The density of North Pacific Ocean waters

Abstract

The densities of 124 samples of seawater from stations at 35°N in the Pacific Ocean have been measured with a vibrating flow densimeter at 25°C. The measured densities were compared with those calculated from the equation of state of Millero et al. (1976b), derived for seawaters of constant relative composition. Values for the excess density Δd(excess) = d(meas) ‐ d(calc) were found to be ±3.8 ± 3.0 × 10−6 g cm−3 from 0 to 490m, 12.5 ±4.2 × 10−6g cm−3 from 490 to 1000 m,; and 17.6 ± 2.6 × 10−6g cm−3 from 1000 to 5834 m. The excess densities for the deep waters are in good agreement with our earlier measurements: 16.1 ± 3.6 × 10−6g cm−3 (Millero et al., 1976c). The values of Δd(excess) predicted by correcting for the increase of alkalinity (ΔAT), total carbon dioxide (ΣCO2), and dissolved silica (ΔSiO2) and nitrate (ΔNO3) in the deep waters (Brewer and Bradshaw, 1975; Millero et al., 1976c) agree with the measured values on the average to ±5.2 × 10−6 g cm−3. In the deep waters the measured values of Δd(excess) are ∼6 × 10−6 g cm−3 higher than the predicted values. The values of Δd(excess) were also calculated by assuming that the changes in salinity due to the added solids affect the density by the same amount as changes in weight‐diluted standard seawater: 106Δd = 757ΔS(‰). The values of Δd(excess) calculated from 106Δd(excess) = 37.9ΔAT + 72.8ΔSiO2 + 47.7ΔNO3 agree with the measured values on the average to ±4.3 × 10−6 g cm−3, independent of the depth. These results indicate that the density changes due to small changes in the composition of deep ocean waters can be accounted for by changes in the salinity due to the mass of added dissolved solids (ΔS(‰) = ΣMi Δni, where Mi is the equivalent or molecular weight and Δni is the change in the equivalents or moles of solute i in 1 kg of seawater).

A global algorithm for estimating Absolute Salinity

“…The fundamental measurements required to provide a method for estimating Absolute Salinity in terms of values of Practical Salinity have been reported in Millero et al (1976aMillero et al ( , 1978Millero et al ( , 2000Millero et al ( , 2008bMillero et al ( , 2009. To this data we add, in Table 2, measurements of density on samples taken from the Southern Ocean.…”

“…2a against the silicate concentrations of the seawater samples using all the data published in Millero et al (1976aMillero et al ( , 1978Millero et al ( , 2000Millero et al ( , 2008bMillero et al ( , 2009) as well as the Southern Ocean data of this paper. These previous papers have considered various measured properties of seawater to correlate with δS A (such as silicate, total alkalinity, total carbon dioxide and nitrate) and found that silicate correlates the best.…”

Thermophysical property anomalies of Baltic seawater

“…However, the chemical composition of seawater is not exactly constant. Regional deviations of seawater composition and properties were occasionally investigated, in particular in the 1970s (Rohde, 1966;Cox et al, 1967;Kremling, 1969Kremling, , 1970Kremling, , 1972Connors and Kester, 1974;Brewer and Bradshaw, 1975;Millero et al, 1978;Poisson et al, 1981;Millero, 2000), but were generally considered of minor relevance and ignored by previous international oceanographic standards (Forch et al, 1902;Jacobsen and Knudsen, 1940;Lewis, 1981;Millero, 2010). However, the effects of these compositional variations are measureable, and are easily the largest single factor currently limiting the accuracy of empirical formulas for the thermodynamic properties of seawater.…”

The density of seawater as a function of salinity (5 to 70 g kg<sup>−1</sup>) and temperature (273.15 to 363.15 K)

“…A number of density measurements on deep waters in the Atlantic (Millero et al, 1976a;1978), Indian Millero et al, 2008a), and Pacific oceans (Millero et al, 1978;2009) and the Red and Baltic Seas (Millero and Kremling, 1976) are higher than the values determined from the equation of state (Millero and Poisson, 1981). This is attributed to the added salts to seawater from the dissolution of SiO 2 (s) and CaCO 3 (s) and the addition of CO 2 and nutrients from the mineralization of organic matter (Brewer and Bradshaw, 1975;Millero, 2000).…”