See more from this Division: General Discipline Sessions
See more from this Session: Geochemistry; Geochemistry, Organic
Abstract:
Experiments were conducted in which slow degassing of CO2 resulted in an increase of saturation state with respect to CaCO3 ¬and eventually nucleation. pH was monitored during the experiments. From the pH at nucleation and the known initial total alkalinity the pCO2 and degree of supersaturation at which nucleation occurred were calculated. Precipitates were examined by SEM and mineralogy determined by both crystal morphology and XRD analyses.
It was observed that the initial alkalinity greatly affects the pCO2 and supersaturation at which nucleation of CaCO3 occurs. At high (~40 mM) alkalinities calcite commonly formed. At what we deemed a reasonable alkalinity (~10 mM) and pCO2 values (<~2500 µatm) calcite was also observed to nucleate, but at higher pCO2 values only aragonite nucleated. As alkalinity was lowered below 10 mM the upper pCO2 value at which calcite could nucleate also decreased. These results point to the need for the consideration of factors other than just the Mg2+:Ca2+ ratio, such as alkalinity and pCO2 values, in CaCO3 nucleation experiments and in trying to explain the reasons for aragonite seas and calcite seas at various times during the Phanerozoic Eon.
See more from this Division: General Discipline Sessions
See more from this Session: Geochemistry; Geochemistry, Organic