The critical point and two-phase boundary of seawater, 200–500°C

Earth and Planetary Science Letters
By:  and 



The two-phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200–500°C. The pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel. The critical point was determined to be in the range of 403–406°C, 285–302 bar and was located by the inflection in the two-phase boundary and by the relative volume of fluid and vapor as a function of temperature. The two-phase boundary of 3.2% NaCl solution was found to coincide exactly with that of seawater over the range tested in the present study. The boundary for both is described by a single seventh-order polynomial equation. The two-phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust. Thus the boundary puts a limit of about 390°C for seawater circulating near the seafloor at active ocean ridges (2.5 km water depth), and about 465°C at the top of a magma chamber occurring at 2 km below the seafloor.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The critical point and two-phase boundary of seawater, 200–500°C
Series title Earth and Planetary Science Letters
DOI 10.1016/0012-821X(84)90149-3
Volume 68
Issue 1
Year Published 1984
Language English
Publisher Elsevier
Description 9 p.
First page 172
Last page 180
Online Only (Y/N) N
Additional Online Files (Y/N) N
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