Meuse:
    • Grevenbicht 1998
    • Lith 2005
    • Kerkdriel 2005
    • Rhine distributaries
    • Tuil 1998 (Waal)
    • Herwijnen 2003 (Waal)
    • Hurwenen 2003 (Waal)
    • Hagestein 2005 (Lek)
  • 11. Late Holocene shells
  • 12. Palaeogeography
  • 13. Results Average δ 18 O per shell
  • 14. Seasonal patterns Slowing down of growth
  • 15. 20 th century shells
  • 16. Predicted shell δ 18 O
    • Water δ 18 O & T  shell δ 18 O
    Grossman & Ku (1986); Dettman et al. (1999)
  • 17. Measured δ 18 O vs. Predicted δ 18 O
  • 18. Measured δ 18 O vs. Predicted δ 18 O: 20 th century shells Juvenile stage
  • 19. Measured δ 18 O vs. Predicted δ 18 O: 20 th century shells Glacier melting Dry summer ???
  • 20. Measured δ 18 O vs. Predicted δ 18 O: monitoring
  • 21. Late Holocene shells
  • 22. Conclusions
    • The shells do not grow in winter
      • Winter floods are not recorded
    • Growth lines usually correspond to winter growth stops, but not always!
    •  18 O shell corresponds well with predicted values
    •   18 O shell is useful proxy
    • 300 - 4500 year old shells show seasonal stable isotope patterns similar to modern shells
      •  no diagenesis
  • 23.
    • Thank you!

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