Dependence of calcite growth rate and Sr partitioning on solution stoichiometry: Non-Kossel crystal growth

Abstract

Seeded calcite growth experiments were conducted at fixed pH (10.2) and two degrees of supersaturation (X = 5, 16), while varying the Ca 2+ to CO 3 2À solution ratio over several orders of magnitude. The calcite growth rate and the incorporation of Sr in the growing crystals strongly depended on the solution stoichiometry. At a constant degree of supersaturation, the growth rate was highest when the solution concentration ratio, r = [Ca 2+ ]/[CO 3 2À ], equaled one, and decreased symmetrically with increasing or decreasing values of r. This behavior is consistent with the kink growth rate theory for non-Kossel crystals, assuming that the frequency factors for attachment to kink sites are the same for the cation and anion. Measured Sr partition coefficients, D Sr , ranged from 0.02 to 0.12, and correlated positively with the calcite growth rate.

Effect of salinity and seawater calcite saturation state on Mg and Sr incorporation in cultured planktonic foraminifera

“…4B), an increase of 0.008 mmol/mol of Sr/Ca per salinity unit is observed. According to Lorens (1981), Nehrke et al (2007) and Tang et al (2008), higher calcite Sr/Ca ratios are mainly associated with higher growth rates in inorganic calcite which is also observed in biogenic calcite (Kısakürek et al, 2008). Results from inorganic experiments (Zuddas and Mucci, 1998) furthermore indicate a positive linear correlation between calcite precipitation rate and ionic strength of the solution.…”

“…We also observe that the regression model predicts a statistically significant Sr/Ca variability due to changes in Ω (p b 0.001; Table 3). In inorganic and biogenic calcite, the Sr/Ca ratio is known to increase with growth rate (Lorens, 1981;Nehrke et al, 2007;Tang et al, 2008;Kısakürek et al, 2008), and a higher [CO 3…”

“…The carbonate saturation state might control the rate of calcite precipitation, which in turn is known to influence trace metal incorporation. This varies depending on the particular trace element studied (Lorens, 1981;Nehrke et al, 2007).…”

Upscaling calcium carbonate precipitation rates from pore to continuum scale

“…The likeliest explanation for most of the discrepancy is that the surface of the calcite spar used in this study has a much lower reactive site density than the calcite seed used in the other studies. A study of calcite precipitation on Iceland spar conducted by Nehrke et al [2007] made use of calcite that was essentially identical to that used in the experiments in this study. Nehrke et al [2007] reported rates ranging from about 10 -6 to 10 -7 mol•m -2 •s -1 , or still 1-2 orders of magnitude faster than those reported here.…”

“…A study of calcite precipitation on Iceland spar conducted by Nehrke et al [2007] made use of calcite that was essentially identical to that used in the experiments in this study. Nehrke et al [2007] reported rates ranging from about 10 -6 to 10 -7 mol•m -2 •s -1 , or still 1-2 orders of magnitude faster than those reported here. However, their surface area normalization was based on grain geometry rather than a BET measurement, with the result that their reported specific surface area was about 1-2 orders of magnitude lower than that determined here.…”