Properties of Sea Water

Equation of State

An empriical relationship between pressure, density, temperature, and salinity for sea water, known as the equation of state, is expressed as a more than 20-term polynomial for the various state variables. Some background can be found here. The equation of state for seawater is quite nonlinear and this fact gives reise to some interesting phenomenon such as the thermobaric effect, as explained here and here. It is possible to use the full polynomial expression, but for reasons of computing efficiency, simpler yet accurate polynomial descriptions are sought . An online, java-based equation-of-state calculator is also available here. We will be using the MATLAB-based equation-of-state routines made available by Phil Morgan.

Computing Exercise

Individual MATLAB routines available from the CSIRO Properties of Sea Water library are avaialable from the table below. The entire libray can be obtained here (zipped). Download the routines and run an example case for each rotuine. You need to create the input for each routine. Along with your input and output results, provide a very brief explanation of what each routine is doing.

Sea Water Property MATLAB Code
Adiabatic temperature gradient SW_ADTG
Thermal expansion coefficient (alpha) SW_ALPHA
Calculate alpha/beta (a on b) SW_AONB
Saline contraction coefficient (beta) SW_BETA
Brunt-Vaisala Frequency Squared (N^2) SW_BFRQ
Copyright and Licence file SW_COPY
Heat Capacity (Cp) of Sea Water SW_CP
Density of sea water SW_DENS
Density of sea water at atmospheric pressure SW_DENS0
Distance between two lat, lon coordinates SW_DIST
Depth from pressure SW_DPTH
Coriolis factor "f" SW_F
Freezing Point of sea water SW_FP
Gravitational acceleration SW_G
Geopotential anomaly SW_GPAN
Geostrophic velocity SW_GVEL
Information on the SEAWATER library SW_INFO
Potential Density SW_PDEN
Pressure from depth SW_PRES
Potential temperature SW_PTMP
Salinity of sea water SW_SALS
Salinity from cndr, T, P SW_SALT
Solubility (saturation) of Ar in seawater SW_SATAr
Solubility (saturation) of N2 in seawater SW_SATN2
Solubility (saturation) of O2 in seawater SW_SATO2
Specific volume anomaly SW_SVAN
Sound velocity of sea water SW_SVEL
Density of standard mean ocean water (pure water) SW_SMOW
Temperature from potential temperature SW_TEMP
Run test suite on library SW_TEST
Version number of SEAWATER library SW_VER


The Properties of Sea Water MATLAB code originates with Phil Morgan and is also available from the SEA-MAT website.