Australia

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Presentation about my PhD research, given at the Australian National University in May 2007.

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Australia

  1. 1. The chemistry of freshwater mussels as a proxy for late Holocene river conditions Emma Versteegh Simon Troelstra Hubert Vonhof
  2. 2. VU University Amsterdam: Department of Paleoclimatology & Geomorphology <ul><li>Marine </li></ul><ul><ul><li>Foraminifera (e.g. single specimens, seasonality) </li></ul></ul><ul><ul><li>Coccoliths (single species) </li></ul></ul><ul><ul><li>Molluscs (seasonality, e.g. ENSO variability) </li></ul></ul><ul><ul><li>Corals </li></ul></ul><ul><ul><li>Sediments (end-member modelling) </li></ul></ul><ul><li>Terrestrial </li></ul><ul><ul><li>Speleothems </li></ul></ul><ul><ul><li>Molluscs (seasonality, e.g. NAO variability) </li></ul></ul><ul><ul><li>Palynology </li></ul></ul><ul><ul><li>Sediments (end-member modelling) </li></ul></ul>
  3. 3. Outline of this talk <ul><li>Aim </li></ul><ul><li>Background </li></ul><ul><li>Setup of the project </li></ul><ul><li>Methods </li></ul><ul><li>Results </li></ul><ul><li>Conclusions </li></ul><ul><li>Future work </li></ul>
  4. 4. Aim <ul><li>Understanding shell chemistry </li></ul><ul><li>Developing a new proxy for river discharge, flood and drought frequencies </li></ul><ul><li>Reconstructing late Holocene (5000 BP – 500 BP) river conditions </li></ul>
  5. 5. 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 in shell carbonate;  18 O shell depends on: </li></ul><ul><ul><li>T </li></ul></ul><ul><ul><li> 18 O water </li></ul></ul><ul><li>Record trace element concentrations in shell carbonate </li></ul><ul><li>Species: Unio crassus , U. pictorum , U. tumidus </li></ul>
  6. 6. Stable oxygen isotopes
  7. 7. Rivers Rhine and Meuse
  8. 8.  18 O Rhine and Meuse
  9. 9. Setup of the project <ul><li>Monitoring experiment </li></ul><ul><li>20 th century shells </li></ul><ul><li>Late Holocene shells </li></ul>
  10. 10. Methods <ul><li>Microsampling </li></ul><ul><ul><li>Merchantek Micromill </li></ul></ul><ul><li>Stable isotopes </li></ul><ul><ul><li>Finnigan MAT 252 </li></ul></ul><ul><ul><li>Finnigan Delta </li></ul></ul><ul><li>Trace elements </li></ul><ul><ul><li>ICP-OES </li></ul></ul><ul><ul><li>LA-ICPMS </li></ul></ul>
  11. 11. Monitoring experiment <ul><li>Cages with living mussels in fish ladders </li></ul><ul><li>- Hagestein (Lek) </li></ul><ul><li>- Lith (Meuse) </li></ul>
  12. 12. 20 th century shells <ul><li>Rivers: </li></ul><ul><li>Meuse </li></ul><ul><li>Rhine / Waal / Lek </li></ul><ul><li>Collection dates: </li></ul><ul><li>1918 </li></ul><ul><li>1977 - 1978 </li></ul><ul><li>1998 - 2005 </li></ul>
  13. 14. Late Holocene shells
  14. 15. Research questions <ul><li>Do growth lines in the shell correspond to yearly winter growth stops? </li></ul><ul><li>Does  18 O shell correspond to predicted  18 O shell ? </li></ul><ul><li>Does the mussel incorporate trace elements in equilibrium with ambient water? </li></ul>
  15. 16. Results: 20 th century shells
  16. 20. Predicted  18 O
  17. 21. Predicted  18 O shell vs.  18 O shell  18 O shell corresponds well with predicted values   18 O shell is useful proxy
  18. 22. <ul><li>Growth stop occurs at 11.9°C </li></ul>Predicted  18 O shell vs.  18 O shell
  19. 23. Calculated  18 O water vs. monthly mean  18 O water
  20. 24. Trace elements
  21. 25. Trace elements Winter Winter Winter Winter
  22. 26. Results: Late-Holocene shells
  23. 27. Conclusions <ul><li>In winter no carbonate is precipitated </li></ul><ul><li>Growth lines usually correspond to winter growth stops, but not always! </li></ul><ul><li> 18 O shell corresponds well with predicted values </li></ul><ul><li>  18 O shell is useful proxy </li></ul><ul><li>Several trace elements show seasonal patterns </li></ul><ul><li>It is not yet clear if this is due to: </li></ul><ul><ul><li>Water composition </li></ul></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>Biological fractionation (vital effects) </li></ul></ul><ul><li>Ca. 4500y old shells show seasonal stable isotope patterns similar to modern shells </li></ul><ul><ul><li> no diagenesis (?) </li></ul></ul>
  24. 28. Future work <ul><li>Stable isotope analyses of monitoring shells </li></ul><ul><li>More stable isotope analyses of late Holocene shells </li></ul><ul><li>Trace element analyses (LA-ICPMS) on monitoring, 20 th century and Holocene shells </li></ul>
  25. 29. What to do with LA-ICPMS? <ul><li>Resolve slowly-growing parts of shells </li></ul><ul><li>Establish relationship between trace element composition of water and shell </li></ul><ul><li>Resolve growth lines of long-living freshwater pearly mussel Margaritifera margaritifera (>150y old) </li></ul><ul><li>North Atlantic Oscillation variability </li></ul>
  26. 30. Preliminary results LA-ICPMS
  27. 31. Preliminary results LA-ICPMS
  28. 32. Polymesoda
  29. 33. <ul><li>Thank you! </li></ul>

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