Equilibrium constants of triethanolamine in major seawater salts

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl₂ or CaCl₂), with binary mixtures of MgCl₂ and CaCl₂, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl₂, while it is increased by the other electrolytes used in this work.     

Observation of abnormal solubility behavior of aromatic hydrocarbons in seawater

The Setschenow and McDevit—Long equations are applied to aromatic hydrocarbons in seawater by using solute surface area and recently available solubility data to evaluate the Setschenow constant. It is demonstrated that this approach avoids a previously encountered problem with the McDevit-Long equation while also pointing out fundamental theoretical discrepancies. Compounds that do not fit the presented semi-empirical relationship are of interest as they may exhibit abnormal partitioning behavior in seawater. Using this approach it is suggested that 1,2-benzanthracene and benzo(a)pyrene exhibit abnormal solution behavior in seawater.     

An improved model for the calculation of CO2 solubility in aqueous solutions containing Na, K, Ca, Mg, Cl, and SO4

An improved model is presented for the calculation of the solubility of carbon dioxide in aqueous solutions containing Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and SO₄²⁻ in a wide temperature–pressure–ionic strength range (from 273 to 533 K, from 0 to 2000 bar, and from 0 to 4.5 molality of salts) with experimental accuracy. The improvements over the previous model [Duan, Z. and Sun, R., 2003. An improved model calculating CO₂ solubility in pure water and aqueous NaCl solutions from 273 to 533K and from 0 to 2000 bar. Chemical Geology, 193: 257–271] include: (1) By developing a non-iterative equation to replace the original equation of state in the calculation of CO₂ fugacity coefficients, the new model is at least twenty times computationally faster and can be easily adapted to numerical reaction-flow simulator for such applications as CO₂ sequestration and (2) By fitting to the new solubility data, the new model improved the accuracy below 288 K from 6% to about 3% of uncertainty but still retains the high accuracy of the original model above 288 K. We comprehensively evaluate all experimental CO₂ solubility data. Compared with these data, this model not only reproduces all the reliable data used for the parameterization but also predicts the data that were not used in the parameterization. In order to facilitate the application to CO₂ sequestration, we also predicted CO₂ solubility in seawater at two-phase coexistence (vapor–liquid or liquid–liquid) and at three-phase coexistence (CO₂ hydrate–liquid water–vapor CO₂ [or liquid CO₂]). The improved model is programmed and can be downloaded from the website http://www.geochem-model.org/programs.htm.     

Rates of oxygen transfer from air bubbles to aqueous NaCl solutions at various temperatures

Experiments have been conducted to investigate the effects of temperature on the interfacial surface area and on the rate of oxygen transfer from air bubbles dispersed in aqueous NaCl solutions. Tests were also conducted to estimate the effects of salt concentration on the size of the bubbles. In addition to NaCl solutions, seawater was used in some tests. The temperature effects were investigated at 5, 10, 15, 20, 25, and 30°C. The results showed a pronounced effect of the salt on the size of the bubbles, which first decreased sharply with increasing concentration, but showed no further drop when the concentration was increased beyond 0.6 M. Both in seawater and in the 0.6 M solution, the mass transfer rate, K_LA, increased almost linearly when temperature was increased within the range from 5 to 25°C. The salt solution, as well as the seawater, showed an increase of K_LA of 60–70% over that in pure water at the same temperatures. This effect was the result of increased surface area of bubbles because of decreased coalescence. The increase in surface area was strongly temperature dependent, especially between 15 and 20°C. Contrary to this behavior the surface area in pure water showed, practically, no temperature dependence. The results are explained and discussed on the basis of ion-water interactions.     

Improved thermodynamic calculations for concentrated mixed electrolyte systems including ion pairing (or the absence of it)

Knowledge of the activity coefficients of solutes under temperature and pressure ranges of interest is generally required for calculations of the physicochemical properties of aqueous multicomponent electrolyte solutions such as seawater. Whilst these activity coefficients are well characterized for the predominant salts individually, fewer data are available for minor components under a sufficiently wide range of conditions and there are significant interactions between some of the chemical species involved which can substantially alter the required activity coefficients in mixtures.For these reasons, accurate thermodynamic predictions for seawater and other multi-electrolyte solutions in moderate or high concentration are more difficult than is often supposed. In particular, progress in this area has been slowed by uncertainty regarding the nature and extent of ion pairing in concentrated strong electrolyte solutions, a problem that has been debated for decades. Zdanovskii's rule, described originally almost a century ago but widely neglected, provides a fundamentally sound method for calculating the properties of mixed electrolyte solutions. Modelling developments are described, which accord with various types of experiment, from our laboratory and from the chemical literature. It has become clear that, when treated in an appropriate way based on solvent activity, linear mixing behaviour of strong electrolyte solutions can be considered the norm. This is an inevitable consequence, first recognized by Guggenheim, of the cancellation of ion pairing and other interactions as, conceptually, one ion replaces another. Stronger solute–solute interactions, described by equilibrium constants, can then easily be coupled in a thermodynamically consistent manner.     

Oxidation of copper(I) in seawater at nanomolar levels

The oxidation and reduction of nanomolar levels of copper in air-saturated seawater and NaCl solutions has been measured as a function of pH (7.17–8.49), temperature (5–35 °C) and ionic strength (0.1–0.7 M). The oxidation rates were fitted to an equation valid at different pH and ionic strength conditions in sodium chloride and seawater solutions:

The reduction of Cu(II) was studied in both media for different initial concentrations of copper(II). When the initial Cu(II) concentration was 200 nM, the copper(I) productions were 20% and 9% for NaCl and seawater, respectively. The effect of speciation of copper(I) reduced from Cu(II) on the rates was studied. The Cu(I) speciation is dominated by the CuCl₂⁻ species. On the other hand, the neutral chloride CuCl species dominates the Cu(I) oxidation in the range of 0.1 M to 0.7 M chloride concentrations.     

Investigations of iron coordination and redox reactions in seawater using Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes

Iron coordination and redox reactions in synthetic and coastal seawater were investigated at nanomolar concentrations using ⁵⁹Fe radiometry and ion-pair solvent extraction of iron chelated by sulfoxine (8-hydroxyquinoline-5-sulfonate) and BPDS (bathophenanthroline disulfonate). Using sulfoxine, we determined the rate at which the monomeric Fe(III) hydroxide species present in seawater of pH 8 are complexed by the microbial siderophore deferriferrioxamine B and the synthetic chelator EDTA (ethylenediaminetetraacetic acid). Forward rate constants of 2 × 10⁶M⁻¹s⁻¹ and 20 M⁻¹s⁻¹, respectively, were obtained. The kinetics of these reactions have not been measured previously at pH values near that of seawater. Conditional equilibrium constants measured for the Fe(III)-EDTA system are consistent with published stability constants for EDTA complexes and for Fe(III) hydrolytic equilibria minus the neutral Fe(OH)₃^o species, suggesting it is not quantitatively significant near pH 8. Commercial humic acid was found to have sufficient affinity for iron to compete with Fe(III) hydrolysis in seawater, and limited evidence was obtained for an interaction with dissolved organic matter in coastal seawater.In our investigations of redox reactions using BPDS to trap Fe(II) produced in the medium, we observed enhanced photoreduction of Fe(III) by humic acid as well as reduction induced by solutes released from phytoplankton in seawater of pH 8. Although the method is sensitive enough to work at near-oceanic levels of iron, the difficulty in distinguishing Fe(II) generated by Fe(III)-BPDS interactions from Fe(II) produced by other means limits its utility. This analytical ambiguity may be generalizable to other methods which measure ferrous iron in seawater using Fe(II)-specific ligands.     

Ionic activity coefficients in aqueous mixtures of NaCl and MgCl2

Methods developed earlier, based on hydration numbers for individual ionic species, have been extended to the calculation of ionic activity coefficients in aqueous systems of two electrolytes MX and NX₂ with a common unhydrated anion (X⁻). The data required include the mean activity coefficients of MX and NX₂ in the mixtures, together with the osmotic coefficient. The procedure is illustrated by a calculation of γ_Na, γ_Mg, and γ_Cl in a mixture of NaCl and MgCl₂ closely approximating the composition of seawater with salinity of 35‰.     

White-light promoted degradation of leucopterin and related pteridines dissolved in seawater, with evidence for involvement of complexation from major divalent cations of seawater

The photochemical instability of several related pteridines in seawater was investigated by aseptic incubation of solutions at 20–22°C under illumination from cool-white light of intensity 6 kerg cm⁻² sec⁻¹, and the chemical changes were spectrophotometrically monitored. All the pteridines showed markedly accelerated degradation from this illumination relative to their behaviour in total darkness.Pterin and lumazine were degraded very slowly with zero-order reaction kinetics, while the other pteridines photolysed rapidly (according to first-order kinetics) with decomposition rates increasing in the order dioxylumazine (2,4,6,7-tetrahydroxypteridine) < leucopterin < isoxanthopterin < xanthopterin < oxylumazine (2,4,6-trihydroxypteridine). Excepting leucopterin and dioxylumazine, the photolysis rates were attributable to the pH of seawater and not its salt content; this was also the case with oxylumazine which required the salt content of seawater for decomposition in darkness. Leucopterin and dioxylumazine (both 6,7-dihydroxylated pteridines) gave evidence of complexation with the major divalent cations (Ca²⁺, Mg²⁺) of seawater, by virtue of which their photolytic degradation rates were enhanced to magnitudes obtained in pH-10 buffer without seawater. It is proposed that such complexation produces structural forms of these pteridines analogous to their normal ionic forms at pH 10–12.The photolysis of the 6-hydroxylated pteridines (xanthopterin, oxylumazine) proceeded via intermediate formation of their corresponding 7-hydroxylated derivatives (leucopterin, dioxylumazine).     

The non-biological oxidative degradation of dissolved xanthopterin and 2, 4, 6-trihydroxypteridine by the pH or salt content of seawater

The degree of chemical instability of xanthopterin and related pteridines in seawater was studied with a view to assessing its role in the ecological turnover of these compounds in the marine environment. Solutions of these compounds in natural and synthetic seawater, brines containing one or more component salts of seawater, and buffers covering a wide pH range were incubated aseptically at 22–25°C in complete darkness and the chemical changes were spectrophotometrically monitored.Pterin, lumazine, and isoxanthopterin were completely stable in seawater, while the other pteridines degraded in the order dioxylumazine < leucopterin < xanthopterin <<< oxylumazine (the trivial names oxylumazine and dioxylumazine are used to denote 2, 4, 6-trihydroxy- and 2, 4, 6, 7-tetrahydroxy-pteridine, respectively). Apart from oxylumazine, the chemical instability of the other pteridines was correlated with pH corresponding to that of seawater. The high instability of oxylumazine was shown to be due to the salt content of seawater and not its pH; this pteridine required minimal concentrations of salt and traces of heavy-metal ions (such as Cu²⁺) to show significant chemical change. When the salt present was NaCl or KCl only, oxylumazine showed 1:1 oxidative conversion to dioxylumazine, but with the total salts of seawater the conversion was 2:1 with half of the oxylumazine being degraded, apparently by ring-cleavage, to unidentified non-pteridine products; this latter degradation is attributed to the total complex of ions present in seawater. In contrast to oxylumazine, xanthopterin gave evidence of 1:1 oxidative degradation via leucopterin in seawater, and this degradation appeared to be independent of trace metal ions. Chemical mechanisms are suggested for the observed degradations, and the ecological implications of the latter are discussed.     

Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean

Recent electrochemical measurements have shown that iron (Fe) speciation in seawater is dominated by complexation with strong organic ligands throughout the water column and have provided important thermodynamic information about these compounds. Independent work has shown that iron exists in both soluble and colloidal fractions in the Atlantic Ocean. Here we have combined these approaches in samples collected from a variety of regimes within the Atlantic Ocean. We measured the partitioning of Fe between soluble (< 0.02 μm) and colloidal (0.02 to 0.4 μm) size classes and characterized the concentrations and conditional stability constants of Fe ligands within these size classes. Results suggest that equilibrium partitioning of Fe between soluble and colloidal ligands is partially responsible for the distribution of Fe between soluble and colloidal size classes. However, a significant fraction of the colloidal Fe was inert to ligand exchange as soluble Fe concentrations were generally lower than values predicted by a simple equilibrium partitioning model.In surface waters, strong ligands with conditional stability constants of 10¹³ relative to total inorganic Fe appeared to dominate speciation in both the soluble and colloidal fractions. In deep waters these ligands were absent, and instead we found ligands with stability constants 12–15 fold smaller that were predominantly in the soluble pool. Nevertheless, significant levels of colloidal Fe were found in these samples, which we inferred must be inert to coordination exchange.     

Determination of Henry's law constants for hexachlorocyclohexanes in distilled water and artificial seawater as a function of temperature

Henry's law constants were determined for α- and γ-hexachlorocyclohexane (HCH) as a function of temperature (0.5–45°C) in artificial seawater (SW; 30‰) and distilled water (DW) using the gas stripping method. Water samples (1–5 ml) were withdrawn from the stripping vessel during the stripping process (30–360 h), solvent extracted and analyzed by gas chromatography—electron-capture detection. The effect of bubbling depth was checked to ensure that bubbles leaving the system were at equilibrium with HCHs in the aqueous phase. Henry's law constants determined at 35 and 45°C in SW were significantly higher (P≤ 0.05) than in DW for both α- and γ-HCH, but not at lower temperatures. The slopes (m) and intercepts (b) of log H vs. 1 / T plots were: α-HCH (DW, 0.5–45°C); m = −2810 ± 110, B = 9.31 ± 0.38; α-HCH (SW, 0.5–23°C); M = −2969 ± 218, B = 9.88 ± 0.76; γ-HCH (DW, 0.5–45°C); M = −2382 ± 160, B = 7.54 ± 0.54; γ-HCH (SW, 0.5–23°C); M = −2703 ± 276, B = 8.68 ± 0.96. Henry's law constants determined in this study compared well with those calculated from reported vapor pressure and solubility data.     

Stability of ion pairs from gypsum solubility degree of ion pair formation between the major constituents of seawater

The stability constants of the ion pairs NaSO₄^?, KSO₄^?, MgSO₄^?, CaSO₄, MgCl⁺ and CaCl⁺ were determined at 25°C and 0.7 M formal ionic strength, by measuring the solubility of gypsum (CaSO₄ · 2H₂O) in different media. The media used contained one or two of the following electrolytes: NaCl, KCl, MgCl₂, NaClO₄, Mg(ClO₄)₂, Na₂SO₄. Values for the stability constants are 1.22, 1.84, 12.3, 30.6, 0.48 and 1.20 M^?1, respectively, and the solubility product for gypsum is 2.87 · 10^?4M². The distribution of the main constituents of seawater was calculated using these results and the values of the carbonate and bicarbonate constants given by Dyrssen and Hansson (1972–1973). The solubility of gypsum in seawater as calculated and determined experimentally was 21.43 mM and 21.10 mM, respectively.     

The interaction of manganese(II) with the surface of calcite in dilute solutions and seawater

The interaction of Mn²⁺ with the surface of calcite in aqueous solutions is complex. In dilute solutions the Mn²⁺ is rapidly absorbed, MnCO3₃ nucleates on the calcite surface and then grows by a first order reaction with respect to the initial Mn²⁺ concentration. At higher ionic strengths in NaCl solutions, the rate of these processes is slower, but the same general pattern persists. In solutions containing Mg²⁺, at the concentration of seawater and in seawater, the nucleation phase of the uptake process does not appear to occur. The long-term uptake rate of Mn²⁺ on the surface of calcite in seawater is first order with respect to the dissolved Mn²⁺ concentration. The rate constant is over three orders of magnitude smaller than that found in dilute Mg²⁺-free solutions. A probable explanation for the slower growth rate in seawater is that MnCO₃ is not nucleated on the calcite surface due to the presence of high Mg²⁺ concentrations. The Mg²⁺, through site competition, prevents enough Mn²⁺ from being adsorbed to reach a critical concentration for MnCO₃ nucleation. This behavior is similar to that found for orthophosphate with calcite surfaces in dilute solutions and seawater. It indicates that rhodochrosite cannot nucleate in carbonate-rich recent sediments unless the Mg²⁺ concentration is lowered below that of seawater.Measurements of the solubility of rhodochrosite in seawater gave results from an undersaturation approach to equilibrium in excellent agreement with those found in previous studies in dilute solutions. When equilibrium was approached from supersaturation, approximately fifty times more calcium was precipitated than Mn²⁺. The measured solubility was over twice that determined from undersaturation. It is possible that a Mn—calcite containing 25 to 30 mol% MnCO₃ formed on the rhodochrosite from the supersaturated solutions. Consequently, it is doubtful that pure rhodochrosite controls the concentration of Mn²⁺ even in calcium carbonate-poor marine environments.     

Calibration of a chalcogenide glass membrane ion-selective electrode for the determination of free Fe in seawater: I. Measurements in UV photooxidised seawater

Calibration of a chalcogenide glass membrane, Fe(III)ISE [Fe_2.5(Ge₂₈Sb₁₂Se₆₀)_97.5], in buffered saline media has been undertaken in order to assess the suitability of this ISE for seawater analyses. The electrode slopes in saline citrate and salicylate buffers were 26.3 and 28.2 mV/decade, respectively, for Fe³⁺ concentrations ranging from 10⁻¹⁰ M to less than 10⁻²⁵ M Fe³⁺. The calibration lines in the citrate and salicylate buffers were essentially collinear with the response in unbuffered chloride-free standards containing >10⁻⁵ M Fe³⁺, demonstrating that the response of the FeISE is unaffected by chloride ions. A mechanism involving a combination of charge transfer and ion-exchange of Fe(III), at the electrode diffusion layer, can be used to explain the ≈30 mV/decade slope of the FeISE. The response of the FeISE in UV photooxidised seawater containing 8 nM total Fe was measured as the pH was changed from 8.27 to 3.51. The slope of the response was 24.2 mV/decade [Fe³⁺] calculated as a function of pH using Fe(III) hydrolysis constants for seawater. Moreover, the response was essentially collinear with that in citrate buffers and in unbuffered solutions containing >10⁻⁵ M Fe³⁺ and the slope for the combined data was 26.2 mV/decade. This study was restricted to organic-free seawater because the certainty in Fe(III)–ligand stability constants is insufficient to warrant the selection of an ideal calibration buffer system, and there is evidence that powerful chelating ligands (e.g., EDTA along with humic and fulvic acids) may alter the response of the Fe(III)ISE. The Fe dissolution rate of the FeISE in UV photooxidised seawater was found to be 1.6×10⁻² nmol Fe/min, as measured by cathodic stripping voltammetry (CSV). This would contaminate a 100-ml sample by 0.8–1.6 nM Fe over a typical measurement period of 5–10 min obtained using a stability criterion of 0.5 mV/min. Various methods are proposed for reducing the level of contamination in open ocean samples that contain sub-nanomolar concentrations of iron. The FeISE has the potential to detect free Fe³⁺ at concentrations typically found in natural seawater.     

Dissociation constants of protonated methionine species in seawater media

The dissociation constants (pK₁ and pK₂) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK₂ values were lower than the values in NaCl at the same ionic strength while the pK₁ values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg²⁺ complexes and Pitzer interaction parameters for Mg²⁺ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK₁ and pK₂ between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.     

The effects of temperature and salinity on the aqueous solubility of polynuclear aromatic hydrocarbons

The aqueous solubilities of phenanthrene, anthracene, 2-methylanthracene, 2-ethylanthracene, 1,2-benzanthracene, and benzo(a)pyrene were determined at temperatures ranging from 3.7 to 25.3°C and salinities ranging from 0 to 36.7‰. With the exception of 1,2-benzanthracene, the hydrocarbons experienced salting-out. Their solubilities were insensitive to small changes in salinity and very sensitive to small changes in temperature. On the other hand, 1,2-benzanthracene experienced salting-in, and its solubility was sensitive to small changes in salinity. Potential environmental implications of the data are discussed.     

Vertical and seasonal differences in biogenic silica dissolution in natural seawater in Suruga Bay, Japan: Effects of temperature and organic matter

Vertical and seasonal characteristics of biogenic silica (BSi) dissolution in seawater were investigated by multiple dissolution experiments using seawater collected from surface and mesopelagic layers in Suruga Bay during the period 2002–2004. The dissolution rate coefficients calculated based on temporal changes of BSi concentration varied with the season of sample collection. They ranged from 0.023–0.057 day^− 1 for surface samples and 0.0018–0.0025 day^− 1 for mesopelagic samples for temperatures approaching in situ conditions. Experiments at various temperatures confirmed that BSi dissolution depends on temperature in natural seawater. Dissolution rate coefficient (day^− 1) of BSi correlated significantly with temperature (°C), and Q₁₀ was 2.6. Addition of bioavailable organic matter to low-bioactivity seawater enhanced the protease activity and abundance of bacteria, and increased BSi dissolution rate by a factor of 1.4–2.0. There is clear evidence that BSi dissolution is accelerated by bacterial activity and potentially limited by bioavailable organic matter in natural seawater. Dissolution rates and total decreases of BSi concentration were lower during experiments using mesopelagic samples than in those using surface samples. This suggests that dissolution of BSi varies with depth and that BSi in the mesopelagic water is more resistant to the dissolution than that in the surface water. This lower dissolution rate was caused by lower temperature and lower bacterial activity due to less bioavailable organic matter in mesopelagic water. Our results provide a mechanistic understanding of variations in silica cycling within the seasonally and vertically differing marine environment.     

Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K_i^equ), total ligands concentration (L_iT) and association/dissociation rate constants (k_i¹,k_i^- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K₁^equ: 11.2–13.0, log K₂^equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k₁¹:6.1–20 × 10³ (M s)^− 1, k₂¹: 1.3–6.3 × 10³ (M s)^− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM_C, i.e. 1 mg_CL^− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).     

A Gibbs–Pitzer function for high-salinity seawater thermodynamics

A high-salinity Gibbs function for seawater is derived from Pitzer equations of the sea salt components, in conjunction with the 2003 Gibbs function of seawater for low salinities. Various properties, computed from both formulations by thermodynamic rules, are compared with each other, and with high-salinity measurements. The new Gibbs–Pitzer function presented in this paper is valid in the range 0–110 g kg⁻¹ in absolute salinity, −7 to +25 °C in temperature, and 0–100 MPa in applied pressure. The formulation is expressed in the International Temperature Scale 1990 (ITS-90), and is consistent with the International Standard for Fluid Water (IAPWS-95), and with the 2005/2006 equations of state of ice Ih.