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Calcite

Aragonite. Calcite. Vaterite. Solid Phases. Calcite - most common and stable Aragonite - often kinetically favored Vaterite - rare in nature. Potential Causes of Whitings. Increased temperature Increased Ca 2+ and/or CO 3 2- phytoplankton blooms combination of all of above.

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Calcite

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  1. Aragonite Calcite Vaterite

  2. Solid Phases • Calcite - most common and stable • Aragonite - often kinetically favored • Vaterite - rare in nature

  3. Potential Causes of Whitings • Increased temperature • Increased Ca2+ and/or CO32- • phytoplankton blooms • combination of all of above

  4. Background: Nucleation • Homogeneous nucleation - from solution • Heterogeneous Nucleation - on a substrate • Induction time

  5. Background: Saturation State • Often denoted by W • = (aCa2+aCO32-)/Karagonite • If W > 1 for a mineral in solution, precipitation is favored

  6. We know increasing temperature and nutrient concentrations enhances aragonite growth. Nodularia spumigena 10mm However, it is much less clear whether phytoplankton act as nucleation "seeds".

  7. Simple Nucleation Experiments • Add excess Ca2+ to Pyramid Lake water until whiting is observed. • Quantify how much Ca2+ is required for given conditions

  8. Collection bottle Filtration apparatus Clock or watch Stir plate Burette Glass flask 0.1 M CaCl2 solution Thermometer Notebook and pen pH meter (optional) Equipment Required

  9. Variables to Keep Constant • Temperature • Stir rate • Interval of Ca2+ additions • Particulates in solution

  10. Procedure • Add drops of 0.1M CaCl2 solution in predetermined time intervals • Record time and pH after each addition • Stop when whiting is observed

  11. Data • The main variable of interest is the amount of titrant required to produce the whiting event.

  12. whiting observed aragonite growth whiting observed

  13. Results: Nucleation with and without phytoplankton Aragonite nucleates in waters with phytoplankton more readily

  14. Results: Nucleation with and without filtering Aragonite nucleates in unfiltered waters more readily

  15. SEM Imaging • Aragonite crystals look similar in experiments performed with and without added phytoplankton.

  16. nucleated in the presence of nodularia control experiment

  17. Discussion/Conclusions • The amount of added Ca2+ required for nucleation was reproducible in control exps. • Filtering appears to have an effect on nucleation • Nucleation occurs more readily in the presence of phytoplankton; suggesting that algal blooms may enhance whiting events.

  18. General implications for natural systems • Natural waters are commonly supersaturated with respect to CaCO3 minerals, but the concentration and chemical nature of natural inhibitors will determine whether, and at what rate crystal growth actually occurs. • Substances that enhance nucleation of crystals do not necessarily affect mechanisms of growth, as these are two very different processes.

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