Aragonite dissolution rate

Acker J.G., Byrne R.H., Ben-Yaakov S., Feely R.A. and Betzer P.R. (1987) The effect of pressure on aragonite dissolution rates in seawater. Geochim. Gosmochim. Acta 51, 2171-2175. 

The dissolution rate for calcite and aragonite have been described in terms of the following rate law (Plummer et al., 1978 Busenberg and Plummer, 1986 Chou and Wollast, 1989. ... 

Figure 2.10. Dissolution rates as a function of pH for aragonite, calcite, witherite, dolomite, and magnesite. (After Chou et al., 1989.)...

The rate of reaction is dependent on the nucleation and growth rates of calcite, not the dissolution rate of aragonite. Curiously, it has also been observed that absolute rates are strongly dependent on the aragonitic material used. This observation appears to contradict the generally held conclusion that rates are strictly dependent on calcite nucleation and precipitation rates, not the dissolution rate of aragonite. 

Figure 7.19. Comparison of calcite and aragonite dissolution and precipitation rates at a Pc02 = 0-96 atm. (After Busenberg and Plummer, 1986b.)...

In order to understand the chemistry of calcium carbonate accumulation in the deep oceans, the sources of calcium carbonate, its distribution in recent pelagic sediments, the saturation state of seawater overlying deep-ocean sediments with respect to calcite and aragonite, and the relation between saturation state and dissolution rate must be known. These aspects of calcium carbonate chemistry are examined in this paper. 

Figure 10. Rate of calcite and aragonite dissolution as a function of depth as determined by Milliman (AO) in water column experiments in the Sargasso sea...

Figure 16. Log of the dissolution rate vs. the log of (1 — Cl) for synthetic aragonite and pteropods (after Ref. 57)...

Figure 17. Log of the dissolution rate vs. total carbonate ion concentration for synthetic aragonite, pteropods, calcitic Pacific Ocean sediment, and foraminifera in the 125-500 iim size fraction. (A) indicates ihe aragonite equilibrium total carbonate ion concentration at 25°C, 1 atm (26). (C) indicates the calcite equilibrium total carbonate ion concentration at 25°C, 1 atm (25).

Figure 19. Change in the rate of synthetic aragonite dissolution, relative to dissolution in very low phosphate seawater, as a function of time (57)...

Carbonate minerals are among the most chemically reactive common minerals under Earth surface conditions. Many important features of carbonate mineral behavior in sediments and during diagenesis are a result of their unique kinetics of dissolution and precipitation. Although the reaction kinetics of several carbonate minerals have been investigated, the vast majority of studies have focused on calcite and aragonite. Before examining data and models for calcium carbonate dissolution and precipitation reactions in aqueous solutions, a brief summary of the major concepts involved will be presented. Here we will not deal with the details of proposed reaction mechanisms and the associated complex rate equations. These have been examined in extensive review articles (e.g., Plummer et al., 1979 Morse, 1983) and where appropriate will be developed in later chapters. 

Betzer et al. (1984, 1986) studied the sedimentation of pteropods and foraminifera in the North Pacific. Their sediment trap results confirmed that considerable dissolution of pteropods was taking place in the water column. They calculated that approximately 90% of the aragonite flux was remineralized in the upper 2.2 km of the water column. Dissolution was estimated to be almost enough to balance the alkalinity budget for the intermediate water maximum of the Pacific Ocean. It should be noted that the depth for total dissolution in the water column is considerably deeper than the aragonite compensation depth. This is probably due to the short residence time of pteropods in the water column because of their rapid rates of sinking. 

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