Gsa Houston 2008

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Presentation given at the GSA annual meeting in Houston TX October 5-9 2008

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Gsa Houston 2008

  1. 1. Equilibrium precipitation of  18 O and  13 C in unionid freshwater mussels Emma Versteegh Hubert Vonhof, Simon Troelstra, Dick Kroon Paleoclimatology & Geomorphology
  2. 2. Freshwater mussels <ul><li>Common </li></ul><ul><li>Archaeological finds </li></ul><ul><li>Museum collections </li></ul><ul><li>Seasonal growth increments </li></ul><ul><li>Precipitate  18 O,  13 C in shell aragonite </li></ul><ul><li>Species: Unio crassus , U. pictorum , U. tumidus </li></ul>
  3. 3. Rivers Meuse and Rhine
  4. 4. Oxygen isotopes <ul><li>Meuse </li></ul><ul><li>Low δ 18 O in winter due to depleted precipitation </li></ul><ul><li>High δ 18 O in summer due to increased evaporation and enriched summer precipitation </li></ul><ul><li>Rhine </li></ul><ul><li>Additional factor: Alpine snow melt in summer -> negative excursions in summer </li></ul>
  5. 5. δ 18 O rivers Snow melt High discharge Flood Dry summer
  6. 6. Research questions <ul><li>Can freshwater mussel shell chemistry serve as a proxy for past water composition (and river conditions)? </li></ul><ul><li>-> Do freshwater mussels precipitate aragonite in equilibrium with ambient water? </li></ul><ul><ul><ul><li>δ 18 O </li></ul></ul></ul><ul><ul><ul><li>δ 13 C </li></ul></ul></ul><ul><li>-> What is the temperature of growth cessation? </li></ul>
  7. 7. Monitoring experiment: collecting and tagging Unionids
  8. 8. Monitoring experiment: cages in fish ladders
  9. 9. Monitoring locations
  10. 10. Methods <ul><li>Water sampling </li></ul><ul><li>Microsampling </li></ul><ul><ul><li>Merchantek Micromill </li></ul></ul><ul><li>Stable isotopes </li></ul><ul><ul><li>Finnigan Delta+ with Gasbench II </li></ul></ul>
  11. 11. Predicted shell δ 18 O <ul><li>Water δ 18 O & T  shell δ 18 O </li></ul>Grossman & Ku (1986); Dettman et al. (1999)
  12. 12. Predicted shell δ 18 O Meuse Lek (Rhine distributary)
  13. 13. Typical shell δ 18 O record
  14. 14. Monitoring: Shell records (Lek)
  15. 15. δ 13 C of HCO 3 -
  16. 16. Predicted and measured shell δ 18 O Onset of growth: 9.5 °C Growth stop: 14.6 °C
  17. 17. δ 13 C of HCO 3 - and shells
  18. 18. δ 13 C of HCO 3 - and shells
  19. 19. Conclusions <ul><li>Unionid freshwater mussels precipitate aragonite in δ 18 O and δ 13 C equilibrium with ambient water. </li></ul><ul><li>A good model for intra-seasonal growth is needed to gain a more detailed picture of δ 13 C. </li></ul><ul><li>Seasonal growth starts at 9.5 °C and ceases at 14.6 °C. </li></ul>
  20. 20. Thank you!

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