ORIGINAL PAPER The Equation of State for Caspian Sea Waters Frank J. Millero Æ Abzar Mirzaliyev Æ Javid Safarov Æ Fen Huang Æ Mareva Chanson Æ Astan Shahverdiyev Æ Egon Hassel Received: 17 January 2008 / Accepted: 2 July 2008 / Published online: 29 July 2008 Ó Springer Science+Business Media B.V. 2008 Abstract The density q of Caspian Sea waters was measured as a function of temperature (273.15–343.15) K at conductivity salinities of 7.8 and 11.3 using the Anton-Paar Den- sitometer. Measurements were also made on one of the samples (S = 11.38) diluted with water as a function of temperature (T = 273.15–338.15 K) and salinity (2.5–11.3). These latter results have been used to develop an equation of state for the Caspian Sea (r =±0.007 kg m -3 ) q  q 0 À Á kg m 3 ¼ A þ BS þ CS 2 where q 0 is the density of water and the parameters A, B and C are given by A ¼ 0:0350  1:73E-03 T  273:15 ð Þþ 5:2E-05 T  273:15 ð Þ 2  4:947E-07 T  275:15 ð Þ 3 B ¼ 0:9877  3:66E-03 T  273:15 ð Þþ 4:903E-05 T  273:15 ð Þ 2  2:276E-07 T  273:15 ð Þ 3 C ¼1:25E-04 Measurements of the density of artificial Caspian Sea water at 298.15 K agree to ± 0.012 kg m -3 with the real samples. These results indicate that the composition of Caspian Sea waters must be close to earlier measurements of the major components. Model calcu- lations based on this composition yield densities that agree with the measured values to F. J. Millero (&)  F. Huang  M. Chanson Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA e-mail: fmillero@rsmas.miami.edu A. Mirzaliyev  J. Safarov  A. Shahverdiyev Department of Heat and Refrigeration Techniques, Azerbaijan Technical University, H. Javid Avn. 25, AZ1073 Baku, Azerbaijan J. Safarov  E. Hassel Lehrstuhl fu ¨r Technische Thermodynamik, Universita ¨t Rostock, 18059 Rostock, Germany 123 Aquat Geochem (2008) 14:289–299 DOI 10.1007/s10498-008-9037-0