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Seminar Silent Witnesses

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Seminar given for the department in Reading.

Seminar given for the department in Reading.

Published in: Education
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  • 1. Geography and Environmental Science Silent witnesses Freshwater bivalves as archives of environmental variability in the Rhine-Meuse delta Emma A. A. Versteegh H. B. Vonhof, S. R. Troelstra, D. Kroon
  • 2. Rhine and Meuse
  • 3. Floods
  • 4. Droughts
  • 5. Holocene
  • 6. Freshwater mussels Species: Unio crassus, U. pictorum & U. tumidus Common Archaeological finds Museum collections Record water chemistry in growth bands in their shells
  • 7. Oxygen isotopes
  • 8. Oxygen isotopes Meuse Low δ18O values in winter through winter precipitation with little 18O High δ18O values during summer through evaporation and summer precipitation enriched in 18O Rhine Additional factor: Melt water from the Alps during summer → low δ18O values 9
  • 9. δ18O values of the rivers Meltwater High discharge Dry summer
  • 10. Research questions • Do these unionids record δ18O values of river water in their shells? • Can we use this as a proxy for past river dynamics? – Floods? – Droughts?
  • 11. Project plan • Monitoring experiment • 20th century shells (museum collections) • Late Holocene shells (archaeological finds) 12
  • 12. Monitoring experiment: collection and tagging of shells
  • 13. Monitoring experiment: cages in fish ladders
  • 14. Methods • Micro sampling – Merchantek Micromill • Stable isotopes – Thermo Finnigan MAT 252 – Thermo Finnigan Delta+ • Water samples
  • 15. Results: average 18O per shell
  • 16. Seasonal patterns Slowdown of growth
  • 17. Water δ18O & temperature  shell δ18O 1000 ln  = 2.559 (106 T-2) + 0.175 Grossman & Ku (1986); Dettman et al. (1999)
  • 18. Predicted shell δ18O values Lek
  • 19. Shell 18O values
  • 20. Freshwater mussels record ambient 18O values in their shell.
  • 21. Reconstructed water 18O values
  • 22. Reconstruction of discharge
  • 23. Meuse Rhine
  • 24. Back in time
  • 25. 33
  • 26. North Atlantic Oscillation
  • 27. Conclusions Freshwater mussels record ambient water 18O values in their shell. Shell 18O values can be used to determine from which river a shell originates. It is not possible to quantitatively reconstruct river discharge. Extreme droughts and possibly melt water peaks can be detected. NAO-variability during the Middle Ages??
  • 28. So what am I doing here? 42
  • 29. Some other silent witnesses… 43
  • 30. …who also produce CaCO3 44
  • 31. Thank you! Questions?

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