Seminar Silent Witnesses

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Seminar given for the department in Reading.

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Seminar Silent Witnesses

  1. 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. 2. Rhine and Meuse
  3. 3. Floods
  4. 4. Droughts
  5. 5. Holocene
  6. 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. 7. Oxygen isotopes
  8. 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. 9. δ18O values of the rivers Meltwater High discharge Dry summer
  10. 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. 11. Project plan • Monitoring experiment • 20th century shells (museum collections) • Late Holocene shells (archaeological finds) 12
  12. 12. Monitoring experiment: collection and tagging of shells
  13. 13. Monitoring experiment: cages in fish ladders
  14. 14. Methods • Micro sampling – Merchantek Micromill • Stable isotopes – Thermo Finnigan MAT 252 – Thermo Finnigan Delta+ • Water samples
  15. 15. Results: average 18O per shell
  16. 16. Seasonal patterns Slowdown of growth
  17. 17. Water δ18O & temperature  shell δ18O 1000 ln  = 2.559 (106 T-2) + 0.175 Grossman & Ku (1986); Dettman et al. (1999)
  18. 18. Predicted shell δ18O values Lek
  19. 19. Shell 18O values
  20. 20. Freshwater mussels record ambient 18O values in their shell.
  21. 21. Reconstructed water 18O values
  22. 22. Reconstruction of discharge
  23. 23. Meuse Rhine
  24. 24. Back in time
  25. 25. 33
  26. 26. North Atlantic Oscillation
  27. 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. 28. So what am I doing here? 42
  29. 29. Some other silent witnesses… 43
  30. 30. …who also produce CaCO3 44
  31. 31. Thank you! Questions?

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