1. Aragonite
Calcite
Vaterite

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

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

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

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

7. 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".

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

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

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

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

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

13. whiting observed
aragonite
growth
whiting
observed

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

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

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

17. nucleated in the presence
of nodularia
control experiment

18. 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.

19. 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.