Tung Chen

Speed of sound in seawater at high pressures

The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single‐transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) ‐UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) ‐ (UO−UOH2O) =AS (°/oo)+BS (°/oo)3/2 +CS (°/oo)2, where U and UH20 are the speeds of sound in seawater and pure water, respectively; superscripts P and O are used to denote applied pressure P and O (1 atm); A, B, and C are temperature‐ and pressure‐dependent parameters; S (o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high‐pressure pure‐water sound‐speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1‐atm seawater sound‐speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1 over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1 (maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1 (maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure‐water data.

A new high pressure equation of state for seawater

A new high pressure equation of state for water and seawater has been derived from the experimental results of Millero and coworkers in Miami and Bradshaw and Schleicher in Woods Hole. The form of the equation of state is a second degree secant bulk modulus K = Pv0(v0−vp=K0+AP+BP2 K = Kw0+aS+bS32 A = Aw+cS+dS32 B = Bw+eS where ν0 and νP are the specific volume at 0 and P applied pressure and S is the salinity (ℵ). The coefficients KWO, AW, and BW for the pure water part of the equation are polynomial functions of temperature. The standard error of the pure water equation of state is 4.3 × 10−6 cm3 g−1 in νWP. The temperature dependent parameters a, b, c, d, and e have been determined from the high pressure measurements on seawater. The overall standard error of the seawater equation of state is 9.0 × 10−6 cm3 g−1 in νP. Over the oceanic ranges of temperature, pressure, and salinity the standard error is 5.0 × 10−6 cm3 g−1 in νP. This new high pressure equation of state has recently (1979) been recommended by the UNESCO Joint Panel on Oceanographic Tables and Standards for use by the oceanographic community.

The equation of state of pure water determined from sound speeds

The equation of state of water valid over the range 0–100 °C and 0–1000 bar has been determined from the high pressure sound velocities of Wilson, which were reanalyzed by Chen and Millero. The equation of state has a maximum error of ±0.01 bar−1 in isothermal compressibility and is in the form of a secant bulk modulus: K=V0P/(V0−V) =K0+AP+BP2, where K, K0, and V, V0 are the secant bulk moduli and specific volumes at applied pressures P and 0 (1 atm), respectively; A and B are temperature dependent parameters. The good agreement (to within 20×10−6 cm3 g−1) of specific volumes calculated using the above equation with those obtained from other modifications of the Wilson sound velocity data demonstrates the reliability of the sound velocity method for determining equations of state.

Speed of sound in NaCl, MgCl2, Na2SO4, and MgSO4 aqueous solutions as functions of concentration, temperature, and pressure

The speeds of sound in aqueous solutions of NaCl, MgCl2, Na2SO4, and MgSO4 have been measured relative to pure water from 0 to 1 molal ionic strength, 0° to 55 ° C, and 0 to 1000 bar applied pressure. The 1‐atm results have been fitted to polynomial equations of concentration and temperature with standard deviations of about 0.1 m/s, U0−UW0=am+bm3/2+cm2 where U0 and UW0 are the 1‐atm sound speeds in solution and in pure water, respectively; m is molality; and a,b, and c are temperature‐dependent parameters. The effect of pressure on the relative speeds of sound has been fitted to equations of the form (UP−UWP)−(U0−UW0) =dm+em3/2+fm2, where UP and UWP are the sound speeds of the solution and water at applied pressure P and d,e, and f are temperature‐ and pressure‐dependent parameters. The standard deviations of the least‐squares fits are within 0.12 m/s for all the salts.

The carbonate system in the western Mediterranean sea

Abstract Measurements of the pH and total alkalinity have been made on waters collected in the western Mediterranean Sea. These results have been used to examine the elements of the carbonate system, HCO3−, CO32−, CO2, ΣCO2, PCO2, and specific alkalinity. The saturation of Mediterranean Gibraltar is supersaturated with respect to calcium carbonate. Our results for the saturation state (Ω) for Mediterranean waters are in good agreement with the results of Alekin (Geochemistry, 206, 239–242, 1972) and those calculated from the GEOSECS (Geochemical Ocean Sections) test station in the eastern Mediterranean. The saturation state of calcite and aragonite in deep Mediterranean waters in higher than that of deep North Atlantic waters.

The volume and compressibility change for the formation of the LaSO 4 + ion pair at 25°C

AbstractThe apparent molal volumes (φv) and adiabatic compressibilities [φK(S)] of La2(SO4)3 solutions have been determined from density and sound speed data at 25°C. The large positive deviations of φv and φK(S) of La2(SO4)3 from the limiting law have been attributed to the formation of the ion pair LaSO4+. The observed values of φv and φK(S) have been used to estimate the change in the apparent molal volume and adiabatic compressibility for the formation of LaSO4+ from

The apparent molal volumes of aqueous solutions of sodium chloride, potassium chloride, magnesium chloride, sodium sulfate, and magnesium sulfate from 0 to 1000 bars at 0, 25, and 50.degree.C

\Delta \phi (LaSO_4^ + ) = [\phi (obs.) - \phi (2La^{3 + } ,3SO_4^{2 - } )]/\alpha

Comment on ‘A new density relation for pure and saline water’ by B. Gebhart and J.C. Mollendorf

where ϕ(2La3+, 3SO42−) is the apparent molal volume or adiabatic compressibility of the free ions, and α is the degree of association. The value of