The effects of the Mg2+ ion concentration and the ionic products of carbonate upon the induction time for the onset of precipitation and the different mineralogies of calcium carbonates were studied. It was shown that Mg2+ ions delay the spontaneous precipitation of calcium carbonate from supersaturated solutions (e.g. seawater) with respect to calcium carbonate mineral to such an extent that only biogenic removal of skeletal calcium carbonate is possible from the open ocean. Low concentrations of magnesium ions in solution favor calcite formation while aragonite is formed at high magnesium concentrations. The mole% of MgCO3 in magnesian calcite increases with the increase of (Mg2+) in solution and with the increase of (CO32−) in the presence of (Mg2+) in solution.

Slight perturbations of the oceanic DOC by addition of oxalic acid, tryptophan, and sodium humate did not affect the magnesium content of spontaneously precipitated Mg-calcites. However, the copresence of spontaneously precipitated aragonite and of Mg-calcite as a function of the initial degree of supersaturation was changed by the dissolved organic matter. Times of nucleation for carbonates was affected by organic matter at low organic concentrations because of coating and at high concentrations due to complexation.

The correct values of the association constants of MgSO4 and the adequacy of using the Debye—Hückel equation are considered.

Previous estimates of the decomposition of calcium carbonate and organic carbon in deep ocean water are subject to inaccuracies due to (1) the effect of phosphate released from the decomposition of organic matter on titration alkalinity not being properly evaluated, (2) the variation of the preformed properties not being considered, and (3) the input of anthropogenic CO2 not being corrected for. More accurate results are presented here for selected stations in the South Pacific.

The activity of NaCl in artificial seawater was measured potentiometrically with Na+- and Cl− -sensitive electrodes. The salinity of the solutions, examined at 25°C, ranged from 10–40‰ salinity. The change in the activity from 5–25°C was measured at 35‰ salinity.

The apparent solubility product of calcite was measured by saturometry as a function of temperature and salinity. Simplified equations for the carbonic-acid dissociation constants of Mehrbach et al., 1973 (Limnol. Oceanogr., 18: 897–907) have been derived from their experimental data and used to calculate apparent solubility product, K′sp, K′sp at 25°C and 35‰ salinity, was found to be K′sp = 4.70 × 10−7(mol2 kg seawater−2) An equation was fitted to the experimental data, resulting in pK′sp = 6.5795 − 3.7159 × 105(TS) + 0.91056(T/S) − 22.110(1.0/S)

The apparent solubility product of aragonite in 32‰ seawater at 25.0°C is reported as K′sp = (0.869±0.049) × 10−6(mol2 kg seawater−2) thus confirming the value of R.A. Berner, 1976 (Am. J. Sci., 276: 713–730). The apparent solubility product ratio for aragonite and calcite is reported as K′aragoniteK′calcite = 2.05 The deviation of this value from the thermodynamic ratio is atttributed to the formation of a stable low Mg-calcite coating on pure calcite in seawater measurements of solubility.

In this work the concepts of ionic medium, effective ionic strength and free versus total activity coefficients are examined. Then they are applied to the study of permissible and incorrect translations of equilibrium constants from one medium to another. Ionic Media Ionic media are solutions of background electrolytes which are concentrated enough so that the activity coefficients of the electrolytes of interest do not change during processes which are occurring. Typical ionic media are a 1 m HClO4 or NaClO4 solution and seawater. Let us consider the dissolution-precipitation process in seawater in the following example. The normal concentrations of calcium and of carbonate in the near-surface oceanic waters are about [Ca2+] = 0.01 and [CO32-] = 2 x 10-4 M. The CaCO3 in solution is metastable and roughly 200% saturated (1). Should precipitation occur due to an abundance of nuclei, [CO32-] will drop to 10-4 M but [Ca2+] will change

The competition for anions between the cations of the alkali and alkaline earth metals (to form ion pairs) and the cations of heavy metals (to form complexes) is investigated. The interaction is shown to affect the stability constants of the heavy metal complexes and the nature of the ionic species present in aqueous media of high salinity. The theory is discussed with special reference to NaCl-NaClO4 solutions, seawater and the labile complexes of lead and cadmium.

The rates at which concentrations of oxygen and carbon dioxide in Stuart Channel changed due to biological production and to exchange with the atmosphere were determined from measurements of the simultaneous changes in oxygen, pH, and titration alkalinity over a 15‐day period in July 1976. Carbon dioxide was consumed by plankton at a rate of 10.8 µ mol CO 2 ·liter −1 ·d −1 .CO 2 entered the surface layer by atmospheric exchange at a rate of 0.49 µ mol CO 2 ·liter −1 ·d −1 . The piston velocity was calculated to be 2.2 × 10 −3 cm·s 1 . Oxygen was produced at a rate of 14.1 µ mol O 2 ·liter 1 ·d −1 , due to photosynthetic activity. The rate of oxygen loss to the atmosphere was 9.8 µ mol O 2 ·liter −1 ·d −1 . The piston velocity was 1.6 × 10 −3 cm·s −1 .

Decomposition of organic matter changes the concentrations of carbon, nitrogen, phosphorus, oxygen and titration alkalinity (TA) in the ratio 106:16:1:138:–17 (refs 1–3), so the combined effect of decomposing x mol of CaCO3 and y mol of organic matter in 1 kg of seawater on the preformed total CO2 (ΣCO20), preformed TA (TA0), biogenerated ΣCO2 [ΔΣCO2(biol)] and the apparent oxygen utilisation (AOU) can be represented as4 ΔΣCO2=ΣCO2(measured)−ΣCO20=x+106y ΔTA=TA(measured)−TA0=2x−17y ΔΣCO2(biol)=106y; AOU=138y Eliminating x and y from the above equations yields Several early workers5–8 have successfully correlated ΔΣCO2(biol) to AOU with slopes close to the Redfield, Ketchum and Richards (RKR) model1. However, the methods used often have not satisfactorily taken into account the variation of the preformed values for ΣCO2 and TA with sample depth or have mistakenly taken ΔΣCO2(biol) to be equal to ΔΣCO2−O.5ΔTA. The inconsistency between the correlations above and below the thermocline is also not well explained. A modified computational scheme5,8 has recently been developed for calculating the ΣCO2-TA-oxygen correlation with the depth dependent variations of ΣCO20 and TA0 accounted for. The method of calculating ΔΣCO2 is the same as that described in ref. 4 but further useful information has been obtained by plotting ΔΣCO2 against AOU, rather than depth. The results in the Pacific Ocean, presented here, suggest a linear correlation between the bio-generated CO2 and AOU with a slope of 0.722±0.05, in good agreement with that predicted from the RKR model. The deviation of the data from this linear correlation for shallow water can largely be explained by the influences of human induced CO2.

The pH of seawater is a key quantity for the calculation of fossil fuel carbon dioxide transfer into the oceans and of the potential dissolution of calcareous organisms, a sink for the carbon dioxide. Thus, it is important to clarify what is meant by the pH of seawater. New data on chloride interactions with hydrogen ions affects this meaning and is discussed briefly in this work.

Stoichiometric association constants, which have been measured for the ion pairs of Cl− and SO4−2 with Na+, K+, Mg2+, and Ca2+, were used to determine the speciation in an artificial sea water containing only these ions. The resulting distribution is quite different to that found in earlier models in which chloride ion association was ignored. The concentrations of chloride ion pairs with the cations are 4 to 5 times larger than the concentrations of the sulphate ion pairs with the same cations. The total activity coefficients of the neutral salts in sea water calculated from the model are in good agreement with the experimentally measured values. The concentration of MgSO40 calculated to be present agrees with the amount determined from ultrasonic absorption data. The calculated solubility of gypsum is also in good agreement with the measured values.

In this work the conditions required for the presence of two solid phases in equilibrium with a solution are discussed with special reference to the co-existence of magnesium calcites and dolomite in seawater. The criterion is determined in terms of the phase rule and of the solid-seawater ratio.

A partial long-range order model for aqueous electrolyte solutions is proposed to avoid contradictions present in the Debye-Hückel theory. The partial long-range order increases with increasing salt concentration because, as the ions are closer together, the coulombic energy of interaction which generates a quasi-lattice increases. Furthermore, the order decreases with increasing temperature because the thermal energy increases relative to the coulombic attraction of the ions. The long-range order parameter L and a parameter v which results from fluctuations and other effects are obtained for LiCl, NaCl and KCl by comparing the theoretical configurational free energy to the electrical free energy obtained from the experimental activity coefficients. The specific interaction and the cluster integral models are discussed briefly at the end of this work.