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

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

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    Gsa Houston 2008 Gsa Houston 2008 Presentation Transcript

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