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Table 1.5 shows thermo‐physical properties of standard seawater at 40 000 ppm and 25 °C.

Note that the comprehensive thermo‐physical properties of seawater as a function of temperature and salinity are presented in Appendix A.

The major six elements that comprise about 99% of seawater are chlorine (Cl⁻), sodium (Na⁺), sulfate (SO₄²⁻), magnesium (Mg⁺²), calcium (Ca⁺²), and potassium (K⁺), and standard seawater composition at 35 000 ppm are presented in Table 1.6.

Table 1.6 Standard seawater composition at salinity equal to ≈35 000 ppm.

Chemical ion	Concentration (ppm)	Valence	Total salt content (%)	mmol/kg	Molecular weight
Chlorine Cl−	19 345	−1	55.03	546	35.453
Sodium Na+	10 752	+1	30.59	468	22.990
Sulfate SO42−	2701	−2	7.68	28.1	96.062
Magnesium Mg2+	1295	+2	3.68	53.3	24.305
Calcium Ca2+	416	+2	1.18	10.4	40.078
Potassium K+	390	+1	1.11	9.97	39.098
Bicarbonate HCO3−	145	−1	0.41	2.34	61.016
Bromide Br−	66	−1	0.19	0.83	79.904
Borate BO33−	27	−3	0.08	0.46	58.808
Strontium Sr2+	13	+2	0.04	0.091	87.620
Fluoride F−	1	−1	0.003	0.068	18.998
Σxi = 35 151 ppm

Note that Cl makes up to 55% of salt in seawater and NaCl makes up to 86% of salt in seawater.