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Egu2008
 

Egu2008

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Presentation given at the EGU conference in Vienna April 13-18 2008

Presentation given at the EGU conference in Vienna April 13-18 2008

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    Egu2008 Egu2008 Presentation Transcript

    • Stable oxygen isotopes in freshwater mussels (Unionidae) as a proxy for late Holocene floods and droughts of Rhine and Meuse Emma Versteegh Hubert Vonhof Simon Troelstra Dick Kroon
    • Freshwater mussels
      • Common
      • Archaeological finds
      • Museum collections
      • Seasonal growth increments
      • Precipitate  18 O in shell carbonate; shell  18 O depends on:
        • T
        • Water  18 O
      • Species: Unio crassus , U. pictorum , U. tumidus
    • Stable oxygen isotopes
    • Rivers Rhine and Meuse
    • δ 18 O rivers Glacier melting High discharge Flood Dry summer
    • Aim
      • Address the possibilities for shell δ 18 O as a proxy for river discharge and flood and drought frequencies in Meuse and Rhine:
      • Do growth lines in the shells correspond to yearly winter growth cessations?
      • The temperature lower limits below which growth cessation occurs.
      • Do the shells of two species precipitate aragonite in isotopic equilibrium with the ambient water, i. e. predicted values correspond to measured values?
      • Can past river floods and droughts be reconstructed from shell δ 18 O?
    • Methods
      • Microsampling
        • Merchantek Micromill
      • Stable isotopes
        • Finnigan MAT 252
        • Finnigan Delta
      • Water sampling
    • Setup of the project
      • Monitoring experiment
      • 20 th century shells
      • Late Holocene shells
    • Monitoring experiment
      • Cages with living mussels in fish ladders
      • - Hagestein (Lek)
      • - Lith (Meuse)
    • 20 th century shells
      • Meuse:
      • Grevenbicht 1998
      • Lith 2005
      • Kerkdriel 2005
      • Rhine distributaries
      • Tuil 1998 (Waal)
      • Herwijnen 2003 (Waal)
      • Hurwenen 2003 (Waal)
      • Hagestein 2005 (Lek)
    • Late Holocene shells
    • Palaeogeography
    • Results Average δ 18 O per shell
    • Seasonal patterns Slowing down of growth
    • 20 th century shells
    • Predicted shell δ 18 O
      • Water δ 18 O & T  shell δ 18 O
      Grossman & Ku (1986); Dettman et al. (1999)
    • Measured δ 18 O vs. Predicted δ 18 O
    • Measured δ 18 O vs. Predicted δ 18 O: 20 th century shells Juvenile stage
    • Measured δ 18 O vs. Predicted δ 18 O: 20 th century shells Glacier melting Dry summer ???
    • Measured δ 18 O vs. Predicted δ 18 O: monitoring
    • Late Holocene shells
    • Conclusions
      • The shells do not grow in winter
        • Winter floods are not recorded
      • Growth lines usually correspond to winter growth stops, but not always!
      •  18 O shell corresponds well with predicted values
      •   18 O shell is useful proxy
      • 300 - 4500 year old shells show seasonal stable isotope patterns similar to modern shells
        •  no diagenesis
      • Thank you!