Predicting mineral solubility from rate data; application to the dissolution of magnesian calcites

Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

“…Laboratory experiments used to determine Mg-calcite dissolution rate data resulted in diagenetic outcomes, that is, the formation of substantial amounts of calcite (for example, ref. 10), that were not observed in our samples (Supplementary Fig. S17).…”

“…Development of these reef structures is dependent on preservation of the dead CCA skeleton post-mortem. Thus, understanding how declining seawater pH will affect this skeletal preservation is of paramount importance if we are to understand the changes to coral reef structural stability in a high-CO 2 world.In the 1950s-1970s the mineral composition of coralline algae skeletons was determined to be ∼12-18 mol% Mg-calcite [8][9][10] . However, many bulk chemical analyses of tropical coralline algae showed a surplus of magnesium compared with those determined by X-ray diffraction (XRD) using Mg-calcite peak position 8,9 .…”

“…In the 1950s-1970s the mineral composition of coralline algae skeletons was determined to be ∼12-18 mol% Mg-calcite [8][9][10] . However, many bulk chemical analyses of tropical coralline algae showed a surplus of magnesium compared with those determined by X-ray diffraction (XRD) using Mg-calcite peak position 8,9 .…”

“…Recently, we discovered this discrepancy was due to the presence of previously undetected dolomite and magnesite (MgCO 3 ) forming within the cell spaces 4 . Past determinations of thermodynamic solubility for coralline algae were based on the assumption that they were composed of Mg-calcite [10][11][12] . As dolomite was not believed to form in the modern marine environment, determining dolomite solubility under these conditions was considered of limited importance 12 .…”

Experimental and analytic studies to model kinetics and mass transport of carbon dioxide sequstration in depleted carbonate reservoirs

“…It is based on an extrapolation of the concentrations of dissolved components of the dissolution to an ion activity product (IAP) calculated at infinite time at which the rate of change of the concentrations of the components approaches zero (see Garrels et al, 1960;Plummer and Mackenzie, 1974 for methodology). A particularly vexing problem for Mg-calcite solubility studies in dilute solutions is that the solution will become supersaturated with respect to a calcite phase with low Mg-content, which will start to precipitate, while the high Mg-calcite continues to dissolve (Plummer and Mackenzie, 1974;Fig. 2).…”